Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 150733 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 332 AM EDT TUE APR 15 2014 .SYNOPSIS...WARM AND MOIST SOUTHERLY FLOW WILL PERSIST AHEAD OF A COLD FRONT THAT WILL CROSS THE CAROLINAS THIS AFTERNOON AND EVENING. UNSEASONABLY STRONG AND COOL HIGH PRESSURE WILL THEN BUILD EAST ACROSS THE MIDDLE ATLANTIC REGION TONIGHT THROUGH THURSDAY. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 330 AM TUESDAY... SURFACE DEWPOINTS IN THE MIDDLE TO UPPER 60S OVER THE SOUTHEASTERN US WILL CONTINUE TO ADVECT NORTHWARD IN ADVANCE OF A COLD FRONT THAT STRETCHED AT 07Z FROM NW PA SOUTH SOUTHWESTWARD THROUGH THE EASTERN TN VALLEY...TO CENTRAL AL...AND THE TRAILING PARENT POSITIVELY- TILTED UPPER TROUGH AXIS FROM THE WESTERN GREAT LAKES TO THE SOUTHERN PLAINS. A LARGE AREA OF PRE-FRONTAL CONVECTION HAD DEVELOPED WELL DOWNSTREAM OF THE FRONT EARLIER MON...AND THE LEADING EDGE OF THIS ACTIVITY WAS ALREADY LIFTING NORTH ACROSS THE SC BORDER EARLY THIS MORNING. THIS LARGE AREA OF SHOWERS AND ISOLATED TRANSIENT MINI-SUPERCELL STRUCTURES...DRIVEN ALONG A STRENGTHENING LLJ AXIS AND BY A COUPLE OF MCV/S OVER GA...WILL CONTINUE TO SPREAD NORTH ACROSS THE PIEDMONT THROUGH THE MORNING COMMUTE. THOUGH INSTABILITY WILL REMAIN RELATIVELY WEAK/AROUND 250 J/KG UNTIL DIURNAL HEATING AND CONTINUED MOISTURE TRANSPORT OF THE AFOREMENTIONED MID-UPPER 60S TD/S RESULTS IN FURTHER DESTABILIZATION BY MIDDAY...LOW AND DEEP SHEAR PROFILES ARE SUPPORTIVE OF CONTINUED MINI-SUPERCELL STRUCTURES CAPABLE OF PRODUCING STRONG WIND GUSTS AND PERHAPS EVEN AN ISOLATED TORNADO IN LOCALLY DEEPER CONVECTION. THE MORE APPRECIABLE SEVERE THREAT - GENERALLY EAST OF US HWY 1 - WILL EVOLVE DURING THE MIDDAY TO AFTERNOON HOURS AS THE WARMING AND MOISTENING BL YIELDS 1000-1500 J/KG OF MLCAPE...AND AS THE AFOREMENTIONED COLD FRONT AND OVERLYING LARGER SCALE FORCING FOR VERTICAL MOTION ACCOMPANYING THE UPPER TROUGH SPREAD ACROSS CENTRAL NC BETWEEN 18-22Z THIS AFTERNOON. 1) LINEAR FRONTAL FORCING...2) FORECAST DEEP SHEAR VECTORS ORIENTED GENERALLY PARALLEL TO THE FRONT...AND 3) FORECAST HODOGRAPHS THAT STRAIGHTEN WITH TIME (AFTER DISPLAYING A CYCLONICALLY-CURVED CHARACTER THIS MORNING)... SUGGEST THE CONVECTIVE MODE WILL TRANSITION TO A MORE LINEAR ONE SUPPORTIVE OF LINE SEGMENTS AND EMBEDDED TRANSIENT CIRCULATIONS THIS AFTERNOON. DAMAGING STRAIGHT LINE WINDS WILL CONSEQUENTLY BE THE PRIMARY THREAT...THOUGH AN ISOLATED TORNADO OR TWO WOULD BE POSSIBLE IF THE MESOLOW ABOUT 100 MILES SE OF MONTGOMERY AL HOLDS TOGETHER AND TRACKS THROUGH THE NC PIEDMONT...AS THE 00Z NAM SUGGESTS...AROUND 18Z. EVEN BEHIND THE PRE-FRONTAL AND FRONTAL CONVECTION...THE TRAILING UPPER FORCING AND RESULT WESTWARD SLOPE OF THE SATURATED AXIS ACROSS THE FRONTAL ZONE SUGGESTS SOME POST-FRONTAL LIGHT RAIN - SIMILAR TO WHAT HAS DEVELOPED OVER THE CENTRAL TN VALLEY THIS MORNING - WILL LINGER INTO THE EVENING HOURS. FLASH FLOOD GUIDANCE VALUES BETWEEN 2 AND 3 INCHES ACROSS THE CWA SUGGESTS FLOODING WILL NOT BE A WIDESPREAD THREAT ENOUGH TO WARRANT A WATCH...THOUGH A COUPLE OF FLS/S...OR FFW/S MAINLY FOR URBAN AREAS...MAY ULTIMATELY BE NEEDED. TEMPERATURES TODAY - STARTING OFF WARM IN THE 65-70 DEGREE RANGE - WILL BE TRICKY GIVEN THE MULTIPLE ROUNDS OF CONVECTION...FOLLOWED QUICKLY BY THE FRONTAL PASSAGE. PREVIOUSLY FORECAST UPPER 60S WEST TO AROUND 80 EAST LOOKS GOOD...WITH A STRONG SOUTHERLY BREEZE WITH GUSTS TO NEAR 3O MPH...BECOMING A WEST TO NORTHWESTERLY ONE WITH SIMILARLY STRONG GUSTS LATE THIS AFTERNOON AND EVENING. MINIMAL ADJUSTMENT NEEDED FOR LOWS IN STRONG CAA TONIGHT...INTO THE 30 TO 37 DEGREE RANGE...COOLEST WEST. THE FREEZE WATCH WILL CONSEQUENTLY BE UPGRADED TO A WARNING.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... AS OF 235 AM TUESDAY... WED AND WED NIGHT: RISING HEIGHTS ALOFT/DNVA AND ASSOCIATED STRONG SUBSIDENCE WILL RESULT IN FURTHER DEEP LAYER DRYING (SUNSHINE) WED...FOLLOWED BY GENERALLY NEUTRAL VERTICAL MOTION...BUT WITH A STILL STRONGLY CAPPED AND RESIDUALLY DRY REGIME OVER OUR REGION THROUGH WED NIGHT. BENEATH THE STRONG SUBSIDENCE ALOFT...SURFACE HIGH PRESSURE WILL CONSEQUENTLY BECOME UNSEASONABLY STRONG INTO THE 1040-1045 MB RANGE AS IT BUILDS FROM THE OH VALLEY TO NEW ENGLAND. COOL NORTHEASTERLY FLOW AND DRY ADIABATIC MIXING THROUGH 900 MB...WITH A COUPLE OF DEGREES ADDED TO ACCOUNT FOR A USUAL SLIGHT COOL BIAS WITH THIS TECHNIQUE LIKELY IN PART OWING TO A SUPER- ADIABATIC NEAR SURFACE LAYER...SUPPORTS HIGHS IN THE LOWER TO MIDDLE 50S. PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1300-1310 METER RANGE AT 12Z THU...WITH OPTIMAL RADIATIONAL COOLING...WOULD SUPPORT MIDDLE 20S. HOWEVER...A PROJECTED 4-6 MB RISE IN MSL PRESSURE WITH THE STRENGTHENING HIGH WED NIGHT WILL LIKELY MAINTAIN A NORTHEASTERLY STIRRING FOR MOST AREAS OVERNIGHT...THOUGH WITH TYPICALLY COOLER/SHELTERED AREA LIKELY TO EXPERIENCE PERIODS OF CALM. IN ADDITION...MOISTURE ADVECTION IN NORTHEASTERLY FLOW BENEATH THE CAPPING INVERSION MAY RESULT IN SCT TO BKN LOW CLOUDS MAINLY IN THE COASTAL PLAIN LATE. AS SUCH...TEMPERATURES ARE APT TO DISPLAY A RELATIVELY LARGE RANGE...FROM 28-30 DEGREES IN RURAL WESTERN PIEDMONT LOCATIONS (IN CLOSEST PROXIMITY TO THE RIDGE AXIS) TO AROUND FREEZING IN URBAN AREAS FROM RDU WESTWARD TO THE TRIAD...TO 33-37 DEGREES IN THE COASTAL PLAIN AND EASTERN SANDHILLS. -MWS THURSDAY THROUGH THURSDAY NIGHT: THIS PERIOD SHOULD REMAIN DRY WITH HIGH PRESSURE RIDGING IN FROM THE NORTHEAST...ALTHOUGH EXPECT CLOUDS TO INCREASE DURING THE EVE/OVERNIGHT...ESPECIALLY ACROSS THE SOUTH AND EAST...AS A LOW DEVELOPS OFF THE COAST. WITH THE CONTINUED NE FLOW AND CAA...STILL EXPECT TEMPS TO BE BELOW NORMAL. HOWEVER... GIVEN LOW-LEVEL THICKNESSES INCREASING FROM THE PREVIOUS NIGHT BY A GOOD 30-40 METERS...EXPECT TEMPS TO INCREASE BY 5-10 DEGREES...HIGHS IN THE LOW TO MID 60S AND LOWS IN THE UPPER 30S TO LOW 40S. -KCP && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 300 AM TUESDAY... THERE IS STILL A SLIGHT CHANCE OF RAIN ACROSS THE SOUTHEAST FRIDAY NIGHT/SATURDAY MORNING AS THE ELONGATED LOW OFF THE COAST MOVES AWAY FROM THE AREA...OTHERWISE THE LATEST GFS AND ECMWF RUNS KEEP THE FORECAST DRY THROUGH MONDAY. AN UPPER LEVEL LOW SKIRTS NORTH OF CENTRAL NC SATURDAY NIGHT/SUNDAY. THE GFS IS A BIT MORE AMPLIFIED WITH THE LOW...BRINGING IT CLOSER TO THE AREA. DESPITE THE STRONG UPPER LEVEL FORCING AND MOISTURE IN THE UPPER LEVELS...THE DRY AIR EXPECTED IN THE MID LEVELS MAY BE ENOUGH TO KEEP THINGS DRY. HIGHS FRIDAY IN THE MID TO UPPER 60S WITH LOWS IN THE MID 40S TO AROUND 50 DEGREES. HIGH PRESSURE TO THE NORTH WILL RIDGE INTO THE AREA SUNDAY AND MONDAY. ASIDE FROM SOME HIGH CLOUDS...EXPECT EASTER SUNDAY TO BE DRY AND MOSTLY SUNNY. HIGHS MAINLY IN THE LOW TO MID 70S WITH LOWS IN THE MID TO UPPER 40S THROUGH THE END OF THE PERIOD. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 200 AM TUESDAY... 24 HOUR TAF PERIOD: MVFR/IFR CONDITIONS ACROSS THE AREA WILL LIKELY DECREASE FURTHER INTO IFR/LIFR BY DAYBREAK TUESDAY. HEAVY SHOWERS AND THUNDERSTORMS ARE APPROACHING FROM THE SOUTHWEST...ALREADY IMPACTING KINT AND KGSO...AND LIKELY MOVING OVER KFAY AND KRDU OVER THE NEXT COUPLE HOURS (AND KRWI THEREAFTER). THOUGH IT IS POSSIBLE THE CIGS MAY IMPROVE SLIGHTLY WITH THESE HEAVY SHOWERS...VISBYS WILL LIKELY DECREASE. AS ALREADY SEEN AT KINT AND KGSO...SOUTHWEST WINDS WILL BECOME GUSTY (20-25 KTS) AS THE LOW LEVEL FLOW STRENGTHENS. IF THERE IS A BREAK IN THE PRECIP TUESDAY MORNING...CONDITIONS MAY IMPROVE BACK TO MVFR...BUT EXPECT MORE SHOWERS AND THUNDERSTORMS TO MOVE ACROSS THE AREA AHEAD OF THE COLD FRONT...EXPECTED TO MOVE FROM WEST TO EAST THROUGH CENTRAL NC DURING THE LATE AFTERNOON/EARLY EVENING. ALTHOUGH WINDS WILL REMAIN STRONG AND GUSTY THROUGH THE TAF PERIOD...EXPECT THEM TO VEER TO THE WEST THEN NORTHWEST BEHIND THE FRONT. CIGS WILL LIFT AND VISBYS WILL IMPROVE BEHIND THE FRONT... WITH VFR CONDITIONS EXPECTED BY THE END OF THE PERIOD. -KC LOOKING AHEAD: MOSTLY VFR CONDITIONS WILL PERSIST THROUGH THE END OF THE WORK WEEK. THERE COULD BE SOME MORNING STRATUS BOTH FRIDAY AND SATURDAY MORNING AS MOISTURE ONCE AGAIN INCREASES AHEAD OF OUR NEXT SYSTEM APPROACHING FROM THE SOUTH THIS WEEKEND. -KRD && .CLIMATE... THE FOLLOWING ARE THE RECORD LOW TEMPERATURES FOR WED AND THU MORNING... AND THE RECORD LOW MAXIMUM TEMPERATURES FOR WED: WED 04/16 THU 04/17 LOW/YEAR LOW MAX/YEAR LOW/YEAR FAY: 28/1943 56/1950 31/1953 GSO: 25/1943 48/1929 29/1953 RDU: 28/1950 46/1890 29/1962 && .RAH WATCHES/WARNINGS/ADVISORIES... FREEZE WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY MORNING FOR NCZ007>010-021>026-038>041-073>077-083-084. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS/KCP LONG TERM...KCP AVIATION...KCP CLIMATE...MWS

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