Chicago Weather Forecast (O'Hare Official) 5:16 am CDT Aug 10, 2017 with Forecast Discussion

Today: A 30 percent chance of showers and thunderstorms, mainly after 5pm. Partly sunny, with a high near 83. Southwest wind 5 to 10 mph, with gusts as high as 20 mph.

Tonight: Showers and thunderstorms likely, mainly before 9pm. Mostly cloudy, with a low around 65. Southwest wind 5 to 10 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Friday: Partly sunny, with a high near 78. West northwest wind 5 to 10 mph.

Friday Night: Mostly cloudy, with a low around 61. North northwest wind 5 to 10 mph.

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

Saturday Night: Partly cloudy, with a low around 60.

Sunday: Mostly sunny, with a high near 78.

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 62.

Tuesday: Sunny, with a high near 81.

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

Wednesday: Sunny, with a high near 81.

Amf Ohare IL
 41.98°N 87.9°W

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


305 AM CDT Thu Aug 10 2017


Through tonight...

Surface high pressure has been holding firm overnight across northern Illinois, but is now progged to shift off to the southeast. Aloft, there is a lead wave in MN/IA out ahead of a compact shortwave trough across the upper Midwest.

This lead wave will pass northern Illinois this morning, though it does not appear to be very strong as it does so thus it will be hard to get any more than limited shower/sprinkle activity in the drier airmass south of the Wisconsin border this morning. The compact and seasonally strong upper trough will shift southeast this afternoon across Wisconsin. The associated surface low also tracks north, but unstable conditions ahead of the system`s cold front. The associated height falls coupled with some modest moisture advection will lead to some weak instability 500-1000 J/KG which would promote scattered storms. The strength of the wind field suggests there could be some stronger storms in spite of the somewhat limited instability, and with an organized front the storms could congeal if they from across western IL and spread southeastward through the afternoon or early evening. Gusty winds would be the prime concern, though large hail is also a concern as is locally heavy rainfall.

The cold front will slowly shift southeast on Friday, but will likely still be draped across our southeastern counties (Ford/Iroquois into Benton/Newton/Jasper IN), which would suggest a few showers remain possible overnight into early Friday morning in these areas.




Friday through Wednesday...

After some morning cloud cover behind the front Friday morning, cooler and drier air will filter in. Colder air aloft and a subtle lake enhanced frontal boundary is likely causing several models to hint at a few isolated showers Friday.

Expansive high pressure will again return this weekend and into next week. Cyclonic flow will continue aloft resulting in occasional clouds, and northeast flow will maintain our mild and dry conditions. At this point earlier runs of the ECMWF were hanging onto some showers Saturday night into Sunday across our far southern counties, but at least the current operational run is largely dry like the GFS ensembles for Sunday. The same scenario is in place for Monday, but if the front is south of the region then precip chances remain low. Eventually a ridge aloft will shift east and allow for some warming but still continued dry conditions until late in the coming week.



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

High pressure continues east while a low pressure system will drift east across northern Wisconsin today. Southwest winds and VFR skies are expected. Southwest winds may gust to arnd 15 kt this afternoon. Higher gusts are possible if there is less cloud cover.

I`m thinking precip over southern MN and northern IA will weaken as it reaches northern IL this morning. I kept a VCSH at RFD as a couple dying showers may reach the RFD area. I expect new thunderstorm development along the low`s cold front in the mid to late afternoon. Debated making the PROB30s for TS into Tempos, but still have too many questions about timing and coverage at this time. West winds and VFR ceilings are expected behind the cold front tonight.




High pressure will slowly push over the Atlantic today while low pressure over Minnesota will reach the northern end of the lake tonight. South winds of 10-20 kt are expected ahead of the low. Winds veer to the northwest behind the low. High pressure builds over the upper Midwest Friday night, which may result in northerly winds of 15-25 kt. Right now it looks like winds and waves will remain below Small Craft Advisory conditions.

North winds ease Saturday night/Sunday as the high builds over the lake.  Baggy high pressure will lead to light winds in variable directions across the lake most of next week.




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Hazardous Weather Outlook National Weather Service Chicago/Romeoville IL 417 AM CDT Thu Aug 10 2017

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019- 110930- 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- 417 AM CDT Thu Aug 10 2017 /517 AM EDT Thu Aug 10 2017/


.DAY ONE...Today and Tonight.

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


Scattered thunderstorms are expected mid to late afternoon through mid evening. Some of the storms could be strong to possibly severe. Widespread severe storms are not anticipated. The main hazards are damaging wind and large hail.

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

Friday...   Limited morning Thunderstorm Risk I-55 southeastward. Sunday...   Low chance of a thunderstorm south of a Pontiac to Rensselaer line.


Spotters may be needed late this afternoon and early evening.


Moving east at 40 mph.