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  • Tim McGill

Sailing Back Into Summer

Finally Feeling More Like July


Tuesday was the 6th straight day with below average temperatures. It was the 9th day out of 13 so far this month to be below average. O'Hare had a high of 80° on Tuesday after five straight days of failing to get that warm. The month is now running about 3° below average.


The feeling you get as you head out the door today is what summer is supposed to feel like. Today's highs with the help of some sunshine and a southwest wind will soar to near 90°.


The HRRR model has our highs pushing well into the 80s today.


Temperatures won't be the only thing climbing today. The dew points will increase too. Dew points are the preferred measurement of moisture for meteorologists. Dew points climb well into the 60s today and my hit 70° on Thursday before falling back into the 50s this weekend. Dew points in the 60s are very muggy and 70° or more is oppressive.


So sunshine and a gusty southwest breeze will send our highs soaring to near 90° today. Dew points go from moderately high this afternoon to very high tonight and tomorrow.


Winds gust today and tomorrow to 20 mph or greater with stronger winds possible in some thunderstorms mainly tonight and Thursday.


The best chance of rain overall is late tonight and then ramping up through the day on Thursday. The potential is there for strong to severe storms. More on that in my discussion below.


The National Blend Of Models has highs climbing to near 90° today and then staying in the 80s Thursday before sliding back into the 70s on Friday. The weekend and following week should see highs of 80° or more with several days flirting with 90°.


We may be moving towards a warmer than average end to July. The signal is strongest for a warm end to the month just north and northwest of her but we are favored for an above average period too. The 6-10 day forecast has outlooked us for above average temperatures overall from July 19th through July 23rd. The longer range 8-14 day forecast also favors us for above average temperatures overall from July 21st through July 27th. Average highs are in the middle 80s for the middle of July.



The even longer range Subseasonal Experiment (SubX) temperature anomaly forecasts keeps us sandwiched between an expected warmer than average plains and western half of the country and a cooler middle and eastern part of the US. A close examination of these forecasts shows we are expected to be right around average overall for the end of July as start to August. The temperature anomaly forecast for the week ending July 30th has us outlooked for temperatures near normal. The forecast for the following week ending on August 6th also has Chicago outlooked for about average temperatures too.



Rain To Target Driest Areas?

O'Hare has seen less than a quarter of an inch of rain for July so far. July is now down 1.23" of rain below average. O'Hare is over five and a half inches of rain below average since the start of meteorological spring on March 1st.


Here is a recap on the latest US Drought Monitor analysis that I posted on Friday (it does not include any of our weekend rainfall or rain this week so far):


Comparing this week's analysis to last week's shows only the slightest improvement. The portions of Illinois in a moderate drought (level 1 of 4) dropped from 7.55% to 7.40%. The severe drought area (level 2 of 4) remains unchanged at 2.22%. The extreme drought area (level 3 of 4) is unchanged at .96%.


The seven day stretch ending on early Monday morning has been particularly dry for the city and our northern and northwest suburbs. Portions of Lake, McHenry, Kane & Will County have only seen about 10% to 25% of average rainfall for this period. It has truly been feast or famine with rainfall lately. The areas shaded in blue and purple southwest of the city have received anywhere from 150% to 400% of average rainfall over this span.


I plan to post about the latest drought analysis on Friday. I am not expecting any improvement in light of the dry start we have seen to July.


The latest GFS model run has our best and only decent chances for rain over the next 10 days coming tonight, through the day Thursday and into early Friday. We then enter a long stretch of dry weather from the weekend through all of next week.



Some of our storms tonight and through the day Thursday may be strong or even severe. Our northern most suburbs have the best chance for strong storms tonight and into early Thursday. The Storm Prediction Center has placed our southern suburbs in a marginal risk (level one out of 5) area for severe weather. Most of us are in a slight risk area (level 2 out of 5) with the northwest corner of the state in an enhanced risk area (level 3 out of 5). The greatest threat would be damaging winds with heavy downpours but a few tornadoes can't be ruled out.


The Storm Prediction Center convective outlook for Friday and Friday night has us in a marginal risk area for severe storms. The best chance for these would be overnight Friday into the early morning hours.


A marginal risk is level 1 out of 5 possible risk levels. It is the low end of the risk categories but means "an area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity".



The GFS model total rainfall forecast through Friday morning offers some hope for the driest parts of northern Illinois. This is probably overdone as the models have been overestimating rainfall lately. The model suggests around two to three inches of rain is possible. Locally heavier rainfall is a possibility with some of these thunderstorms.



The longer range precipitation probability forecast starts off favoring a dry pattern then moves us to near normal precipitation. he latest 6-10 day forecast has the Chicago area favored for below average precipitation overall from July 19th through July 23rd with the highest probabilities over our area. The longer range 8-14 day forecast keeps us favored for about average precipitation overall from July 21st through July 27th.





Here is my 7 day forecast:


Today: Partly to mostly sunny, breezy & warmer, more humid High: 88


Thursday: Mostly cloudy, showers & thunderstorms likely (some strong) Low: 71 High: 83


Friday: Sct. showers/t-storms mainly early, mainly cloudy Low: 68 High: 76 (cooler lakeside)


Saturday: Partly to mostly sunny, spotty shower possible Low: 67 High: 80 (cooler lakeside)


Sunday: Mostly sunny Low: 67 High: 85 (cooler lakeside)


Monday: Partly to mostly sunny Low: 68 High: 86 (cooler lakeside)


Tuesday: Mostly sunny Low: 69 High: 87


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