Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 241915 AFDRAH AREA FORECAST DISCUSSION 310 PM EDT FRI APR 24 2015 .SYNOPSIS...A SERIES OF UPPER DISTURBANCES WILL CAUSE UNSETTLED WEATHER ACROSS CENTRAL NC THROUGH THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 310 PM FRIDAY... MID-UPPER LEVEL S/W RIDGE WILL DRIFT ACROSS THE FORECAST AREA TONIGHT. THIS WEATHER FEATURE WILL INITIALLY CAUSE MOSTLY CLEAR SKIES OVERHEAD. THE ATTENDANT DRY AIR MASS (SFC DEWPOINTS THIS AFTERNOON DOWN INTO THE 20S) WILL ALLOW THE ATMOSPHERE TO COOL EFFICIENTLY AFTER SUNSET. WHILE NOT AS COOL AS LAST NIGHT...LATE EVENING TEMPS SHOULD BE IN THE 40S TO NEAR 50. MOST PLACES WILL LIKELY ACHIEVE THEIR MIN TEMPS SHORTLY AFTER MIDNIGHT. DURING THE OVERNIGHT HOURS...INCREASING MID-HIGH LEVEL CLOUDS ASSOCIATED WITH AN AREA OF LOW PRESSURE CROSSING THE LOWER MS VALLEY WILL INCREASE WEST-TO EAST ACROSS CENTRAL NC. THIS INCREASING/THICKENING CLOUD COVER SHOULD CAUSE TEMPS TO HOLD STEADY OR POSSIBLY SLOWLY RISE DURING THE PRE-DAWN OURS. CANNOT RULE OUT THE POSSIBILITY OF A SHOWER OR TWO SKIRTING ALONG OUR WESTERN PERIPHERY BEFORE 7 AM. ELSEWHERE NO RAIN SHOULD OCCUR. MIN TEMPS NEAR 40 FAR NE TO THE MID- UPPER 40S WEST. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... AS OF 310 PM FRIDAY... INCREASING LOW LEVEL WARM AIR ADVECTION ASSOCIATED WITH AN UPPER LEVEL DISTURBANCE MOVING EAST ACROSS THE DEEP SOUTH INTO THE SE U.S. WILL CAUSE AREAS OF RAIN TO INCREASE IN COVERAGE AND INTENSITY SATURDAY ACROSS CENTRAL NC. EXPECT THE BULK OF THE RAIN TO OCCUR WEST OF THE HIGHWAY 1 CORRIDOR THROUGH MID DAY...THEN OVERSPREAD THE REMAINDER OF THE REGION IN THE AFTERNOON. THE RAIN FALLING THROUGH THE DRY SUB CLOUD LAYER MAY CAUSE AN IN-SITU OR WEAK HYBRID DAMMING EVENT TO OCCUR...MAINLY LIMITED TO THE NORTHWEST PIEDMONT. THE TIMING OF THE RAIN WILL HAVE AN IMPACT ON HIGH TEMPS FOR THE DAY. EXPECTING THE RAIN NOT TO ARRIVE IN THE RDU AREA UNTIL CLOSE TO MID DAY WHICH SHOULD ALLOW FOR SOME TEMP RECOVERY. IN THE TRIAD...EXPECT THE RAIN TO START BETWEEN 8 AM AND 12 PM. DUE TO THE RAIN ARRIVING SHORTLY AFTER DAYBREAK...TEMPS IN THE TRIAD MAY STRUGGLE TO WARM MUCH ABOVE THE LOWER 50S. LATE IN THE AFTERNOON...THE PASSAGE OF THE 850MB WARM FRONT ACROSS OUR SOUTHERN COUNTIES MAY ERODE THE STABLE LAYER ENOUGH TO ALLOW FOR THE DEVELOPMENT OF A FEW THUNDERSTORMS. WITH BETTER INSTABILITY LYING TO OUR SOUTH...LOW LEVEL FLOW WILL BE ADVECTING THIS SLIGHTLY UNSTABLE AIR MASS INTO OUR SOUTHERN COUNTIES INTO THE EVENING HOURS. SHEAR WILL BE SUFFICIENT TO SUPPORT ORGANIZED CONVECTION AND LATEST CAM DEPICTIONS SUGGEST A FEW STORMS CROSSING THE SC BORDER SATURDAY EVENING. WHILE CANNOT RULE OUT THE POTENTIAL FOR A SEVERE STORM NEAR THE SC BORDER SATURDAY NIGHT...CONFIDENCE NOT HIGH ENOUGH AT THIS TIME TO MENTION IN FORECAST OR THE HWO. THE CONTINUED NEWD PROGRESSION OF THE 850 MB WARM FRONT SHOULD PUSH THE RAIN OUT OF THE NE PIEDMONT/NORTHERN COASTAL PLAIN SATURDAY EVENING...WITH SCATTERED SHOWER HIGHLY PROBABLE IN ITS WAKE. WITH THE WARM AIR ALOFT ABOVE THE RELATIVELY COOL SFC LAYER...WILL LIKELY SEE AREAS OF FOG AND/OR LOW CLOUDS OVER THE PIEDMONT AND NORTHERN COASTAL PLAIN SATURDAY NIGHT. MAX TEMPS SATURDAY LOW-MID 50S NW TO THE MID 60S SOUTH. MIN TEMPS SATURDAY NIGHT UPPER 40S/NEAR 50 NORTH AND THE MID-UPPER 50S SOUTH. && .LONG TERM /SUNDAY THROUGH FRIDAY/... AS OF 300 PM FRIDAY... SUNDAY: EXPECT WARM MOIST WEST-SOUTHWESTERLY FLOW TO START THE PERIOD...WITH THE RETREATING WARM FRONT INVOF THE NC/VA BORDER. AN UPPER LEVEL SHORTWAVE WILL TRAVERSE THE REGION DURING THE DAY SUNDAY. AT THE SURFACE...A WEST-EAST ORIENTED LOW OVER THE CAROLINAS WILL SLOWLY BE PUSHED SOUTH AND EAST AS A COLD FRONT SLIDES THROUGH THE REGION. EXPECT SOME RAIN TO MOVE THROUGH CENTRAL NC FROM NORTH TO SOUTH AHEAD OF THE FRONT...ENDING LATE SUNDAY EVENING...ALTHOUGH THE EXACT TIMING REMAINS UNCERTAIN. THE 12Z GFS SOLUTION IS CLOSE TO THE 00Z ECMWF SOLUTION WITH RESPECT TO TIMING OF THE FRONT...THE 12Z CANADIAN LAGS 6-12 HOURS BEHIND. WILL CONTINUE TO LEAN MORE TOWARD THE ECMWF...WITH THE FRONT MAKING ITS WAY THROUGH THE AREA BY SUNDAY NIGHT. HIGHS WILL DEPEND ON THE TIMING OF THE FRONT AND IF AND HOW MUCH SKIES CLEAR ACROSS THE SOUTH DURING THE DAY. FOR NOW...EXPECT A WIDE RANGE OF HIGHS...MID 50S NORTH TO POTENTIALLY LOW 70S SOUTH. SUNDAY NIGHT THROUGH TUESDAY NIGHT: AS PREVIOUSLY STATED...THE RAIN SHOULD BE OUT OF THE REGION BY SUNDAY NIGHT...AND EXPECT THE WEATHER TO REMAIN DRY THROUGH TUESDAY NIGHT UNDER NW FLOW AND SUBSIDENCE ALOFT. AT THE SURFACE...COLD BUT WEAKENING HIGH PRESSURE WILL GRADUALLY BUILD INTO THE AREA THROUGH THE PERIOD. HIGHS WILL GENERALLY BE IN THE MID 60S TO LOW 70S...LOWS IN THE LOW TO MID 40S. WEDNESDAY AND THURSDAY: THERE IS QUITE A BIT OF DIVERGENCE BETWEEN THE MODELS DURING THIS PART OF THE FORECAST...THUS THERE IS NOT A LOT OF CONFIDENCE WITH RESPECT TO TIMING AND INTENSITY OF VARIOUS FEATURES. GENERALLY SPEAKING THOUGH...EXPECT A SURFACE LOW TO DEVELOP OVER THE GULF COAST ON WEDNESDAY AND SLOWLY MOVE EAST- NORTHEAST TOWARD THE CAROLINAS THROUGH THURSDAY. ALOFT...THOUGH THERE IS UNCERTAINTY ON WHETHER IT WILL BE CUTOFF OR OPEN...EXPECT AN UPPER LEVEL LOW TO DEVELOP OVER OK/TX ON TUESDAY AND MOVE EAST TOWARD THE CAROLINAS TUESDAY NIGHT/EARLY WEDNESDAY. THE ECMWF SEEMS TO BE MORE INTENSE/AMPLIFIED AND QUICKER MOVING INTO THE AREA THAN THE GFS AT THIS TIME. REGARDLESS...EXPECT INCREASING RAINFALL CHANCES BEGINNING LATE TUESDAY NIGHT/WEDNESDAY MORNING THROUGH THURSDAY AND POSSIBLY THURSDAY NIGHT. WITH THE LOW LEVEL FLOW DEPENDENT ON THE POSITION OF THE LOW...AND THE TEMPERATURES DEPENDENT ON THE LOW LEVEL FLOW...THERE IS A HIGH DEGREE OF UNCERTAINTY IN THE TEMPERATURES FOR WEDNESDAY AND THURSDAY AND THERE COULD QUITE POSSIBLY BE A LARGE RANGE OF TEMPERATURES FROM NW TO SE ACROSS THE AREA. HIGHS IN THE MID 60S TO NEAR 70 DEGREES AND LOWS UPPER 40S TO LOW 50S. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... AS OF 1245 PM FRIDAY... HIGH LIKELIHOOD THAT VFR CONDITIONS WILL CONTINUE ACROSS CENTRAL NC THROUGH TONIGHT. HIGH PRESSURE NEAR THE SURFACE AND ALOFT WILL SLOWLY EDGE EAST THIS AFTERNOON AND TONIGHT. SKIES WILL REMAIN MOSTLY CLEAR THROUGH MIDNIGHT. AFTERWHICH...MID AND HIGH LEVEL CLOUDS WILL THICKEN WEST-TO-EAST ACROSS THE AREA. STEADY NW WINDS 8- 11KTS WILL SUBSIDE NEAR SUNSET AND BECOME LIGHT FROM THE SW. AVIATION CONDITIONS WILL DETERIORATE SATURDAY...STARTING IN THE WESTERN SECTIONS SATURDAY MORNING...AND IN THE EAST BY THE AFTERNOON HOURS. AREA OF RAIN WILL DEVELOP...AIDING TO MOISTEN THE LOWER LEVELS OF THE ATMOSPHERE. THIS WILL LEAD TO THE FORMATION OF STRATUS WITH CEILINGS IN THE IFR/LOW END MVFR RANGE OVER MOST OF CENTRAL NC BY LATE AFTERNOON SATURDAY...AND IFR/LIFR CEILINGS EXPECTED SATURDAY NIGHT. AREAS OF RAIN WILL BE MOST WIDESPREAD SATURDAY AFTERNOON INTO SATURDAY NIGHT. THE RAIN WILL GRADUALLY DIMINISH LATE SATURDAY NIGHT. ANOTHER ROUND OF RAIN SHOWERS WILL AFFECT THE AREA SUNDAY. THE AREA OF LOW PRESSURE WILL SCOOT ACROSS CENTRAL NC SUNDAY AFTERNOON. AS THIS SYSTEM MOVES OFF THE COAST SUNDAY NIGHT...WEST-NW FLOW BEHIND THE EXITING SYSTEM WILL ADVECT A DRIER MORE STABLE AIR MASS LEADING TO IMPROVING AVIATION CONDITIONS. EXPECT VFR CONDITIONS TO DOMINATE MONDAY AND TUESDAY. CHANCES FOR SUB VFR CONDITIONS WILL INCREASE TUESDAY NIGHT INTO WEDNESDAY AS A LOW PRESSURE SYSTEM APPROACHES FROM THE SW. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...WSS SHORT TERM...WSS LONG TERM...KCP AVIATION...WSS

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