Absolute Vorticity

I left a date range on the thread title for now as that can be changed with time. The window of opportunity for us is Tues night thru all of Wed for the best snows. Not sure yet if the system will be strong enough to linger overnight into early Thurs. The amount of QPF and duration we see depends on how quickly this system comes together. We know air temps will be in the teens and 20s so a high ratio, fluffy snowfall is likely. We need a faster phasing of the upper low for a big one.

We will begin with the latest QPF amounts from the major models, This is for CVG.

3Z SREF Mean around 3"
6Z NAM - 0.60" (Snow is not quite done yet)
6Z GFS - 0.27"
0Z Euro - 0.24"
0Z CMC = Was a disjointed mess, not much QPF.
6Z RGEM - Almost a swing and a miss

6Z GEFS snowfall mean is 3"
EPS is good for 2-3" as well

We have a long ways to go with this one but once our current system gets out of the way, we'll see how things go.

Les has started the thread and off we go. This upcoming system is a more typical storm compared to the one we just went through but again always challenges with most winter storms. The one challenge that we won't have to worry about is precip types. That helps a ton when trying to make a snowfall forecast.

The main challenge I see at this point is going to be dry air to overcome. The arctic air mass is really cold but with the mid-week system its keeping us out of the deep freeze. If that storm was not around we would no doubt see temps near 0. That is not going to happen as the winds become zonal across the central plains on Monday while we have a trough starting to dig south. So this is allowing moisture to advance northward rather quickly starting late Monday in that part of the world. As the trough is digging a low pressure will try to develop along the gulf coast. This should probably be later Tuesday or Wednesday. If this one gets to strong in a short time that can rob moisture flow to the north but at this time that low seems to be on the weaker side. The upper system should get with the zonal flow starting later Monday and work eastward through Wednesday.

Big storm chances for us are not great but folks south of I-64 could see a decent snow and I call over 4 inches decent. Folks towards I-70 though could have a hard time of getting 1 inch. At this point in time and my first call locally would be 1-3 inches from north to south. This is nothing like the storm in January but still getting 1-3 inches and temps in the mid 20's no doubt can cause some travel problems.

Will watch and see the models today as I would expect any major changes to happen later today of this evening concerning the models.

Can we see more snow than the 1-3 and sure but we could also be under the 1 inch if things went bad. So not set in stone as again we must watch the trough develop on Monday and how deep is this trough. My guess folks in the Missouri Valley and lower Ohio Valley and Tn valley may get their biggest snows of the year with this system.

Agreed Tim. All we have to figure out is how much QPF we get, Ratios IMO should be in that 17 to 20:1 range for this event. So 0.20" of QPF would be 3.5 to 4" of snow as an example.

9Z SREF mean is up to about 4" now for CVG.

tron777 wrote: ↑Sun Feb 16, 2025 8:37 am 9Z SREF mean is up to about 4" now for CVG.

Hey Les does the mean include today's snow?

tpweather wrote: ↑Sun Feb 16, 2025 8:41 am

tron777 wrote: ↑Sun Feb 16, 2025 8:37 am 9Z SREF mean is up to about 4" now for CVG.

Hey Les does the mean include today's snow?

Nope. I subtracted it. The mean is almost at 7" when you combine today with next week's snow. The SREF and NAM are typically the more amp'ed up models anyway.

tron777 wrote: ↑Sun Feb 16, 2025 8:43 am

tpweather wrote: ↑Sun Feb 16, 2025 8:41 am

tron777 wrote: ↑Sun Feb 16, 2025 8:37 am 9Z SREF mean is up to about 4" now for CVG.

Hey Les does the mean include today's snow?

Nope. I subtracted it. The mean is almost at 7" when you combine today with next week's snow.

Thanks and was not sure. Of course over the next day or two we will get a better ideal because some of the goofy ones will be off the board and this usually means that the mean will come down some. Again one of these where you start watching for the mean in Indy and Columbus. This gives us an ideal how the models are seeing the dry air. If we can those 2 places to have the mean towards 3 inches I would be thrilled but again they could also go lower and be 1 inch. Again not the most complicated storm but how dry the air is but on the counter side of that is the ratio's should be greater than the normal 10-1 and probably closer to 15-1

The Nam is running and always try and see what has changed with the model from 24 hours ago. So far precip further north at hour 48

tpweather wrote: ↑Sun Feb 16, 2025 9:21 am The Nam is running and always try and see what has changed with the model from 24 hours ago. So far precip further north at hour 48

This should be another good run. I just hope it doesn't cave in future runs and it can gain some more support.

You can see the warm push of air all the way to the border of Oklahoma and Kansas. This is a good sign imo. If this continues then yes some mixing issues in southern Kentucky but still too early for making that call. Mid-Feb the warmth becomes more of a player as we head toward spring so we can see its already putting up a little fight on the models

If the rain / snow line can get into SKY, then we will get buried!

Also the streak of snow across central Illinois,Indiana into our area is growing. Maybe not much snow but what it does is help in getting the atmosphere moist and getting rid of some of the dry air in place. Small items make a difference.

tpweather wrote: ↑Sun Feb 16, 2025 9:32 am Also the streak of snow across central Illinois,Indiana into our area is growing. Maybe not much snow but what it does is help in getting the atmosphere moist and getting rid of some of the dry air in place. Small items make a difference.

Seeing some lighter WAA snows before the main course arrives is perfect for not only priming the pump, but to prolong the event as well. Much to like on this run. I just hope the GFS and others spring back to life a little bit.

I like seeing the low more inland too and not buried down into the Gulf. That is the track we want to see.

tron777 wrote: ↑Sun Feb 16, 2025 9:36 am I like seeing the low more inland too and not buried down into the Gulf. That is the track we want to see.

Les a great run and the low on this run is developing further north and not along the gulf coast. Huge difference in possible outcome

BTW roads covered and my guess ice is forming underneath.

NAM has us snowing with temps in the upper teens for the most part Tues night into Wed morning. Love seeing these higher ratios! Could be 5-6" on the ground by Wed morning if you believe this model. That is what the data shows when taking the high end snow to liquid ratio into account. If you can get 0.50" of QPF you're looking at a double digit storm again. Not forecasting this, just saying what the potential is should this system pan out as shown.

My Lord... the NAM gives CVG 0.55" of QPF again like the 6Z run did. Please, oh please, please be right for once NAM!

Watch the RGEM next as it has been heading north since the noon run yesterday. I expect that to continue with today's run.

What a beauty

tpweather wrote: ↑Sun Feb 16, 2025 9:56 am Watch the RGEM next as it has been heading north since the noon run yesterday. I expect that to continue with today's run.

It's not going to be as amp'ed up as the NAM. I can already tell that much.

tron777 wrote: ↑Sun Feb 16, 2025 10:01 am

tpweather wrote: ↑Sun Feb 16, 2025 9:56 am Watch the RGEM next as it has been heading north since the noon run yesterday. I expect that to continue with today's run.

It's not going to be as amp'ed up as the NAM. I can already tell that much.

Not sure yet Les as I see the RGEM digging the trough a little further southwest which I thought was one of the main factors in how this storm plays out.

The NAM had a 1007 MB low over S CO at 60 hours and the RGEM has it at 1010 MB over S NM. Big difference!

NAM has the high over S Canada at 1052 MB. RGEM is really strong at 1060 MB! So that isn't good either.

The RGEM did bump north with the snow shield to be fair Tim and you did predict that would happen. This model (really all of them) aren't close as of yet to what the NAM is trying to sell.