Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 010655
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
255 AM EDT WED OCT 01 2014

.SYNOPSIS...WEAK HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE
NORTH TODAY THROUGH THURSDAY. A COLD FRONT WILL APPROACH FROM THE
WEST LATE FRIDAY... AND SWEEP EAST THROUGH THE AREA FRIDAY NIGHT
INTO SATURDAY MORNING. COOL HIGH PRESSURE WILL PUSH IN FROM THE WEST
SATURDAY AFTERNOON THROUGH SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 235 AM WEDNESDAY...

FOR TODAY: AS WAS THE CASE LAST NIGHT... THE MOST IMMEDIATE CONCERN
IS THE DEVELOPMENT OF DENSE FOG EARLY THIS MORNING... FOSTERED BY
CLEAR SKIES AND CALM WINDS. THUS FAR THE LOWEST VSBYS HAVE BEEN OVER
NORTHERN SECTIONS OF THE FORECAST AREA. RECENT HRRR MODEL RUNS SHOW
THIS FOG/STRATUS SPREADING OVER NEARLY THE ENTIRE FORECAST AREA OVER
THE NEXT COUPLE OF HOURS... AND NOT IMPROVING UNTIL THE 14Z-16Z TIME
FRAME... REASONABLE CONSIDERING THE SLOW DISPERSION SEEN YESTERDAY.
A DENSE FOG ADVISORY WILL LIKELY BE NEEDED FOR A LARGE CHUNK OF
CENTRAL NC THROUGH MID MORNING. WE SHOULD ALSO SEE POCKETS OF VERY
LIGHT MIST WITHIN THE MORE DENSE FOG. THE DISSOLUTION OF THE
FOG/STRATUS WILL POST THE NEXT CHALLENGE... GIVEN YESTERDAY`S SLOW
IMPROVEMENT... AND WILL FOLLOW PERSISTENCE AS WELL AS THE HRRR
TRENDS AND SHOW SLOWLY INCREASING SUNSHINE DURING THE LATE MORNING
AND EARLY AFTERNOON... WITH THE SUN BREAKING THROUGH LAST OVER THE
NORTHERN TIER. EXPECT A FEW HIGH THIN CLOUDS TO SPREAD OVER THE AREA
LATE THIS AFTERNOON. THESE CLOUDS... NOTED ON IR AND WATER VAPOR
IMAGERY... NOW EXTEND OVER TN INTO THE LOWER MISS VALLEY AND ARE
ASSOCIATED WITH A WEAK WAVE UNDERCUTTING THE WEAK MID LEVEL RIDGE
BUILDING IN FROM THE WEST. OVERALL... THIS EQUATES TO A TREND FROM
DAYBREAK FOG/STRATUS TO PARTLY THEN MOSTLY SUNNY SKIES. THICKNESSES
ARE 5-10 M HIGHER THAN NORMAL... SO EXPECT HIGHS FROM THE UPPER 70S
TO NEAR 80 OVER PIEDMONT (WHERE CLOUDS SHOULD LINGER THE LONGEST) TO
THE LOWER 80S ELSEWHERE.

FOR TONIGHT: MOSTLY CLEAR SKIES IN THE EVENING SHOULD GIVE WAY TO
ANOTHER ROUND OF PATCHY FOG/STRATUS... LIKELY LESS WIDESPREAD AND
LESS DENSE THAN THIS MORNING OR YESTERDAY. IN ADDITION TO THE FEW
HIGH CLOUDS PASSING OVERHEAD... NAM/GFS BUFR SOUNDINGS INDICATE A
SHOT OF MOISTURE IN THE 925-700 MB LAYER ASSOCIATED WITH SUBTLE MASS
CONVERGENCE ALONG A WEAK LOW-MID LEVEL RETREATING WARM FRONT. THE
NAM IS MUCH MORE BULLISH WITH SUCH CLOUDS THAN THE GFS... SO SOME
UNCERTAINTY REGARDING EXTENT AND COVERAGE REMAINS. BUT IF THESE
CLOUDS COME TO PASS... THEY WOULD MITIGATE FOG DEVELOPMENT TONIGHT.
WILL REFRAIN FROM INCLUDING FOG IN THE FORECAST FOR NOW... AS IT
COULD SIMPLY BE LIGHT FOG. WILL SHOW A TREND TO PARTLY CLOUDY SKIES
TONIGHT ESPECIALLY ACROSS THE NORTH AND NE. MILD LOWS OF 58-62. -GIH

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 250 AM WEDNESDAY...

FOR THU/THU NIGHT: THE MID LEVEL CLIPPER LOW CONTINUES MOVING OFF
THE NORTHEAST COAST THU/THU NIGHT... WHILE DEEP AND AMPLIFYING MID
LEVEL TROUGHING SHIFTS EAST OVER THE PLAINS.... AND THIS WILL BRING
A MODEST MID LEVEL RIDGE OVER NC. THE SURFACE HIGH CENTERED OVER THE
CANADIAN MARITIMES WILL CONTINUE TO EXTEND WEAKLY TO THE SW/SOUTH
INTO NC... ALTHOUGH ITS SOUTHERN END WILL START TO WEAKEN AND SHIFT
A BIT TO THE NE IN RESPONSE TO THE ENCROACHING WARM SECTOR AND
SLOWLY INCREASING LOW LEVEL WINDS FROM THE SW. EXPECT FAIR TO PARTLY
CLOUDY SKIES AS LOW LEVEL MOISTURE TRANSPORT STRENGTHENS (ESPECIALLY
OVER THE WESTERN HALF OF NC). THE MODELS DEVELOP PATCHES OF VERY
LIGHT PRECIP OVER CENTRAL/ERN NC EARLY THU THROUGH THU AFTERNOON...
WITH ADDITIONAL LIGHT PRECIP MAINLY OVER THE VA PIEDMONT THU NIGHT.
WITH THE MID LEVELS STILL DRY WITH SUBSIDENCE WITHIN THE RIDGE
ALOFT... ANY MOISTURE AND FORCING FOR ASCENT WOULD BE ROOTED VERY
LOW. AND AT THIS TIME... WE DON`T QUITE SEE THE LIFT AND MOISTURE
NECESSARY FOR ANYTHING BETTER THAN SPRINKLES. THUS... WILL LEAVE
POPS UNDER 15% AND MENTION NOTHING GREATER THAN SPRINKLES.
THICKNESSES INCH UP FURTHER... SUGGESTING HIGHS NEAR 80 TO 84
(COOLER READINGS NORTHEAST). LOWS MAINLY IN THE LOW 60S... AND WE
SHOULD SEE AREAS OF CLOUDS AND LIGHT FOG THU NIGHT AHEAD OF THE
INCOMING STORM SYSTEM. -GIH

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 250 AM WEDNESDAY...

FRIDAY AND FRIDAY NIGHT: A DEEPENING UPPER LEVEL LOW OVER THE UPPER
MID-WEST WILL MOVE EASTWARD FRIDAY AND FRIDAY NIGHT...WHILE THE
TROUGH DIGS SOUTH INTO THE OH/TN RIVER VALLEY. A POTENT COLD FRONT
WILL ACCOMPANY THE SURFACE TROUGH APPROACHING THE REGION FRIDAY AND
FRIDAY NIGHT AS THE LOW CONTINUES ITS NORTHWARD TREK INTO CANADA.
THE MODELS ARE STILL IN GOOD AGREEMENT WITH BOTH THE TIMING OF THE
FRONT AND THE PRECEDING CONVECTION. THERE HAS BEEN LITTLE CHANGE IN
THE MODELS SINCE THE LAST FORECAST UPDATE...THUS HAVE KEPT RAINFALL
CHANCES AND AMOUNTS NEARLY THE SAME. EXPECT CHANCES TO INCREASE FROM
NW TO EAST LATE FRIDAY MORNING THROUGH FRIDAY EVENING...DECREASING
AGAIN THROUGH EARLY SATURDAY MORNING AS THE COLD FRONT MOVES INTO
THE AREA. ALTHOUGH THERE IS DESCENT SHEAR AND LOW LEVEL LAPSE
RATES...THE WEAK INSTABILITY AND MID-LEVEL LAPSE RATES...COMBINED
WITH THE LATE DIURNAL TIMING...SHOULD MINIMIZE THE SEVERE THREAT.
EXPECT HIGHS GENERALLY IN THE MID 70S TO LOW 80S AND LOWS MAINLY IN
THE MID 50S NW TO MID 60S SE...ALTHOUGH BOTH WILL BE DEPENDENT ON
THE CONVECTION AND TIMING OF THE FRONT.

SATURDAY THROUGH TUESDAY: THE COLD FRONT WILL MOVE THROUGH THE
REGION BY SATURDAY EVENING...WITH COOLER AND DRIER AIR MOVING IN
BEHIND IT AS HIGH PRESSURE BUILDS IN. ONCE THE PRE-FRONTAL
CONVECTION MOVES OUT OF THE AREA...THE REST OF THE WEEKEND SHOULD
REMAIN DRY. THE UPPER LEVEL TROUGH WILL LINGER OVER THE ATLANTIC
COAST...WITH POSSIBLE DISTURBANCES YIELDING A SLIGHT CHANCE FOR SOME
RAIN MONDAY AND TUESDAY. ASIDE FROM THAT...THE REMAINDER OF THE
FORECAST SHOULD ALSO BE MOSTLY DRY. HOWEVER...THERE IS QUITE A BIT
MORE UNCERTAINTY AND DISAGREEMENT BETWEEN THE MODELS IN THIS PART OF
THE FORECAST...THUS CONFIDENCE IS LOW AT THIS TIME. HIGHS SATURDAY
WILL AGAIN BE DEPENDENT ON THE FRONT...BUT FOR NOW EXPECT MID 60S NW
TO MID 70S SE WHILE LOWS SATURDAY NIGHT WILL BE QUITE A BIT COOLER
THAN PREVIOUS NIGHTS...MID 40S NW TO LOW 50S SE. HIGHS ON SUNDAY
SHOULD BE THE LOWEST OF THE EXTENDED PERIOD...MID 60S TO LOW 70S.
HIGHS MONDAY AND TUESDAY WILL BE GENERALLY IN THE LOW TO MID 70S.
MEANWHILE...LOWS SHOULD INCREASE FROM THE UPPER 40S TO LOW 50S
SUNDAY NIGHT INTO THE LOW TO MID 50S MONDAY AND TUESDAY NIGHTS.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
AS OF 125 AM WEDNESDAY...

CHANCES ARE GOOD FOR IFR/LIFR CONDITIONS AT RDU/RWI/FAY UNTIL MID
MORNING. THE COMBINATION OF MOSTLY CLEAR SKIES AND CALM WINDS HAS
PROMPTED FORMATION OF AREAS OF FOG... DENSE IN SPOTS. THIS FOG IS
EXPECTED TO FILL IN ACROSS MUCH OF CENTRAL AND ERN NC OVER THE NEXT
FEW HOURS... HOLDING THROUGH 14Z OR 15Z BEFORE SLOWLY DISPERSING.
THERE IS MUCH MORE UNCERTAINTY AT INT/GSO... WHERE FOG IS CURRENTLY
LIGHT/PATCHY... AND HIGH-RES MODEL OUTPUT PLACES THE WESTERN EDGE OF
THE FOG/STRATUS JUST EAST OF THE TRIAD AREA. WILL HAVE SCTD LOW
STRATUS AND LIGHTER FOG AT INT/GSO... WHILE AT RDU/RWI/FAY... WILL
INDICATE LIFR CIGS/VSBYS UNTIL 14Z/15Z. AFTER THIS TIME... EXPECT A
TREND TO VFR CONDITIONS AT ALL CENTRAL NC TAF SITES THROUGH THE REST
OF TODAY... AS WEAK HIGH PRESSURE EXTENDS OVER THE REGION. RENEWED
FOG DEVELOPMENT IS EXPECTED TOWARD THE END OF THE TAF VALID PERIOD
(06Z THU). SURFACE WINDS WILL STAY LIGHT/VARIABLE.

LOOKING BEYOND 06Z EARLY THU MORNING... MVFR OR IFR VSBYS IN FOG MAY
DEVELOP ONCE AGAIN AND AFFECT CENTRAL NC TERMINALS FROM 08Z-13Z THU
MORNING. OTHERWISE... EXPECT VFR CONDITIONS THU. A FEW SPRINKLES OR
SHOWERS ARE POSSIBLE MAINLY AT RWI/FAY THU AFTERNOON/EVENING... BUT
SUB-VFR CONDITIONS ARE NOT EXPECTED. PATCHY FOG MAY AGAIN DEVELOP
EARLY FRI MORNING. A STRONG FRONTAL SYSTEM WILL BRING INCREASING
SURFACE WINDS FROM THE SW AND A GOOD CHANCE OF SUB-VFR CONDITIONS IN
SHOWERS AND STORMS LATE FRI AFTERNOON THROUGH FRI NIGHT/EARLY SAT
MORNING. VFR CONDITIONS SHOULD THEN RESUME SAT AFTERNOON... LASTING
THROUGH SUNDAY. -GIH

&&

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

&&

$$

SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...HARTFIELD
LONG TERM...KC
AVIATION...HARTFIELD


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