Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 151846 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 245 PM EDT WED APR 15 2015 .SYNOPSIS...
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CHILLY HIGH PRESSURE WILL EXTEND INTO THE CAROLINAS AND VIRGINIA FROM THE NORTHEAST THROUGH THURSDAY NIGHT. A WEAK AREA OF LOW PRESSURE WILL DEVELOP OFF THE SOUTHEAST COAST ON THURSDAY AND DRIFT NORTHEAST AND MOVE AWAY FROM THE REGION ON FRIDAY. WEAK HIGH PRESSURE WILL EXTEND INTO THE REGION FOR LATE FRIDAY INTO SATURDAY BEFORE THE NEXT STORM SYSTEM APPROACHES ON SUNDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 230 PM WEDNESDAY... A LULL IN PRECIPITATION THIS AFTERNOON AS A SECONDARY WAVE OF DRIER AIR HAS WORKED INTO THE AREA FROM THE NORTHEAST. THIS HAS LIFTED CLOUD BASES TO VFR LEVELS AND REDUCED QPF AMOUNTS SIGNIFICANTLY OVER THE AREA. BACK TO THE WEST A HEAVIER SWATH OF MODERATE PRECIPITATION AND A FEW EMBEDDED THUNDERSTORMS HAS MOVED INTO UPSTATE SOUTH CAROLINA. THIS HAS BEEN LARGELY FOCUSED ON THE CONVERGENCE OF THE SURFACE COLD FRONT AND THE 850 MB TROUGH EXTENDING ACROSS THE AREA. IT HAS HAD SOME HELP FROM SOME UPPER LEVEL SPEED DIVERGENCE AT 500 MB. THIS BAND OF HEAVIER MOISTURE SHOULD MOVE INTO SOUTHWESTERN PORTIONS OF THE CWA OVER THE NEXT COUPLE OF HOURS AND TRANSLATE EASTWARD WITH TIME. WITH THIS RAIN WILL MOST LIKELY COME SOME LOWERING OF THE CEILINGS BACK TO MVFR LEVELS BUT NOT MUCH LOWER. TEMPERATURES THIS AFTERNOON HAVE BEEN LARGELY DEPENDENT ON RAINFALL DISTRIBUTION AND THE OPACITY OF THE CLOUD COVER. BOTH HAVE BEEN LESS IN THE EAST...WHICH IS WHERE THE WARMEST TEMPS HAVE BEEN. MAINLY MID TO UPPER 50S IN THE NW AND LOW TO MID 60S IN THE SOUTHEAST. HIGH RESOLUTION MODELS SHOW RAIN SPREADING THROUGH ALMOST THE ENTIRE CWA BY 00Z BUT THE INFLUENCES FROM DRIER AIR TO THE NORTHEAST BEGIN TO ADVANCE SOUTHWESTWARD AND RAIN GETS SHUT OFF DURING THE OVERNIGHT HOURS FROM NORTHEAST TO SOUTHWEST WITH MOST RAIN REMAINING SOUTH AND WEST OF I-40 FROM WINSTON-SALEM TO THE COAST THROUGH SUNRISE. COOL OVERNIGHT WITH LOWS IN THE UPPER 40S BUT POSSIBLY AS LOW AS THE MID 40S IN THE NORTHEAST WHERE THE DRIER AIR RESIDES. SREF PROBABILITIES INDICATE THAT SUB VFR CLOUD COVER AND VISIBILITIES WILL BE MORE LIKELY ON WESTERN AND SOUTHERN FRINGES OF THE CWA WITH THE REST OF THE AREA EXPECTED TO REMAIN VFR. WHILE THIS SEEMS LIKE A DECENT SCENARIO IT SHOULD BE NOTED THAT FORECAST CONFIDENCE IS LOW GIVEN THE COLD AIR DAMMING PATTERN AND SOME OF THE OTHER LOWER RESOLUTION MODELS INDICATING SOME SUB-VFR CEILINGS AND VISIBILITIES OVERNIGHT.
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&& .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
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AS OF 230 PM WEDNESDAY... AS HIGH PRESSURE MOVES EASTWARD INTO A MORE FAVORABLE POSITION FOR HYBRID DAMMING ON THURSDAY MORNING...MODELS ALSO INDICATE THE DEVELOPMENT OF A COASTAL LOW OFF OF SOUTH CAROLINA. THE COMBINATION OF THE TWO SUGGESTS A VERY SHARP FRONTAL BOUNDARY EARLY BUT AS THE DAY PROGRESSES A THIRD PLAYER WILL BE A STRONGER LOW PRESSURE SYSTEM MOVING ACROSS NORTHERN QUEBEC. THIS LOW...ALONG WITH A SHORTWAVE WEST OF THE APPALACHIANS WILL HELP PUSH THE HIGH SOUTHEASTWARD THROUGH THE DAY...MOVING FROM A MORE HYBRID TO AN IN-SITU DAMMING SCENARIO. IN THE PROCESS HOWEVER...THE INFLUENCE OF THE HIGH SHUTS OFF PRECIPITATION IN THE NORTHEAST THROUGH THE MORNING HOURS WITH ONLY LIGHT SCATTERED RAIN EXPECTED DURING THE AFTERNOON. SO BEST CHANCES FOR RAIN WILL AGAIN BE IN THE SOUTHWEST...SPURRED ON BY ISENTROPIC LIFT THAT WILL BE MOST PREVALENT DURING THE MORNING HOURS AND THEN LESS SO IN THE AFTERNOON. WHILE CONDITIONS WILL BE CLOUDY AND THERE WILL BE CHANCES FOR RAIN MOST OF THE DAY...QPF VALUES SHOULD BE VERY LOW...NAMELY LESS THAN A TENTH OF AN INCH. TEMPERATURES WILL FOLLOW THE TYPICAL CAD PATTERN WITH LOWEST MAX TEMPS IN THE WEST (MID 50S) WITH MIDDLE 60S EAST OF I-95. PRECIPITATION IS EXPECTED TO WIND DOWN AFTER SUNSET BUT CONDITIONS WILL REMAIN CLOUDY THROUGH THURSDAY NIGHT. LOWS IN THE LOW TO MID 50S NW TO SE.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 210 PM WEDNESDAY... FRI-SAT NIGHT: LATEST MODEL RUNS HAVE COME INTO BETTER AGREEMENT ON THE LATE-WEEK PATTERN. A MID LEVEL LOW WILL HOLD NEAR THE CO/NM BORDER... WELL SEPARATED FROM THE NORTHERN STREAM WHICH WILL FEATURE ONE POTENT SHORTWAVE TROUGH ZIPPING ESE ACROSS ONTARIO/SRN QUEBEC AND NRN NEW ENGLAND... AND A SECOND WAVE CROSSING BC AND THE CANADIAN PRAIRIE PROVINCES. THE WEAK MID LEVEL WAVE OVER THE MIDATLANTIC COAST EARLY FRI WILL SHIFT OFFSHORE DURING THE MORNING... AND SUBSIDENCE IN THE WAKE OF THIS WAVE WITH MID LEVEL SHORTWAVE RIDGING BETWEEN THE EXITING WAVE AND THE SOUTHWEST STATES LOW SHOULD BRING ABOUT A PERIOD OF LARGELY DRY WEATHER FRI INTO SAT. WILL RETAIN CHANCE POPS IN THE ERN CWA EARLY FRI TO ACCOUNT FOR LINGERING MOISTURE AND LIFT... BUT THEN WILL TREND BY MIDDAY TO DRY WEATHER AREAWIDE AS WEAK SURFACE HIGH PRESSURE BUILDS IN WITH DIFFLUENT DOWNGLIDE AT 850 MB. WHILE FORECAST SOUNDINGS SHOW ABUNDANT MID LEVEL DRY AIR ESPECIALLY LATER IN THE DAY... LOW LEVEL MOISTURE WILL TAKE LONGER TO DISPERSE... AND AS SUCH FORECAST SOUNDINGS SHOW WEAK INSTABILITY IN THE AFTERNOON... UP TO 500-750 J/KG OF MUCAPE MAINLY IN THE NW. WILL INCLUDE A LATE-DAY SLIGHT CHANCE OF A STORM OR TWO... WITH THE THREAT ENDING QUICKLY BY MID EVENING WITH THE LOSS OF HEATING. EXPECT DRY WEATHER OVERNIGHT INTO AT LEAST THE FIRST PART OF SATURDAY AS THE MID-HIGH LEVEL DRYING PERSISTS. A FEW SHOWERS MAY FORM LATE IN THE DAY ESPECIALLY OVER THE WRN AND SRN CWA... AS THE 850 MB ANTICYCLONE SHIFTS TO OUR EAST WITH THE ONSET OF SOUTHEASTERLY LOW LEVEL ATLANTIC-SOURCE FLOW... WHILE SRN STREAM ENERGY EJECTING FROM THE BASE OF THE LOW TOWARD NC RESULTS IN A GRADUAL INCREASE IN DPVA FROM THE SW. THE SOUTHWEST LOW STARTS TO OPEN UP AND LIFT NE SAT AND GETS PICKED UP BY THE WRN CANADA SHORTWAVE TROUGH... CULMINATING IN A LARGE BROAD TROUGH WITH A SLIGHT POSITIVE TILT EXTENDING THROUGH CENTRAL NOAM. MOISTURE EXTENT AND DEPTH OVER NC AS WELL AS FORCING FOR ASCENT WILL CONTINUE TO INCREASE FROM THE SW SAT NIGHT WITH THE MID LEVEL RIDGE AXIS SHIFTING TO OUR EAST... AND WILL INDICATE BOTH INCREASING POPS AND CLOUDS FROM THE SW LATE SAT THROUGH SAT NIGHT. IN ADDITION... THE STRONG WAVE CROSSING NEW ENGLAND WILL HELP DRAW DOWN A BACKDOOR FRONT TO NEAR THE VA/NC BORDER LATE SAT NIGHT WITH COOL HIGH PRESSURE OVER WRN QUEBEC NOSING SOUTHWARD... AND THIS MAY PROVIDE A LITTLE EXTRA LOW LEVEL FOCUS FOR PRECIP AS WE HEAD INTO EARLY SUNDAY. EXPECT SLIGHTLY ABOVE NORMAL TEMPS... WITH HIGHS IN THE 70S TO AROUND 80 (WARMER SAT THAN FRI) AND LOWS IN THE UPPER 50S TO LOWER 60S. FOR SUN-WED: OUR RAIN CHANCES APPEAR TO PEAK SUN/SUN NIGHT AS THE AXIS OF THE LONGWAVE TROUGH EXTENDING FROM LOW PRESSURE OVER SRN MANITOBA DOWN TO THE GULF STATES PIVOTS TO THE NE. THE SURFACE MAP WILL FEATURE AN EXPANSIVE FRONTAL SYSTEM... EXTENDING FROM AN OCCLUSION OVER THE SOUTH CENTRAL CANADA THROUGH THE GREAT LAKES... DOWN THROUGH THE MID SOUTH... GULF STATES... AND SOUTHEAST STATES... ALL SWEEPING TOWARD THE ENE SUN/MON. MODELS AGREE FAIRLY WELL ON INCREASING AND DEEPENING MOIST INFLOW FROM BOTH THE ATLANTIC AND GULF ALONG WITH STRENGTHENING DYNAMIC FORCING FOR ASCENT OVER NC... AND HAVE GONE WITH LIKELY POPS SUN/SUN NIGHT. COULD SEE SOME HEAVY RAIN. POPS SHOULD TREND DOWN IN COVERAGE DURING MONDAY BUT WE COULD END UP WITH SCATTERED STORMS IN THE AFTERNOON... AS WE SEEM TO GET A MID LEVEL DRY PUNCH INTO THE WARM SECTOR AS THE BROAD TROUGH AXIS SLOWLY LIFTS OUT TO OUR NE. LARGE LOW PRESSURE WILL THEN SIT AND SPIN OVER THE UPPER MIDWEST/ NORTHERN GREAT LAKES AND ADJACENT CANADIAN PROVINCES INTO MIDWEEK WITH ROUGHLY ZONAL FLOW OVER THE SRN HALF OF THE CONUS... SO EXPECT DRY WEATHER AND FAIRLY SEASONABLE TEMPS. THE GFS BRINGS A QUICK SHOT OF LIGHT PRECIP IN FROM THE WEST EARLY WED... BUT THIS DOESN`T LOOK WELL SUPPORTED AND WILL KEEP WED DRY FOR NOW. -GIH && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 144 PM WEDNESDAY... 24 HOUR TAF PERIOD: THE MAJORITY OF CEILINGS ACROSS THE AREA HAVE RISEN TO VFR LEVELS THIS AFTERNOON BUT RADAR SHOWS A LARGE AREA OF MODERATE TO HEAVY RAIN MOVING INTO THE NORTHWEST PIEDMONT AND WOULD NOT BE SURPRISED TO SEE CEILINGS DROP BACK TO MVFR THERE IN THE NEXT COUPLE OF HOURS. AS THIS NEW BATCH OF MOISTURE WORKS EASTWARD...EXPECT SIMILAR FALLS IN CEILINGS AT KFAY AND PERHAPS KRDU AND KRWI BUT THESE TWO STATIONS HAVE THE BEST CHANCE OF REMAINING VFR THROUGH THE TAF PERIOD. THAT BEING SAID FORECAST CONFIDENCE IN CEILINGS IS VERY LOW AT THIS TIME BUT HIGH RESOLUTION MODELS SHOW THAT PERHAPS THE NORTHEASTERN HALF OF THE AREA REMAIN VFR THROUGH THE PERIOD WITH THE BEST CHANCE FOR LOWER CEILINGS ACROSS THE SOUTH AND WEST. PERIODS OF RAIN CAN BE EXPECTED THROUGH THE AFTERNOON AND EVENING...PARTICULARLY IN THE SOUTHWEST WITH RAIN HOLDING OFF IN THE NORTHEAST UNTIL LATER IN THE AFTERNOON ON THURSDAY. VISIBILITIES ARE A LOW CONFIDENCE FORECAST AS WELL GIVEN THE PATTERN BUT SREF ENSEMBLE MEMBERS SHOW THAT THE LIKELIHOOD OF VISIBILITIES DROPPING BELOW VFR LEVELS OVERNIGHT IS LOW AND CURRENT OBSERVATIONAL PATTERNS LEND SUPPORT TO THIS SOLUTION BEING MORE LIKELY. WINDS WILL REMAIN OUT OF THE NORTHEAST THROUGH THE PERIOD AT 5-10 KTS. LONG TERM: UNSETTLED PATTERN CONTINUES WITH CHANCES FOR ADVERSE CONDITIONS THROUGH THE WEEKEND...AND ON SUNDAY IN PARTICULAR AS A FRONTAL ZONE CROSSES THE AREA THROUGH MONDAY MIDDAY WITH A POSSIBLE RETURN TO VFR CONDITIONS ON TUESDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BLAES NEAR TERM...ELLIS SHORT TERM...ELLIS LONG TERM...HARTFIELD AVIATION...ELLIS

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