Chicago Weather Forecast (O'Hare Official) 9:16 pm CDT Aug 26, 2017 with Forecast Discussion

Tonight: Mostly cloudy, with a low around 61. South southeast wind around 10 mph, with gusts as high as 15 mph.

Sunday: A 40 percent chance of showers and thunderstorms, mainly after 4pm. Mostly cloudy, with a high near 78. South wind around 10 mph, with gusts as high as 15 mph.

Sunday Night: A 50 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 62. South wind around 5 mph.

Monday: A chance of showers, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 76. Southwest wind around 5 mph becoming east southeast in the afternoon. Chance of precipitation is 50%.

Monday Night: Scattered showers and thunderstorms. Mostly cloudy, with a low around 62. East wind around 5 mph becoming calm in the evening. Chance of precipitation is 40%.

Tuesday: A chance of showers, with thunderstorms also possible after 1pm. Partly sunny, with a high near 78. Chance of precipitation is 30%.

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

Wednesday: Mostly sunny, with a high near 79.

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

Thursday: Mostly sunny, with a high near 76.

Thursday Night: Mostly clear, with a low around 58.

Friday: Sunny, with a high near 76.

Friday Night: Partly cloudy, with a low around 59.

Saturday: Mostly 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


737 PM CDT Sat Aug 26 2017


Very light rain/sprinkles along and north of I-80 will diminish in the next hour or two as a compact shortwave wrings out a bit of moisture out of mid level cloud deck. Satellite depicts some breaking up of the clouds behind this wave, but expect additional clouds ahead another weak wave in the northwest flow aloft late tonight into early Sunday, with some lower light precip chances a across north central IL during the morning. Best chances of precipitation still look to be later in the day into the evening.




Through Sunday night...

Primary concern through Sunday night is with precipitation chances and timing.

Water vapor imagery this afternoon shows a trough digging into the Upper Mississippi Valley region and Upper Great Lakes. Large shield of rainfall is currently moving east across WI and far northern IL but encountering some drier air and has been weakening. Precipitation with this lead wave is likely to continue to generally wane this evening as it moves farther into the drier air mass. Even so, a few showers or sprinkles are possible this evening, especially north of I-80.

The upper trough is forecast to close off a deep tropospheric circulation tomorrow as it moves south into WI. Weak surface low and associated cold front should near the MS River by early evening. Better chance for meaningful destabilization and greatest coverage of convection looks to be our western CWA and point west Sunday afternoon. By Sunday evening, precip chances will spread east across the outlook area, but with loss of diurnal heating the tendency should be for a weakening trend with t-storms and transition to mainly just showers.

- Izzi



Monday through Saturday...

Guidance is in pretty good agreement in moving this upper low very slowly southward and it looks to be in our area Monday afternoon. The mid-upper level cold pool should set the stage for moderate destabilization and scattered showers and t-storms, especially in the afternoon. Very weak shear environment in the vicinity of the upper low should keep severe threat minimal, though set-ups like this can sometimes result in funnel clouds and perhaps even a brief, weak landspout when developing convection interacts with ambient vorticity associated with the upper low and particularly with any nearby boundaries (lake breeze). Shouldn`t be a big problem, just something to watch for. Some showers could linger into Tuesday eastern CWA as the upper low slowly shifts east.

In the wake of the upper low, we should transition to a mainly quiet northwest flow pattern through the rest of the week with mainly dry weather and slightly below average temps. By next weekend, upper flow is forecast to flatten out some and in advance of next shortwave. WAA ahead of this shortwave looks to warm temps up back to normal or a bit above normal heading into next weekend along with slowly increasing chances for showers/storms.

- Izzi


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

No real big changes to the TAFs, with generally VFR conditions expected. In the near term, weak forcing allowing for thicker cloud cover and scattered sprinkles to move across the terminals. Did include mention in the TAFs, but don`t anticipate this preci Pto last too much longer. Weak lake breeze continuing to meander around ORD and MDW, however, at this point should not be any big wind difference on either side with east southeast winds expected. Then anticipate a southeast to south wind for the remainder of the period. Do think there will be a couple of periods when scattered showers will once again be possible. The first is early Sunday morning, when possible upstream development over Iowa could drift across northern Illinois. Lower confidence with this possibility, so have left out of the TAFs at this time. Higher chances for showers will arrive late Sunday afternoon into the evening, as a larger system draws near. Given the anticipated scattered nature, did not change the current prob30 but could see this expanded upon with later forecasts.




High pressure is centered east of Lake Michigan this afternoon and will continue to shift away from the region as low pressure takes shape over the Upper Midwest. Relatively light flow in place today will increase out of the southeast tonight and further increase out of the south Sunday, peaking with gusts to around 30 kt much of the day Sunday. The low center is expected to move south across WI Sunday night and into IL Monday. Winds will diminish under the weaker gradient near the low center and back to the east. High pressure will build back over the region Tuesday and Wednesday then a cold front is expected to push south across the Lake Wednesday night into Thursday with moderate north winds overspreading the lake in its wake.




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