(Also Includes references to Spring of 2011)
By: Bill Deedler: Southeast Lower Michigan Weather Historian
Overall, I look for summer temperatures to average around normal. Local analogue data for this summer generally shows normal to below normal averages. At the same time, projections for the upper wind pattern suggest ridging over the south-central part of the country will periodically expand into the Great Lakes bringing more heat into the region. The temperature outlook is a tough call and will mainly depend on the how strong the ridge becomes and its placement. At this time, it looks like the ridge will oscillate from just to our west (Midwest) to the eastern third of the country. This will bring periods of heat and cool downs (while working in conjunction with the upper low in Eastern Canada). Number of 90 degree days should be about average for the summer, 8-12.
It is interesting that the summer analogues (like the spring) continue to favor below normal temperatures for the summer. This matched well with the actual spring pattern, while the overall dominant trend (number of cool days) did fit the analogue projection, the magnitude of below normal departures were indeed, less. And as in the spring, I feel the analogue’s temperature departures are a bit too cool and in the end, I expect temperature departures to place within -0.5 to +1.0 of the norm.
Overall rainfall this summer is challenging due to this past spring’s wet pattern and the trend the analogues show for the summer. In the spring data, I favored a wetter spring especially from the Flint to Port Huron areas (the I-69 corridor) south to the Ohio border. The analogues favored normal to above normal rainfall with some years making the top 10 wettest springs. Of course, this spring was indeed very wet with Flint ranking at the top with the all time wettest, Detroit the second wettest and Saginaw somewhat lower in 10th spot (see below in spring data). The Summer analogues still show some wet years but now the overall preference is trending toward drier. The drier part of the summer showed up at different times and not necessarily mid-late which is more common. Overall, I look for near normal rainfall (locally above in heaviest storms) as the storm track remains active but with a trend toward rainfall events being less often.
Most striking of the analogue trends is the likelihood of a warmer June (or warm first half of the summer) relative to average and a cooler July and/or August. July's contained the biggest below normal departures /-1.7/ of the summer. Out of the 12 summers, all the Julys contained normal to below normal temperatures with six below normal. August also showed six years with below normal temperatures though not as great of a departure is noted in the average. The cooler Julys were mainly found in the earlier years.
As stated above, overall I feel the analogues a bit cooler than what I expect with the summer averaging around normal. Their pattern is reflecting the likely trend of the summer (actually not unlike our last analogue, 2008).
Rainfall amounts are all over the board, not surprising when you have neutral conditions and dealing with summer convective rains. It is reflective of where the fronts hover during the summer. If the ridge is a little stronger than the driving force of the cold fronts /Canadian upper low & upper wind flow/, then the likelihood of a drier summer results. If the conflict along the fronts settles more in the southern Lakes region, then a wetter summer results as the fronts gets stuck in our neck of the woods. One trend that does show up is a somewhat drier pattern materializes from the wetter springs. I feel we will see both patterns this summer and thus, around normal in the general call. We shall see.
La Nina - Neutral Summer 2011 Analogues
More to Follow: Pacific/Hemispheric trends & Severe Weather Potential
Spring was wet, wet, wet, but not nearly as cool as one might think!
Overall spring temperatures* for Southeast Michigan:
Detroit*: 47.7 was just 0.6 below the norm of 48.3
Flint* : 45.8 which was actually 0.4 above the norm of 45.4
Saginaw*: 44.9 like Detroit was 0.6 below the norm of 45.5
I stated in the spring outlook I thought the analogue average temperatures/departures were too cold but still, the dominant temperature trend (more cool or warm days) would favor the cool side. As it turned out, the spring temperatures for Southeast Michigan /ave 46.1 just -0.3 below the 46.4 norm/ and well less than a degree below normal being well within the normal range. The number of cool days this past spring were many and many people have commented to me about the “lousy spring”. Looking at just the average temperature and departures would counter that claim, truly another case where statistics lie as the dominant pattern was cool! None of the three cities even placed in the top 20 coolest springs (tell that to your friends). I also stated I thought the warm spells would have enough gusto to erase enough of the cool departure dominant trend.
From the Outlook:
The analogues this go-around are strongly suggesting a cooler than normal spring (see the details in Analogues section). The best chance of below normal temperatures generally speaking, are in March and May. Spring has a good chance of being cooler than normal early and again late in the season is the best way to look at it. I feel the magnitude of the cold in the analogues is too strong and warm spells will offset the cooler weather that is anticipated. I look for a spring closer to normal than the analogues portray.
Spring Rains Were Aplenty
No disagreement here it was wet and the stat’s clearly reflect that! Detroit came in second place for wettest spring on record with 14.60” /1947 was the wettest at 16.31”/ Flint handily smashed its record wet spring with 17.00” even, /the previous wettest spring was in 13.80” in 1945/. And, while it was wet further north in Saginaw, the magnitude wasn’t nearly as great as in Flint nor Detroit. Saginaw received 11.88” which placed further down the list in tenth position.
From the Outlook:
The local analogue springs displayed a dominance of normal to above normal precipitation with four relatively wet springs, six normal and three dry. Spring of 1943 placed second wettest at Detroit and contained an extremely wet May (second wettest) with 8.03” of rainfall. In May of 1956, 6.03” of rainfall /seventh wettest/ was measured in Detroit and that contributed to the 4th wettest spring. Both of these springs were also wet at Flint and Saginaw. On the flip side, 1971 was a very dry spring in Detroit with only 4.48” of rain making it the 5th driest spring at Detroit while 1925 just made the driest list at 19th place with 6.07”.
Making the decision
The main trend of the analogues was for norm to above normal precipitation, though I did have a few exceptionally dry springs to confuse the issue. I decided that the wetter springs were the way to go (along with suggesting where the wettest would be) by the recent past matching well with the wetter analogues.
From the Outlook:
I expect the precipitation to be near normal to above across the entire region. We’ll keep the best chance of above normal precipitation where the trend has been since last summer, from the I-69 corridor south to the Ohio border.
*NWS spring/monthly CLM write-ups N/A at press time