Chicago Weather Forecast (O'Hare Official) 9:18 am CDT Aug 7, 2017 with Forecast Discussion

Today: A slight chance of showers between 1pm and 4pm. Mostly cloudy, then gradually becoming sunny, with a high near 74. North northeast wind 5 to 10 mph, with gusts as high as 20 mph. Chance of precipitation is 20%.

Tonight: Clear, with a low around 58. North wind 5 to 10 mph becoming west northwest after midnight.

Tuesday: Sunny, with a high near 82. Northwest wind around 5 mph.

Tuesday Night: Mostly clear, with a low around 62. West northwest wind around 5 mph becoming calm in the evening.

Wednesday: Mostly sunny, with a high near 82. West wind around 5 mph becoming south in the afternoon.

Wednesday Night: Partly cloudy, with a low around 64.

Thursday: A 20 percent chance of showers and thunderstorms after 1pm. Partly sunny, with a high near 80.

Thursday Night: A chance of showers and thunderstorms. Mostly cloudy, with a low around 63.

Friday: A slight chance of showers and thunderstorms. Partly sunny, with a high near 79.

Friday Night: Partly cloudy, with a low around 63.

Saturday: A slight chance of showers and thunderstorms. Partly sunny, with a high near 79.

Saturday Night: A slight chance of showers and thunderstorms. Mostly cloudy, with a low around 63.

Sunday: Mostly sunny, with a high near 79.

Amf Ohare IL
 41.98°N 87.9°W

National Weather Service Chicago/Romeoville, IL
GO Current Forecast Discussion


635 AM CDT Mon Aug 7 2017


Through tonight...

An area of showers across southern Wisconsin/far northern Illinois will dissipate as the E-W shortwave producing the precipitation continues to shift eastward this morning. There is also some weak warm advection induced light rain/drizzle across the I-39 corridor, and this should also slowly decay in the next few hours.

Our region will remain in cyclonic flow aloft with a few smaller scale shortwaves rotating eastward through a modest mid-upper level jet axis. One of these scoots by to our north, but another wave across the central plains will arrive later today. Its arrival will be coincident with a weak cold front currently across northern Illinois. MLCAPE forecast from the RAP and a peak a forecast soundings do depict weak and skinny instability profiles which would suggest a minimal thunder risk. Also the moisture profile weakens through the day, which also implies limited coverage of showers today but still enough of a signal to hold onto chance/slight chance.

A fairly quick drying of the atmospheric column will commence this evening as the upper low to our northeast continues its eastward trek, and the corresponding subsidence will allow surface high pressure to take up residence across northeast Illinois tonight and continue this week.




Tuesday through Sunday...

Quiet conditions will continue through midweek as the surface high will hold in place across the lower Great Lakes region through Wednesday before gradually shifting east to the eastern Great Lakes and Ohio Valley. Meanwhile aloft fairly benign and flat westerly aloft will allow dry conditions initially.

Later in the week a bit more amplified northwest flow will take aim at the midwest and bring us renewed precipitation chances. An upper level trough currently across northern Alberta will work its way southeastward, merging with other shortwave energy and an axis of modest moisture return. Some timing differences with how quickly this gets into the region, as early as late Wednesday to some time Thursday. Thursday/Thursday night appears to be the greatest chance of showers and maybe some storms. A cold front will push through Thursday night as the upper low also clears east of the region, which should largely make for drier conditions Friday. Broad but expansive cyclonic flow will remain in place for the weekend, but no clear organized waves, supports lower chances of showers during this period and temperatures at or just a bit under seasonal normals.



.AVIATION... For the 12Z TAFs...

A few isolated showers are mainly south of the terminals, and VFR cloud cover has spread across the region. Northeast winds are expected and speeds will be at or around 10 kt this afternoon. Decent flow off of the lake should help clouds diminish along the shore. However, a lake breeze may trigger additional scattered rain showers early this afternoon near DPA. The showers may get close to ORD, but I do not have enough confidence to include VCSH at ORD. Skies clear and winds back to northwesterly this evening.




A cold front over central Lake Michigan will reach the southern end of the lake early this morning.  North winds increase to 15-25 kt over the southern end of the lake. Kept the small craft advisory for the northwest Indiana nearshore waters going.  Winds and waves should stay below small craft advisory criteria across the IL waters.

Winds become west tonight as high pressure spreads over the western Great Lakes, and then winds back to southerly behind the low Wednesday night. A weak low is forecast to move over the lake early Friday morning. Northerly winds up to 20-25 kt follow the low Friday afternoon/evening. High pressure then builds over the upper midwest this weekend.



.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...Beach Hazards Statement...INZ001-INZ002...2 PM Monday to 4 AM      Tuesday.

LM...Small Craft Advisory...LMZ743-LMZ744-LMZ745...2 PM Monday to 4      AM Tuesday.

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