Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 010140
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
930 PM EDT TUE SEP 30 2014

.SYNOPSIS...WEAK HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE
NORTH THROUGH THURSDAY. A STRONG COLD FRONT WILL CROSS THE CAROLINAS
FROM THE WEST LATE FRIDAY AND EARLY SATURDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 930 PM TUESDAY...

THE PROBLEM OF THE NIGHT WILL BE THE LIKELIHOOD OF FOG DEVELOPMENT
AGAIN OVER THE NE PIEDMONT AND N COASTAL PLAIN... AGAIN POTENTIALLY
DENSE.

IT TOOK MUCH OF THE DAY TO DISSOLVE THE STRATUS LAYER OVER A GOOD
PORTION OF THE NORTHEAST PIEDMONT INTO THE CENTRAL PIEDMONT. THE END
RESULT WAS LITTLE IN THE WAY OF EVAPORATION OF TOP SOIL MOISTURE
THIS AFTERNOON IN THIS REGION. DEW POINTS FAILED TO MIX OUT AND DRY
AND WERE STILL IN THE LOWER 60S IN THESE AREAS THIS EVENING. THERE
HAS BEEN A RAPID LOW LEVEL INVERSION SET UP THIS EVENING WITH THE
LINGERING MOIST BOUNDARY LAYER... CLEAR SKIES... AND STRONG DIURNAL
TEMP FALL WITH SUNSET. THIS IS ESPECIALLY EVIDENT AT MID-EVENING
FROM ROXBORO AND RALEIGH TO ROCKY MOUNT AND HALIFAX. THERE ARE
REPORTS OF FOG ALREADY IN THIS REGION... SOME LOCALLY BECOMING DENSE
(1/4 MILE VSBY OR LESS). WITH THE TEMP/DEW POINT TEMP SPREAD ALREADY
LESS THAN 3 DEGREES... FOG APPEARS INEVITABLE.

ELSEWHERE... AFTERNOON SUN LED TO SOME DECENT EVAPORATION AND LED TO
HIGHS AROUND 80. THERE WAS ENOUGH MIXING IN THAT THE LOW LEVEL
INVERSION WAS SLOWER TO SET UP FROM GREENSBORO AND
SOUTH AND WEST.

BOTTOM LINE... FOG SHOULD DEVELOP OVERNIGHT. AREAS OF DENSE FOG WILL
BE POSSIBLE AGAIN ESPECIALLY FROM ROXBORO AND RALEIGH NORTH AND EAST
TO ROCKY MOUNT AND ROANOKE RAPIDS. A DENSE FOG ADVISORY MAY BE
NEEDED LATER IF THE DENSE FOG IS THOUGHT TO BECOME WIDESPREAD TO
BECOME A HAZARD TO EARLY MORNING COMMUTERS. FOR NOW... WE WILL TREND
TOWARD THAT SCENARIO BY PLACING AREAS OF FOG IN THE FORECAST.

OTHERWISE... MOSTLY CLEAR. PATCHY FOG ELSEWHERE. LOWS 55-60 WEST AND
LOWER 60S EAST AND SOUTH. FOG SHOULD LIFT AS A STATUS DECK OF CLOUDS
AGAIN WED... AND MAY LINGER AGAIN UNTIL LATE MORNING IN THE NE
ZONES. -PWB

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
AS OF 235 PM TUESDAY...

WED/WED NIGHT: COMPLEX PATTERN IN THIS PERIOD WITH A NON-ZERO CHANCE
FOR PRECIPITATION. THE UPPER LOW PROGRESSING THROUGH THE MID-
ATLANTIC TONIGHT WILL MOVE OFFSHORE THE MID-ATLANTIC COAST ON WED AS
A SHORTWAVE RIDGE BUILDS OVER THE TN/OH VALLEY. SMALL AMPLITUDE
WAVES DIGGING SE INTO VA ON THE WESTERN PERIPHERY OF THE EXITING
UPPER LOW ON WED COULD PERHAPS PROVIDE A GLANCING BOUT OF DPVA
DURING THE DAY...OTHERWISE...ONE WOULD EXPECT SUBSIDENCE TO
GRADUALLY TAKE HOLD LATE WED INTO WED NIGHT AS THE SHORTWAVE RIDGE
PROGRESSES TO THE SPINE OF THE APPALACHIANS. BOTH THE GFS/NAM
DEVELOP VERY LIGHT PRECIP OVER THE NORTHERN PIEDMONT WED...WHILE THE
NAM GENERATES ADDITIONAL PRECIP WED NIGHT. IT IS DIFFICULT TO
ASCERTAIN WHY MODEL GUIDANCE IS DEVELOPING PRECIPITATION WED/WED
NIGHT...ESP WITH WEAK LOW-LEVEL FLOW AND MARGINAL/SHALLOW
INSTABILITY (EQUILIBRIUM LEVEL ~10 KFT). AT THIS TIME WILL CONTINUE
TO INDICATE A DRY FCST. HIGHS WED SLIGHTLY WARMER THAN TODAY...IN
THE LOWER 80S. LOWS WED NIGHT IN THE UPPER 50S/LOWER 60S. -VINCENT

THURSDAY AND THURSDAY NIGHT: SYNOPTIC SCALE SUBSIDENCE WILL PREVAIL
ACROSS CENTRAL NC ON THURSDAY AS HEIGHTS INCREASE OVER THE
AREA...DOWNSTREAM OF THE SOUTHERN STREAM TROUGH EJECTING EASTWARD
OUT OF THE CENTRAL/SOUTHERN ROCKIES...PROGRESSING EASTWARD INTO THE
SOUTHERN PLAINS/LOWER MS VALLEY THURSDAY NIGHT. IF CURRENT TIMING
HOLDS UP...IT SHOULD REMAIN DRY THROUGH THURSDAY NIGHT AS GFS BUFR
SOUNDINGS REMAIN STRONGLY CAPPED ALOFT...WITH STRENGTHENING
SOUTHERLY RETURN FLOW LEADING TO AN INCREASE IN CLOUDS FROM WEST-
EAST. HIGHS 80 TO 85. LOWS IN THE LOWER TO MID 60S.

FRIDAY AND FRIDAY NIGHT: MODELS INDICATE PHASING NORTHERN STREAM AND
SOUTHERN STREAM TROUGHS ACROSS THE UPPER MS VALLEY/UPR MIDWEST AND
INTO THE GREAT LAKES FRIDAY AND FRIDAY NIGHT. MODELS ARE IN REALLY
GOOD AGREEMENT WITH THE TIMING OF THE ACCOMPANYING COLD FRONT
PASSAGE INTO THE AREA LATE FRIDAY AFTERNOON/FRIDAY EVENING...EXITING
EASTERN PORTIONS OF THE FORECAST AREA BY DAYBREAK SATURDAY.  THE
LEAD SOUTHERN STREAM WAVE OVER THE LOWER MS VALLEY/TN VALLEY FRIDAY
MORNING REALLY SHEARS OUT/DAMPENS AS IT LIFTS NORTHWARD INTO MID-
ATLANTIC REGION FRIDAY EVENING/NIGHT...RESULTING IN WEAK UPPER LEVEL
SUPPORT WITH EASTWARD ADVANCING 30-35KT SWLY LLJ FOCUSING STRONG
MOISTURE TRANSPORT AND LOW-LEVEL CONVERGENCE WITHIN A BAND OF
CONVECTION ALONG THE FRONT. LATE DIURNAL TIMING AND MODEST LAPSE
RATES ALOFT WILL RESULT IN LIMITED/WEAK INSTABILITY(200-400
MUCAPE)...THWARTING ANY SEVERE THREAT. HAVE INCREASED POPS TO LIKELY
ACROSS THE FORECAST AREA FRIDAY NIGHT...DECREASING WEST TO EAST
DURING THE PREDAWN HOURS AS FRONT MOVES EASTWARD TOWARDS THE COAST.
PROGRESSIVE NATURE OF SYSTEM WILL LIMIT RAINFALL AMOUNTS...WITH
AVERAGE QPF AMOUNTS OF A 0.25-0.50".

MAX TEMPS FRIDAY AFTERNOON WILL DEPEND ON ARRIVAL/ONSET OF
SHOWERS/CONVECTION...ESPECIALLY IN THE WEST. UNDER THICKENING CLOUD
COVER...A BIT COOLER THAN THURSDAY RANGING FROM MID 70S WEST TO
LOWER 80S EAST. MIN TEMPS WILL DEPEND ON WEST-EAST TIMING OF FROPA
FRIDAY NIGHT THROUGH THE AREA...RANGING FROM LOWER/MID 50S NORTHWEST
TO LOWER/MID 60S SE.


&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 235 PM TUESDAY...

IN THE WAKE OF THE FRONTAL PASSAGE SATURDAY MORNING...DRY CONDITIONS
WILL PREVAIL THROUGH EARLY NEXT WEEK AS SFC HIGH PRESSURE OVER THE
SOUTHERN PLAINS/LOWER MS VALLEY BUILDS EAST THROUGH THE
PERIOD...SHIFTING EAST OFF THE SOUTHEAST COAST ON MONDAY. AFTER A
CHILLY SATURDAY NIGHT/SUNDAY MORNING IN WHICH FAVORABLE RADIATIONAL
CONDITIONS WILL HELP SUPPORT MIN TEMPS IN THE MID TO UPPER 40S
ACROSS A LARGE PORTION OF THE FORECAST AREA...TEMPERATURES WILL
MODERATE TO NEAR NORMAL BY MONDAY.

TIMING/MAGNITUDE OF THE NEXT SYSTEM STILL IN QUESTION AS NORTHERN
STREAM ENERGY ROTATING SOUTHEASTWARD THROUGH THE BASE OF THE
AMPLIFIED TROUGH LOOKS TO IMPACT THE REGION LATE MONDAY-TUESDAY TIME
FRAME. UNTIL MODEL DISCREPANCIES CAN BE IRONED OUT WITH THIS CLIPPER-
LIKE TROUGH...WILL INDICATE CONSERVATIVE/SLIGHT CHANCE
POPS...ESPECIALLY GIVEN POTENTIAL FOR LIMITED MOISTURE AVAILABILITY.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
AS OF 800 PM TUESDAY...

HIGH PRESSURE OVER THE AREA HAS LEAD TO MOSTLY CLEAR SKIES THIS
EVENING. IN ADDITION...WINDS WILL BECOME MOSTLY CALM OVER THE NEXT
COUPLE OF HOURS. THESE CLEAR SKIES AND LIGHT/CALM WINDS SHOULD LEAD
TO ANOTHER NIGHT OF FOG. HOWEVER...IT IS NOT A SURE BET AS MODELS
ARE IN DISAGREEMENT (WITH ONE SHOWING PREDOMINATELY VFR CONDITIONS
ALL NIGHT). NEVERTHELESS... GIVEN A SIMILAR SET UP TO LAST NIGHT
(MINUS THE LIGHT RAIN THAT OCCURRED ON MONDAY)...WENT AHEAD AND
INCLUDED IFR/LIFR VSBYS/CIGS IN ALL TAF SITES EXCEPT THE TRIAD WHERE
THERE IS SLIGHTLY DRIER AIR (BUT STILL INCLUDED SOME SUB-VFR
CONDITIONS). CONDITIONS SHOULD IMPROVE TO VFR BY THE MID MORNING
HOURS OF WEDNESDAY...WITH JUST SOME MID/HIGH CLOUDS AND LIGHT AND
VARIABLE WINDS FOR THE REMAINDER OF THE TAF PERIOD GIVEN THE HIGH
PRESSURE OVERHEAD.

OUTLOOK...VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH LATE
WEDNESDAY/EARLY THURSDAY MORNING AS WEAK HIGH PRESSURE EXTENDS INTO
THE REGION FROM THE NORTH. MVFR/IFR CIGS/VSBYS MAY DEVELOP EARLY
THURSDAY MORNING AS THE HIGH BEGINS TO SHIFT OFFSHORE. OTHERWISE...
THE NEXT CHANCE FOR ADVERSE AVIATION CONDITIONS WILL BE LATE FRI AND
EARLY SAT AS A STRONG COLD FRONT CROSSES THE CAROLINAS FROM THE
WEST.

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...PWB
SHORT TERM...VINCENT/CBL
LONG TERM...CBL
AVIATION...KRD/VINCENT


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