Saturday, January 12, 2013

Dangerous roads likely tonight- Winter Weather Advisory

Overnight master control operator just came in and reported very slick roads!  Please, please be careful tonight!  Untreated roadways will become dangerous.

11:00pm Update:  Expect a sleet/graupel/snow mix to continue tonight as the back edge of the snow extends into northeast Missouri.  A mixture now of sleet/snow is falling at WTVO.  Be careful driving tonight.

Storm Reports:
A snow emergency has been issued for the village of Machesney Park beginning tonight and lasting through 11am Sunday.  All vehicles must be removed from village streets during a snow emergency.  Light snow continues to move into the area with a heavier band of snow west of Rockford stretching from Monroe, WI to Savanna, IL.

(11:16:34 PM) nwsbot: Local Storm Report by NWS LOT: Cortland [Dekalb Co, IL] trained spotter reports FREEZING RAIN of U0.00 INCH at 11:10 PM CST -- moderate freezing rain with a light glaze on elevated surfaces.

(10:59:22 PM) nwsbot: Local Storm Report by NWS MKX: Edgerton [Rock Co, WI] trained spotter reports SNOW of M0.5 INCH at 10:58 PM CST -- snow recently changed to mixture of sleet and freezing rain.

(10:51:29 PM) nwsbot: Local Storm Report by NWS LOT: Huntley [Mchenry Co, IL] cocorahs reports SLEET of E0.25 INCH at 09:50 PM CST -- estimated 1/4 inch sleet mixed with snow accumulation the north side of huntley.

10:24pm: DE Kalb [De Kalb Co, IL] public reports FREEZING RAIN of E0.00 INCH at 10:15 PM CST -- follow up to report from 950 pm. freezing rain still occurring. freezing on contact with ground...with temperature down to 26 degrees.

10:22pm: DE Kalb [De Kalb Co, IL] public reports SNOW of E0.2 INCH at 09:50 PM CST -- estimated 0.2 inches of mixed snow/ice on ground. streets covered...grasss still visible in spots. precipitation had changed to light freezing rain at time of report.

(6:40:02 PM) nwsbot: Local Storm Report by NWS LOT: Capron [Boone Co, IL] trained spotter reports FREEZING RAIN of E0.00 INCH at 06:33 PM CST -- sleet and freezing rain. a little slippery on walks and street

(4:49:56 PM) nwsbot: Local Storm Report by NWS LOT: Rockford [Winnebago Co, IL] broadcast media reports SLEET of E0.00 INCH at 04:15 PM CST -- sleet reported on se side of rockford

A Winter Weather Advisory remains in effect for Jo Daviess, Stephenson, Carroll, Whiteside, Winnebago, Boone, Ogle, McHenry, DeKalb and Lee counties through Sunday morning.

Weather Breakdown:

A mixture of sleet, freezing rain and snow will occur this evening and last through roughly 10pm before switching over to all snow overnight tonight.  Areas east of Rockford, however, will see a longer period of sleet/freezing rain and this could lead to minor ice accumulations on roadways the closer you get to Chicago.

925mb - Cold air at the surface

850 mb - Warmer air at 3,000 ft

Low pressure developing on the southern end of a cold front that passed early this morning will bring moisture northward into Illinois and Wisconsin.  At the same time temperatures at the surface will be cooling below freezing but temperatures aloft will actually be warming.  The first image on the left is a meso-analysis of current temperatures a few hundred feet above the surface.  Anything left of the black line indicates a temperatures below freezing and anything on the right of the line indicates a temperature above freezing.  Now, if we go just a few thousand feet above there is actually a warm wedge of air over northern Illinois and southern Wisconsin (see how the black line is further west on the second image).  This means that as precipitation falls from the clouds it's moving into the shallow 'warmer' layer causing any frozen precipitation to partially melt before refreezing again once reaching the surface.  This is why we'll initially see a mix of sleet and freezing rain.  As the atmosphere continues to cool from top down any wintry mix will eventually change over to all snow; likely after about 10pm/11pm.  Just how quickly this change over occurs will determine how much overall snow we receive by dawn Sunday.  If the change over is slow then we'll experience more of a sleet/snow mixture which will cut back on totals.  If the change over occurs sooner then totals of 2" to maybe 3" of snowfall will be possible.  Keep in mind, we've just come off of about a weeks worth of 40° weather so the ground isn't completely frozen and any snow that falls may initially melt on contact.  Bottom line, after about 9pm/10pm roads will become slick.  If you have to travel tonight or early Sunday morning use caution!  Conditions will improve after 7am Sunday morning. 

No comments:

Post a Comment