Chicago Weather Forecast (O'Hare Official) 8:17 am CDT Aug 8, 2017 with Forecast Discussion

Today: Sunny, with a high near 83. Northwest wind around 5 mph.

Tonight: Mostly clear, with a low around 62. North 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 southeast in the afternoon.

Wednesday Night: Partly cloudy, with a low around 64. South southeast wind around 5 mph.

Thursday: Partly sunny, with a high near 82. South wind around 5 mph.

Thursday Night: A chance of showers, with thunderstorms also possible after 1am. Mostly cloudy, with a low around 64. Chance of precipitation is 40%.

Friday: A 20 percent chance of showers before 1pm. Partly sunny, with a high near 79.

Friday Night: Partly cloudy, with a low around 62.

Saturday: Partly sunny, with a high near 78.

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

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.

Amf Ohare IL
 41.98°N 87.9°W

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


612 AM CDT Tue Aug 8 2017


Through Wednesday...

If you like warm summer days with low humidity and plentiful sun, well today will indeed fit the bill. Though it will be a chilly start in spots. Sprawling surface high pressure is locked in place the plains, upper Midwest, and Midwest regions with largely clear skies in place. Aloft the region is in northwest flow, but PW values are low. With surface heating today and slightly cooler temps aloft there will likely be some cumulus clouds this afternoon, but they will be of the fair weather and scattered variety. With the light pressure gradient, expect lake breeze development this afternoon. Still expect temps to reach the low 80s inland, and near 80 even at the lake shore before the onshore flow. There will be mostly clear skies, possibly some high clouds from more active flow to the west. Surface high pressure will only slowly shift east on Wednesday and the airmass will change little. Therefore expect similar conditions except a few more higher clouds.




Wednesday night through Monday...

Clouds will be on the increase ahead of upper level low pressure currently across the Canadian Rockies that will shift toward Lake Superior on Thursday. Additional energy aloft across the Great Basin will be embedded in the flow on the southern end of this low. This system will pass through the lower Great Lakes Thursday night with an accompanying band of generally lighter rain showers for our area, as the better upper forcing and associated surface low development will track north of the area. The later arrival suggests the thunder threat is on the lower side, with the best chances across north Central Illinois.

Beyond this system, it appears that the upper air pattern will setup to be one of very broad troughing across much of the eastern half of the country. We get a weak cold front with the aforementioned low that will make Friday a bit cooler. Some guidance also hints at some convection along the remnant frontal boundary, but it is still unclear how far south the front will be. This uncertainty lingers into the weekend, as the upper pattern would suggest unsettled conditions, but a large area of surface high pressure will expand across the midwest and will also act to shove the front into Central IL or even farther south and keep the area dry and on the cooler side of normal through early next week.



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

Quiet conditions are expected under high pressure today. Northwest winds and VFR cumulus clouds develop by mid morning. A lake breeze will likely develop, but I am uncertain how far inland it will get. Decided to keep the lake breeze moving through ORD, MDW, and GYY. Wind speeds behind the lake breeze will be less than 10 kt. Winds become westerly this evening. Southwest winds and SCT VFR clouds are expected tomorrow.




High pressure builds over the lake today. Southwest winds are expected, but lake breezes will form over the southern end of the lake. Winds become southerly as the high shifts east Wednesday. A low pressure system will move over the lake Friday, and winds become northwest to north behind it.  The low will continue northeast and high pressure will build in over the upper Midwest this weekend.





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Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
349 AM CDT Tue Aug 8 2017

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-
349 AM CDT Tue Aug 8 2017 /449 AM EDT Tue Aug 8 2017/


.DAY ONE...Today and Tonight.

Minor flooding on portions of the Pecatonica River will ease
later today.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Thursday night and Saturday night into early Sunday...
  Limited Thunderstorm Risk.


Spotter activation will not be necessary through tonight.