This will not be the typical blog post. I am not showing model data at least not very much. We've seen plenty, it seems to be all anyone talks about. The models are a TOOL not the end all to the weather. Instead I am going to focus a little on the meteorology. There is no hype here, just my opinion of what will happen and why. It is a difficult forecast to do in these situations especially in a 2:30 second weather cast. Clearly what will happen in Seymour, Indiana will be very different from downtown Louisville which will be different from Campbellsville, Kentucky and all are in our coverage area. So, as I type this Huntingburg (Dubois County) is at 36 and our southern viewing area is in the 50's. The current NWS radar is showing an increase in precip to the NW, the sign the winter storm is coming together. A mix of rain, sleet and snow with temperatures near 32 is occurring over Southern Illinois. Clearly the cold air and the precipitation are coming, but in what form and how will it impact and accumulate. This is where I may differ a little. Here is the one piece of model information I will present.
OUTPUT FROM NAM 12Z DEC 05 13 TTPTTR1R2R3 VVVLI PSDDFF HHT1T3T5 SDF//927364 01599 102610 62161307 06013879265 02401 173213 56060807 12018949563 12703 193513 55020107 18028979466 05111 220111 53000102 24048989869 09811 200312 53000102 30103979971 14511 170215 54000105 36046969673 -9418 230116 47989801 42003953716 -1122 293413 41979496 48000923215 -2126 343514 38939295 54000881919 -1027 373507 38959395 60000931335 -0927 370210 39939596 BNA//907668 01697 132015 64191508
I have bolded what is important. In black those are liquid precipitation totals and it totals 2.25" from roughly mid evening tonight to early evening Friday. Now imagine if that was snow! a 10-1 ratio is nearly 2 ft! In green those are temperatures (in celsius) at a few levels surface to just above. 00 is freezing and note the other levels are above freezing right into late tomorrow. The blue area is humidity levels at those same levels and they drop big time late tomorrow .Now keep in mind this is only metro Louisville I am speaking of. This data suggets a prolonged period of low to mid 30s on temperatures both surface and a few thousand feet above. That is not much of a snow or freezing rain set up. It is more sleet and a cold rain. Even if it gets a little colder (which is possible) it is still more sleet. Late in the event the transition to snow occurs but at that point the atmosphere quickly dries out. During the day I would think the combination of residual heat from the warmth of yesterday, the treatment of chemicals on the roads and the fact we dont drop much below 32 would keep the main roads wet.
I can think back to numerous events where it looked potentially bad and once the true cold air comes in things dry out. This makes sense meteorologically speaking since colder air can not hold as much moisture as warmer air. Inevitably when these set ups come in from the north the deeper moisture exits. If we keep enough moisture aloft in place (warmer air holds more) that just solidifies my sleet scenario not snow. Topography also plays a role here. We are at a lower elevation in the metro than you are to the NE and especially NNW of the city. Once into Orange and Washington and Scott counties of Indiana the snow and ice scenario is more plausible to me. I think we will see a very sharp cutoff so places like Seymour and Bedford and Paoli and Scottsburg could get 4-6 inches of snow. We may get an inch or so in Louisville very late in the day before the drying comes in but I am betting the majority in the metro is a sleet and cold rain with temperatures near freezing. Now if we do drop colder (IF) then this becomes more serious and that will have to be evaluated in a more nowcasting sense on Friday.
This brings me to Sunday which in my view may be far more impactful. We should easily be in deep cold air (in the 20's) at the surface. Then we warm up just above on a robust SW wind. This looks like an ideal freezing rain set up (Sunday morning) then the question becomes when or if the surface gets to 32. It may Sunday afternoon or evening but we could see 1/4 to 1/2 inch of rainfall before it does. Weather systems from the SW are usually more of a concern to me than those from the NW and this too makes sense meteorologically.
So for forecast highlights I see our northern areas getting several inches of snow tomorrow, a mixed bag but more sleet than anything for the metro and then a mix to just mostly rain to the south. Sunday is ice to rain south, mostly ice in the middle that could start as light snow and end as light rain and snow to freezing rain up north.. Oh and after that, the coldest air of the season pours in.
As an aside I am not working at WAVE today, this is from home. So my thoughts may or may not agree with the other 5 people of the WAVE 3 weather team. It is their call as to what they are forecasting on air. We won't know how it goes until the weather occurs. I will be in the seat though this weekend both Saturday and Sunday. I will likely have updates on Friday.