Tuesday, January 29, 2013

From spring to winter in 24 hours: Storms possible this afternoon/evening...accumulating snow Wednesday

3:40pm Update:  Copious amounts of moisture continue to move northeast from Missouri.  Rain will continue through the remainder of the evening before switching to snow by Wednesday morning!

(3:18:59 PM) nwsbot: DVN issues Winter Storm Warning valid at Jan 30, 1:00 AM CST for Cedar, Clinton, Dubuque, Jackson, Jones [IA] and Jo Daviess, Stephenson [IL] till Jan 30, 6:00 PM CST

(3:18:59 PM) nwsbot: DVN issues Winter Weather Advisory valid at Jan 30, 1:00 AM CST for Henry, Louisa, Muscatine, Scott, Van Buren [IA] and Scotland [MO] and Carroll, Mercer, Rock Island, Whiteside [IL] till Jan 30, 6:00 PM CST

  (3:00:36 PM) nwsbot: MKX issues Winter Weather Advisory valid at Jan 30, 6:00 AM CST for Jefferson, Ozaukee, Rock, Walworth, Washington, Waukesha [WI] till Jan 30, 9:00 PM CST

(3:00:36 PM) nwsbot: MKX issues Winter Storm Warning valid at Jan 30, 3:00 AM CST for Columbia, Dane, Green, Green Lake, Marquette [WI] till Jan 30, 6:00 PM CST

(1:28:52 PM) nwsbot: Local Storm Report by NWS DVN: 4 WNW Dubuque [Dubuque Co, IA] trained spotter reports HEAVY RAIN of M0.97 INCH at 01:25 PM CST -- lots of standing water in the grass.

1:00 pm Update: The cold front is knocking on our doorstep early this afternoon.  Temperatures ahead of the front have warmed into the upper 50s/low 60s while temperatures behind the front have dropped into the 30s and 40s.  The leading edge of the rain is now moving into northwest Illinois with light rain being reported from Moline to Dubuque and even a little drizzle in Freeport.  These showers will continue to move north/northeast throughout the remainder of the afternoon and evening with rain beginning in Rockford by 2pm.  Heavy rainfall with totals between 1.5" and 2" will be the main concern later this afternoon and evening.  A few of the embedded storms could produce some stronger wind gusts. 

11:00 am Update: A Winter Storm Watch has now been extended to cover Stephenson, Carroll, Whiteside and Jo Daviess counties beginning at midnight night and lasting through 6pm Wednesday.

Previous Discussion:

An impressive weather event will begin to unfold this afternoon and evening as daily high temperature records are shattered and possibly even all-time January record highs!

Let's first break down what's going to happen for the remainder of this morning.  A very warm and moist atmosphere is in place and this has been the trigger for scattered storms early this morning.  By this afternoon low pressure and a strong cold front will sweep through southern Wisconsin and northern Illinois bringing with it storms that are currently near Wichita, KS and Kansas City, MO.  The Storm Prediction Center has extended the slight risk further north to include parts of Winnebago, Ogle, Lee, Whiteside, DeKalb and McHenry counties...along with most of northeast Illinois.  The bulk of severe weather will occur to the south, mainly over Arkansas, later today but stronger storms aren't out of the question in northern Illinois.  Skies will likely remain mostly cloudy limiting the amount of heating that will take place but with such strong winds within the jetstream and such a moisture rich atmosphere, some of that energy could get transferred down to the surface causing storms to produce damaging winds; an isolated tornado is possible as well but the risk remains low.  Along with the threat for stronger storms, a greater threat today will be heavy rainfall.  Aerial Flood Watches have been issued for Winnebago, Boone, McHenry, Ogle, Lee and DeKalb counties as rainfall totals could exceed two inches; especially if stronger storms move through.  We'll be closely monitoring any storms that form after 3pm today.

If heavy rain wasn't enough the potential for accumulating snow, especially west of Rockford, is becoming even more likely.  The cold front has slowed down some which may delay the onset of cold air moving in overnight night and early Wednesday but from Monroe to Freeport to Mt. Carroll and points west accumulating snowfall of more than 6" will be possible by Wednesday night.  In fact, Winter Storm Watches have been issued for Green County in southern Wisconsin and for Jo Daviess County in northwest Illinois beginning late tonight.  If the axis of heaviest snow shifts further east then Rockford could be dealing with a winter storm by Wednesday afternoon! 

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