Spring Review and Summer 2004 Outlook for Southeast Lower Michigan

Summertime Variability is the Name of the Game

Written by: William R. Deedler, Weather Historian
National Weather Service Detroit/Pontiac, MI
June 1st, 2004

Update - Summer 2004 Update for Southeast Michigan
issued June 20th, 2004

Quick jumps on this page:

Note: Dark red and italicized text is taken directly from the 2004 Spring Outlook issued March 8th, 2004.

Sea surface temperature forecast; click on image to enlarge As we move into the summer months, on a northern hemispheric scale, the long standing and basically Neutral Pacific pattern continues to dominate at this time. This upcoming summer will be our second summer with mainly neutral conditions over the Pacific. Latest indications are that the dominant neutral temperature pattern (or near normal Pacific sea surface temperatures /SST/) are expected to hold through the summer and into the fall.

While downwind effects on the US from El Niño and La Niña decrease during the summertime, this is especially true during a Neutral State when both summertime lighter upper winds and neutral conditions prevail. Over the past several seasons, the upper wind pattern over the U.S. has been mainly amplified and progressive but with occasional "lock-in" patterns materializing (lock-in: meaning the placement of upper ridges and troughs "stall" over portions of the country). While the combination of these patterns limit any definite trend expectations for the summer, there were other patterns mentioned in the following local summer outlook. This researched data resulted in the following local summer outlook for Southeast Lower Michigan.


Local Study Findings

Temperatures

While the data reviewed is extremely variable, look for temperatures to average around normal to above normal. This is not to say there will not be intermittent cool periods during the summer as the upper wind flow occasionally backs to the northwest. In fact, of particular concern is the persistently cool and aggressive upper air pattern that continues to hold over Eastern Canada with only some weakening likely. At the same time, however, strong ridging across the southern/central U.S. should routinely push heat and humidity back into the area. In the end, it is expected that the above normal temperatures will at least offset the below normal temperatures, leading to the near normal to above normal readings.

Rainfall

The pattern of relatively tranquil weather followed by a notably wet and stormy period that commenced last winter has persisted strongly into the spring. This was evidenced recently by one of the driest Aprils on record being followed by the wettest and stormiest Mays! Overall, this pattern is expected to persist into the summer but hopefully not as extreme. Therefore, while significant dry and wet periods will persist, it is felt that overall, rainfall will average near normal to above. Several of the springs - summers researched displayed this feast/famine rainfall pattern. Because of the extreme variability found with the summer storm patterns, areas with below normal rainfall would not all be a surprise either.

Recapping the Spring Action and Recent Trends:

Observed North Atlantic Oscillation; click on image to enlarge The decidedly longer trend of normal to below normal temperatures of the past few years began showing signs of erosion during the winter months as temperatures swung between below normal and above normal. As the late winter into spring evolved, a trend toward a normal to above normal temperature regime gradually overtook the earlier dominant cooler trend. In spite of some notable cold blasts during the spring, the overall average temperature was above normal over the entire region. The relatively warm spring weather also correlated nicely with the North Atlantic Oscillation /NAO/ spoken about numerous times in these outlooks. The NAO was mainly positive throughout the spring and thus, any residual late season polar outbreaks were brief and limited.

The increased temperature and weather volatility of the past winter also carried into the Spring of 2004 (Chart-1) across all of Southeast Lower Michigan. As the spring progressed, the weather remained quite variable. The normally volatile month of March lived up to its reputation and contained record or near record warmth after its opening and again, near its close. A strong cold snap mid month was accompanied by two to five inches of snow. As a result of these contrasts, March evolved into a wet month at most locations. By the time April was completed on the calendar, temperatures averaged above normal but mainly due to just a couple of brief but strong warm spells. Along with the warmer weather in April came much drier conditions with most of the region receiving well below normal rainfall. Nearly a century had passed since an April had been this dry /.69"/ in Detroit, placing fourth for driest Aprils on record. Flint with an April total of .70" had its second driest April, whereas Saginaw never placed in the top 20 driest list since it received more rain with 1.74."

Contrasting air masses and wavering fronts over the southern Great Lakes during much of May created nearly persistent storm action with severe weather, record rainfalls and flooding. Right out of the gate, severe weather and very heavy rains hit the region the first week of May and it remained active through the month. All stations (DTW/FNT/MBS/DTX) reported over eight inches of rain, which gave all areas record or near record rainfall totals for May. Days containing thunderstorms amounted to 14, which broke the old record of 11 back in 1896. This total of 14 thunderstorm days also tied for first place the most thunderstorm days ever recorded in Detroit in a calendar month (tying June 1892, July 1902, and just last August 2004). Out of the three spring months researched, May had the best chance to have above normal rainfall.

In the final tally, Spring of 2004 ended up warm and wet across all of Southeast Lower Michigan. This was quite a change from the dominant trend the past several seasons of generally normal to below normal weather.

CHART - 1

2004 - SPRING AVERAGE TEMPERATURE AND RAINFALL/DEPARTURES
 DetroitFlintSaginawWhite Lake

MAR(T)40.4/+3.539.1/+5.437.0/+3.537.5
 (P)3.29/+0.772.36/+0.142.16/-0.262.92
APR(T)50.8/+2.749.9/+4.547.3/+1.848.2
 (P)0.69/-2.360.70/-2.431.74/-1.080.39
MAY(T)60.9/+1.159.6/+2.556.2/-1.458.1/+
 (P)8.46/+5.418.19/+5.458.14/+5.258.55/+

Spring
Average
(T)50.7/+2.449.5/+4.146.8/+1.347.9/+
Total(P)12.44/+3.8211.25/+3.1612.04/+3.9111.86/+

Spring(T)48.345.445.5 
Normals(P)8.628.098.13  
Spring 2004
City Warmest / Wettest
Detroit 7th / 8th
Flint 4th / 7th
Saginaw -- / 6th

It was stated in the Spring Outlook that the weather volatility of the past several months would not only persist but likely to increase:

"The spring data, like the winter data, shows quite a variety of potential dominant weather patterns. One thing true to most springs (and very predominant in our previous few outlooks) are the fluctuations in the temperature patterns. The continuation of the "roller-coaster" pattern in the spring holds true, especially during these Neutral to weak El Niño Springs."

It was proposed that temperatures would continue on the strong roller-coaster pattern along with a potential for late season snows. There were a couple of times in mid and very late April were measurable snowfall occurred over portions of the area. Late in April /27th/, snow showers left .3" of snow here at the NWS White Lake and a tenth at Flint, this in spite of April being an overall mild month. The .3 of an inch at White Lake was the second latest measurable snowfall recorded here at the NWS office since records began November 1995.

In spite of some notable cold blasts during the spring, the overall average temperature averaged above normal over the entire region. This was more contrary to the prevalent pattern of the past winter (and earlier) when temperatures averaged normal to below. Whether or not this warmer trend seen this spring is sustainable throughout the summer, is one of the big questions we will try to answer here along with the expected rainfall pattern.

Severe Weather Season: Early and Active, A Summer Preview?

While the timing of our severe weather season varies somewhat year to year, generally it commences in April with our most active months being June and July. Another item noted in the spring outlook, which also contained a severe weather season preview, was that in the more anomalous winter years, notable periods of tranquil weather alternated with periods of very active thunderstorms and severe weather into the summer.

"Several of the most anomalous years showed peaks in thunderstorms early and again later in the severe weather season."

While it was difficult to pick a particular month or exact time period this trend would possibly appear, it did materialize again this spring. However, in the study it was more often April and/or June that was the stormy month rather than May. Yet, more of concern here was the development of the trend of notable tranquility/concentrated storm activity. It was April this year that was a fairly tranquil month with little in the way of rainfall, let alone thunderstorms and severe weather. Well below normal rainfall fell at both Detroit and Flint which led to one of their driest Aprils on record. May, on the other hand, turned out to be very concentrated with storms and numerous severe weather events. It is interesting to note, that since there were generally two periods of concentrated storms during the severe weather season, another stormy period seems quite possible sometime during the summer.

Solving Summer's Season

Comparing last summer's /2003/ research to this summer's reveals even more complicated issues. Gone are the more decisive temperature trends that surfaced in last summer's outlook where normal to cooler summers dominated (and last summer confirmed). Gone, also, are any notable precipitation trends mentioned in last summer's outlook (also confirmed). One possible speculation may be that the second and third year of a Neutral Pacific pattern may result in even more variability in our weather since there is even a longer duration of negligible Pacific affects (which also may apply to the winters).

Surprisingly, however, both summer studies still do carry a few similar traits. Despite the Summer of 2003 having more cooler summers, both summer's ultimate average temperature came up right near normal (71.0 vs this summer's 71.3). In addition, and like last summer's July in the study, this summer's July contained the biggest departure (both -) for any of the summer months (72.5/-1.0 for 2003 and 72.8/-0.7 for 2004). Interestingly, and as a side note, last July's actual temperature finished almost exactly on that average in the study with 72.6, which made for a comfortable July (hopefully history will repeat itself with this July's average in the study at 72.8). Another similar pattern seems to be evolving for early this June, like last year's early June, cool or below normal temperatures (last June heated up later in the month).

When all stats in this summer's are averaged out, they zero in, right on the normals (see Chart-2 ). For example, take a look at the average rain for the 13 summers /9.52/ and compare it to the 100 year norm /9.50/! And again, the summer temperatures are so variable that the average for the researched summers fell at 71.3 degrees, while the 30 year norm sits at 71.4 and the 100 year norm at 71.0 even. Want even more variety in the summers? Numerous (an incredible 9 out of the 13) summers made or placed just outside the top 20 lists for: warmest, coolest, wettest and driest summers (not to mention the monthly top twenty lists). Since we have all this variance, maybe the recent trends (winter-spring) may add a helping hand.

The following Chart-2 represents the summers researched (all data is from the Detroit records which has the largest data base).

Chart - 2

DetroitSummerJuneJulyAugust 

 Temp/ PcpnTemp/ PcpnTemp/ PcpnTemp/ Pcpn 
1971-2000
30 Year
Normals
71.4/ 9.8169.0/ 3.5573.5/ 3.1671.8/ 3.10 
100 Year
Average
(approx)
71.0/ 9.50 

Summer ofTemp/ PcpnTemp/ PcpnTemp/ PcpnTemp/ PcpnOverall Summer
1901+ 72.5/10.78 +68.9/ 2.08-7- 76.8/ 5.50 (15)71.9/ 3.20/20th Warmest/
1920- 69.4/13.34 ++69.1/ 5.49 (11)69.7/ 3.6569.5/ 4.20/15th Wettest/
1933+ 74.0/ 5.90 ---1- 74.6/ 1.19 -8--18- 75.4/ 2.4772.0/ 2.24/4th Warmest/
/17th Driest/
1942+/- 71.1/ 9.78 +/-69.0/ 2.3173.6/ 3.3570.6/ 4.12 
1953+ 72.9/ 7.26 ---17- 70.9/ 3.0973.5/ 2.65-13- 74.3/ 1.52/15th warmest/
1959+ 73.5/ 9.35 +/-70.1/ 1.01 -3-74.1/ 1.27 -17--3- 76.3/ 7.07 (5)/9th Warmest/
1967- 68.9/ 9.09 -70.4/ 4.2369.0/ 2.85(8)67.3/ 2.01/20th Coolest/
1975+/- 71.2/12.20 ++69.0/ 2.3972.2/ 1.9872.3/ 7.83(2) 
1978- 69.8/ 6.39 --66.8/ 2.69(17)70.6/ 1.9771.9/ 1.73/20th Driest/
1979- 68.3/11.99 ++66.6/ 4.04(14)70.4/ 4.96(13)67.9/ 2.99/13th Coolest/
1981- 70.1/ 9.94 +/-68.0/ 3.3372.4/ 4.2970.0/ 2.32 
1993- 72.5/ 9.82 +/-67.5/ 6.05 (8)-17- 75.5/ 2.17-10- 74.5/ 1.60 
2001+ 72.4/ 7.49 --69.6/ 3.4173.6/ 1.16 -11--15- 74.1/ 2.92/Just Below
20th Warmest/

Mean:71.3/ 9.5269.3/ 3.2172.8/ 2.9471.7/ 3.37 
 
(  ) Monthly Coldest or Wettest Ranking
-  - Monthly Warmest or Driest Ranking
+   above normal++ well above (2.00"+)
-   below normal-- well below (2.00"+)
+/- normal (within .5 degree or .50" precipitation)

Reverting back to the winters that contained some similar traits to this past winter (1958-59, 1966-67, 1978-79, 1980-81 and 2001-01) and a bit of temperature trend evolves for the summer. Three out of the five summers: 1967, 1979, 1981 all contained cooler than normal temperatures. Therefore, does this help tip the scales toward a cooler than on average summer? This, of course, is assuming the overall cooler than normal trend hasn't changed - or has it? Reviewing more recent surface and upper air data/trends from the spring /Mar-May/ argues it has and suggests a warmer pattern of above normal temperatures may be in the works. Is this recent trend, now our friend? Studying the recent NAO also supports a warmer than normal summer (but remember, the NAO are unpredictable past a week or so ahead). Checking back over spring's pattern, let's see which springs in the 13 winters studied, if any, resembled this past spring. First off, let me state that none of the springs in the study were as warm as this past spring. Thus, the three warmest springs in the study and closest to this past spring were in 1942 /50.3/ and 8th warmest spring, 1959 /48.4/ and 2001 /49.1/ are examined. As one can see by the following summer temperatures (Chart-2) the results suggest a near normal to warmer summer. In the Summer of 1942, temperatures averaged near normal, while the summer of 1959 and just recently, the summer of 2001 both averaged above normal. Remember also, two of those three winter's (1958-59 and 2000-01) were among the winters that contained similarities to this past winter and both successive summers were warm. Thus, considering all the very mixed data presented here and maybe a bit more importantly, the latest spring trends and the parallel previous winters and springs just mentioned, leads to our local summer outlook.

Recapping:

Temperatures

While the data reviewed is extremely variable, look for temperatures to average around normal to above normal. This is not to say there will not be intermittent cool periods during the summer as the upper wind flow occasionally backs to the northwest. In fact, of particular concern is the persistently cool and aggressive upper air pattern that continues to hold over Eastern Canada with only some weakening likely. At the same time, however, strong ridging across the southern/central U.S. should routinely push heat and humidity back into the area. In the end, it is expected that the above normal temperatures will at least offset the below normal temperatures, leading to the near normal to above normal readings.

Rainfall

The pattern of relatively tranquil weather followed by a notably wet and stormy period that commenced last winter has persisted strongly into the spring. This was evidenced recently by one of the driest Aprils on record being followed by the wettest and stormiest Mays! Overall, this pattern is expected to persist into the summer but hopefully not as extreme. Therefore, while significant dry and wet periods will persist, it is felt that overall, rainfall will average near normal to above. Several of the springs - summers researched displayed this feast/famine rainfall pattern. Because of the extreme variability found with the summer storm patterns, areas with below normal rainfall would not all be a surprise either.

If conditions warrant, look for an update mid summer.

Here's to good weather whenever and where ever your vacation falls this summer.

Check back in the early fall for this summer's write up and a brief fall outlook.


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