Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 241442 AFDRAH AREA FORECAST DISCUSSION 1045 AM EDT FRI APR 24 2015 .SYNOPSIS...COOL HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE NORTHWEST TODAY. A WARM FRONT WILL MOVE IN FROM THE SOUTHWEST LATE TONIGHT...AND THEN STALL ACROSS THE REGION THROUGH THE WEEKEND... BRINGING UNSETTLED WEATHER AS WAVES OF LOW PRESSURE TRACKING EAST ALONG THE FRONT. && .NEAR TERM /THROUGH THIS AFTERNOON/...
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AS OF 1045 AM FRIDAY... SFC HIGH WILL SETTLE OVERHEAD THIS AFTERNOON WHILE MID-UPPER LEVEL HEIGHTS INCREASE AS S/W RIDGE EDGES EAST FROM THE MS RIVER VALLEY. SUBSIDENCE ALOFT WILL MAINTAIN MOSTLY CLEAR SKIES OVER THE REGION. 850MB THERMAL TROUGH WILL LIFT NORTH-NE THIS AFTERNOON. THIS WILL COMMENCE A LOW LEVEL WARM AIR ADVECTION REGIME. AFTER THE CHILLY START TO THE DAY WITH MIN TEMPS IN THE 30S ACROSS A LARGE PORTION OF CENTRAL NC...MOST PLACES WILL WARM TO AROUND 60- LOWER 60S BY MID DAY...TOPPING OUT IN THE 65-70 DEGREE RANGE AT MID- AFTERNOON. THESE AFTERNOON TEMPERATURES COMBINED WITH DEWPOINTS IN THE UPPER TEENS AND 20S WILL YIELD MINIMUM RH VALUES IN THE 15-20 PERCENT RANGE THIS AFTERNOON...ABNORMALLY LOW FOR THIS TIME OF YEAR.
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&& .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... AS OF 325 AM FRIDAY... A PLUME OF PACIFIC MOISTURE CROSSING MEXICO WILL BE DRAWN EASTWARD TODAY AS A WEAK UPPER LOW NEAR THE CA/AZ BORDER AREA OPENS UP AND LIFTS ACROSS THE PLAINS STATES. THE ASSOCIATED SURFACE WILL MOVE INTO THE MID-MISSISSIPPI RIVER VALLEY WHILE THE ATTENDANT WARM FRONT LIFTS THROUGH THE SOUTHEAST US. MID-CLOUDS WILL THICKEN FROM WEST TO EAST FRIDAY NIGHT AS WARM ADVECTION SPREADS ACROSS THE REGION....RESULTING IN LOWS RANGING FROM THE LOW 40S IN THE CLEARER EASTERN AREAS AND UPPER 40S TO AROUND 50 IN THE OVERCAST WESTERN AREAS. SOME AREAS OF LIGHT RAIN MAY REACH THE WESTERN PIEDMONT PRIOR TO 12Z SATURDAY...BUT THE MORE INTENSE 290-300K LAYER ISENTROPIC ASCENT IS PROGGED TO COME DURING THE DAY ON SATURDAY...AND MORE SO DURING THE AFTERNOON...AS THE SURFACE LOW MOVES TOWARD THE LOWER OHIO VALLEY REGION. A BAND OF RAIN DURING THE DAY SHOULD LOCK IN A COLD POOL OVER CENTRAL NC AND KEEP THE WARM FRONT DRAPED ACROSS THE SOUTHERN PORTIONS OF THE AREA...WHERE THE PROSPECTS OF SOME WEAK DESTABILIZATION...MAINLY ELEVATED...WILL BE GREATEST DURING THE LATE AFTERNOON AND EVENING HOURS BASED ON THE PREFERRED NAM AND ECMWF SOLUTIONS. WILL TRANSITION THE CHARACTER OF PRECIP IN THE FORECAST FROM RAIN TO SHOWERS DURING THE LATER AFTERNOON...WITH A SLIGHT CHANCE OF THUNDER FROM THE SOUTHERN PIEDMONT TO THE SANDHILLS DURING THE EVENING. WHILE MODELS STILL SHOW SOME DIFFERENCES IN QPF AMOUNTS...THE ECMWF AND SREF SHOW WHAT SEEMS TO BE THE MORE REASONABLE DISTRIBUTIONS...WITH THE HIGHER AMOUNTS AROUND A THIRD OF AN INCH ACROSS THE SOUTH AND LIGHTER AMOUNTS TO THE NORTH. TEMPS ARE TRICKY FOR SATURDAY AND WILL DEPEND ON THE TIMING OF PRECIP DURING THE FIRST HALF OF SATURDAY. HAVE SLOWED THE ARRIVAL OF PRECIP A LITTLE IN THE EAST...SO WILL NUDGE TEMPS UP OVER THE COASTAL PLAIN...BUT STILL EXPECT A STRONG GRADIENT FROM LOWER 50S NORTHWEST TO LOWER 60S SOUTHEAST. THERE SHOULD THEN BE A DECREASE IN SHOWER ACTIVITY SATURDAY NIGHT AS A DRY SLOT SURGES IN FROM THE WEST AND THE SURFACE LOW TRANSITIONS OFFSHORE. EXPECT SKIES TO REMAIN OVERCAST...HOWEVER...AND TEMPS WILL ONLY FALL A FEW DEGREES INTO THE UPPER 40S TO MID 50S. && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 400 AM FRIDAY... A WPC-FAVORED BLEND OF THE 00Z/24TH ECMWF AND NAM SUGGESTS A LEAD SFC LOW WILL BE MOVING AWAY FROM THE NC COAST EARLY SUN...IN ASSOCIATION WITH THE PASSAGE AND SHEARING/DEAMPLIFICATION OF THE SOUTHERN STREAM UPPER LOW LOCATED OVER NW MEXICO THIS MORNING. A COLD FRONT WILL EXTEND WNW INVOF THE NC/SC BORDER...TO A SECONDARY SFC LOW FORECAST TO DEVELOP EAST ACROSS THE SOUTHERN-CENTRAL APPALACHIANS AND OFF THE SC COAST BY SUN EVE. LOW LEVEL FRONTOGENESIS AND ISENTROPIC UPGLIDE AHEAD OF THE SECONDARY LOW WILL SUPPORT CONTINUED WIDESPREAD LOW CLOUDS...AND A GOOD TO LIKELY PROBABILITY OF RAIN SUN...MORE SHOWERY IN NATURE INVOF THE SFC FRONT NEAR THE SC BORDER. THE PROXIMITY OF THE SFC FRONT WILL ALSO SUPPORT A LARGE RANGE IN TEMPERATURES FROM THE 50S OVER THE NORTHERN PIEDMONT AND NORTHERN-CENTRAL COASTAL PLAIN WHERE OVERCAST WILL LIKELY HOLD THROUGHOUT THE DAY...TO LOWER 70S NEAR THE SC BORDER...WHERE BRIEF PARTIAL CLEARING WILL BE POSSIBLE DURING THE MIDDAY TO EARLY AFTERNOON HOURS INVOF THE FRONT. A PERIOD OF RELATIVELY TRANQUIL AND COOL CONDITIONS...WITH LOWS IN THE 40S AND HIGHS IN THE MIDDLE 60S TO LOWER 70S (WARMEST TUE)... CAN BE EXPECTED EARLY NEXT WEEK...AS A DEEP VORTEX MIGRATES SLOWLY AWAY FROM THE NE US. THE PRESENCE OF THE VORTEX AND UNSEASONABLY DEEP CYCLONIC FLOW CENTERED OFF THE NEW ENGLAND COAST...BENEATH HIGHER LATITUDE BLOCKING FLOW...WILL MAINTAIN A SOUTHWARD-SUPPRESSED STORM TRACK AND FOCUS FOR PRECIPITATION ACROSS THE SOUTHEAST STATES BY THE MIDDLE OF NEXT WEEK. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... AS OF 640 AM FRIDAY... HIGH CONFIDENCE IN VFR CONDITIONS THROUGH THE NEXT 24 HOURS...WITH SUB-VFR CONDITIONS TO FOLLOW. RELATIVELY LIGHT NORTH-NORTHWESTERLY WINDS WILL CONTINUE FOR MOST AREAS THIS MORNING...INCREASING TO AROUND 10KT TODAY AS HIGH PRESSURE OVER THE OHIO VALLEY REGION BUILDS EAST. MOSTLY CLEAR SKIES WILL SLOWLY GIVE WAY TO HIGH CLOUDS FROM THE SOUTHWEST THIS EVENING AND THEN MORE MID CLOUDS BETWEEN 7-10K FT OVERNIGHT. OUTLOOK... THE APPROACH OF A WARM FRONT AND LOW PRESSURE SYSTEM WILL BRING WIDESPREAD RAIN AND MVFR/IFR CEILINGS SATURDAY AND SATURDAY NIGHT. MODELS ARE A BIT SLOWER IN BRINGING IN SUB-VFR CEILINGS ON SATURDAY...HOLDING OFF MVFR CONDITIONS UNTIL LATE MORNING OR EARLY AFTERNOON. LOW CEILINGS ARE EXPECTED TO LINGER INTO SUNDAY... WITH A GRADUAL IMPROVEMENT EXPECTED SUNDAY AFTERNOON. VFR CONDITIONS SHOULD RETURN BY MONDAY AND PERSIST INTO TUESDAY AS WEAK HIGH PRESSURE BUILDS INTO OUR REGION FROM THE NORTH-NW. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...WSS SHORT TERM...22 LONG TERM...RAH AVIATION...22

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