Chicago Weather Forecast (O'Hare Official) 8:16 pm CDT Aug 12, 2017 with Forecast Discussion

Tonight: Mostly clear, with a low around 58. North wind around 5 mph becoming calm.

Sunday: Mostly sunny, with a high near 80. Calm wind becoming east around 5 mph in the afternoon.

Sunday Night: Partly cloudy, with a low around 60. East wind around 5 mph becoming calm in the evening.

Monday: Mostly sunny, with a high near 82. Calm wind becoming south around 5 mph in the morning.

Monday Night: Partly cloudy, with a low around 64. Southeast wind around 5 mph becoming calm in the evening.

Tuesday: Mostly sunny, with a high near 85.

Tuesday Night: A 20 percent chance of showers after 1am. Partly cloudy, with a low around 67.

Wednesday: A chance of showers and thunderstorms. Partly sunny, with a high near 85.

Wednesday Night: A chance of showers and thunderstorms. Mostly cloudy, with a low around 70.

Thursday: A chance of showers, mainly after 1pm. Partly sunny, with a high near 85.

Thursday Night: Partly cloudy, with a low around 67.

Friday: Mostly sunny, with a high near 83.

Friday Night: Partly cloudy, with a low around 65.

Saturday: Mostly sunny, with a high near 82.

Area Forecast Discussion below ad ...

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


829 PM CDT Sat Aug 12 2017


Evening Update...

Forecast appears to be generally in good shape this evening, with the only tweaks made to lower overnight min temps a bit in some areas, especially the Fox/Rock river valley regions where a few upper 40`s are possible again tonight.

00Z surface analysis depicts a broad area of high pressure stretching from the Upper Mississippi Valley to the western Lakes. The center of the high will move across the forecast area overnight and early Sunday, as subsidence persists in the wake of the mid-level trough exiting the region to the east, and downstream of another short wave propagating through the Northern Plains. Mainly clear skies and light/calm winds in the vicinity of the surface high center should allow for strong radiational cooling overnight, which should again allow for temps dipping to the lower to middle 50`s across most areas outside of the Chicago urban core, and a few upper 40`s most likely in our typically cooler spots similar to this morning. These calm/clear conditions will also set up the potential for some patchy shallow fog, again mainly away from warmer urban locations.

Otherwise, no other significant changes made to the going forecast. Surface winds turn more east-southeasterly tomorrow as the high drifts off to the east of the area. Dry and pleasant conditions will continue with a little moderation in temps. It does appear that high cloud cover will increase from the west/northwest during the afternoon as the Northern Plains short wave moves into the Upper Mississippi Valley, but pretty good weather to finish up the weekend.




Through Sunday...

A broad upper level trough continues to swing across the Great Lakes this afternoon. Water vapor also shows a closed upper low moving eastward across North Dakota which will take its` time passing north of the area later Sunday into Monday. A shortwave ridge is out ahead of this circulation and will pass overhead tonight. Surface high pressure stretching from Minnesota to Missouri will move in tonight and crest the area early Sunday. Late afternoon clouds will dissipate into early evening and the north to northeast breeze will diminish. Light and variable or even calm winds will prevail overnight and radiational cooling will ensue supporting some patchy/shallow fog development, mainly in rural and less urban areas. Light winds will be in place Sunday and favor a east to northeast direction early then trend southeasterly toward evening. Expect to see less stratocu development but high clouds will likely increase through the day ahead of the advancing upper low to the north. Temps should warm to levels several degrees higher than today given more sunshine and some modest mid level warming.




Sunday night through Saturday...

An extended period of dry conditions is expected through much of the long term period. High pressure will be parked over the Great Lakes and upper Midwest into early next week. The weak pressure gradient persisting across the region will allow the development of daily lake breezes. While temperatures should trend back closer to near seasonal normal levels, low to middle 80s through the long term forecast period, lake breeze development will keep the lakefront cooler than inland locations through Wednesday. The longer range models are trending a little faster in tracking a series of weak shortwaves passing across the middle and upper Mississippi Valley Tuesday and Wednesday, bringing the next chance for any pcpn to the region. The longer range guidance is also trending stronger with a shortwave lifting out of the central Rockies Tuesday night or early Wednesday, inducing a deepening surface low. While the GFS and ECMWF differ in the strength of the low, they generally agree on the track and timing, with the main sfc low lifting to western Lake Superior Wednesday night. The low should continue to lift northeast while dragging a cold front across the region Thursday. Scattered showers and thunderstorms may develop in advance of the front, but the greatest chance for pcpn will be Wednesday into Wednesday night as the front pushes across the area.


.AVIATION... For the 00Z TAFs...

650 pm...North/northeast winds generally under 10kts early this evening will become light and variable overnight as weak high pressure moves across the area. Winds will become light easterly Sunday morning and turn southeasterly Sunday afternoon...though its possible a lake breeze may keep winds more easterly at ord/mdw and northeast at gyy. Patchy fog is possible overnight into Sunday morning though confidence is low and fog is most likely in the usual/rural locations. Continued with tempo mention at rfd/dpa but trends will need to be monitored later tonight. cms



Low pressure over southern Quebec this afternoon will continue to lift northeast as high pressure spreads across the upper Mississippi Valley. This will maintain brisk northerly flow through this evening. The pressure gradient will gradually relax from the west allowing winds to diminish overnight tonight. Small craft advisory conditions will persist over the Indiana nearshore waters east of Burns Harbor through this evening.

The high pressure will spread into the Great Lakes region tonight allowing winds to diminish overnight. High pressure ridging will remain over the the Great Lakes region into the middle of next week. allowing for relatively light and somewhat variable winds while the ridge of high pressure dominates the area. South flow will increase Wednesday ahead of low pressure moving east out of the northern Plains.


.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...Beach Hazards Statement...INZ001-INZ002 until 10 PM Saturday.

LM...Small Craft Advisory...IN nearshore waters until 10 PM Saturday.

+ + + + + +

Important links below ad ...
NWS Forecast Chicago (O'Hare)
(NEXRAD Radar Chicago)
(Chicagoland Weather Radar)
(Satellite Cloud Cover East United States)
(US Weather Forecast Chart)
Ultraviolet Index/UV Index
Chicagoland Sunrise, Sunset and Solar Information for Chicago area
Chicagoland Moonrise, Moonset and Lunar Phase information for Chicago area

Full climate/weather details
(Desktop Mac/PC links)

Chicago record high temperatures

Chicago record low temperatures

Chicago extreme records

Chicago normal temperatures

Chicago Weather Radar

Chicago Weather Forecast

See also ...
Arlington Heights Weather Forecast
Chicago allergy weather
Chicago arthritis weather
Chicago respiratory weather

Much of the information in, Chicago Weather Stations and Chicago Weather Station consists of material from the National Weather Service, which is in the public domain (See ABOUT section).

Hazardous Weather Outlook National Weather Service Chicago/Romeoville IL 329 PM CDT Sat Aug 12 2017

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019- 132030- 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- 329 PM CDT Sat Aug 12 2017 /429 PM EDT Sat Aug 12 2017/


.DAY ONE...Tonight.


  Limited Fog Risk.   High Swim Risk for Porter County Indiana beaches.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

Sunday...   Limited Fog Risk.

Tuesday through Thursday...   Limited Thunderstorm Risk.


Spotter activation will not be necessary through tonight.