A TALE OF TWO EXTREMES...
A strong summer storm has been working its way across the region the past 24 hours. While not a severe weather producer, the vigorous disturbance has kicked up scattered showers and storms. For those of you in the north, the big news is much need rain fell where it was in high demand. Unfortunately, it was too much of a good thing in spots with some 3-4 inch downpours Monday afternoon. A flash flood warning was issued for Dubuque County. Here's the Doppler radar estimates Monday evening with a clear emphasis for the heavier rain to be in the NE half of the area.
The 24 hour rainfall total of 3.20 inches in Dubuque Monday was an all-time record of August 14th.
The energy associated with the system was unusually strong for early August featuring a closed circulation situated over EC Iowa Monday. The "bowling ball" as we call it showed up nicely below as it heads for the Great Lakes.
The vorticity (forcing) is very evident on the satellite imagery spinning through Iowa. There's a classic dry slot ahead of the closed low while directly under it, the cold pocket is producing low clouds and wrap around showers and thunderstorms. Two distinct rounds of vorticity brought rain, one Sunday night and the other Monday afternoon and evening. Until the system clears Tuesday morning, the remaining instability will be strong enough to generate patchy clouds and isolated showers east of the Mississippi. Most areas stay dry.
More likely, north winds will also add a little chill to the air early Tuesday morning gusting to 20 mph with readings in the 50s. Highs will eventually rebound into the 70s with skies becoming mostly sunny in the afternoon.
Wednesday another NW flow disturbance takes aim on the upper Midwest as it dives southeast out of Canada. It will be moisture starved ensuring most of its rain remains to the north. That said, there is a lower end chance of broken showers and storms in the NE late Wednesday night. Anything that can reach that area should be light and brief. Ahead of the front, highs Wednesday will warm into the low 80s with SW winds. Thursday, northerly breezes return behind the front and highs cool a few degrees returning to the upper 70s.
A LATE SUMMER HEAT SURGE...
A significant pattern change unfolds late week with a heat dome building and expanding across the nation's mid-section. Current indications are that the 500mb ridge (the core of the heat) establishes itself over the central Midwest Sunday-Thursday of next week. Such a position would keep the "ring of fire" north of the region resulting in strong subsidence (or sinking air) locally. Highs should reach the 90s no later than Sunday and could remain there through at least Wednesday. Just how hot will depend on the amount of water vapor in the air (dew points). I do expect at least a couple days in the mid 90s with Tuesday potentially reaching the upper 90s in a few locations. WPC has a slight risk outlook for excessive heat issued for August 22nd and 23rd.
The Climate Prediction Center shows a 90 percent chance of well above normal temperatures in the period August 19-23rd.
As I mentioned, the active storm track (ring of fire) is well to the northwest keeping the sensible weather hot but dry with most of the active thunderstorms over the upper Midwest.
It does appear that the heat should break late next week as the jet buckles back into its familiar NW flow structure, something we've seen so much of this summer. That suppresses the heat dome and gets temperatures back below normal by next weekend (August 26-27th).
Before that, here's the 500mb jet on the GFS next Monday the 21st as the heat intensifies.
These are the associated temperature departures. These are highly inflated due to the inability of the GFS to handle mixing ratios during times of high heat. Take at least 10 degrees off what is shown.
Just 4 days later the ridge has collapsed and is replaced by this trough and its NW flow.
Temperatures hit the skids and go from way above to below normal. That is a radical change. Talk about the tale of two extremes!
Meantime, Tuesday will be a day of pleasant temperatures with highs in the mid to upper 70s and dew points in the mid 50s. Enjoy this brand of summer, the other side of the pillow is on the way this weekend. Roll weather...TS
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