Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 231117
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
715 AM EDT WED APR 23 2014

.SYNOPSIS...A COLD FRONT CROSSING THE REGION WILL MOVE OFFSHORE THIS
MORNING. HIGH PRESSURE WILL BUILD IN FROM THE NORTHWEST THROUGH
THURSDAY. ANOTHER COLD FRONT WILL APPROACH FROM THE WEST ON FRIDAY.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
AS OF 305 AM WEDNESDAY...

FOR TODAY/TONIGHT: COLD FRONT CURRENTLY MAKING ITS WAY THROUGH
CENTRAL NC. PATCHY FOG HAS FORMED IN THE COMPARATIVELY LIGHT FLOW
AND HIGHER-DEWPOINT AIR AHEAD OF THE FRONT... BUT EXPECT CLEAR SKIES
WITH RAPID DRYING BEHIND THE FRONT ALONG WITH A WIND SHIFT TO WNW
THEN NW. STRONG SHORTWAVE TROUGH AND VORTICITY MAX PASSAGE OVER THE
NORTHEAST AND MIDATLANTIC COAST MAY BRING A FEW CLOUDS ACROSS
NORTHEAST SECTIONS... BUT OTHERWISE SKIES WILL BE GENERALLY CLEAR
TODAY WITH A DRY AND STABLE COLUMN NOTED UPSTREAM AND ON FORECAST
SOUNDINGS. THICKNESSES INDICATE HIGHS OF 68-74. BRISK WINDS FROM THE
NW ARE EXPECTED TO BE SUSTAINED AT 13-18 MPH WITH PERIODIC GUSTS TO
20-25 MPH. THIS WIND COMBINED WITH THE DROP IN HUMIDITY TO AROUND
25% WILL BRING ABOUT A RISK FOR ADVERSE FIRE BEHAVIOR (SEE
DISCUSSION BELOW). CONTINUED CLEAR TONIGHT WITH LIGHT WINDS AS THE
HIGH PRESSURE RIDGE NOSES IN FROM THE NORTH. LOWS TONIGHT 37-44...
COLDEST IN THE VA BORDER COUNTIES AND IN OUTLYING AREAS OF NRN
PIEDMONT. THE POTENTIAL EXISTS FOR PATCHES OF FROST IN THESE
ISOLATED SPOTS... BUT EVEN THESE COLDER LOWS ARE A BIT ABOVE WHAT WE
NORMALLY NEED FOR A FROST ADVISORY... SO WILL HOLD OFF FOR NOW A
REASSESS THE NEED LATER TODAY.

FOR THU/THU NIGHT: ANOTHER GENERALLY CLEAR DAY EXPECTED... WITH
ANOTHER REINFORCING FRONT DROPPING THROUGH FROM THE NORTH TO KNOCK
THICKNESSES BACK DOWN TO READINGS NEARLY 30 M BELOW NORMAL. DESPITE
PLENTY OF SUNSHINE WITH A SURFACE RIDGE NOSING IN FROM THE NORTH AND
WEAK MID LEVEL RIDGING BUILDING IN FROM THE WEST... WE SHOULD SEE
BELOW-NORMAL HIGHS OF 67-73. A WARM FRONTAL ZONE WILL APPROACH
CENTRAL NC FROM THE SW LATE THU NIGHT... RESULTING IN A
STRENGTHENING FLOW FROM THE SW AND QUICKLY INCREASING LOW LEVEL
MOISTURE FROM SW TO NE. MOIST ISENTROPIC UPGLIDE RAMPS UP AROUND
295K ESPECIALLY IN THE SW HALF OF THE CWA... SO WILL TREND TOWARD
INCREASING CLOUDINESS AREAWIDE AND MENTION PATCHY DRIZZLE OVER THE
FAR SW CWA (INCLUDING WINSTON-SALEM / ASHEBORO / ALBEMARLE /
WADESBORO / LAURINBURG) LATE THU NIGHT. MILDER LOWS OF 46-53. -GIH

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 325 AM WEDNESDAY...

A PROGRESSIVE SHORTWAVE AND ASSOCIATED SURFACE FRONTAL ZONE WILL
MOVE INTO THE TENNESSEE AND OHIO VALLEYS FRIDAY MORNING...THEN
ACROSS THE MOUNTAINS DURING THE DAY ON FRIDAY.  MODEL SOLUTIONS HAVE
ACTUALLY DIVERGED A BIT REGARDING THE TIMING OF THE BEST FORCING AND
SUBSEQUENT QPF.  THE GFS CONTINUES TO BE THE FASTER SOLUTION...WITH
THE UPPER TROUGH AND LOBE OF VORTICITY MOVING ACROSS CENTRAL NC BY
MIDDAY...WHILE THE TRAILING FRONTAL ZONE CROSSES THE AREA DURING THE
AFTERNOON AND EVENING.  THIS SEEMS TO SUGGEST POSSIBLE SHOWERS
EARLIER IN THE DAY LESS POTENTIAL FOR HEATING AND DESTABILIZATION
AHEAD OF THE FRONT.  THE ECWMF HAS TRENDED SHARPER AND A BIT DEEPER
WITH THE TROUGH...WHICH LEADS TO A SLOWER SOLUTION BUT BETTER
HEATING...PARTICULARLY OVER THE COASTAL PLAIN.  LOW-LEVEL MOISTURE
RETURN AHEAD OF THE FRONT IS WEAK BUT SHOULD ALLOW DEWPOINTS TO RISE
INTO THE UPPER 50S AND LOWER 60S...WHICH COMBINED WITH FORECAST
HIGHS IN THE 75-81 RANGE BUT WEAK MID-LEVEL LAPSE RATES...SHOULD
YIELD WEAK INSTABILITY...MAYBE 500-1000 J/KG MAINLY ACROSS THE SOUTH
AND EAST. DEEP LAYER IS FORECAST TO BE ON THE ORDER OF 25-
35KT...THOUGH STRONGEST TO THE NORTH AWAY FROM BETTER INSTABILITY.
POTENTIAL FOR SEVERE SEEMS LIMITED GIVEN THE MARGINAL
SHEAR/INSTABILITY...BUT THE SLOWER TREND WITH THE ECMWF AND STRONGER
DCVA WOULD SUPPORT A LITTLE BETTER CHANCE.  GIVEN THAT THE MID-LEVEL
FLOW WILL BE WESTERLY AND DRYING...WILL KEEP POPS IN THE CHANCE
RANGE WITH HIGHS IN THE MID 70S WEST TO LOWER 80S EAST.

THE COLD FRONT SHOULD PUSH EAST OF THE CWA BY MIDNIGHT FRIDAY NIGHT
AND BRING PRECIP CHANCES TO AN END.  A SECONDARY FRONTAL ZONE IS
FORECAST TO APPROACH BUT REMAIN NORTH OF THE AREA. THUS THE MAIN
SENSIBLE IMPACT WILL BE LOWER HUMIDITY ON SATURDAY...WITH FORECAST
HIGHS IN THE UPPER 70S AND LOWER 80S.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
AS OF 325 AM WEDNESDAY...

THE PROGRESSIVE FLOW OVER THE CONUS THIS WEEK IS FORECAST TRANSITION
TO A MORE AMPLIFIED AND EVEN BLOCKED FLOW NEXT WEEK...THOUGH THE GFS
AND ECMWF DONT YET AGREE ON THE DEGREE OF BLOCKING IN THE FLOW.
IN GENERAL...A STRONG TROUGH WILL EJECT OUT OF THE SOUTHERN PLAINS
THIS WEEKEND AND THEN LIKELY CLOSE OFF INTO AN UPPER LOW OVER THE
MIDWEST STATES BY MONDAY.....WITH ANOTHER LOW OVER THE NORTHERN
ATLANTIC AND A SHORTWAVE RIDGE IN BETWEEN.   THE BIG QUESTION WILL
BE WHERE A FRONTAL ZONE TO OUR NORTH ENDS UP ON SUNDAY AND THEN HOW
QUICKLY PRECIP SPREADS EAST ALONG THE FRONT MONDAY AND TUESDAY AS
THE UPPER LOW MOVES SLOWLY TO THE EAST.  THE GFS SUGGEST THE FRONT
WILL UNDERCUT THE UPPER RIDGE AND SLIP BACKDOOR INTO THE AREA BY
SUNDAY...WHILE THE ECMWF KEEP THE FRONT WELL NORTH OF NC.  PRECIP
CHANCES SHOULD INCREASE DRAMATICALLY BY TUESDAY AS THE UPPER LOW
FINALLY MOVES EAST OF THE MISSISSIPPI RIVER.  TEMPS DURING THE TIME
FRAME WILL BE MOSTLY AROUND NORMAL...THOUGH UNCERTAINTY GROWS INTO
MONDAY AND TUESDAY AS THE POTENTIAL FOR CLOUD COVER AND PRECIP GROW.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AS OF 715 AM WEDNESDAY...

A COLD FRONT WILL SWEEP ESE THROUGH CENTRAL NC THIS MORNING. HIGH
CONFIDENCE IN VFR CONDITIONS TODAY THROUGH TONIGHT... WITH FEW TO NO
CLOUDS AND NO FURTHER RESTRICTIONS TO VSBYS AS HIGH PRESSURE BUILDS
IN FROM THE NW. OF SOME CONCERN HOWEVER IS THE SHIFT OF WINDS WITH
FRONTAL PASSAGE TO NORTHWESTERLY. SUSTAINED WINDS OF 12-16 KTS MAY
GUST UP TO 20-25 KTS FROM DAYBREAK THROUGH LATE AFTERNOON. THIS MAY
CAUSE CROSSWIND PROBLEMS AT GSO/RDU/RWI/FAY TODAY. WINDS WILL
DIMINISH SOON AFTER 22Z.

LOOKING BEYOND 12Z THU MORNING: CONTINUED VFR THROUGH THU EVENING
WITH A HIGH PRESSURE RIDGE IN PLACE ACROSS CENTRAL NC. A WARM FRONT
WILL APPROACH FROM THE SW THU NIGHT... BRINGING WINDS FROM THE SW
AND A GOOD CHANCE OF IFR CONDITIONS... WHICH SHOULD GRADUALLY
IMPROVE TO MVFR FRI MORNING WITH SCATTERED SHOWERS AND STORM FROM
FRI MORNING INTO THE AFTERNOON. A COLD FRONT WILL THEN MOVE THROUGH
BY FRI EVENING... WITH HIGH PRESSURE TO FOLLOW... BRINGING LIGHT
WINDS AND VFR CONDITIONS OVER THE WEEKEND. -GIH

&&

.FIRE WEATHER /TODAY THROUGH EARLY THIS EVENING/...
AS OF 330 AM WEDNESDAY...

...INCREASED FIRE DANGER TODAY DUE TO GUSTY WINDS AND LOW HUMIDITY...

A COLD FRONT WILL PUSH SOUTHEAST OF THE AREA THIS MORNING.
INCREASING WINDS FROM THE NORTHWEST SUSTAINED AT 12-18 MPH WILL
GUSTS OCCASIONALLY TO AS HIGH AS 22-29 MPH. THESE WINDS... COMBINED
WITH MINIMUM RELATIVE HUMIDITY VALUES OF 21-27 PERCENT... AND
SOMEWHAT LOW FINE FUEL MOISTURE IN THE 7-8% RANGE... WILL POSE A
THREAT FOR ADVERSE FIRE BEHAVIOR TODAY. WILL REISSUE A SPECIAL
WEATHER STATEMENT ADDRESSING THE INCREASED FIRE DANGER... AND WILL
CONTINUE THE HEADLINE IN PRE-SUPPRESSION FIRE WEATHER PRODUCTS.

THE RH WILL BE A BIT HIGHER ON THU... WITH LIGHTER WINDS... HOWEVER
THE FINE FUELS ARE LIKELY TO BE EVEN DRIER. THEREFORE... THOSE
INVOLVED IN OUTDOOR BURNING SHOULD CONTINUE TO USE EXTRA CAUTION.

&&

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

&&

$$

SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...SMITH
LONG TERM... SMITH
AVIATION...HARTFIELD
FIRE WEATHER...HARTFIELD



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