Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 231152
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
652 AM EST FRI JAN 23 2015

.SYNOPSIS...HIGH PRESSURE WILL BUILD ACROSS VA AND NC THIS MORNING.
MEANWHILE...A LOW PRESSURE SYSTEM WILL TRACK JUST INLAND OF THE
SOUTHEAST US COAST THROUGH TONIGHT...THEN OFFSHORE THE MIDDLE
ATLANTIC AND NEW ENGLAND COAST ON SATURDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 330 AM FRIDAY...

A POSITIVELY TILTED TROUGH OVER THE SOUTHERN  PLAINS WILL CONTINUE
TO MOVE EAST ACROSS THE GULF COAST STATES TODAY AND THEN BEGIN TO
LIFT ACROSS THE CAROLINAS LATER TONIGHT.  CYCLOGENESIS APPEARS TO BE
UNDERWAY SOUTH OF NEW ORLEANS THIS MORNING... AND THIS LOW FORECAST
IS TO TRACK ACROSS SOUTHERN GEORGIA AND UP THE CAROLINA COASTAL AREA
TONIGHT.

A LARGE AREA RAIN IS CURRENTLY SPREADING ACROSS ALABAMA AND
GEORGIA...WITH A FEW RADAR ECHOES AND TRACE REPORTS AS FAR EAST AS
AIKEN GEORGIA...BUT THE LEADING EDGE STILLS APPEARS TO BE DWINDLING
AS IT ENCOUNTERS THE DRIER AIR ASSOCIATED WITH A 1030MB SURFACE HIGH
CENTERED OVER SOUTHEAST VIRGINIA.  THE HRRR HAS A PRETTY GOOD HANDLE
ON THIS AND SUGGESTS MEASURABLE PRECIP MAY REACH THE SOUTHERN
PIEDMONT BY 15Z.  THE WETBULB FREEZING LINE IS CURRENTLY NEAR
HIGHWAY 64 AND SHOULDN`T MOVE MUCH MORE TO THE SOUTH AS  MID CLOUDS
CONTINUE TO POUR IN FROM THE WEST AND TEMPS STABILIZE.  RAP
SOUNDINGS SHOW JUST ENOUGH WARMING PRIOR TO THE ARRIVAL OF PRECIP TO
KEEP ALL PRECIP LIQUID AT ONSET.

ISENTROPIC LIFT REALLY INCREASES BY 18Z AND EXPECT RAIN TO BE
WIDESPREAD ACROSS THE ENTIRE AREA AFTER 21Z....WITH THE HEAVIEST
RAINFALL OCCURRING BETWEEN 00Z AND 06Z AS A 50KT LOW LEVEL JET
SURGES ACROSS CENTRAL AND EASTERN NC. THERE ARE STILL SOME
DIFFERENCE IN THE TRACK OF THE SURFACE LOW...THE ECMWF A GOOD 50 TO
75 MILES FURTHER INLAND THAN THE GFS.  PREFERENCE IS FOR THE MORE
EASTERN TRACK OF THE GFS AND NAM GIVEN THAT A STRONG CAD AIRMASS
WILL DEVELOP IN RESPONSE TO THE RAIN THIS AFTERNOON. THE WEDGE FRONT
WILL LIKELY SHIFT INLAND AS THE LOW APPROACHES BUT THE TRUE WARM
SECTOR SHOULD REMAIN CONFINED TO THE COAST WHERE ANY SEVERE THREAT
WOULD ALSO REMAIN.

MODEL QPF IS RATHER HIGH TONIGHT...WITH AS MUCH AS ONE INCH IN THE
WEST AND NEAR 2 INCHES EAST OF I-95...AND THIS SEEMS VERY REASONABLE
GIVEN PW INCREASING TO AS MUCH AS 200 PERCENT OF NORMAL AND A
PLETHORA OF 1 TO 2 INCH TOTALS ALREADY REPORTED UPSTREAM ACROSS
LOUISIANA AND MISSISSIPPI.  CONTEMPLATED A FLOOD WATCH GIVEN RECENT
RAINFALL EVENTS AND SOIL MOISTURE...BUT WITHOUT CONVECTION THE
FLOODING MAY MAY ISOLATED TO SOME OF THE SMALL CREEKS AND STREAMS
THAT ARE ALREADY RUNNING HIGHER THAN NORMAL.  SOME MINOR RIVER
FLOODING IS ALSO POSSIBLE ON THE NEUSE AND TAR RIVERS.

TEMPS WILL RISE A LITTLE TODAY...MORE SO IN THE EAST...BUT AS PRECIP
MOVES IN THEY WILL LEVEL OFF OR EVEN DROP A BIT...WITH HIGHS INLY
REACHING THE MID 30S NORTHWEST TO MID 40S SOUTHEAST.  TEMPS WON`T
CHANGE MUCH OVERNIGHT...DROPPING MAYBE 2 TO 3 DEGREES.


&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 330 AM FRIDAY...

MODELS DEPICT A BRIEF PERIOD OF MID-LEVEL DRYING AS A DRY SLOT
SURGES ACROSS THE AREA LATE TONIGHT...BUT THE ARRIVAL OF THE UPPER
TROUGH AND STRONGER DCVA SHOULD CAUSE PRECIP TO REDEVELOP OR
REINTENSIFY EARLY SATURDAY...MAINLY ACROSS THE EASTERN HALF OF THE
AREA.  RAINFALL TOTALS MAY NOT BE AS HIGH WITH THE SURFACE LOW
HAVING MOVED OFF TO THE NORTHEAST...BUT MODELS SHOW ANOTHER HALF
INCH POSSIBLE PRIOR TO 15Z.  PRECIP WILL THEN END FOR MUCH OF THE
AREA AS MORE PRONOUNCED DRYING ALOFT DEVELOPS.  HOWEVER... A
DEFORMATION BAND EXPECTED TO DEVELOP OVER THE TENNESSEE VALLEY WILL
PIVOT ACROSS AT LEAST THE NORTHERN HALF OF THE AREA AROUND MIDDAY.
RAPID MID-LEVEL COOLING AND RESATURATION OF THE ICE-NUCLEATION ZONE
SUGGESTS RAIN COULD MIX WITH OR CHANGE OVER TO SNOW WITHIN THIS
BAND...BUT FORECAST SOUNDINGS HAVE THE LOWEST 2000 FT OF THE
BOUNDARY LAYER ABOVE FREEZING AND THIS MAY BE TOO MUCH MELTING TO
OVERCOME.  WILL BE INTERESTING TO SEE HOW THIS UNFOLDS...THOUGH NO
IMPACTS WOULD BE EXPECTED.

THE BAND SHOULD DEPART THE NORTHEAST CWA BY 18Z TO 21Z...WITH CLEAR
SKIES BY 00Z TO 03Z.  COLD ADVECTION WILL BE RELATIVELY STRONG
SATURDAY EVENING...RESULTING WIND GUSTS OF 20-25MPH FOR THE FIRST
HALF OF THE NIGHT.  LOWS WILL DROP INTO THE LOW TO MID 30S.  -BLS

SUN AND SUN NIGHT: A STRONG PACIFIC JET WILL ROUND A WESTERN CONUS
RIDGE AND CAUSE AN ASSOCIATED NORTHERN STREAM SHORTWAVE TROUGH TO
AMPLIFY SHARPLY FROM THE NORTHERN PLAINS TO THE CAROLINAS AND VA
THROUGH SUN NIGHT. A CLIPPER SURFACE LOW WILL ACCOMPANY THE
SHORTWAVE TROUGH AND CROSS THE UPPER MIDWEST AND OH VALLEY SUN AND
THE CENTRAL APPALACHIANS AND MIDDLE ATLANTIC STATES SUN NIGHT. WSW
LOW LEVEL FLOW AHEAD OF THE CLIPPER LOW...AND IN BRIEF SHORTWAVE
RIDGING BETWEEN THIS SHORTWAVE TROUGH AND AN INTENSE CYCLONE
APPROACHING NOVA SCOTIA (OUR FRI-SAT WEATHER MAKER)...WILL RESULT IN
A MOSTLY SUNNY AND MILD DAY IN THE 50S TO END THE WEEKEND.

THE PASSAGE OF THE SHORTWAVE TROUGH AND ASSOCIATED COLD POOL ALOFT
CHARACTERIZED BY H5 TEMPERATURES AROUND MINUS 30 - AND POCKET OF MID
LEVEL LAPSE RATES AROUND 7 C/KM - WILL CAUSE AN AREA OF SHOWERS TO
PIVOT EAST ACROSS CENTRAL NC OVERNIGHT. ALL LIQUID IS ANTICIPATED
OWING TO A 1500-3000 FT DEEP ABOVE FREEZING BOUNDARY LAYER...LOWEST
AND COLDEST ONCE THE SHOWERS ARE MOVING OUT. LOWS...AND WITH
CLEARING SPREADING INTO THE PIEDMONT BY DAYBREAK...WITHIN A FEW
DEGREES EITHER SIDE OF 35.  -MWS

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 345 AM FRIDAY...

JUST AS QUICKLY AS THE CLOUDINESS AND SHOWERS ASSOCIATED WITH THE
"ALBERTA CLIPPER"/NORTHERN STREAM SHORTWAVE WAVE MOVE OUT...
ADDITIONAL SHEAR VORTICITY IN FAST NW FLOW ALOFT WILL AMPLIFY INTO
THE TROUGH BASE...TO NEAR AND JUST OFFSHORE THE COAST OF THE
CAROLINAS...THROUGH WED MORNING. TYPICAL MEDIUM RANGE TIMING AND
AMPLITUDE DISTANCES BECOME MAGNIFIED DURING THIS TIME...WITH THE 00Z
ECMWF REPRESENTING THE SOUTHERNMOST - AND CONSEQUENTLY RELATIVELY
WETTEST FOR CENTRAL NC - SOLUTIONS FOR THE PERIOD MON-TUE. BASED ON
A PREFERRED SLIGHTLY LESS AMPLIFIED/MORE NORTHWARD CONSENSUS OF
MODEL CLUSTERING REPRESENTED WELL BY THE 00Z GFS...THE RELATIVE
HIGHEST PROBABILITY OF PRECIPITATION (IN THE CHANCE RANGE) SHOULD BE
CENTERED TOWARD THE NORTHEAST PIEDMONT WITH THE ARRIVAL OF THE LEAD
SHEAR VORTICITY AND POSSIBLE INTERACTION WITH A LOW LEVEL MOIST AXIS
OVER EASTERN NC THROUGH MON NIGHT. ANY PRECIPITATION THAT WERE TO
FALL AFTER DARK MON...AFTER TEMPERATURES PEAK IN THE UPPER 40S TO
LOWER 50S...WOULD BE IN THE FORM OF LIGHT SNOW OWING TO STRONG DEEP
LAYER COOLING MON NIGHT - A CASE OF "THE COLD AIR CHASING THE
MOISTURE".

TRAILING SHEAR VORTICITY WILL CARVE THE TROUGH OFF THE COAST OF THE
CAROLINAS TUE-TUE NIGHT. ASSOCIATED RE-STEEPENING OF THE LAPSE RATES
ALOFT...AND LIFT/MOISTENING OF THE COLUMN...WILL RESULT IN YET
ANOTHER SLIGHT TO CHANCE OF RAIN SHOWERS - OR SNOW SHOWERS WHERE/IF
THE SUB-CLOUD LAYER FULLY WET-BULBS AND THEORETICALLY "MELTS OUT" A
PROJECTED 1500-2000 FT ABOVE FREEZING BOUNDARY LAYER.  THE REMAINDER
OF THE LONG TERM WILL BE DRY AND CHILLY... PARTICULARLY WITH RESPECT
TO LOWS BOTH WED AND THU MORNINGS...AS MODIFIED ARCTIC HIGH PRESSURE
DRIFTS OVERHEAD IN THE WAKE OF THE TROUGH AXIS MOVING AWAY FROM THE
NC COAST.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
AS OF 650 AM FRIDAY...

VFR CONDITIONS...UNDER THE INFLUENCE OF CONTINENTAL POLAR HIGH
PRESSURE BUILDING EAST ACROSS THE VIRGINIAS THIS MORNING...WILL
PREVAIL UNTIL MIDDAY-EARLY AFTERNOON...AT WHICH TIME LIFT AND
MOISTURE WILL HAVE SUFFICIENTLY INCREASED AND CAUSED RAIN AND
ASSOCIATED MVFR CEILINGS AND VISIBILITIES TO OVERSPREAD OUR AREA
DOWNSTREAM OF A STORM SYSTEM APPROACHING FROM THE NORTHERN GULF OF
MEXICO. RAIN INTENSITY WILL FURTHER INCREASE...AND AVIATION
CONDITIONS FURTHER DETERIORATE TO LIFR-IFR...THROUGH THE AFTERNOON
AND EVENING. IN ADDITION...THE ARRIVAL OF AN EAST SOUTHEASTERLY TO
SOUTHERLY LOW LEVEL JET AT 2000 FT...ATOP MUCH LIGHTER EASTERLY
WINDS AT THE SURFACE...WILL PROMOTE A GOOD CHANCE OF LOW LEVEL WIND
SHEAR CONDITIONS AT EASTERN TERMINALS THIS EVENING. PERIODS OF RAIN
AND DRIZZLE...AND LIFR CONDITIONS...WILL CONTINUE OVERNIGHT...AS THE
LOW PRESSURE SYSTEM TRACKS JUST INLAND OF THE COAST OF THE
CAROLINAS.

OUTLOOK: RAIN WILL LINGER THROUGH MIDDAY SAT...WHILE CEILINGS AND
VISIBILITIES GRADUALLY RISE THROUGH MVFR RANGE...TO VFR BY
AFTERNOON...AS THE LOW PRESSURE SYSTEM TRACKS UP THE MIDDLE ATLANTIC
COAST AND AWAY FROM CENTRAL NC. A COUPLE OF UPPER LEVEL DISTURBANCES
WILL BRING A RENEWED CHANCE OF BRIEF SUB-VFR CONDITIONS AND RAIN
SHOWERS TO THE AREA SUN NIGHT-MON NIGHT...THE LATTER OF WHICH COULD
MIX WITH OR CHANGE TO LIGHT SNOW AS COLDER TEMPERATURES ARRIVE BY
MON EVENING.

&&

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

&&

$$

SYNOPSIS...MWS
NEAR TERM...BLS
SHORT TERM...BLS/MWS
LONG TERM...MWS
AVIATION...MWS


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