Northern IL 5 Day Snowcast


O’Hare

Today:  17/5, Snow Totaling 2-5” by late evening.

Tuesday:  19/14, Snow Totaling 1-2” by Wednesday morning.

Wednesday:  22/5

Thursday:  21/14, Snow Likely

Friday:  24/12, Snow Possible

 

Rockford

Today:  16/1, Snow Totaling 2-5” by late evening.

Tuesday:  15/8, Snow Totaling 1-2” by Wednesday morning.

Wednesday:  20/0

Thursday:  21/11, Snow Likely

Friday:  22/12, Snow Possible

 

Quad Cities

Today:  17/0, Snow Totaling 3-6” by late evening.

Tuesday:  15/8, Snow Totaling 1-2” by Wednesday morning.

Wednesday:  19/5

Thursday:  23/14, Snow Likely

Friday:  24/12, Snow/Rain/Freezing Rain possible

 

Discussion:



Snow, snow, snow.  That will be the main premise of this forecast discussion.

Today:  Snow will begin for western sections of northern IL prior to the noon hour.  It appears to reach the collar counties of Chicago by around noon.  And finally, Chicago proper between noon-3pm.  Today’s snow will be characterized as an efficient producer thanks to the stout DGZ (Dendritic Growth Zone) be collocated with the best areas of vertical motion.  Snow will be “fluffy” due to these atmospheric conditions.  Generally, cities like DeKalb, Peoria, and as far east as Kendall County could see totals of 3-6”.  Areas in northeast IL around Lake, McHenry counties appear to be in the 2-4” range, as well as areas south through Chicago to Kankakee.  Upstream observations have been ranging from 1/4 to 3/4mi visibilities, between that and accumulations, rush hour will be a huge issue for today.  Winds 5-10mph.

The 3KM NAM NEST’s depiction of the DGZ and vertical motion for today’s snow.

Tomorrow:  Snow looks likely again.  Guidance has trended towards another clipper-like system impacting the region.  Overall duration looks short, and QPF generally is 0.08”-0.10”, but given the favorable thermal profile depicted by some members of guidance, and location of vertical motion, I cannot discount the idea of another 1-3” being possible tomorrow across northern IL.  It is likely we will cover this later with a TAM.  The bulk of the precipitation will occur during the overnight hours and could be in progress still Wednesday morning for rush hour.  Either way, it probably will be a slow go in the morning.  Winds 5-10mph.

The NAM’s depiction for the DGZ and vertical motion for Tuesday night.

Wednesday:  Aside from some snow lingering around in the morning, there is a chance we could see some mood-flakes around the Chicagoland area Wednesday afternoon as the main mid-level shortwave comes through the area.  Accumulations would be minimal with this afternoon activity.  If there is one benefit of these setups, it would be the light winds.  For Wednesday, winds should remain 5-10mph.  Expect that it will remain cloudy most of the day.

500mb Vorticity on the 12z NAM for Wednesday. This would be possibly responsible for some flurries during the day.

Thursday:  Another day, and another possibility of snow.  It is still a way out, but guidance has hinted at this possibility for a while.  At this point, there is some divergence with how this event is being handled.  The GFS has been bullish on the setup, and the Euro is not far off from that solution.  The NAM on the other hand, shows a drier scenario.  But, this is not exactly the NAM’s most accurate time period.  At this time, I will say that there appears to be a favorable setup for waves ejecting from the Pacific Northwest, with cyclogenesis appearing across northern Colorado.  How the waves interact play a huge role in the evolution of the surface low pressure system.  But, it appears that in response to cyclogenesis, there will be ongoing warm air advection occurring across the Central Plains and Midwest.  And with that, isentropic ascent again becomes the major player in snow production here.  Models have hinted a long-duration event, with some snow possibly beginning Thursday afternoon.  The area of divergence among solutions occurs after Thursday, and the track/corresponding axis of heaviest snow differs by 100-150mi.  So, at this point, I will keep snow in the forecast, but amounts will come at a later point.

Friday:  Snow, rain, or even freezing rain could be possible with the end of the week system.  At this point, I feel confident to mention precipitation, but beyond that, I will forgo mentioning totals of any variety.  How the surface low pressure system ejects out of the plains will play a role in what we receive.

This week is without a doubt the most active looking week we have had all winter.



The Euro’s depiction of Thursday’s setup.

This is the same depiction of Thursday from the Euro, but it also has the mean 500mb trough overlayed.