Another 24 hours has passed and models still trending towards a complex weather system impacting the area tomorrow into Thursday morning. Below are some graphics on the storm system. In addition, language for the winter storm watch is also posted.
.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/…
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SIGNIFICANT WINTER STORM PRIMED TO IMPACT THE REGION LATE
WEDNESDAY THROUGH THE DAY THURSDAY…
OVERVIEW…
MODELS HAVE COME INTO GOOD AGREEMENT AS AFOREMENTIONED NRN AND SRN
STREAM ENERGY WL PHASE INTO A POTENT SHORTWAVE OVER THE GULF STATES
WED/WED NIGHT. CLOUDS WILL INCREASE LATE TONIGHT AND EARLY WED AS
THE SYSTEM APPROACHES FROM THE SOUTH. CYCLOGENESIS IS EXPECTED TO
OCCUR OVER THE NERN GULF WED PM, AS AMPLIFYING FLOW BEGINS TO LIFT
MOISTURE NWD. SFC HIGH PRESSURE TO THE NORTH WILL BEGIN TO
RETREAT…BUT WILL REMAIN RIDGED DOWN ACROSS NORTH CENTRAL VA.
STRONG SPEED MAX WILL EMERGE FROM THE BASE OF THE SHORTWAVE…FURTHER
ENHANCING THE FLOW OVER THE SE, WHICH WILL SERVE TO EJECT THE
SHORTWAVE NE. A WINTER STORM WATCH REMAINS IN EFFECT FOR THE CWA
WITH THE EXCEPTION OF THE SOUTHERN TIDEWATER AND NE NC. IF CURRENT
TRENDS HOLD WITH 12Z SUITE, UPGRADES TO WARNINGS/ADVISORIES WOULD
BE NEEDED TODAY OR THIS EVENING. MANY FACETS TO THIS EVENT…WHICH
BREAK DOWN AS FOLLOWS:
PRECIPITATION…
MODEL CONSENSUS HAS SLOWED ONSET OF PCPN BY A FEW HOURS, BUT
GIVEN THAT WAA PRECIP/OVERRUNNING IS OFTEN REALIZED QUICKER THAN
MODELS INDICATE, DID NOT CHANGE ONSET TIMING FROM PREVIOUS
FORECAST. MODELS IN GENERAL AGREEMENT WITH THE TRACK OF THE SFC
LOW…LIFTING IT ALONG THE SE COAST LATE WED TO JUST OFFSHORE LATE
WED NIGHT-EARLY THURS MORNING. 11/00Z ECMWF TRACKS THE LOW ALONG
THE SE COASTAL PLAIN AND INTO SE VA/NE NC THU MORNING.
CHC POP WED MORNING/AFTN RAMP UP TO CATEGORICAL POPS WED AFTN/NIGHT
AS THE POTENT SHORTWAVE AND STRONG WINDS ALOFT PROVIDE DYNAMICAL
FORCING FOR ASCENT (STRONG AGEOSTROPHIC LIFT) OVER THE MID-
ATLANTIC. STRONG HEIGHT FALLS WILL ALSO PRODUCE STRONG Q-VECTOR
CONVERGENCE/FRONTOGENETIC FORCING OVER THE REGION (STRONGEST
BETWEEN H6-7). THIS RESULTS IN PERIODS OF MODERATE PRECIP
UNDERNEATH THIS BANDING. PRECIP WILL BEGIN AS ALL SNOW FOR ALL BUT
FAR SE WHERE TEMPS WILL BE WARM ENOUGH FOR RAIN…POSSIBLY A BRIEF
PERIOD OF SLEET AS LAYER MOISTENING ENSUES. THE PERIOD OF HEAVIEST
SNOWFALL LOOKS TO BE WED EVENING INTO EARLY THU MORNING. SFC LOW
APPROACHES COASTAL PLAIN FROM THE SOUTH, AND WARM AIR MOVING IN
ALOFT SHOULD START MIXING IN SOME SLEET, EVENTUALLY CHANGING THE
SNOW OVER TO SLEET OR R/ZR PER BUFR SOUNDINGS. PRECIP WILL BEGIN
TO TRANSITION TO ALL RAIN OVER THE SE…BUT REMAIN ALL SNOW OVER
THE PIEDMONT. A MIXED BAG OF PRECIP FROM SOUTH CENTRAL VA INTO
EAST-CENTRAL VA (MAINLY I-95 EAST) AS A WARM NOSE WARMS TEMPS TO
~2-4C BTWN 950 AND 850MB. THIS WILL PRODUCE PERIODS OF
SNOW/SLEET/RAIN/FREEZING RAIN. STILL TOO EARLY TO IRON OUT EXACT
PTYPES IN THIS TRANSITION ZONE…BUT IT SEEMS VERY POSSIBLE THAT
THERE COULD BE ACCUMULATING ICE ON TOP OF SEVERAL INCHES OF SNOW
OVER CNTRL VA. DRY AIR WILL BEGIN TO PUNCH INTO THE SE AS THE LOW
LOCATES JUST OFF THE VA COAST THU MORNING, WHICH WILL EVENTUALLY
TURN INTO JUST LGT RA/DZ ACROSS THE SE AS MOISTURE ALOFT SLACKENS.
MEANWHILE, MOISTURE AXIS WILL LOCATE FROM THE PIEDMONT INTO NRN VA
AND THE MD ERN SHORE. MODELS INDICATE STRONG DYNAMICS IN THIS
MOISTURE AXIS WITH STRONG LIFT IN THE SNOW GROWTH LEVEL. MODEL GEO
POT VORT IS ALSO NEGATIVE IN THIS REGION…WHICH ALSO PORTENDS TO
POSSIBLY ENHANCING BANDING BEHIND THE DEPARTING LOW. WILL MAINTAIN
LIKELY POPS ACROSS THE REGION THURS AFTERNOON AS THE PV ANOMALY
CATCHES UP WITH THE LOW. THIS WILL CAUSE THE LOW TO OCCLUDE AND
SLOW ITS FORWARD PROGRESS. WILL NEED TO MONITOR THIS AREA AS TEMPS
MAY BE WARM ENOUGH FOR RAIN…BUT DYNAMIC COOLING MAY TRANSITION
IT BACK TO SNOW BEFORE PCPN TAPERS OFF.
TEMPERATURE…
OBVIOUSLY DEPENDANT ON EXACT TRACK. USED A BLENDED SOLUTION FROM THE
ECMWF/CMC/NAM (BLENDED IN THAT ORDER) FOR TEMPS/THICKNESSES.
OPERATIONAL ECMWF WAS A SHADE EAST IN THIS LAST 00Z RUN…AND HENCE
THE FORECAST HAS SHIFTED THE MIXED PRECIP AXIS FARTHER WEST. HIGHS
WED GENERALLY IN THE L30S INLAND…TO U30S IMMEDIATE COAST. LOWS WED
NIGHT IN THE 20S NW TO MID 30S SE. IGNORED NUMERICAL GUIDANCE FOR
MAXIMA ON THU FORECAST AS THEY ARE TYPICALLY TOO HIGH IN ONGOING
PCPN. UNDERCUT GUIDANCE AND KEPT HIGHS IN THE MID 30S INLAND…TO
LOW 40S COASTAL AREAS.
QPF/SNOWFALL TOTALS…
GENERALLY ACCEPTED WPC GUIDANCE FOR QPF AMOUNTS, THOUGH DID MIX IN A
BLEND OF AFOREMENTIONED MODEL GUIDANCE. QPF RANGE FROM ONE INCH NW
TO AN INCH AND THREE QUARTERS SE.
SNOWFALL AMOUNTS WILL RANGE FROM 10-14 INCHES OVER THE PIEDMONT
(ALL SNOW) TO 5-10 INCHES ALONG THE I-95 CORRIDOR…WITH 3-5″ FOR
THE NRN NECK/PENINSULA…WESTERN TIDEWATER AND INTR NE NC (LOWER
AMOUNTS IN CNTRL VA DUE TO WINTRY MIX). LITTLE…IF ANY
ACCUMULATION IN S/E TIDEWATER. IN MARYLAND, HIGHEST TOTALS WILL BE
IN USUAL SPOTS N/W OF 50 IN WICOMICO/DORCHESTER COUNTIES…WITH
MIXING RESULTING IN LOWER TOTALS ALONG AND EAST OF 13. PLEASE
REFER TO SNOWFALL GRAPHICS FOR MORE INFO.
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