Chicago Weather Forecast (O'Hare Official) 3:18 am CDT Aug 11, 2017 with Forecast Discussion

Today: Mostly cloudy, with a high near 76. West northwest wind 5 to 10 mph, with gusts as high as 15 mph.

Tonight: Partly cloudy, with a low around 59. North northwest wind 5 to 10 mph.

Saturday: Sunny, with a high near 77. North wind 5 to 10 mph.

Saturday Night: Mostly clear, with a low around 59. North northeast wind 5 to 10 mph becoming light and variable in the evening.

Sunday: Mostly sunny, with a high near 79. Calm wind becoming east around 5 mph in the afternoon.

Sunday Night: Partly cloudy, with a low around 61.

Monday: Mostly sunny, with a high near 79.

Monday Night: Mostly clear, with a low around 61.

Tuesday: Sunny, with a high near 82.

Tuesday Night: Mostly clear, with a low around 63.

Wednesday: Sunny, with a high near 84.

Wednesday Night: A slight chance of showers and thunderstorms. Partly cloudy, with a low around 66.

Thursday: A slight chance of showers and thunderstorms. Mostly sunny, with a high near 82.

Amf Ohare IL
 41.98°N 87.9°W

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


247 AM CDT Fri Aug 11 2017


Through tonight...

Primary concern is with cloud cover today. GOES-16 IR imagery early this morning shows extensive mid level overcast over IL and the southeast half of IA in advance of advance of trough axis. While numerical guidance isn`t handling this cloudiness well, simple extrapolation suggests that the back edge of this mid deck will progress across the CWA this morning. Also some lower clouds over WI that some guidance suggests will expand south and east into at least northern portions of the area this morning. Areal extent of this lower cloudiness isn`t particularly large, so what low clouds do filter in from the north this morning will be battling the high sun angle and deepening mixing boundary layer`s tendency to mix this moisture out. Given these trends, suspect that there will be cloudiness around but inclined to not go as pessimistic as MOS guidance today with the exception of at least partial sunshine in the wake of the morning altostratus deck moves east.

- Izzi



Saturday through Thursday...

An extended period of dry conditions expected through much of the long term period. High pressure over the Great Lakes will set the stage for weak daily lake breezes through Tuesday. A shortwave trough will pass south of the region Monday with latest guidance continuing to suggest that any precip threat with this wave remaining south of the CWA. Initially, temps into early next week will average several degrees below average, but a moderating trends back toward normal temps and muggier conditions is expected heading into the middle of next week in advance of the next trough. GFS and ECMWF differ on the timing (Wed vs Thu) of that trough`s impacts on our CWA, which argues for keeping pops low at this time until models come into better agreement.

- Izzi


.AVIATION... For the 06Z TAFs...

A cold front will shift across the eastern terminals around daybreak. There is a possibility for a period of MVFR CIGS following this frontal passage during a portion of the morning. However, there are questions as to how far east towards the Chicago area these lower CIGS will get after daybreak. For this reason, its possible that the CIG heights mix out into the lower VFR range as they approach the Chicago TAF sites. For this time, I have not made any major changes to the MVFR forecast for the morning. KRFD will have the best potential for a period of these MVFR CIGS.

Otherwise expect northwesterly winds during much of the day at most terminals. The only exception will be at GYY, where a lake breeze should help turn the winds more north-northeasterly off the lake by early afternoon. It appears the lake breeze may struggle to move inland into northeastern IL. For this reason, it may not make it ORD or MDW, but this potential will need to be monitored later today.




Low pressure centered over the U.P. of Michigan early this morning will push a cold front over the lake this morning. Expect winds to increase out of the northwest following this front. The strongest winds look to be over the northern half of the lake, where winds up around 25 KT are expected. Winds will then turn northerly 15 to 25 kt tonight into early Saturday over the lake as surface high pressure builds eastward over the Upper Midwest. These northerly winds could result in the need for a small craft advisory for large waves for some of the southern Lake Michigan near shore zones, but at this time it appears the strongest winds and highest waves may remain over portions of northwestern Indiana and the Western Lower Michigan near shore waters.

The surface high will shift over the Western Great Lakes by Sunday. It then appears that high pressure may remain dominate over the region into early next week. This should result in a light and variable wind regime over the lake, with lake breeze processes likely driving an onshore wind each afternoon.




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Hazardous Weather Outlook...CORRECTED National Weather Service Chicago/Romeoville IL 356 PM CDT Thu Aug 10 2017

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019- 112100- Winnebago-Boone-McHenry-Lake Illinois-Ogle-Lee-De Kalb-Kane- DuPage-Cook-La Salle-Kendall-Grundy-Will-Kankakee-Livingston- Iroquois-Ford-Lake Indiana-Porter-Newton-Jasper-Benton- 356 PM CDT Thu Aug 10 2017 /456 PM EDT Thu Aug 10 2017/


.DAY ONE...Tonight.

WEATHER HAZARDS EXPECTED:   Elevated Thunderstorm Risk...with an associated:     Limited Tornado Risk. Limited Hail Risk...up to golf ball size.     Elevated Thunderstorm Wind Damage Risk...up to 60 MPH.


Scattered thunderstorms are expected along and ahead of a cold front through this evening. Some of these storms may become severe, with the greatest severe risk mainly northwest of Interstate 55 until 8 pm. Large hail and damaging winds are expected to be the primary severe hazards. The severe risk should diminish by the mid evening.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Saturday...   High Swim Risk.


Spotters will likely be needed into this evening.


East at 30 mph.