NO PAIN NO GAIN...
Showers and thunderstorms have blossomed over much of the region overnight and are likely to continue into the morning before diminishing later Friday afternoon. The catalyst is a strong warm front which is driving a healthy dose of warm air advection. Additionally, abnormally high water vapor levels combined with a 50kt low level jet is (and will continue) to drive pockets of heavy rain. Some parts of the area, especially north of the Quad Cities could end up with totals of 1 to perhaps 2 inches. The heavy rain threat in this area is a possibility until the set-up wanes later Friday. The Weather Prediction Center has a marginal risk in effect for excessive rains that covers most of my area which seems too far south.
WPC's QPF models indicate potential rain totals in this range. The majority of my area gets a good soaking with the higher amounts northwest of I-80. Radar trends have me thinking this is too far south.
Especially considering the latest HRRR really shoves the heavy rain band north, so much so that most of it is north of HWY 30 with very little south of I-80.
The official NWS forecast may end up a bit too far southeast and too heavy with the placement of the heavier totals if the latest models verify. They seem to be a good 50-60 miles further NW than the graphic indicates. Hard to say with storms just beginning to develop.
SPC also has a marginal risk of a strong storm at least through the morning hours Friday. The primary threat would be from hail, especially closer to the warm front. In general, any elevated hailers would likely produce smaller stones than those required to meet severe limits. Currently the threat appears low.
The outflow from the convection (cold air descending from the updrafts) will make it tough for the warm front to advance Friday morning. That said, it will make slow progress but as I've alluded to for several days, models really struggle with this sort of situation in the early spring and tend to project the warm front further north than it actually gets. I think it will take much of the day before it passes I-80. That means a rather sharp cut-off in temperatures with a cool day in the north and a warm one down south, especially south of HWY 34. The HRRR has this for highs later Friday afternoon. Notice the 30 degree spread from Dubuque to Keokuk. If overnight storms are less intense and widespread than indicated, the warm air will have a chance of making progress that's further north than shown. Straight up, its a very difficult call that's impossible to precisely nail.
Here's what the EURO indicates.
NO PAIN, NO GAIN...
You've all heard the saying, "no pain, no gain". Well, in this case the pain of the heavy rain and crummy weather to start Friday will lead to big temperature gains Saturday. Friday night the warm front surges northward ending the rain placing my region squarely in the warm sector of an intensifying storm over the Plains. With deep mixing Saturday, winds are going to be an issue, perhaps reaching gusts of up to 35 mph, that's close to wind advisory criteria. However, the stout winds provide a major benefit as they allow highs to soar into the upper 70s to low 80s under partly sunny skies. With dew points around 60 the day will have that moist feel to it that spring is known for at times in late April and May. It should be the warmest day of the year so far. Well deserved too with April as a whole running far below normal.
With the warmth and moisture established there will be CAPE (instability) in place Saturday. However, there is a bit of a cap in place and any forcing that would break it remains out west near a cold front. That makes for a dry day with just some passing clouds at times.
Towards evening Saturday, the cold front is expected to turn active with thunderstorms popping over central Iowa as the cold front impinges on the instability out there. The line of broken showers and storms is expected to reach my far western counties in Iowa after 9 or 10:00pm Saturday night. A strong storm or two is possible but that will be contingent on how much instability remains after sunset. If the storms are a couple hours slower that effectively eliminates the threat. As it is, any showers and storms (no matter how strong) will weaken as they approach the Mississippi late Saturday night and early Sunday. The progressive nature of the front should have it out of my eastern counties in Illinois around mid-morning Sunday ending any remaining showers. Breezy, cooler, and drier air sweeps in for the afternoon. Highs should range from the low to mid 60s. As you can see SPC keeps the severe weather risk just west of my area Saturday afternoon and night.
Once the cold front passes it allows another healthy shot of fresh Canadian air to descend on the Midwest and it seems likely that highs Monday and Tuesday remain in the range of 45 to 50 degrees. You can see the extent of the cold air by Tuesday's temperature departures which are a good 15 to 18 degrees below normal...once again!
Once it returns, the cool air looks to be a fixture through the first week of May. Here's the week 1 and week 2 temperature departures from the EURO ensembles. Not extreme but still a bit on the cool side.
Week 1 April 21-28
Week 2 April 29-May 6th
Precipitation still has a generous look to it through that period. Here's the departures.