Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251045 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 645 AM EDT WED MAR 25 2015 .SYNOPSIS...HIGH PRESSURE ALONG THE MID-ATLANTIC COAST WILL PUSH A BACKDOOR COLD FRONT SOUTHWESTWARD THROUGH THE CAROLINAS THIS MORNING. A WARM FRONT WILL APPROACH FROM THE SOUTHEAST THIS AFTERNOON...THEN TEMPORARILY STALL OVER THE REGION TONIGHT. THE WARM FRONT WILL LIFT NORTH OF THE AREA ON THURSDAY...AS A COLD FRONT APPROACHES FROM THE WEST. && .NEAR TERM /TODAY AND TONIGHT/... AS OF 445 AM WEDNESDAY... OVERVIEW: CANADIAN HIGH PRESSURE WILL BUILD SOUTHWARD ALONG THE MID- ATLANTIC COAST THIS MORNING...THEN SHIFT OFFSHORE THIS AFTERNOON INTO TONIGHT AS A SHORTWAVE TROUGH AND ATTENDANT SFC LOW TRACK NE ACROSS THE GREAT LAKES. MEANWHILE...SHORTWAVE ENERGY OVER THE NORTHERN ROCKIES THIS MORNING WILL DIG SE INTO THE LOWER MIDWEST LATE THIS EVENING/TONIGHT...WITH AN ATTENDANT SFC LOW AND ASSOCIATED COLD FRONT PROGRESSING THROUGH THE CENTRAL MS RIVER VALLEY. TEMPERATURES: CHALLENGING FORECAST. COLD ADVECTION IN THE WAKE OF THE BACKDOOR FRONT HAS ALREADY DROPPED TEMPS TO ~45F IN THE NE COASTAL PLAIN...AND TEMPS ARE EXPECTED TO FALL INTO THE 40S VIRTUALLY EVERYWHERE BY SUNRISE...PERHAPS NEAR 50F IN THE FAR SW PIEDMONT. OVERCAST CEILINGS AT OR BELOW 2 KFT HAVE ALREADY DEVELOPED OVER MOST OF CENTRAL NC...IN ASSOC/W LOW-LEVEL WARM ADVECTION ATOP THE COOLER NEAR-SFC AIRMASS CURRENTLY ADVECTING INTO THE REGION. LIGHT RAIN OR DRIZZLE IS EXPECTED TO DEVELOP OVER WESTERN PORTIONS OF THE STATE WHERE LOW-LEVEL WARM ADVECTION WILL BE THE STRONGEST... AND THE CAD WEDGE IS UNLIKELY TO BREAK IN THE NW PIEDMONT... ESP GIVEN LITTLE OR NO SYNOPTIC PUSH TO THE WARM FRONT EXPECTED TO ADVANCE GRADUALLY WEST/NW TOWARD THE HWY 1 CORRIDOR THIS AFTERNOON. WITH THE ABOVE IN MIND...EXPECT HIGHS RANGING FROM THE UPPER 40S/LOWER 50S IN THE FAR NW PIEDMONT TO LOWER 70S IN THE FAR SE COASTAL PLAIN WHERE CAD EROSION WILL OCCUR EARLIER IN THE DIURNAL HEATING CYCLE. EXPECT NEAR STEADY TEMPS IN THE TRIAD OVERNIGHT... PERHAPS RISING A FEW DEGREES BY SUNRISE. ELSEWHERE...EXPECT TEMPS TO REMAIN NEARLY STEADY IN THE UPPER 50S WEST OF HWY 1 TO LOWER/MID 60S EAST AND ESP SE OF HWY 1. PRECIP TODAY: WITH SHORTWAVE RIDGING ALOFT AND LITTLE IN THE WAY OF SMALL AMPLITUDE WAVES...UPPER LEVEL FORCING WILL BE CONFINED TO CYCLONIC SHEAR VORTICITY ON THE NORTHERN PERIPHERY OF A ~90 KT JET STREAK DURING THE LATE AFTERNOON HOURS. AS A RESULT...FORCING WILL LARGELY BE CONFINED TO LOW-LEVEL WARM ADVECTION TODAY...STRONGEST IN WESTERN PORTIONS OF THE STATE WHERE INCREASINGLY RICH LOW-LEVEL MOISTURE IS PROGGED TO ADVECT INTO THE REGION FROM THE SE COAST /ATLANTIC/. A MODIFIED ELEVATED MIXED LAYER EMANATING FROM THE HIGH PLAINS HAS ADVECTED INTO THE REGION THIS MORNING...WITH SPC MESOANALYSIS INDICATING H7-H5 LAPSE RATES ON THE ORDER OF 7-7.5 C/KM OVER WESTERN NC AT 08Z. WITH A CAD WEDGE IN PLACE...THIS FEATURE WILL SERVE AS AN EFFECTIVE CAP UNTIL SUFFICIENT LOW-LEVEL WARMING/MOISTENING CAN BE ACHIEVED. H85 MOISTENING BENEATH THE MODIFIED EML OVER THE FAR WESTERN PIEDMONT THIS AFTERNOON MAY YIELD ELEVATED INSTABILITY ON THE ORDER OF 1500-2000 J/KG (MUCAPE) BY 21Z...AND SFC MOISTENING IN THE SE COASTAL PLAIN MAY BE SUFFICIENT TO YIELD 500-1000 J/KG MLCAPE. LOW-LEVEL WAA AND CYCLONIC SHEAR VORTICITY OVER THE WESTERN PIEDMONT MAY BE SUFFICIENT TO YIELD ELEVATED CONVECTION THIS AFTERNOON...THOUGH CONFIDENCE IN COVERAGE/ INTENSITY IS LOW GIVEN A LACK OF SHORTWAVE ENERGY /DPVA/. THOUGH DIURNAL DESTABILIZATION WILL OCCUR IN THE SE COASTAL PLAIN AND ISOLD LOW-TOPPED SHOWERS CANNOT BE RULED OUT...FORCING FOR ASCENT WILL LARGELY BE CONFINED TO WEAK/SHALLOW CONVERGENCE UNLIKELY TO OVERCOME THE MID-LEVEL CAP. PRECIP TONIGHT: LOW-LEVEL WARM ADVECTION WILL STRENGTHEN OVER CENTRAL NC TONIGHT AS A ~30 KT LLJ ADVECTS AN INCREASINGLY WARM/MOIST LOW-LEVEL AIRMASS BENEATH THE MODIFIED ELEVATED MIXED LAYER IN PLACE. FLOW ALOFT WILL STRENGTHEN FROM THE SOUTHWEST AS SHORTWAVE ENERGY DIGS INTO THE PLAINS...RESULTING IN AN INCREASED POTENTIAL FOR SMALL AMPLITUDE WAVES TO TRACK INTO THE REGION... THOUGH NO SIGNIFICANT WAVES ARE PROGGED AT THIS TIME. MOISTENING WILL NO DOUBT RESULT IN MARGINAL NOCTURNAL DESTABILIZATION GIVEN THE PRESENCE OF RELATIVELY STEEP MID-LEVEL LAPSE RATES...THOUGH WITH SUCH A DRY AIRMASS AT/ABOVE H7...COVERAGE/INTENSITY OF CONVECTIVE PRECIPITATION REMAINS UNCERTAIN...THOUGH MOST GUIDANCE DOES INDEED INDICATE MEASURABLE PRECIP OVER MOST OF CENTRAL NC OVERNIGHT. SEVERE: IF LOW-LEVEL MOISTENING AND DEEP-LAYER FORCING ARE SUFFICIENT TO INITIATE DEEP ELEVATED CONVECTION IN THE PRESENCE OF MODERATE INSTABILITY ACROSS THE WESTERN PIEDMONT LATE THIS AFTERNOON...STRONG EFFECTIVE DEEP-LAYER SHEAR AND STEEP MID-LEVEL LAPSE RATES WOULD SUPPORT A POTENTIAL FOR ELEVATED SUPERCELLS WITH AN ENHANCED THREAT OF LARGE HAIL...THOUGH THE PROBABILITY OF REALIZING SUCH A SCENARIO IS LOW ENOUGH TO PRECLUDE MENTION OUTSIDE OF THIS DISCUSSION. -VINCENT && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 445 AM WEDNESDAY... EXPECT THE CAD WEDGE TO ERODE THU MORNING TO EARLY THU AFTERNOON AS A SFC LOW TRACKS NE THROUGH THE OH VALLEY INTO THE MID-ATLANTIC... ESTABLISHING A WARM SECTOR OVER MOST (IF NOT ALL) OF CENTRAL NC. WITH THE STRONGEST WARM ADVECTION ALREADY NORTH OF THE REGION AND UNIDIRECTIONAL /SW/ FLOW ALOFT...FORCING FOR ASCENT WILL BE ON THE WEAK SIDE OF THE SPECTRUM THROUGH EARLY/MID AFTERNOON... UNTIL THE LOW-LEVEL TROUGH PROGRESSES EAST OF THE MOUNTAINS AND THE SFC COLD FRONT APPROACH FROM THE WEST LATE THU AFT/EVE INTO THU NIGHT. EXPECT A LOW CHANCE FOR PRECIP THROUGH 18Z THU ASIDE FROM LINGERING DRIZZLE PRIOR TO WEDGE EROSION...FOLLOWED BY AN INCREASING POTENTIAL FOR SHOWERS FROM WEST-EAST LATE THU AFTERNOON INTO THU NIGHT AS THE FRONT PROGRESSES INTO THE FOOTHILLS AND WESTERN PIEDMONT. OUTSIDE OF THE WESTERN PIEDMONT...THUNDER APPEARS QUESTIONABLE GIVEN UNFAVORABLE DIURNAL TIMING AND DPVA ATTENDANT THE AMPLIFYING UPPER LEVEL TROUGH PROGGED TO LAG BEHIND THE COLD FRONT /WARM SECTOR/. EXPECT HIGHS IN THE MID/UPPER 70S...EXCEPT PERHAPS IN THE NW PIEDMONT WHERE LOWER 70S APPEAR MORE LIKELY. LOWS THU NIGHT WILL DEPEND ENTIRELY ON THE PROGRESS OF THE COLD FRONT...WITH TEMPS REMAINING IN THE LOWER/MID 60S IN ADVANCE OF THE FRONT. AT THIS TIME WILL INDICATE TEMPS FALLING INTO THE 40S IN THE TRIAD BY SUNRISE FRI...BUT REMAINING STEADY ELSEWHERE. -VINCENT && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 330 AM WEDNESDAY... STRONG COLD FRONT WILL BE OFFSHORE OR MOVING OFFSHORE BY FRIDAY MORNING AND STRONG COLD AIR ADVECTION WILL BE UNDERWAY TO OFFSET THE POTENTIAL FOR LIMITED INSOLATION. LINGERING ANAFRONTAL SHOWERS DRIVEN BY THE COLD AIR ADVECTION WILL LINGER IN THE EAST THROUGH MID DAY. THESE WILL BE FOLLOWED DURING THE AFTERNOON INTO EARLY EVENING BY ADDITIONAL LIGHT SHOWERS WHICH WILL BE FORCED BY A TRAILING MID LEVEL SHORT WAVE WHICH WILL HAVE SUFFICIENT LINGERING MOISTURE IN THE LOW LEVELS ABOVE THE MIXING LEVEL TO PRODUCE SCATTERED SHALLOW CONVECTION. HIGHS WILL BE IN THE MID 50S WEST TO UPPER 50S EAST. LINGERING CLOUD COVERAGE AND OVERNIGHT MIXING WILL FORTUNATELY AID IN SOFTENING THE TEMPERATURE CRASH FRIDAY NIGHT AS LOW LEVEL THICKNESSES FALL NEARLY 100 METERS (25-30 DEGREES BY RULE OF THUMB) IN THE 24 HOUR PERIOD FROM FRIDAY MORNING TO SATURDAY MORNING. GUIDANCE HAS BEEN CONSISTENTLY INDICATING MID TO UPPER 30S...AND WILL CONTINUE THIS TREND WITH A WARY EYE ON THE POSSIBILITY THAT CLEARER/CALMER CONDITIONS MIGHT ALLOW US TO RADIATE LOWER. THE UPPER TROF AXIS IS OVER THE AREA ON SATURDAY AND HIGHS WILL STALL IN THE UPPER 40S ACROSS THE NORTHERN TIER TO LOWER 50S ELSEWHERE AS THE COLD AIR ADVECTION OFFSETS INCREASED SUNSHINE AS SURFACE HIGH PRESSURE MIGRATES EAST INTO THE MID ATLANTIC. AS THE HIGH BUILDS IN...RADIATIONAL CONDITIONS WILL BE NEAR IDEAL ON SATURDAY NIGHT AND SUNDAY MORNINGS DAWN MINS WILL BE IN THE UPPER 20S NORTH TO NEAR FREEZING IN THE SOUTH. WE WILL BEGIN TO SEE MODIFICATION OF THE AIRMASS SUNDAY UNDER STRONG SUN AND NEUTRAL TEMPERATURE ADVECTION...AND HIGHS WILL BE MOSTLY IN THE MID 50S. WE HAVE LOW LEVEL RETURN FLOW AND SLOWLY RISING H5 HEIGHTS SUNDAY NIGHT INTO MONDAY TO INITIATE A MODERATING TREND IN THE TEMPS. A FAST MOVING SHORT WAVE AND ASSOCIATED FRONT WILL DIVE SOUTHEAST AND ACROSS THE AREA ON MONDAY...AND WHILE WE COULD SEE SOME SHOWERS SQUEEZED OUT BY THIS SYSTEM...THEY WOULD BE LIGHT AS ITS LIMITED AVAILABLE MOISTURE WILL BE PRECIPITATED OUT AS IT MOVES ACROSS THE MOUNTAINS. WILL MAINTAIN A DRY FORECAST FOR NOW WITH HIGHS MONDAY AND TUESDAY REACHING THE 60S AFTER MORNING LOWS FROM 40 TO 45. WEDNESDAY IS LOWER CONFIDENCE...BUT LOOKS TO BE DRY WITH HIGHS REACHING THE LOWER 70S. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... AS OF 645 AM WEDNESDAY... 24-HR TAF PERIOD: MVFR CEILINGS WILL PREVAIL AT ALL TERMINALS THIS MORNING IN ASSOC/W LOW-LEVEL WARM ADVECTION ATOP A COOL SFC AIRMASS RECENTLY DEPOSITED IN THE WAKE OF A BACKDOOR COLD FRONT PROGRESSING SOUTHWESTWARD THROUGH CENTRAL NC. CEILINGS ARE EXPECTED TO RANGE FROM 1000-2000 FT AGL WITH AN EASTERLY WIND AT 5-10 KT. RWI/FAY/RDU: CEILINGS SHOULD GRADUALLY LIFT TO HIGH-END MVFR OR LOW- END VFR (2500-3500 FT AGL) BY EARLY AFTERNOON WHERE THE CAD WEDGE WILL GIVE WAY TO A WARM FRONT PROGRESSING WESTWARD TO THE HWY 1 CORRIDOR. MVFR/VFR CONDITIONS WILL PREVAIL THE REMAINDER OF THE AFTERNOON...THOUGH CEILINGS WILL LIKELY DETERIORATE TO IFR AND PERHAPS LIFR AFTER MIDNIGHT. INT/GSO: FURTHER NW WHERE THE CAD WEDGE WILL REMAIN FIRMLY IN PLACE...MVFR TO BORDERLINE IFR CEILINGS (~1000 FT AGL) ARE EXPECTED TO PREVAIL TODAY...WITH FURTHER DETERIORATION TO LIFR (CEILINGS 200- 400 FT AGL) LIKELY AFTER MIDNIGHT. LOOKING AHEAD: ADVERSE AVIATION CONDITIONS WILL PREVAIL THE REMAINDER OF THE WORK WEEK. CEILINGS ARE EXPECTED TO IMPROVE TO MVFR AND POSSIBLY VFR DURING THE DAY THU AS A WARM SECTOR BECOMES MORE FIRMLY ESTABLISHED OVER CENTRAL NC...THOUGH CEILINGS WILL LIKELY TAKE LONGER TO IMPROVE AT THE INT/GSO TERMINALS AND MAY REMAIN SUB- VFR THE ENTIRE DAY. ISOLD TO SCT CONVECTION CANNOT BE RULED OUT AT ANY TERMINAL THU AFT/EVE INTO THU NIGHT AS A COLD FRONT PROGRESSES INTO THE REGION FROM THE NW. OVERCAST MVFR/IFR CEILINGS WILL RETURN EARLY FRI MORNING IN THE WAKE OF THE FRONT...PERSISTING THROUGH THE DAY AT EASTERN TERMINALS...BEFORE STRONG COLD ADVECTION ARRIVES AND ALLOWS IMPROVEMENT FRI NIGHT. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...VINCENT LONG TERM...MLM AVIATION...VINCENT

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