Afternoon Weather Update

A heavier band of precipitation is lifting north near the Illinois/Wisconsin state line.  Within this band, heavier wet snow or a mix of rain and wet snow has been occuring.  Where the heavy snow has fallen the flakes have been very large!  This mixture of rain/snow will continue before completely changing over to all snow by this evening.  Minor accumulations are likely where the snow falls this afternoon.  This will keep roads wet and slushy.

WINTER WEATHER ADVISORY FOR NORTHERN ILLINOIS COUNTIES, ROCK AND WALWORTH COUNTIES BEGINNING AT 6PM THIS EVENING.

Light rain mixed with snow is now beginning to lift north of I-88 late this morning and will continue northward through the afternoon.  There is a very warm layer a few thousand feet above the surface which should support the rain going through the afternoon, however, right above the warm layer colder temperatures are found.  These colder temperatures will eventually begin to trickle down allowing some snow to mix with the rain.  As the low begins to move closer this evening a complete change over to snow will occur; this appears to be somewhere during the 6pm to 8pm time frame.  Right after the complete change over to snow is the greatest potential for thundersnow to occur.  If thundersnow were to happen, totals would likely be increased due to higher snowfall rates. These rates could exceed an inch per hour.

Right along the I-88 corridor holds the greatest potential on totals possible exceeding six inches.  This puts Lee, Ogle, DeKalb and maybe even southern McHenry counties in the bullseye.  Further north snow totals will likely range from 3" to 6" and further south totals will be a little less.  

The dynamics of this storm are that of what we would typically see in spring in terms of instability, hence the potential for thundersnow.  Temperatures will range from 31° to about 36° as the change over to snow occurs and will slowly fall overnight.  With temperatures in the lower 30s the snow that does fall will be heavy and wet in nature.  Winds will begin to pick up tonight, but hopefully there shouldn't be too many concerns with blowing and drifting just because the snow will have some weight to it.  The reason an advisory has been issued for all is because the heaviest of the snow will fall later this evening and overnight when there won't be a lot of traffic on the roads.  The snow should be winding down by daybreak Friday.  

Many weather concerns today

Dense Fog Advisory issued for Winnebago, Boone, McHenry, Ogle, Lee and DeKalb counties through 8am


First order of business is the fog and freezing fog this morning.  Dense fog has formed across northern Illinois and southern Wisconsin as moisture continues to pool in the Midwest.  The fog will last through the morning and as temperatures have fallen well below freezing, there will likely be slick spots found on elevated surfaces, sidewalks and parking lots.  Visibility has gone down to less than a quarter mile in many locations so be sure to give yourself extra time.

Once we get rid of the fog this morning all eyes will turn to our evolving storm system currently across the Plains.  Light rain is now falling across southern Iowa and Missouri this morning out ahead of a warm front.  As this system moves closer, I would expect light rain or a mixture of rain and snow to begin either late this morning or early afternoon.  By this evening any rain/snow mixture should change over to all snow and potentially become a heavy, wet snow.  The heaviest of the snow will likely fall after about 6pm tonight and into the overnight as low pressure tracks out of the Plains and into Missouri and southern Illinois. 

Winter Storm Watches continue for Winnebago, Boone, McHenry, Ogle, Lee and DeKalb counties while a Winter Weather Advisory has been issued for Rock and Walworth counties beginning this evening.  Our western counties have been dropped from this watch because of the more southern track of the low.  The heaviest of the snow is likely to fall just to our south and across northeast Illinois where totals could near six inches as the best lift and forcing will be found there.  Overall, about 3" to 6" will fall, but some of this snow may melt initially when it reaches the ground due to the recent mild weather.  Our northwest counties may experience totals closer to the 3" mark or less due to the fact that they're further away from the forcing of the storm.  In the band of the heaviest snow, this is where totals may exceed the six inch mark.  I want to continue to stress that this system has changed dramatically over the past 24 hours so some adjustments will likely be needed going forward today.

Still Watching Big Snow Potential...

8:50pm Update: The NWS Chicago office is now including the rest of the Stateline area in the Winter Storm Watch. Time frame is Thursday evening into Thursday night.

Although the NWS in Chicago has yet to include its counties in the Winter Storm Watch, Stephenson, Jo Daviess, Carroll, and Whiteside counties are still in this watch on Thursday.

I can't criticize the good folks at the Chicago office for not including us in this watch. This is a very complicated forecast, perhaps the trickiest one we've had so far this "winter." There is still a lot of uncertainty as to where the surface low will track tomorrow, and this could throw a wrench into the above snowfall forecast.

Right now, this low is in southeastern Montana and is about to cross into northeastern South Dakota. Some of our models suggest this low will track along the I-80 corridor, just to our south. This solution would suggest light rain mixed with snow for the Stateline, with little or no accumulation. However, other model solutions suggest this low will move into central Iowa by morning, then re-develop further south over southern Illinois in the afternoon. If this happens, colder air would reach the area and most of our precipitation would fall as snow. Recent trends lead me to believe that the southern track will be closer to reality, which would mean wet, heavy snow for the Stateline area.

With a strong piece of energy moving through the jet stream late in the afternoon into early evening, snowfall rates could briefly approach 1" per hour, with some "thundersnow". Although this could lead to a quick 2-4" for some of us, snow accumulations earlier in the event will be limited by warm ground and air temperatures above freezing. That's why I think 3-6" will be the rule for most locations.

Thursday's Snow Potential Update

The latest morning model runs have started to come in regarding Thursday's storm and snow potential.  Unfortunately, they have come in stronger with the low as well as with more moisture. 

A Winter Storm Watch has been issued for Jo Daviess, Stephenson, Carroll and Whiteside counties beginning at 6am Thursday.  A Winter Storm Watch has been issued for Green, Rock and Walworth counties beginning at 8am Thursday. 

Low pressure will move out of the Plains later tonight and almost overhead by Thursday mid-morning.  The morning run of the GFS takes the low across northern Illinois while the NAM is a little further north.  With these likely tracks the heaviest snow band would set up across northern Iowa, southern Wisconsin and northern Illinois.  I want to stress that the exact track of this storm is still uncertain and ultimately this is going to affect where the heaviest axis of snow falls.  Right now it appears to be along the Highway 20 corridor.  The total QPF, or amount of moisture/precipitation, with this storm is between about 0.30" and 0.60"  Using a 10:1 ratio that would yield snowfall totals between 3" and 6".  Temperatures will likely be in the low to mid 30s during the time the snow falls so this could lead to more of a wet snow.  One important aspect to keep an eye on along with the track will be the temperatures aloft.  There will be a brief period of southerly winds ahead of the low which may warm the upper layers.  If that were to occur there's a possibility of rain mixing with the snow which may cut down on totals. 

Updates will continue here later this evening and tonight!  Further analysis and monitoring of this system will be done throughout the day today!  Stay tuned!

Active and unsettled weather this week

Strong jet stream winds are currently moving into the Pacific Northwest bringing rain and snow to Washington and Oregon, but also aiding in the development of quick moving storm systems that have been moving across the U.S the past several days.  The first impacted us early Tuesday morning with the snow and then again this morning as light snow fell south of Rockford.  The next storm to hit will come late tonight.  Low pressure has been developing across the eastern Rockies and will quickly move through the Midwest by Thursday morning.  As it does, a warm front will lift closer to the Stateline this evening which could induce a few light rain or even snow showers.  As the low moves closer tonight it will pull in a little warmer air aloft which may keep the mixture of rain/snow before changing over to snow showers by Thursday morning.  Just like Tuesday morning, the possibility remains for accumulating snow Thursday - some of which you may have to shovel!
The low pressure will then move into Ohio and actually strengthen as 130 kt jet streams winds move overhead.  On the backside of the low a trough of low pressure will extend northwest through Wisconsin and Minnesota which will keep the snow chance going Thursday night and Friday.  High pressure finally moves in Saturday afternoon giving a little more sunshine.  The sunshine will fade away to clouds by Sunday afternoon, however, as a stronger low moves into the Plains by Sunday night.

A Week's Worth of 40s

The unusually mild winter continues for the Stateline area. We hit 43 degrees this afternoon, marking the 7th day in a row in which the mercury has climbed to 40 degrees or higher. Our average high for this date is 36. Tomorrow and Thursday should also be in the 40s, but cooler weather is in-store for Friday. If our forecast high of 36 works-out for Friday, our consecutive 40-degree day stretch will stop at nine.

Tuesday Morning Weather Update

The main batch of snow has moved east, however, there is a little redevelopment on the backside of the low.  This light snow, possibly mixed with rain & sleet, is currently moving through Stephenson, Carroll and Whiteside counties and should be near the Rockford Metro within the next 30 minutes.  Once this passes that will be it for precipitation, but the clouds will remain and winds will begin to pick up.









5:30:00 AM) nwsbot: DVN: 4 Wsw Loran [Jo Daviess Co, IL] trained spotter reports SNOW of E1.0 INCH at 05:28 AM CST -- light to moderate snow continues.

Light snow will continue to fall for the next several hours this morning as low pressure moves through central Illinois.  Accumulations will remain light with many locations receiving an inch - possibly close to two.  The snow has begun to accumulate a little on roadways, sidewalks and parking lots this morning.  Roads will remain wet and there could be a few slick spots this morning.  The back edge of the snow is right along the Mississippi River and will be moving through north-central Illinois through mid to late morning.  There may be a period where light rain or even sleet mixes with the snow.  Winds will begin to pick up behind the low from the west/southwest gusting close to 35 mph.  Temperatures will