-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 140045
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
845 PM EDT THU MAR 13 2014

.SYNOPSIS...
HIGH PRESSURE CENTERED OVER THE REGION WILL MOVE OFFSHORE ON
FRIDAY. A MOIST SOUTHERLY RETURN FLOW WILL PREVAIL THROUGH
SATURDAY NIGHT...FOLLOWED BY INCREASING CLOUD COVER AND RAIN
ON SUNDAY AS A LOW PRESSURE SYSTEM TRACKS EAST THROUGH THE LOWER
MISSISSIPPI RIVER VALLEY INTO THE DEEP SOUTH.

&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
-- Changed Discussion --
AS OF 845 PM THURSDAY...

...OVERNIGHT...

WINDS WERE BEGINNING TO DIE OFF. DEW POINTS ARE VERY LOW SO
EXCEPTIONAL RADIATIONAL COOLING POTENTIAL. CLEAR SKIES AND LIGHT
WINDS SHOULD LEAD TO LOWS IN THE LOWER TO MID 20S.

FRIDAY...HIGH PRESSURE SLIDES EAST AND A RETURN FLOW
DEVELOPS...ESPECIALLY OVER WESTERN NC WHERE THE PRESSURE GRADIENT IS
STRONGER BETWEEN THE HIGH AND A MODEST 995MB LOW CROSSING THE GREAT
LAKES.  DEWPOINTS WILL RECOVER A BIT INTO THE TEENS AND LOW
20S...BUT WITH HIGHS LIKE TO REACH THE LOWER 60S...RELATIVE HUMIDITY
VALUES WILL STAY IN THE UPPER TEENS AND LOWER 20S FRIDAY AFTERNOON.
WITH WARMING DRIVING THE DRY CONDITIONS...THE NC FOREST SERVICE
SUPPORTS ANOTHER FIRE WEATHER WATCH FOR FRIDAY.  CONDITIONS MAY END
UP BEING BORDERLINE FOR A RED FLAG WARNING...PARTICULARLY CLOSER TO
THE COASTAL PLAIN. SEE FIRE WEATHER SECTION BELOW.

FRIDAY NIGHT...MOISTURE WILL CONTINUE TO INCREASE OVERNIGHT...THOUGH
NOT ENOUGH FOR A GLANCING BLOW FROM A SHORTWAVE OVER THE GREAT LAKES
TO PRODUCE ANY PRECIP.  INSTEAD...FORECAST SOUNDINGS SHOW MOSTLY MID-
LEVEL MOISTURE ABOVE 700MB.  UNDER MORE CLOUD COVER AND A LIGHT
SOUTHWESTERLY WIND...LOWS WILL BE A BIT MILDER IN THE UPPER 30S TO
LOWER 40S.
-- End Changed Discussion --

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
AS OF 250 PM THURSDAY...

FOR SAT/SAT NIGHT: UPCOMING STORM SYSTEM STARTS TO TAKE SHAPE... AS
MID LEVEL TROUGHING DIGS OVER THE FAR SRN PLAINS/NRN MEXICO. A DEEP
VORTEX OVER HUDSON BAY AND CORRESPONDING DIGGING TROUGH COVERING THE
NRN LAKES/ST LAWRENCE VALLEY/NORTHEAST STATES PUSHES AN INITIALLY
DRY BACKDOOR FRONT SOUTHWARD TOWARD NC... WITH A LIKELY FRONTAL
PASSAGE (BASED ON CONSENSUS OF MODEL GUIDANCE) SAT EVENING OR SOON
AFTER MIDNIGHT. AHEAD OF THE FRONT... WEAK SHEARED VORTICITY CROSSES
NC ON THE FAR SOUTH END OF THE AFOREMENTIONED POLAR TROUGH EARLY
SAT... BRINGING MID CLOUDINESS ACROSS THE FORECAST AREA DURING THE
DAY WITH DECENT MOISTURE ABOVE 750 MB NOTED ON FORECAST SOUNDINGS...
IN CONJUNCTION WITH SCATTERED FLAT CU ATOP THE MIXED LAYER. FORECAST
THICKNESSES START OUT ABOUT 10 M ABOVE NORMAL AND WARM FURTHER AHEAD
OF THE APPROACHING BACKDOOR FRONT... SUGGESTING WARM HIGHS IN THE
UPPER 60S TO LOWER 70S... A TAD HIGHER THAN THE PREVIOUS FORECAST
AND IN LINE WITH MODEL RUN-TO-RUN WARMING TRENDS FOR SAT. THE CORE
OF THE INCOMING POLAR HIGH WILL MOVE FROM MANITOBA SLOWLY TOWARD
LAKE SUPERIOR THROUGH SAT NIGHT... STILL FAR TO OUR NW... HOWEVER
ITS VAST EXPANSE AND HIGH DENSITY LOOK TO BE ENOUGH TO PUSH AT LEAST
SOMEWHAT COLDER AIR SOUTHEASTWARD INTO CENTRAL NC SAT NIGHT... AS
THE BACKDOOR FRONT SETTLES JUST SOUTH OF THE STATE. EXPECT
THICKENING AND LOWERING CLOUDS SAT NIGHT AS SOUTHWESTERLY
OVERRUNNING FLOW INCREASES ATOP THE STRENGTHENING SURFACE FRONTAL
ZONE... A RESULT OF THE APPROACHING 850 MB LOW TRACKING INTO THE
LOWER MISS VALLEY. THE NAM/GFS/ECMWF HOLD THE STRONGEST FORCING FOR
ASCENT SW OF THE FORECAST AREA UNTIL AFTER DAYBREAK SUN... AND NAM
FORECAST SOUNDINGS RETAIN RATHER DRY AIR BELOW 850 MB... SO WILL
KEEP JUST A SMALL CHANCE OF RAIN OVER THE SW CWA ONLY LATE SAT
NIGHT. HAVE ADJUST LOWS DOWN SLIGHTLY (MAINLY NORTH) TO 41-47 TO
REFLECT THE COLDER AIR PUSHING INTO THE NRN CWA.

FOR SUNDAY: THE PLAINS TROUGH DEEPENS FURTHER TO THE SSW OVER TX/NE
MEXICO SUNDAY... SENDING POCKETS OF DPVA NORTHEASTWARD TOWARD NC...
JUST AS THE POLAR HIGH CENTER DRIFTS FROM LK SUPERIOR TO LK HURON...
WITH A SURFACE LOW FORMING OVER MS/AL. THE SLOW APPROACH OF THE
DEEPENING 850 MB LOW TO OUR SW OVER THE CENTRAL GULF STATES WILL
LEAD TO FURTHER STRENGTHENING OF THE OVERRUNNING FLOW OVER NC ATOP
THE SLOPED FRONTAL ZONE (MODELS INDICATE 30-40 KTS SRLY FLOW AT 850
MB). WITH THE INCOMING DPVA AND ADDITIONAL HIGHER-ROOTED FORCING FOR
ASCENT WITHIN THE RIGHT ENTRANCE REGION OF THE UPPER JETLET OVER/OFF
THE NORTHEAST STATES... HAVE LITTLE DOUBT THAT WE`LL SEE A WET SUNDAY
WITH RAIN OVERSPREADING CENTRAL NC. THE DEEP LAYER LIFT MAY SUPPORT
LOCALLY HEAVY RAINFALL... ALTHOUGH THE GFS`S STRONGER 850 MB LOW
OVER SE LA CAUSES ITS HEAVIEST RAIN TO FALL TO OUR SOUTH. AT ANY
RATE... MOST PLACES SHOULD SEE MEASURABLE RAIN... AND WILL RAISE
POPS TO CATEGORICAL SUNDAY. EXPECT STEADY TO FALLING THICKNESSES AS
THE RAIN MOVES IN... ALTHOUGH THEY SHOULD REMAIN ABOVE NORMAL WITH
THE BULK OF THE MUCH COLDER AIR STILL TO OUR NORTH. HAVE CUT BACK
SUNDAY HIGHS -- ESPECIALLY NORTH -- TO 51-58... AND WOULD NOT BE
SURPRISED IF SUNDAY HIGHS NEED TO BE BUMPED DOWN FURTHER IN LATER
FORECASTS. -GIH

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 255 PM THURSDAY...

FOR SUNDAY NIGHT-TUE: THE SURFACE LOW IS LIKELY TO WEAKEN OVER AL/GA
AS SECONDARY LOW CENTERS FORM JUST OFF THE GA/SRN SC COAST SUNDAY
NIGHT THROUGH MONDAY... WHILE THE 850 MB LOW SHIFTS EASTWARD PUSHING
THE BETTER MOISTURE FLUX TO OUR EAST. WHILE PRECIP RATES SHOULD BE
RAMPING DOWN DURING THIS PERIOD... THERE WILL REMAIN PLENTY OF DEEP
MOISTURE WITH PERSISTENT LIFT AS THE MID LEVEL TROUGH APPROACHES
WITH LINGERING STRONG UPPER DIVERGENCE... SO WILL MAINTAIN HIGH
CHANCE POPS SUN NIGHT/MON... WITH LOWER CHANCES LINGERING THROUGH
MON NIGHT/TUE AS THE MID LEVEL TROUGH SHIFTS OVER THE REGION.
REGARDING PTYPE... AS THE COASTAL LOWS DEVELOP AND HELP TO REINFORCE
THE NNE LOW LEVEL FLOW INTO NC... THE GFS/ECMWF SHOW THE HEART OF
THE POLAR HIGH HOLDING NORTH OF THE ST LAWRENCE SEAWAY AND
RETREATING FURTHER NORTH MONDAY... WHICH BRINGS INTO QUESTION THE
AVAILABILITY OF COLD AIR THAT WOULD SUPPORT A NON-LIQUID PTYPE. BUT
THE MODELS HAVE BEEN CONSISTENT RUN-TO-RUN AS GFS FORECAST SOUNDINGS
AS WELL AS ECMWF PARTIAL THICKNESSES SUGGEST A TRANSITION LATE SUN
NIGHT/MON TO A WINTRY MIX OF MAINLY SNOW/SLEET. THE ECMWF IS MORE
EMPHATIC WITH ITS COLUMN COOLING THAN THE GFS... TRENDING TO WINTRY
PRECIP OVER 12 HOURS SOONER... BUT THERE IS ENOUGH CONFIDENCE AND
CONSISTENCY BETWEEN THE GFS/ECMWF REGARDING THE SURFACE PATTERN...
APPROACHING TROUGH... AND EVENTUAL THERMAL STRUCTURE TO RETAIN A
MENTION OF WINTRY PRECIP LATE SUN NIGHT THROUGH MONDAY. CERTAINLY A
LOT OF QUESTIONS REMAIN IN THIS LOWER-CONFIDENCE TIME FRAME... AND
WE CAN`T IGNORE THE FACT THAT IT`S MID MARCH AND SIGNIFICANT WINTRY
PRECIP IS QUICKLY BECOMING CLIMATOLOGICALLY UNFAVORABLE. WILL KEEP
IT AS A RAIN/WINTRY MIX FOR NOW... ALTHOUGH STRICT INTERPRETATION OF
FORECAST SOUNDINGS SUPPORTS A PERIOD OF ALL-SNOW OVER PARTS OF
CENTRAL NC... EVEN HEADING INTO MONDAY NIGHT AS THE CORE OF THE MID
LEVEL TROUGH (AND THUS THE HEART OF THE MID LEVEL COLD AIR) TRACKS
OVERHEAD.

FOR TUE NIGHT THROUGH THU: EXPECT MID LEVEL RIDGING BEHIND THE
DEPARTING TROUGH WITH THE COOL (BUT SLOWLY MODIFYING) SURFACE RIDGE
CONTINUING TO STRETCH ACROSS NC FROM THE NORTH. YET ANOTHER BROAD
BUT DEEPENING TROUGH PUSHES THROUGH THE CENTRAL CONUS/GREAT LAKES
REGION WED/THU... AND THE APPROACH OF THE ASSOCIATED COLD FRONT
SHOULD BRING IN A CHANCE OF RAIN LATE WED INTO THU. THE GFS IS MUCH
FASTER THAN THE ECMWF... MAKING WED WETTER THAN THU... SO GIVEN
THIS UNCERTAINTY WILL KEEP POPS IN THE LOW CHANCE RAIN FOR NOW. -GIH

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 700 PM THURSDAY...

24-HR TAF PERIOD: CLEAR SKIES /VFR CONDITIONS/ WILL RULE THROUGH THE
TAF PERIOD IN ASSOCIATION WITH COLD HIGH PRESSURE OVER THE REGION.
NORTHWEST WINDS SUSTAINED AT 10-15 KT WILL RAPIDLY DIMINISH AND
BECOME LIGHT/VARIABLE OR CALM BY 00-01Z THIS EVENING. BY LATE FRIDAY
MORNING TO EARLY FRIDAY AFTERNOON (15-18Z) WINDS WILL BACK TO THE
SOUTHWEST AND INCREASE TO 10-13 KT WITH OCCASIONAL GUSTS UP TO 20 KT
THOUGH GUSTS OF THAT MAGNITUDE MAY BE CONFINED TO THE INT/GSO
TERMINALS.

LOOKING AHEAD: SUB-VFR CONDITIONS WILL BE POSSIBLE SATURDAY MORNING
(PRIMARILY AT THE INT/GSO TERMINALS) IN ASSOC/W A RELATIVELY MOIST
LOW-LEVEL SOUTHERLY RETURN FLOW...THOUGH THE LATEST MODEL GUIDANCE
SUGGESTS A LOWER OVERALL POTENTIAL THAN PRIOR MODEL RUNS. ADVERSE
AVIATION CONDITIONS ARE EXPECTED SUNDAY THROUGH EARLY NEXT WEEK IN
ASSOCIATION WITH A SERIES OF UPPER LEVEL DISTURBANCES AND ATTENDANT
LOW PRESSURE SYSTEMS CROSSING THE REGION FROM THE WEST. -VINCENT

&&

.FIRE WEATHER...
AS OF 305 PM THURSDAY...

WINDS WILL DIE OFF BY SUNSET THIS EVENING...AND THE CURRENT RED FLAG
WARNING WILL EXPIRE AT 6PM.  HIGH PRESSURE OVER THE AREA TONIGHT
WILL SHIFT OFFSHORE AND LEADING TO WARMING ON FRIDAY.  RELATIVE
HUMIDITY VALUES WILL FALL BACK INTO THE UPPER TEENS AND LOWER 20S
ACROSS MOST OF CENTRAL NC.  WINDS WILL BE STRONGEST OVER THE WESTERN
PIEDMONT WHERE GUSTS WILL LIKELY EXCEED 20MPH.  COORDINATION WITH
THE NCFS LEAD TO A FIRE WEATHER WATCH FOR ALL OF CENTRAL NC FOR
FRIDAY.  IT IS POSSIBLE THAT ONLY A PORTION OF CENTRAL NC WILL BE
UPGRADED TO A RED FLAG WARNING.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
FIRE WEATHER WATCH FROM FRIDAY MORNING THROUGH FRIDAY
AFTERNOON FOR NCZ007>011-021>028-038>043-073>078-083>086-088-
089.

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...BADGETT/SMITH
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...VINCENT
FIRE WEATHER...SMITH