WFO RAH Logo


FXUS62 KRAH 121124
 AFDRAH
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE RALEIGH NC
 318 AM EDT TUE APR 12 2011
 
 .SYNOPSIS...
 A COLD FRONT WILL MOVE SLOWLY EASTWARD THROUGH THE AREA LATE THIS 
 MORNING AND AFTERNOON. AN UPPER LEVEL LOW PRESSURE AREA DRIFTING 
 OVER THE REGION WILL KEEP WEATHER UNSETTLED THROUGH WEDNESDAY. WEAK 
 HIGH PRESSURE WILL BUILD IN FROM THE WEST WEDNESDAY NIGHT THROUGH 
 THURSDAY. 
 
 &&
 
 .NEAR TERM /TODAY AND TONIGHT/...
 AS OF 255 AM TUESDAY...
 
 THE STACKED LOW-MID LEVEL VORTEX LOCATED OVER KY EARLY THIS MORNING 
 WILL WOBBLE SLOWLY EASTWARD ACROSS VA THROUGH TONIGHT... WHILE AT 
 THE SURFACE... LOW PRESSURE LOCATED JUST EAST OF THE VORTEX ALOFT 
 PASSES BY JUST TO OUR NORTH WITH THE TRAILING COLD FRONT SHIFTING 
 SLOWLY EAST THROUGH THE AREA. THE MODELS HAVE ALL BEEN TRENDING 
 SLOWER WITH THIS SYSTEM... BY ABOUT 4-6 HRS SINCE THEIR SUNDAY 
 EVENING RUNS. THE BROAD DISORGANIZED BAND OF SHOWERS AND ISOLATED 
 STORMS JUST TO OUR WEST WITHIN THE TROWAL AIR STREAM WILL CONTINUE 
 SPREADING EASTWARD THROUGH CENTRAL NC THIS MORNING... ALTHOUGH 
 ACTIVITY SHOULD DECREASE IN COVERAGE AND INTENSITY GIVEN THE 
 NARROWING AND WEAKENING WARM CONVEYOR BELT... THE WARMER TEMPS ALOFT 
 OVER CENTRAL/ERN VA... AND THE WANING LOW LEVEL CONVERGENCE. THE 
 LATEST HRRR MODEL RUNS DEPICT THIS QUITE WELL. WILL KEEP POPS AS A 
 BAND OF LOW CHANCES CROSSING CENTRAL NC THIS MORNING. ATTENTION THEN 
 TURNS TO POTENTIAL DEVELOPMENT OF ANOTHER BAND OF SHOWERS AND STRONG 
 STORMS ON THE EDGE OF THE INCOMING MID LEVEL DRY SLOT NOW PUNCHING 
 UP THROUGH MS/AL INTO ERN TN. WITH THIS DRYING ALOFT AND COOLING AS 
 THE MID LEVEL LOW APPROACHES... AND WITH THE LINGERING HIGH SURFACE 
 DEW POINTS AND WARM TEMPS HEATING UP INTO THE MID 70S TO NEAR 80... 
 INSTABILITY SHOULD BE INCREASING BY EARLY-MID AFTERNOON AHEAD OF THE 
 COLD FRONT... PARTICULARLY FROM RALEIGH TO THE NORTH AND EAST WHERE 
 THE GFS DEPICTS MLCAPE INCREASING TO OVER 1000 J/KG WITH 0-3 KM BULK 
 SHEAR OF 40-50 KTS AND SOUTHERLY WINDS OF 80-90 KTS AT 500 MB. AFTER 
 A BRIEF LULL IN POPS... WILL BRING IN ANOTHER GOOD CHANCE OF 
 SHOWERS/STORMS FROM MIDDAY THROUGH MID-LATE AFTERNOON. WITH THIS 
 GROWING INSTABILITY AND FAVORABLE WIND FIELD... EXPECT A FEW STORMS 
 TO BECOME STRONG TO SEVERE... MAINLY FROM RALEIGH TO THE NORTH AND 
 EAST FROM THE LUNCH HOUR ON THROUGH MID-LATE AFTERNOON. DAMAGING 
 WIND APPEARS TO BE THE GREATEST THREAT... ALTHOUGH THE RISK OF HAIL 
 IS ALSO ELEVATED ESPECIALLY FROM THE TRIAD AND TRIANGLE NORTHWARD 
 NEAR THE COLD POOL ALOFT. WILL TREND POPS DOWN AFTER 00Z AS THE 
 FRONT MOVES SLOWLY EAST OUT OF THE CWA... ALTHOUGH WILL RETAIN A 
 RISK OF ISOLATED SHOWERS AND A GOOD BIT OF CLOUD COVER OVERNIGHT 
 OVER THE NRN CWA AS MOISTURE CONTINUES TO POOL HERE WITH WEAK BUT 
 PERSISTENT ISENTROPIC UPGLIDE. HIGHS TODAY 73-79 AND LOWS TONIGHT 
 43-49. -GIH
 
 &&
 
 .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
 AS OF 315 AM MONDAY...
 
 MODELS AGREE FAIRLY WELL ON PLACING THE MID LEVEL LOW OVER NE VA AND 
 DC WEDNESDAY MORNING WITH THE SURFACE LOW OVER DE/SRN NJ AND A 
 SECONDARY SURFACE TROUGH DOWN THROUGH THE NC PIEDMONT. FORECAST 
 SOUNDINGS SHOW ENOUGH MOISTURE IN THE LOWEST 2 KM NORTH AND EAST OF 
 RALEIGH TO PUT A MENTION OF ISOLATED SHOWERS HERE... JUST AHEAD OF 
 THE SURFACE TROUGH... THROUGH WEDNESDAY MORNING. THEN THE NORTHWEST 
 LOW LEVEL FLOW AS THE LOW MOVES TO OUR NNE WILL BRING ABOUT LOW 
 LEVEL DRYING WITH OVERALL SUBSIDENCE IN THE MID/UPPER LEVELS. EXPECT 
 GRADUALLY CLEARING SKIES ACROSS THE CWA FROM SSW TO NNE THROUGH 
 WEDNESDAY NIGHT WITH THE BREEZY AND GUSTY NW WIND DIMINISHING. WITH 
 THE LONGER-RESIDING CLOUDS WEDNESDAY... HAVE BROUGHT HIGHS DOWN 
 SLIGHTLY TO 66-72... IN LINE WITH STATISTICAL GUIDANCE. LOWS 41-47. 
 -GIH 
 
 BROAD LOW AMPLITUDE SHORTWAVE RIDGING WILL SHIFT OVERHEAD 
 THURSDAY...WHILE COOLER HIGH PRESSURE SETTLES ACROSS THE CENTRAL 
 APPALACHIANS.  1000-850MB THICKNESSES ARE FORECAST TO BE SLIGHTLY 
 BELOW NORMAL AT NEAR 1340M AT 12Z THURSDAY...SO WILL STICK WITH 
 HIGHS NEAR NORMAL IN THE LOWER 70S.  OVERNIGHT LOWS WILL REBOUND A 
 FEW DEGREES THURSDAY NIGHT AS THE HIGH SLIPS OFFSHORE AND RETURN 
 FLOW DEVELOPS...49-53. -SMITH
 
 &&
 
 .LONG TERM /FRIDAY THROUGH MONDAY/...
 AS OF 315 AM TUESDAY...
 
 PACIFIC JET ENERGY DIGGING ACROSS THE ROCKIES WILL DEEPEN A SYSTEM 
 FROM THE LESS OF THE ROCKIES TO THE MID MS RIVER VALLEY REGION ON 
 FRIDAY. OUTSIDE OF THE 12Z/11TH ECMWF.. THERE HAS BEEN GOOD GENERAL 
 AGREEMENT BETWEEN THE GFS/ECMWF ON THE UPPER WAVE CUTTING OFF AND 
 THE SYSTEM BECOMING VERTICALLY STACKED AS THE A ~995MB SURFACE LOW 
 LIFTS NE FROM MO TO THE GREAT LAKES.  ONGOING CONVECTION SUPPORTED BY
 THE SFC ATTENDANT SURFACE FRONT/PREFRONTAL TROUGH AND A SPEED MAX 
 SURGING INTO THE BASE OF THE UPPER LOW IN A  MODESTLY UNSTABLE 
 AIRMASS OVER THE GULF COAST SHOULD BE APPROACHING THE SOUTHERN 
 APPALACHIANS BY 00Z SATURDAY.  MODELS ALSO INDICATED THE UPPER 
 TROUGH AXIS WILL BECOME NEGATIVELY TILTED AS IT REACHES THE 
 CAROLINAS SATURDAY NIGHT.  DIFFLUENT UPPER LEVEL FLOW AND 
 STRENGTHENING DEEP LAYER SHEAR WILL SUPPORT A SEVERE THREAT...THOUGH 
 THE DEGREE OF PREFRONTAL DESTABILIZATION WILL BE KEY WITH 
 OVERNIGHT/EARLY SATURDAY TIMING.  A SLIGHTLY SLOWER TIMING... AS 
 SUGGESTED BY THE ECMWF...COULD POSE A GREATER SEVERE WEATHER THREAT 
 ON SATURDAY.  WILL SEE CONTINUED INCREASE IN HIGHS FROM THURSDAY TO 
 FRIDAY...THOUGH A SOUTHEASTERLY LOW LEVEL FETCH FROM THE STILL COOL 
 ATLANTIC LOOKS TO KEEP HIGHS FROM STRAYING TOO FAR FROM 
 CLIMO...71-76.  SLOWER TIMING ON SATURDAY MAY ALLOW HIGHS TO CREEP 
 HIGHER INTO THE UPPER 70S TO AROUND 80 IN THE EAST.
 
 AS THE SYSTEM DEPARTS THE REGION LATE SATURDAY...MODELS DIVERGE 
 CONCERNING THE AMPLIFICATION AND LOCATION OF THE MEAN UPPER TROUGH 
 AXIS GOING INTO NEXT WEEK.  THE GFS SHOWS MORE EAST COAST TROUGHING 
 AND WNW FLOW OVER NC...WHILE THE ECMWF DEVELOPS LOW AMPLITUDE WSW 
 FLOW AND MODERATES THE AIRMASS OVER NC MORE QUICKLY.  THIS HAS 
 IMPLICATIONS FOR BOTH TEMPS AND MOISTURE AVAILABILITY AS THE NEXT 
 SYSTEM APPROACHES MONDAY/MONDAY NIGHT.
 
 &&
 
 .AVIATION /12Z TUESDAY THROUGH FRIDAY/...
 AS OF 725 AM TUESDAY...
 
 CURRENT VFR CONDITIONS ACROSS CENTRAL NC TERMINAL FORECAST SITES MAY 
 BECOME PREDOMINANTLY MFVR FOR A FEW HOURS THIS MORNING. A STRONG MID 
 LEVEL LOW PRESSURE SYSTEM WAS CENTERED OVER KY OVERNIGHT WITH A 
 TRAILING SLOW-MOVING COLD FRONT EXTENDING THROUGH ERN TN AND FAR SW 
 NC. A BAND OF WARM ADVECTION SHOWERS AND ISOLATED STORMS ALONG AND 
 AHEAD OF THE FRONT WILL MOVE THROUGH THE INT/GSO AREAS FROM 
 12Z-14Z... IN THE RDU AREA 13Z-15Z... AND THROUGH RWI/FAY 13Z-16Z 
 THIS MORNING... ACCOMPANIED BY MVFR CIGS/VSBYS. A BRIEF PERIOD (HALF 
 HOUR OR LESS) OF IFR CIGS IS POSSIBLE. CIGS WILL RISE BACK TO VFR 
 WEST TO EAST DURING THE MID-LATE MORNING... THEN ANOTHER BROKEN 
 NARROW BAND OF SHOWERS/STORMS IS EXPECTED TO DEVELOP OVER THE 
 CENTRAL PIEDMONT AFTER 17Z THIS AFTERNOON... AND ANOTHER PERIOD OF 
 MVFR CIGS IS POSSIBLE WITH BRIEF MVFR-IFR VSBYS IN AND NEAR 
 SHOWERS/STORMS. A FEW OF THESE STORMS MAY CONTAIN SMALL HAIL. AFTER 
 21-23Z... VFR CIGS WILL RETURN AND LAST THROUGH 06Z. WINDS WILL 
 REMAIN CHALLENGING FOR AIRCRAFT... BRISK AND GUSTY FROM THE SSW THIS 
 MORNING THROUGH MIDDAY... THEN BECOMING SOUTHWESTERLY THROUGH 21Z 
 BEFORE SHIFTING TO WNW AND DIMINISHING AFTER 21Z AT INT/GSO AND 
 AFTER 00Z AT RDU/FAY/RWI.  
 
 LOOKING BEYOND 12Z WEDNESDAY MORNING... VFR CONDITIONS WILL DOMINATE 
 FROM WEDNESDAY THROUGH THURSDAY EVENING. PATCHY IFR FOG IS POSSIBLE 
 THURSDAY NIGHT INTO FRIDAY MORNING. ANOTHER STORM SYSTEM WILL BRING 
 A GOOD CHANCE OF MVFR/IFR CONDITIONS WITHIN SHOWERS AND 
 THUNDERSTORMS LATE FRIDAY THROUGH MIDDAY SATURDAY... ALONG WITH 
 STRONG GUSTY SOUTH WINDS BECOMING SW. -GIH
 
 &&
 
 .RAH WATCHES/WARNINGS/ADVISORIES...
 NONE.
 
 &&
 
 $$
 
 SYNOPSIS...HARTFIELD
 NEAR TERM...HARTFIELD
 SHORT TERM...HARTFIELD/SMITH
 LONG TERM...SMITH
 AVIATION...HARTFIELD