Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 181931
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
330 PM EDT SAT APR 18 2015

.SYNOPSIS...A WARM FRONT WILL LIFT SLOWLY NORTHWARD ACROSS CENTRAL
NC LATE TONIGHT THROUGH SUNDAY. A COLD FRONT WILL APPROACH FROM THE
WEST ON MONDAY...THEN TRACK EASTWARD THROUGH CENTRAL NC MONDAY NIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 330 PM SATURDAY...

WEAK CONVERGENCE ALONG A WEST-EAST ORIENTATED LOW LEVEL BOUNDARY
COUPLED WITH AFTERNOON HEATING HAS ALLOWED ISOLATED-SCATTERED
SHOWERS TO DEVELOP. DUE TO WEAK STEERING FLOW...SHOWERS ARE
DEMONSTRATING LITTLE MOVEMENT. AS THE AFTERNOON WEARS ON...COULD SEE
AN ISOLATED THUNDERSTORM OR TWO. AFTER 22Z...SHOULD START TO SEE A
DECREASE OVER MOST OF THE NORTHERN COUNTIES WITH LOSS OF HEATING.
ACROSS THE FAR SOUTH IN CLOSE PROXIMITY TO A STALLED 850MB
BOUNDARY...A FEW SHOWERS WILL LIKELY PERSIST THROUGH MUCH OF THE
EVENING HOURS.

ISENTROPIC UPGLIDE WILL INCREASE OVER THE FAR WESTERN-SW COUNTIES
AFTER MIDNIGHT AS A S/W APPROACHES FROM THE SW. THIS SHOULD LEAD TO
AN INCREASING SHOWER THREAT AFTER MIDNIGHT WITH SHOWERS LIKELY
OCCURRING BY DAYBREAK WEST OF A LINE FROM LEXINGTON-LAURINBURG.

OVER THE FAR NE...A SLIGHTLY DRIER/MORE STABLE AIR MASS WILL FILTER
INTO THE REGION...ASSOCIATED WITH A NARROW SFC RIDGE. THIS SHOULD
CAUSE DEWPOINTS TO BRIEFLY LOWER INTO THE UPPER 50S.  MIN TEMPS
SHOULD VARY FROM THE MID 60S FAR SOUTH-SE TO NEAR 60 ACROSS THE FAR
NORTH-NE.


&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
AS OF 330 PM SATURDAY...

SUNDAY...AN INCREASINGLY MOIST AIR MASS (PRECIP WATER VALUES 1.5-1.7
INCHES PROBABLE BY AFTERNOON) COUPLED WITH DECENT CONVERGENCE IN THE
LOWER LEVELS AND INCREASING DIVERGENCE ALOFT (DUE TO THE NOSE OF
300MB JET CROSSING THE NORTHERN GULF) WILL CAUSE SHOWERS TO
OVERSPREAD CENTRAL NC FROM THE SW. LOW LEVEL WIND WILL HAVE AN
UPSLOPE COMPONENT OVER THE WESTERN PIEDMONT...SUGGESTING A SUSTAINED
PERIOD OF SHOWERS WITH MODERATE TO BRIEFLY HEAVY RAINFALL RATES
LIKELY. WHILE NOT ANTICIPATING WIDESPREAD FLOODING ISSUES AT THIS
TIME...PROLONGED MODERATE RAINFALL IN THE URBANIZED AREAS OF THE
TRIAD COULD LEAD TO STREET FLOODING ALONG WITH SIGNIFICANT RISES
ALONG AREAS CREEKS AND STREAMS. WILL REFRAIN FROM ISSUING A FLASH
FLOOD WATCH AT THIS TIME AS BEST LIFT PROJECTED TO OCCUR OVER THE
FOOTHILLS/HIGHER TERRAIN OF WESTERN NC.

LATEST MODEL GUIDANCE HAS TRENDED MORE UNSTABLE LATE SUNDAY-SUNDAY
EVENING ACROSS THE SOUTHERN HALF OF CENTRAL NC WITH BULK SHEAR
INCREASING 35-40KTS AND MLCAPE 500-1000J/KG(NAM). WHILE CANNOT RULE
OUT THE POTENTIAL FOR AN ISOLATED STRONG/SEVERE STORM SUNDAY NIGHT
OVER THE SOUTHERN COUNTIES...FEEL THAT SEVERE POTENTIAL BETTER
FARTHER SOUTH ACROSS GA/SOUTHERN SC WHERE ATMOSPHERE WILL HAVE A
BETTER CHANCE TO DESTABILIZE.

WIDESPREAD SHOWERS AND OVERCAST SKIES SHOULD LIMIT TEMP RECOVERY
SUNDAY. HIGH TEMPS SHOULD VARY FROM THE MID 60S-LOWER 70S FAR SOUTH-
SOUTHEAST

OTHERWISE...SHOULD SEE SHOWER DECREASING IN COVERAGE AND INTENSITY
SUNDAY NIGHT FROM THER SW AS MID LEVEL S/W LIFTS NEWD INTO THE
NORTHERN MID ATLANTIC. THE APPROACH OF YET ANOTHER S/W (VERY POTENT)
TOWARD DAYBREAK MONDAY WILL CONTINUE A THREAT SHOWERS OVERNIGHT. MIN
TEMPS 60-65.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
AS OF 255 PM SATURDAY...

MON/MON NIGHT: WILL HOLD ONTO JUST A FEW HOURS OF SHOWERS IN THE FAR
NE EARLY MON MORNING... CONSIDERING THAT THE MODELS HAVE BEEN
TRENDING A BIT FASTER TO MOVE PRECIP OUT OF CENTRAL NC... AND WILL
FOLLOW WITH A PERIOD OF NO POPS FOR MID TO LATE MORNING... UNTIL THE
ONSET OF CONVECTION. STILL LOOKS LIKE A GOOD PROBABILITY OF STRONG
TO SEVERE STORMS MON AFTERNOON INTO EARLY EVENING WITH A FEW
SUPERCELLS POSSIBLE. WE`LL BE FULLY IN THE WARM SECTOR WITH WARM
MOIST AIR NEAR THE GROUND AND A GOOD PUNCH OF MID LEVEL DRY AIR
COMING IN FROM THE SW. LATEST MODEL RUNS ARE SHOWING A LITTLE BETTER
INSTABILITY THAN YESTERDAY`S RUNS FOR MON AFTERNOON... WITH MUCAPE
OF 1000-2000 J/KG ON THE GFS AND 1500-3000 J/KG ON THE NAM... AND
SREF MEAN MLCAPE VALUES PEAKING AT 1200-1500 J/KG... ALTHOUGH THE
DEEP LAYER SHEAR STILL LOOKS MARGINAL AT AROUND 30 KTS. NAM/GFS BUFR
SOUNDINGS SHOW A WEAK CAP LOCATED BETWEEN 1 AND 2 KM AGL IN THE
MORNING... BREAKING EARLY IN THE AFTERNOON... AND ONCE IT DOES...
CONVECTION SHOULD DEVELOP AND BECOME VIGOROUS QUICKLY WITH BROAD AND
DEEP CAPE IN THE MID-UPPER LEVELS. DYNAMIC FORCING FOR ASCENT WILL
BE PRESENT AS WELL WITH STRONG UPPER DIVERGENCE IN THE LEFT EXIT
REGION OF A 140 KT SUBTROPICAL JET... AND A SHOT OF MID LEVEL DPVA
AS THE TROUGH AXIS ROTATES UP THROUGH THE AREA. WILL MAINTAIN A
MENTION IN THE HAZARDOUS WEATHER OUTLOOK OF DAMAGING WIND AS THE
PRIMARY THREAT GIVEN THE ABUNDANCE OF DRY AIR 700-300 MB... HOWEVER
THE EXPECTED CAPE IN THE -10C TO -30C LAYER APPEARS SUFFICIENT TO
SUPPORT LARGE HAIL IF WE CAN GET ENOUGH MOISTURE ALOFT. THICKNESSES
ARE PROJECTED TO START THE DAY AROUND 20 M ABOVE NORMAL... SO HIGHS
IN THE UPPER 70S TO MID 80S (NW TO SE) LOOK ATTAINABLE WITHIN GOOD
WARM AIR ADVECTION. WILL TREND OUT SHOWERS/STORMS IN THE MID-LATE
EVENING FROM WEST TO EAST... WITH COLD FRONTAL PASSAGE EXPECTED LATE
OVERNIGHT. LOWS FROM THE LOWER 50S NW TO AROUND 60 SE.

TUE-SAT: THE COLD FRONT WILL HAVE PUSHED OFF THE COAST BY DAYBREAK
TUE... AS MILD HIGH PRESSURE BUILDS IN FROM THE WEST. A LARGE VORTEX
IS EXPECTED TO SIT AND SPIN OVER THE NRN GREAT LAKES THROUGH
MIDWEEK... BEFORE WOBBLING EASTWARD TO NEW ENGLAND BY LATE SAT...
ALL THE WHILE ENCOMPASSING A LARGE CHUNK OF CENTRAL AND EASTERN NOAM
INCLUDING THE MIDATLANTIC REGION. AS THE MODIFIED SURFACE HIGH
BUILDS IN... EXPECT TEMPS TO BE A BIT BELOW NORMAL TUE/WED... BUT
READINGS WILL REBOUND ONCE THE SURFACE HIGH DRIFTS TO OUR SOUTHEAST
AND OFFSHORE LATE WED... SO EXPECT TEMPS BACK UP NEAR NORMAL THU.
ONE PARTICULARLY POTENT WAVE ROTATING THROUGH THE BROAD BASE OF THE
LOW LATE IN THE WEEK IS LINKED TO A SURFACE COLD FRONT WHICH IS
EXPECTED TO PUSH SOUTHEAST THROUGH NC LATE THU OR THU EVENING.
IMPROVING MOISTURE STREAMING INTO NC AHEAD OF THIS FRONT SHOULD
YIELD A FEW SHOWERS MAINLY WED NIGHT AND THU... HOWEVER THE LOW
LEVEL FLOW WILL REMAIN LIGHT WITH MINISCULE TAPPING OF ATLANTIC OR
GULF MOISTURE... AND LITTLE IN THE WAY OF FORCING FOR ASCENT GIVEN
THE FAST WNW GENTLY CYCLONIC FLOW ALOFT... SO EXPECT POPS TO HOLD
UNDER CLIMATOLOGY. FRONTAL PASSAGE LATE THU WILL INTRODUCE A COOLER
AIR MASS IN THE FORM OF A SPRAWLING CANADIAN HIGH EXPANDING SSE FROM
CENTRAL CANADA FOR FRI/SAT... SO WILL TREND BACK TO DRY WEATHER WITH
BELOW NORMAL TEMPS. -GIH

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
AS OF 145 PM SATURDAY...

WHILE MOST LOCATIONS ACROSS CENTRAL NC WILL HAVE VFR CONDITIONS
THROUGH THIS EVENING...THERE WILL BE LOCALIZED AREAS OF MVFR
CEILINGS AND VISIBILITIES IN THE VICINITY OF SHOWERS. THESE ADVERSE
CONDITIONS WILL BE MOST LIKELY TO OCCUR NEAR KFAY THROUGH 22Z.

MOSTLY VFR CONDITIONS WILL GRADUALLY BECOME MVFR IN AREAS AFTER 05Z
AS AREAS OF FOG DEVELOP WITH SPOTS OF IFR/LIFR CEILINGS POSSIBLE.

AVIATION CONDITIONS WILL DETERIORATE SUNDAY MORNING AS AN
APPROACHING LOW PRESSURE SYSTEM WILL CAUSE RAIN SHOWERS TO
OVERSPREAD CENTRAL NC FROM THE SW. EXPECT MVFR CEILINGS WITH THIS
SHIELD OF SHOWERS. NEAR SFC WINDS WILL BE ELY...SUSTAINED 10-15KTS
WITH GUSTS 20-25KTS.

THE RAIN WILL DIMINISH FROM THE SW AFTER 00Z MONDAY WITH SHOWERS
VERY SPOTTY AFTER 06Z. RESIDUAL MOISTURE WILL LIKELY CAUSE
WIDESPREAD IFR/MVFR CEILINGS UNTIL EARLY MONDAY MORNING.

A STRONG LOW PRESSURE SYSTEM WILL TRAVERSE CLOSE TO CENTRAL NC
MONDAY. THIS SYSTEM INTERACTING WITH AVAILABLE MOISTURE AND
INSTABILITY WILL BRING A GOOD CHANCE FOR SCATTERED STRONG TO SEVERE
THUNDERSTORMS MONDAY AFTERNOON-MONDAY EVENING.

IMPROVING AVIATION CONDITIONS WITH WIDESPREAD VFR CONDITIONS
ANTICIPATED FOR TUESDAY THROUGH THURSDAY.

&&

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

&&

$$

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



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