Potential December 12th-13th threat

[BullCityWx]

[YoRyz]

We should reopen the other thread & merge this in!

[BullCityWx]

yeah....about this run.

[SBUWX23]

yeah....about this run.

Fully expected to see something like this.

[BullCityWx]

Fully expected to see something like this.

I'd even be worried about this thing at this point if I lived in Indiana and Ohio.

[NCSNOW]

Fully expected to see something like this.

Train Wreck in the making. Off to bed, maybe 12z or euro can throw some love tomorrow

[SBUWX23]

Hour 162 has severe potential written all over it for the SE

[CAD_Wedge_NC]

Somewhat of a CAD look showing up at 150h...... but it quickly gets scoured out.

[YoRyz]

Ok, we know that last thread was a train wreck. Let's try to keep this one more on topic.

[MotoWeatherman]

This run has flurries written all over it for north GA behind the front.

[TheVille]

This run has flurries written all over it for north GA behind the front.

Me want more than flurries!

[tazaroo]

It looked like the first clipper stayed way North along the border and didn't deliver any cold air to the Southeast at all. I guess this is the result when the Pacific trumps the Atlantic.

[Cyclonicjunkie]

Thats a big dog of a storm on the 0z and I will take it, as a Miller B can be great for my area, but would much rather have the B switched to an A

[weatherfide]

I'll take flurries! It's really all I should look for in this pattern. Looks like after the monster cold trough, the pattern relaxes and we go zonal. Rather mundane, mild after next weekend. Blah.

[Cyclonicjunkie]

Just when I was discounting the HPC for referring to the Great Appalachian Storm of 1950

THIS EXTREME SOLUTION IS SIMILAR TO THE GREAT

STORM OF 25-26 NOV 1950. WHAT IS DISCONCERTING IS THAT CPC D+8 TO

D+11 ANALOGS HAVE INDICATED A SYNOPTIC PATTERN MATCHING THOSE

DATES FOR WEEKS INCLUDING TODAYS. THAT WAS ALSO A LA NINA YEAR

WITH A STRONG NEGATIVE NAO

The GFS goes and creates a simular monster.

[Gastonwxman]

0z Euro Ensemble has our storm somewhat further south but still unfavorable for wintry precipitation. It now cuts through TN and NC.

[DaculaWeather]

Per the latest AFD from Atlanta:

HAVE CONTINUEDSLIGHT CHANCE TO CHANCE POPS SATURDAY AND SUNDAY AS LOW MOVES INTOTHE OHIO RIVER VALLEY BY LATE WEEKEND...PULLING AMPLE GULF MOISTURE INTO THE STATE. STRONG NORTHWEST FLOW IS EXPECTED TO RESUME IMMEDIATELY BEHIND THE FRONTAL BOUNDARY AS IT PUSHES THROUGH THE STATE LATE SUNDAY...WITH SIGNIFICANT DROPS IN 1000 TO 850MB AND 850TO 700 MB THICKNESSES. WITH RESIDUAL MOISTURE ACROSS THE STATE COINCIDING WITH COLDER CONDITIONS...COULD SEE SOME SNOW SHOWERS ACROSS PORTIONS OF NORTH GEORGIA. HIGH UNCERTAINTY THIS FAR OUT IN MODELS MEANS THINGS COULD CHANGE...AND WILL HAVE TO MONITOR AS NEXTWEEK APPROACHES.

[FallsLake]

6z GFS has shifted south from 0z and definitly has a CAD look, but would need to shift a little more to keep the CAD through the entire event. It seems we had a storm either last year or the year before that was similarly forecasted by the models (big flip flops and then a shifts to the south/east starting at 120hrs).

[WXinCanton]

6z GFS has shifted south from 0z and definitly has a CAD look, but would need to shift a little more to keep the CAD through the entire event. It seems we had a storm either last year or the year before that was similarly forecasted by the models (big flip flops and then a shifts to the south/east starting at 120hrs).

Yeah it has a pretty strong CAD signal. Maybe the some of the CAD experts can chime in.

[weatherheels]

Yeah it has a pretty strong CAD signal. Maybe the some of the CAD experts can chime in.

Not anywhere close to an expert but I would think with a track like that it wouldnt matter how strong the CAD was because it would get pushed out. I just don't see anyone in the SE, without elevation, getting any significant winter weather out of a track that is currently being shown by the GFS>

[Cyclonicjunkie]

Not anywhere close to an expert but I would think with a track like that it wouldnt matter how strong the CAD was because it would get pushed out. I just don't see anyone in the SE, without elevation, getting any significant winter weather out of a track that is currently being shown by the GFS>

Tennessee and Kentucky is considered the SE, but I guess its a matter of what you consider significant

[burgertime]

I'm going to wait till about Wed. before I make any judgement.

[eyewall]

Well if it is a HSLC event I sure as hell hope it works out this time in this area. The last two severe events of that nature have been a bust here. I guess the best hope is it resets the favorable pattern following it leading to a snow event closer to Christmas.

[Brick Tamland]

Unless we get a huge sudden shot of cold air, I don't see anything but rain for the beginning of next week. Local forecast from WRAL has highs near 60 for Sunday. Maybe things will start get cranking again after the 15th like some have aluded to.

[WeatherNC]

Agree with the QC that as of now, this a RN and Thunderstorm event for most of the SE, with some scattered sn-showers on the back side for western portions, but we are still 7 days out so nothing certain can be ascertained at this point, just that the overall setup holds potential, and a storm in the period is likely.

GFS is on the fast side of the guidance envelope, and as you can see from the graphic below, has been trending deeper with the trough on the operational run over the past 24 hours, but does not show the level of continuity one would like to draw any useful conclusions. However, it is starting to show some evidence of a potential cutoff in or near the TN Valley, and hinting at a transfer to the Coast around ILM, which would make sense given the placement of the upper level low, if we do indeed see one develop on future runs. Also note the strength and placement of the 50-50, as it varies significantly from run to run, and is not closed off in the upper levels on any of these runs.

In the next graphic, I am going to omit the 12 and 18z GFS ens means, as they were dissimilar and did not exemplify the trends being seen in the operational run over the past 24 hours. As with the op, you can see the trough has trended a little deeper, and the ridging off the coast of S Cal, a little more stout. As a result, the mean has displaced the surface reflection to in or near ILM, but this is still a weak signal compared to the Euro mean.

The ECMWF, both in the operational run and ens mean, shows us what the GFS has been trending towards over the last 24 hours. More ridging off the southern coast of California, the absence of a 50-50 low, and a sharper trough over the eastern US, with some evidence of a potential UL cutoff near the base of the trough. Without access to the 12hr panels, the two graphics below use the day 7 panel from the 12 and 0z runs.

0z operational EC is starting to show hints of a transfer off the NC coast, whereas the 12z run depicted a storm that went from the TN Valley to northern NE. The 0z run also does something the 12z run did not and that is close off a 522dm ULL in or near the upstate of SC at 192hrs. This idea has some support from the GFS, and could be a mechanism for getting a transfer to the coast quicker than what is currently progged. A trend towards the 0z EC would be good for those in the SE wanting SN out of this...

The 0z ens mean of the EC has trended east, considerably compared to the 12z iteration. Trough is deeper, with evidence of a close off in the OH Valley. Furthermore, the slp placement near the tidewater area would suggest several members are at least keying in on a potential transfer, quicker than what the operational run suggests.

Just some random thoughts and what not this AM, as I am drinking some coffee looking over things. As is almost always the case at this range, a more subdued solution, taking a compromise of the middle road, and backing off the intensity some, makes for a safer, and usually more accurate forecast. It will be interesting to see if the trends shown above continue for the next several days, or do we see a reversal back to a dominant TN Valley to NE track. Nevertheless, the perturbations will continue through the week, look for continuity, support, and take the conservative route, which is usually RN around here.

[Weather Czar]

Thanks for the info and great post weathernc.

[packfan98]

Thanks for the info and great post weathernc.

Ditto from me. I wonder if the GFS will lose all grasp of reality like it often does in the 4-7 day time period?

[Weather Czar]

Ditto from me. I wonder if the GFS will lose all grasp of reality like it often does in the 4-7 day time period?

So far following these storms since the mega phased big app snowstorm the euro and Canadian showed at the beginning of Nov. The gfs has been doing a little better this fall/winter season.

[tnweathernut]

I know that back in the 90s the old MRF had issues characteristically displaying poor skill in resolving shortwaves moving through the base of mean troughs. This often left the MRF too weak and undefined with the shortwaves, even as close as 2-4 days out. I don't know if this is still true with the GFS of today.

Is there a met or pro forecaster that can tell me if this is still true with this model today or if they have largely fixed that issue?

[WeatherNC]

Prelim extended from the HPC this morning, good read...

PRELIMINARY EXTENDED FORECAST DISCUSSION

NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD

857 AM EST MON DEC 06 2010

VALID 12Z FRI DEC 10 2010 - 12Z MON DEC 13 2010

UPDATED PRELIMS FOLLOWED THE CONTINUITY OF THE EARLY PRELIMS WITH

MOSTLY COSMETIC CHANGES. SOME CHANGES TO FRONTAL STRUCTURE WERE

MADE TO BETTER FIT THERMAL PATTERNS. THE CONTINUITY OF THE NEW

00Z/06 ECMWF ENSEMBLE MEAN WAS VERY GOOD FROM THE CORRESPONDING

12Z/05 MEAN. PERHAPS THE MOST MEANINGFUL PIECE OF NEW INFORMATION

IS THAT NEW ENSEMBLE SPAGHETTI PLOTS SUPPORT THE MORE AMPLIFIED

SCENARIO FOR SAT-MON AS A MAJOR STORM DEVELOPS OVER THE OH

VLY/CENTRAL APPALACHIANS/MID AND N ATLANTIC COAST STATES. IN FACT

THE DETERMINISTIC GFS IS IN THE PREFERRED AMPLIFIED ECMWF FAMILY

OF SOLUTIONS. THE ECMWF FAMILY OF SOLUTIONS IS CLEARLY PREFERRED

OVER THE FLATTER GEFS MEAN SOLUTION FOR SUN/MON DAYS 6-7. THE

EARLY PRELIM DISCUSSION FOLLOWS BELOW.

MEDIUM RANGE GUIDANCE SHOWS OVERALL IMPROVED AGREEMENT UPON THE

EVOLUTION OF AN AMPLIFIED WRN RIDGE/ERN TROF CONFIGURATION BY THE

LATTER HALF OF THE FCST PERIOD. HOWEVER THERE WERE STILL

MEANINGFUL DIFFS AMONG LATEST MODEL/ENSEMBLE RUNS AND CONSECUTIVE

RUNS OF INDIVIDUAL MODELS WITH RESPECT TO THE VIGOROUS LOW

PRESSURE EXPECTED TO AFFECT THE ERN HALF OF THE CONUS IN RESPONSE

TO THE AMPLIFYING TROF ALOFT. THE 00Z DETERMINISTIC ECMWF SHOWED

A DAYS 5-7 SAT-MON SFC TRACK THAT IS ON THE NRN AND EVENTUALLY WRN

SIDE OF THE MODEL/ENSEMBLE SPREAD. THE INCREASING AMPLITUDE OF

THE PATTERN PRECLUDES FULLY DISCOUNTING OF THE 00Z ECMWF

SCENARIO....BUT IT WOULD BE DESIRABLE TO SEE SOME CONTINUITY

ESTABLISHED BEFORE PUTTING TOO MUCH WEIGHT IN THAT DIRECTION. AS

ORIGINATING PAC ENERGY IS CARRIED BY PROGRESSIVE FLOW ALOFT AND

DOES NOT REACH THE WEST COAST UNTIL EARLY DAY 4 FRI... PREFERRED

TO EMPHASIZE THE MOST AGREEABLE SOLN CLUSTER AT THIS TIME...

CONSISTING OF THE 00Z/06 GFS AND 12Z/5 ECMWF/ECMWF ENSEMBLE MEAN.

THESE SOLNS ARE USED IN A NEARLY EVEN BLEND FOR DAYS 5-7 SAT-MON.

THE 00Z GEFS MEAN APPEARS TOO WEAK/PROGRESSIVE BUT HAS TRENDED

SLOWER TOWARD CONSENSUS OVER THE PAST DAY.