THE BEAT GOES ON...
With a mid-summer heat dome in place, the beat went on for our steamy and at times stormy weather pattern Tuesday. As far as heat goes, Tuesday was the worst of summer so far with dew points in the mid to upper 70s and highs reaching well into the 90s. Heat index values up to 105 were common with some local spots tapping out greater than 110. In Oskaloosa, Iowa, the ASOS observation at 3:00pm. showed a 100 degree temperature with a dew point of 78. That generated a searing 118 degree heat index.
A number of places in southeast Iowa came very close to reaching the century mark. Some NWS reported highs.
WASHINGTON.....99
FT. MADISON......99
KEOKUK..............99
MT. PLEASANT...99
MUSCATINE........99
VINTON................98
BURLINGTON......97
IOWA CITY...........97
Moline..................97
Here's the upper air pattern at 500mb responsible for the oppressive conditions. The heat ridge is centered over Arkansas with heat and humidity on the NW fringe aimed directly at Iowa.
Under the ridge, where the air is compressed it sinks and heats up. As a result heat advisories and warnings were posted from Iowa to Louisiana.
Here's some of the heat index values reported around 2:00pm Tuesday. There's a 109 showing at the Quad City Airport in Moline.
WHAT'S NEXT...
Wednesday's weather will be heavily reliant on Tuesday night's convection. A forward propagating thunderstorm complex known as an MCS advanced rapidly through my region Tuesday evening. It generated a significant cold pool that drove storms southeast of the region shortly after midnight. Rain cooled air (or at least cool outflow) will keep temperatures lower in the northern half of the region. Further south, how far the cool air can penetrate is in doubt and Wednesday is likely to be another toasty day here. The EURO is indicating highs that look like this. In most areas they are down 8-10 degrees signifying the end is here (or coming) for this round of heat. If heat advisories are issued Wednesday, they would likely be for the area near and south of HWY 34.
With far less instability Wednesday and subsidence kicking in, models are not at all excited about rainfall or severe weather prospects. At this point, SPC only indicates a marginal risk of severe storms near and south of I-80..
The Weather Prediction Center even shows a broad swath of excessive rainfall potential through Iowa and northern Illinois Wednesday. I'm sure that is unlikely and the outlook will be altered significantly southeast of my area in later updates.
After that, Thursday brings another round of forcing and potentially a heavy rain set-up in much of my area. I'm seeing signs of another healthy round of precipitation that could reach the 1-2 inch threshold if trends holds. That on top of what's recently fallen could lead to some hydro issues. Here's rainfall totals from Tuesday's storms thanks to the Iowa Flood Center.
Those rains were preceded by these totals Monday.
Here are the 2 day composites which show some 6" plus amounts from NE Iowa into NC Illinois since Sunday morning.
Additional heavy rains would cause rises on area rivers and streams. The Thursday period will need to be monitored for its rain potential in the next 24 hours.
On a positive note, notice what happens in the period Friday-Monday (days 3-7). The heavy rain threat is pushed well to the south.
The reason for the change is the breakdown of the ridge that's currently over the SC United States. It's expected to retrograde to the west allowing high pressure and NW flow to dominate the weekend and all of next week. That brings pleasant summer weather back to the Midwest with seasonal highs and lower than normal humidity. Here's what the 500mb pattern is projected to look like.
Temperatures July 11th-16th may even be a touch below normal of the EURO has its way. At least that's what its 5 day departures are hinting at.
Additionally, rainfall during that 5 day period is well below normal with dry air prevailing.
To summarize, Wednesday will be far less hot and humid, a welcome change. Additionally, rain chances look low until the next wave of rain arrives Thursday. After that, a nice period of summer weather arrives for the weekend and much of next week. Sounds good to me! Have a great hump day and roll weather...TS
