May UPDATE: Temperature flip, multi-day severe storms
Friday, May 12, 2017, 11:41 - An active spring weather pattern will continue into May, with cooler-than-normal temperatures taking hold for parts of the country – including some areas that have enjoyed quite mild conditions through the spring so far.
Storm outbreaks may be more infrequent in the early part of the month, but we will be entering the climatological peak of the Great Plains tornado season, and severe weather potential is likely to increase in the latter half of May.
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April comes to an end: Highlights
Before we get to the details on May, let’s take a quick look back at the month of April. April started off with a period of powerful tornadic storms, particularly across the Deep South.
Later in the month storms and temperature swings gave way to a period of widespread warmth for many. Though in line with our April outlook, wet and cool conditions lingered across the Pacific Northwest.
As the above temperature anomaly (departure from normal) map shows, the warmest conditions relative to normal were centered in the Great Lakes and Ohio Valley, which finished out the month 4-6°F warmer than normal.
The early part of May will see a distinct pattern change, which will bring cooler conditions to many locations that saw persistent warmth in late April. A deep trough setting up over the eastern half of North America will bring a chill from the Rockies to the East Coast, and all the way to the Gulf of Mexico.
Cooler than normal temperatures will dominate the eastern third of the country right through the Mother’s Day weekend, with the exception of the Deep South where early summer heat and humidity will attempt to surge into the region at times.
However, a major pattern change will begin to unfold during the week after Mother’s Day, which will result in a pattern similar to what we saw during the month of April with cooler than normal weather in the west and a return to above normal temperatures for the east. The model forecast below for the final 10 days of May illustrates the temperature pattern that we expect. From the Midwest to the Northeast this will bring a quick transition from April-like weather to early summer heat and humidity.
Unfortunately, this pattern also favors a very active period of severe weather. A multi-day severe weather event is likely during the week after Mother’s Day and the pattern looks to support additional rounds of severe weather through late May as surges of warm and humid air from the Gulf clashes with the cooler continental air centered over the West.