WHEN IT RAINS, IT POURS
Weather in the Midwest is fickle, I don't think anybody would dispute that fact. Rains come, they go, they hit and they miss. Spring is a time when rains are generally plentiful and widespread. In April and parts of May they can be stratiform, which means they are fairly steady and predictable, being parts of storms systems covering large areas.
We are at that time of year now where instability increases as temperatures steadily warm. Thunderstorms, that are convective in nature (far more vertical in development), become more common than stratiform events. That typically means rains are more scattered and amounts show greater variability. Thunderstorms also are far more dynamic and produce much heavier amounts in shorter periods. Sometimes one part of town gets drenched with an inch of rain and the other side stays dry. Due to this hit-and-miss nature, it's important to get good widespread soaking rain events during spring because summer varies widely from storm to storm. Some years you get them, some you don't.
I bring this up because weather models over the 10-day period, May 20-30th, show the central Midwest close to what's known as a baroclinic boundary. Notice, temperatures to the NW are cool (higher pressure), while those to the SE are warm (lower pressure). It's an accurate representation of where the storm track will be situated as the warmth of summer tries to make inroads further north. It happens every year.
With the clash of air masses near the baroclinic boundary in mid-May, the potential exists for an active period of weather that may have severe weather potential. If nothing else, it certainly exhibits traits of well above normal precipitation with regular systems traversing the boundary. The "wild card" in such a set-up is where the storm track is most consistently positioned. That determines the degree of instability and the location of the greatest rain threat. For now, the Weather Prediction Center shows much of my northern counties in a heavy rain risk between May 18-22
The Climate Prediction Center extends and expands the heavy rain threat SE through much of the central Midwest May 23rd-29th.
As one would expect, CPC's 6-10 day outlook has my area with near to above normal temperatures and above normal precipitation chances. In general, the big picture certainly points to a stormy, wet, long range period.
The EURO reinforces the idea, showing this for total precipitation through May 30th
Those amounts are 1–3 inches above what's normal in the 10-day departures below.
I'll have more on the short range and weekend forecast below, but first this message.
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WARMER DAYS ARE HERE AGAIN
Wednesday was a stunning May day, and frankly one that's hard to beat any time of the year. Thursday will not meet the challenge, with the day potentially marred by some passing clouds and perhaps even a shower or thunderstorm. It will take a while for the atmosphere to saturate, so outside a brief late morning shower or sprinkle, any wet weather of consequence should hold off until afternoon or evening. At that time, diurnal heating could build enough CAPE for a few storms that could produce some brief downpours in the SE, but they look localized and most likely from the Mississippi east. Highs of 70-75 are expected. Here's what the convective allowing models (CAMS) show for rain potential. Amounts are minimal in most areas, if any falls at all.
The 3k NAM
The HRRR
Friday, Saturday, and Sunday are looking mainly dry and warm during the daytime hours. Highs Friday should hit the mid to upper 70s. Saturday, with a fast moving wave arriving late, an evening thunderstorms is possible, particularly in the north closer to the best forcing. With highs in the low to mid 80s, capping may be sufficient to keep any storms widely scattered. Obviously, before that, Saturday will be a summery day, with its warmth and dew points that may inch into the low to mid 60s.
Sunday, behind Saturday evening's weak wave, a bubble of high pressure starts the day sunny and with lower humidity. Later in the day, southerly winds return, allowing a quick surge of moisture. After another warm day Sunday with highs of 81 north to 86 south, the stage is set for thunderstorms to develop Sunday night over western Iowa that could bleed into my area during the late night and part of Monday. This is the first wave of what could be multiple periods of wet weather next week.
That is all for now, have a terrific Thursday and roll weather...TS
