Chicago Weather Forecast (O'Hare Official) 2:19 pm CDT Aug 27, 2017 with Forecast Discussion

This Afternoon: Mostly cloudy, with a high near 78. South wind around 10 mph, with gusts as high as 20 mph.

Tonight: A 50 percent chance of showers and thunderstorms, mainly after 9pm. Mostly cloudy, with a low around 62. South wind around 5 mph.

Monday: A chance of showers and thunderstorms before 7am, then a chance of showers between 7am and 1pm, then a chance of showers and thunderstorms after 1pm. Mostly cloudy, with a high near 76. South wind around 5 mph. Chance of precipitation is 50%.

Monday Night: A chance of showers and thunderstorms before 1am, then a slight chance of showers. Mostly cloudy, with a low around 62. East wind around 5 mph becoming calm in the evening. Chance of precipitation is 40%.

Tuesday: A slight chance of showers, with thunderstorms also possible after 1pm. Partly sunny, with a high near 78. Northeast wind 5 to 10 mph. Chance of precipitation is 20%.

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

Wednesday: Mostly sunny, with a high near 80.

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

Thursday: A slight chance of showers before 1pm. Mostly sunny, with a high near 76.

Thursday Night: Mostly clear, with a low around 57.

Friday: Sunny, with a high near 76.

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

Saturday: Mostly sunny, with a high near 81.

 Amf Ohare IL  41.98°N 87.9°W

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

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220 PM CDT Sun Aug 27 2017

.SHORT TERM... 218 PM CDT

Through Monday...

The first batch of rain from this morning continues to weaken as it moves east over the lake and enters drier air. More moisture will shift east into northern IL and northwest IN later this afternoon and evening. Additional shortwave energy around the base of the deep upper low across MN will pivot eastward leading to several periods of expanded shower coverage. The first batch will focus across our southwestern counties and will initially be void of thunder, but given some heating ahead of this current activity, this would be the area that could see some thunderstorms later this afternoon. Expect a gradual expansion of shower coverage from southwest to northeast more so later this evening and overnight. With decreasing heights aloft and more moisture there is some thunder potential later this evening into the overnight as well.

If we had to pick another dry period beyond this ongoing one, then that would generally be Monday morning, though there could be a few showers. The upper low will pivot overhead Monday afternoon when we would likely see some cloud breaks. Expect additional shower and storm chances, though scattered coverage seems appropriate. There is basically no shear through the column, and thus any storms would be pulsy, but could also throw outflow boundaries, and with the steep low level lapse rates, will need to monitor for landspouts and other weaker low level circulations.

KMD

&&

.LONG TERM... 204 PM CDT

Monday night through Sunday...

Upper low is expected to be in place over northern Illinois Monday evening and gradually open up and shift to east central Indiana by Tuesday afternoon. Steep mid and upper lapse rates will persist under the influence of the upper low through midday Tuesday allowing additional chances for scattered showers and thunderstorms. Later in the day Tuesday, mid level height rises will build overhead resulting in subsidence aloft and weakening lapse rates. In response, PoPs should lower through the day and expect most areas to be dry by late afternoon or evening.

By Wednesday, temperatures should moderate some closer to normal as the upper low continues to move away from the area and high pressure builds into the midwest. Meanwhile, to the north, another upper wave is progged to dig into the Great Lakes region dislodging a fairly cold airmass from Canada into the eastern Great Lakes. Locally, we`ll just get a glancing blow of colder air, but do expect temperatures to return to below normal Thursday and Friday. Primarily dry conditions should occur across northern Illinois and northwest Indiana through the latter half of the week, but there is a chance for a few showers and thunderstorms mainly on Thursday as a cold front associated with the aforementioned upper wave drops across the region.

Flattening upper ridge will translate across the region next weekend allowing temperatures to once more moderate to or even warm slightly above normal. As the upper pattern becomes more zonal throughout the weekend, low amplitude shortwaves could bring showers and thunderstorms to the region, but confidence in timing and location at this distance is low.

Deubelbeiss

&&

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

Concerns are additional shower and possible storm timing, and then low cigs or some fog late tonight into early Monday.

The first batch of rain continues to weaken as it moves east and enters drier air. More moisture will shift east into northern IL and northwest IN later this afternoon and evening. Additional shortwave energy around the base of the deep upper low across MN will pivot eastward leading to several periods of expanded shower coverage. Confidence on timing at any one location is not very high, but at this time feel the best chance would be later this evening and into the overnight hours. With decreasing heights aloft and more moisture, there is thunder potential this evening, with showers remaining a concern again overnight.

After these waves of rain, some lower cigs or vis are possible toward daybreak, though again confidence on specifics are only medium-low. With the upper low pivoting overhead, showers remain a concern through the TAF period, but generally this pattern favors the afternoon time frame. Winds will generally hold a south- southeast direction through midday Monday, though expect some variability late tonight into Monday.

KMD

&&

.MARINE... 204 PM CDT

This afternoon, Lake Michigan falls between a broad area of high pressure over Quebec and New England and low pressure centered over western Lake Superior. A moderate southerly gradient is over Lake Michigan with winds gusting to around 25 kt. Winds should relax some tonight and Monday as the low tracks south across Wisconsin falling to 10-15 kt or less Monday night through early Wednesday as high pressure transits the region. A cold front is expected to then move down the lake later in the day Wednesday and Wednesday night with north winds to around 30 kt expected in its wake.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None.

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