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Wintry 2/11-2/12 ULL Magic or More Cold Rain

Review of the Feb26,-27 2004 Macdaddy ULL:

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NCSNOW said:
Review of the Feb26,-27 2004 Macdaddy ULL:

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ra.6909.gif
Click to expand...

The big difference between this event and Feb 26-27 2004 is the Feb 2004 had a nice 50-50 low south of Atlantic Canada to keep some feed of cold air going into the cut-off upper low. There's a ridge in its place this time, which means there is going to be even less cold air to work with here. Not a good sign for big snow outside the mountains.

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Nomanslandva said:
NWS RKE not biting yet.

.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 220 AM EST Wednesday...

Drier and warmer for early next week...

On Sunday the closed low moving across the Deep South will skirt
our area to the south and move offshore Monday. This system
presents the best chance for precipitation over the next 7 days,
although most of the rain will mainly be over NC and eastern
VA.
Click to expand...
I really don't understand KBCB sometimes. I can understand not mentioning snow at this time. But they are even pessimistic about precipitation period.
 
Webberweather53 said:
No. All of that cooling is being driven by lift + dynamical cooling aloft from heavy precipitation. There's no legitimate cold air anywhere in sight for this upper low to tap into.
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There is colder/drier air to the north with the push from new england. 35 knot jet at 925mb is helping to cool the piedmont. It's the only reason they're getting snow on the GFS... if you can't see that, then I dunno what to tell you. We can argue how "legitimate cold" it is I guess. But it's clearly colder than locations west of the apps.
 
Webberweather53 said:
Despite all the pretty 10:1 SLR maps from the GFS suite, I'm still having a hard time seeing how this works out in a big way for areas outside the mountains. I still can see some snow for sure, but I think it's going to be a very sloppy, low-end event in the best case scenario here.

I can't find any really good examples where an upper low totally cut off from the mean flow like this & crushed the piedmont + coastal plain. Cut off upper lows are fine but you usually still need at least a little injection of cold air continuing to funnel into the ULL.

This is a composite of 15 upper low cases I could find since the 1950s that actually worked out for folks east of the mountains. Notice the ridge anomaly to the west of the cut-off over the Upper Midwest & southern Canada helping to keep some injection cold air going into the base of this cut-off upper low.
View attachment 132471



Notice in our setup however, the ridge completely comes over the top and basically shuts off the tap of cold air from the north & you're having to rely entirely on precipitation rates to cool the column to freezing. If you're hoping for a big snow outside the mountains, this pattern isn't a good one for setups like these.


View attachment 132470
Click to expand...

Just to reinforce what I was talking about w/ the upper low composite in this previous post. You can see the high to the NW of the cut-off upper low over Minnesota & Manitoba feeding continental polar air into the base of the upper low. Yes, the upper low is also making its cold air, but it's not completely cut off from a cold air source & has a way to advect more in as heavy precipitation is ongoing. This weekend's setup doesn't have this tap of cold available to it, it's going to be that much more marginal for folks outside the mountains.



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rburrel2 said:
There is colder/drier air to the north with the push from new england. 35 knot jet at 925mb is helping to cool the piedmont. It's the only reason they're getting snow on the GFS... if you can't see that, then I dunno what to tell you.
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That cold air over New England is not getting advected into the upper low. This cold air is leftovers from the midwest & OH valley.
 
Webberweather53 said:
That cold air over New England is not getting advected into the upper low. This cold air is leftovers from the midwest & OH valley.
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I'd disagree because every push south with the confluence over new england has lead to a shift south in temperature isotherms for the northern piedmont of NC. All of that helps even at mid levels.. colder 850's are good.

Nobody is going to argue with you that this isn't a marginal setup with no decent cold air source. But it's the best opportunity we've had all year... we'll track and hope for the best. Mountains seem like a lock for a solid hit either way.
 
rburrel2 said:
I'd disagree because every push south with the confluence over new england has lead to a shift south in temperature isotherms for the northern piedmont of NC. All of that helps even at mid levels.. colder 850's are good.

Nobody is going to argue with you that this isn't a marginal setup with no decent cold air source. But it's the best opportunity we've had all year... we'll track and hope for the best. Mountains seem like a lock for a solid hit either way.
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You can disagree with me all you want, but the facts are this air mass is not coming from New England, as the backward HYSPLIT trajectories from the GFS show.

It's stale, leftover table scraps from the midwest.

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Webberweather53 said:
Despite all the pretty 10:1 SLR maps from the GFS suite, I'm still having a hard time seeing how this works out in a big way for areas outside the mountains. I still can see some snow for sure, but I think it's going to be a very sloppy, low-end event in the best case scenario here.

I can't find any really good examples where an upper low totally cut off from the mean flow like this & crushed the piedmont + coastal plain. Cut off upper lows are fine but you usually still need at least a little injection of cold air continuing to funnel into the ULL.

This is a composite of 15 upper low cases I could find since the 1950s that actually worked out for folks east of the mountains. Notice the ridge anomaly to the west of the cut-off over the Upper Midwest & southern Canada helping to keep some injection cold air going into the base of this cut-off upper low.
View attachment 132471



Notice in our setup however, the ridge completely comes over the top and basically shuts off the tap of cold air from the north & you're having to rely entirely on precipitation rates to cool the column to freezing. If you're hoping for a big snow outside the mountains, this pattern isn't a good one for setups like these.


View attachment 132470
Click to expand...
Spot on and that's what worry's me webb is where having to rely on surface temps to cool enough during precip to either make it or break it. Someone is going to get plastered while a few miles down the road it's a cold rain. I'd only be confident at this point if I was above 2500".
 
Nomanslandva said:
NWS RKE not biting yet.

.LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 220 AM EST Wednesday...

Drier and warmer for early next week...

On Sunday the closed low moving across the Deep South will skirt
our area to the south and move offshore Monday. This system
presents the best chance for precipitation over the next 7 days,
although most of the rain will mainly be over NC and eastern
VA.
Click to expand...
They are always wait until last second campers, I remember one system we had that I myself thought we would get 2-4 inches and they had a trace for us. Then I was right and they were late to put out an advisory.
 
Webberweather53 said:
No one is derailing this discussion.
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Actually as the argument between two posters continues, it does derail the discussion... sometimes it best to make a point then move on from it. It isn't a competition in here.
 
The 925mb jet can crush the hopes and dreams of Oconee and Pickens county as seen here with that God awful snow hole. I've seen it happen before, but it's not set in stone yet. We need a further west track to avoid getting the turn towards NNE winds at this level. Not only does it cut off the Cold air feed from the Northeast, but as the winds turn more northerly we start downslope warming.

A track more like the ICON keeps that from happening until after the precip pulls out though.
Screen Shot 2023-02-08 at 8.08.06 AM.pngScreen Shot 2023-02-08 at 8.08.31 AM.png
 
metwannabe said:
Actually as the argument between two posters continues, it does derail the discussion... sometimes it best to make a point then move on from it. It isn't a competition in here.
Click to expand...

The argument is about this setup and where the cold air is actually coming from, but yea I guess that's somehow off topic for this thread.
 
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