IS THAT FALL I SMELL...
It's been one heck of a week weather wise. After a fall like start with 60s for highs on Monday, a steady diet of sunshine and warm air allowed temperatures to reach 80 by Wednesday and remain there the rest of the week. Here's the tale of the tape in the Quad Cities. Notice too the predominance of warmth so far this month with 11 of the 16 days at 80 or above. Normal highs are now in the mid 70s.
We've got a good 5 more days of this type of warmth before a pattern change is implemented next week. If my schnoz is working correctly, I smell fall like temperatures in our not to distant future. I'll get to that in a moment. First, let's talk the weekend and how long our summer fling will continue.
In regards to weekend temperatures, one of the driving factors will be clouds, the other potential precipitation. The way things currently stand, much of the showers and storms that develop are expected to be nocturnal and tied to forcing Saturday night and again Sunday evening. With that being the case, enough sunshine is expected both days to drive highs into the low to mid 80s, warmest in the south. Moisture has also been steadily increasing with 2 days of southerly flow and dew points will reach the range of 65 to 70, with the highest levels Sunday when water vapor pools ahead of a cool front. Humidity will be a noticeable feature through at least Tuesday of next week.
Here's what the EURO indicates for highs in the Quad Cities through Monday.
That brings us to rain chances and they are certainly there. As mentioned most of the showers and storms are expected to be during the overnight hours. That does not preclude a few early in the day both Saturday and Sunday, especially in my western counties in Iowa.
Coverage Saturday night looks to increase as the low level jet ramps up after sunset and impinges on the instability built up during the day. However, there is still a large spread regarding the areal coverage and extent of any storms. It currently appears the risk of strong storms would remain to the west of my area. What remains of these storms could produce pockets of heavy downpours as they get into parts of the region later Saturday night. SPC currently has a slight risk out for isolated severe weather southwest of a line from Ames to Newton and back to Lamoni.
Any lingering storms depart early Sunday allowing the atmosphere to destabilize with heating in the afternoon. Late in the day or evening, convection is expected to pop up ahead of a cold front. Current indications show the front progressing into my central counties when this occurs. That argues for the greater rain chances Sunday night to be over the southern half of my region, roughly I-80 south. The 3k NAM builds some respectable CAPE indicating enough instability for a few strong storms in that part of my area,
SPC has much of the region near and south of HWY 30 highlighted in a slight severe weather risk Sunday evening. I could see SPC moving the risk outlook further south towards I-80 if tonight's trends hold.
For the weekend as a whole, models are suggesting this for total rainfall through Sunday night.
THE NBM (national model blend)
The Weather Prediction Center
Once the front exits Monday should be a warm but dry day under a weak ridge of high pressure. Most places should be back in the low 80s for highs. Monday night a ridge riding disturbance swings across my far northern counties bringing a chance of late night storms there. Otherwise, warm air aloft is flooding the Midwest allowing a cap tp build Tuesday and Wednesday. With that in place those 2 days appear to be dry and very warm, especially Tuesday when highs could clip 90 in the SW half of my area.
Wednesday both the EURO and GFS bring a healthy cold front into the region. The EURO is faster and cuts the warmth off early in the north cutting highs there to about 80. The rest of the region reaches the mid to upper 80s before the cold front gets established late day. The GFS being slower allows the entire area to experience another toasty day in the mid 80s north to low 90s south. That issue will be resolved in the next 24-48 hours.
That cold front does mean business but only in sense of temperatures. The timing and dynamics do not look good for any storms as it passes Wednesday. However, strong northerly winds develop Wednesday night and Thursday bringing a very fresh brand of weather to the Midwest. The GFS indicates readings 30-35 degrees cooler than just 24 hours earlier. Some of that is due to post frontal clouds and showers which the EURO does not depict. I would say 25-30 degrees cooler is a realistic scenario as highs remain in the low to mid 60s.
Come Friday morning, parts of the upper Midwest could see their first 30 degree lows. Most of my area should be well into the 40s.
So, as I said off the top, I do smell fall and interestingly enough its arrival coincides with what's officially the first day of astronomical fall (Thursday, September 22nd). All right, have a great weekend and enjoy the diversity in seasons the next week will bring. Roll weather...TS