940 FXUS62 KRAH 080446 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1245 AM EDT WED MAY 8 2013 .SYNOPSIS... AN UPPER LEVEL LOW PRESSURE SYSTEM WILL MOVE NORTHWARD AWAY FROM THE REGION TODAY. WEAK HIGH PRESSURE CENTERED OVER THE ATLANTIC WILL NOSE WESTWARD INTO THE SOUTHEAST THURSDAY AND FRIDAY... THEN A COLD FRONT WILL APPROACH FROM THE NORTHWEST EARLY SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1016 PM TUESDAY... MID/UPPER LEVEL LOW LOCATED IN THE VICINITY OF GSO AT 00Z. SPOKES OF VORTICITY ROTATING AROUND THIS FEATURE PROVIDING ENOUGH LIFT THROUGH THE MARGINALLY MOIST AIR MASS TO TRIGGER ISOLATED-SCATTERED SHOWERS ACROSS THE PIEDMONT THIS EVENING. SOME OF THE CAM RADAR DEPICTIONS AS WELL AS THE 12Z ECMWF SUGGEST THAT THE BAND OF SHOWERS CURRENTLY CROSSING THE SOUTHERN PIEDMONT WILL RIDE UP HIGHWAY 1 INTO THE TRIANGLE AREA WHILE ANOTHER AXIS OF ISOLATED-SCATTERED SHOWERS WILL LIKELY MOVE INTO THE WESTERN PIEDMONT OVERNIGHT-EARLY WEDNESDAY. HAVE ADJUSTED POPS TO REFLECT THIS TREND. CURRENT TEMP FORECAST APPEARS ON TRACK WITH MIN TEMPS 50-55. ADDED PATCHY FOG TO THE FORECAST AS PARTIAL CLEARING WILL ALLOW COOLING OF THE MOIST NEAR SURFACE AIR MASS...PROMOTING FOG DEVELOPMENT. NOT HIGHLY CONFIDENT THAT DENSE FOG WILL DEVELOP. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 245 PM TUESDAY... WEDNESDAY AND WEDNESDAY NIGHT: THE UPPER LEVEL LOW WILL TRACK THROUGH VA TOWARD THE DELMARVA WED INTO WED NIGHT...AND SHORTWAVE ENERGY ROTATING INTO CENTRAL NC AROUND THE WEST/SW PERIPHERY OF THE UPPER LEVEL LOW IN THE PRESENCE OF MARGINAL BOUNDARY LAYER MOISTURE AND FAVORABLE DIURNAL TIMING WILL RESULT IN SCATTERED SHOWERS AND ISOLD THUNDERSTORMS ACROSS THE AREA ONCE AGAIN...WITH THE RELATIVE BEST CHANCE IN THE NORTHERN PIEDMONT AND NE COASTAL PLAIN DURING THE AFTERNOON. EXPECT CHANCES TO DIMINISH AFTER SUNSET IN ASSOC/W NOCTURNAL STABILIZATION AND SUBSIDENCE IN THE WAKE OF SHORTWAVE ACTIVITY PROGRESSING OFFSHORE INTO THE ATLANTIC AROUND THE EASTERN PERIPHERY OF THE UPPER LOW TO THE N/NE. EXPECT HIGHS WED SIMILAR BUT PERHAPS SLIGHTLY WARMER THAN TODAY...IN THE LOWER TO MID 70S. LOWS WED NIGHT IN THE LOWER TO MID 50S. -VINCENT THURSDAY AND THURSDAY NIGHT: HEIGHT RISES AND ASSOCIATED DEEP LAYER SUBSIDENCE WILL PROVIDE FOR MOSTLY CLEAR SKIES OVERALL. A LINGERING LEE SURFACE TROUGH AND RELATIVELY UNCAPPED BUT DEEP BOUNDARY LAYER THROUGH 850 MB...BENEATH STILL STEEP MID LEVEL LAPSE RATES AROUND 6.5 C/KM...SUGGEST A SHOWER OR STORM WOULD BE POSSIBLE DURING THE AFTERNOON. HOWEVER...THE AFOREMENTIONED LARGER SCALE SUBSIDENCE AND DEEP DRYNESS SUGGESTS THE PROBABILITY WILL BE LESS THAN 20 PERCENT. HIGHS GENERALLY IN THE LOWER 80S...AND LOWS IN THE MIDDLE TO UPPER 50S. -MWS && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 110 PM TUESDAY... AROUND REX BLOCKING OVER THE WESTERN US...SPLIT FLOW ACROSS THE EASTERN TWO THIRDS OF THE COUNTRY WILL GRADUALLY TRANSITION TOWARD NORTHERN STREAM DOMINANCE OWING TO THE AMPLIFICATION OF A VORTEX INVOF THE SOUTHERN TIP OF HUDSON BAY DURING THE WEEKEND AND EARLY NEXT WEEK. THE PASSAGE OF A LEAD SHORTWAVE TROUGH THROUGH THE NORTHEAST ON FRIDAY WILL FIRST SHARPEN A LEE TROUGH OVER WESTERN NC FRI AFTERNOON...THEN PROPEL A LEAD SURFACE COLD FRONT INTO THE APPALACHIANS AND CAROLINAS ON SATURDAY. A STRONGER POLAR FRONT ATTENDING THE AFOREMENTIONED HUDSON BAY VORTEX WILL THEN OVERTAKE THE LEAD FRONTAL ZONE AND SWEEP ACROSS CENTRAL NC SUNDAY...WITH CONTINENTAL POLAR HIGH PRESSURE BUILDING IN FOR MON-TUE. AS SUCH...THE PREVIOUS FORECAST OF CHANCE OF SHOWERS AND STORMS OVER THE WESTERN PIEDMONT FRI...TRANSITIONING TO SOLID CHANCE AREA-WIDE SATURDAY THROUGH SUNDAY NEEDS LITTLE ADJUSTMENT. ANY ORGANIZED CONVECTIVE MODE WOULD BE FAVORED DURING THE WEEKEND...WHEN WARM SECTOR MID LEVEL FLOW WILL BE MAXIMIZED AROUND 40-50 KTS...WITH OTHERWISE DISORGANIZED/PULSE MODES UNTIL THEN. TEMPERATURES WILL CONSEQUENTLY BE VARIABLE...PEAKING IN THE MIDDLE 80S FRI...AND SAT IN THE COASTAL PLAIN...TRENDING TO THE MID-UPPER 60S IN THE CP HIGH PRESSURE MON...AND REBOUNDING TO AROUND 70 DEGREES BY TUE. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 1245 AM WEDNESDAY... LIKELIHOOD IS INCREASING THAT MOST CENTRAL NC TAF SITES WILL SEE VFR CIGS/VSBYS THROUGH THIS MORNING... ALTHOUGH A BRIEF PERIOD OF IFR VSBYS IS POSSIBLE AT INT/GSO NEAR AND JUST BEFORE DAYBREAK. CONSIDERABLE CONVECTIVE-DEBRIS CLOUDINESS FROM YESTERDAY'S SHOWERS AND STORMS ARE BASED ABOVE 5 THOUSAND FT AGL AND SHOULD CONTINUE TO OVERSPREAD INT/GSO/RDU THROUGH THE NIGHT... EVENTUALLY REACHING FAY/RWI AS WELL LATER TODAY. DESPITE THE OTHERWISE-FAVORABLE CONDITIONS OF LIGHT WINDS AND HIGH HUMIDITY WITH A DAMP GROUND... THE PRESENCE OF THESE CLOUDS WILL LOWER THE CHANCES OF FOG AND IFR/LIFR EARLY THIS MORNING. FAY WILL SEE THE FEWEST OF THESE HIGHER-BASED CLOUDS LATER THAN OTHER SITES... SO FAY HAS THE BEST CHANCE (BUT STILL LOW) OF SEEING LOW STRATUS DEVELOP. OTHERWISE... EXPECT VFR CONDITIONS TO DOMINATE MUCH OF TODAY INTO TONIGHT. SCATTERED SHOWERS AND STORMS ARE EXPECTED TO AFFECT INT/GSO MAINLY FROM 16Z-20Z... RDU MAINLY FROM 17Z-21Z... AND RWI/FAY MAINLY FROM 19Z-23Z... AND A PERIOD OF MVFR-IFR CIGS/VSBYS IN AND NEAR SHOWERS/STORMS IS LIKELY. LOOKING BEYOND 06Z TONIGHT: VFR CLOUDS ARE EXPECTED TO CLEAR OUT LATE... AND SUB-VFR FOG IS POSSIBLE TONIGHT PRIMARILY 08Z-12Z AT ALL SITES. OTHERWISE VFR CONDITIONS SHOULD DOMINATE INTO SATURDAY MORNING. AN APPROACHING COLD FRONT WILL BRING A CHANCE OF SUB-VFR CONDITIONS IN SHOWERS/STORMS SATURDAY AFTERNOON INTO SUNDAY. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...WSS SHORT TERM...VINCENT/MWS LONG TERM...MWS AVIATION...HARTFIELD