Current surface temperatures as of 9am.

O’Hare

Today:  26/8, Sunny

Tomorrow:  31/22, Sunny

Wednesday:  37/33, Sunny w/ Fog overnight

Thursday:  35/23, Fog/Rain in the morning, cloudy overall with some clearing possible late overnight

Friday:  25/10, Sunny

 

Rockford

Today:  20/2, Sunny

Tomorrow:  27/19, Sunny

Wednesday:  35/30, Sunny w/ Fog overnight

Thursday:  35/20, Fog/Rain in the morning, cloudy overall with some clearing possible late overnight

Friday:  23/8, Sunny

 

Quad Cities

Today:  19/6, Sunny

Tomorrow:  31/22, Sunny

Wednesday:  37/31, Sunny w/ Fog overnight

Thursday:  36/19, Fog/Rain in the morning, cloudy overall with some clearing possible late overnight

Friday:  23/10, Sunny

 

Forecast Discussion:

I hope everyone got the fill of snow this past week and weekend.

This upcoming week features a little different pattern.  It should be marked by warmer weather, but for northern IL, some of the warmth will be diminished due to our now stout snowpack.  With the snowpack, the albedo of the earth’s surface in northern IL has increased, and thus the reflective nature of snow/ice should prevent absorption of solar energy.  Also, there are chances of rain this week, but I tepidly approach those scenarios due to the modification of temperatures at the surface with such a stout snowpack.

Today:  It should be a nice start to the week with sunny skies, and temperatures in the mid-20’s.  High pressure will be in control for today.  The center of high pressure should scrape through northern IL during the evening, and due to this timing, the overnight temperatures will moderate some as southerly flow begins on the backside of the high pressure.  For more rural areas, temperatures should not be as low as they were this morning.

Tomorrow:  High pressure moves east, and southerly flow returns.  During the middle of the week a low-pressure system appears to track across southern Ontario.  Due to this, there will be an increase in the low-level jet and corresponding surface winds.  Temperatures will moderate some tomorrow, and I would expect the high 20’s to be obtainable for the more rural sections of northern IL, and lower 30’s being possible for the more urban areas.

Wednesday:  I expect winds to turn southwesterly through Thursday later morning, and with this warm air advection response, there should be a weak return of low-level moisture as well.  By Wednesday, the GFS shows low 40-degree dewpoints inching their way into the area by afternoon.  A scenario such as this would result in some additional melting of the snowpack, and also some fog developing, especially Wednesday night into Thursday morning.  I will approach these scenarios with caution, though.  I am not sold on the idea of temperatures moderating nearly as much as guidance wants to show.  I would hedge my bets on temperatures maxing out in the mid-upper 30’s for urban areas Wednesday, and low-mid 30’s for rural areas.  Overnight, it could approach freezing for the more rural locations, and if fog were to develop, I would be concerned with the Thursday morning rush hour possibly.  It is a little early to hit on this, so at this time I will only mention fog.

The 6z GFS’ depiction of surface dewpoints later Wednesday.

Thursday:  Guidance varies on frontal passage timing, but in general, it appears that Thursday will feature a cold front passage.  If it were to hold off till early afternoon, we could possibly see temps climb into the mid-30’s, but that is based on not only the timing, but also the low-level clouds.  There is a good chance that Thursday morning will remain foggy ahead of the cold front, and with that, temps may not moderate much.  In my point forecast locations, I intend on lowering them a little vs. guidance.  There is also a small chance with some anafrontal precipitation in the form of snow due to the primary passage of the shortwave.  This would be primarily during the late evening if it were to occur.  And I will only mention the slight chance as of now.

The 6z GFS’ depiction of the shortwave trough approaching the area late evening on Thursday.

Friday:  The end of the week should feature not only the cold front, but also falling temperatures.  If clouds manage to clear out Thursday night, we could see the morning temperatures on Friday lower than what guidance shows.  Currently, guidance sticks to possible single digits creeping in during Friday morning; with a stout snowpack and clearing, those could be lower if it were to happen.  We will monitor that closer during midweek as guidance gets a better handle on the overall timing.  Friday should feature temperatures in the mid-20’s, and lows in the single digits for the rural areas.

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