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  • Tim McGill

Rain Chances Dry Up After Today

Drought Deficit Grows


The area of northern Illinois in a moderate drought expanded just a bit over the past week. Our best chance of rain over the next several days is today. It looks like the rain that may fall will not come close to putting a significant dent in our drought. About 40% of the area will see scattered showers and thunderstorms today with a few spots getting soaked because of the abundant moisture in the air. Some of these storms could be strong with damaging winds the biggest threat.


O'Hare has seen only a trace of rain in the past two weeks. We are down over 4 inches below average for rainfall since May 1st and over 8 inches since March 1st. We are about two weeks away from starting July, typically the driest month of summer.


Here is a short recap of my drought update from yesterday's post:


The U.S. Drought Monitor says 8.52% of the state is in a moderate drought. That is an increase of 1.6% compared to last week's analysis. 20.89% of the state is considered "abnormally dry" which is an increase from 16.97% last week. "Abnormally dry" is just one level away from a moderate drought. The amount of Illinois in a severe drought remains unchanged at 4.58%.


A look at rainfall departure from average over the past sixty days might be the best visual to help define our drought. Portions of northern Cook County, northern Kane county, about half of McHenry county and nearly all of Lake County have only received about 10% to 25% of the average rainfall we normally see during this period. Most of northern Illinois has seen between about 25% to 50% of average rainfall for the past nearly two months.



The HRRR model total precipitation forecast through 10 pm tonight is not promising. It shows only widely scattered pockets of rain mainly from near the city and then southward.



The GFS model suggests scattered showers and thunderstorms today too. There should be about 40% coverage with these. Rainfall chances evaporate though after today. The next decent chance for rain comes on Friday.


The latest GFS model total rainfall forecast through Sunday morning shows a range of rainfall from about a tenth of an inch to nearly four tenths of an inch. Keep in mind that with the scattered nature of this rainfall it could be a feast or famine situation. Some spots could get soaked with more than four tenths of an inch and many spots could get nothing at all.



I ran the total rainfall forecast out through next Saturday morning. Aside from areas well west of the city, most of the area would get about a third of an inch to around six tenths of an inch in total (including today's rainfall if this verifies. Some of the area could be running a deficit of over 9 inches of rain since the start of spring by Saturday.


The long range precipitation probability forecasts offer only slight hope for a little more rainfall. The latest 6-10 day forecast has us outlooked for below average precipitation overall from June 17th through June 21st but the probabilities had dropped slightly. The longer range 8-14 day forecast now favors us for near normal precipitation overall from June 19th through June 25th. We are at the point that a return to near normal rainfall is something to get excited about.






Dropping Dew Points Bring Relief


June has sure come in hot. The month is now running nearly 9° above average. Friday was the 5th day out of 11 this month with a high of 90° or above. We aren't done with the 90s yet.


Average highs for today's date are around 80°. The HRRR model pushes highs today into the lower 90s again away from the lakefront but keeps it cooler (upper 70s) lakeside. The combination of heat and humidity will make it feel like the upper 90s to near 100°.


It may be a few degrees cooler Sunday but the big difference will be the drop in dew points. Dew points give meteorologists the best measurement of moisture in the air. They slip from the 60s today into the 50s for tomorrow. It should feel less like Florida on Sunday as the humidity levels drop dramatically. It will almost feel like fall by Tuesday morning with not just lower dew points but actual air temperatures falling into the 50s too. The hourly forecast shows our best chance of rain today is from midday to early this evening.



The National Blend Of Models has our highs falling from the 90s today to the 70s by Tuesday. We will see a couple of cooler than average days (barely) before we bounce back to near 90° for Thursday and Friday.




Warmer Pattern Signal Not As Strong


The longer range temperature probability forecasts both have us outlooked for a continuation of our warmer than average pattern. The signal isn't as strong compared to recent model runs but they still favor us to be above average overall from the end of next week and well into the following week. The strongest signal for anomalous warmth remains out west. The 6-10 day forecast has outlooked us for above average temperatures overall from June 17th through June 21st. The longer range 8-14 day forecast favors us for above average temperatures overall from June 19th through June 25th. Average highs for these two periods are in the lower 80s.



The even longer range Subseasonal Experiment (SubX) temperature anomaly forecast keeps us favored to be warmer than average for the end of June and start of July. The average highs for this period are in the lower 80s. The temperature anomaly forecast for the week ending June 25th has us outlooked for above average temperatures overall but on the lower end of the spectrum. The forecast for the following week ending on July 2nd also has Chicago outlooked for above average temperatures overall with a stronger signal.




Here is my 7 day forecast:


Today: Cloud/sun mix, sct. showers/t-storms, humid High: 92 (78 lakeside)


Sunday: Mostly sunny, less humid Low: 66 High: 87 (74 lakeside)


Monday: Mostly sunny Low: 68 High: 83 (cooler lakeside)


Tuesday: Mostly sunny Low: 61 High: 79 (cooler lakeside)


Wednesday: Mostly sunny Low: 58 High: 78 (cooler lakeside)


Thursday: Mostly sunny Low: 59 High: 87


Friday: Partly/mostly sunny, sct. showers/t-storms possible Low: 65 High: 88


#ilwx

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