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  • Tim McGill

Great Timing For A Wonderful Weekend

Near Miss On Wednesday

Mesocyclone Over Western LaSalle County Wednesday (Courtesy Of Logan Bundy)

There were nearly three dozen reports of tornadoes in Iowa yesterday during an outbreak of severe weather that impacted four Midwest states. We had two rounds of storms here. The first moved into our far western suburbs during the afternoon. It produced a photogenic storm in western LaSalle county. The picture above appears to show a mesocyclone. The National Weather Service was tracking a storm that had shown signs of circulation in that area. No funnel clouds or tornadoes were reported though.

The stronger second round of storms fired up late last night in Iowa and spread eastward into Wisconsin and Illinois into the early morning hours today. The storm reports graphic shows blue markers near Rockford. That represents wind damage reports. There were several in northwest Illinois but nothing in the immediate Chicago area.

The Storm Prediction Center has placed most of our area in a marginal risk (level one out of 5) area for severe weather. The greatest threat from any strong storms today would be damaging winds with heavy downpours. My analysis suggests to me the best chance for strong storms would be near or south of I-80.

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".

Warming Up Next Week

It actually felt like July on Wednesday. O'Hare had a high of 84°. That was the warmest day in a week. Cloud cover with some scattered showers and a wind eventually shifting off the lake will keep us cooler today. The HRRR model suggests upper 70s for highs today with temperatures cooler along the lakefront. The average high for today is 85°.

Our temperatures fall a bit today and tomorrow and our dew point will slowly drop too. Dew points are the preferred measurement of moisture for meteorologists. Dew points will be high today as they approach 70° but then fall into the lower to middle 60s by this evening. They may fall into the 50s by Saturday as more comfortable air slides south into our region.

Winds turn off the lake today and stay off the lake through Friday. This helps keep us below average today and tomorrow with highs in the 70s. It will be a bit breezy Friday afternoon with winds gusting to near 20 mph.

There is a decent chance for at least some scattered showers on and off today through Friday evening. A few thunderstorms are possible mainly south of the city.

The National Blend Of Models has a couple of cooler days before we bounce back to around average (middle 80s) by Sunday and keeps us there through at least a week from Saturday. Next week will be a warmer week than this one. The timing is perfect for this weekend as we dry out and warm up a bit. Plenty of sunshine on Saturday and Sunday with highs near 80° Saturday and lower humidity and then warming into the lower 80s Sunday.

The last several runs of the long range temperature probability forecasts have favored us for warmer than average summer weather. That hasn't changed with the most recent run. The 6-10 day forecast has outlooked us for above average temperatures overall from July 20th through July 24th. The longer range 8-14 day forecast also favors us for above average temperatures overall from July 22n through July 28th. 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.

Still Hoping For More Rain

The first two weeks of July have yielded under a quarter of an inch of rain so far at O'Hare. July is now down 1.35" of rain below average. O'Hare is now near six 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. Our hardest hit drought areas did not get any significant rain yesterday so I am not expecting any improvement in the updated analysis.

The latest GFS model run offers at least some hope for rain today, tonight and Friday. It will come in the form of mainly scattered showers but a few thunderstorms will be mixed in too. We then enter a dry stretch from Saturday through early Wednesday.

The GFS model total rainfall forecast through Saturday morning keeps the heaviest rainfall south of the city. The range of rainfall in this forecast is from a quarter of an inch north of the city to about a half inch in the city, nearly an inch in some western suburbs and almost two inches well south of Chicago.

The longer range precipitation probability forecasts first favor us for a dry period than a return to near normal rainfall. the latest 6-10 day forecast has the Chicago area favored for below average precipitation overall from July 20th through July 24th with the highest probabilities just to our west. The longer range 8-14 day forecast has us favored for about average precipitation overall from July 22nd through July 28th.

Here is my 7 day forecast:

Today: Cloudy, cooler, showers early & late, a few t-storms possible mainly south High: 78

Friday: Sct. showers/t-storms early & late, peeks of sun Low: 68 High: 74 (cooler lakeside)

Saturday: Partly to mostly sunny, spotty shower possible Low: 67 High: 79 (cooler lakeside)

Sunday: Mostly sunny Low: 67 High: 84 (cooler lakeside)

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

Tuesday: Mostly sunny Low: 69 High: 87 (cooler lakeside)

Wednesday: Partly to mostly sunny, sct. shower/t-storm possible Low: 71 High: 84 (cooler lakeside)


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