In my last blog, I stated strongly contrasting air masses would rule the second half of May...cold...warm with more storms and rain as a result. The second half of May certainly lived up to that projection with several warm days rudely interrupted by notable cold snaps. Impressive cold snaps that actually brought temperatures down into the 30s along with scattered frosts as late as the 23rd. Take a look at these low temperatures for the morning of the 23rd across Southeast Lower Michigan.
However, in spite of the of the cold interjections, May still managed to average several degrees above normal and that was primarily a result of a very warm first half of the month. Temperatures the first couple of weeks averaged at one point as much as 10 degrees above normal before settling back to about half of that. Analogue projections had called for a changeable spring with colder than average weather early, moderating to normal and above normal by the time May rolled around along with overall, drier than average predominate conditions. March's temperatures averaged below normal across the region along with drier than normal conditions, where as warmer winds commenced in April bringing temperature averages up a couple degrees above normal weather but with continued drier than average rainfall. By the end of April, most areas were two inches or more below normal for rainfall.
May's weather was a mixed bag as far weather with again warm and cool air masses interchanging but with a decided preference to warmer. Not surprising, along with the conflicting air masses was the pick up in wet weather. After two months of relatively dry weather; May's rainfall averaged near normal to above normal (especially at the end of the month and over the south) with rather frequent periods of showers and strong thunderstorms. Actually the month's rainfall was generally below normal across much of Southeast Lower Michigan until the last two days when very heavy rains from a stalled front and attending low pressure wiped out most deficits for the month. Interestingly, while the heavier rains wiped out the deficit for May and led to a normal to above normal rainfall statistic across the south (Ann Arbor through metro Detroit) for May and the spring; areas to the north remained below normal for the spring. This is one of those cases across the south where the trend of the spring was actually dry, yet the rainfall amounts were normal to above but mainly due to just two days, the 30th and 31st of May.
Note the heavy rainfall map across Southeast Lower Michigan From 8am 5/30/15 - 8am
5/31/15 and this does not include the rainfall after 8am on Sunday, the 31st.
This is a summary of the past - now what about the future?
Summer 2015 Outlook for Southeast Lower Michigan
Overall; I look for temperatures to average around normal but with notable swings as the upper low and troughing in eastern Canada via for dominance against upper ridging, aided and at times, even suppressed by El Nino affected winds across the south. This is a difficult forecast as we dealing with two distinctive upper wind patterns, not always present in such fashion in the summer. The outcome is not only going to be affected by conflicting air masses but also with the timing and the extent of dominance by each air mass.
That being said; In the end, I look for temperatures averaging between +1.5 degrees and -1.5 degrees of the summer norms across Southeast Lower Michigan...a bit wider range than typical. Interestingly, this oscillating range may very well sum up the summer on a week or two and/or a monthly basis.
I look for rainfall to be quite variable as mixed data presents conflicting results and where and how much may also be exasperated more than what is typical for many summers. Taking all data (past and present) into account; rainfall is expected to be above normal over the southern sections of Southeast Lower Michigan and normal to possible even below across the Saginaw Valley and Thumb Region. As with temperatures, timing of the wettest and driest periods will be quite variable - not unlike the spring.
Look for my entire, detailed Outlook coming this week.
Bill Deedler -SEMI_WeatherHistorian