-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 052011
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
300 PM EST WED MAR 5 2014

.SYNOPSIS...A BACKDOOR COLD FRONT WILL PUSH SOUTH THROUGH THE REGION
TONIGHT AS CANADIAN HIGH PRESSURE ADVANCES INTO NEW ENGLAND AND
EXTENDS SOUTHWARD INTO THE MID ATLANTIC. A LOW PRESSURE SYSTEM WILL
STRENGTHEN ALONG THE GULF COAST ON THURSDAY...THEN TRACK NORTHEAST
ALONG OR OFFSHORE THE SOUTHEAST COAST ON FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 250 PM WEDNESDAY...

REST OF TODAY INTO TONIGHT: A PRONOUNCED SMALL AMPLITUDE SHORTWAVE
CENTERED IN UPSTATE SC AT 18Z WILL DEAMPLIFY AS IT TRACKS ENE
OFFSHORE THE CAROLINA COAST BY MIDNIGHT (03-06Z). MEANWHILE...1040
MB ARCTIC HIGH PRESSURE CENTERED JUST SOUTHWEST OF JAMES BAY THIS
AFTERNOON WILL MOVE SOUTHEAST TOWARD NEW ENGLAND TONIGHT...WITH A
PRONOUNCED SFC RIDGE AXIS EXTENDING SOUTHWARD THROUGH THE MID-
ATLANTIC AND CAROLINAS...THE LEADING EDGE OF WHICH WILL BE MARKED BY
A BACKDOOR COLD FRONTAL PASSAGE FROM N/NNE TO S/SSW BETWEEN 00-06Z.
LOWS THU MORNING WILL BE A FUNCTION OF SHALLOW LOW-LEVEL COLD
ADVECTION IN THE WAKE OF THE BACKDOOR COLD FRONT AND CLEARING SKIES
FROM WEST-EAST (THOUGH PERHAPS NOT ENTIRELY CLEAR ESP SOUTHEAST) IN
ASSOC/W SUBSIDENCE IN THE WAKE OF SHORTWAVE ENERGY MOVING OFFSHORE
LATE THIS EVENING. GIVEN THE LATEST GUIDANCE...EXPECT LOWS SLIGHTLY
LOWER THAN PREVIOUSLY INDICATED...RANGING FROM THE UPPER 20S NORTH
TO LOWER 30S SOUTH. DO NOT ANTICIPATE ANY CHANCE FOR PRECIPITATION
THROUGH 12Z THU GIVEN SUBSIDENCE IN THE WAKE OF THE AFOREMENTIONED
SHORTWAVE COMBINED WITH SHALLOW COLD ADVECTION. ADDITIONALLY...ANY
LOW-LEVEL WARM ADVECTION WILL LIKELY REMAIN CONFINED ALONG OR JUST
OFFSHORE THE CAROLINA COAST THROUGH SUNRISE. -VINCENT

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
-- Changed Discussion --
AS OF 300 PM WEDNESDAY...

...A WINTRY MIX IS LOOKING MORE LIKELY... MAINLY OVER THE NORTHWEST
PIEDMONT THURSDAY NIGHT INTO EARLY FRIDAY... THIS INCLUDES THE
PIEDMONT TRIAD AND ROXBORO...

... RAIN IS EXPECTED ELSEWHERE... BUT MAX MIX WITH A LITTLE SLEET
AND FREEZING RAIN THURSDAY EVENING FROM ALBEMARLE TO RALEIGH TO
ROCKY MOUNT...

THE MID/UPPER LOW CURRENTLY EXITING THE TEXAS PANHANDLE IS FORECAST
TO TAKE A SOUTHERLY TRACK ALONG THE GULF COAST THURSDAY NIGHT...
THEN SLOWLY TURN ENE ALONG THE SOUTH CAROLINA COAST FRIDAY...
EXITING THE NC FRIDAY EVENING. THIS SOLUTION IS A PREFERRED BLEND OF
THE 12Z/GFS/ECMWF/UKMET. THE LATEST MODEL GUIDANCE HAS BEEN TRENDING
COLDER WITH LESS OF A WARM NOSE IN THE MID-LEVELS BACK OVER THE
NORTHWEST PIEDMONT FOR THE MAIN PART OF THE EXPECTED PRECIPITATION
EVENT. FOR THE SURFACE LOW PRESSURE DEVELOPMENT/TRACK EXPECTED FROM
THE GULF OF MEXICO NORTHEAST JUST OFFSHORE THE SC/NC COAST THURSDAY
NIGHT AND FRIDAY... IT IS HARD TO ARGUE WITH WPC`S PREFERENCE OF A
BLEND OF THE 12Z/UKMET WITH THE 00Z/ECMWF AND ECMWF ENSEMBLE MEAN
FOR THE FORECAST SOLUTION. THERE HAS BEEN A SLOWING TREND WITH THE
GUIDANCE AND CONFIDENCE HAS ALSO INCREASED WITH BETTER CLUSTERING
FROM THE ENSEMBLE PLOTS.

ANOTHER CRITICAL FEATURE IS THE PRONOUNCED VERY COLD PARENT SURFACE
HIGH PRESSURE THAT IS FORECAST TO BUILD FROM NEW ENGLAND DOWN THE
EASTERN SEABOARD INTO NC/UPSTATE SC LATE WEDNESDAY NIGHT AND
THURSDAY... AND BE IN PLACE THURSDAY EVENING. THIS HIGH IS OF
SUFFICIENT STRENGTH (1040ISH+ MB) AND PREFERRED LOCATION NY/NEW
ENGLAND TO DELIVER COLD DRY AIR INTO OUR REGION AS THE STORM
ARRIVES. ONE QUESTION HAS BEEN HOW QUICKLY THE HIGH WILL RETREAT AND
THIS APPEARS TO BE THURSDAY NIGHT. HOWEVER... CLASSICAL DAMMING IS
EXPECTED TO UNFOLD THURSDAY EVENING AS THE MAIN PRECIPITATION
SATURATES THE COLUMN QUICKLY.

IN ADDITION... THE WARM NOSE ALOFT IS ALSO CRITICAL AS MODELS HAVE
BEEN TRENDING COOLER WITH TIME WITH LESS OF A WARM NOSE REACHING
WELL BACK INTO THE FOOTHILLS/BLUE RIDGE. WE WERE NOT BITING OFF
TOTALLY ON THESE SOLUTIONS AS THERE IS STILL A LOT OF UNCERTAINTY.

IF THESE TRENDS CONTINUE... A WINTER WEATHER ADVISORY OR EVEN A
WINTER STORM WATCH MAY BE NEEDED IN THE NW PIEDMONT FOR THURSDAY
NIGHT INTO EARLY FRIDAY FOR A WINTRY MIXTURE OF MOSTLY FREEZING RAIN
WITH EVEN SOME MEASURABLE SNOW AND SLEET. THE WARM NOSE ALOFT MAY
ACTUALLY EVEN VERIFY LESS INTENSE IF THE LIFT IS STRONG ENOUGH TO
OFFSET THE WAA ABOVE THE NEAR SURFACE COLD NOSE. THIS MAY LEAD TO A
CHANGE TO WET SNOW AT TIMES IN HEAVIER PRECIPITATION. THE TRACK OF
THE MID LEVEL LOW IS ALSO CRITICAL... AND THIS REMAINS WELL SOUTH
AND EAST OF OUR REGION THIS MODEL RUN... SUPPORTING COLDER AIR
ALOFT.

... THE NORTHWEST PIEDMONT TO ROXBORO AND OXFORD...

RIGHT NOW... THE FORECAST 1000/850 AND 850/700 PARTIALS INDICATE
1295-1305M/1545-1555M DURING MUCH OF THE OVERNIGHT PERIOD THURSDAY.
NOMOGRAMS SUGGEST A WINTRY MIXTURE WITH MORE SNOW/SLEET THE LESS THE
WARM NOSE... AND MORE IN THE WAY OF FREEZING RAIN/RAIN IF THE WARMER
NOSE VERIFIES. WE WILL LOOK TO SURFACE WET BULB FORECASTS FOR
PLACEMENT OF THE MOST CRITICAL REGION THAT WOULD LIKELY SEE THE
HIGHEST PROBABILITIES OF THE WINTRY MIXTURE/ICING. CURRENT FORECASTS
INDICATE WET BULBS OF 30-32 FROM NEAR LEXINGTON TO GREENSBORO TO
ROXBORO THURSDAY NIGHT... AND SUB 30 POSSIBLE FROM WINSTON-SALEM AND
THE PTI AIRPORT NORTH AND WEST. THESE WILL BE THE MOST CRITICAL
LOCATIONS FOR POTENTIAL WINTER WEATHER. HERE... WE WILL FORECAST A
MIXTURE OF FREEZING RAIN AND SLEET... POSSIBLY WET SNOW AT TIMES.
GLAZING OF ICE OF 0.1 TO 0.2 POSSIBLE... WITH SNOW AND SLEET OF LESS
THAN AN INCH. THESE ARE PRELIMINARY NUMBERS AND WILL LIKELY CHANGE
AS THE STORM EVOLVES. TEMPERATURES SHOULD FALL TO NEAR THE WET
BULBS... UPPER 20S TO AROUND 30. COLD AIR DAMMING SHOULD BE LOCKED
IN FOR A WHILE. HOWEVER... TEMPS SHOULD SLOWLY RISE TO NEAR OR ABOVE
32 MOST AREAS... INTO THE MID TO UPPER 30S. UNLESS PRECIPITATION
RATES CONTINUE HEAVY... PRECIPIATION SHOULD CHANGE TO RAIN. WET SNOW
CAN NOT BE RULED OUT IN HEAVIER BANDS.

...TO THE SOUTH AND EAST INCLUDING ALBEMARLE TO RALEIGH TO ROCKY
MOUNT... RAIN IS EXPECTED THAT MAY MIX WITH A LITTLE SLEET OR
FREEZING RAIN THROUGH MIDNIGHT... THEN CHANGE TO RAIN AS TEMPS RISE
SLOWLY OVERNIGHT. WET BULBS NEAR 32 DO SUPPORT SOME GLAZING... BUT
ONLY ON ELEVATED SURFACES. RAINFALL RATES SHOULD LIMIT ICING. LOWS
31-32... RISING TO 34-35 OVERNIGHT. RAIN IS EXPECTED FRIDAY. MAY BE
SOME WET SNOW (NON ACCUMULATING) DUE TO THE WET GROUNDS DURING HEAVY
PRECIP BANDS/RATES FRIDAY. HIGHS 37-44.

ALL RAIN IS EXPECTED FROM ROCKINGHAM TO LILLINGTON TO WILSON
SOUTHWARD DURING THE EVENT WITH WET BULBS LIKELY REMAINING ABOVE 33
AND RISING TOWARD 40 OVERNIGHT. RAIN FRIDAY... HIGHS IN THE 40S.

THE BOTTOM LINE AT THIS POINT IS THAT WE ARE CONFIDENT THAT THE
NORTHWEST PIEDMONT HAS THE BEST CHANCE OF A WINTRY MIX... WITH
LESSER CHANCES CLOSER TO THE TRIANGLE AND NIL POINTS SOUTH AND EAST
OF THE ROCKINGHAM TO RALEIGH TO WILSON AREAS.

MODELS HAVE TRENDED TOWARD MORE OF A WINTRY MIX... WITH MORE
FREEZING RAIN AND EVEN SNOW/SLEET OVER THE NW PIEDMONT

CONFIDENCE IN THE PREDOMINATE PRECIP TYPE AND POSSIBLE ACCUMULATIONS
IS STILL LOW GIVEN SOME OF THE DIFFERENCES IN THE EXTEND OF THE
DAMMING... THE SURFACE/850MB LOW TRACK... AND WESTERN
EXTENT/STRENGTH OF THE WARM NOSE.

PRECIPTATION SHOULD END LATE FRIDAY BUT TEMPERATURES SHOULD REMAIN
ABOVE FREEZING FRIDAY AFTERNOON AND NIGHT KEEPING ADDITIONAL
PROBLEMS WITH FREEZING VERY LOW.
-- End Changed Discussion --

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
AS OF 310 PM WEDNESDAY...

DRY AND WARMER THIS WEEKEND. HIGHS RETURN TO THE LOWER TO MID 60S
BOTH SAT-SUN... CONTINUING MONDAY. LOWS GENERALLY MID TO UPPER 30S.

THE NEXT SYSTEM MAY BE DELAYED... BUT TUE-WED THE CHANCE OF RAIN
SHOULD INCREASE AS ANOTHER SOUTHERN BRANCH MID/UPPER LOW APPROACH.
CONTINUED MILD THROUGH MIDWEEK.
-- End Changed Discussion --

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 245 PM WEDNESDAY...

24-HR TAF PERIOD: ASIDE FROM LINGERING MVFR CEILINGS EAST OF I-95
THROUGH 21-00Z...EXPECT VFR CONDITIONS TO PREVAIL THROUGH MOST OF
THE 18Z TAF PERIOD...WITH AN INCREASING CHANCE FOR SUB-VFR CEILINGS
AND PRECIPITATION FROM SOUTH-NORTH THURSDAY AFTERNOON. LIGHT WINDS
WILL BECOME NORTHEAST AT 10-13 KT IN THE WAKE OF A BACKDOOR COLD
FRONT BETWEEN 02-05Z THIS EVENING...REMAINING NORTHEAST AT 10-15 KT
WITH GUSTS UP TO 20 KT DURING THE DAY THU.

LOOKING AHEAD: WIDESPREAD ADVERSE AVIATION CONDITIONS ARE EXPECTED
THURSDAY EVENING INTO FRIDAY AS A LOW PRESSURE SYSTEM TRACKS
NORTHEAST ALONG THE CAROLINA COAST. VFR CONDITIONS WILL RETURN IN
THE WAKE OF THIS SYSTEM OVER THE WEEKEND. -VINCENT

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...VINCENT
SHORT TERM...BADGETT
LONG TERM...BADGETT
AVIATION...+VINCENT