...And I want to stress the word *potential*! There's been a lot of talk recently about the potential for a major winter storm to move into the Midwest late next week. In fact, it was first pointed out Wednesday morning that two possible systems could affect the Stateline with an active weather pattern beginning to take shape.Before you begin to change/cancel any plans for next week let's remember that this system is a week away and things will change. The storm system in question remains well off shore in the North Pacific and is being sampled by a very limited amount of observational data. It will take likely until early next week before we're able to gain a better understanding of exactly where this storm will go, how much moisture it will pull from the Gulf, how much cold air will become wrapped in behind the system, etc. However, for the past couple days two of our more reliable weather computer models have held their own with this low developing near Oklahoma and lifting northeast into central Illinois - which is typically a more favorable track for accumulating snow in the Midwest - however they have also changed the intensity and speed of this system which is something that will continue until the storm moves onshore. It's hard to say at this point that there will be a major winter storm for the Stateline next Thursday and Friday, but it's also hard to say there won't be and it's something you should continue to monitor and keep in the back of your mind going into the weekend. We'll be here day in and day out tracking both systems; Monday night/Tuesday and Thursday/Friday, and continue to provide the latest information right here! Stay tuned!
Let me explain. Our forecast models work by taking current weather conditions and applying them to complicated mathematical equations. This eventually gives us the computer's forecast. The thing to remember is each day of the forecast is dependent on the day before it. In this example, we have rain on Thursday and snow on Friday.
Since each day's forecast depends on the day before it, any change in the forecast can compound on itself over time, meaning small changes turn into bigger ones over the course of several days or a week. In this example, we made Monday warmer. That, in turn, can make the computer warm temps up over the long haul... meaning rain on Friday instead of snow.
The main low pressure system is spinning through southern California with a slug of moisture lifting north in Texas, Oklahoma and Kansas. Currently heavy snow is falling in northern Oklahoma and south central Kansas where snowfall rates of 1" to 2" per hour are possible through the afternoon. The weather remains quiet across Northern Illinois and Southern Wisconsin with high pressure overhead.
Winter Storm Warnings (shaded in pink) and Winter Storm Watches (shaded in blue) have been issued for the Plains and Midwest with Ice Storm Warnings (shaded in purple) for northern parts of Arkansas. As of right now the only county under any sort of watch remains Whiteside County where a Winter Storm Watch will go into effect Thursday afternoon. The system has slowed a bit and this will allow the bulk of snow to fall after dark Thursday with a timeframe right now looking at after 6pm and lasting through 5am Friday morning. Good news for Thursday travels but not so good news for the Friday morning commute. Snowfall totals are becoming a little more clearer and while not a crippling snow storm we will see a decent amount. Preliminary snow totals call for 3"-6" to fall in N. IL and S. WI with lesser amounts towards Indiana and higher amounts downstate and in Iowa. The storm will have a decent amount of moisture and even a little instability with it so it's possible that thundersnow may occur late Thursday night! If this were to happen higher snowfall totals would be observed as snowfall rates would increase during that time. Snow to liquid ratios will remain average ranging from 10:1 to 13:1 meaning whatever snow does fall will have a little weight with it. Winds will also increase from the southeast causing some blowing and drifting.
The Winter Storm Impact forecast keeps things quiet through Thursday afternoon with the first flakes possibly falling around dinnertime southwest of Rockford towards the Quad Cities. Snow will increase in coverage from south to north with the heaviest of the snow falling overnight. Warmer and drier air becomes wrapped into the low from the south with a rise in temperatures expected by Friday morning. This could create a mix of snow and freezing drizzle for a period before a switch back over to light snow by Friday afternoon. Stayed tuned for further updates!
Let's start off with Tuesday's watches and warnings. Most of the Stateline is under a Winter Storm Watch on Tuesday because of accumulating snow and strong winds that will cause blowing, drifting, and reduced visibilities.
Just like last week's storm system, here's what we know for sure. There will be accumulating snow on Tuesday and strong winds will make it messy, especially for the evening commute home. Snow will still be possible Wednesday, but it will not be as messy as Tuesday.
While it seems this next storm hasn't received as much of attention as the one last week, it has and will pack a punch for the Plains and Mississippi River Valley. Winter Storm Watches (blue shading) continue for a portion of Northern Illinois but have been canceled for Rock and Walworth counties. The reasoning - a slight shift south with the storm track was observed earlier this morning.
Looking over some of the latest data that has come in this morning it looks like snowfall totals reaching anything higher than 3" may be hard to come by. Temperatures at the surface Tuesday will remain very close to freezing and it's possible that we may even rise into the low to mid 30s now that we've been able to melt away some of the current snow. As the snow melt continues the models have had a very hard time picking up on this feature because it's occurring on a very fine scale. This means by the time the snow were to begin Tuesday models are forecasting surface temperatures slightly cooler than what they may actually end up being. Also, with slightly warmer temperatures there is a chance that a wintry mix may occur at the onset during Tuesday afternoon before enough cooler air aloft wraps into the storm to allow a transition over to snow. Low pressure will track out of Texas this afternoon and into Southern Illinois by Tuesday afternoon. As of right now it appears as if the band of heaviest snow may occur just to the south and east of the Rockford area with Southeast Wisconsin, Northeast Illinois and maybe even around the Quad Cities receiving some of the higher snow totals.
The next winter storm has already moved into the Pacific Northwest and will dive out of the southern Rockies and into the panhandles of Oklahoma and Texas by Sunday night. By Monday the low will be moving near the Missouri/Arkansas border and then to St. Louis, MO by Monday night. Tuesday the low will be tracking across central Illinois before moving into Michigan by Wednesday. Unlike this past storm that just came through, this one looks to take a more southern track. One reason, the recent snowfall we received will act somewhat like a baroclinic zone ( mini frontal boundary ). Storm systems tend to follow where there is the greatest temperature gradient. An area that has snow cover on the ground often times is cooler than a surrounding area that doesn't have as much or very little snow cover. As of Saturday afternoon the ground was white down through central Illinois and almost all of Missouri. Now by Sunday some of the snow will have likely melted due to the sunshine expected, but there should still be a little snow left on the ground. Some accumulating snow will be likely across the area Tuesday but the temperature profile may be a bigger factor with this storm than with the last. Warmer air wrapping into the storm from the east and southeast could cause a mixture of sleet, rain or even freezing rain from a line east of Kenosha, WI to Woodstock to Rochelle to Dixon while areas west of that line have a greater probability of all snow.
Accumulating snow will occur for parts of Northern Illinois and Southern Wisconsin but just like the last storm, this one will also be in a weakening phase when it arrives. Once this main low passes it'll continue to spin in the eastern Great Lakes for the next few days keeping snow in the forecast through next Thursday.
While Thursday night's "winter storm" fizzled out as it moved into the Stateline, we'll have another shot at some decent snow totals starting Monday night. Model runs have a low pressure passing to our south Monday night and Tuesday, putting us at risk for being in the bulls-eye of heaviest snowfall.
The overall timing of the forecast and the hazards with this storm haven't changed. We're still talking heavy bursts of snow late this evening through the early morning hours combined with wind gusts of 30mph to create lowered visibilities and blowing and drifting snow. Roads will be messy Friday morning, although winds and snow will calm significantly heading into the afternoon.
As was mentioned earlier, a dry wedge of air has wrapped itself around low pressure currently in northern Missouri. This has essentially ended the heavy snow from south to north and will continue to do so through the remainder of the morning. There are, however, snow showers in Iowa that will rotate through later today. 
Heavy snow with snowfall rates of 2" per hour continues to fall in Northeast Kansas and Northern Missouri! Even thundersnow has been reported near Topeka, KS with thunder, sleet, snow and freezing rain in Joplin, MO. This storm is headed in our direction later today but will be weakening as it does.