Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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234 FXUS62 KRAH 191446 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1045 AM EDT TUE MAY 19 2015 .SYNOPSIS...A SURFACE TROUGH WILL STRENGTHEN OVER VA AND THE CAROLINAS TODAY...AHEAD OF A COLD FRONT THAT WILL CROSS OUR REGION TONIGHT. THE FRONT WILL STALL OVER SC ON WED...THEN RETREAT NORTH IN ADVANCE OF AN AREA OF LOW PRESSURE THAT WILL CROSS THE CAROLINAS ON THU. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1045 AM TUESDAY... 12Z UPPER ANALYSIS SHOWS WEAK MID TO UPPER LEVEL HEIGHT FALLS ASSOC WITH THE TROUGH DEEPENING OVER THE GREAT LAKES REGION. MEANWHILE...W TO WSW FLOW IN THE LOWER TO MID LEVELS PERSISTS OVER THE CAROLINAS ASSOC WITH A RIDGE OVER THE NORTHERN GULF COAST REGION. MEANWHILE... 850 MB ANALYSIS SHOWS MOISTURE POOLED EAST OF THE SOUTHERN APPALACHIANS...INCREASING TOWARD THE COAST. 12Z GSO SOUNDING SHOWS PWAT AROUND 1.5 INCHES...WHICH IS ABOVE CLIMO FOR THIS TIME OF YEAR. SFC ANALYSIS SHOWS A COLD FRONT ACROSS THE OH AND TN VALLEYS...WHICH IS GRADUALLY MOVING EASTWARD...AND A BROAD PIEDMONT TROUGH IN PLACE ACROSS OUR REGION WITH DWPTS RANGING FROM THE MID 60S ACROSS THE TRIAD TO AROUND 70 ACROSS THE EASTERN PIEDMONT AND COASTAL PLAIN. WHILE FORCING MECHANISMS RIGHT NOW GENERALLY APPEAR TO BE MODEST...AS THE AFOREMENTIONED COLD FRONT MOVES EAST LATER TODAY...COMBINED WITH PLENTY OF LOW LEVEL MOISTURE TO WORK WITH AND PIEDMONT TROUGH IN PLACE...CURRENT FORECAST SHOWING SCATTERED TO NUMEROUS SHOWERS AND TSTMS LATER THIS AFTERNOON AND INTO THE EVENING STILL APPEARS TO BE ON-TRACK...WITH THE BEST COVERAGE AND HEAVIEST RAINFALL AMOUNTS ACROSS THE EASTERN HALF OF OUR CWA WHERE MOISTURE IS MOST ABUNDANT. CURRENT TEMPERATURES TRENDS SUPPORT OUR CURRENT FORECAST HIGHS TODAY RANGING FROM THE UPPER 80S NW TO AROUND 90 ELSEWHERE. PREV NEAR TERM DISC AS OF 410 AM TUESDAY...A PAIR OF WEAK MID LEVEL TROUGHS...ONE INITIALLY OVER THE SOUTHERN APPALACHIANS AND ANOTHER OVER THE LOWER MS AND WESTERN TN VALLEYS WILL MOVE EAST ACROSS CENTRAL NC TODAY...BUT ASSOCIATED MID LEVEL HEIGHT FALLS WILL BE RELATIVELY LIMITED. DESPITE THE LIMITED LARGER SCALE FORCING FOR ASCENT...THE MODELS CONTINUE TO INDICATE THE PIEDMONT WILL DRIFT EAST INTO THE COASTAL PLAIN...THOUGH CONTINUED WNW 925-850 FLOW WILL LIKELY SUPPORT THE RE-DEVELOPMENT OF A LEE TROUGH OVER THE FOOTHILLS AND PIEDMONT. WHILE BOTH MAY SERVE AS A FOCUS FOR BECOME A FOCUS FOR SCATTERED SHOWER AND STORM DEVELOPMENT THIS AFTERNOON...THE MODELS CONTINUE TO INDICATE THE LEAD TROUGH AND ASSOCIATED AXIS OF STRONGEST LOW LEVEL CONVERGENCE OVER THE COASTAL PLAIN...WHERE BOUNDARY LAYER MOISTURE CHARACTERIZED BY SFC DEWPOINTS IN THE UPPER 60S AND ASSOCIATED MLCAPE AROUND 1500 J/KG WILL BE MAXIMIZED...WILL BE THE MOST CONVECTIVELY-ACTIVE ONE. MEANWHILE... THE AFOREMENTIONED DOWNSLOPE FLOW WILL LIKELY CAUSE DEWPOINTS TO MIX OUT INTO THE UPPER 50S TO LOWER 60S TO THE WEST OF THE LEAD SURFACE TROUGH AXIS...OVER THE WESTERN PIEDMONT...WHICH SHOULD TEND TO LIMIT BOTH STORM COVERAGE AND INTENSITY. WEAK MID-LEVEL LAPSE RATES; WEAK SHEAR; AND WEAK DCAPE ALL SUGGEST ASSOCIATED PULSE/MULTI-CELL UPDRAFTS WILL BE TOO SHORT-LIVED FOR THE DEVELOPMENT OF SEVERE HAIL OR WIND PRODUCTION. HIGH TEMPERATURES SIMILAR TO MON...TO PERHAPS A COUPLE OF DEGREES COOLER OWING TO THE EXPECTED GREATER CONVECTIVE COVERAGE. TONIGHT: A COLD FRONT STRETCHING FROM THE GREAT LAKES TO THE SOUTHERN PLAINS THIS MORNING WILL MOVE EAST OF THE MOUNTAINS AND ACROSS CENTRAL NC LATE TONIGHT. ALTHOUGH THE MAJORITY OF SHOWERS AND STORMS WILL DISSIPATE AND/OR DRIFT EAST OF CENTRAL NC BY LATE EVENING-MIDNIGHT...THE PASSING FRONT MAY FOCUS AN ISOLATED SHOWER OR TWO OVERNIGHT. AREAS OF FOG WILL BE POSSIBLE TONIGHT WHERE PRECEDING RAIN OCCURS DURING THE AFTERNOON AND EVENING...UNTIL THE COLD FRONT AND ASSOCIATED DRIER AIR ARRIVE FROM THE NW LATE...WITH LOWS IN THE 60S.
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&& .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 425 AM TUESDAY... THE COLD FRONT WILL DRIFT SOUTH INTO SC DURING THE DAY WED...WHICH WILL CAUSE A DRIER AND SLIGHTLY COOLER AIR MASS TO SETTLE ACROSS CENTRAL NC...WITH HIGHS GENERALLY IN THE MIDDLE 80S TO AROUND 90 DEGREES - WARMEST OVER THE SOUTHERN PIEDMONT. A SHORTWAVE TROUGH WILL MIGRATE EAST ACROSS THE UPPER MIDWEST AND OH VALLEY AND SUPPORT THE STRENGTHENING OF AN AREA OF LOW PRESSURE OVER SC WED NIGHT...WHEN A FEW SHOWERS MAY DEVELOP AND OVERSPREAD THE NC PIEDMONT. LOWS AGAIN IN THE 60S. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 335 AM TUESDAY... A WAVE OF LOW PRESSURE MOVING ALONG THE FRONTAL ZONE DRAPED ACROSS THE MID-SOUTH AND CAROLINAS IS FORECAST TO SLOWLY DEEPEN AS IT MOVES SOMEWHERE NEAR THE NC/SC ON THURSDAY AND THEN OFF THE NC COAST THURSDAY NIGHT. THE GFS CONTINUES TO BE A WEAKER AND SOUTHERN OUTLIER WHEN IT COMES TO THE LOCATION OF THE FRONT AND TRACK OF THE WAVE...SO WILL LEAN TOWARD THE ECMWF/NAM...WHICH HAVE SUPPORT FROM THE ECMWF ENSEMBLE. THE FORCING ALOFT WILL BE MOSTLY WEAK WITH THIS SYSTEM AS THE LEAD SOUTHERN STREAM SHORTWAVE DEAMPLIFIES OVER THE MIDWEST AND MERGES WITH A TRAILING NORTHERN STREAM WAVE THAT PASSES TO OUR NORTH THURSDAY AFTERNOON. HOWEVER...WEAK HEIGHT FALLS AND GOOD LOW-LEVEL CONVERGENCE NEAR THE FRONTAL ZONE/SFC LOW WILL LEAD TO SCATTERED SHOWERS/STORMS THAT MAY BECOME NUMEROUS OVER THE COASTAL PLAIN THURSDAY AFTERNOON/EVENING PENDING DESTABILIZATION AS DEWPOINTS CREEP BACK INTO THE UPPER 60S. IF MORNING SHOWERS AND/OR CLOUDS DONT LIMIT HEATING TOO MUCH THEN SOME WEAK CAPE MAY DEVELOP. A CONDITIONAL SEVERE THREAT MAY THEN EXIST GIVEN 30-35KT OF MID- LEVEL FLOW AND BACKED LOW-LEVEL FLOW AHEAD OF THE SURFACE LOW....MAINLY EAST OF I-95 WHERE THE THE PARAMETER SPACE FOR SOME ROTATING STORMS WOULD BE MAXIMIZED. THE DEEPER NAM SHOWS BETTER POTENTIAL THAN THE ECMWF...SO AT THIS TIME THE SEVERE THREAT IS LIKELY LOW BUT WORTH WATCHING. HIGHS WILL RANGE FROM THE MID 70S NORTH TO LOW OR MID 80S SOUTH DEPENDING ON HOW ROBUST MID CLOUDS ARE AS THEY ADVECT IN FROM THE WEST EARLY IN THE DAY. PRECIP WILL COME TO AN END THURSDAY NIGHT AND EARLY FRIDAY AS THE SURFACE LOW MOVES OFF THE COAST AND A MUCH MORE STABLE AIRMASS FILTERS OVER THE REGION...COURTESY OF A RELATIVELY STRONG HIGH PRESSURE THAT WILL BUILD ACROSS THE GREAT LAKES. THICKNESSES DROP OFF SIGNIFICANTLY FRIDAY AND SUGGEST HIGHS IN THE MID 70S TO LOW 80S FRIDAY AND SATURDAY. THE PATTERN WILL THEN SHIFT BACK TO TROUGHING OUT WEST AND A SUB-TROPICAL RIDGE OVER THE SOUTHEAST US...WHICH WILL BRING TEMPS BACK TO AND ABOVE NORMAL BY EARLY NEXT WEEK. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... AS OF 750 AM TUESDAY... AN AREA OF LIFR STRATUS AND FOG CENTERED AROUND CLT HAS DEVELOPED DURING THE PAST SEVERAL HOURS...AND THERE IS A SLIGHT CHANCE THAT SOME OF THESE PATCHY CONDITIONS WILL OCCUR AROUND GSO THROUGH 13- 14Z...WHERE OVER ONE HALF INCH OF RAIN OCCURRED ON MON. OTHERWISE... VFR CONDITIONS ARE ANTICIPATED UNTIL SHOWERS AND STORMS RE-DEVELOP THIS AFTERNOON...WITH THE RELATIVE GREATEST CHANCE AT RWI AND FAY... IN THE VICINITY OF A SURFACE TROUGH AND ASSOCIATED AXIS OF LOW LEVEL CONVERGENCE. AREAS OF FOG WILL THEN BE POSSIBLE TONIGHT WHERE PRECEDING RAIN OCCURS DURING THE AFTERNOON AND EVENING...UNTIL A COLD FRONT AND ASSOCIATED DRIER AIR ARRIVE FROM THE NW LATE...BUT INCLUSION OF SUCH SUB-VFR CONDITIONS IN THE TAFS WOULD BE PRE-MATURE UNTIL IT BECOMES CLEARER WHERE AND HOW MUCH RAIN MATERIALIZES. OUTLOOK: AN AREA OF LOW PRESSURE WILL TRACK ACROSS THE CAROLINAS AND RESULT IN A CHANCE OF SUB-VFR CEILINGS AND RAIN LATE WED NIGHT AND EARLY THU...FOLLOWED BY SHOWERS AND STORMS THU AFTERNOON. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...RAH/26 SHORT TERM...26 LONG TERM...22 AVIATION...26

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