Absolute Vorticity

Continue discussion here.

One thing to watch is timing/strength. The Euro is similar to 12z but the “dry slot” got nudged a bit east reducing our totals. Main reason being that the southern wave is weaker and misses us. Still a solid advisory event locally but we do need to keep an eye on that. That’d be the difference between an advisory event and a warning event.

I’ve got two runs between now and map making (06z and 12z) but I am currently leaning toward maintaining the 1-3” call for the metro. I want to stay conservative for now given the reasons I mentioned above. If things continue to be more aggressive I can adjust upward by tomorrow. But I wast to play it cautious on this one.

06z NAM illustrates one of my concerns. It phases the storm but it happens a bit too late and the low tracks too far north and we get the dry slot.

So close to being a great track for us though!

Now you've done it Trev. The kiss of death!

QPF from the globals At CVG:

6Z NAM - 0.09" stops at 1pm Friday.
0Z GFS: 0.25"
0Z Euro: 0.12"

Naturally, this snow weenie will ride the Canadian!

6Z RGEM looked nice around 0.35" to 0.40" of QPF. The 0Z Ensembles... GEFS had 0.25" and the EPS 0.17".

0.28" at CVG from the 6Z GFS.

6Z RGEM has snow moving in from the SW Thurs afternoon with periods of snow continuing into the evening hours. Weak low moves into TN and Eastern KY. We get the dry slot though after 1 or 2am thru about 7am Friday. Light snow returns on the backside and ends sometime Fri afternoon. the models stops Friday at 1pm with a touch more snow yet to come. QPF is in that 0.30 to 0.40" range depending on your location.

Good morning and waiting on the movers this morning. The models just need to find out if we get two smaller systems to come through or like the CMC a phase between the two closer to us and a decent. snow. Though rates may be lower and probably in the 12-1 range every flake will stick as the ground temp is well below 32. At least we have a system or systems to follow. Next week the warming takes place and still worried about a frz/rain event as models almost never get this correct when you have a cold snap followed by a big warm up. Sure the return flow will be strong but again with temps most likely below zero this weekend and snow on the ground in many places including south of us much of the warming is melting the snow. Yes the frz/rain will switch over to plain rain at sometime but models will be late to the party on this item.

Latest thinking from the boys on this event - Seems to fit our narrative on this forum.

At some point on Thursday morning, precipitation will begin to
develop in advance of another shortwave moving into the area from
west to east. The initial forcing early Thursday may actually be
more the result of some right entrance region jet energy, but a
second round of forcing will arrive later Thursday into Friday, more
closely associated with the incoming 500mb shortwave. Finally,
additional forcing will arrive Friday morning, as another shortwave
rotates southeast out of the upper Midwest through the region. All
in all, there appear to be three separate sources of forcing, all of
which will produce snow across the ILN forecast area through a 36
hour period -- focused at different times and in different
locations. The generally cold temperatures will support snow ratios
well greater than 10-1 (15-1 appears likely, or even 20-1 late in
the event). Thus, even modest QPF amounts could produce greater than
an inch of accumulation. Overall, the ensemble probabilities seem to
suggest a widespread 1-3 inches of snow through the duration of the
Thursday-Friday time frame, but with low confidence in specific
locations of the higher amounts. Cannot totally discount the
probability of this being a 2-4 inch type of event, given the high
ratios, and the potential for multiple rounds of snow in any given
location. For now, will continue to mention accumulating snow in
the HWO, as this is still out on Day 3/4 of the forecast.

Cold northwesterly flow will bring some additional light snow or
snow showers to the area Through Saturday, before high pressure
builds back into the region.

tpweather wrote: ↑Tue Jan 16, 2024 6:17 am Good morning and waiting on the movers this morning. The models just need to find out if we get two smaller systems to come through or like the CMC a phase between the two closer to us and a decent. snow. Though rates may be lower and probably in the 12-1 range every flake will stick as the ground temp is well below 32. At least we have a system or systems to follow. Next week the warming takes place and still worried about a frz/rain event as models almost never get this correct when you have a cold snap followed by a big warm up. Sure the return flow will be strong but again with temps most likely below zero this weekend and snow on the ground in many places including south of us much of the warming is melting the snow. Yes the frz/rain will switch over to plain rain at sometime but models will be late to the party on this item.

Good morning Tim! I'm sure you'll be glad when the move is done so you will have more time to hopefully enjoy this upcoming event!

NBM. Probably a safe route for now.
The 06z NAM concerns me a bit so I would like to see if the 12z continues or shakes it. Biggest area of uncertainty in my forecast is the tri-state area and points west unfortunately lol. Higher confidence north and east.

I like what Tim mentioned. Do we see any interaction between the two waves or are they going to remain separate? That will be the difference between a little bit of snow or something more meaningful. Then, I also like Trev's point about a possible dry slot which some guidance is showing. Lots to iron out in the next couple of days.

tron777 wrote: ↑Tue Jan 16, 2024 6:34 am I like what Tim mentioned. Do we see any interaction between the two waves or are they going to remain separate? That will be the difference between a little bit of snow or something more meaningful. Then, I also like Trev's point about a possible dry slot which some guidance is showing. Lots to iron out in the next couple of days.

I’ll add another one: they interact but too late for us. I.e. the 06z NAM.

Trevor wrote: ↑Tue Jan 16, 2024 6:36 am

tron777 wrote: ↑Tue Jan 16, 2024 6:34 am I like what Tim mentioned. Do we see any interaction between the two waves or are they going to remain separate? That will be the difference between a little bit of snow or something more meaningful. Then, I also like Trev's point about a possible dry slot which some guidance is showing. Lots to iron out in the next couple of days.

I’ll add another one: they interact but too late for us. I.e. the 06z NAM.

Yes! That is also a risk. Need more coffee as I'm not fully awake yet.

tron777 wrote: ↑Tue Jan 16, 2024 6:40 am

Trevor wrote: ↑Tue Jan 16, 2024 6:36 am

tron777 wrote: ↑Tue Jan 16, 2024 6:34 am I like what Tim mentioned. Do we see any interaction between the two waves or are they going to remain separate? That will be the difference between a little bit of snow or something more meaningful. Then, I also like Trev's point about a possible dry slot which some guidance is showing. Lots to iron out in the next couple of days.

I’ll add another one: they interact but too late for us. I.e. the 06z NAM.

Yes! That is also a risk. Need more coffee as I'm not fully awake yet.

Les that is my concern that yes they get together but just a hair to late for us to get a snowfall bigger than 3 inches. This early in the game its still on but again we need the correct timing. Though temps will head towards the upper 20's on Thursday the ratio should still be decent enough and even .20 can give us 2-3 inches.

Tim... I still like the original prelim call of 1-3". I think Trev also mentioned the same thing. Even ILN's AFD I posted agrees. The potential for a 2-4" event is there also. We wait and see.

Nothings been resolved just yet from the 3 scenario deal mentioned the other day.

I think a 1-3” call is a great call for now. Hopefully by 12z runs today the models will agree more to a scenario. I think 1-3 is a solid call with a despot for a while.

Bgoney wrote: ↑Tue Jan 16, 2024 7:12 am Nothings been resolved just yet from the 3 scenario deal mentioned the other day.

Agreed... all options are still on the table. Hopefully, we will see some clarity with the 12Z suite today. Although it may take a couple more runs to fully resolve things. I think we have a full 24 hours plus until the energy gets onshore from the Pacific.

Nothing set in stone and the Euro has been terrible and this last system the model still has not found the storm that blasted the Tn Valley and lower Ohio Valley. That model in the winter tends to do better with stronger systems but get a front stalled it has major problems. The gfs was not much better though it finally found the system late in the game.

I'm not liking the 12Z NAM. All of the frontogenic snow for Thurs is north of our coverage area and then, the second piece is mainly for folks north of the river. A complete shut out for us south of the river.

NAM and EU are hunting the same scent only NAM is more moisture starved

If these 500v northern waves don’t consolidate and stay in spaghetti form , they will be moisture starved

Bgoney wrote: ↑Tue Jan 16, 2024 9:53 am If these 500v northern waves don’t consolidate and stay in spaghetti form , they will be moisture starved

Agreed. 12Z RGEM does show some consolidation and most folks get a nice snowfall out of the deal with 0.30" or so of QPF for the region. So that is the difference to your point 100%.