...The Winter of 1997-98...Sometimes Calm, Sometimes Wild, But Through It All, Unseasonably Mild... By: William R. Deedler, Weather Historian, WFO Pontiac/Detroit Mi With effects of El Nino helping to keep the Arctic air at bay, the winter of 1997-98 will definitely be remembered across Southeast Lower Michigan as unseasonably mild and wet, especially January into February. December differed somewhat from January and February, yet it too was milder than normal, but not by nearly as much and it also was a bit drier than normal. Even with being milder and drier, a picturesque snowstorm hit the area from Flint south through metro Detroit on December 10th, leaving 2 to 7 inches of snow with the heaviest falling in Detroit's west and northern suburbs. It turned out that this storm produced the heaviest snow that metro Detroit would see during the winter months of December through February. The snow was lost by the Christmas Season, when it would have been most appreciated, only to be replaced by heavy rain and sleet Christmas Eve and nothing but scattered snow showers Christmas Day. During January, the abnormally mild winter weather got into full swing. Temperatures averaged 8 to 10 degrees above normal across Southeast Lower Michigan. It turned out to be the seventh warmest January on record in Detroit (back to 1870) and the fourth warmest in Flint (back to 1943). The warmest of the weather arrived during the first week of the New Year. Even with the mild weather, snowfall only averaged 2-4 inches below normal with generally 8-12 inches falling and nearly all of that fell during the second half of the month. A fairly active storm track during the month brought above normal rainfall to all of the region. Precipitation averaged one to two inches above normal and this trend continued right into February, with the notable exception of the first week. During this week, exceptionally nice, early spring-like weather was experienced by all in Southeast Lower Michigan, including several spring loving birds and animals who, like the rest of us probably wondered, "What happened to winter"? Temperatures averaged a good 10 degrees above normal with little, if any rainfall. Readings frequently pushed into the 50s during the afternoon, flirting with, but never quite breaking, the existing record highs. While it did cool down somewhat by mid-month, temperatures never went below normal. In fact, every single day in February at both Detroit and Flint averaged above normal, a rare climatic statistic, indeed! In the end, February's temp- eratures averaged about 11 degrees above normal across Southeast Lower Michigan. It became the second warmest February on record in Detroit (including the warmest this century) and the warmest on record in Flint. As February unfolded, the temporary reprieve from storm systems and rainfall during the first 10 days ended. Both Detroit and Flint again had more than the usual amount of rain in February (which is normally one of the drier months). Rainfall was especially plentiful in metro Detroit, where rainfall amounts averaged about two inches above normal. Besides the unusually mild temperatures experienced during February, another just as outstanding weather feature was the almost non-existence of snow. Only a trace of snow fell in Detroit during February and .4 in Flint. This was the first time that only a trace of snow was recorded at Detroit during any February since 1880. In fact, only one other winter month (Dec-Feb), recorded less snow and that was in December 1889 when no snow fell. At Flint, the .4 of snow that fell was the least ever recorded during February (or any other winter month, for that matter), since 1950. Another incredible temperature fact that had never occurred before in Detroit since 1870, was the absence of single digits. Through March 20th, 1998, no single digits had been recorded at Detroit Metro Airport during the winter season of 1997-98. The lowest temperatures recorded were two 11 degree readings, one on December 31st and the other on January 14th. The temperature statistics of the winter of 1997-98 in Southeast Lower Michigan are as follows... TEMPERATURES ------------------------------------------------------------- December January February Winter Normal ------------------------------------------------------------- Detroit 32.3 32.8 36.7 33.9 25.5 (Depart) (+4.0) (+9.9) (+11.3) (+8.4) Flint 29.9 29.9 34.6 31.5 24.1 (Depart) (+2.7) (+8.4) (+11.1) (+7.4) _____________________________________________________________ The Detroit area averaged about 8 1/2 degrees above normal or what is typical during a winter. The average temperature of 33.9 put the winter of 1997-98 into fourth place for warmest winters on record since 1870. One has to look back to the dust bowl days of the 1930's, to the winter of 1931-32, to find a warmer winter. That winter placed second for warmest with an average temperature of 35.6. The other two mild winters (first and third place), occurred in the 1800's. Third place belongs to the winter of 1889-90 with an average 35.0. Finally, the warmest recorded winter in Detroit's weather history occurred way back in 1881-82 with a very mild average temperature of 37.0 degrees. This mild winter average was helped immensely by an unusually warm February, which averaged 39.5 degrees. And what winter, did this winter replace as the fourth warmest winter? Why, it was none other than the El Nino winter of 1982-83, our last "strong" El Nino winter. What could be more fitting and logical, since this year's El Ninos strength was expected to be at least equal, if not exceed that of 1982-83. At Flint, the average temperature of 31.5 degrees also did not place this past winter in first place for warmest. After a scan of the climate records, the honor of first place stayed with the El Nino winter of 1982-83. During that winter, Flint averaged 32.2 degrees or .7 warmer than this past winter. One hypothesis as to why Flint was unable to beat the winter average of 1982-83 and Detroit did, would be because of the expansive heat island effect of metro Detroit. Since the winter of 1982-83 (and especially in the western suburbs, where Detroit Metro Airport is located), an expansion of commercial and housing development has taken place. Occasionally, even Metro Airport's (as compared to Detroit City Airport, where records were taken before 1959) overnight low temperatures are artificially inflated due to the urban sprawl thats happening around it. This is especially true when a southeast to norheast, to north wind blows. Then again, when checking nearby Toledo Ohio's winter average temperature, it was found they too, like Detroit, had exceeded their winter average of 1982-83. One of the classic effects of El Nino is the development of an unusually strong southern stream (southern U.S.) storm track during the winter months. This prediction certainly rang true across that region with frequent low pressure systems dumping heavy amounts of precipitation along with some notable severe weather outbreaks in the deep south. When the storm track pivoted northward into the Great Lakes states, Southeast Lower Michigan was frequently either in the storm track or near it. This was especially true for metro Detroit, January into February, which caused the above normal precipitation. PRECIPITATION _____________________________________________________________ ------------------------------------------------------------- December January February Winter Normal ------------------------------------------------------------- Detroit 1.89 2.78 3.60 8.27 6.32 (Depart) (-.93) (+1.02) (+1.86) (+1.95) Snow/Dpt 6.1/-4.8 8.3/-3.5 T/-9.2 N/A 41.7 _____________________________________________________________ Flint 1.06 3.16 1.65 5.87 4.78 (Depart) (-1.05) (+1.77) (+.37) (+1.09) Snow/Dpt 6.9/-4.4 8.0/-4.3 .4/-9.9 N/A 48.9 _____________________________________________________________ ------------------------------------------------------------- Though the season snowfall total is yet to be determined, it is fairly safe to say that snowfall across the region will come in below normal. That is, unless we get a big clobbering this spring. I has happened, as evidenced by the 24.5 inches of snow that fell on April 6th, 1886, the most ever in a single day in Detroit! While this past winter's weather pattern started out resembling that of 1972-73 in December, January into February were more similar to the December/January 1983 pattern. Temperatures averaged well above normal during both winter periods with very little snowfall. During this past winter, the El Nino effect seemed to grow as the winter evolved, reaching its maximum in February whereas in 1982-83, the effect was strongest earlier in the winter. Looking at this spring, let's reflect back to the springs that followed the strong El Nino winters of 1972-73 and 1982-83. Similarities are spotted in both springs. First off, both springs averaged wetter than normal including above normal snowfall (both through April and in 1973, into May)! In addition, temperatures generally started the spring at/or above normal but eventually went below normal by late spring. Both Mays (1973/83) averaged below normal in temperatures and above normal in rainfall. Checking all El Nino years back to 1950 (total of 11) showed much more variability in spring-time temperature and precipitation than the strongest El Nino years. The cooler/wetter trend of the post strong El Nino springs obviously contains far fewer years and subsequent data; therefore, its reliability is certainly questionable. Severe weather frequency after El Nino winters since 1950 (total of 11) was even more variable. Just looking at confirmed tornado statistics in Southeast Lower Michigan showed the following... 1952 - 0 1970 - 0 1987 - 8 1959 - 2 * 1973 -22 * 1988 -12 1964 - 4 1977 -10 1992 - 2 1966 - 2 1983 - 9 * The above years average to 6.5 tornadoes per year, while the average number of tornadoes annually during the past 50 years comes to 6.6, virtually no difference. Narrowing this data down to the three strong El Ninos(*), 1958-59, 1972-73 and 1982-83 just reflects the broad spectrum of results. There were only 2 tornadoes confirmed during the severe weather season of 1958; on the other hand, there were 22 confirmed in 1973 (the most ever) and nine were confirmed in 1983. Another variable that must be considered here, though, is the better tracking and reporting procedures that have evolved since the 1950s/60s, when generally fewer tornadoes were reported. I wish to thank my fellow employee Rich Pollman for his research into Southeast Lower Michigan's tornado statistics in El Nino years.