Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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317 FXUS62 KRAH 010828 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 428 AM EDT SUN MAY 1 2016 .SYNOPSIS... A WARM FRONT WILL RETREAT NORTH ACROSS THE MIDDLE ATLANTIC STATES TODAY...AHEAD OF SLOW-MOVING LOW PRESSURE THAT WILL CROSS THE OHIO VALLEY THROUGH TONIGHT. WARM SOUTHWESTERLY FLOW WILL RESULT THROUGH EARLY THIS WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 415 AM SUNDAY... A BAND OF SHOWERS AND ACCOMPANYING MCV WILL MOVE IN WSW FLOW ALOFT ACROSS A REMNANT COOL/STABLE/WEDGE AIRMASS OVER CENTRAL NC THIS MORNING. THE PASSAGE OF THIS AREA OF SHOWERS MAY TEMPORARILY SLOW AN OTHERWISE STEADY NORTHWARD RETREAT OF A WARM FRONT THAT NOW ARCS AROUND THE THE LEE OF THE SOUTHERN AND CENTRAL APPALACHIANS - FROM NORTH- CENTRAL GA NEWD TO NEAR KCLT...THEN SEWD TO THE CENTRAL SC COAST. THE RETREAT OF THE WARM FRONT WILL RESULT IN AN ASSOCIATED EROSION/SCATTERING/LIFTING OF THE PRECEDING LOW CLOUDS...AND A SUBSEQUENT DEVELOPMENT OF A WARM AND BREEZY SW WIND. WHILE THE AIR MASS WILL CONSEQUENTLY MODERATELY DESTABILIZE AS TEMPERATURES WARM THROUGH THE 70S AND UPSTREAM SURFACE DEWPOINTS IN THE 60S SURGE NEWD...AND BECOME RIPE FOR THE DEVELOPMENT OF SHOWERS AND STORMS LATER THIS AFTERNOON...THE ABSENCE OF ANY NOTABLE TRIGGERS OVER CENTRAL NC (BOTH AT THE SURFACE AND ALOFT) --ASIDE FROM LOW PREDICTABILITY MESOSCALE ONES SUCH AS DIFFERENTIAL HEATING ALONG THE RETREATING WARM FRONT AND/OR LOW AMPLITUDE WAVES IN THE AFOREMENTIONED WSW FLOW ALOFT-- YIELDS A SOMEWHAT UNCERTAIN EVOLUTION OF CONVECTION LATER THIS AFTERNOON THROUGH TONIGHT. INDEED...THERE IS NO CLEAR SIGNAL IN HI-RESOLUTION CAM GUIDANCE. IT SEEMS REASONABLE THAT AT LEAST A COUPLE OF CLUSTERS OF STORMS WILL DEVELOP IN THE UPSTREAM WARM SECTOR --BENEATH A REMNANT EML PLUME SAMPLED BY RAOBS OVER THE LOWER-MIDDLE MS VALLEY LAST EVENING-- BOTH INVOF THE WESTERN EXTENSION OF THE COLD AIR DAMMING/WEDGE FRONTAL SEGMENT (IE. OVER THE LOWER OH VALLEY)...AND ALONG THE EAST- FACING SLOPES OF THE CENTRAL APPALACHIANS. SOME OF THIS ACTIVITY WILL THEN LIKELY DEVELOP EASTWARD ACROSS THE MIDDLE ATLANTIC STATES...MAINTAINED BY THE EASTWARD MIGRATION OF THE EML PLUME AND ASSOCIATED RELATIVELY STEEP /6-7 C/KM/ MID LEVEL LAPSE RATES...THIS AFTERNOON AND EVENING. BULK SHEAR WILL BE STRONGEST/ AROUND 40-45 KTS/ AND SUPPORTIVE OF SUPERCELLULAR STORM MODES ACROSS THE VIRGINIAS...WITH PROGRESSIVELY WEAKER VALUES / TO AROUND 30 KTS/ AND MORE FAVORABLE FOR MULTI- CELLULAR MODES OVER SOUTHERN NC. THE SEVERE WEATHER THREAT WILL CONSEQUENTLY BE GREATEST OVER THE NORTHERN NC PIEDMONT...WHERE BOTH LARGE HAIL AND DAMAGING WINDS WOULD BE FAVORED. THE ATMOSPHERE WILL REMAIN MOIST AND CONDITIONALLY UNSTABLE THROUGH TONIGHT...SO A CHANCE OF SHOWERS AND STORMS WILL CONTINUE OVERNIGHT. IT WILL ALSO BE MORE HUMID...WITH SURFACE TEMPERATURES AND DEWPOINTS IN THE 60S AND SUPPORTIVE OF AREAS OF LOW CLOUDS... THOUGH NOT AS WIDESPREAD AS THOSE SUPPORTED BY THE WEDGE REGIME OF THE PREVIOUS TWO NIGHTS.
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&& .SHORT TERM /MONDAY AND MONDAY NIGHT/...
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AS OF 355 AM SUNDAY... THE FRONTAL ZONE LINGERING JUST TO OUT SOUTH IS EXPECTED TO LIFT BACK NORTH TODAY AND RESIDE OVER NORTH-CENTRAL VA ON MONDAY. WARM SECTOR HEATING AND PW RISING TO 1.5" WILL RESULT IN MODEST DESTABILIZATION...WITH NAM/GFS FORECAST SOUNDINGS INDICATING UPWARDS OF 1500-2000 J/KG MLCAPE...AIDED IN PART BY MID-LEVEL LAPSE RATES AROUND 6.5C/KM. DESPITE THE ENHANCED BOUYANCY AND MOISTURE...RELATIVELY UNIFORM SOUTHWESTERLY FLOW ALOFT AND ONLY A WEAK LEE TROUGHING MAKES ADDITIONAL FORCING FOR ASCENT SOMEWHAT NEBULOUS...WITH THE BIGGER PIECES OF UPPER-LEVEL ENERGY OVER THE SOUTHERN ROCKIES CENTRAL PLAINS TRACKING ACROSS THE LOWER GREAT LAKES AND OHIO VALLEY REGIONS. THIS ALSO KEEP CENTRAL NC ON THE SOUTHERN FRINGES OF THE STRONGER 50KT MID-LEVEL FLOW...LIMITING DEEP LAYER SHEAR TO 25-30KT. A FEW STRONG STORMS ARE CERTAINLY POSSIBLE..BUT THE SEVERE THREAT APPEARS LOW. WILL KEEP CHANCE POPS HIGHEST IN THE EAST WHERE MOISTURE IS BETTER. HIGHS 80-83. A SLOW MOVING COLD FRONT DRAPED FROM THE MO VALLEY TO THE OH VALLEY TODAY WILL FINALLY GET A KICK EAST INTO THE APPALACHIANS MONDAY NIGHT AS THE FINAL SHORTWAVE EJECTS OUT OF THE SOUTHERN ROCKIES AND ACROSS THE OH VALLEY. RENEWED MOISTURE TRANSPORT AND WEAK HEIGHT FALLS SHOULD RESULT IN INCREASING PRECIP CHANCES OVER WESTERN NC MONDAY EVENING AND CONTINUING EAST WITH THE COLD FRONT ON TUESDAY. A STRONGER SHORTWAVE WILL THEN SWING THROUGH THE DEEP SOUTH LATE TUESDAY AND ACROSS CENTRAL NC ON WEDNESDAY. HEIGHT FALLS AHEAD OF THE SHORTWAVE AND THE AFOREMENTIONED COLD FRONT INTERACTING WITH A MOIST A MODERATELY UNSTABLE AIRMASS OVER EASTERN NC MAY RESULT IN A BETTER SEVERE THREAT TUESDAY AFTERNOON...PARTICULARLY GIVEN 35-40KT FOR DEEP LAYER SHEAR AS THE MAIN BELT OF WESTERLIES SHIFTS EAST. MONDAY NIGHT LOWS WILL BE RAISED INTO THE LOWER 60S GIVEN THE SLOWER TIMING OF THE FRONT...WITH HIGHS TUESDAY IN THE MID/UPPER 70S.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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AS OF 355 AM SUNDAY... THE PATTERN IN THE EXTENDED STILL APPEARS TO BE HEADED TOWARD AN OMEGA BLOCK..WITH A STOUT RIDGE OVER THE WESTERN US AND A DEEP UPPER LOW DEVELOPING OVER THE MID-ATLANTIC REGION...WITH H5 HEIGHTS 2-3 STD BELOW NORMAL OVER THE SOUTHEAST US. THIS WILL SUPPORT THE CONTINUED POTENTIAL FOR PERIODS OF SHOWERS...ESPECIALLY ACROSS THE NORTHERN HALF OF THE CWA EACH DAY HEADED INTO THE WEEKEND. A REINFORCING COLD FRONT ON THURSDAY WILL BRING THE COOLEST PERIOD WHEN H10-H95 THICKNESSES ARE FORECAST TO DIP BELOW 1340M...SUGGESTING HIGHS IN THE IN THE 60S FOR MUCH OF THE AREA. LONGER RANGE ENSEMBLE FORECASTS SHOW A SLOW BREAK DOWN OF THE BLOCKING PATTERN...SO TEMPS SHOULD REMAIN BELOW NORMAL THROUGH NEXT WEEKEND.
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&& .AVIATION /06Z SUNDAY THROUGH THURSDAY/... AS OF 215 AM SUNDAY... INCREASINGLY MOIST SW FLOW JUST ABOVE A RELATIVELY COOL AND STABLE LAYER OF AIR NEAR THE SURFACE WILL RESULT IN THE EXPANSION AND LOWERING OF IFR-MVFR CEILINGS THIS MORNING. A WARM FRONT WILL RETREAT NORTH ACROSS CENTRAL NC LATE THIS MORNING-MIDDAY AT FAY AND MIDDAY-EARLY AFTERNOON ELSEWHERE...WITH AN ASSOCIATED EROSION/ SCATTERING/LIFTING OF THE PRECEDING LOW CLOUDS...AND A SUBSEQUENT DEVELOPMENT OF A WARM AND BREEZY SW WIND. HOWEVER...THE EASTWARD PROGRESSION/PASSAGE OF AN AREA OF SHOWERS THROUGH THE SAME TIME FRAME MAY TEMPORARILY SLOW THOSE PROCESSES AND THE CONSEQUENT RETURN TO VFR CONDITIONS. WHILE THE AIR MASS WILL CONSEQUENTLY DESTABILIZE AND BE RIPE FOR THE DEVELOPMENT OF SHOWERS AND STORMS LATER THIS AFTERNOON...THE ABSENCE OF ANY NOTABLE TRIGGER BOTH AT THE SURFACE AND ALOFT --ASIDE FROM LOW PREDICTABILITY MESOSCALE ONES SUCH AS DIFFERENTIAL HEATING ALONG THE RETREATING WARM FRONT-- SUGGEST ASSOCIATED FORECAST CONFIDENCE IS TOO LOW TO MAINTAIN A PROLONGED/SEVERAL HOUR PERIOD OF THUNDER TO ACCOUNT FOR SUCH OCCURRENCE AT A GIVEN POINT/TAF SITE. THE ATMOSPHERE WILL REMAIN MOIST AND CONDITIONALLY UNSTABLE THROUGH TONIGHT...SO A THREAT OF SHOWERS AND STORMS WILL CONTINUE THROUGH THE 24-HR TAF PERIOD...THOUGH STILL WITH LOW CONFIDENCE ON OCCURRENCE/LOCATION/TIMING GIVEN A CONTINUED ABSENCE OF ANY TRIGGERS APPARENT AT THIS TIME RANGE. OUTLOOK: A SERIES OF WAVES OF LOW PRESSURE WILL TRACK ALONG A STALLED FRONTAL ZONE ALONG THE MIDDLE ATLANTIC AND SOUTHEAST UNITED STATES COAST...WITH ASSOCIATED PERIODS OF RAIN AND SUB-VFR CONDITIONS OVER CENTRAL NC...LATE MON NIGHT THROUGH WED. A POLAR VORTEX WILL MEANWHILE MIGRATE FROM THE ARCTIC CIRCLE TO THE MIDDLE ATLANTIC STATES THROUGH THE END OF THE WEEK...WITH RESULTANT ENHANCED AFTERNOON CLOUDINESS AND SHOWERS/STORMS...AS DIURNAL HEATING OCCURS BENEATH VERY COLD TEMPERATURES ALOFT ATTENDING THE VORTEX. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...26 SHORT TERM...22 LONG TERM...22 AVIATION...26

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