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  • Tim McGill

Still Feels Like Florida But Relief Coming

It's Not The Heat, It's The Humidity


It felt like the lower 90s yesterday before we actually made it to 90° at O'Hare. High humidity made it a muggy day. Gulf Coast level moisture has been nudging north with a storm system since Sunday and it arrived yesterday. Relative humidity and dew points are two ways we can measure the amount of moisture in the air.



Dew points are the preferred measurement of moisture used by most meteorologists. Here is the National Weather Service's explanation of dew point:


The dew point is the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%. At this point the air cannot hold more water in the gas form. If the air were to be cooled even more, water vapor would have to come out of the atmosphere in the liquid form, usually as fog or precipitation.


Tuesday's dew points were some of the highest we have seen so far this year. They reached well into the 60s with a few spots hitting 70°. We were in the "humid" to "very humid" range.


Those high dew points combined with rather warm temperatures (upper 80s) gave us a heat index in the lower 90s. Heat index values will be similar today.



Tuesday's high of 91° at O'Hare means we are now running just under 8° above average for the month overall. There was a lack of scattered showers and thunderstorms yesterday which meant more sunshine than most models (and myself) predicted. That extra sunshine helped our temperatures soar. The HRRR model pushes highs today near 90° away from the lakefront but keeps it cooler (70s) lakeside.


The National Blend Of Models warms us up to 90° or more Friday through Sunday. Cooler air arrives early next week which will be accompanied by a drop in dew points.


It will still be hot on Sunday but dropping dew points means it will feel more comfortable. A cold front comes through late Saturday to bring us some relief from the high humidity. Dew points drop into the 40s early next week.


So while it will still be hot on Sunday, it won't be as steamy as the past few days. The GFS model has temperatures topping out around 90°.



The temperature anomaly forecast for Sunday afternoon shows most of the country will be seeing anomalous warmth. We will be around 10° or more above average. Average highs on Sunday are near 80°. So even though it will be nearly as hot on Sunday as it was on Tuesday, it should feel a lot less sticky.




Another Discouraging Drought Forecast


O'Hare picked up just .01" of rain yesterday. We are now down 1.12 inches of rain for the month and down just over 8 inches of rain since March 1st. With those kind of numbers it is likely our drought has deepened this week. I'll have the latest analysis from the U.S. Drought Monitor on Friday.


The HRRR model total precipitation forecast into this evening suggests spotty or isolated showers and thunderstorms today. The best chance for these is along or south of I-80 which is closer to an upper level low and also along a weak, light lake breeze.


HRRR Model Total Precipitation Forecast Through This Evening

The GFS model brings the next decent chance of rain here late Saturday with the arrival of a cold front. There could be a few stronger storms that produce gusty winds and large hail. Aside from that threat of rain and another shot early Monday, this is an overall dry forecast.

GFS Model Cloud Cover & Precipitation Meteogram For O'Hare

The latest GFS model total rainfall forecast through this weekend doesn't offer much hope for drought relief. Most of us would pick up about a tenth to two tenths of an inch of rain with some areas well west of the city possibly picking up around a half inch of rain in total.


GFS Model Total Precipitation Forecast Through Monday Morning

In light of our drought situation the longer range precipitation probability forecasts are not good. They both point to a drier than average period overall. The latest 6-10 day forecast has us outlooked for below average precipitation overall from June 14th through June 18th. That is for next Monday through Friday. The longer range 8-14 day forecast continues to favor us for below average precipitation overall from June 16th through June 22nd. If these forecasts verify, our drought could not only intensify but also expand in coverage.







Warm Next Week Then About Average


The western nearly two thirds of the country is outlooked to be above average overall in terms of temperature next week. The Chicago area is included in this forecast for next Monday through Friday. After that, it appears we will get back to about average. The 6-10 day forecast has outlooked us for above average temperatures overall from June 14th through June 18th with probabilities between 30% and 50%. The longer range 8-14 day forecast drops us to about average overall from June 16th through June 22nd. Average highs for these two periods are in the lower 80s.



The even longer range Subseasonal Experiment (SubX) temperature anomaly forecast brings back the warmth 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: Partly/mostly sunny, pm isolated shower/t-storm possible High: 89 (76 lakeside)


Thursday: Partly to mostly sunny Low: 67 High: 86 (cooler lakeside)


Friday: Mostly sunny Low: 68 High: 90 (cooler lakeside)


Saturday: Partly/mostly sunny, sct. showers/t-storms late Low: 70 High: 91 (cooler lakeside)


Sunday: Mostly sunny, less humid Low: 69 High: 90 (cooler lakeside)


Monday: Mostly sunny Low: 66 High: 84 (cooler lakeside)


Tuesday: Mostly sunny Low: 61 High: 80 (cooler lakeside)


#ilwx

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