Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 311935 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 230 PM EST SAT JAN 31 2015 .SYNOPSIS...ARCTIC HIGH PRESSURE OVER THE CAROLINAS TODAY WILL MOVE OFFSHORE THROUGH EARLY SUNDAY...AHEAD OF A LOW PRESSURE SYSTEM THAT WILL MOVE EAST ACROSS THE TN VALLEY AND MIDDLE ATLANTIC STATES LATE SUNDAY THROUGH EARLY MONDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 230 PM SATURDAY... HIGH PRESSURE ENCOMPASSING THE SOUTHEAST US WILL SHIFT OFFSHORE TONIGHT AS THE MID-LEVEL RIDGE OVER THE DEEP SOUTH FLATTENS IN RESPONSE TO A SHORTWAVE DIGGING THROUGH THE CENTRAL PLAINS. THE UPPER LEVEL FLOW WILL BECOME MORE SOUTHWESTERLY AND ALLOW THE EXPANSIVE CIRRUS OVER THE CENTRAL US TO SPREAD EAST. MODELS ARE IN PRETTY GOOD AGREEMENT THAT THE ENTIRE AREA WILL BE MOSTLY CLOUDY AFTER MIDNIGHT...THOUGH THE CLOUD DECK SHOULD BE THICKER OVER THE WEST. THUS...TEMPS WILL LIKELY DROP RAPIDLY AFTER SUNSET...ESPECIALLY IN THE EAST...BEFORE THE COOLING LEVELS OFF WITH THE INCREASING CLOUDS. GUIDANCE SEEMS TOO WARM IN THE EAST...SO WILL TAKE A FEW DEGREES OFF MAV/MET VALUES...WITH SOME MID 20S EAST TO AROUND 30 IN THE WEST. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 300 AM SATURDAY... SUNDAY: MINOR MID-LEVEL IMPULSES EMANATING FROM THE UPPER TROUGH/CLOSED LOW OVER THE SOUTHWEST US WILL EJECT EASTWARD AND MOVE THROUGH THE AREA IN ADVANCE OF THE NORTHERN STREAM TROUGH AMPLIFYING OVER THE CENTRAL PLAINS. ASSOCIATED WEAK DPVA WILL RESULT IN EXTENSIVE MID/HIGH LEVEL CLOUDINESS OVER THE AREA ON SUNDAY...HOWEVER GRADUAL MOISTENING OF AN INITIALLY DRY ~10KFT SUB- CLOUD LAYER LEFT(REMAINS OF THE MODERATING CP AIRMASS)WILL KEEP IT DRY ACROSS MUCH OF CENTRAL NC DURING THE DAYLIGHT HOURS. THE EXCEPTION WILL BE ACROSS THE FAR WESTERN ZONES WHERE A FEW SHOWERS COULD DEVELOP LATE IN THE AFTERNOON AS THE WARM MOIST CONVEYOR FEED BEGINS TO PUSH EAST OF THE MOUNTAINS. HIGHS SUNDAY IN THE LOWER 50S NORTH TO MID 50S SOUTH. SUNDAY NIGHT: AFOREMENTIONED NORTHERN STREAM TROUGH WILL CONTINUE TO PROGRESS EASTWARD...REACHING THE SOUTHERN/CENTRAL APPALACHIANS BY DAYBREAK MONDAY. DEEPENING SURFACE LOW....MOVING EASTWARD ALONG THE LEADING EDGE OF THE ASSOCIATED 180-200 METER 500MB HEIGHT FALLS... WILL TRACK ACROSS THE SOUTHERN OHIO VALLEY AND THROUGH THE VIRGINIAS DURING THE PREDAWN HOURS...DRAGGING A SFC COLD FRONT INTO THE NC FOOTHILLS. STRONG DEEP MOISTURE TRANSPORT IN ADVANCE OF THE FRONT...WITHIN THE STRENGTHENING 60-65KT SOUTHERLY LLJ WILL SUPPORT A 4-6 HOUR WINDOW OF CATEGORICAL POPS ACROSS THE AREA SUNDAY NIGHT. QPF AMOUNTS LOOK TO BE IN THE 0.25-0.50" RANGE...LIMITED BY THE INTRUSION OF A MID-LEVEL SLOT RACING IN FROM THE WEST. HAVE NO PLANS TO INCLUDE ANY THUNDER AT THIS TIME AS MODELS CONTINUE TO SHOW MODEST MID-LEVEL LAPSE RATES (6.5-6.8 C/KM)WITH LESS THAN <200 J/KG OF MUCAPE ACROSS THE AREA. EXPECT A NON-DIURNAL TEMP TREND SUNDAY NIGHT...WITH LOWS OCCURRING BEFORE MIDNIGHT...WITH TEMPERATURES THEN WARMING OVERNIGHT OWING TO STRONG WAA. LOWS SUNDAY NIGHT IN THE MID 40S NORTHWEST TO LOWER 50S SOUTH. MONDAY AND MONDAY NIGHT: AGGRESSIVE MID-LEVEL DRY AIR INTRUSION WILL OVERTAKE THE AREA FROM THE WEST BETWEEN 12 TO 18Z MONDAY IN ADVANCE OF THE PASSAGE OF THE NORTHERN STREAM TROUGH PASSAGE MONDAY AFTERNOON. THIS WILL BRING AN ABRUPT END TO PRECIP ACROSS THE AREA MONDAY MORNING...WITH RAIN/SHOWERS EXITING THE COASTAL PLAIN DURING THE MID TO LATE MORNING. EQUALLY IMPRESSIVE WILL BE STRONG POST- FRONTAL DRY COLD AIR ADVECTION REGIME...WITH BREEZY/BLUSTERY CONDITIONS AS BUFR SOUNDINGS INDICATING 38-40KTS AT THE TOP OF THE MIXED LAYER(SIMILAR TO IF NOT STRONGER THAN THE GUSTS WE HAD YESTERDAY). LOOK FOR TEMPERATURES FALLING THROUGH THE AFTERNOON AS YET ANOTHER CP AIRMASS BUILDS INTO THE AREA MONDAY NIGHT AND INTO THE DAY ON TUESDAY. MORNING HIGHS RANGING FROM MID UPPER 40S NORTHWEST TO MID 50S SOUTHEAST. IF PROJECTED LOW-LEVEL THICKNESSES AOA 1270M VERIFY AND WE DECOUPLE AS MODELS SUGGEST...EXPECT LOWS TUESDAY MORNING IN THE LOWER 20S...WITH UPPER TEENS POSSIBLE IN THE TYPICALLY COLDER LOCATIONS. && .LONG TERM /TUESDAY THROUGH FRIDAY/... AS OF 300 AM SATURDAY... BOTH THE ECMWF AND THE GFS PASS A MID-LEVEL SHORTWAVE THROUGH CENTRAL NORTH CAROLINA TUESDAY AS A BROAD...PROGRESSIVE TROUGH ALOFT MOVES THROUGH. HOWEVER...WITH SURFACE HIGH PRESSURE IN PLACE AND EXTENDING ACROSS THE GULF A PERIOD OF PARTLY TO POSSIBLY MOSTLY CLOUDY SKIES SHOULD ONLY ACCOMPANY THE SHORTWAVE. AFTER EXPECTED BRIEF CLEARING BEHIND THE MID-LEVEL WAVE...IN THE FAST AND SLOWLY BACKING FLOW ALOFT BOTH THE ECMWF AND THE GFS FORECAST INCREASING UPPER-LEVEL MOISTURE WEDNESDAY INTO WEDNESDAY NIGHT WITH A COLD FRONT MOVING THROUGH WEDNESDAY NIGHT. BOTH THE GFS AND ECMWF ARE DRY INTO THE OVERNIGHT HOURS OF WEDNESDAY WITH SURFACE HIGH PRESSURE AHEAD OF THE COLD FRONT EXTENDING OVER THE GULF COAST AND LIMITING LOW-LEVEL MOISTURE RETURN. FOR THIS FORECAST...WILL HAVE DRY CONDITIONS TUESDAY INTO THE OVERNIGHT HOURS OF WEDNESDAY. MEX MOS AND ECMWF MOS GUIDANCE POPS ARE BELOW CLIMATOLOGY DURING THIS PERIOD. GUIDANCE DIFFERENCES ARE FAIRLY OBVIOUS BY LATE WEDNESDAY NIGHT. MUCH WILL DEPEND ON HOW DEEP THE UPPER TROUGH MOVING THROUGH SOUTHERN CANADA ENDS UP BEING DURING THE MIDDLE OF THE WEEK. THE ECMWF HAS BEEN CONSISTENT OVER THE LAST COUPLE OF RUNS OR SO WITH A DEEPER UPPER TROUGH EXTENDING THROUGH THE GREAT LAKES INTO THE OHIO VALLEY. THIS SUPPRESSES THE TRACK OF AN UPPER LOW FORECAST BY BOTH THE GFS AND THE ECMWF TO DEVELOP OVER OLD MEXICO...KEEPING DEEPER MOISTURE TO OUR SOUTH AND RESULTING IN DRY CONDITIONS FOR CENTRAL NORTH CAROLINA THROUGH THE END OF THE WEEK. THE GFS...ALSO CONSISTENT WITH ITSELF...IS NOTICEABLY LESS AMPLIFIED WITH THE CANADIAN UPPER TROUGH SUCH THAT THE WEAKENING UPPER LOW IS ABLE TO MOVE TOWARD THE CAROLINAS BY THURSDAY ALONG WITH MORE MOISTURE. THE GFS FORECASTS PRECIPITATION OVER CENTRAL NORTH CAROLINA BY 12Z THURSDAY WHICH...IF IT OCCURS...WOULD BE LIQUID AS GFS PARTIAL THICKNESSES ARE WELL INTO THE RAIN REGIME AT THAT TIME. DUE TO THE GUIDANCE UNCERTAINTY...THE PRUDENT COURSE APPEARS TO BE MAINTAINING CONSISTENCY WITH THE ONGOING FORECAST...A CHANCE OF RAIN IN CENTRAL NORTH CAROLINA OVERNIGHT WEDNESDAY INTO THURSDAY WITH CHANCES LOWEST AND BASICALLY NEAR SLIGHT IN THE TRIAD TO HIGHER CHANCES ALONG AND EAST OF A LINE FROM ABOUT KMEB TO KRWI. IF THE GFS VERIFIES EXACTLY THERE WOULD BE CONCERN ABOUT PRECIPITATION TYPE IN THE LINGERING MOISTURE BY THURSDAY NIGHT...BUT A DRY ECMWF WITH NEAR SOUTHEAST CONUS LOW PRESSURE MOVING OFFSHORE AND A DRY PREVIOUS FORECAST WILL RESULT IN A DRY CURRENT FORECAST THURSDAY NIGHT THROUGH FRIDAY NIGHT...THOUGH TURNING CHILLY AT THE END OF THE WEEK. THE WARMEST DAY OF THE PERIOD SHOULD BE WEDNESDAY. 1000-850MB THICKNESSES WOULD SUGGEST HIGHS AT LEAST IN THE MID TO UPPER 50S... FAIRLY COINCIDENT WITH THE MEX AND MEE MOS GUIDANCE...BUT WILL LEAN ABOUT A CATEGORY COOLER TOWARD THE HPC GUIDANCE FOR HIGHS IN THE LOWER TO MID 50S DUE TO THE ANTICIPATED PRESENCE OF AT LEAST SOME UPPER-LEVEL CLOUD COVER. THICKNESSES COOL AT THE END OF THE WEEK AND...DESPITE DIFFERENCES IN OTHER DETAILS...1000-850MB THICKNESSES...AND HPC AND MUCH OF THE MOS GUIDANCE...KEEP HIGHS ONLY IN THE MID 30S TO LOWER 40S FRIDAY. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... AS OF 100 PM SATURDAY... SKIES ARE CLEAR ACROSS CENTRAL NC THIS AFTERNOON WITH HIGH PRESSURE ACROSS THE SOUTHEAST US. WINDS WILL REMAIN LIGHT AND MOSTLY VARIABLE OR WESTERLY THIS AFTERNOON. INCREASING MID/HIGH CLOUDS OVER THE CENTRAL US WILL SPREAD EAST TONIGHT BUT CEILINGS WILL REMAIN ABOVE 10K FT. HIGH PRESSURE WILL THEN SHIFT SOUTHEAST BY EARLY SUNDAY AND WINDS WILL BECOME SOUTHWESTERLY DURING THE DAY...INCREASING TO 8-12KT DURING THE AFTERNOON WITH A FEW GUSTS TOWARD 20KT POSSIBLE AT MAINLY KGSO AND KINT. OUTLOOK...CEILINGS WILL LOWER TO MVFR BY LATE SUNDAY AFTERNOON AND EVENING AHEAD OF A LOW PRESSURE SYSTEM MOVING THROUGH THE TENNESSEE/OHIO VALLEY. RAIN WILL OVERSPREAD THE AREA SUNDAY NIGHT...LIKELY CAUSING CEILINGS TO DROP TO IFR LEVELS...AS A STRONG LOW-LEVEL JET SURGES ACROSS THE REGION. A COLD FRONT WILL THEN SWING ACROSS CENTRAL NC ON MONDAY...WITH GUSTY NORTHWEST WINDS IN ITS WAKE MONDAY AFTERNOON. VFR CONDITIONS ARE THEN EXPECTED THROUGH MIDWEEK && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...BLS SHORT TERM...CBL LONG TERM...DJF AVIATION...BLS

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