Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 260153 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 846 PM EST TUE NOV 25 2014 .SYNOPSIS...A DEVELOPING LOW PRESSURE SYSTEM WILL STRENGTHEN ALONG THE NORTH CAROLINA COAST TONIGHT...THEN TRACK NORTHEAST OFFSHORE THE MID-ATLANTIC COAST ON WEDNESDAY. A POTENT UPPER LEVEL DISTURBANCE WILL CROSS THE REGION LATE WEDNESDAY NIGHT AND THURSDAY MORNING. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 846 PM TUESDAY... RAIN CONTINUES TO OVERSPREAD NC THIS EVENING IN RESPONSE TO THE BACKING LOW TO MID LEVEL FLOW ASSOCIATED WITH APPROACH OF SEVERAL WAVES IN THE STRONG SUBTROPICAL JET ALOFT. THE MAIN SURFACE LOW PRESSURE WAS DEVELOPING NW OF TAMPA FLORIDA... IN THE NE GULF OF MEXICO. THIS LOW IS EXPECTED TO STRENGTHEN AND TRACK NE ALONG THE MAIN COASTAL BOUNDARY TONIGHT... REACHING OFF THE NC COAST WEDNESDAY. WAA PRECIPITATION WILL CONTINUE TO OVERSPREAD OUR REGION AS THE ATLANTIC GETS TAPPED IN ADDITION TO THE GULF OF MEXICO OVERNIGHT. WITH THE LACK OF A COLD HIGH TO SUPPLY INITIAL OR INCOMING COLD AIR - ONLY THE HIGHER PEAKS OF THE BLUE RIDGE SHOULD GET ANY APPRECIABLE SNOW ACCUMULATIONS. RAIN IS EXPECTED THROUGHOUT OUR REGION... EVEN IN OUR FAR NW PIEDMONT TRIAD AS THE THERMAL PROFILE IS FORECAST TO REMAIN WARM ENOUGH FOR ALL RAIN THROUGH THE NIGHT AND THE END OF THE EVENT NOONISH WEDNESDAY (AIDED BY THE WARM BOUNDARY LAYER FORECAST EVEN WITH ADEQUATE COOLING ALOFT NEAR THE END OF THE MAIN PRECIPITATION). NOTE THIS EVENING THAT IS WAS STILL IN THE 50S IN WASHINGTON DC AS OF 800 PM... AND THE DEW POINTS WERE CLOSE TO 40. THIS CLEARLY SHOWS THE LACK OF COLD DRY AIR FOR THE SYSTEM TO WORK WITH AND BRINGS CONFIDENCE TO A HIGH LEVEL FOR THE PRECIPITATION TYPE TO BE RAIN FOR OUR REGION. ONE OF THE STRONGEST SIGNALS FOR ALL RAIN WAS THE SURFACE WET BULBS FORECASTS THROUGH THE END OF THE MAIN PRECIPITATION EVENT IN OUR NW ZONES ON WEDNESDAY ONLY DIP TO SLIGHTLY BELOW 40... SUGGESTING LITTLE IF ANY CHANCE OF A MIX OR CHANGE TO WET SNOW BEFORE ENDING EAST OF THE BLUE RIDGE... EVEN WITH RAPIDLY COOLING ALOFT. HIGH CONFIDENCE IN ALL RAIN FOR THIS EVENT. SOME OF THE LATEST GUIDANCE SUGGESTS 1 INCH OR MORE QPF WIDESPREAD ACROSS THE REGION. RUNOFF PROBLEMS ARE NOT EXPECTED DUE TO THE RECENT 30-60 DAY DRY PERIOD.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... AS OF 210 PM TUESDAY... FOR WEDNESDAY: AS THE ABOVE-NOTED FORCING FEATURES CONTINUE TO PROMPT DEEP AND RAPID ASCENT WHILE DEEP MOISTURE (PW FROM 1" WEST TO 1.5" EAST) REMAINS IN PLACE... WIDESPREAD RAIN WILL CONTINUE THROUGH WED MORNING. STORM TOTAL RAINFALL FROM TONIGHT THROUGH WED MORNING IS LIKELY TO RANGE FROM THREE-QUARTERS OF AN INCH TO AN INCH AND A QUARTER... WITH A FEW HIGHER TOTALS POSSIBLE IN THE FAR EASTERN COUNTIES (WHERE MOIST ISENTROPIC UPGLIDE WILL BE STRONGEST) AND IN THE FAR WEST BENEATH ANY BANDED PRECIP. MODELS AGREE ON PRECIP ENDING FROM SSW TO NNE FROM LATE WED MORNING THROUGH EARLY WED AFTERNOON... LIKELY EXITING THE NE CWA PRIOR TO 3 PM AS THE VORTICITY MAXIMUM SWINGS NE OVER CENTRAL NC. THE CHANCE OF A MIX WITH WET SNOW WED MORNING AS THE VORTICITY MAXIMUM PASSES OVERHEAD (POTENTIALLY CAUSING FOCUSED STRONGER LIFT THAT COULD FURTHER COOL THE LOW LEVELS) REMAINS PLAUSIBLE... BUT IS UNLIKELY TO BE WIDESPREAD OR GENERATE ANY IMPACT. THE GFS IS TOO WARM (ABOVE- FREEZING SURFACE-BASED LAYER DEPTH NEAR 2K FT) AND HAS BEEN TRENDING WARMER... AND WHILE THE NAM IS COOLER (WARM LAYER DEPTH LESS THAN 1000 FT)... THE SREF PTYPE PLUMES INDICATE VERY LOW CHANCES OF ANYTHING BUT RAIN. WILL CONTINUE WITH A PURELY LIQUID FORECAST AT THIS TIME... BUT WILL CLOSELY MONITOR TRENDS IN BOTH MODEL DATA AND UPSTREAM CONDITIONS. WE SHOULD HAVE A SHORT WINDOW OF PARTIAL SUNSHINE ESPECIALLY ACROSS THE SW WED... AND THIS WILL MAKE HIGH TEMPS A CHALLENGE... AS ANY INSOLATION WILL CAUSE INITIALLY CHILLY READINGS TO WARM UP QUICKLY. WILL STICK WITH HIGHS OF 45-51... WHICH IS IN LINE WITH THE LATEST GUIDANCE... HOWEVER THESE COULD BE TOO COOL IF WE GET APPRECIABLE SUNSHINE. FOR WED NIGHT: FOCUS THEN QUICKLY SHIFTS TO THE CLIPPER WAVE AND LOW NOW OVER WRN ND... POISED TO DIVE SOUTHEAST THEN TRACK EASTWARD ACROSS NC/VA LATE WED NIGHT. MODELS AGREE ON PRECIP SPREADING EASTWARD OVER NRN NC... MAINLY ALONG/NORTH OF HIGHWAY 64... FORCED BY STRONG DPVA WITH THE STRENGTHENING VORTICITY MAX... A SHOT OF MODEST UPPER DIVERGENCE... AND STEEP 850-500 MB LAPSE RATES ON THE ORDER OF 7.0 C/KM. WILL RETAIN GOOD CHANCE POPS IN THE NORTH (ESPECIALLY NEAR THE VA BORDER) STARTING MID-LATE EVENING... SPREADING POPS EASTWARD OVER THE NORTHERN THIRD OVERNIGHT... WITH LITTLE TO NO POPS ACROSS THE SOUTH. QPF SHOULD BE LIGHT... GIVEN THAT FORCING WILL BE ROOTED FAIRLY HIGH WITH MODEST PRECIP WATER... PLUS SREF PROBABILITIES OF MEASURABLE RAINFALL ARE RATHER SMALL AND CONFINED JUST TO THE NW AND FAR NORTH. THERMAL PROFILES WITH THIS ALSO SUGGEST JUST A CHILLY LIGHT RAIN... ALTHOUGH IF WE DO ACHIEVE SOME INSTABILITY AND FOCUSED ASCENT... WE COULD SEE A BRIEF MIX WITH WET SNOW NEAR THE VA STATE LINE. AGAIN... THE VERY LOW PROBABILITY PRECLUDES MENTIONING IT IN THE FORECAST AT THIS TIME... BUT WILL MONITOR TRENDS. LOWS IN THE MID 30S... CLOSE TO GUIDANCE AND THE PREVIOUS FORECAST LOWS. -GIH && .LONG TERM /THURSDAY THROUGH TUESDAY/... AS OF 230 PM TUESDAY... THURSDAY AND THURSDAY NIGHT: A FAIRLY STRONG VORT MAX WILL ACCOMPANY THE PASSAGE OF THE 500 MB TROUGH AXIS ON THURSDAY. ALTHOUGH MOISTURE TOTALS ARE FAIRLY LOW THERE COULD BE A BRIEF PERIOD OF LIGHT RAIN...POSSIBLY MIXED WITH A SNOWFLAKE OR TWO THROUGH MID MORNING...BUT THEN THERMAL PROFILES SUGGEST ANYTHING THAT FALLS THEREAFTER WILL BE ALL LIQUID. PRECIPITATION OF ANY KIND SHOULD BE ENDING BY AFTERNOON. MAX TEMPERATURE IN THE UPPER 40S TO MID 50S NORTH TO SOUTH. DRIER AIR MOVES IN FOR THURSDAY NIGHT AS WELL AS CLEARING SKIES WHICH WILL HELP LOWS DROP INTO THE MID 20S TO NEAR 30 DEGREES. FRIDAY THOUGH MONDAY NIGHT: THE LONGWAVE TROUGH WILL MOVE OFFSHORE ON FRIDAY AND THE UPPER LEVEL FLOW WILL GRADUALLY BEGIN TO FLATTEN OUT. AS THIS HAPPENS...A SURFACE HIGH WILL BUILD INTO THE AREA FROM THE OHIO VALLEY. THIS WILL MOVE DIRECTLY OVERHEAD FOR THE WEEKEND AND THEN CONTINUE A SLOW EASTWARD MOVEMENT OUT TO SEA BY SUNDAY BEFORE STALLING OVER THE SOUTHWEST ATLANTIC FOR THE EARLY PORTION OF NEXT WEEK. THE RESULT WILL BE SOME COOL TEMPERATURES EARLY IN THE PERIOD WITH A WITH A WARMING TREND EACH DAY FROM FRIDAY THROUGH MONDAY. HIGHS WILL RANGE FROM THE MID 40S TO NEAR 50 DEGREES ON FRIDAY AFTERNOON...MODERATING TO THE LOW 50S FOR SATURDAY BEFORE CLIMBING INTO THE LOW 60S SUNDAY AND UPPER 60S ON MONDAY. LOWS WILL START OUT IN THE MID TO UPPER 20S FRIDAY MORNING AND CLIMB TO THE LOW TO MID 40S BY EARLY NEXT WEEK. WINDS WILL GO FROM NORTHWESTERLY ON FRIDAY TO SOUTHERLY BY SATURDAY AND MAINTAIN A SOUTHWESTERLY DIRECTION THROUGH THE END OF THE PERIOD. WITH HIGH PRESSURE IN CONTROL AND ZONAL FLOW ALOFT...NO PRECIPITATION IS EXPECTED DURING THIS TIMEFRAME. TUESDAY: A WEAK FRONTAL ZONE WILL SLOWLY DROP ACROSS THE MID- ATLANTIC ON TUESDAY. WHILE MODEL QPF VALUES WITH THE FRONT ARE VERY SMALL...BOTH THE ECMWF AND GFS ARE IN VERY GOOD AGREEMENT IN REGARDS TO A 1045 MB HIGH THAT WILL MOVE ACROSS EITHER SOUTHERN CANADA OR NY AND NEW ENGLAND AND MOVE INTO A GOOD POSITION TO SET UP A CLASSICAL/HYBRID COLD AIR DAMMING EVENT. THEREFORE WILL START TEMPS TUESDAY ON THE COLDER SIDE OF GUIDANCE...MID 50S NORTH TO LOW 60S SOUTH. WITH THIS PATTERN...CAN EXPECT SOME DRIZZLE/LIGHT RAIN IN THE TRIAD WITH ISENTROPIC LIFT...SO HAVE INTRODUCED SLIGHT CHANCES THERE...OTHERWISE DRY. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 700 PM TUESDAY... 24-HR TAF PERIOD: EXPECT RAPIDLY DETERIORATING CONDITIONS THIS EVENING INTO TONIGHT AS A RAPIDLY DEEPENING LOW PRESSURE SYSTEM TRACKS NORTHEAST ALONG THE CAROLINA COAST. MODERATE RAIN AND IFR/LIFR CEILINGS WILL OVERSPREAD THE REGION FROM SOUTH TO NORTH OVERNIGHT. WINDS WILL BECOME NORTH NORTHEAST AT 10-15 KT WITH GUSTS TO 20 KT AFTER ~06Z...STRENGTHENING TO 15-25 KT WITH GUSTS POSSIBLY AS HIGH AS 30-35 KT BETWEEN 12-17Z WED. PRECIPITATION WILL LIGHTEN AND BEGIN TO TAPER OFF BY THE END OF THE TAF PERIOD...WITH CEILINGS IMPROVING TO MVFR/VFR AND WINDS BECOMING WNW/NW AFTER 18Z WED AFTERNOON. LOOKING AHEAD: VFR CONDITIONS ARE EXPECTED TO RETURN IN THE WAKE OF THE LOW PRESSURE SYSTEM WED EVENING...HOWEVER...MVFR/IFR CEILINGS AND SHOWERS ARE EXPECTED TO REDEVELOP LATE WED NIGHT/THU MORNING AS A POTENT UPPER LEVEL DISTURBANCE CROSSES THE REGION FROM THE WEST. VFR CONDITIONS WILL RETURN TO ALL TERMINALS LATE THU/THU NIGHT AND PERSIST INTO THE WEEKEND AS HIGH PRESSURE BUILDS INTO THE CAROLINAS FROM THE WEST. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...PWBADGETT SHORT TERM...HARTFIELD LONG TERM...ELLIS AVIATION...VINCENT

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