LACROSSE, WISCONSIN CLIMATE

Todd Rieck
Weather Service Forecast Office
LaCrosse, Wisconsin

I.

PREFACE

The purpose of this publication is to provide a comprehensive look at the climate for La Crosse, Wisconsin. It is hoped that the many facts and figures contained in this publication will provide information and insight for our many users, from the general public and media, to those with economic interests across the area.

All temperatures are in degrees Fahrenheit, and all precipitation records are measured in inches. Unless otherwise noted, normal records are for the period 1961-1990, monthly and daily temperature records date back to 1873, monthly precipitation dates back too 1873, daily precipitation back to 1896, monthly snowfall back to 1893, and daily snowfall back to 1948. All data are up-to-date through October 1997.

II.

INTRODUCTION

The city of La Crosse is situated on the east-bank of the Mississippi River at the confluence of Mississippi, Black, and La Crosse Rivers. The official records are taken at the La Crosse Municipal Airport which is 6-l/2 miles north of the main Post Office, on the north end of French Island. This island is about six-miles long from north to south and two-to-four-miles wide with the Mississippi River to the west and the old channel of the Black River to the east. A rather level sandy plain exists on each side of the river extending between the Wisconsin and Minnesota bluffs that rise 450-to-500 feet above the valley floor. The distance from bluff-to-bluff has an average of about five-miles. The Mississippi River bends to the northwest and continues directly southward from the city.

The prevailing winds in the area are from the northwest from January through April and southerly during the remainder of the year. The situation of the city and airport in a natural bowl between the bluffs results in somewhat colder temperatures at night due to the settling of cooler air. Valley fogs often persist to midmorning. Steep sided hills with narrow valleys are characteristic of most of the surrounding area.

The flow of the Mississippi River is regulated by dams built for the purpose of navigation, but the reservoirs have limited storage capacity. La Crosse is in the area of Pool No.8 with a mean sea level elevation of 63l feet. When the river reaches an elevation of 639 feet, with open gate operation, there is considerable flooding of land near the river and some industrial sections of the city.

The invigorating continental-type climate results in wide and frequent variations in temperature. General storms moving eastward or northeastward into our area bring warmer weather and supply most of our moisture. These are usually followed by cooler air from Canada. The winters are cold and humid. The summers are warm with moderate humidities, while periods of hot and humid weather occur occasionally, usually lasting from a few days to a week at a time.

Sixty percent of the precipitation falls during the main growing season, extending from May through September. Most of the summer rainfall is caused by thunderstorms. Some damage from heavy rains, high winds, and hail occurs each year, but tornadoes are infrequent and cover very small areas. Snow is frequent and is the predominant form of precipitation in winter. Heavy snow sometimes falls with larger amounts observed on ridge tops. Ice storms are not numerous since La Crosse is usually north of the main path of freezing rain.

Farming is diversified with dairying the leading activity. The more important field crops are corn, oats, and hay. Some of the more specialized crops are soybeans, tobacco, small fruits, and cranberries. Commercial apple orchards are numerous across the Mississippi River in Minnesota.

Figure 1. This summary is derived from the National Climatic Data Center's annual summaries for La Crosse.

III.

ANNUAL CLIMATE OF LA CROSSE

The climate of La Crosse is highly continental with warm summers and very cold winters. The average annual temperature is 46.3 degrees Fahrenheit. July is the warmest month with an average temperature of 73.5 degrees Fahrenheit while January is the coldest month with an average temperature of 14.4 degrees Fahrenheit. The warmest temperature ever recorded in La Crosse has been 108 degrees Fahrenheit which occurred on July 13, 1995 and on July 14, 1936. The coldest temperature in the weather history of La Crosse was 43degrees Fahrenheit below zero back on the January 18, 1873.

Precipitation in La Crosse averages about 30 inches a year with nearly 70 percent of the annual precipitation falling during the spring and summer months from April through September. Annual precipitation has ranged from a maximum of 44.74 inches in 1881 to a low of 16.77 inches in 1910. The wettest months are normally in the summer with June through September all averaging just less than four-inches of rainfall each. The winter months are normally the driest since snow usually contains only about 0.10 inches of water equivalent per inch of snowfall. January and February are therefore normally the driest months of the year with an average of slightly less than one-inch of melted equivalent precipitation each.

Average temperatures and precipitation for the four seasons are given in Table 1. For this purpose, Winter is defined as December through February, Spring is defined as March through May, Summer as June through August, and Fall as September through November.

 

TABLE 1

 

 

Temperature is in degrees and precipitation is in inches.

 

 

  avg. temp. avg. precip.
Winter 19.7 4.2
Spring 46.3 8.1
Summer 70.8 11.6
Fall 49.1 7.7

 

Average winter snowfall in La Crosse is 42.5 inches with the average monthly totals being fairly evenly distributed from December through March. January is on average the snowiest month with just over ten-inches. December and March average nine-inches while February has about eight-inches. November and April averages are about four to two-inches of snow respectively. Measurable snow has been observed as early as October 13 and as late as May 15.

Snowfall records in La Crosse are perhaps not as high as one would expect in this part of the country. The highest seasonal snowfall total is 78.7 inches in 1961-1962, while the record for a calendar day is 14.4 inches on December 3, 1990. The highest snowfall for a month is 39.6 inches in January 1929. The least snowfall in a season was 1967-1968 when only 7.7 inches fell.

 A.  Seasonal Variations

Seasonal changes in west-central Wisconsin are usually sharply defined. However, they do not correspond very well to either the official calendar seasons or the three-month "meteorological seasons" as defined in the previous section. By any criteria, winter is the longest of the four seasons in La Crosse while summer lasts somewhat longer than either spring or fall.

 B. Winter Weather

The true winter weather season normally begins in mid to late November and extends into late March. Periods of cold weather are still likely both before and after these dates, but this four-month-plus period is the time when average temperatures are at or below freezing and most precipitation falls in the form of snow.

The average high temperature drops to the freezing mark on December 5 and stays at freezing or below until February 24. The majority of days in midwinter have highs from the mid teens to the mid 30s, although Arctic outbreaks may bring periods of frigid weather when high temperatures stay below zero for several days in a row. La Crosse averages 26 nights per winter when the temperature falls to zero or below with 11 such nights usually occurring in January.

There are several tracks which storm systems may take to produce snow in western Wisconsin. The heaviest snows usually develop when low pressure systems develop in the southern plains states and move northeastward into Missouri and Illinois. These storms often produce six to ten-inch snowfalls and may cause snows in excess of one foot such as those which occurred in January 1996 and March 1997.

More common are the lows which track southeastward from Alberta, Canada and the northern plains states toward the Upper Mississippi Valley. These lows typically produce lighter snows in the one to four-inch range. Widespread blowing and drifting of snow may occur with these systems if the area of low pressure is strong.

The La Crosse area will experience freezing or mixed precipitation when cold high pressure is in place at the surface and the warm front approaches the region from the south. The warm air is forced to rise, causing precipitation to freeze as it falls into the cold air.

Winter is, on average, the cloudiest season of the year in La Crosse with lengthy periods when low clouds cover the sky. These clouds are typically stratus or stratocumulus which develops on the western side of storms which cross the upper Midwest. Clear weather in the winter is most likely to occur when a fresh dry Arctic air mass moves south from Canada into the Midwest.

The prevailing wind directions during most of the winter are either from the northwest or from the south. The average wind speeds in winter are between eight and nine mph which is, perhaps surprisingly, slightly less than the average wind speed in spring and fall.

 C. Spring Weather

Spring weather normally begins around the end of March and extends into early June, at which time the average high temperature has reached the mid to upper 70s. Thus, some typical spring lasts just slightly more than two months but may seem much shorter when cold weather lingers into April and parts of May.

Average high temperatures in the spring rise from about 50 degrees at the beginning of April to the middle 70s by the end of May. Average lows rise from around 30 to the lower 50s during the same time interval. Freezing temperatures are common during the first half of April when invading Canadian air masses are still very cold. The last frost is usually around the first week of May in the city of La Crosse but low lying areas in the surrounding countryside are more likely to see frosts into the middle of the month.

The jet stream gradually moves northward as spring progresses but the track of surface lows is often still to the south of Wisconsin, especially in April. Significant snows are still possible when polar air is in place over the upper Midwest and lows track through the central Mississippi valley. Severe weather becomes more likely when the lows begin to track further to the north of La Crosse later in the spring. The frequency of thunderstorms increases during the spring with an average of three days with thunderstorms in April and six such days in May.

Spring is, on average, the windiest season of the year and April is usually the windiest month in La Crosse. This is largely due to the strong temperature difference at this time of the year when the polar regions are still cold but the southern U.S. has warmed up significantly.

 D. Summer Weather

Summer typically lasts about three months in La Crosse, extending from early June through the first week in September. After the very changeable spring weather, summer usually features consistently warm temperatures in this part of Wisconsin. The average high temperature is 80 degrees Fahrenheit or above from June 14 through the August 25. There are normally 17 days when the mercury reaches the 90 degrees Fahrenheit mark during a La Crosse summer averaging four in June, seven in July and five in August.

Summer temperatures in La Crosse average 2 to 5 degrees warmer than other cities in Wisconsin, including Madison, Milwaukee, Green Bay and Eau Claire. This is partly due to the fact that La Crosse is closer to the warmer weather of the plains' states and further away from the cooler Great Lakes. Afternoon temperatures at the airport and other river valley locations also tend to be warmer than on the surrounding ridge tops and higher elevations. This difference is most pronounced during the summer season.

Summer is normally the wettest of the seasons in La Crosse due to the increased frequency of thunderstorms. Each month, from June through September, the average is just under four inches of precipitation with June, July and August each averaging between seven and eight days with thunderstorms.

Despite the greater precipitation, summer is still the sunniest season of the year in La Crosse with an average of about ten clear days in each month and about 70 percent of the possible sunshine in July and August. Summer is also the least windy of the seasons with average speeds between 7 and 8 mph. The prevailing wind direction is from the south.

 E. Fall Weather

Fall weather typically begins during the second week in September and lasts until about the third week in November. Fall is therefore another short season, lasting just a little longer then two months. Average high temperatures drop from the low 70s in the middle of September to around 60 by the middle of October. The cooling then accelerates during late fall with normal highs only around 40 degrees by November 20. Average lows fall from the low 50s in mid September to the mid 20s by November 20. The average first frost in La Crosse occurs during the first week in October.

Average rainfall drops sharply from September to October with the latter month only seeing an average of just over two inches of precipitation. This decrease is mainly due to the fact that tropical type air masses usually stay south of Wisconsin in October and the likelihood of thunderstorms drops to around two days per month in La Crosse. November is somewhat drier yet with an average of only 1.73 inches of precipitation.

September and October are typically among the sunnier months in La Crosse with an average of nine to 11 clear days respectively. November is, however, the cloudiest month of the year with only an average of six clear days. This increase in clouds is due to the onset of the winter season stratus clouds.

The first snowflakes of the season usually occur in October but measurable snows normally don't develop until November when an average of 4.4 inches occurs. The earliest heavy snowfall in La Crosse was the 9.2 inches which occurred on November 1, 1991.

Wind speeds typically increases during the fall season with October and November having average speeds between 9 and 10 mph. The prevailing wind direction is still from the south during the fall months.

IV.

MONTHLY CLIMATOLOGY

 A. January Climatology

January is the coldest month of the winter in La Crosse. The average temperature for the month is 14.4 degrees Fahrenheit with an average daily high of 23.5 and an average low of 5.3. Our warmest January occurred back in 1880 when the monthly mean temperature was a balmy 31.7 while the coldest January on record was in 1912 when the average for the entire month was 1.1 degrees below zero.

On the average you can expect temperatures to fall to zero or below on 12 days during the month of January. The coldest temperature in the weather records of La Crosse occurred on January 18, 1873 when the mercury plunged to a frigid 43 degrees below zero. By contrast, the warmest January reading occurred more recently in 1981 when it reached 57 on January 25.

A detailed look at the climatology of this past century in La Crosse indicates that an average January has one day when the mercury does not rise to the zero mark. There are also normally three days with highs in the single digits, six days with highs in the teens, nine days in the 20s, nine days in the 30s and three days when high temperatures reach into the 40s.

January is normally a very dry month with an average of only .93 inches of water equivalent precipitation. The wettest January was in 1886 with 3.44 inches of precipitation while the driest occurred in 1981 with only .12 inches.

An average January has 10.2 inches of snow which makes it the snowiest month of the year but just slightly ahead of March. The snowiest month on record was in 1929 when 39.6 inches fell. More recently, 29.7 inches fell in 1979. January normally has eight days with measurable precipitation but only three days with an inch or more of snowfall.

January is one of the cloudiest months of the year with an average of 17 cloudy, seven partly cloudy and seven clear days. Daylight does begin to increase during January. Total possible daylight increases from eight hours 59 minutes on January 1 to 9 hours and 50 minutes on January 31.

The average wind speed in January is 8.7 mph with the prevailing direction from the south.

 B. February Climatology

February is the second coldest month of the year in La Crosse being somewhat warmer than January and just slightly colder than December. The average temperature for the month is 19.9 degrees with an average daily high of 29.6 and an average daily low of 10.1. Our coldest February occurred in 1936 when the average temperature was only 4.3 degrees while the warmest was way back in 1878 when the monthly average was a balmy 37.3.

An average February has seven days when the mercury falls to 0 degrees Fahrenheit or lower and also has 16 days when the high temperature stays at or below freezing. The 36 degrees below zero reading on February 3, 1996 tied the record for the coldest February temperature ever in La Crosse which had previously been set on February 8, 1971. The reading of -34 degrees Fahrenheit on February 2, 1996 also tied for the third coldest temperature ever recorded in La Crosse in February. The warmest temperature recorded was 65 degrees on February 12, 1882 and also on February 15, 1921.

The majority of days in February have high temperatures in either the 20s or 30s with an average of eight days in the 20s and ten days in the 30s. A typical February also has one day with a high between 0 and 10 degrees above, four days with highs in the teens, four days with highs in the 40s and one day when the mercury rises into the 50s.

An average February has 8.0 inches of snow which is two to three inches less than the other winter months. However, February is also a shorter month. February is the driest month of the year with an average of only 0.90 inches of melted precipitation. The wettest was in 1922 when 4.04 inches of precipitation fell while the driest was in 1969 when only 0.05 inches occurred. The snowiest February occurred in 1959 when 31.0 inches fell while the least snowiest was in 1954 with only 0.5 inches.

An average February has eight clear days, seven partly cloudy days and 13 cloudy days, thus making February somewhat sunnier than the other months from November through March. The length of daylight also increases sharply, from 9 hours and 52 minutes on the first of the month to 11 hours and 8 minutes on February 28.

The average wind speed is 8.6 mph with the prevailing direction from the northwest.

 C. March Climatology

March is the last of the winter months in La Crosse with the transition toward spring starting to occur by month's end. The normal high rises from 35 degrees on March 1 to 50 on March 31 while the average low increases from 16 degrees on the March 1 to 31 on March 31. The monthly mean temperature for March is 32.8 degrees. The warmest March in the weather history of La Crosse was in 1878 with an average temperature of 46.9 while the coldest occurred in 1899 with an average of 21.2.

March still averages one day when the mercury drops to zero or lower and averages seven days when the high temperature stays at freezing or below. The coldest March temperature in La Crosse was 28 degrees below zero on the first in 1962 while the warmest reading was a balmy 84 degrees on March 29, 1986. Below zero readings have occurred as late as March 26 when the temperature fell to 2 degrees Fahrenheit below in 1962.

The majority of days in March have high temperatures in the 30s or 40s, but the month typically has a large range of temperatures. On average, there is one day with a high in the teens, four days with highs in the 20s, ten days in the 30s, nine days in the 40s, four in the 50s, two in the 60s and one day in the 70s.

Average March snowfall is 10.0 inches which makes it the second snowiest month in an average La Crosse winter, trailing January by only two tenths (0.2) of an inch. The snowiest March occurred in 1959 when 33.5 inches fell including the record 24-hour March snowfall of 15.7 inches on March 6, 1959. The March with the lease snow occurred in 1919 and 1973 when only a trace of snow fell.

March averages 1.98 inches of melted precipitation which is more than twice as much as either January or February. There are normally ten days with measurable precipitation during the month. The wettest March was in 1876 with 4.23 inches while the driest was in 1910 with only 0.03 inches.

There are normally seven clear, seven partly cloudy and 17 cloudy days in March. The amount of possible sunshine increases rapidly, from 11 hours and 11 minutes on March 1 to 12 hours and 41 minutes on March 31.

The average wind speed in March is 9.2 mph which makes it slightly windier than the preceding winter months but not as windy as April or even May. Prevailing wind direction is northwest.

 D. April Climatology

April is the first full month of the short spring season in the La Crosse area although temperatures may often still feel quite wintry, especially during the first part of the month. The average high rises from 51 degrees on April 1 to 65 on April 30, while the average low warms from 31 degrees Fahrenheit on April 1 to 43 at the end of the month. The normal mean temperature for the month is 47.7 degrees Fahrenheit. The warmest April in La Crosse occurred in 1915 with an average temperature of 56.8 while the coolest April occurred in 1907 with an average of only 39.8 degrees Fahrenheit.

Daily high temperatures are quite variable in April, thus making the term "normal high" rather misleading. Climatology of the past century indicates that an average April in La Crosse will have two days with highs in the 30s, six days in the 40s, nine days in the 50s, eight days in the 60s, four days in the 70s and one day with a high in the 80s.

The coldest temperature ever recorded in La Crosse during April was 7 degrees Fahrenheit on April 1, 1984 and also on April 6, 1982. The warmest April temperatures were 93 degrees Fahrenheit on April 22, 1980 and on April 29, 1910. La Crosse's earliest 90 degrees Fahrenheit reading occurred on April 6, 1991.

April average precipitation is 2.88 inches, which makes it wetter than any of the previous winter months but still drier than any of the following spring or summer months. There are normally three days with thunderstorms during April in La Crosse. The wettest April occurred in 1973 with 7.31 inches of precipitation while the driest was in 1879 with only 0.42 inches. More recently, April 1993 and April 1994 were the third and fourth wettest in La Crosse weather history with 6.55 and 6.51 inches of precipitation respectively.

Average snowfall in April is only 2.0 inches, but heavy snows can occur, although not as frequently as in areas of Wisconsin further to the north. La Crosse's snowiest April was in 1973 when 17.0 inches fell and the greatest 24-hour snowfall in April also occurred that year when 10.3 inches fell on April 9 of the month.

April is one of the cloudier months of the year with an average of seven clear days, seven partly cloudy ones and 16 cloudy days. However, the amount of daylight does increase considerably during the month with 12 hours and 45 minutes of possible sunshine on April 1, climbing to 14 hours and 7 minutes on April 30.

April is on average the windiest month of the year in La Crosse with a mean wind speed of 10.8 mph. Strong temperature differences between the northern and southern parts of the U.S. and the resulting strong pressure forces are the main cause of these winds. The prevailing wind direction is from the northwest.

 E. May Climatology

May is the second of the spring months in La Crosse with temperatures normally quite a bit warmer than those seen in April. Cold periods do still occur though with some resulting frosts, and snow is still possible although quite rare. The normal mean temperature for May is 59.5 degrees Fahrenheit that about 12 degrees Fahrenheit warmer than April. The normal high rises from 66 degrees Fahrenheit on May 1 to 76 on May 31, while the normal low increases from 43 degrees Fahrenheit on May 1 to 53 at the end of the month. La Crosse's warmest May occurred in 1934 with an average temperature of 68.0 degrees Fahrenheit while the coolest was in 1907 with a mean temperature of 50.8 degrees Fahrenheit.

The majority of days in May have highs in either the 60s or 70s, but there is quite a bit of variation in May maximum temperatures. On average, there is one day with a high in the 40s, four days in the 50s, nine days in the 60s, ten days in the 70s, six days in the 80s and one day with a high reaching the 90s.

The highest temperature ever recorded in La Crosse during May was 107 degrees Fahrenheit on May 31, 1934. That is the only occurrence of 100 degrees Fahrenheit temperatures in May in La Crosse's recorded weather history. The coldest temperature recorded in May in La Crosse was 26 degrees Fahrenheit which has occurred four times, most recently on May 9, 1945. Freezing temperatures are still possible throughout May as the latest occurrence of 32 degrees Fahrenheit temperatures in La Crosse is on the June 4, 1945.

May average precipitation is 3.26 inches which makes it slightly wetter than April but not as wet as the summer months which lie ahead. The wettest May in La Crosse was in 1960 with 8.83 inches of precipitation while the driest occurred in 1887 with only 0.50 inches of rainfall. The maximum one day rainfall in May occurred on May 19, 1912 with 3.06 inches. Thunderstorms become more frequent in May (normally six days) than in the earlier part of spring.

Only two Mays have had more than one inch of total snowfall in La Crosse. The greatest snowfall was 6.6 inches in 1935 while 5.2 inches fell in 1911. Most May snows have been either trace amounts or a few tenths of an inch.

May is slightly sunnier than April but still has more clouds on the average than the summer months. There are normally seven clear days, nine partly cloudy ones and 15 cloudy days. Length of daylight increases from 14 hours and 11 minutes on May 1 to 15 hours and 13 minutes on May 31 as the summer solstice rapidly approaches.

May and November are tied as the second windiest month of the year in La Crosse with an average wind speed of 9.4 mph. The prevailing wind direction is from the south.

 F. June Climatology

June is the first month of meteorological summer in the La Crosse area even though the season doesn't officially begin until around June 21. Average highs are in the upper 70s and low 80s for the entire month rising from 76 degrees Fahrenheit on June 1 to 83 degrees Fahrenheit on June 30. The average low rises from 53 degrees Fahrenheit on June 1 to 61 degrees Fahrenheit on the June 30. The normal mean temperature for the month is 68.5 degrees Fahrenheit.

La Crosse's warmest June was in 1933 with an average of 76.5 degrees Fahrenheit while the coolest was in 1969 when the mean temperature was only 61.4 degrees Fahrenheit. Four of La Crosse's ten warmest June's have occurred in the past ten years, including 1987, 1988, 1991 and 1995. The warmest temperature ever recorded in June was 102 degrees Fahrenheit on June 20, 1933 and again on June 21, 1988. The coolest June temperature was 32 degrees Fahrenheit on June 4, 1945.

Daily high temperatures are not quite as variable in June as they are in April and May with most days reaching either the 70s or 80s. On average, there is one cool day with a high in the 50s, three days in the 60s, 11 days in the 70s, 12 days in the 80s and three days with highs reaching the 90s.

June is, on average, the second wettest month of the year in La Crosse with 3.90 inches of precipitation, trailing August just slightly. Much of this rain occurs during thunderstorms and there are normally eight days with thunderstorms during the month. The wettest June occurred in 1899 with 11.56 inches of precipitation while 1993 was the second wettest June with 10.79 inches of rainfall. The driest June was in 1910 when only .37 inches of precipitation fell. The heaviest one day total of precipitation in June was 3.82 inches on June 16, 1984.

June is one of the sunnier months with an average of seven clear days, 11 partly cloudy ones and 12 cloudy days. June features the longest daylight hours of the year with a maximum of 15 hours and 29 minutes of possible sunshine on June 20 and 21.

June is also slightly less windy than the preceding spring months with an average wind speed of 8.4 mph. The prevailing wind direction in June is from the south.

 G. July Climatology

July is the warmest month of the year in the La Crosse area and marks the midpoint of the summer season. The normal mean temperature for the month is 73.5 degrees Fahrenheitwith an average high of 84.5 degrees Fahrenheit and an average low of 62.3 degrees Fahrenheit. The average high peaks at 85 degrees Fahrenheit on July 13 and stays at 85 degrees Fahrenheit through July 29 before beginning a slow downward trend at the end of the month.

Our warmest July occurred in 1936 with an average temperature of 79.5 degrees Fahrenheit while the coolest was in 1891 with an average of only 66.8 degrees Fahrenheit. More recently, 1992 was the second coolest July in La Crosse with a mean temperature of 68.0 degrees Fahrenheit. The hottest temperature ever recorded in La Crosse has been 108 degrees Fahrenheit with both occurrences happening in July. The first was on July 14, 1936 and the record was then tied on July 13, 1995. The coolest temperature recorded in July was 41 degrees Fahrenheit on July 22, 1947.

The majority of the days in a La Crosse July have highs in the 80s with an average of 17 such occurrences. There will also normally be one July day with a high in the 60s, seven days in the 70s and six days in the 90s.

Average precipitation in July is 3.79 inches which makes it just slightly less wet than either June or August. July averages eight days with thunderstorms thus tying it with June for the most thunderstorm occurrences. The wettest July was in 1883 with 11.03 inches of precipitation while the driest was in 1967 with only 0.16 inches of rainfall. The greatest one day rainfall total in July was 5.24 inches on July 27, 1987.

July is the month with the highest percentage of sunshine in La Crosse with an average of ten clear days, 11 partly cloudy ones and ten cloudy days. The hours of daylight do begin to decrease, however, with 15 hours and 25 minutes of possible sunshine on July 1 decreasing to 14 hours and 38 minutes by July 31.

The average wind speed in July is 5.6 mph which makes it the least windy month of the year. The prevailing wind direction is from the south.

 H. August Climatology

August is the second warmest month of the year in the La Crosse area with average temperatures just slightly cooler than July. The normal mean temperature is 70.8 degrees Fahrenheit with an average high of 81.6 and an average low of 59.9. The normal high temperature does drop from 84 on the first to 78 on August 31.

Our warmest August was in 1947 with an average temperature of 78.2 degrees FahrenheitF, while August 1995 came in a close second with a mean temperature of 77.8 degrees Fahrenheit. The coolest August in La Crosse weather records was 64.8 degrees Fahrenheit in 1927. The warmest temperature ever in a La Crosse August was 105 degrees Fahrenheit on August 1, 1988 while the coolest temperature was 35 degrees Fahrenheit on August 30, 1915.

The normal distribution of August high temperatures are similar to July with just a few more days in the 70s and slightly fewer days in the 80s or 90s. An average August has two days with highs in the 60s, ten days in the 70s, 15 days in the 80s and four days with highs in the 90s.

Average August precipitation is 3.92 inches thus edging out June as the wettest month of the year. As in the earlier summer months, most of this rainfall is associated with thunderstorm activity (normally seven days during the month). August 1980 was the wettest August in La Crosse with 9.84 inches of precipitation closely followed by August 1981 with 9.56 inches of rain. The driest August was in 1894 with only 0.35 inches of precipitation.

August skies are normally quite sunny with an average of nine clear days, 11 partly cloudy ones and 11 cloudy days. The length of daylight does decrease quite markedly by the end of the month with 14 hours and 36 minutes of possible sunshine on August 1 dropping to 13 hours and 16 minutes on August 31.

The mean wind speed in August is 7.4 mph, thus making it the least windiest month of the year. The prevailing wind direction is from the south.

 I. September Climatology

September marks the beginning of the autumn season in La Crosse although the first ten days or so of the month usually still have summer-like temperatures. The normal mean temperature for the month is 61.8 degrees Fahrenheit with an average high of 72.4 degrees Fahrenheit and an average low of 51.2 degrees Fahrenheit. The normal high drops from 77 on September 1 of the month to 67 on September 30.

Our warmest September occurred in 1938 with an average temperature of 68.5 degrees Fahrenheit, while the coldest was in 1890 with a very unseasonably cold average of 48.8 degrees Fahrenheit. La Crosse had the mercury hit the 100 degrees Fahrenheit mark three times in September with the warmest reading being 101 degrees Fahrenheit on September 6 of the month in 1922. The coldest temperature recorded in a La Crosse September has been 23 degrees Fahrenheit which occurred on September 29, 1949.

An average September still has one day with a high in the 90s along with six days with highs in the 80s, 11 days with highs in the 70s, nine-days in the 60s and three days with highs only in the 50s.

September is still a relatively wet month with an average rainfall of 3.79 inches tying it with July as the third wettest month in La Crosse. The average daily rainfall is actually higher in early September than at any other time of the year except for late June. There are normally five days with thunderstorms during the month. The wettest September occurred in 1881 with 10.87 inches while the driest was in 1940 when only .29 inches of rain fell.

September is a little more cloudy than the preceding summer months with an average of nine sunny days, nine partly cloudy days and 12 cloudy days. The hours of daylight shorten considerably in September going from a possible 13 hours and 13 minutes of sunshine on September 1 to 11 hours and 47 minutes of possible sunshine on September 30.

The average wind speed in September is 8.1 mph which makes it slightly windier than July or August but less windy than any of the other nine months. The prevailing wind direction is from the south.

 J. October Climatology

October marks the middle of the fall season in La Crosse with average temperatures showing a marked decline from the beginning to the end of the month. The normal high drops from 67 degrees Fahrenheit on October 1 to 52 degrees Fahrenheit on October 31, while the normal low drops from 46 to 35 at the end of the month. The normal mean temperature for October is 50.2 degrees Fahrenheit with an average high of 60.2 and an average low of 40.2 degrees Fahrenheit.

Our warmest October occurred in 1963 with a mean temperature of 61.2F degrees Fahrenheit. The coldest was in 1890 (a very cold year!), that had an average temperature of only 37.6 degrees FahrenheitF. The warmest temperature ever in October was 93 degrees Fahrenheit on October 6, 1963 (one of only two days when the mercury has reached 90 in a La Crosse October). The coldest October temperature was 6 degrees Fahrenheit above zero on the October 25, 1887.

An average October has one day with a high in the 80s, six days with highs in the 70s, ten days with highs in the 60s, nine days in the 50s, four days in the 40s and one day with a high only in the 30s. This large range underscores the high variability of October temperatures.

Average October precipitation is 2.20 inches which is quite a bit less than in the preceding warmer months. This is mainly due to the fact that tropical air masses which can hold more water are not that common in La Crosse after mid September. However, the wettest October was also the wettest month ever in La Crosse. This occurred in 1900 when 12.09 inches of rain fell. The driest October was in 1952 when only 0.02 inches of rain occurred.

October averages 11 sunny days, seven partly cloudy days and 13 cloudy days. The amount of daylight continues to drop rapidly with 11 hours and 45 minutes of possible sunshine on October 1, decreasing to 10 hours and 18 minutes of possible sunshine on October 31.

The average wind speed in October is 9.2 mph which ties it with March as the fourth windiest month of the year. The average wind direction is again from the south.

 K. November Climatology

The month of November marks the transition from fall to winter in western Wisconsin as it does across much of the upper Midwest. The average temperature drops more rapidly in November than it does in any other month. The normal high temperature at La Crosse drops 17 degrees Fahrenheit from 52 on the November 1 to 35 on November 30. The normal low drops 14 degrees Fahrenheit from 34 on November 1 to 20 on November 30. The average daily temperature drops below freezing by November 23. Late November also marks the time when the first sub zero temperatures of the season may occur.

During the month of November, the main polar jet stream usually migrates south of La Crosse to a position over the central U.S. This migration allows developing storm systems to track further south than they usually do earlier in the fall. If these storms track through the southern half of Iowa or the northern half of Illinois, La Crosse is likely to experience its first measurable snows of the winter season.

The average temperature for the month of November is 35.6 degrees Fahrenheit with an average high of 43.4 and an average low of 27.7. La Crosse's warmest November occurred in 1931 when the average temperature was 43.2 degrees Fahrenheit while the coldest November occurred back in 1880 with an average temperature of only 25.1 degrees Fahrenheit. The "all time record high" for the month is 80 degrees Fahrenheit on November 1, 1933 while the record low is 21 degrees Fahrenheit below zero November 29, 1875.

A typical November in La Crosse has one day with a high in the teens, three days with highs in the 20s, eight days with highs in the 30s, nine days in the 40s, six days in the 50s, and three days with highs in the 60s.

Average November precipitation is 1.73 inches with a record maximum of 7.24 inches in 1876 while only a trace of precipitation occurred in the driest November in 1976. More recently, 1991 was the third wettest November with 6.25 inches of precipitation.

November snowfall averages 3.5 inches but amounts are highly variable from year to year. Many November's have seen only a trace of snow, but in 1991 La Crosse established its record November snowfall of 30.3 inches. This total included the record 24 hour November snow of 13.0 inches on November 23.

November is tied with December as the cloudiest month of the year in La Crosse. A normal November sees 18 cloudy days, six partly cloudy days and only six clear days. The amount of daylight also continues to drop quite rapidly from 10 hours and 15 minutes on the November 1 to only 9 hours and 11 minutes on November 30.

The mean wind speed in November is 9.6 mph making it the second windiest month of the year behind April. The prevailing wind direction is from the south.

 L. December Climatology

The month of December marks the first full month of meteorological winter in the La Crosse area. The monthly mean temperature is 20.3 degrees Fahrenheit with an average daily high of 28.1 and an average low of 12.5 degrees Fahrenheit. December is also the month when below zero temperatures usually return to La Crosse with an average of six sub-zero days occurring during the month. The coldest temperature ever in La Crosse during December occurred on Christmas eve in 1872 when the mercury plunged to 37 below, while the warmest December reading was 64 degrees Fahrenheit that occurred on December 2, 1982.

Three of the four-coldest Decembers in La Crosse history occurred during the 1980s. The coldest December ever was in 1983 when the average temperature was only 6.4 degrees Fahrenheit that 1985 was the second coldest ever with an average temperature of 91 degrees Fahrenheit.. In contrast, three of the warmest La Crosse Decembers all occurred back in the Nineteenth Century with the warmest being 39.3 degrees Fahrenheit in 1877. Such temperatures are notable since La Crosse has not experienced a December with a monthly average temperature above freezing since 1932.

An average December in La Crosse has two days with highs in the single digits, four days with highs in the teens, eight days with highs in the 20s, 12 days with highs in the 30s, four days with highs in the 40s and one day with a high in the 50s.

The average snowfall in La Crosse during December is 8.7 inches which makes it the third snowiest month, just behind January and March. The average melted, equivalent precipitation is, however, only 1.27 inches, which actually makes December, on average, the third driest month of the year. Total precipitation has ranged from 0.01 inches in 1943 to 3.43 inches in 1875. Snowfall has ranged from a trace in 1979 to 30.4 inches in 1990. There are normally nine days with measurable precipitation and three days with one or more inches of snowfall.

La Crosse has 19 cloudy days in an average December, which is more than any month. A typical December also has seven clear and five partly cloudy days. The amount of daylight also bottoms out in December reaching a minimum of 8 hours and 54 minutes on December 21 and 22.

The average wind speed in December is 8.9 mph which makes the month slightly less windy than the preceding fall months. The prevailing wind direction is again from the south.

V.

ACKNOWLEDGEMENTS

Richard Albrecht, a meteorologist at the CWSU in Aurora ILL, wrote the annual, seasonal, and monthly summaries that are found in the beginning of this publication.

Many thanks to Dan Baumgardt, Science and Operations Officer at WSO-La Crosse, who proofed this publication and provided many helpful hints and ideas.

And a big thank you to the rest of the La Crosse staff who never seemed to be at a loss with suggestions for new sets of climate data that interested them.

VI.

SOURCES

Much of the information was researched using "in-house" National Weather Service data bases and monthly climate summaries.

The International Station Meteorological Climate Summary CD ROM, Ver. 3.0 from March 1995. This CD was jointed produced by the Fleet Numerical Meteorology and Oceanography Detachment, National Climatic Data Center (NCDC), and USAFETAC OL-A.

TABLES:

Normal Temperatures (1961-1990)

Normal Precipitations

Monthly Normals (1961-1990)

Temperature Records

Heat Waves

Cold Snaps

Precipitation Records

Seasonal Temperature Records

Seasonal Precipitation Records

Record Heating Degree Days

Averages

Percentages

El Nino

Flying Weather

Holidays

Appendix

 


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