NC/VA Sunday Snow Threat

[weatherheels]

Looks like todays 12z run of the GFS pretty much says this clipper will be moisture starved, which is usually what happens. I find the NAM hard to believe, I think it's over doing the amount of moisture this system will have after crossing the Apps. These usually dont work out well for us east of the Mountains, unless you're far enough east for some throw back moisture. Either way, we've got something to watch and talk about for a bit.

[Lee]

Still looking good up this way from the clipper as well as upslope

[Brick Tamland]

Well, it would be our luck not to even see some snow Saturday night/Sunday.

[WeatherNC]

Looks like todays 12z run of the GFS pretty much says this clipper will be moisture starved, which is usually what happens. I find the NAM hard to believe, I think it's over doing the amount of moisture this system will have after crossing the Apps. These usually dont work out well for us east of the Mountains, unless you're far enough east for some throw back moisture. Either way, we've got something to watch and talk about for a bit.

yeah, that is what I am leaning towards. Anyone remember the clipper we had last winter, or it might have been 2 winters ago, not sure... Models were painting a general tenth of an inch east of the mountains leading up to the event, and we ended up with just passing clouds. That gives a general idea as to what we could be getting, saving grace I guess is that the piece is not onshore yet in the Pac NW, and won't be for another 12-18 hours, so sampling won't be thorough until the 12z runs tomorrow. Also was some missing RAOB data in the 12z runs today, most notably for NC was MHX's short report to 526mb...

SENIOR DUTY METEOROLOGIST NWS ADMINISTRATIVE MESSAGE

NWS NCEP CENTRAL OPERATIONS CAMP SPRINGS MD

1443Z THU DEC 02 2010

THE NCEP 12Z MODEL CYCLE IS RUNNING SMOOTHLY AND IS ON

TIME.

12Z RAOB RECAP...

BRW/70026 - PURGED ALL TEMPS/HGTS 925MB AND ABV...TEMPS

UP TO 10C COLD/HGTS OVR 100M LO.

ASY/70414 - 10145. UNFAVORABLE WEATHER.

MHX/72305 - SHORT REPORT TO 526MB.

BOI/72681 - PURGED TEMPS/Q 599-549MB...WET BULB EFFECT.

CAR/72712 - PURGED TEMPS/Q 850-844MB...WET BULB EFFECT.

GYX/74389 - PURGED TEMPS/Q 863-849MB...WET BULB EFFECT.

GUM/91212 - 10142. GROUND EQ FAILURE.

ROR/91408 - NO 12Z REPORT.

$$

WOOLDRIDGE/SDM/NCO/NCEP

[Lee]

Looks like todays 12z run of the GFS pretty much says this clipper will be moisture starved, which is usually what happens. I find the NAM hard to believe, I think it's over doing the amount of moisture this system will have after crossing the Apps. These usually dont work out well for us east of the Mountains, unless you're far enough east for some throw back moisture. Either way, we've got something to watch and talk about for a bit.

The NAM is known for a wet bias. The GFS on the other hand since a tweak to scale back awhile back, actually has a dry bias, especially on this side of the APPS. This bias shows big time with NW flow events and upslope ..

Take this last rain event for instance. The GFS had us getting a storm total of 1.25 to 1.50" of rain. We received 2.50- better than 3 inches in spots!

[Lee]

yeah, that is what I am leaning towards. Anyone remember the clipper we had last winter, or it might have been 2 winters ago, not sure... Models were painting a general tenth of an inch east of the mountains leading up to the event, and we ended up with just passing clouds. That gives a general idea as to what we could be getting, saving grace I guess is that the piece is not onshore yet in the Pac NW, and won't be for another 12-18 hours, so sampling won't be thorough until the 12z runs tomorrow. Also was some missing RAOB data in the 12z runs today, most notably for NC was MHX's short report to 526mb...

Now, that close up precip snapshot clearly shows one of the GFS's QPF output flaw. That heavier band(>.25) stretching down to NE TN should be along the upslope area along the KY/VA and NC/TN border area's. It has it pretty much between the 2.

BTW, does anyone know if that precip back in south central KY is reaching the ground? if so, look where the 12Z had it when initialized.

[WeatherNC]

12z Canadian looks like the GFS, trace amounts of QPF east of the mountains

[WeatherNC]

If it is any very small token, the majority of the 12z gfs ens members, on Allan's site, are wetter than the op through central and eastern NC, not much, but at-least it is something to grasp at. All but a few would indicate >0.10"

http://raleighwx.americanwx.com/models/gfsensemble/members/12zf060.html

And just to add, and ask... What makes this a clipper? My understanding was that clippers come from Canada, i.e. Manitoba Mauler, Saskatchewan Screamer, Alberta Clipper, etc... This package is originating from the Pac and entering NA in Northern California, it does not even really touch Canada, except for maybe some interaction with energy up there near Montana. How does this fit the meteorological definition, or is simply a parallel being drawn to the general definition of a fast moving ship?

[eyewall]

If it is any very small token, the majority of the 12z gfs ens members, on Allan's site, are wetter than the op through central and eastern NC, not much, but at-least it is something to grasp at. All but a few would indicate >0.10"

http://raleighwx.ame...rs/12zf060.html

And just to add, and ask... What makes this a clipper? My understanding was that clippers come from Canada, i.e. Manitoba Mauler, Saskatchewan Screamer, Alberta Clipper, etc... This package is originating from the Pac and entering NA in Northern California, it does not even really touch Canada, except for maybe some interaction with energy up there near Montana. How does this fit the meteorological definition, or is simply a parallel being drawn to the general definition of a fast moving ship?

It is not really a true clipper due to its origin but the parallel would make sense. It will be moving quickly like a clipper with limited moisture and approaching us from a similar direction. Either way they never usually work out well for NC unless you are near the coast and there is redevelopment offshore. We can often get screwed too if a lee side trough or meso low forms and warms things up. See last year's "fizzled flizzard" the nearly resulted in some weenie suicides.

[WeatherNC]

It is not really a true clipper due to its origin but the parallel would make sense. It will be moving quickly like a clipper with limited moisture and approaching us from a similar direction. Either way they never usually work out well for NC unless you are near the coast and there is redevelopment offshore. We can often get screwed too if a lee side trough or meso low forms and warms things up. See last year's "fizzled flizzard" the nearly resulted in some weenie suicides.

That is the one I was thinking of when I stated earlier about a clipper that screwed us recently, thought is was last year but was not sure. Went back and looked at some archived model data and most were painting marginal thermal profiles and decent QPF. Checked the RAH map and only a couple places in the center of the state, outside of the mountains, saw any frozen, and it was less than 1". That system however, had some southern stream energy to work with, which strengthened the coastal, but was a predominant RN event and confirmed suicide warning...

[eyewall]

That is the one I was thinking of when I stated earlier about a clipper that screwed us recently, thought is was last year but was not sure. Went back and looked at some archived model data and most were painting marginal thermal profiles and decent QPF. Checked the RAH map and only a couple places in the center of the state, outside of the mountains, saw any frozen, and it was less than 1". That system however, had some southern stream energy to work with, which strengthened the coastal, but was a predominant RN event and confirmed suicide warning...

That would be the one! I wish it could be erased from my memory, but I also wish I was in the Buffalo, NY Southtowns right now.

[BullCityWx]

For what it's worth, the euro snowfall total map doesnt show any accumulations outside of the mountains of VA/NC and the very, very NW tip of SC.

[griteater]

The models are looking interesting with this clipper system no doubt, but these types of system climatologically rarely bring significant snows east of the mountains. I can only 1-2 instances where they have surprised me and hit Raleigh with 1-3" but usually this was deeper into the winter with colder ground and surface temperatures where snowfall was maximized very high snow to liquid ratios.

Yeah, significant clipper events are rare, but they can produce if the upper wave diving down is strong and you are just north of the vort max. Also, it helps to have upper support from a jet streak.

Here are a few good ones I recall from past years:

Feb 5-6, 1984

http://www.meteo.psu...1984/us0206.php

Jan 23, 2003

http://www.meteo.psu...2003/us0123.php

Jan 20, 2009

http://www.meteo.psu...2009/us0120.php

[Cyclonicjunkie]

See last year's "fizzled flizzard" the nearly resulted in some weenie suicides.

LMAO

[strongwxnc]

I the three years I lived in Boone, this was the only time that a snow storm gave more to my mothers home in Rutherford County then to me in Watauga County.

Yeah, significant clipper events are rare, but they can produce if the upper wave diving down is strong and you are just north of the vort max. Also, it helps to have upper support from a jet streak.

Here are a few good ones I recall from past years:

Jan 23, 2003

http://www.meteo.psu...2003/us0123.php

[WeatherNC]

For what it is worth, 18z NAM still persistent in painting a wide swath of >0.25" QPF through portions of NC, axis has shifted slightly north of the 12z run, and is warmer, which is to be expected given the shift. Still looking like someone outside of the mountains will see a couple dendrites, just figuring out where and the miniscule amount is the hard part right now. Will update this post once the station totals are available on Allan's site. Thickness is solidly in the wintery weather zone here, not far from all SN on this run. Soundings, even though I have not checked, would likely show the surface and first 50mb, slightly above, which could be overcome as long as there is sufficient saturation in the column above, isothermal ftw!

[griteater]

And then there was one in Dec 2000 where we were under a Winter Storm Warning and didn't receive a flake.

http://www.meteo.psu.edu/~gadomski/NARR/2000/us1203.php

[WeatherNC]

Sounding for KPGV from the 18z NAM at 60hrs, dendritic growth zone around 14k ft (sounding is in meters) is very close to saturated, and temps are around -14C... Obviously would like that to look a little better in regards to moisture aloft, but that this is still a frozen precip sounding at the surface.

[BullCityWx]

NCZ070-030900-
GASTON-
INCLUDING THE CITIES OF...GASTONIA
417 PM EST THU DEC 2 2010

DATE           12/02/10      FRI 12/03/10            SAT 12/04/10            SUN
EST 3HRLY     16 19 22 01 04 07 10 13 16 19 22 01 04 07 10 13 16 19 22 01 04 07
UTC 3HRLY     21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12

MIN/MAX                      28          53    28 29 31          49          33
TEMP             41 36 33 30 29 43 51 52 42 37 34 31 30 39 46 47 42 38 36 34 33
DEWPT            22 22 21 21 21 23 23 23 26 27 25 25 25 27 28 30 33 34 32 31 28
RH               46 56 61 69 72 45 33 32 53 67 69 78 81 62 49 51 70 85 85 89 82
WIND DIR         SW NW NW  N NW  N  W  W SW  N NE NE NE  E  S  S SW NW  N  N  N
WIND SPD          2  4  3  2  2  3  4  5  1  2  2  1  2  2  3  3  1  2  4  2  2
CLOUDS           B2 B2 FW FW SC FW FW FW SC SC B1 B2 OV B2 B2 OV OV OV B2 CL CL
POP 12HR                      5           5           5          30          30
QPF 12HR                      0           0           0        0.02        0.03
RAIN SHWRS                                                  S  C  C  C  S      
SNOWSHWRS                                                               S      
WIND CHILL             29                                              32      
MIN CHILL              28    26    31          29    26    29          31    28

[BullCityWx]

And then there was one in Dec 2000 where we were under a Winter Storm Warning and didn't receive a flake.

http://www.meteo.psu...2000/us1203.php

Man, that one still stings.

[rduwx]

Man, that one still stings.

It does! The numbers that were being thrown out and to end up w/ just flurries was hard to swallow.

[eyewall]

RAH Disco:

THIS EVENING AND TONIGHT:

BROAD NWLY CYCLONIC FLOW ALOFT UNDERNEATH THE EASTERN US TROUGH

WILL STEER SHORTWAVE ENERGY OVER THE CENTRAL MS VALLEY ACROSS THE

SOUTHERN APPALACHIANS AND OVER THE SAVANNAH RIVER VALLEY AND

CAROLINAS TONIGHT. CIRRUS WILL CONTINUE TO THICKEN WITH THE APPROACH

OF THE UPPER DISTURBANCE...RESULTING IN MOSTLY CLOUDY SKIES BY THE

EVENING. A QUICK SHOT OF DECENT DPVA WILL STREAK ACROSS THE AREA

OVERNIGHT. FCST SOUNDINGS SHOW A 3-HR WINDOW OF SATURATION AND LIFT

IN THE DENDRITIC GROWTH ZONE BETWEEN 00-06Z ACROSS THE NORTHERN HALF

OF THE FORECAST AREA WITH CLOUD BASES 5-7 KFT RANGE. SHOULD

DEFINITELY SEE SOME VIRGA AS THE FROZEN METEORS FALL AND EVAPORATE

THROUGH THE VERY DRY SUB-CLOUD LAYER FEATURING SFC DEWPOINTS IN THE

TEENS. CAN NOT ENTIRELY RULE OUT A FEW FLURRIES REACHING THE GROUND

AS WELL. ASSOCIATED CLOUD COVER WILL PROVIDE SOME INSOLATION...SO

NOT AS COLD AS LAST NIGHT. OVERNIGHT LOWS IN THE UPPER 20S TO LOWER

30S.

FRIDAY AND FRIDAY NIGHT:

EXPECT MINOR SYNOPTIC SCALE HEIGHT RISES WITH SUBSIDENCE IN THE WAKE

OF THE SHORTWAVE DISTURBANCE FRIDAY MORNING. LOW LEVEL THICKNESSES

ARE PROGGED TO COMPARABLE TO TODAY...BUT ABSENCE OF CIRRUS SHOULD

ALLOW HIGH TEMPERATURES A CATEGORY WARMER ACROSS THE BOARD. HIGHS 47

TO 52.

HIGH LEVEL MOISTURE IN ADVANCE OF THE NEXT NW FLOW ALOFT DISTURBANCE

SHOULD BEGIN TO SPREAD EAST INTO WESTERN...POSSIBLY CENTRAL PORTIONS

OF THE STATE LATE FRIDAY NIGHT/SATURDAY MORNING. LOW TEMPS FRI

NIGHT WILL DEPEND ON THE TIMING AND OPACITY OF THE CIRRUS SHIELD.

MIN TEMPERATURES SHOULD GENERALLY BE IN THE UPPER 20S TO LOWER 30S.-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...

-- Changed Discussion --AS OF 300 PM THURSDAY...

THE NEXT AFOREMENTIONED PACIFIC NORTHWEST SHORTWAVE WILL INITIALLY

DAMPEN OUT OVER THE NORTHERN PLAINS...BUT THEN RE-INTENSIFIES OVER

THE MIDWEST AND OHIO VALLEY ON SATURDAY AND SATURDAY NIGHT AS IT

ADVANCES EAST-SOUTHEAST IN THE FAST NWLY FLOW ALOFT AND AT THE NOSE

OF A 100KT H5 JET. WHILE THERE CONTINUES TO BE SOME MODEL

TIMING/AMPLITUDE DIFFERENCES...OVERALL MODEL CONSENSUS BRINGS THE

BRUNT OF THE DPVA AND LEFT EXIT REGION DIVERGENCE ACROSS THE AREA

SATURDAY NIGHT. DESPITE THE SHORTWAVE VORT BEING

CHANNELED/STRETCHED ...THE VORTLOBE IS STILL RATHER POTENT...WITH

MODELS INDICATING THAT UPPER PV ANOMALY WILL EXTEND DOWN TO 550MB.

MOISTURE THIS TIME AROUND(COMPARED TO TONIGHT NWLY FLOW

DISTURBANCE)IS MUCH DEEPER EXTENDING FROM ROUGHLY 600MB(-18C) TO THE

SURFACE WITH SUFFICIENT SATURATION IN THE DENDRITIC GROWTH ZONE.

CENTRAL NC LOOKS TO LIE JUST ALONG THE LIGHT PRECIP SHIELD AS THE

ATTENDANT WEAK SURFACE LOW PASSES ACROSS THE AREA WITH THE DEEP

DOWNSLOPE COMPONENT DEFINITELY HINDERING QPF AMOUNTS.

WITH SFC TEMPERATURES IN THE MID TO UPPER 30S SATURDAY

EVENING/NIGHT...QPF RATES SHOULD GREATLY DETERMINE THE P-TYPE.

WITH LIGHT QPF AMOUNTS EXPECT...ONLY SEVERAL HUNDREDTHS...THE MAIN

PRECIP TYPE SHOULD BE RAIN...WITH ANY STRONG 35 TO 40 DBZ

SHOWER-HIGHER PRECIP RATE BRINGING A BRIEF BURST OF SNOW OR

FLURRIES. NO IMPACTS ARE EXPECTED FROM THE MIX...ALTHOUGH IT MIGHT

MAKE FOR A PRETTY WINTRY SCENE AS GROUND TEMPS ARE CURRENTLY IN THE

UPPER 40S TO LOWER 50S.-- End Changed Discussion --

[Jon]

WITH ANY STRONG 35 TO 40 DBZ

SHOWER-HIGHER PRECIP RATE BRINGING A BRIEF BURST OF SNOW OR

FLURRIES. NO IMPACTS ARE EXPECTED FROM THE MIX...ALTHOUGH IT MIGHT

MAKE FOR A PRETTY WINTRY SCENE AS GROUND TEMPS ARE CURRENTLY IN THE

UPPER 40S TO LOWER 50S.-- End Changed Discussion --

Like that last bit...looks like dynamic cooling would bring some pretty good snowfall, correct? Even if it is for a split second, if the the liquid precip gets heavy, this could be a good first snow as it could be a little more than microscopic flurries (but of course not amount to too much on the ground). They seem a lot more confident in what this will produce over central/northern NC than they were this morning.

[griteater]

In looking at the 12z NAM and GFS, the one thing that doesn't look right to me is that the models are showing the sfc low moving through SC (NAM) or along the NC/SC border (GFS) while the 500 mb vort max tracks through northern NC. In this type of setup, I would think that the sfc low would be tracking along or just south of the track of the vort max (i.e. through central or northern NC), with the bulk of the precip north of there. From what I've seen over the years with this setup, you do NOT want to be south of the vort max in order to see any noteworthy precip. Also, the colder the environment this wave is dropping down into, the better - for maximizing the precip generation. In this case, the temps are borderline for snow. The model trends going forward regarding the strength and path of the vort max should spell out where any noteable snow occurs.

[WeatherNC]

I made a couple .gif to look at the overall trend in QPF amounts with the American guidance over the past 24hrs... 0z-18z, with a 2s pause at the end

Amounts are meager, but you can see the differences between the two models, best bet would be to halve the NAM totals which would place them inline with the GFS, excluding the 12z run which looks like a hiccup compared to the other 3 for the day. General consensus is for a band of heavier amounts, with the possibility for a few flakes from SW VA to the NC Coastal Plain.

[SBUWX23]

18z NAM BUFR soundings reveal a rain snow mixture at RDU saturday evening. Precip rates would certainly determine PTYPE taken VERBATIM but I am not buying this solution just yet. I feel like the clipper will actually track a bit further north than simulated on the NAM hence warmer air and maybe less precip overall.

[BullCityWx]

18z NAM BUFR soundings reveal a rain snow mixture at RDU saturday evening. Precip rates would certainly determine PTYPE taken VERBATIM but I am not buying this solution just yet. I feel like the clipper will actually track a bit further north than simulated on the NAM hence warmer air and maybe less precip overall.

Couldnt agree more.

[WeatherNC]

18z NAM BUFR soundings reveal a rain snow mixture at RDU saturday evening. Precip rates would certainly determine PTYPE taken VERBATIM but I am not buying this solution just yet. I feel like the clipper will actually track a bit further north than simulated on the NAM hence warmer air and maybe less precip overall.

We have seen it several times, quick hitting disturbances out of the NW flow, trend north in the last 24 hours. Not sure if that will hold true this go round as the 300mb jet streak on both the american models has trended a little stronger, as well in a more favorable orientation for bringing the energy through northern NC. A "bit" meaning southern VA, is very much in the realm of possibility, just as the system going a little farther south is. Best moisture aloft looks to come through here between 0 and 6z Sunday. 18z NAM would be a couple slushy inches verbatim based on thickness and soundings, but the disagreement in QPF totals compared to the other guidance is somewhat concerning. I am not one to throw all in on the NAM, while ignoring everything else. Feel those totals should be halved, to bring them inline with the global models. Short-wave is just coming onshore in the west, so if this time tomorrow after it is thoroughly sampled, models are still painting a general 0.10" then I will hold my breath and be prepared for nothing. If the NAM is still insistent on a quarter inch plus for isolated areas east of the mountains, then it will be interesting to see which amounts verify.

[NCSNOW]

Heres a surface wetbulb map off 12z eta/Nam if anyones interested for Sat. Earls webpage has some pretty good short term modeling links to play around with for free. Maybe Sat will give me chance to try out.

http://www.wxcaster.com/models_main.htm

[SBUWX23]

00z nam is south with its QPF field. Barely trace amounts RDU north. Too inconsistent from run to run. The 500 mb VORT is slower and the shortwave itself is flatter. There also appears to be a PVA min across northern NC and southern VA due a weaker vort across the southern part of the state.