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