Chicago Weather Forecast (O'Hare Official) 11:17 am CDT Sep 16, 2017 with Forecast Discussion

This Afternoon: Sunny, with a high near 88. South wind around 10 mph.

Tonight: Partly cloudy, with a low around 68. South wind around 10 mph.

Sunday: A 40 percent chance of showers and thunderstorms, mainly after 1pm. Partly sunny, with a high near 82. South wind 5 to 10 mph becoming northwest in the afternoon.

Sunday Night: A 20 percent chance of showers before 1am. Partly cloudy, with a low around 60. North wind around 5 mph.

Monday: Mostly sunny, with a high near 78. East northeast wind around 5 mph.

Monday Night: A 50 percent chance of showers and thunderstorms. Mostly cloudy, with a low around 63.

Tuesday: A 30 percent chance of showers and thunderstorms, mainly before 1pm. Partly sunny, with a high near 79.

Tuesday Night: A slight chance of showers and thunderstorms. Mostly cloudy, with a low around 65.

Wednesday: A slight chance of showers and thunderstorms. Mostly sunny, with a high near 82.

Wednesday Night: A slight chance of showers and thunderstorms before 1am. Partly cloudy, with a low around 65.

Thursday: Mostly sunny, with a high near 82.

Thursday Night: A slight chance of showers and thunderstorms. Partly cloudy, with a low around 64.

Friday: A chance of showers and thunderstorms. 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


616 AM CDT Sat Sep 16 2017


Through tonight...

Today will be a lot like Friday with dry conditions and high temps in the upper 80s away from the lake.  Southeast winds will kee Ptemperatures in the low 80s along the lake.

Most models have convection along an approaching cold front dissipating before reaching north central IL tonight.  Therefore, went with a dry forecast through 7AM Sunday.




Sunday through Friday...

A cold front moves through the region Sunday.  Isolated showers and dissipating thunderstorms may bring light rain to areas west of I-55 Sunday morning. Guidance disagrees on how strong forcing will be and how much convection will form along and east of I-55 Sunday afternoon. Have medium confidence in scattered or higher storm coverage Sunday afternoon. The recent dry spell could limit how many storms form. CAPE values are forecast to stay below 1000 J/kg and shear less than 20 kt. PWATs on the other hand will be well above normal around 1.8 inches with only 20 kt steering flow. Therefore, whatever storms do form may produce heavy rain and move slowly.

The theme of next week will be transient shortwave troughs that bring multiple chances of showers and storms. Monday evening looks particularly interesting with a stronger vorticity lobe and short wave trough reaching the mid Mississippi Valley.  PWAT values remain around 1.5-1.75 inches. Guidance has CAPE values around 1000 J/kg, but fatter CAPE profiles. Shear remains low around 20 kt. Best coverage appears to be along the I-39 corridor and south of I-80.

Another weaker wave may force showers and storms Tuesday, and I have less confidence in timing and coverage.  Showers may continue into Wednesday morning. A cold front stalls to the west of the forecast area, and guidance differs on if/when showers and storms associated with the front will impact the region.  Kept a chance of showers and storms in the forecast Wednesday night, but thinking Thursday will be mostly dry.

Seasonal to slightly above normal temperatures are expected throughout the extended.



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

Early this morning, low pressure is centered over MN with a trailing cold front stretching across the mid Missouri Valley. Modest southerly winds and VFR conditions will be in place out ahead of the front through the day today. The cold front is expected to cross the Mississippi Valley around daybreak Sunday with a decaying line of showers and thunderstorms crossing into northern Illinois. There is an off chance some of this precipitation could be near RFD Sunday morning. Better chances for showers and thunderstorms will be in place after the current TAF valid period Sunday afternoon as precipitation redevelops along the front near or just east of the Chicago area terminals.




Moderate southerly flow will be in place through at least midday Sunday on the western edge of ridge of high pressure over the Appalachians and ahead of an approaching cold front. Winds are expected to remain in the 15 to 25 kt range through much of the time frame. The front will make its way down Lake Michigan through the day Sunday turning winds northerly. High pressure will build in behind the front and move just north of Lake Michigan on Monday allowing winds to veer back to southeast by Tuesday. South to southeast winds will generally prevail through the end of the week.




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