MORNING PREVIEW: Weather, Traffic Friday, November 12, 2021

NWS FORECAST: KORD | KPWK | Forecast Graph O’Hare

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 O’HARE FORECAST … 

Today: Scattered snow showers after 10am. The snow could be heavy at times. Cloudy, with a high near 40. Breezy, with a southwest wind 15 to 20 mph, with gusts as high as 30 mph. Chance of precipitation is 50%.

Tonight: Scattered snow showers, mainly before 8pm. Mostly cloudy, with a low around 33. West wind 10 to 15 mph, with gusts as high as 25 mph. Chance of precipitation is 30%.

Saturday: Mostly cloudy, with a high near 40. West northwest wind 10 to 15 mph, with gusts as high as 20 mph.

Saturday Night: Rain and snow likely, becoming all snow after 2am. Mostly cloudy, with a low around 33. Southwest wind around 10 mph. Chance of precipitation is 60%. New snow accumulation of less than one inch possible.




Brief snow before dawn in Elgin …

According to the NWS Chicago office, the primary forecast concern in the short term remains the potential for snow showers/squalls today which could result in hazardous travel due to rapidly changing conditions over short distances.

In the immediate near term, light showers, mixed with some graupel and snow continue west of Chicago and into the northwest suburbs. This activity is associated with the lead vort max wrapping around a vertically stacked closed upper low that remains the dominant weather feature across the central and eastern CONUS. Precipitation associated with this southern vort max has had a bit more longevity than many of the models had suggested earlier and there have even been a few lightning strikes. This activity is expected to lift north and east out of the area over the next couple of hours.

Meanwhile, the center of the 995 mb surface low remains well to our northwest in east central Minnesota. Additional vort maxes continue to wind around the closed upper low which will bring snow showers into northern Illinois later this morning. The more vigorous of these features is expected to wrap around the southwest side of the low and move across the area by sometime this afternoon providing additional support for ascent. Thus, late morning through the afternoon is when we expect the greatest coverage of snow showers. Despite surface temperatures being above freezing for much of the day, model soundings remain favorable for graupel/snow showers across the area. Steep low-level lapse rates show that this warm layer is very shallow, with saturation into the dendritic growth layer (-10 to -20C). Based on pattern recognition and given the deep layer of ascent in place along with a narrow axis of instability, do think that heavier snowfall rates are likely. This combined with gusty winds mixing down to the surface would result in sudden visibility reductions, and a quick coating of snow, possibly including roadways under the heaviest squalls. Even though road temperatures are still above freezing, the snowfall rate may be high enough to overcome the rate of melting, which would create slippery conditions. Some rumbles of thunder, but not mentioned in the formal forecast.




Not everyone will end up under the heaviest snow showers, which may be a bit more hit and miss. In fact, if there is any accumulating snow, it may fall in narrow “streaks”, with a noted Horizontal Convective Roll-esque look to some of the model QPF (Quantitative Precipitation Forecast) output. However, given a consistent signal in model guidance and upstream observations, the NWS Chicago office will continue to message snow shower/squall potential and any associated travel impacts, especially given it is the first real chance for snow of the season. Be prepared for rapidly changing weather conditions if out driving today!

The coverage and intensity of snow showers will ease with sunset, but a few lighter snow showers/flurries may linger into the evening and overnight hours along with some lake effect precipitation into northwest Indiana. Saturday lacks sufficient ascent and moisture in the mid-levels to support additional snow/snow showers during the daylight hours. There may be a narrow saturated layer for some virga-type showers or a few flurries, but expect mostly dry conditions before our next weather system arrives Saturday evening/night, which is discussed in more detail in the long term discussion below. Temperatures Saturday will trend a bit cooler with highs in the upper 30s to around 40.

DEW

Grass dry, no dew on vehicles with a dew point depression of about 10 to 5°F under overcast skies.

Weather Radar shows precipitation from about Rockford to Peoria moving east at 7:55 a.m.

Is it cloudy over Chicago?

Arlingtoncardinal.com/clouds | Arlingtoncardinal.com/temps

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