WORKING UP SOME WETTNESS...
So far the week's weather has been nothing short of beautiful. Comfortable temperatures and low humidity have brought the Midwest chamber of commerce weather. Wednesday will be another fine day but changes are underway that will bring warmer readings and rain chances. Here's what's going on.
The weather charts early Wednesday depict northwest flow in the upper levels of the atmosphere. Within the long wave pattern a short wave is shown approaching the Midwest Wednesday night. Ahead of it, moisture is on the increase as you can see with precipitable water vapor increasing Wednesday morning over central Iowa.
With the return of southerly winds temperatures will also be warmer with the HRRR popping highs into the mid to upper 80s, roughly 4 to 5 degrees above normal.
Dew points will remain near 60 so it will be a warm day but not an oppressive one. Further west where the moisture is pooling there will be some instability as CAPE values could exceed 2,000 j/kg by Wednesday evening.
As the front acts on that Wednesday night showers and storms will form in NW Iowa and Minnesota and drop southeast overnight. By the time they reach my area instability will weaken such that only garden variety showers and a few storms will remain. As the fronts slowly inches southeast Thursday lingering light showers could fester much of the day. Friday there could be an isolated shower or sprinkle but for most it should be a dry day. Clouds will dictate how warm temperatures get both Thursday and Friday. For now upper 70s to low 80s have the most support among available guidance.
As far as rainfall is concerned, amounts should generally be light with a few pockets of moderate rain where a thunderstorm can manage to flourish. My northern and western counties (west of the Mississippi) are favored for the larger amounts. Here's what models suggest for rain Wednesday night through Thursday.
The national blend of models (NBM)
The weekend forecast will be dictated by a series of mid level disturbances riding the upper level winds out of the Plains. With time a persistent southerly fetch will force deeper moisture into the Midwest. Unfortunately, there are lots of inconsistencies with the forcing tied to critical synoptic features and their movement over time. This makes it difficult to time the bands of precipitation that are likely to occur. Confidence is fairly high there will be rain but low on where and how much. My best guess is rain holds off until Saturday night and then could be around on again off again into Monday. Cloud cover will again play a big role in how warm temperatures get. Even with substantial cloud cover the deep southerly flow show keep readings Saturday through Monday close to 80. Any breaks for sun could pop some mid 80s south but heavier clouds and rain could keep some spots in the mid to upper 70s, especially north. Again, the most likely range is upper 70s to low 80s. Here's what the national model blend indicates over the next 10 days. In general, highs go from near normal through the weekend to below normal by the middle of next week.
The potential is there for some significant rain, (an inch or more), in the Saturday night through Monday night period. Again, due to mesoscale details that are yet to be determined confidence is lower than I would like to see but the trend for heavier rain is there in the national blend of models. Here's what it depicts through Tuesday including what it sees Wednesday night and Thursday. This is likely going to bounce around a lot in the next couple days as models get a better handle in dynamics, timing, and positioning.
With that, I will call it a post. Enjoy your hump day, changes are coming. Roll weather...TS