Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011521 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1120 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 1120 AM SUNDAY... A MESOSCALE CONVECTIVE VORTEX (MCV) INTERACTING WITH AVAILABLE MOISTURE AND MODEST LIFT AIDING TO MAINTAIN A BROKEN BAND OF CONVECTION OVER THE SOUTHERN COUNTIES OF CENTRAL NC THIS MORNING. THIS FEATURE SHOWING UP NICELY ON REGIONAL RADAR TRAVERSING EAST ALONG THE NC/SC BORDER. A MID LEVEL VORTICITY (PER WATER VAPOR IMAGERY) APPEARS TO BE RESPONSIBLE FOR THE SCATTERED CONVECTION OCCURRING OVER THE NORTHERN PIEDMONT AND ON INTO VA. THESE FEATURES WILL CONTINUE TO TRAVERSE EAST AND EXIT OUR COASTAL PLAIN COUNTIES PRIOR TO MID AFTERNOON. SUBSIDENCE BEHIND THESE FEATURES WILL INITIALLY INHIBIT ADDITIONAL CONVECTIVE DEVELOPMENT THROUGH MID-LATE AFTERNOON. BY 20Z- 21Z...PARTIAL HEATING SHOULD ALLOW FOR SCATTERED DEVELOPMENT OVER THE PIEDMONT COUNTIES. WHILE PARAMETERS IN PLACE FOR T-STORM DEVELOPMENT...APPEARS BULK OF CONVECTION WILL REMAIN BELOW SEVERE CRITERIA. WIDESPREAD CLOUDINESS AND BANDS OF SHOWERS/T-STORMS INITIALLY LIMITING TEMP RECOVERY THIS MORNING. THIS WILL LIKELY AFFECT MAX TEMP FORECAST AS PARTIAL SUN MAY NOT BECOME PROMINENT UNTIL AFTER 18Z...POSSIBLY TOO LATE TO HAVE ANY APPRECIABLE EFFECTS. MAY NEED TO ADJUST MAX TEMPS DOWN A FEW DEGREES MOST LOCATIONS FROM PREVIOUS FORECAST. -WSS 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. -26
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&& .SHORT TERM /MONDAY AND MONDAY NIGHT/... 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. && .LONG TERM /TUESDAY THROUGH SATURDAY/... 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. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... AS OF 750 AM SUNDAY... 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 AND STORMS 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 AREA-WIDE TO ACCOUNT FOR SUCH OCCURRENCE AT A GIVEN POINT/TAF SITE. INSTEAD...HAVE INCLUDED A PROB30 GROUP WITH THUNDER ONLY AT TRIAD TAF SITES FOR NOW...IN CLOSEST PROXIMITY TO THE AFOREMENTIONED RETREATING WARM FRONT AS IT LIFTS INTO VA THIS AFTERNOON. THE ATMOSPHERE WILL REMAIN MOIST AND CONDITIONALLY UNSTABLE THROUGH TONIGHT...SO THERE WILL REMAIN A SMALL CHANCE OF SHOWERS AND STORMS THROUGH THE 24-HR TAF PERIOD...WITH THE RELATIVE BETTER CHANCE BEFORE MIDNIGHT. IN ADDITION...AN INCREASINGLY HUMID AIRMASS WILL SUPPORT THE RE-DEVELOPMENT OF AREAS OF LOW STRATUS LATE TONIGHT... PARTICULARLY AT EASTERN TAF SITES. 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...WSS/26 SHORT TERM...22 LONG TERM...22 AVIATION...26

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