Make no mistake about it, we are set to sizzle Saturday with a big day of heat and humidity planned. Already the NWS has issued heat advisories for that unruly combination. Most areas can expect it to "feel" like 100-105. The advisory goes into effect at noon and lasts until 9:00 pm Saturday evening.
Here's what the HRRR indicates for potential heat indices around the Midwest Saturday afternoon.
When it's all said and done Saturday, it could be one of the warmest days of the summer in terms of the actual high. To date, the highest temperature this year at the NWS office in the Quad Cities has been 97 and that occurred way back in May. The HRRR is predicting 96.
Heat remains a concern for Sunday but it's not as cut and dry as Saturday's set-up. Thanks to the approach of a slow moving cold front moisture will be pooling over the region and in some places dew points could reach the mid-70s. That alone will make for an uncomfortable day. However, heat advisories may be confined to the area south of HWY 30 where temperatures will continue in the mid 90s. Up north, showers and thunderstorms, at the very least some debris clouds will limit heating keeping conditions just cool enough to avoid advisories there. Down south it looks like another scorcher where the EURO indicates heat indices up to 105.
While the forecast is pretty straight forward Saturday, it gets quite a bit more challenging Saturday night through Monday morning with regards to thunderstorms. As I mentioned above, a cold front descends on the area from the north Sunday. By that time deep tropical moisture covers the region. The EURO indicates water vapor over all of my area of 2.00 to 2.70 inches, in other words the atmosphere is like a sponge...just ready to get squeezed.
Such deep moisture and heat will no doubt lead to instability which lends itself to thunderstorm potential as forcing from the front arrives. With such high levels of moisture, any decent updraft would have a chance of producing heavy rain in a short period of time. This is not a concern for my area until Sunday morning when storms could go up in the north. If these are part of a an MCS (mesoscale convective system) they may have a strong enough cold pool to propagate into my central counties during the day. Whatever develops could also leave an outflow boundary for additional storms in the afternoon. These small scale details which are big players in thunderstorm development, can't be seen at this distance so it makes the timing and coverage aspect difficult to pinpoint.
With CAPE reaching close to 3,000 j/kg there will be enough instability for a few strong storms, especially if peak heating is realized.
Overall, the threat of strong storms appears isolated despite the available instability with the stronger upper level flow too far north to support widespread organized severe weather. However, lightning and heavy rain is very much on the table, especially Sunday night. In fact, the 6 hour lightning flash rate on the EURO is maxed out between 7pm and 1:00am Sunday evening.
The bottom line is that showers and storms will be in the forecast Sunday and Sunday night until the front can clear the south later Monday. Currently guidance shows the heavier rains over the northern half of my area but that is contingent on the speed of the front which could be altered by where storms develop up north Saturday night and how strong they become. Here's what models are currently suggesting for rain totals.
THE Weather Prediction Center outlook
The national model blend (NBM)
The Weather Prediction Center does indicate a slight risk of excessive rains Sunday in my northern counties.
Once the system departs late Monday the remainder of next week looks very nice. Highs on the EURO are in the low to mid 80s and humidity will be noticeably lower. A nice break.
Well, I'd tell you to enjoy the sauna Saturday but I'm sure that goes without saying. Hey, at least you don't have to shovel it. Have a fantastic weekend and roll weather...TS