Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 021934 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 335 PM EDT TUE SEP 2 2014 .SYNOPSIS...AN AREA OF HIGH PRESSURE WILL EXTEND OVER THE REGION TODAY. A WEAK SURFACE FRONT WILL SETTLE SOUTHWARD ACROSS CENTRAL NC ON WEDNESDAY. HIGH PRESSURE WILL BUILD BACK OVER THE AREA FOR THE REMAINDER OF THE WORK WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 335 PM TUESDAY... A S/W APPROACHING FROM THE NW HAS HELPED TO SHARPEN A SURFACE TROUGH OVER THE WESTERN AND SOUTHERN PIEDMONT. WEAK CONFLUENCE ALONG THIS FEATURE IN A MODERATELY UNSTABLE AIR MASS HAS HELPED TO TRIGGER SCATTERED CONVECTION IN THE SOUTHERN PIEDMONT AND WESTERN SANDHILLS. THIS CONVECTION MOVING SLUGGISHLY EAST-SE AS WINDS ALOFT ARE RELATIVELY LIGHT. EXPECT CONVECTIVE COVERAGE TO INCREASE OVER THE PIEDMONT AFTER 21Z AS THE S/W GETS CLOSER...FURTHER INCREASING CONVERGENCE ALONG THE SURFACE TROUGH. THE SHEAR AXIS ASSOCIATED WITH THE S/W WILL DRIFT SEWD INTO THE PIEDMONT/NORTHERN COASTAL PLAIN THIS EVENING...THEN INTO THE SANDHILLS AND SOUTHERN COASTAL PLAIN OVERNIGHT. SINCE THE MAIN S/W ENERGY WILL BE LIFTING AWAY FROM OUR REGION...BEST SUPPORT FOR CONVECTION WILL BE FROM LOW LEVEL LIFT. THUS ONCE THE SUNSETS...EXPECT CONVECTIVE COVERAGE TO DECREASE. BULK SHEAR IS WEAK OR NON-EXISTENT SO THREAT FOR ORGANIZED CONVECTION APPEARS LOW. CELLS WHICH ARE ABLE TO SUSTAIN CORES ALOFT FOR 15 -20 MINUTES STAND THE BEST CHANCE OF PRODUCING LOCALIZED WIND GUSTS 35- 50KTS. ALSO FREQUENT TO EXCESSIVE LIGHTNING WILL ACCOMPANY THE STRONGER STORMS. WHILE BULK OF CONVECTION WILL DIMINISH BY MID-LATE EVENING...EXPECT A FEW SHOWERS/STORMS TO CONTINUE WELL INTO THE NIGHT AS THE SHEAR AXIS AND ATTENDANT SURFACE TROUGH DRIFT SEWD INTO THE REGION. WHERE HEAVY RAINFALL OCCURS THIS AFTERNOON-EVENING AND SKIES PARTIALLY CLEAR OVERNIGHT...COULD SEE PATCHES OF FOG DEVELOP AFTER MIDNIGHT. MIN TEMPS NEAR 70-LOWER 70S. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... AS OF 335 PM TUESDAY... SHEAR AXIS AND ATTENDANT SURFACE BOUNDARY WILL LIE ACROSS THE SOUTHERN COUNTIES OF CENTRAL NC. ISOLATED SHOWERS AND STORMS ALONG THIS FEATURE WEDNESDAY MORNING WILL GROW IN COVERAGE AS THE ATMOSPHERE HEATS UP...LEADING TO GREATER LOW LEVEL INSTABILITY. RELATIVELY WEAK STEERING FLOW SUGGEST THAT THE STORMS WILL BE SLOW MOVING. IF STORMS OCCUR OVER URBAN LOCATIONS...THIS MAY LEAD TO MINOR FLOODING OF STREETS AND POOR DRAINAGE AREAS. PLAN TO CAP POPS AT 50 PERCENT ACROSS THE SOUTH...DWINDLING TO 25-35 PERCENT ACROSS THE NW. MAX TEMPS WEDNESDAY DEPENDENT ON WHEN CONVECTIVE COVERAGE INCREASES AND WHETHER ANY PERIODS OF PARTIAL SUN OCCUR. BETTING ON SOME PARTIAL SUN INT HE LATE MORNING-EARLY AFTERNOON PRIOR TO CONVECTION INCREASING AFTER 2-3 PM. IF SKIES REMAIN OVERCAST OR CONVECTION BECOMES ACTIVE BY LUNCHTIME...MAX TEMPS MAY END UP BEING 5-6 DEGREES COOLER. CONTINUED WARM AND MUGGY WEDNESDAY NIGHT WITH SCATTERED CONVECTION SLOWLY DIMINISHING/DISSIPATING. MIN TEMPS NEAR 70-LOWER 70S. && .LONG TERM /THURSDAY THROUGH TUESDAY/... AS OF 255 PM TUESDAY... FOR THU/FRI: CONTINUED WARM/HUMID WITH DAILY SCATTERED SHOWERS AND STORMS. AT THE SURFACE... THE WEAK FRONTAL ZONE WILL LIKELY HAVE WASHED OUT BY THU MORNING... AND THE SURFACE HIGH CENTERED OFF THE SOUTHEAST COAST WILL INTRODUCE A MOIST CONFLUENT LOW LEVEL FLOW OFF THE ATLANTIC INTO NC. A POSITIVELY TILTED TROUGH WILL SHIFT FROM MT/DAKOTAS/SCENTRAL CANADA EARLY THU ACROSS ONT/QUE BY FRI NIGHT... PROPELLING A COLD FRONT THROUGH THE GREAT LAKES/MID MISS VALLEY. AS THE FLAT RIDGE HOLDS ACROSS THE SOUTHEAST/MIDSOUTH/GULF STATES HOWEVER... WE`LL STAY WITHIN AN ENVIRONMENT CHARACTERIZED BY WEAK SHEAR AND MODERATE INSTABILITY (TEMPERED BY WARM MID LEVELS). PW VALUES SHOULD STAY ABOVE NORMAL AT 1.7-1.9"... NOT UNEXPECTED GIVEN THE TROPICAL NATURE OF THE INCOMING AIR MASS... AND SUFFICIENT TO SUPPORT SCATTERED CONVECTION ALONG THE SEA BREEZE... DYING FRONTAL ZONE... OR ANY OTHER SUBTLE BOUNDARY. WILL RETAIN AFTERNOON AND EVENING STORM CHANCES BOTH DAYS... WITH TEMPS HOLDING ABOUT A CATEGORY ABOVE NORMAL AS THICKNESSES STAY AROUND 10 M ABOVE NORMAL. FOR SAT-TUE: STILL EXPECT A TRANSITION FROM THE WARM/HUMID WEATHER TO MORE SEASONABLE CONDITIONS LATE IN THE WEEKEND. THE INITIAL MID LEVEL TROUGH OVER ERN QUEBEC WILL CONTINUE SHIFTING EAST OVER THE MARITIMES... WHILE A STRONG SLUG OF STRONG VORTICITY EMANATING FROM A STRONG COLD VORTEX OVER THE BEAUFORT SEA WILL PUSH EASTWARD CLOSE ON ITS HEELS... CROSSING HUDSON BAY ON SUNDAY. THIS SHOULD PUSH THE SURFACE COLD FRONT TO JUST NW OF NC BY SUN... AND WELL INTO THE STATE BY EARLY MON. BOTH THE GFS AND ECMWF TRACK THEIR COOL PARENT HIGHS OVER THE ST LAWRENCE VALLEY/SRN QUEBEC MON/TUE... WITH THE COLD FRONT PUSHING TO ERN NC AND ACROSS NWRN SC. THIS MODEL AGREEMENT LEADS TO GROWING CONFIDENCE THAT THE PARENT HIGH WILL BE DENSE ENOUGH TO PUSH THIS COOLER AIR WELL INTO CENTRAL NC... ALTHOUGH IT MAY NOT HAPPEN UNTIL LATE SUN NIGHT INTO MON MORNING. WILL FOLLOW THIS TREND WITH TEMPS HOLDING ABOVE NORMAL SAT/SUN (BUT NOT AS WARM IN THE NORTH SUN DUE TO MORE CLOUDS) WITH HIGHS IN THE MID 80S TO NEAR 90... BUT THEN EXPECT TEMPS TO PLUNGE FOR MON/TUE WITH THICKNESSES DROPPING TO 10-20 M BELOW NORMAL... YIELDING HIGHS NEAR 80 TO LOWER 80S. REGARDING PRECIP CHANCES... WE`RE LIKELY TO SEE SCATTERED TO PERHAPS NUMEROUS SHOWERS AND STORMS LATE SAT THROUGH AT LEAST SUN NIGHT... BOTH ALONG THE PREFRONTAL PIEDMONT TROUGH AND AHEAD OF AND WITH THE FRONT ITSELF. SHOWER/STORM CHANCES ARE EXPECTED TO PEAK SUN AFTERNOON. WITH THE MID LEVEL TROUGH AXIS SWINGING THROUGH THE REGION MON... WE MAY SEE LINGERING CHANCES FOR RAIN ESPECIALLY SOUTH AND EAST. THE SURFACE RIDGE NOSING IN FROM THE NORTH LATE MON INTO TUE ACCOMPANIED BY LOWERING PW VALUES SHOULD MEAN MOSTLY DRY WEATHER TUE... AS THE MID LEVEL TROUGH AXIS LIFTS NE AWAY FROM THE REGION FOLLOWED BY WEAK MID LEVEL SHORTWAVE RIDGING OVER THE CAROLINAS. -GIH && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 110 PM TUESDAY... EXPECT VFR CONDITIONS TO PERSIST ACROSS CENTRAL NC THROUGH THIS EVENING. THERE WILL BE ISOLATED THUNDERSTORMS THIS AFTERNOON AND TONIGHT WITH BRIEF INSTANCES OF MVFR/IFR CONDITIONS IN VICINITY OF THE STORMS ALONG WITH WIND GUSTS 25-40KTS AND FREQUENT LIGHTNING. A FEW STORMS MAY PERSIST PAST MIDNIGHT AS A SURFACE FRONT SETTLES SOUTHWARD INTO CENTRAL NC. THIS SAME FEATURE MAY POOL MOISTURE LONG IT...CAUSING AREAS OF FOG AND/OR LOW CLOUDS TO DEVELOP. THIS ADVERSE CONDITIONS ARE EXPECTED TO BE SPOTTY WITH THE KRWI AND KFAY TERMINALS HAVING THE BEST CHANCE OF EXPERIENCING SUB-VFR CONDITIONS EARLY WEDNESDAY MORNING. SCATTERED CONVECTION WILL BE MORE PROMINENT WEDNESDAY AFTERNOON- EVENING...MAINLY ACROSS THE SOUTHERN COUNTIES INCLUDING IN VICINITY OF THE KFAY TERMINAL. OTHERWISE VFR CONDITIONS ARE EXPECTED TYPICAL SUMMERTIME WEATHER CONDITIONS ANTICIPATED THURSDAY THROUGH SATURDAY WITH AREAS OF EARLY MORNING FOG AND LOW CLOUDS GIVING WAY TO VFR CONDITIONS ASIDE FROM SUB-VFR CONDITIONS IN VICINITY OF SCATTERED AFTERNOON-EARLY EVENING CONVECTION. ON SUNDAY...A FRONT WILL BE APPROACHING FROM THE NW. THIS WEATHER SYSTEM WILL LIKELY ENHANCE THE PROBABILITY OF CONVECTION ACROSS CENTRAL NC. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...HARTFIELD AVIATION...WSS

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