Chicago Weather Forecast (O'Hare Official) 4:16 pm CDT Sep 7, 2017 with Forecast Discussion

Tonight: A slight chance of showers before 7pm, then a slight chance of showers after 3am. Mostly cloudy, with a low around 54. West wind 5 to 10 mph becoming north after midnight. Winds could gust as high as 20 mph. Chance of precipitation is 20%.

Friday: A 20 percent chance of showers before 8am. Partly sunny, with a high near 66. East northeast wind 5 to 10 mph, with gusts as high as 15 mph.

Friday Night: Mostly clear, with a low around 51. Northeast wind 5 to 10 mph.

Saturday: Sunny, with a high near 69. East southeast wind 5 to 10 mph.

Saturday Night: Clear, with a low around 50. East wind 5 to 10 mph.

Sunday: Sunny, with a high near 70.

Sunday Night: Clear, with a low around 51.

Monday: Sunny, with a high near 73.

Monday Night: Mostly clear, with a low around 56.

Tuesday: Mostly sunny, with a high near 75.

Tuesday Night: Partly cloudy, with a low around 58.

Wednesday: Mostly sunny, with a high near 75.

Wednesday Night: Partly cloudy, with a low around 56.

Thursday: Sunny, with a high near 74.

 Amf Ohare IL  41.98°N 87.9°W

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


232 PM CDT Thu Sep 7 2017


Through Friday...

Deep upper trough will persist across the Great Lakes through tomorrow with temperatures continuing to run below normal and occasional low chances for a few sprinkles or light showers as low amplitude shortwave pivot across the region. In particular, modest drying is noted on water vapor imagery digging across Lake Superior this afternoon and guidance brings this wave across far southeastern WI late this evening. A few diurnal showers/sprinkles are possible area-wide this afternoon, but expect the best chance for any precipitation to be with this wave during the evening hours and favored over far northeastern Illinois.

Broad high pressure over Ontario will build south across the Great Lakes overnight with winds flipping northeasterly across the CWA through the day tomorrow. While there could be some low level moisture/cloud cover off of Lake Michigan, larger scale descent is expected as the upper trough axis shifts farther east and an axis of mid-level height rises overspreads the western Great Lakes region. This should favor dry conditions throughout the day Friday.




Friday night through Thursday...

A period of quiet weather still expected across the area this weekend into early next week, as large upper level trough shifts to the east and large high pressure settles in across the region. Precip chances could arrive sometime during middle part of next week, tied to the remnants of Irma. However, low confidence with this solution at this time.



.AVIATION... For the 18Z TAFs...

Modest west to northwest flow and VFR conditions will prevail rest of this afternoon into the early evening with high pressure centered south of the terminals over the mid-Mississippi Valley. Winds should drop off this evening and overnight and may become variable in some locations. Another high will build south across Ontario into the western Great Lakes region late tonight into Friday morning turning winds northeast and eventually ENE tomorrow. Ceilings are a little less certain tomorrow. NAM and NAM based guidance for instance are suggesting there may be some MVFR clouds off of Lake Michigan tomorrow afternoon, but the model consensus maintains VFR conditions. Will introduce scattered MVFR level clouds to the TAF for now and if confidence increases will lower conditions to MVFR.




West northwest winds in place across the lake this afternoon, while surface trough and boundary are situated across the central Great Lakes. In this pattern, showers continue develop over much of the lake and will likely persist at least through late this evening. Similar conditions over the lake will also support a chance of waterspouts as well as at least isolated thunder. This front expected to drop south over the lake tonight into early Friday morning, helping for a wind shift to the north. Behind this front, high pressure will settle in place across the Great Lakes region helping to bring an end to the precip/waterspout chances. These northerly winds should not be overly strong, but a long fetch will support building waves again. Should stay just under small craft criteria, with highest waves of 3 to 5 feet. However, will need to monitor for slightly stronger winds and slightly higher waves.




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