Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 190707
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
305 AM EDT SAT APR 19 2014

.SYNOPSIS...LOW PRESSURE OVER THE NORTHEASTERN GULF OF MEXICO THIS
MORNING WILL DRIFT VERY SLOWLY ALONG THE SOUTHEAST US COAST THROUGH
THE WEEKEND.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
AS OF 305 AM SATURDAY...

FOR TODAY/TONIGHT: THE MOST DREARY WEATHER OF THE WEEKEND WILL OCCUR
IN THE NEXT 12-18 HOURS... WITH CERTAIN RAIN FOR ALL. THE LATEST
SURFACE AND UPPER AIR ANALYSES SHOW THE RESPECTIVE LOW CENTERS OVER
NE FL AND SRN AL... SHIFTING VERY SLOWLY EASTWARD. THE SURFACE HIGH
TO OUR NNE OVER DELMARVA-NJ THAT IS SUPPLYING THE CHILLY NE FLOW IS
POISED TO BE SUPPLANTED BY A LARGER AND COLDER HIGH NOW CENTERED
OVER ONTARIO... WHICH WILL BE USHERED INTO OUR REGION THANKS TO A
WEAK NRN STREAM FRONT EXTENDING FROM UPSTATE NY THROUGH THE OH
VALLEY AND PUSHING TO THE ESE... ATTENDING A SWIFT-MOVING MID LEVEL
TROUGH. IDEALLY JUXTAPOSED UPPER JET CORES ON THE EAST SIDE OF THIS
TROUGH (RIGHT REAR QUAD OVER NC) AND ON THE EAST SIDE OF THE VORTEX
OVER AL (LEFT FRONT QUAD OVER NC) HAVE STRENGTHENED THE UPPER
DIVERGENCE OVER NC... SUPPORTING A BROAD SWATH OF MOSTLY LIGHT-MDT
RAIN OVER NC. WITH ABUNDANT MID LEVEL MOISTURE IN PLACE AND THIS
UPPER LEVEL FORCING FOR ASCENT COMBINED WITH MID LEVEL DEFORMATION
AND MASS CONVERGENCE AROUND 850 MB SHOULD CONTINUE TO GENERATE
WIDESPREAD RAIN THROUGH THIS MORNING. LARGE SCALE MODELS DEPICT THE
BEST LIFT IN A BAND ACROSS THE SW PORTION OF CENTRAL NC... WHERE THE
UPPER DIVERGENCE AND LOW LEVEL CONVERGENCE WILL BE WELL CORRELATED
IN THE VERTICAL... AND THIS IS INDICATED AS WELL BY SREF
PROBABILITIES AND THE LATEST HRRR RUNS. THIS AREA COULD SEE UP TO AN
ADDITIONAL 1.0-1.5 INCHES OF RAIN... MOST FALLING THIS MORNING.
LATEST OBSERVED RAINFALL SO FAR RANGES FROM JUST A FEW HUNDREDTHS
NEAR THE VA BORDER TO JUST UNDER AN INCH IN THE FAR SOUTH (SCOTLAND
TO SAMPSON CO)... WITH AREAS FROM THE TRIANGLE ACROSS THE SOUTHWEST
CWA SEEING AROUND 0.30-0.40 INCH SO FAR. WHILE THE FLASH FLOOD
GUIDANCE IS LOWEST IN THIS SW QUADRANT OF THE FORECAST AREA (AROUND
1.75" IN 1 HR)... THE ADDITIONAL RAINFALL IS EXPECTED TO BE LIGHT
ENOUGH SUCH THAT THIS RATE WON`T BE ACHIEVED. BUT A GRAND TOTAL OF 2
INCHES OR MORE OF RAIN IN THIS AREA COULD LEAD TO SOME STREET
FLOODING ESPECIALLY IN THOSE VULNERABLE AREAS NEAR CREEKS AND IN
TOWNS. THEN BY THIS AFTERNOON... THE AFOREMENTIONED WEAK NRN STREAM
FRONT WILL HAVE ALLOWED THE CHILLIER HIGH TO BUILD SOUTHWARD INTO NC
AS IT CROSSES SRN QUEBEC AND THE ST LAWRENCE VALLEY THROUGH
TONIGHT... HELPING TO DRY OUT THE LOW LEVELS OVER NC FROM THE NORTH.
ALSO LATER TODAY THE UPPER LEVELS WILL GRADUALLY DRY OUT AS THE DRY
SLOT ALOFT PUNCHES IN FROM THE SOUTH... AND THIS DRYING ABOVE 0C
SHOULD LEAD TO A SLOW TREND TO MOSTLY LIGHT PATCHY DRIZZLE... WITH
THE TRANSITION LAST TO OCCUR OVER THE NW PIEDMONT WHERE THE
DEFORMATION BAND WILL MOST LONG-LIVED. SO... IN TERMS OF SENSIBLE
WEATHER... WILL START THE DAY WITH 100% POPS... GRADUALLY TRENDING
DOWN TO GOOD CHANCES OF RAIN OR DRIZZLE DURING THE LATE AFTERNOON AS
THE CHANCES FOR MEASURABLE PRECIP DROP. MODELS DISAGREE ON EXACTLY
WHERE AND HOW MUCH PRECIP THERE MIGHT BE TONIGHT... BUT BASED ON THE
LARGE SCALE PATTERN... WILL KEEP A LOW CHANCE OF LIGHT RAIN LATE
TONIGHT OVER THE SOUTHEAST... WHERE ONSHORE-DIRECTED FLOW WILL LAST
THE LONGEST. TEMPS ARE CHALLENGING TO SAY THE LEAST... WITH SOME
STATISTICAL GUIDANCE APPEARING OVERLY OPTIMISTIC GIVEN THE
WIDESPREAD CLOUDS AND RAIN FOR MUCH OF THE DAY. HAVE FOLLOWED HIGH-
RES AND RAPID-UPDATE GUIDANCE INCLUDING THE LOCAL WRF / HRRR / RAP /
GRIDDED LAMP FOR TEMPS TODAY... GIVING HIGHS FROM THE MID 50S IN THE
SOUTH TO UPPER 50S IN THE FAR NORTHWEST. EXPECT CLOUDS TO LINGER
THROUGH TONIGHT... BUT WITH RAIN/DRIZZLE DWINDLING ESPECIALLY FROM
NW TO SE. LOWS 45-50.

FOR SUN/SUN NIGHT: THE MID LEVEL LOW IS EXPECTED TO SHIFT SLOWLY OFF
SAVANNAH EARLY SUN THEN SLOWLY FILL AS IT HEADS ESE THROUGH SUN
NIGHT. MODELS INDICATE ABUNDANT MOISTURE HANGING ON IN THE 850-700
MB LAYER OVER NC SUNDAY... WITH A PERSISTENT COOL AND BRISK
NORTHEAST LOW LEVEL FLOW FEEDING IN FROM THE CHILLY BUT PROGRESSIVE
AND MODIFYING SURFACE HIGH TO OUR NE. LOW LEVEL THICKNESSES ARE
EXPECTED TO BE AROUND 15-20 M BELOW NORMAL... INDICATING HIGHS
NEARLY 2 CATEGORIES BELOW NORMAL. EXPECT HIGHS OF 64-68... WITH
PARTIAL SUNSHINE LATE IN THE DAY AS MID LEVEL RIDGING STARTS TO
BUILD IN FROM THE WEST. CLEARING SKIES SUN NIGHT... ALTHOUGH THERE
MAY BE ENOUGH RESIDUAL MOISTURE IN THE NORTHEAST CWA WITH A
CONTINUED ATLANTIC FETCH TO BRING ABOUT PATCHY LOW STRATUS
DEVELOPMENT OVERNIGHT. LOWS 40-47. -GIH

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 255 AM SATURDAY...

THE SLOW MOVING CUT OFF LOW IMPACTING THE REGION THIS WEEKEND IS
FORECAST TO BE EAST OF THE CAROLINAS SUNDAY NIGHT...WITH AN
ELONGATED SURFACE RIDGE EXTENDING FROM THE MID-ATLANTIC STATES INTO
THE NC. AS THE LOW MOVES OFF TO THE NORTHEAST...WINDS SHOULD BACK
AROUND TO MORE NORTHERLY THAN NORTHEASTERLY AND ALLOW SOME DRIER AIR
TO WORK INTO CENTRAL NC FROM THE NORTH.  THE NAM ISNT QUITE AS DRY
AS THE GFS AND ECMWF...SHOWING SOME MOISTURE LINGERING AROUND 850MB
EAST OF I-95. WHILE THE AIRMASS WONT BEGIN TO MODERATE SIGNIFICANTLY
UNTIL TUESDAY...STRONGER HEATING SHOULD SUPPORT HIGHS REACHING THEIR
POTENTIAL OF UPPER 60S AND LOWER 70S.

A PROGRESSIVE TROUGH MOVING THROUGH THE CENTRAL US WILL APPROACH THE
REGION MONDAY NIGHT AND EARLY TUESDAY...WITH THE ASSOCIATED FRONTAL
ZONE PROJECTED TO CROSS CENTRAL NC TUESDAY AFTERNOON AND EVENING.
AHEAD OF THE SYSTEM...LOWS WILL BE MUCH MORE MILD MONDAY NIGHT WITH
INCREASING MID/HIGH CLOUDS AND A WEAK RETURN FLOW ACROSS THE WESTERN
PIEDMONT.  LOWS IN THE LOWER 50S WEST AND UPPER 40S EAST.  SOUTH TO
SOUTHWESTERLY FLOW WILL INCREASE ON TUESDAY AHEAD OF THE APPROACHING
FRONT.  MODELS CURRENTLY FORECAST A DEWPOINT RECOVERY INTO THE MID
AND UPPER 50S...WHICH COMBINED WITH HIGHS IN THE UPPER 70S TO AROUND
80 AND WEAK MID-LEVEL LAPSE RATES WOULD SUGGEST WEAK
INSTABILITY...MAINLY ACROSS THE WEST.  MODEST SHEAR MAY SUPPORT A
FEW STRONG STORMS...BUT WITHOUT BETTER UPPER SUPPORT THE THREAT OF
SEVERE WEATHER LOOKS ISOLATED AT THIS POINT.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 255 AM SATURDAY...

BEHIND TUESDAYS SYSTEM...CANADIAN HIGH PRESSURE WILL BUILD ACROSS
MUCH OF THE EASTERN US ON WEDNESDAY AND THURSDAY.  THURSDAY LOOKS TO
BE THE COOLEST DAY AS THICKNESSES FALL BACK BELOW NORMAL...WITH
HIGHS MAYBE 5-10 DEGREES BELOW NORMAL...BUT THEN QUICKLY REBOUND ON
FRIDAY AS ANOTHER PROGRESSIVE UPPER TROUGH APPROACHES FROM THE WEST.
THIS NEXT SYSTEM RESEMBLES THE EARLY WEAK SYSTEM...THOUGH
POTENTIALLY WITH A LITTLE MORE MOISTURE AVAILABLE FROM THE GULF.
THE CURRENT FORECAST WILL REMAIN DRY...WITH THE BETTER CHANCE OF
PRECIP JUST BEYOND THE END OF THE FORECAST ON FRIDAY NIGHT AND
SATURDAY.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AS OF 145 AM SATURDAY...

AN EXPANSIVE STORM SYSTEM CENTERED ON THE FL GULF COAST WILL AFFECT
THE SOUTHEAST STATES AND CAROLINAS THROUGHOUT TODAY AND TONIGHT.
CURRENTLY... DESPITE FAIRLY WIDESPREAD LIGHT RAIN... WITH THE
EXCEPTION OF FAY... VFR CONDITIONS DOMINATE WITH MOST VSBYS AOA 6SM
AND CIGS AOA 4 000 FT... WHILE FAY HAS SEEN A BAND OF HEAVIER RAIN
BRINGING IN IFR CIGS AND MVFR VSBYS. THESE IFR CIGS ARE LIKELY TO
CONTINUE TO ADVECT INTO FAY THROUGH 12Z... AND MAY CREEP INTO THE
VICINITY OF RWI. AT INT/GSO/RDU... VFR CIGS AND VSBYS ARE EXPECTED
TO PREVAIL THROUGH 12Z... ALTHOUGH VSBYS MAY BRIEFLY DROP TO MVFR IN
ANY HEAVIER RAIN BANDS. AFTER 12Z... RDU/RWI SHOULD FALL TO MAINLY
MVFR... LASTING UNTIL AROUND 19-21Z... WITH BRIEF IFR CIGS POSSIBLE
BETWEEN 12Z AND 16Z. INT/GSO SHOULD REMAIN VFR... ALTHOUGH A BRIEF
DROP TO MVFR 12Z-16Z THIS MORNING IS POSSIBLE. FAY IS LIKELY TO
EXPERIENCE THE WORST AVIATION CONDITIONS WITH IFR CONDITIONS HOLDING
THROUGH 06Z TONIGHT. AT INT/GSO/RWI/RDU... CIGS ARE EXPECTED TO
IMPROVE TO VFR AFTER 21Z AS DRIER LOW LEVEL AIR NOSES IN FROM HIGH
PRESSURE TO THE NORTH... WITH JUST PATCHY DRIZZLE AT MOST FROM 21Z
THROUGH THE END OF THE TAF VALID PERIOD (06Z SUN).

LOOKING BEYOND 06Z SUN... EXPECT IMPROVEMENT TO MVFR AT FAY 06Z-09Z
THEN TO VFR BY 12Z... AND MAINLY VFR CIGS AT ALL OTHER SITES THROUGH
SUNDAY. EXPECT VFR CONDITIONS TO DOMINATE THROUGH MON NIGHT. PASSAGE
OF A MID LEVEL TROUGH AND SURFACE COLD FRONT FROM THE NW WILL BRING
A RISK OF SUB-VFR CONDITIONS TUE/TUE NIGHT. VFR CONDITIONS RETURN
FOR WED. -GIH

&&

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

&&

$$

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



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