Monday morning update: Tracking the snow

1:50 pm Update: Heavy snow falling from Janesville down I-39/90 to Rockford to Davis Junction where visibility has fallen near zero.









Thundersnow possible south of Shabbona as lightning has been detected south of Highway 30.  Expected heavier snowfall rates in southern DeKalb County












1:00 pm Update: Heaviest of the snow will fall between now and 3pm acroos Northern Illinois and Southern Wisconisn.  Visibility remains under half a mile with the heavier snow as snowfall rates of an inch per hour are likely.  Road conditions will continue to remain hazardous into the evening commute, so please use caution if you need to head out.




Technical discussion regarding possibility of moderate to heavy snowfall through the afternoon

SUMMARY...MODERATE TO LOCALLY HEAVY SNOW WILL CONTINUE TO DEVELOP EASTWARD THIS AFTERNOON ACROSS THE SOUTHERN HALF OF WI...MUCH OF NORTHERN/PARTS OF CENTRAL IL INCLUDING THE CHICAGO METRO AREA...INTO NORTHERN/WEST-CENTRAL INDIANA AND SOUTHWEST LOWER MI. WITH THE HEAVIEST SNOW...RATES WILL EXCEED 1+ IN/HR FOR A COUPLE HOUR DURATION. ADDITIONALLY...SOME THUNDERSTORMS AND MIXED WINTER PRECIPITATION INCLUDING SOME SLEET/FREEZING RAIN AND SNOW WILL BE POSSIBLE PARTICULARLY ACROSS NORTH-CENTRAL/EAST-CENTRAL IL INTO NORTHWEST INDIANA. DISCUSSION...A PROGRESSIVE/MODESTLY AMPLIFYING SHORTWAVE TROUGH CENTERED OVER THE LOWER MO RIVER VALLEY LATE THIS MORNING WILL CONTINUE STEADILY EASTWARD THROUGH THE AFTERNOON. PROGRESSION OF THIS SHORTWAVE TROUGH AND ASSOCIATED DPVA/WARM ADVECTION AND UPPER JET EXIT REGION INDUCED DIVERGENCE WILL LEAD TO A GENERAL EASTWARD SPREAD OF RELATIVELY STRONG UVV ACROSS THE REGION THIS AFTERNOON...PARTICULARLY ACROSS SOUTHERN WI/LOWER MI AND THE NORTHERN HALVES OF IL/INDIANA. SIMILAR TO 12Z OBSERVED SOUNDINGS...REGIONAL FORECAST SOUNDINGS GENERALLY REFLECT AMPLE UVV COINCIDENT WITH A SATURATED MID-LEVEL DENDRITIC LAYER SUPPORTIVE OF MODERATE/LOCALLY HEAVIER SNOW FOR A MULTI-HOUR DURATION...PARTICULARLY GIVEN INFLUENCES OF WEAK ELEVATED INSTABILITY ESPECIALLY ACROSS PARTS OF IL/INDIANA. THE 12Z OBSERVED SOUNDING FROM LINCOLN IL SAMPLED AROUND 60 J/KG OF MUCAPE BASED ABOVE 700 MB...WITH NEARLY 700 J/KG OF MUCAPE PER 12Z SPRINGFIELD MO. ESPECIALLY GIVEN THE PROXIMITY OF THE UPPER DRY SLOT AS PER WATER VAPOR IMAGERY...AVAILABLE INSTABILITY WILL CONTINUE TO SUPPORT THUNDERSNOW AND/OR MIXED PRECIPITATION IN ASSOCIATION WITH THUNDERSTORMS SUCH HAS BEEN REPORTED RECENTLY AT CHAMPAIGN IL /KCMI/ AND IS OTHERWISE EVIDENT IN RADAR/LIGHTNING NETWORK DATA ACROSS CENTRAL/PARTS OF NORTHEAST IL THIS MORNING.

11:35 am Update: Band of heavier snow will move into western Illinois through 12:30pm which is where the heaviest of the snow is expected to fall.  Also watching another area of heavier snow southeast of Rockford that will move into northeast Illinois through early afternoon.  Again, heaviest of the snow is expected to fall through 3pm with the snow winding down into the evening.  It's within the bands of heavier snow that snowfall rates of an inch to an inch and a half per hour will be possible.  Earlier this morning around 11:30am there were a few lightning strikes that were indicated around Davenport, IA which would have indicated thundersnow.  So far, I haven't seen many reports of that coming from that area but it's possible a brief period of thundersnow did occur. 



Western counties bumped up in expiration time of Winter Storm Warning.  Winter Storm Warning now in effect until 4pm for Stephenson, Jo Daviess, Carroll and Whiteside counties.  The remainder of the Stateline remains under the warning until 6pm.

10:10 am Update: First Warn Weather Watcher Tony Celani is reporting near white-out conditions in Poplar Grove as heavier snow lifts north of Belvidere in Boone County.  While a few areas are getting a little break from the heavier snow, it's a break that won't last for long.  Heavier snow moving into Northwest Illinois from Lena to Mt. Carroll will continue to move east through 11am with more snow found further west in Iowa.  This will continue to track east into Northern Illinois through 2pm/3pm.

7:55 am Update: Getting numerous reports of blowing & drifting snow across the Stateline and near white-out conditions with winds gusting to 35 mph.  There have also been reports of sleet mixing with the snow where the heaviest snow has moved out from Freeport to Byron.  This initial band will pull into Southeast Wisconsin by 10am with the second round coming soon after.



Previous morning update:

A Winter Storm Warning remains in effect for the entire Stateline through 6pm this evening as snow has already begun to fall south of Rockford along the leading edge of warmer air aloft.  The snow will overspread the Highway 20 corridor within the next hour and with winds increasing from the southeast, visibility will be lowered through mid-morning.

Greatest time frame of impact from the snow will
be from now through 4pm as the heaviest snow is expected to fall through the early afternoon, but strong winds will produce near white-out conditions in open and rural areas.   The snow will quickly accumulate on roads as surface temperatures remain below freezing causing roads to become slick through the afternoon/early evening commute.

This system is a fast moving system, but it has the potential to drop a decent amount of snow in a short amount of time.  Still looks like, area wide, we'll receive 4" to 6" but with the potential for snowfall rates reaching an inch to inch and a half per hour during a period between 11am and 3pm, locally higher amounts will be possible.

This is a very dynamic, ever changing, storm system so be sure to bookmark this page as we keep you updated throughout the morning, afternoon and evening.