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Major National Winter Storm Dec 25-28

am19psu

By am19psu,
in Weather Forecasting and Discussion

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ksstormhunter

ksstormhunter

Posted
Posted

SmartCast Analysis for 25 Dec/01Z to 26 Dec 01Z ( Base on my model output only)

http://smartwxmodel.net/update.htm

First the winter side of the storm system:

Currently Targeting the area of Tinker to McAlester this hour. My model showing the heaviest snow along this corridor.

McAlester Region: Tracking the snow to begin around 18Z, with periods of heavy snow, with snowfall rates of 1.3” per hour. In addition, winds look to increase to around 30MPH along the same timeframe, so look for blowing snow. Right now looking at 8.5” of snow in this area.

Tinker AFB/OKC Region: Showing a period of mixed precip from 06Z to 11Z, then changing to all snow by 12Z. Looking at visibilities down to less than ½ mile, and snowfall rates of up to 1.1” per hour possible. Right now looking max of 7.1” of snow accumulation in this area. In addition, looking at winds gusting to 35 to 40mph, which will create temporary blizzard conditions in this area.

Vance AFB Region: Looking to be on the fringe of the snow, but still looking at 3.1” of snow possible. Snow will begin around 09Z, and will be heaviest from 16Z to 20Z. In addition, winds will be gusting up to 35MPH during this time, so look for reduce visibility and blowing snow.

Damaging Wind Potential:

Hobart, Lawton, Lubbock, Childress, and Clinton are all targeted for winds 45 to 50MPH winds during the next 24 hours. In addition, looking at snowfall from 1” to 3” possible. This will also cause tempo conditions of reduce vis and blowing snow.

Severe Wx Potential:

My model currently tracking the highest instability areas in the Lufkin to Lake Charles area. Looking at over 65% chance for tornadic events in this area. In addition, forecasted hail projected around 2.3” to 2.6” and convective winds of 55 to 60MPH Possible. In addition, heavy rainfall is possible in these areas with precip totals of 1.3 to 1.9” possible.

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Indystorm

Indystorm

Posted
Posted

Yeah, this run of the NAM is really bad news...I've got Christmas things tonight including Midnight Mass but I'll hopefully get around to detailing a little more.

Between evening services up here in Elkhart, Tony, but am shifting my attention from snow to the svr wx in Dixie for Christmas. Having just vacationed in NOLA and Natchez a month ago I am quite concerned.

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Disc

Disc

Posted
Posted

I really hope people in those areas are paying attention and it concerns me more than usual because they won't be expecting this stuff during this time of the year. Many of the folks will be occupied with family and friends and may not get the message. Very scary soundings throughout the entire risk area.

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WeatherQ

WeatherQ

Posted
Posted

Yeah, this run of the NAM is really bad news...I've got Christmas things tonight including Midnight Mass but I'll hopefully get around to detailing a little more.

Tony, those hodographs, low level shear profiles and just the power of that system suggest A very ill-winded Christmas in the Deep South. Be careful. Merry Christmas.

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Ground Scouring

Ground Scouring

Posted
Posted

Lake Charles, LA: (This one is nasty)

Natchez, MS:

The projected 0-1-km SRH values coupled with the SR winds in the 900-850-mb column are near the parameters that would support violent tornadoes, especially given the 35-kt+ SR inflow over southern MS north almost to KGWO. The consistent trend toward a more rapid deepening of the surface low in SE TX, along with the minimum of junk convection (which I have mentioned before), on the NAM allows the warm front to progress to about KGWO by 21Z Tuesday, with Td's AOB 60°F just to the south--in the area with maximum mean 0-3-km SRH. This really widens the corridor for strong/violent tornadoes in a region boxed by KESF-KMSY in the south and KMLU-north of KMEI. At this point areas as far north as Delhi, LA, Pickens, MS, and Geiger, AL, are in play for strong tornadoes beginning tomorrow afternoon. 0-1-km helicity really maximizes near these northern cities, where all the factors mentioned--juicy Td's, retreating warm-frontal convergence, likely outflow boundaries, and insane potential for rotation along with moderately-sized hail and intense downbursts--really come together to favor a potential for a few violent tornadoes. I would also keep the MDT along a line extending to BMH due to very strong low-level shear and a temperature profile which favors possible, isolated strong tornadoes and large downbursts overnight Tuesday-Wednesday as the pre-frontal QLCS moves into S/C AL. Overall, I am getting very concerned that we will probably see at least one violent tornado with several long-lived supercells plus a high damaging-wind/moderate hail threat. At least insofar as the violent/long-track tornado probability is concerned, climatology for December probably should be thrown out a bit as the dynamics involved here suggest more of a January-type potential for violent tornadoes.

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Ground Scouring

Ground Scouring

Posted
Posted

With off-the-charts SRH and incredible hodographs, the risk for embedded spinups in this area will still be noteworthy, but I'm skeptical of long-trackers along the I-20 corridor as things stand. The 12z WRF-NMM shows no discrete activity ahead of the line, FWIW.

This is not directed against you specifically, but to others...the NAM reflectivity is not always an accurate predicator of mesoscale convective coverage due to issues with resolution. Its parameters are useful to determine overall convective modes, but the resolution does not always allow the model to accurately display what its parameters would define as the actual QPF / storm-modular output.

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Srain

Srain

Posted
Posted

Can we split the 2 aspects of this storm, or no?

Adam and I decided in the beginning to cover both aspects of this event. Since the societal impacts are for both winter and severe, we'll leave this thread as a general event thread on the Main Page for greater exposure to the community as a whole. We are in Storm Mode for that reason...;)

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brettjrob

brettjrob

Posted
Posted

This is not directed against you specifically, but to others...the NAM reflectivity is not always an accurate predicator of mesoscale convective coverage due to issues with resolution.

To clarify, I was referring to the 4km NMM, so resolution should not be an issue there (and it's decent at predicting mode). We'll see what 00z shows shortly.

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Srain

Srain

Posted
Posted

Interesting discussion from FWD this evening. One of the things I noticed this afternoon was the short wave was in fact a bit further S in New Mexico ~vs~ SE Colorado that the models had been suggesting. This could have rather significant implications in both the cold and warm sector and the severe threat expected.

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE FORT WORTH TX

912 PM CST MON DEC 24 2012

.UPDATE...

WE HAVE ANALYZED THE 00Z UPPER AIR DATA AND HAVE WATCHED THE

SURFACE OBS CLOSELY FOR SIGNS OF ANY DISCREPANCIES BETWEEN THEM

AND THE MODEL DATA. THE BIG THING THAT STANDS OUT ARE THAT THE

SURFACE LOW IN NORTHEAST NEW MEXICO AT 6PM WAS ABOUT 80 MILES

FARTHER SOUTH THAN ALL OF THE MODELS HAD FORECAST 24 HOURS AGO.

WHEN DEALING WITH A SWINGING/DIGGING UPPER LEVEL SYSTEM...THE

SURFACE PRESSURE PATTERN AND PRESSURE TENDENCIES OFFER ENORMOUS

CLUES ON THE FUTURE TRACK OF A POTENTIAL VORTICITY ANOMALY BEFORE

IT CLOSES OFF TO BECOME A FULL FLEDGED UPPER LOW. THE 3PM AND 6PM

SURFACE ANALYSIS SHOWED A LARGE REGION OF PRESSURE FALLS ACROSS

NEW MEXICO AND WEST TEXAS IN ADVANCE OF THE SYSTEM. GIVEN THE

ORIENTATION OF THE PRESSURE FALLS AND LOCATION OF THE SURFACE

LOW...IT CAN BE DETERMINED WITHOUT EVEN LOOKING AT A FORECAST

MODEL THAT THE UPPER LOW HAS NOT FINISHED DIGGING SOUTH. THE BIG

QUESTION IS HOW FAR SOUTH WILL THE UPPER LOW MAKE IT BEFORE IT

BEGINS TO SWING BACK TO THE NORTHEAST. AT THIS HOUR PRESSURE FALLS

CONTINUE IN THE REGION FROM LUBBOCK TO MIDLAND...WITH ANOTHER

PRESSURE FALL AREA DEVELOPING IN SOUTHEAST TEXAS. EXTRAPOLATING

SUGGESTS THE UPPER LOW WILL TRACK JUST SOUTH OF LUBBOCK BY SUNRISE

AND TO NEAR WACO BY SUNSET. AS THE LOW APPROACHES WACO...A WARM

FRONT WILL BE ORGANIZING OUT OF THE WEAK STATIONARY FRONT

CURRENTLY ANALYZED FROM SAN ANTONIO TO HOUSTON. BAROCLINIC QG

THEORY SUGGESTS THAT ONCE LOW LEVEL WARM ADVECTION BEGINS IN

EARNEST ACROSS SOUTHEAST TEXAS BY MORNING...IT WILL INDUCE HEIGHT

RISES TO THE SOUTHEAST OF OUR UPPER LOW WHICH WILL CAUSE THE LOW

TO CLOSE OFF AND FINISH DIGGING SOUTH...AND START ITS GRADUAL

TURN TO THE NORTHEAST. TOMORROW EVENING I WOULD EXPECT THE LOW TO

TRACK FROM NEAR WACO TO NEAR SHREVEPORT. IN SUMMARY THE USUAL

MEDIUM RANGE MODELS APPEAR TO BE A LITTLE TOO FAR NORTH WITH THE

TRACK OF THE UPPER LOW. OUR EXPECTATIONS FOR THE TRACK OF THE LOW

ALIGN WELL WITH THE RAP FORECAST WHICH IS TO THE SOUTH OF ALL

OTHER MODELS...SO WE WILL USE THE RAP HEAVILY.

OUR FORECAST HAS BEEN ON THE SOUTHERLY SIDE AND SNOWIER SIDE OF

THE MODEL GUIDANCE. SO ALTHOUGH WE ARE SEEING AN EVEN MORE

SOUTHERLY TRACK COME TO FRUITION...THIS DOES NOT NECESSARILY

MEAN THE FORECAST SNOW AMOUNTS NEED TO BE AMENDED MUCH. THIS IS IN

PART DUE TO THE DIFFICULTY IN GETTING THE COLDER/SUBFREEZING AIR

FARTHER SOUTH BEFORE THE PRECIPITATION ENDS. THE EXCEPTION IS THE

NORTHWEST ZONES WHERE THE MORE SOUTHERLY TRACK SUGGESTS MORE

PRECIP WILL FALL IN SUBFREEZING AIR. DUE TO THE TERRAIN EFFECTS

HERE...COLD AIR HAS AN EASY TIME GETTING INTO OUR NORTHWEST ZONES

WHEN WE HAVE A NORTH/NORTHEAST SURFACE WIND. HAVE EXPANDED THE

SNOW ADVISORY TO INCLUDE YOUNG/JACK/WISE COUNTIES...AND HAVE

INCREASED SNOW TOTALS TO THE 2-4 INCH RANGE FROM BOWIE TO SHERMAN.

THE NORTHEAST ZONES LIKELY WONT SWITCH TO SNOW UNTIL LATE

AFTERNOON...AS COLD AIR WILL HAVE TROUBLE MOVING IN AT THE SURFACE

DUE TO THE LEE SHADOW WARMING EFFECT OF THE OZARK PLATEAU. MOST OF

THE SNOW THAT OCCURS THERE WILL BE AFTER 6 PM AND WILL BE HIGHLY

DEPENDENT ON WHETHER MESOSCALE BANDING CAN SET UP IN THE WAKE OF

THE UPPER LOW. THE NEW NAM HAS FINALLY FORECAST SOME SIGNIFICANT

BANDING TO OCCUR...THUS WILL LEAVE THE ADVISORY ALONE IN THIS

AREA...BUT CONFIDENCE IS A LITTLE LOWER IN THE NORTHEAST ZONES FOR

2+ INCHES OF SNOW.

FARTHER TO THE SOUTH OF THE ADVISORY...FOR THE I-20 CORRIDOR AND

INCLUDING THE METROPLEX...THERE IS NOW HIGH CONFIDENCE THAT SNOW

WILL OCCUR. HOWEVER ALL INDICATIONS ARE THAT IT WILL STILL BE A

BRIEF 1-3 HOUR EVENT WITH NOT ENOUGH TIME TO GET ACCUMULATIONS

OVER AN INCH. IT MUST BE STRESSED THAT WITH TEMPERATURES FALLING

INTO THE 20S BY SUNSET...ANY APPRECIABLE MOISTURE REMAINING ON

BRIDGES...OVERPASSES AND EVEN SURFACE STREETS WILL LIKELY RE-

FREEZE INTO BLACK ICE. ALTHOUGH WE ARE USING 1+ INCH AS CRITERIA

FOR THE COUNTIES IN THE WINTER WEATHER ADVISORY AREA...WE MAY

EXPAND THE ADVISORY SOUTH INTO THE METROPLEX OVERNIGHT DUE SOLELY

TO TRAVEL IMPACTS.

FINALLY CONCERNING THE SEVERE WEATHER THREAT. WITH A MORE SOUTHERLY

TRACK OF THE UPPER LOW...THIS MEANS THERE IS LESS OF A CHANCE OF THE

WARM FRONT MAKING IT INTO THE SOUTHEAST CWA TONIGHT AS IT WILL

LIKELY STAY SOUTHEAST OF THE AREA. ELEVATED THUNDERSTORMS ARE STILL

EXPECTED TO RAPIDLY INCREASE IN COVERAGE AFTER 3 AM...WITH ELEVATED

INSTABILITY HIGH ENOUGH FOR A FEW SEVERE HAIL STORMS SOUTH OF I-20.

HAVE TONED DOWN THE DAMAGING WIND AND TORNADO THREAT FROM OUR

PRODUCTS...BUT WE WILL CONTINUE TO ADVERTISE HAIL STORMS POSSIBLE

LATE TONIGHT AND EARLY TOMORROW MORNING.

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Ground Scouring

Ground Scouring

Posted
Posted

The strength of the dry punch between 00-06Z Wednesday on the 00Z NAM is just incredible...indicating the intensity of the mid-level system. This allows the QLCS to remain mostly or entirely discrete supercells from extreme E LA / SW MS all the way to GA. In particular, it shows three rounds of tornado-producing supercells: a first round of storms starting 12Z Tuesday with elevated storms becoming surface-based in E/C LA; a second, prolonged (meaning nocturnal) outbreak beginning at 21Z Tuesday in S/C MS; and a third, afternoon event at 21Z Wednesday in C AL extending into W GA. The orientation of the surface-700-mb bulk shear relative to the front, in particular, really helps to maintain discrete supercells for a long period of time. This almost reminds me of 04/27/2011, as frightening as it may be to invoke.

http://www.emc.ncep....yle/spcprod/00/

Given the trends, I am starting to think that a Day-1 High Risk for overall TOR and Severe Wind probabilities may be in order.

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