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Jan 22-23 East Coast Storm Discussion


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Latest From GSP Looking Good :santa: :

 

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
AS OF 215 PM TUESDAY...MODELS ARE IN VERY GOOD AGREEMENT IN THE NEXT
UPCOMING STORM TO AFFECT OUR AREA THURSDAY THRU SATURDAY. A DYNAMIC
TROF WILL DIG ACRS THE PLAINS ON THURSDAY...THEN CLOSE OFF AND DRIFT
EAST ACRS THE SOUTHEAST STATES ON FRIDAY THRU SATURDAY. STRONG
CYCLOGENESIS WILL OCCUR ACRS THE LOWER MS VALLEY THURSDAY...WITH A
1003 MB LOW REACHING THE ERN TN VALLEY BY MIDDAY FRIDAY. FROM
THERE...THE MODELS HAVE TRENDED TOWARD A MILLER-B LOW...WITH A
SECONDARY LOW DEVELOPING ALONG THE COASTAL FRONT INVOF MYRTLE
BEACH...THEN BECOMING THE PRIMARY LOW AND LIFT UP THE COAST FRIDAY
NIGHT THRU SATURDAY. THE EXCEPTION TO THIS TREND IS THE 12Z
ECMWF...WHICH HAS A MORE SOUTHERN TRACK OF THE LOW AND MORE
MILLER-A-LIKE. SINCE THE 12Z ECMWF IS NOT IN THIS FCST PACKAGE...THE
FCST SHOWS A MORE MILLER-B TYPE IMPACT. THAT IS...A BROAD AREA OF
MIXED P-TYPE CONCERNS WITH POTENTIAL FOR WARNING CRITERIA ICE ACCUMS
ALONG THE NRN NC BLUE RIDGE AND FOOTHILLS. THE EXACT P-TYPE
TRANSITIONS AND THE SNOW AND ICE ACCUMS WILL LIKELY BE REFINED AS WE
GET CLOSER TO THE EVENT.


SO POPS SHUD RAMP UP FROM SW TO NE ON THURSDAY...TO CATEGORICAL ACRS
THE ENTIRE CWFA BY FRIDAY MORNING. THE STRONGEST FORCING WITH
POTENTIAL FOR HEAVY RAIN AND STRONG HIGH-ELEV WINDS WILL BE FROM 06Z
TO 18Z FRIDAY. BY MID TO LATE AFTN...A DRY SLOT SHUD PUNCH THRU THE
AREA FORM THE SOUTH...AS THE UPPER LOW CROSSES THE AREA TO EAST.
THEN THE WRAP-AROUND MOISTURE AND DEFORMATION-ZONE PRECIP SHUD PIVOT
IN FROM THE NORTH FRIDAY EVENING. THIS MOISTURE SHUD GRADUALLY TAPER
OFF TO JUST NW FLOW UPSLOPE SNOW SHWRS BY SATURDAY MORNING...AND
THOSE SHWRS WILL END AROUND DAYBREAK SUNDAY.

AS FOR P-TYPE AND ACCUMS...I TOOK A BLEND OF ALL AVAILABLE MODEL
THICKNESSES AND USED THE WINTER WX NOMOGRAM...WITH SOME MINOR
TWEAKS...AND STUCK CLOSE TO WPC QPF. THIS RESULTS IN MAINLY RAIN
THURSDAY...THEN AS COLD AIR DAMMING AND DYNAMICAL COOLING OF THE
PROFILES OCCURS...AS TRANSITION TO WINTRY MIX OF SLEET...ICE...AND
SNOW IN THE I-40 CORRIDOR...AND PERHAPS AS FAR SOUTH AS THE SOUTHERN
FRENCH BROAD VALLEY THURSDAY NIGHT THRU FRIDAY. THEN ALL P-TYPE
CHANGES TO SNOW OR RA/SN MIX FRIDAY EVENING THRU SATURDAY. ACCUMS
ARE HIGHLY DEPENDENT ON THE TIMING OF P-TYPE TRANSITIONS. THE LATEST
FCST HAS MORE FREEZING RAIN AND SLEET AND LESS SNOW. BUT IF THE 12Z
ECMWF IS ON TO A NEW TREND...THEN WE MAY TREND TOWARD MORE SNOW.


TEMPS WERE WEIGHTED CLOSELY TO THE RAW MODEL OUTPUT DURING THE
HEAVIEST PRECIP. SO HIGHS THURSDAY IN THE UPR 30S TO MID
40S...COOLING TO THE UPR 20S TO MID 30S THU NIGHT. THEN WITH THE
PRECIP AND CAD ON FRIDAY TEMPS WARMING VERY LITTLE...WITH HIGHS IN
THE 30S TO LWR 40S.


FOR FRIDAY NIGHT THRU SATURDAY NIGHT...COLD AIR WRAPPING AROUND THE
COASTAL STORM WILL KEEP BELOW NORMAL TEMPS. HIGHS IN THE 20S MID 30S
IN THE MTNS...AND LWR-MID 40S IN THE PIEDMONT. LOWS IN THE 20S TO
MID 30S FRIDAY NIGHT...AND TEENS TO UPR 20S SATURDAY NIGHT.

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Question for mets: How does the deform band work with an ULL that isn't a bowling ball, but rather is a part of an energy transfer setup? Don't really see a deform band being depicted by the models (I know they are often slow to pick up on those). 

 

The heaviest band of persistent precip will be on the NW side of the upper level low.....check 500mb. Even though the surface low transfers to the coast, the ULL just continues to work ENE. 

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I like the way it is setting up..  It is also nice that the main model suites are somewhat in agreement now.  Hope they continue to trend the same.. for the sake of putting human safety at the forefront.  The quicker we know what's going to happen the quicker folks can prepare.

 

RAH is taking forever to get out their AFD again.

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"THE MODELS HAVE TRENDED TOWARD A MILLER-B LOW"

 

GSP is also not moving away from the Miller-B, hence the dry slot involvement which more often than not skips Upstate SC.

Notice they indicated that the 12Z Euro was not part of that forecast package......I would expect big changes in the next update.

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The heaviest band of persistent precip will be on the NW side of the upper level low.....check 500mb. Even though the surface low transfers to the coast, the ULL just continues to work ENE. 

 

Thanks -- so really no difference between the deform band for this type of an ULL and others where there is no surface low transfer. Gotcha -- appreciate it -- better get some rest tonight -- going to be a LONG week!!!

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Its not a true miller B on the Euro or a true miller A for that matter...it has an energy transfer but not typical of a miller B

 

It is a bit of a hybrid in terms of the overall synoptic development. The upstream pattern is more similar to that of a Miller-A in the sense that there is an amplifying upstream ridge with no split flow aloft but downstream you clearly have confluent flow which is typical of Miller-B's.

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From RAH:

 

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
AS OF 335 PM TUESDAY...

THE MAIN STORY DURING THIS TIME WILL BE OUR FIRST NOTABLE WINTER
STORM OF 2016. THIS FORECAST CYCLE...WE DECIDED TO NOT FOCUS SO MUCH
ON QPF NUMBERS THAT WILL INEVITABLY CHANGE WITH FUTURE MODEL
RUNS...BUT RATHER FOCUS ON WHAT WE ARE VERY CONFIDENT WILL OCCUR
FROM A CLIMATOLOGIC PERSPECTIVE...WHICH IS THE LIKELIHOOD THAT A
CLASSIC MILLER B STORM SYSTEM WILL AFFECT OUR AREA THURSDAY NIGHT
THROUGH SATURDAY. UNLIKE OUR BRIEF WINTRY WEATHER EPISODE THIS PAST
SUNDAY...THE STORM SYSTEM LATER THIS WEEK WILL BE PRECEDED BY COLD
HIGH PRESSURE TO OUR NORTH THAT WILL ALLOW FOR WINTRY PRECIP ACROSS
MUCH OF OUR AREA AT LEAST DURING THE ONSET OF THE STORM THURSDAY
NIGHT. USING CLIMATOLOGY BLENDED WITH THE MOST RECENT MODELS...
CONFIDENCE IS GROWING THAT LOW PRESSURE WILL TRACK FROM THE LOWER
MISS VALLEY NEWD LATE THURSDAY...AND TRANSITION TO THE CAROLINA
COAST BY FRIDAY EVENING IN A CLASSIC MILLER B FASHION...BEFORE
EXITING TO THE NE SATURDAY MORNING. WITH THESE SITUATIONS...WE
USUALLY SEE WAA-DRIVEN PRECIP DEVELOP FROM SW TO NE...AND WITH THE
COMBINATION OF ANTECEDENT NEAR-SFC COLD AIR AND EVAP COOLING IN THE
LOWEST 75-100MB...LIGHT PRECIP AT THE ONSET THURSDAY NIGHT APPEARS
LIKELY TO FALL IN THE FORM OF LIGHT SNOW...SLEET...AND/OR FREEZING
RAIN. THEN AS THE LOW LEVEL WARM NOSE JUST OFF THE SFC SURGES
NORTHWARD AHEAD OFTHE SFC LOW...PRECIP SHOULD CHANGE TO FREEZING
RAIN (WHICH IN THIS CASE WOULD OCCUR IN THE HOURS JUST PRIOR TO
SUNRISE FRIDAY)...THEN CHANGING TO ALL RAIN FROM SOUTH TO NORTH AND
NORTHWEST AFTER SUNRISE AND AS THE DAYTIME PROGRESSES FRIDAY. AS IS
USUALLY THE CASE...THE PART OF OUR CWA THAT WILL SEE FROZEN/FREEZING
PRECIP LASTING THE LONGEST...PERHAPS WELL INTO THE LATE MORNING
HOURS...WILL BE ACROSS OUR NORTH AND NORTHWEST PIEDMONT ZONES...
GENERALLY NORTH OF THE I-85 CORRIDOR.  HOWEVER...EVEN THOSE ZONES
ARE LIKELY TO CHANGE TO RAIN DURING THE ATERNOON FRIDAY AS WARM AIR
SURGES NORTHWARD.

THE NEXT PHASE OF STORM WILL OCCUR FRIDAY NIGHT INTO SATURDAY...AS
COLDER AIR MOVES INTO OUR AREA IN THE WAKE OF THE DEPARTING LOW. AS
SUCH...REMAINING MOISTURE INVOF OF THE UPPER LOW AS IT MOVES ACROSS
WILL RESULT IN A PERIOD OF LIGHT SNOW FOR MUCH OF OUR CWA DURING
THIS TIME...WITH PERHAPS SOME LIGHT ACCUMULATIONS.

MANY FINER DETAILS ARE EXPECTED TO CHANGE AND COME INTO BETTER FOCUS
AS WE GET CLOSER. BUT SUFFICE IT TO DAY...DEPENDING ON THE DURATION
OF FROZEN/FREEZING PRECIP COUPLED WITH QPF AMOUNTS AS WE GET
CLOSER...WINTER STORM WATCHES/WARNINGS AND/OR ADVISORIES WILL LIKELY
BE WARRANTED AS WE GET CLOSER.

ANOTHER CONCERN WORTH CONSIDERING IS THE FLOODING POTENTIAL ON
FRIDAY AFTER THE CHANGE-OVER TO RAIN.  GIVEN THE RECENT WET
CONDITIONS THIS SEASON...IT WOULDN`T TAKE MUCH HEAVIER RAIN TO
PRODUCE LOCALIZED FLOODING AND SUBSEQUENT RIVER FLOODING...
PARTICULARLY ON THE NEUSE AND/OR TAR RIVERS.  ALL SAID...ITS
IMPORTANT TO STAY TUNED FOR FUTURE FORECAST CYCLES AS MORE SPECIFIC
DETAILS REGARDING PRECIP TYPE AND ACCUMULATION "NUMBERS" WILL BE
PRESENTED AS CONFIDENCE IN THE STORM TRACK INCREASES WITH FUTURE
RUNS.

AFTER THIS SYSTEM EXITS...LOOK FOR FAIR BUT SLIGHTLY COLDER-THAN-
NORMAL WEATHER FOR SUNDAY INTO MONDAY.

&&
 

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RAH isn't ready to jump the gun on this yet...  they are waiting until later model runs to focus on amounts.  I don't blame them.

 

Anyone who has lived in central NC for a while knows that RAH is VERY conservative.  As is Fishel...  Fishel will probably downplay this big time tonight.

 

Now, what I'm looking at with the models and their discussion is the warm nose.  They seem to be pretty confident in Friday being mostly rain for RDU.  Will this storm have such a prominent warm nose?  Will the CAD stand firm?

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