COLOR MY WORLD...
There's some good looking trees showing up in my neighborhood as falls colors begin to reveal themselves around the region. The Iowa DNR suggests that most or the peak colors in my area (including Illinois) occur the second and third weeks of October in my northern counties (HWY 30 north) and the third and fourth weeks from there south.
According to the DNR, the weather throughout the fall season has much to do with the development of fall color in trees. Cool night temperatures destroy chlorophyll quickly, but below freezing temperatures inhibit production of red pigments. The brightest displays of color occur when we have an early fall of bright sunny days and cool nights. These are excellent conditions for the development of red pigments. Cloudy days and warm nights will produce less brilliant colors because chlorophyll breaks down slowly and the red pigments are not formed quickly enough. Dry weather causes a greater buildup of sugars in the leaves, enhancing the production of the red pigments. Windy, rainy weather causes many leaves to fall prematurely, lessening the intensity of the display. A killing frost will destroy the leaf cells and the coloration process will not function effectively. So far conditions have been favorable for the vivid colors we all look forward to.
While we have at least a couple weeks to go before color reaches full intensity, the process is well underway to our north in Minnesota and Wisconsin where the northern half of those states will reach peak color in the next week. It should be nearing the northern Iowa border around October 15th. Below are the updated fall color reports for Minnesota and Wisconsin.
Following another spectacular day Tuesday, the satellite reveals a swirl in the clouds over South Dakota Tuesday night. That is an upper air disturbance that is going to break down the the ridge that's produced about 10 days of top notch weather as it arrives Wednesday.
Initially clouds will enter the area which is a good indicator that moisture is trying to return. Later in the afternoon, forcing from the upper level energy will attempt to pop some showers as it plows east. However, low levels remain quite dry and saturation is going to be a challenge. Much of the light rain that forms over central Iowa will get eaten up (and may even dry up completely) as it enters my counties in eastern Iowa. That spells little if any rain from this wave.
Another slight chance of showers exists Thursday as a potent cold front zips southeast. Most guidance shows little more than spotty brief showers of sprinkles...if that. So, despite the mention of rain probabilities both Wednesday and Thursday, I see little of it and it would not be shocked for much of the region to see just trace amounts. Not what the doctor ordered for my parched NW counties. Here's what models are suggesting for rainfall totals through Thursday.
The national model blend
The biggest impacts of the energy passage will be the winds and chilly temperatures that follow the cold front Thursday night and Friday. After highs again in the 68 to 76 degree range Thursday, a big drop is expected Friday with highs remaining in the low to mid 50s, in some spots nearly 20 degrees colder than a day earlier. Take a look at the 24 hour temperature change at 1:00pm Friday.
With the gusty winds and falling temperature Thursday night wind chills to start Friday morning will be in the upper 30s to mid 40s. You will want the coat.
The next challenge is how cold does it get Friday night. Skies are expected to be clear and the air quite dry. If the ridge axis is directly overhead (it will be close), winds should go light and radiational cooling quite effective. That could get lows to freezing or a bit below. Still some time to analyze the potential but frost and freezing temperatures appear likely. The national blend of models indicates this for lows Saturday morning.
COOL, CALM, AND COLLECTED WEEKEND...
After the frosty start the remainder of Saturday will be sunny but crisp. Highs should be confined to the mid and upper 50s, well below normal. Sunday the sunshine continues but return flow boosts highs back into the 60s for a more seasonal brand of weather to close out the weekend. Not bad...
Next week a nice warm-up kicks in with highs pushing 70 by Tuesday and well into the 70s Wednesday. At that point another strong front is expected to bring significantly colder weather by the end of the week. The EURO also hints at a system that could finally bring a decent rain threat back into the Midwest. Much depends on phasing, a process which is complicated and uncertain at this distance. Something to keep an eye on for sure.
With that a sign off wishing you a productive day. Roll weather...TS