Christmas Storm VI

[crossthread]

We have NOT reached forcasted temps with high clouds coming into from the west on the horizion!...

KILM current afd

they keep "waffleing"

Short term /Saturday through Sunday night/...

as of 2:30 PM Friday...the models have not been kind to US forecasters

today. HPC stated in their model diagnostic discussion (pmdhmd) this

afternoon that the 12z GFS and NAM models had numerous

initialization errors...and the 00z European model (ecmwf) also had difficulty

resolving several disturbances in the flow aloft over southern

Canada. Confidence is much below normal for what is now just a

24-48 hour forecast.

What is known is this: a significant upper low over Texas will move

east along the Gulf Coast Saturday and partially phase with a

disturbance currently dropping south through the western Great

Lakes. (The degree of this phasing is what the models are having

trouble with as it will determine the strength and path the surface

low takes through the broad baroclinic zone offshore) surface low

pressure will develop along the Gulf Coast tonight...will cross

Florida Saturday night...then accelerating up the U.S. East Coast

Sunday while deepening into a major winter storm.

The model consensus over the past couple of days has been for the

surface low to track 75-100 miles southeast of chs...and 175-200

miles east of Cape Fear Sunday morning. A zone of middle-level ascent

preceding the system should develop precipitation across the central

Carolinas on Christmas day. This should bring mainly rain into the

I-95 counties late Christmas day...with precipitation spreading down

to the coast Christmas night. The atmosphere will steadily cool

through the event...with critical temperature/thickness thresholds

for snow likely hit during the evening hours for the Lumberton and

Bennettsville areas. Snow will mix in with rain as far east as White

Lake...Whiteville...Dillon...Marion and Florence after midnight

Christmas night. Accumulating snow Christmas night should be limited

to Bladen...Robeson...Dillon...Marlboro and Darlington counties...

with forecast amounts generally less than 1 inch through daybreak

Sunday.

Sunday morning...precipitation should still be ongoing especially

near the coast while cold air accelerates eastward behind the

surface low wrapping up offshore. Snow accumulations after daybreak

Sunday could reach 1-2 inches in the Cape Fear counties of

southeastern North Carolina including Wilmington. Last night's model

guidance and the new 12z models show more substantial wrap-around

moisture in the 700-925 mb layer persisting through the day

Sunday...indicating a better potential for snow flurries or even

snow showers to persist into the afternoon hours. Despite the

moisture column growing more shallow with time...cold advection is

intense enough to keep the top of the cloud layer at -9c to -12c

which is well-correlated with snow Crystal growth. After

collaboration with the National Weather Service offices in Raleigh and Newport/Morehead

City...no winter storm watches or advisories will be raised just yet

due to low overall confidence.

Residual moisture should exit the coast Sunday night with clearing

skies and very cold air building in on northwest winds. Given the

amount of wind expected...low temperatures will not go as low as the

850 mb temperatures (-9c) might suggest...with lows dipping into the lower

20s in most areas.

current obs:

46.6 °F Clear

Windchill:47 °F

Humidity:46%Dew Point:27 °F

Wind:7.5 mph

Wind Gust:11.2 mph

Pressure:30.13 in (Steady)

[phil882]

I'm liking the way the 18z nam is so far... stronger with the southern stream s/w (which is good as that will provide added vorticity and latent heat from more moisture advection) and the northern stream s/w, or the wave that I alluded too before is stronger at 12 hours.

[burgertime]

@30 our low is much stronger and further north of 12z NAM

[KChuck]

gsp just posted wwa for along i85 corridor

[Supercane]

NAM looks a lot better. Northern stream is digging further SW, and at 30hr there is a 1010mb low south of Mobile with heavier QPF spreading across the SE (compared to last run).

[NEGa]

gsp just posted wwa for along i85 corridor

just saw that.

i wish it were better lol, but at this point i would take an inch (and hope that it gets just a little stronger...adding another inch or two ) also i have just been threatened by my mom and sister that i am NOT to use my iphone at tonight's church service. lol

* * *

URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC

256 PM EST FRI DEC 24 2010

...WINTER WEATHER TO AFFECT PORTIONS OF THE WESTERN CAROLINAS AND

NORTH GEORGIA CHRISTMAS DAY THROUGH MONDAY...

.A DEVELOPING STORM SYSTEM IS EXPECTED TO BRING LIGHT SNOWFALL TO

THE MOUNTAINS AND PORTIONS OF THE PIEDMONT SATURDAY. AFTER AN

ARCTIC COLD FRONT MOVES THROUGH THE REGION LATE SATURDAY...

NORTHWEST WINDS WILL INTERACT WITH MOISTURE OVER THE MOUNTAINS TO

PRODUCE SCATTERED TO NUMEROUS SNOW SHOWERS SATURDAY NIGHT THROUGH

MONDAY. THIS MAY RESULT IN HEAVY SNOWFALL ACCUMULATIONS ACROSS THE

HIGHER MOUNTAINS ALONG THE TENNESSEE BORDER.

GAZ010-017-NCZ068>071-SCZ001>010-251000-

/O.NEW.KGSP.WW.Y.0032.101225T1400Z-101226T0500Z/

RABUN-HABERSHAM-CLEVELAND-LINCOLN-GASTON-MECKLENBURG-

OCONEE MOUNTAINS-PICKENS MOUNTAINS-GREENVILLE MOUNTAINS-

GREATER OCONEE-GREATER PICKENS-GREATER GREENVILLE-SPARTANBURG-

CHEROKEE-YORK-ANDERSON-

INCLUDING THE CITIES OF...CLAYTON...CLARKESVILLE...SHELBY...

LINCOLNTON...GASTONIA...CHARLOTTE...GREENVILLE...SPARTANBURG...

GAFFNEY...ROCK HILL...ANDERSON

256 PM EST FRI DEC 24 2010

...WINTER WEATHER ADVISORY IN EFFECT FROM 9 AM SATURDAY TO

MIDNIGHT EST SATURDAY NIGHT...

THE NATIONAL WEATHER SERVICE IN GREENVILLE-SPARTANBURG HAS ISSUED

A WINTER WEATHER ADVISORY FOR SNOW...WHICH IS IN EFFECT FROM 9 AM

SATURDAY TO MIDNIGHT EST SATURDAY NIGHT.

* LOCATIONS...THE I-85 CORRIDOR IN NORTH AND SOUTH CAROLINA...AS

WELL AS THE GEORGIA AND SOUTH CAROLINA MOUNTAINS.

* HAZARDS...LIGHT SNOW...MIXED WITH OR CHANGING TO RAIN AT TIMES.

* TIMING...MID-MORNING THROUGH CHRISTMAS EVENING.

* ACCUMULATIONS...AROUND 1 INCH.

* IMPACTS...SLICK SPOTS MAY DEVELOP ON ELEVATED SURFACES...SUCH AS

BRIDGES AND OVERPASSES.

* TEMPERATURES...HIGHS IN THE UPPER 30S. LOWS IN THE UPPER 20S.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A WINTER WEATHER ADVISORY MEANS THAT PERIODS OF SNOW...SLEET...OR

FREEZING RAIN MAY CAUSE TRAVEL DIFFICULTIES. BE PREPARED FOR

SLIPPERY ROADS AND LIMITED VISIBILITIES...AND USE CAUTION WHILE

DRIVING.

[strongwxnc]

@24 the NS S/W is further SW and Stronger than the same time as the 12.

West ridge looks sharper also. Almost N to S.

[beanskip]

24 hours -- heavier QPF than 12 z run breaking out from B'ham to Atlanta to Murphy -- this could be good ....

[strongwxnc]

After reading the AFD GSP is playing a good card with the WWA. IMO

just saw that

* * *

URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC

256 PM EST FRI DEC 24 2010

.

[burgertime]

@33 it looks to be sending our low little south and not making the turn

[NEGa]

After reading the AFD GSP is playing a good card with the WWA. IMO

i would agree and am pretty happy. however, the last few times it snowed there were no advisories, and the last few advisories led to little (or no) snow

but an advisory for snow on christmas? never thought i would ever see that, esp in ga

[burgertime]

@36 it looks like it's starting to move due east so it might be making the turn.

[CandymanColumbusGA]

Out of curiosity which products will you blend for your temp forecast? As you say, cloud cover, heavier precip....such difference makers down south. T

Well, from the records I have kept with temperatures and verifying to the NAM/GFS, the GFS actually has the lows better, then I take the average of the GFS/NAM with a little more emphasis on the NAM for highs. I look at the RUC every once in a while. I use the WSI RPM model to help with cloud cover within the next 48 hours, and right now it has the clouds from Auburn to La Grange coming in around 7/8 in the morning. If this verifies, then temperatures will be at their lowest, and it has been my experience that temps won't warm up all that much. Now comes the strength of the rain to get those temps down near freezing at the surface for snow/sleet. Frankly, I feel that from say.... Columbus to Macon (maybe a little south) north to Atlanta could see more sleet than snow, but MAINLY rain, as temps below 850 are freezing, but slightly above freezing at 700.

[strongwxnc]

Yup. Left my county out of the WWA. ? Guess they really think this is an I-85 special.

i would agree and am pretty happy. however, the last few times it snowed there were no advisories, and the last few advisories led to little (or no) snow

but an advisory for snow on christmas? never thought i would ever see that, esp in ga

[phil882]

This run is leaps and bounds better than the 12z run, in fact its more amplified at 500mb than the 12z gfs!

Look at the nice finger of precipitation that starts up right along the I-85 coordoor at 24 hours.

[Gastonwxman]

Someone on here posted another model known as the HRRR from last week. Does anyone here know if that is a good model to use or are there faults with it?

[Itunis]

NAM drops .1"-.25" for the ATL metro between 24-30, with 850s well below freezing. Total QPF over .25"

[burgertime]

@39 it looks like our low has gotten all sheered out. Wetter run then the 12z NAM though.

[Lookout]

18z nam actually changes all the precip over to snow over most of north georgia per soundings. Temps drop to near freezing in places like rome early in the morning, gainesville is near freezing and all snow by noon, and it changes over here shortly there after. This is a much better run temp/snow wise. It goes to show what I mentioned earlier, whereever that band of precip sets up, temps will cool enough for all snow.

Makes you wonder if this trend will continue

[NEGa]

This run is leaps and bounds better than the 12z run, in fact its more amplified at 500mb than the 12z gfs!

Look at the nice finger of precipitation that starts up right along the I-85 coordoor at 24 hours.

and a very nice strip of 1" snow across much of n ga

[phil882]

This is a great run for the I-85 coordoor and points west. This run allows enough amplification to allow the northern stream s/w to dig in and tap into the moisture from the southern stream s/w and produce a significant band of moderate snowfall. Keep in mind that this is total precip though 36 hours, so heavier amounts will occur near the coasts as the coastal band merges with the coastal low precip shield.

[beanskip]

Would love some met interpretation comparing the 12z GFS 5h maps to the 18z NAM. From this chair they look pretty similar -- NAM even looks sharper with digging -- main differences I see is NAM has the southern disturbance a touch farther south and the northern stream much stronger.

[georgiawx11]

FFC is now saying rain/snow mix will change to rain Saturday afternoon, whereas earlier they were saying it would change to snow Saturday afternoon.

[Itunis]

NWS Huntsville has just put the NErnmost two counties of AL under a WWA. I expect FFC to at least put the top tier of counties under one, as moisture is more plentiful over the N GA mtns.

Advisories now out north of Rome-Gainesville

[strongwxnc]

Give this a read.

The Southern SW might fail us but as Phil pointed out.

@39 it looks like our low has gotten all sheered out. Wetter run then the 12z NAM though.

[WidreMann]

Guys, don't forget that the 18z NAM is using 12z GFS bogus data. So it might be suspect. As will also the 18z GFS.

[Brian]

FFC is now saying rain/snow mix will change to rain Saturday afternoon, whereas earlier they were saying it would change to snow Saturday afternoon.

Oh how typical of them, and yesterday they said 2-4 inches......

[packbacker]

I thought the 18z NAM was based off the 12z GFS somehow?

[georgiawx11]

Advisories now out north of Rome-Gainesville

North of Cedartown-Gainesville.

[FoothillsNC]

ha ha I love it. The southern stream once again holds on a longer period, now all the way to Fl. Panhandle before the model goes *poof* with it. Also, good backing in easern Ala, and Ga, with a good snow axis that probaly stays put from eastern Alabama across most of N Ga (down to ATL but not sure on temps) and across the western Carolinas. From this point, we 've got good backside digging, probably even better lookng than before , so I'm still thinking the models are UNDERFORECASTING the surface low and the moisture expansion across most of eastern Al, most of GA as well as most of the Carolinas. Nothings really changed in my mind. The door is very much open to phasing and the surface low in the gulf getting pulled northeast across Fl. panhandle. So, who knows how the precip shield will end up looking, but I think if your in GA near the 20/85 and western Carolinas teh precip should arrive. Cant say how heavy yet.