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February 8-12 model Discussion II


Isopycnic

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The thing that makes me uneasy is that the 12z Euro was slightly further north than 00z. The JMA has come in significantly further north (and despite what others think... it generally has better record than the gfs in the medium range). An encouraging sign is that the UKMET actually went south. Normally if both the ECWMF and UKMET are on board with a trend, its worth paying attention to. However, to see the guidance diverge like this, its really hard to get a definitive trend right now. Its going to take many many more runs to resolve whats going on currently. This thing could easily still trend north of the Carolinas (I think a Lakes Cutter however is unlikely by this point).

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Approximations From ECMWF 12z Feb 5 2011:

ATL 1.15"

AHN 1.30"

MAC 1.00"

CHA .75"

MEM .40"

BNA .40"

TYS .55"

TRI .70"

HSV .45"

LIT .65"

GSP 1.25"

CLT 1.30"

CAE 1.30"

HKY 1.15"

AVL 1.10"

GSO 1.15"

RDU 1.35"

FAY 1.50"

CHS 1.25"

ILM 1.50"

RIC 1.55"

JAN .95"

DCA .90"

Foothills, you sure on MEM? Looks much higher per on Acccu Pro euro output..close to .80.

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Foothills, you sure on MEM? Looks much higher per on Acccu Pro euro output..close to .80.

.79 for Memphis

In all my approximations, I took away the qpf from the Sun through Tuesday period, so as to give everybody the chance to see what the next storm alone drops, and I stand by my approximations.

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Just saw the thickness maps for the euro for 500-1000mb. Looks like the area that stays all snow is north of I40 west of I77

Yep, not really a good track for a widespread SE sn-storm, many areas would changeover to IP or RN verbatim. 850 low forms near Jackson MS at 120hrs, then tracks to Montgomery AL, before cutting towards the upstate of SC and offshore near Elizabeth City at 138hrs.

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Eeek...I'm scared we see a Jan 10-type gradient with a sharp cutoff right around ATL.

I would not be worried about soundings or p-type at this stage.....Just worry about the position and strength of the players. The rest will be a product of how these players interact. This storm has a lot of potential folks but I am sure that this will not be the solution that verifies. However it could be close.

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The euro slp track over the southern deep south, verbatim, doesn't favor an all snow scenario in NC. Would probably be a lot of sleet or grauple over central and southern portions. Obviously it could change, but the warm nose in situations like this can sometimes be very high up in the atmosphere, in the 700-600MB range. Just enough warmth to change you over to sleet/grauple.

I have access to the 850mb heights... and it looks like the 850mb low center passes over Upstate SC, and goes right over Raleigh, NC. Thus folks to the north of the low should be mainly snow. Of course its really not smart to focus on particulars, since it will likely change quite a bit five days out.

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I have access to the 850mb heights... and it looks like the 850mb low center passes over Upstate SC, and goes right over Raleigh, NC. Thus folks to the north of the low should be mainly snow.

While I know that being north of the 850 low is a good thing, I never figured out how far N of it you need to be to have mainly snow. Any thoughts on that? Thanks!

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GSP:

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...

-- Changed Discussion --AS OF 230 PM SAT...THE SYSTEM EXPECTED TO ARRIVE NEXT WED NIGHT

THROUGH THU STILL BEARS CLOSE WATCHING FOR WINTER STORM POTENTIAL.

THIS SYSTEM WILL START AS A POSITIVE TILT SRN STREAM TROUGH

DEVELOPING ACROSS THE FOUR CORNERS AREA TUE NIGHT...MOVING EWD

ACROSS THE SRN PLAINS ON WED. AT THE SFC...SPRAWLING HIGH PRES

STRETCHING FROM THE CENTRAL PLAINS TO THE CAROLINAS WILL PROMOTE

THICKNESS FALLS AND THE INTRUSION OF DRIER AIR FROM THE NORTH ACROSS

THE FORECAST AREA WED. THE ECM REMAINS A GOOD COMPROMISE ON TIMING

OF THE UPPER SYSTEM BETWEEN THE FASTER GFS/GEFS AND THE SLOWER GEM.

WILL THUS GENERALLY FOLLOW ECM TIMING AND PLACEMENT OF THE

ASSOCIATED SFC FEATURES. A WRN GULF COAST SFC REFLECTION SHOULD

DEVELOP LATE WED AHEAD OF THE UPPER WAVE AND TRANSITION QUICKLY TO A

SOUTHEAST ATLANTIC COAST DEEPENING LOW CENTER BY THU MORNING. THERE

IS FAIRLY GOOD CONSENSUS THAT A ROUND OF UPPER DIVERGENCE...DEEP

LAYER QG FORCING...AND LOWER LEVEL ISENTROPIC LIFT WILL ALLOW

PRECIPITATION TO BREAK OUT WED NIGHT...WITH DEFORMATION ZONE FORCING

ACROSS THE REGION INTO THU. THE TIMING IS THUS A BIT MORE CERTAIN

FOR PRECIP IN THE WED NIGHT/THU PERIOD AND POPS WILL BE INCREASED TO

NEAR 50 PERCENT MOST AREAS BY LATE WED NIGHT. THE COLDER PROFILES

PUSHING PTYPE MORE TOWARD SNOW OR SLEET VERSUS RAIN ALSO LOOK TO BE

A BETTER BET GIVEN THE SETUP ON WED. THE BIGGEST QUESTION MARK AT

THIS POINT IS THE POTENTIAL FOR GULF COAST CONVECTION TO INHIBIT

MOISTURE TRANPORT INTO THE REGION AHEAD OF THE WAVE. WE WILL HAVE TO

ENTERTAIN THE IDEA OF OUTLOOKING A WINTER STORM FOR WED NIGHT/THU IN

THE HWO IN THE NEAR FUTURE.

AS THE SYSTEM DEPARTS...BRIEF NW FLOW MOISTURE MAY LINGER ACROSS THE

NRN MTNS THU NIGHT. A REINFORCING SHORTWAVE WILL MAINTAIN THE ERN

TROUGH FRI THROUGH SAT. DRY W TO NW FLOW ALOFT SHOULD DOMINATE THE

PERIOD...WITH SFC HIGH PRESSURE ACROSS THE DEEP SOUTH. TEMPS WILL

REMAIN WELL ON THE COLD SIDE OF CLIMO INTO THE WEEKEND DESPITE THE

BETTER INSOLATION.-- End Changed Discussion --

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Thanks, I'm just going from Accuweather Pro Euro readouts, and that was only for the mid week system, nothing before.

I looked at MEM again and for the first system Sun-Mon they get about .22" and then for the second system (snow) about .60" to .63". So Accu Pro is showing .80" for second system?

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While I know that being north of the 850 low is a good thing, I never figured out how far N of it you need to be to have mainly snow. Any thoughts on that? Thanks!

It varies depending on the storm...typically the stronger a surface low, the closer together the 700mb, 850mb, and surface lows are. During episodes of CAD, you can get a pretty large separation between the 850mb low and the Surface reflection because the upper level are unimpeded by the surface high to the northeast, but the surface cyclone gets stuck, since the colder air near the surface is more dense and prevents the surface low from moving overhead. This case looks more like a hybrid CAD, because the low and the 850mb low are pretty close together. In this case, anybody that is immediately north of the 850mb low will likely stay below freezing throughout the column.

However, the tricky thing to watch is deep layer moisture. In a lot of cases, you might be completely below freezing in a sounding, but the moisture aloft at 700mb and above completely dries out. Not only do you need the atmosphere to be below freezing at all levels, but you also need to have sufficient moisture in the snow growth region (typically above 700mb) in order to allow.snowfall production. Otherwise, you just end up with sleet (if you have moisture above 850mb), or even freezing rain (only strong low level moisture). This is what happened to a lot of folks in last years major winter storm on January 30th, 2009.

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I looked at MEM again and for the first system Sun-Mon they get about .22" and then for the second system (snow) about .60" to .63". So Accu Pro is showing .80" for second system?

I agree with you about 0.60-0.63..still would be a big hit.

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It varies depending on the storm...typically the stronger a surface low, the closer together the 700mb, 850mb, and surface lows are. During episodes of CAD, you can get a pretty large separation between the 850mb low and the Surface reflection because the upper level in unimpeded by the surface high to the northeast, but the surface cyclone gets stuck, since the colder air near the surface is more dense and prevents the surface low from moving overhead. This case looks more like a hybrid CAD, because the low and the 850mb low are pretty close together. In this case, anybody that is immediately north of the 850mb low will likely stay below freezing throughout the column.

However, the tricky thing to watch is deep layer moisture. In a lot of cases, you might be completely below freezing in a sounding, but the moisture aloft at 700mb and above completely dries out. Not only due you need the atmosphere to be below freezing at all levels, but you also need to have sufficient moisture in the snow growth region (typically above 700mb) in order to allow.snowfall production. Otherwise, you just end up with sleet (if you have moisture above 850mb), or even freezing rain (only strong low level moisture). This is what happened to a lot of folks in last years major winter storm on January 30th, 2009.

You are absolutely right.....As a good rule of thumb, you need saturation in a layer that is <-10C in order to get frozen precip......in colder storms this can occur in layers below the 700mb level. However, most of the time, if you lose the saturation in that layer you will get super-cooled water droplets that never re-freeze before hitting the ground (thus freezing drizzle)

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I agree with you about 0.60-0.63..still would be a big hit.

yep, nice swath of snow painted across the mid south. I wouldn't sweat any qpf numbers yet. The good thing to take away from the Euro is it goes from Pos. tilt in western Texas to neutral tilt the rest of the duration through the Southeast, which is just enough to garner good moisture, but not overpowering to turn the snow over to rain or ZR, well in some areas its doing that. Its a trend to watch....a lot of the systems have trended stronger and wetter this season, but that was with cutoff's usually, which this isn't. If the Euro is right with the high damming, then even central GA would probably be in the ice category unless the surface low lifts too far north, say north of Macon. Always a fine line in the South. But just having another chance at any snow after whats already happened is amazing. Crazy Winter for sure.

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