Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 232041 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 340 PM EST SUN NOV 23 2014 .SYNOPSIS...A WARM FRONT WILL SURGE NORTHWARD THROUGH THE CAROLINAS AND MID-ATLANTIC LATE TODAY INTO TONIGHT AS A LOW PRESSURE SYSTEM TRACKS NORTHEAST FROM THE LOWER MIDWEST TO THE GREAT LAKES. AN ASSOCIATED COLD FRONT WILL SWEEP EASTWARD THROUGH THE CAROLINAS MONDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 305 PM SUNDAY... HIGH PRESSURE OFFSHORE STILL EXTENDS ACROSS CENTRAL NC THIS MORNING...WITH STRENGTHENING SOUTHWESTERLY FLOW ALOFT AHEAD OF A LONGWAVE TROUGH OVER THE WEST-CENTRAL US. A VIGOROUS SHORTWAVE CURRENTLY OVER THE LOWER MISSISSIPPI RIVER VALLEY HAS BECOME NEGATIVELY TILED AND WILL LIFT NORTHEAST TOWARD THE GREAT LAKES REGION. OUT OF AHEAD OF THIS WAVE...MOISTURE HAS BEEN STEADILY INCREASING TODAY WITH PW NOW UP TO 1.25 TO 1.5 INCHES. AREAS OF LIGHT RAIN DRIVEN BY 295-300K LAYER ISENTROPIC LIFT WILL CONTINUE THIS AFTERNOON AS WARM ADVECTION AND ISENTROPIC ASCENT STRENGTHEN WITH THE APPROACH OF THE MOIST LLJ THIS EVENING. TIMING... THE LLJ WILL SURGE ACROSS THE AREA THIS EVENING...ALONG WITH A STRONG 850MB WARM FRONT CHARACTERIZED BY 850MB TEMPS IN EXCESS OF 15C. THE NAM PRODUCES A BIT MORE MUCAPE THAN THE GFS/ECMWF...BUT GENERALLY EXPECT ABOUT 300-600 J/KG IN THE SOUTHEAST WITH LESS TO THE NORTHWEST. THE BIGGEST QUESTION WILL BE HOW MUCH SURFACE DEWPOINT RECOVERY OCCURS WITH THE SURFACE WARM FRONT AFTER 00Z. LIGHT PRECIP INTO THE DRY AIRMASS OVER NC TODAY HAS LEAD TO A WEAK IN-SITU CAD AIRMASS...WHICH WILL RETARD BOTH THE RETREATING WEDGE FRONT AND TRUE WARM FRONT. PAST EXPERIENCE SUGGESTS THE WEDGE FRONT WILL END UP BETWEEN THE TRIAD AND TRIANGLE...WHILE THE WARM FRONT WILL MAKE IT TO AT LEAST THE I-95 CORRIDOR. WILL HAVE TO WATCH FOR ELEVATED CONVECTION NEAR THE 850MB FRONT AROUND 00Z..AND THEN THE POTENTIAL FOR BOUNDARY LAYER ROOTED CONVECTION BETWEEN THE SURFACE WARM FRONT AND AN MCS/EFFECTIVE FRONT ASSOCIATED WITH THE VORT LOBE ATTENDANT TO THE MAIN SHORTWAVE. REGARDING THE SEVERE THREAT... HELICITY WILL BE MAXIMIZED IN THE VICINITY OF THE SURFACE WARM FRONT BEFORE WINDS BEGIN TO VEER TO SOUTHERLY...BUT THE OVERALL LOW-LEVEL SHEAR WILL SUPPORT CURVED HODOGRAPHS AND A TORNADO THREAT...PROVIDED LOW-LEVEL DESTABILIZATION OCCURS (STILL THE BIGGEST LIMITING FACTOR). SOME EMBEDDED SUPERCELLULAR STRUCTURE WILL BE POSSIBLE WITHIN THE "PRE-FRONTAL" CONVECTION AND WITHIN THE PRIMARY BAND ITSELF. SPC HAS FOCUSED THE SLIGHT RISK ALONG THE CAROLINA COAST...WITH THE LESSER MARGINAL RISK ALONG I-95. ONCE THE EFFECTIVE FRONT SWEEPS ACROSS THE AREA...PRECIP WILL COME TO AN END FOR THE MOST PART. WHILE THE DRY SLOT WILL SPREAD ACROSS WESTERN NC... THE PRIMARY MOIST AXIS WILL BECOME ALIGNED SOUTHWEST TO NORTHEAST OVER COASTAL NC...SO A FEW ADDITIONAL SHOWERS MAY CONTINUE TO MOVE NORTHEAST THROUGH THE COASTAL PLAIN. TEMPS SHOULD ESSENTIALLY HOLD AROUND THE MID 50S WEST TO MID 60S EAST. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 305 PM SUNDAY... ...WARM AND WINDY CONDITIONS ON MONDAY... THE MID/UPPER LEVELS WILL CONTINUE TO DRY ON MONDAY...WHILE LOW- LEVEL MOISTURE LINGERS WITH THE TRAILING COLD FRONT STILL WEST OF THE MOUNTAINS. WITH SOME BREAKS IN CLOUD COVER AND NO AIRMASS CHANGE...TEMPS ARE EXPECTED TO RISE INTO THE LOW 70S WEST TO MID AND EVEN UPPER 70S EAST (STILL A COUPLE DEGREES SHORT OF RECORDS). MIXING DEPTH IN NAM AND GFS FORECAST SOUNDINGS VARIES BY AS MUCH AS 2000 FT...ESPECIALLY IN THE EAST. WIND FIELDS WILL STILL BE QUITE STRONG...WITH UP TO 50KT IN THE LOWEST 3000FT. HOW MUCH OF THAT WILL BE MIXED DOWN TO THE SURFACE IS A LITTLE UNCERTAIN...BUT AT A MINIMUM IT APPEARS GUSTS TO AROUND 30KT WILL BE POSSIBLE. CONFIDENCE IN WIDESPREAD HIGHER GUSTS IS TOO LOW AT THE MOMENT AND WIND ADVISORY CRITERIA APPEARS OUT OF REACH. WILL CONTINUE MENTION IN THE HWO. WITH DEWPOINTS STILL ELEVATED IN THE COASTAL PLAIN..SOME WEAK INSTABILITY SHOULD DEVELOP. HOWEVER... THERE IS NO REAL SIGNIFICANT TRIGGER FOR ASCENT...SO WILL JUST MAINTAIN A SLIGHT CHANCE IN THE EAST. THE COLD FRONT WILL CROSS THE AREA MONDAY NIGHT. THE GFS IS A BIT QUICKER THAN THE NAM/ECMWF..BUT ALL MODELS HAVE THE COLD FRONT EAST OF THE AREA BY 12Z TUESDAY. LOWS IN THE LOWER 40S WEST TO LOWER 50S EAST. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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AS OF 335 PM SUNDAY... TUE-WED NIGHT: 1025 MB CONTINENTAL POLAR SURFACE HIGH PRESSURE WILL BUILD EAST ACROSS THE MID MS AND TN VALLEYS TUE...THEN NORTHEASTWARD INTO THE NORTHERN MIDDLE ATLANTIC STATES AND NEW ENGLAND TUE NIGHT AND WED. MEANWHILE...THE APPROACH OF A COMPLEX POSITIVELY-TILTED TROUGH ALOFT WILL INDUCE CYCLOGENESIS FROM THE CENTRAL GOM TO THE SOUTHEAST US COAST LATE TUE AND TUE NIGHT...THEN UP SOUTHERN MIDDLE ATLANTIC COAST ON WED. THE PREFERRED CLOSER TO THE COAST/MORE WESTWARD SOLUTION FOR THE LOW TRACK FROM YESTERDAY HAS GAINED INCREASING MODEL SUPPORT SINCE...WITH THE PAST TWO RUNS OF THE CANADIAN NOW CLOSE ENOUGH TO THE COAST TO SPREAD PRECIPITATION THROUGHOUT CENTRAL NC LATE TUE NIGHT THROUGH WED EVENING...LEAVING THE NAM THE LONE WELL OFFSHORE/EASTERN OPERATIONAL OUTLIER. WITH THE ABOVE FAVORED LOW TRACK IN MIND...THE RESULT WILL BE RAIN DEVELOPING FROM THE SOUTH LATE TUE AND ESPECIALLY TUE NIGHT...WITH A COLD RAIN AND TEMPERATURES FALLING INTO THE MIDDLE 30S TO AROUND 40 DEGREES...ON WED. THE TRACK OF THE COASTAL LOW AND PRESENCE OF THE CP HIGH PRESSURE...WHICH ARE FORECAST TO MIGRATE IN TANDEM UP THE EAST COAST...WILL PROVIDE A FAVORABLE PATTERN FOR SNOW ON THE NW SIDE OF THE PRECIPITATION SHIELD. WHILE MOST OF THE SNOW EAST OF THE APPALACHIANS WILL LIKELY NOT MATERIALIZE UNTIL THE SYSTEM MOVES PARALLEL TO THE LARGER METRO AREAS IN THE I-95 CORRIDOR...FORECAST PARTIAL THICKNESS VALUES SPEND TIME IN THE "WINTRY MIXTURE" TO "MEASURABLE SNOW WITH RAIN" PORTION OF THE NOMOGRAM AS THE PRECIPITATION BEGINS TO PULL AWAY DURING THE MIDDAY AND AFTERNOON HOURS WED. GIVEN THE MARGINALLY COLD PARTIAL THICKNESS VALUES/ THERMODYNAMIC PROFILES...AND FREEZING LEVELS AROUND 1000 FT OVER THE PIEDMONT PER GFS BUFR FORECAST SOUNDINGS...ANY SUCH SNOW WOULD LIKELY BE DRIVEN BY SECONDARY FACTORS SUCH AS PRECIPITATION RATES/MELTING...WHICH IS NOT UNCOMMON FOR EVENTS THAT FALL IN THE ABOVE-REFERENCED PORTIONS OF THE NOMOGRAM. WITH THE ABOVE FACTORS IN MIND...THERE IS A HIGH ENOUGH PROBABILITY FOR WET SNOW TO AT LEAST OCCASIONALLY MIX IN TO WARRANT MENTION OF A SLIGHT CHANCE TO CHANCE OF SNOW MAINLY NORTH OF HIGHWAY 64 IN THE GRIDDED AND TEXT FORECAST. THE BREVITY AND INTERMITTENT NATURE OF SNOW DURING OTHERWISE CHILLY RAIN...ABOVE FREEZING BOUNDARY LAYER TEMPERATURES ( ALBEIT ONLY MARGINALLY)...RELATIVELY WARM SOIL TEMPERATURES 9MOSTLY IN THE 50S TODAY)...AND WETNESS FROM THE RAIN WILL ALL MAKE IT EXTREMELY DIFFICULT FOR ANY ACCUMULATION TO OCCUR. NO TRAVEL IMPACTS ARE CONSEQUENTLY EXPECTED. TEMPERATURES WILL...HOWEVER...DIP INTO THE UPPER 20S TO LOWER BEHIND THE SYSTEM WED NIGHT...SO ANY MOISTURE ON THE ROADWAYS COULD RESULT IN PATCHY BLACK ICE THROUGH EARLY THU MORNING. THU-SUN: BENEATH A BROAD TROUGH ALOFT FROM NORTH-CENTRAL CANADA TO THE MIDDLE ATLANTIC COAST...A SERIES OF CLIPPER LOWS WILL TRACK ACROSS THE OH VALLEY AND NORTHERN MIDDLE ATLANTIC STATES...WHICH WOULD FAVOR THE RE-ESTABLISHMENT OF ARCTIC HIGH PRESSURE ACROSS THE NORTHERN HALF OF THE CONUS EAST OF THE ROCKIES (JUST TO THE NORTH OF NC)...THROUGH THE END OF THE WEEK. THE FRONTAL ZONE BETWEEN THE ARCTIC AIR MASS TO THE NORTH AND A MILDER/MORE MODIFIED HIGH PRESSURE SYSTEM OVER THE SOUTHEAST STATES WILL GRADUALLY RETREAT NORTH AS THE FLOW ALOFT LOSES AMPLITUDE/RELAXES TOWARD THE END OF THE FORECAST PERIOD. THE RESULTANT PATTERN OF RELAXING NW TO WNW FLOW ALOFT WOULD RESULT IN A TRANSITION FROM DRY AND COOL CONDITIONS TO DRY AND SEASONABLE ONES THROUGH THE FORECAST PERIOD.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 100 PM SUNDAY... AREAS OF LIGHT RAIN CONTINUE TO MOVE EAST-NORTHEAST ACROSS THE AREA THIS AFTERNOON. LOW-LEVEL DRY AIR HAS KEPT LOW CEILINGS FROM DEVELOPING AT MOST TERMINALS...BUT THE TREND CONTINUES TO BE DOWN AND MVFR/IFR CEILINGS ARE ESSENTIALLY ON THE DOORSTEP OF KGSO/KINT/KRDU/KFAY. EXPECT ALL SITES TO DROP TO IFR BY 21Z AND STAY THERE FOR MUCH OF THE EVENING. WINDS WILL STAY OUT OF THE EAST- NORTHEAST. LATE THIS EVENING...A WARM FRONT WILL MOVE INTO THE AREA FROM THE SOUTH...WHICH SHOULD CASE SOME LIFTING OF CEILINGS AT KFAY AND KRWI BETWEEN 00Z AND 06Z. THE FRONT WILL ATTEMPT TO PUSH ALL THE WAY PAST KRDU TO KGSO/KINT...THOUGH ITS STILL UNCERTAIN WHETHER OR NOT THE TRIAD TERMINALS. AT THE SAME TIME A STRONG 50-60KT LOW LEVEL JET WILL MOVE OVER THE AREA...WHICH MAY CREATE LOW-LEVEL WIND SHEAR FROM KRDU WEST. A FEW STRONG STORMS WILL ALSO BE POSSIBLE...MAINLY FROM KFAY TO KRWI AND EAST. AFTER 06Z...AN EFFECTIVE FRONT WILL SWEEP ACROSS THE AREA AND WINDS WILL TURN TO MORE SOUTH-SOUTHWESTERLY. WIND GUSTS TO 20-25KT WILL BE POSSIBLE...INCREASING TO AS HIGH AS 30-35KT DURING THE DAY ON MONDAY. THERE WILL BE SOME IMPROVEMENT IN CEILINGS DURING THE DAY MONDAY...THOUGH LOW-LEVEL MOISTURE WON COMPLETELY SCOUR UNTIL THE ACTUAL COLD FRONT CROSSES THE AREA MONDAY NIGHT. OUTLOOK...ANOTHER SYSTEM WILL IMPACT THE REGION BY MIDWEEK...THOUGH THERE IS SOME UNCERTAINTY AS TO HOW MUCH OF THE AREA WILL BE IMPACTED BY PRECIPITATION AND ADVERSE AVIATION CONDITIONS AS A SURFACE LOW MOVES ALONG THE EAST COAST. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BSD/VINCENT NEAR TERM...BLS SHORT TERM...BLS LONG TERM...MWS AVIATION...BLS/BSD

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