Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 031625 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1125 AM EST WED FEB 03 2016 .SYNOPSIS...
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A COLD FRONT WILL APPROACH THE CAROLINAS FROM THE WEST THIS AFTERNOON...CROSS THE REGION TONIGHT...THEN STALL ALONG THE COAST ON THURSDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1115 AM WEDNESDAY... TEMPERATURES: EXPECT HIGHS IN THE MID/UPPER 60S TO LOWER 70S... COOLEST NW PIEDMONT AND WARMEST SE COASTAL PLAIN...WITH TEMPS LARGELY DRIVE BY GUSTY SOUTHEAST FLOW (WARM ADVECTION EMANATING FROM THE ATLANTIC). LOWS TONIGHT WILL BE DRIVEN BY NOCTURNAL COOLING AND EVAP COOLING ASSOC/W WIDESPREAD PRECIPITATION IN MOST LOCATIONS... EXCEPT IN THE NW PIEDMONT WHERE COLD ADVECTION SHOULD CONTRIBUTE PRIOR TO SUNRISE THU AS THE ACTUAL COLD FRONT FINALLY PROGRESSES EAST OF THE MOUNTAINS. LOWS WILL RANGE FROM THE MID/UPPER 40S NW TO MID/UPPER 50S SE. PRECIPITATION: ASIDE FROM OCCASIONAL SHOWERS ASSOCIATED WITH WARM ADVECTION THIS MORNING AS THE 925 MB WARM FRONT LIFTS NORTHWARD INTO VA...PRIMARILY IN THE WESTERN PIEDMONT...DRY CONDITIONS SHOULD OTHERWISE PREVAIL THROUGH EARLY AFTERNOON AS THE SHALLOW NOCTURNAL INVERSION (ENHANCED BY LOW-LEVEL WARM ADVECTION OVERNIGHT) OVER CENTRAL NC IS RAPIDLY SUPPLANTED BY A HOMOGENEOUS WARM SECTOR...AS ALREADY EVIDENCED BY GUSTY SOUTH WINDS AND EROSION OF FOG/LOW CEILINGS PER 15Z OBSERVATIONS. THE SW-NE ORIENTED LINE OF CONVECTION CURRENTLY UPSTREAM OF THE REGION HAS OUTRUN LOW-LEVEL FORCING ATTENDANT THE COLD FRONT PROGRESSING EAST TOWARD THE MOUNTAINS... EFFECTIVELY STRANDING ITSELF (TEMPORARILY) IN DEEP SOUTHWEST (LINE- PARALLEL) FLOW ALOFT OVER THE SOUTHERN APPALACHIANS WHERE RICH MOISTURE ADVECTION AND OROGRAPHIC ASCENT ON THE EASTERN SLOPES OF THE APPALACHIANS HAVE AIDED IN MAINTAINING IT. EXPECT THIS FEATURE TO RESUME PROGRESSING TO THE EAST THIS AFTERNOON AS THE LOW-LEVEL TROUGH PREVIOUSLY LEFT BEHIND `CATCHES UP` AND BEGINS TO SHIFT THE FOCUS FOR ADDITIONAL DEVELOPMENT (SFC-92 MB CONVERGENCE) INTO THE FOOTHILLS AND WESTERN PIEDMONT BETWEEN 18-21Z...THE HWY 1 CORRIDOR BETWEEN 21-00Z...AND THE COASTAL PLAIN AFTER 00Z. HAZARDOUS WEATHER: THE SPC INDICATES A MARGINAL RISK OF SEVERE STORMS OVER CENTRAL NC TODAY. DESPITE AN UNSEASONAL RICH AIRMASS /WARM SECTOR/ CHARACTERIZED BY DEWPOINTS IN THE LOW TO MID 60S... PERVASIVE CLOUD COVER AND DEEP MOISTURE /MOIST ADIABATIC LAPSE RATES/ WILL SIGNIFICANTLY HAMPER DIURNAL DESTABILIZATION... LIMITING MLCAPE TO 250-500 J/KG AT BEST (IN SOUTH/SE)...THOUGH MORE LIKELY IN THE 100-250 J/KG RANGE. WITH UPPER LEVEL FORCING LARGELY ABSENT ASIDE FROM SMALL AMPLITUDE WAVES /TRANSIENT DPVA/ IN SW FLOW ALOFT...FORCING FOR ASCENT WILL BE CONFINED TO WEAK/SHALLOW CONVERGENCE ASSOC/W THE PRE-FRONTAL TROUGH OR MESOSCALE BAROCLINIC ZONE (INTERFACE BETWEEN THE SLOW MOVING CONVECTIVE LINE AND ADJACENT WARM SECTOR). GIVEN MARGINAL THERMODYNAMICS...LITTLE IN THE WAY OF UPPER FORCING /DPVA/ (NO SIG. LAYER-LIFTING)...WEAK/SHALLOW LOW- LEVEL FORCING...LINE-PARALLEL ENVIRONMENTAL FLOW...AND WEAK DCAPE...FEW FACTORS REMAIN TO SUPPORT ORGANIZED SEVERE WEATHER IN CENTRAL NC THIS AFT/EVE. OF THOSE FEW...THE 50 KT SOUTHERLY LOW- LEVEL JET IN ADVANCE OF THE FRONT IS PROBABLY THE MOST IMPORTANT ONE...ESP WHEN DOWNWARD MOMENTUM TRANSPORT NEED ONLY TO OCCUR FROM ~2500 FT AGL TO THE GROUND. THE PRIMARY HAZARD ASSOC/W THIS EVENT WILL BE HEAVY RAINFALL AND FLASH FLOODING GIVEN ENVIRONMENTAL CONDITIONS FAVORING HEAVY SLOW-MOVING...I.E. TRAINING CONVECTION. CONFIDENCE IN COVERAGE IS TOO LOW TO WARRANT A FLASH FLOOD WATCH AT THIS TIME...THOUGH SEVERAL FLASH FLOOD WARNINGS MAY ULTIMATELY BE NEEDED...PARTICULARLY IN THE TRIAD. -VINCENT
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 330 AM WEDNESDAY... THE MAIN CHANGE TO THIS FORECAST PERIOD WILL BE TO HOLD ONTO BOTH CLOUDINESS AND THE RAIN CHANCES LONGER... ESPECIALLY OVER THE EASTERN CWA. THE COLD FRONT IS EXPECTED TO SHIFT SLOWLY EAST OF HIGHWAY 1 THURSDAY... EASING TO COASTAL SECTIONS BY THURSDAY EVENING. THE MID LEVEL TROUGH AXIS WILL HOLD WELL TO OUR WEST HOWEVER... FROM THE GREAT LAKES TO THE GULF STATES WITH A FAIRLY SLOW EASTWARD PUSH THU NIGHT... AND THE RESULTING SOUTHWESTERLY STEERING FLOW PARALLEL TO THE FRONTAL ZONE WILL HINDER THE FRONT`S EASTWARD PUSH. MUCH ABOVE NORMAL PW VALUES WILL CONTINUE TO STREAM OVER ERN NC THU/THU NIGHT WITH MULTIPLE WEAK LOW PRESSURE CENTERS TRACKING ALONG THE FRONT OVER COASTAL NC... SO EXPECT A GOOD CHANCE OF RAIN TO HOLD OVER THE ERN CWA INTO THU NIGHT... WHEN A POTENT MID LEVEL VORTICITY MAX EJECTS OUT OF THE TROUGH BASE AND CROSSES THE CAROLINAS THU NIGHT... FINALLY SHOVING THE SURFACE FRONTAL ZONE OFFSHORE. EXPECT HIGHS IN THE 50S TO NEAR 60 THU... WITH CLOUDY SKIES AREAWIDE... GIVING WAY IN THE NW TO PARTIAL CLEARING LATE. LOWS THU NIGHT FROM THE LOWER TO UPPER 30S... ALTHOUGH THE NEAR- OR SUB-FREEZING AIR WILL BE CHASING THE PRECIP... AND NO WINTRY WEATHER IS EXPECTED. -GIH && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 310 AM WEDNESDAY... FRIDAY AND SATURDAY: THE FRONT AND ALL ASSOCIATED PRECIPITATION WILL FINALLY EXIT TO THE EAST ON FRIDAY MORNING. IN ITS WAKE...HIGH PRESSURE WILL FORM OVER THE DEEP SOUTH AND DRY THINGS OUT THROUGH SATURDAY. TEMPERATURES WILL BE COOL...BUT ONLY A FEW DEGREES BELOW NORMAL FOR THIS TIME OF YEAR...AROUND 50 DEGREES FOR DAYTIME HIGHS AND LOWS IN THE UPPER 20S TO LOWER 30S. SUNDAY THROUGH TUESDAY: THE FORECAST STARTS TO BECOME A LOT MORE UNCERTAIN ON SUNDAY AND THIS LACK OF CONFIDENCE PERMEATES THROUGH THE END OF THE FORECAST PERIOD. LOOKING AT THE VERY BIG PICTURE...AS A PREFACE...THE ARCTIC OSCILLATION IS FORECASTED TO START TURNING NEGATIVE ABOUT THIS TIME...INDICATING A HIGHER POSSIBILITY FOR COLDER TEMPERATURES AND POTENTIALLY WINTER WEATHER. AT THE SAME TIME...A VERY DEEP UPPER LEVEL TROUGH WILL DIG DOWN OVER THE MISSISSIPPI VALLEY AND IS PROGGED TO FORM A CUTOFF LOW OVER THE TENNESSEE VALLEY AND PUSH EASTWARD. AT THE SAME TIME...A STRONG SURFACE LOW WILL BEGIN TO FORM OFF OF THE SOUTHEAST COAST AND TRACK NORTHEASTWARD. THE AMOUNT OF INTERACTION BETWEEN THESE TWO FEATURES WILL LIKELY DETERMINE IF WE HAVE ANY PRECIPITATION ON SUNDAY OR NOT. THE EUROPEAN SOLUTION HAS BEEN THE FAVORED SOLUTION FOR THIS SYSTEM WHICH KEEPS PRECIPITATION TO OUR EAST BUT THE GFS HAS COME MORE IN LINE OVER THE PAST COUPLE OF RUNS. THE PROBLEM WITH IT AT THIS TIME IS THAT IT IS PRODUCING A VERY STRONG UPPER LOW WHICH LOOKS ANOMALOUSLY DEEP AT THIS POINT. THIS STRONG UPPER LOW WRAPS PRECIPITATION BACK ACROSS OUR CWA. AFTER CHECKING THIS SCENARIO AGAINST THE ECMWF ENSEMBLE MEMBERS...VERY FEW HAVE THIS HAPPENING BUT THERE ARE A COUPLE OF MEMBERS THAT DEPICT SOMETHING SIMILAR...ENOUGH CAUSE FOR REASONABLE DOUBT. LOOKING AT FORECAST SOUNDINGS...IF THIS OUTLIER SCENARIO WERE TO COME TO FRUITION...THICKNESS VALUES IN THE NOMOGRAM ARE RIGHT ON THE BORDER BETWEEN SNOW...RAIN OR SNOW...AND INDETERMINATE. THIS MEANS THAT AT THIS POINT...THERE IS VERY LOW CONFIDENCE ON WHETHER OR NOT THIS SYSTEM COULD PRODUCE SOME WINTER P-TYPES ACROSS OUR AREA ON SUNDAY. WITH ALL THAT BEING SAID...THE MOST LIKELY PLACES THAT SEE PRECIPITATION WILL BE IN THE EAST...WHERE THICKNESSES WILL MOST LIKELY BE HIGH ENOUGH TO AVOID THE WINTER P-TYPES. THEREFORE HAVE INCLUDED ONLY SLIGHT CHANCE OF RAIN IN THE SOUTHEAST AT THIS TIME IN THE FORECAST WITH THE ASTERISK OF CLOSELY MONITORING FUTURE MODEL RUNS. AFTER A SHORT BREAK ON MONDAY...A SECOND VERY STRONG UPPER TROUGH BRINGS ARCTIC AIR OUT OF CANADA AND A LOW PRESSURE SYSTEM DEVELOPS OVER THE GREAT LAKES. AS THIS DIVES SOUTH...THE POTENTIAL FOR ANOTHER COASTAL LOW EXISTS FOR TUESDAY BUT MODELS ARE VERY FUZZY ON DETAILS BECAUSE ALL OF THIS DEPENDS ON THE EVOLUTION OF THE FIRST TROUGH AND SYSTEM. THEREFORE HAVE KEPT THE FORECAST DRY AT THIS TIME FOR TUESDAY UNTIL MORE DETAILS EMERGE. WITH THICKNESSES PLUNGING EVEN FURTHER...P-TYPE ISSUES COULD POTENTIALLY BECOME A PROBLEM FOR THE MIDDLE OF NEXT WEEK. STAY TUNED. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... AS OF 650 AM WEDNESDAY... POOR AVIATION CONDITIONS WILL DOMINATE OVER THE NEXT 24 HOURS... WITH A PERIOD OF LOW LEVEL WIND SHEAR LIKELY ESPECIALLY AT INT/GSO/RDU THROUGH 16Z-18Z. CONDITIONS ARE CURRENTLY LIFR AT ALL TAF SITES EXCEPT RWI. A WARM FRONT LOCATED NEAR THE NC/SC STATE LINE WILL SURGE NORTHWARD THROUGH THE AREA THIS MORNING... RESULTING IN THE INITIALLY FAIRLY LIGHT SURFACE WINDS FROM THE SE VEERING TO SOUTHERLY AND INCREASING THIS MORNING BETWEEN 12Z AND 15Z. AFTER 15Z THIS MORNING... THE IFR/LIFR CIGS WILL START TO LIFT AND MIX OUT TO MVFR/VFR BRIEFLY BEFORE THE ARRIVAL OF WIDESPREAD SHOWERS AND ISOLATED STORMS FROM THE WEST. CONDITIONS WILL QUICKLY DROP BACK TO MVFR OR IFR FROM WEST TO EAST AS THE SHOWERS/STORMS ASSOCIATED WITH A COLD FRONT CROSSES THE AREA. WINDS WILL BE STRONG AND GUSTY TODAY THROUGH THIS EVENING... SUSTAINED AT 12-18 KTS WITH GUSTS UP TO 20- 30 KTS... AND THESE GUSTS WILL BE STRONGER IN AND NEAR HEAVY SHOWERS AND EMBEDDED STORMS THIS AFTERNOON. AN IMPROVEMENT BACK TO VFR IS EXPECTED AFTER THE COLD FRONT PASSAGE FROM LATE EVENING THROUGH THE OVERNIGHT... WHEN WINDS WILL SHIFT AROUND TO NORTHWEST THEN NORTH. THE LLWS THREAT WILL BE GREATEST AT INT/GSO/RDU AFTER 09Z THIS MORNING AS A 50-60 KT SOUTHERLY LOW LEVEL JET ARRIVES FROM THE WEST. THE LLWS THREAT WILL LARGELY END AROUND 17Z-18Z AS THE JET WEAKENS AND SHIFTS TO OUR OUR EAST. LOOKING BEYOND 12Z THU MORNING... RAIN CHANCES WILL LINGER THROUGH THU AT RWI/FAY AS THE FRONT VERY SLOWLY SHIFTS EAST OF THE COAST... AND FAY/RWI AND PERHAPS RDU WILL LIKELY SEE A RETURN TO AREAS OF RAIN AND MVFR CONDITIONS THU INTO THU NIGHT AS AN UPPER LEVEL DISTURBANCE CROSSES THE REGION. VFR CONDITIONS ARE LIKELY FRI THROUGH SAT AS HIGH PRESSURE BUILDS INTO AND OVER THE AREA FROM THE WEST. LOW PRESSURE TRACKING JUST OFF THE SOUTHEAST COAST ON SUNDAY MAY BRING A CHANCE OF SUB-VFR CONDITIONS AND BRISK WINDS AT RWI/FAY RDU TO END THE WEEKEND. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...HARTFIELD LONG TERM...ELLIS AVIATION...HARTFIELD

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