Heavy sleet is mixing with rain over the western half of the Tri-State. This winter storm has definitely been working on its own schedule…the sleet is arriving about 6 hours later than our prediction yesterday. One of the reasons for the slowdown is that the parent low pressure system out over Kansas is deepening (strengthening), so the storm is coiling up on itself more than marching to the east. The purple areas on the radar show sleet…you can see surface temperatures are above freezing over the southeast portion of the Tri-State.
I've been using models of the wind pattern to try to get a better handle on how this system will affect us this evening. I believe the warmer air will also arrive later than expected, so we may see some travel problems this afternoon for the commute, especially in southern Illinois and on any untreated roads over southwest Indiana and far western Kentucky. This chart shows persistent easterly winds through 8 pm, so these will not warm us as rapidly as a southerly flow.
The NWS has now extended and expanded the winter weather advisory to include most of the Tri-State. The advisory (in blue) will continue until midnight tonight. The pink areas are a winter storm warning…this is where more significant accumulations of snow and ice are now occurring.
Here is the regional radar pic as of early Thursday afternoon. You can see the clear breaks between the all-rain (green), sleet-freezing rain (pink) and snow (blue). I don't think most of the Tri-State will see much accumulation of sleet, but it doesn't take much to create travel problems on untreated roads. You may even hear some rumbles of thunder with the sleet. Even though ground temps are below freezing, there is a pocket of warm air aloft that may support brief, elevated thunderstorms.