SIZZLING SIGNS ON THE HORIZON...
THUNDERSTORM CONDITIONS
Heat. humidity, and a cold front combined to produce some active thunderstorms Thursday afternoon and evening. Up to 4 inches of rain fell around Dubuque, Waterloo, and Mt.Vernon, with numerous locations reporting 1 to 2" totals. The Doppler estimates from the NWS in the Quad Cities shows the greatest concentration of 1 inch plus amounts north of I-80.
Winds of up to 66 mph were measured in Cedar Falls with gusts to 60 also reported near Cedar Rapids and Dubuque. Here you can see the CAPE (convective available potential energy) Thursday afternoon representing the instability that drove the heavy rain and gusty winds. You can also denote the MCV (mesocscale convective vorticity) which enhanced the available forcing along the cold front.
IMPROVEMENT FOR THE WEEKEND
Behind the front and its attendant MCV Friday should be a breezy day with enough subsidence for most areas to stay dry. Even better, temperatures and dew points will be lower making for a far more comfortable day.
Saturday and Sunday northwest flow will be in place as we remain on the north fringes of an intense dome of heat. Small ripples in the flow could produce some widely scattered showers and storms, especially during peak heating. These should decay during the evening and overnight hours. Temperatures will be warm but seasonal staying mainly in the mid to perhaps upper 80s for highs.
ON THE EDGE OF THE HEAT
After that the forecast next week will depend greatly on the position of the heat dome down south. It makes a couple runs at the central Midwest but in general is held at bay just to the south. If that's the way it ends up, we remain near or within the ring of fire which would feature occasional thunderstorms clusters. Aside from the threat of strong storms, some areas could get into significant rains, much like what happened Thursday. That's not a sure bet but it is my hunch right now. The northern half of my area is most favored for the heavier rains. The EURO is hinting at that potential showing some pretty healthy positive departures in my area. Just to our south it's dry where the atmosphere is capped by the depth of the heat dome.
Here's the 500mb jet stream pattern next Wednesday. You can see the zonal flow slicing across the central US containing the heat across the southern half of the nation.
By the end of next week heights are in the rise and so are temperatures. This is a very hot look Saturday July 18th.
SIZZLING SIGNS FOR THE FUTURE
If the EURO is correct with the positioning of the core of the heat (and it has tried to show this scenario a couple times recently and failed), we are in for a couple of days of sizzling and potentially serious heat conditions. These are the highs the EURO shows the 18th. 100 or better up to about I-80
Now the dew points, and this is where things would get serious. Notice the are pooling across my area in the upper 70s to low 80s.
Dew points of that magnitude with actual temperatures around 100 would produce heat index values on a widespread level of 110 to 118 degrees. That's a deadly combination and something I've experienced less than a handful of times.
The Climate Prediction Center sees the threat and does offer a high risk assessment of excessive heat during the period July 17-19th.
I do want to stress that we are more than a week away from such an event and things could certainly change for the better. Already I can tell you the GFS has a far more tolerable look. However, confidence in my mind is growing that significant heat could develop around the central Midwest in the 8-10 day period. Now we wait and hope for the best. Roll weather...TS
