Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 230821 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 320 AM EST SUN NOV 23 2014 .SYNOPSIS...A WARM FRONT WILL APPROACH THE REGION FROM THE SOUTH THIS MORNING...THEN SURGE NORTHWARD THROUGH THE CAROLINAS AND MID- ATLANTIC LATE TODAY INTO TONIGHT AS A POWERFUL 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/...
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AS OF 315 AM SUNDAY... TODAY AND TONIGHT: A POTENT S/W TROUGH WILL LIFT NORTHEASTWARD FROM TX THIS MORNING AND INTO THE CENTRAL APPALACHIANS BY THIS EVENING. MEANWHILE... SURFACE HIGH PRESSURE THAT DEPOSITED DRY/COLD AIR ACROSS CENTRAL NC WILL CONTINUE TO PUSH FURTHER OFFSHORE TODAY. STRENGTHENING LOW LEVEL FLOW IN ADVANCE OF THE POTENT S/W AND ADDITIONAL WEAKER EMBEDDED DISTURBANCES IN THE SOUTHWESTERLY MID LEVEL FLOW WILL HELP SUPPORT AND AREA RAIN MOVING INTO THE AREA THIS MORNING/MAINLY AFTER DAYBREAK. THANKS TO THE DRY MID LEVEL AIRMASS STILL IN PLACE ACROSS CENTRAL NC THIS MORNING THE LEADING EDGE OF THE RETURNS ON RADAR WILL LIKELY JUST HELP TO MOISTEN THE COLUM. HOWEVER... RAIN SHOULD BECOME WIDESPREAD ACROSS THE AREA BY MID MORNING INTO THE AFTERNOON ACROSS CENTRAL NC... FIRST ACROSS THE SOUTH/SOUTHWESTERN REACHES OF THE CWA THEN SPREADING NORTHEASTWARD ACROSS THE AREA. THIS SHOULD HELP TO CREATE AN INITIAL IN-SITU COLD AIR DAMMING AIRMASS. DAYTIME/EARLY EVENING HIGHS ARE EXPECTED TO STRUGGLE TO REACH THE 50 IN THE NORTHWEST PIEDMONT TO THE MID TO UPPER 60S SOUTHEAST... WHERE A RETREATING WARM FRONT WILL BEGIN TO SURGE INTO THE AREA LATE INTO THE DAY/EVENING (WITH CALENDAR DAY HIGHS LIKELY AT MIDNIGHT) THE 850 MB FRONT IS EXPECTED TO SURGE INTO AND ACROSS THE AREA THIS EVENING... WITH 850 MB SOUTHERLY WINDS OF AROUND 50 TO 70 KTS. AS THE SFC-850 MB WARM FRONT MOVES THROUGH THE AREA EXPECT WE COULD SEE A FEW ISOLATED EMBEDDED STORMS... WITH EVEN THE THREAT OF AN ISOLATED TORNADO ACROSS OUR FAR SOUTHEAST (SAMPSON/WAYNE... MAYBE CUMBERLAND AND WILSON AND EDGECOMBE) AS LOW LEVEL AND DEEP LAYER SHEAR WILL BE STRONG... WITH LARGE CYCLONIC LOOPING HODOGRAPHS... BUT INSTABILITY WILL BE MINIMAL TO NIL (BEST CHANCE OF SURFACE BASED INSTABILITY ACROSS OUR FAR SE/E). SPC DAY ONE OUTLOOK CLIPS OUR FAR EAST/SOUTHEAST WITH THE MARGINAL AREA... AND ONLY EXTREME SOUTHERN SAMPSON WITH THE SLIGHT RISK AREA. THE SMALL WINDOW FOR AN ISOLATED SEVERE STORM ACROSS OUR FAR EAST/SOUTHEAST WOULD BE FROM AROUND 00Z TO 04/05Z... WITH THE MAIN THREATS OF AN ISOLATED TORNADO AND/OR DAMAGING WIND GUST. MID LEVEL DRY AIR IS THEN FORECAST TO SURGE INTO OUR AREA... AS WARM FRONT LIFTS NORTH AND NORTHWEST OF OUR AREA. THUS... EXPECT TEMPS WILL RISE THIS EVENING INTO THE EARLY MORNING HOURS... THEN BECOMING STEADY. THUS... LOW TEMPS FOR THE OVERNIGHT PERIOD WILL ACROSS AT THE START OF THE OVERNIGHT. EXPECT TEMPS TO WARM INTO THE 60S AREAWIDE ACROSS THE AREA BY 12Z MONDAY.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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AS OF 1130 PM SATURDAY... MON AND MON NIGHT: THE AXIS OF A 50 KT LLJ...IN DEEP SW FLOW ALOFT...WILL CROSS CENTRAL NC DURING THE DAY MONDAY...IN ADVANCE OF THE SURFACE COLD FRONT THAT IS FORECAST TO CROSS THE AREA LATE MON AND MON EVENING - A SOLUTION BEST REPRESENTED BY THE SLOWER 12Z ECMWF/NAM GUIDANCE. THE PASSAGE OF THE LLJ AND ASSOCIATED MOISTURE TRANSPORT...THEN LATER FRONTAL FORCING/LOW LEVEL CONVERGENCE...WILL SUPPORT SCATTERED SHOWERS - AND ISOLATED THUNDER IN AN AXIS OF LOWER TO MIDDLE 60S SURFACE DEWPOINTS IN THE COASTAL PLAIN - ENDING FROM WEST TO EAST DURING THE AFTERNOON AND EVENING HOURS. STRONG AND INCREASINGLY UNIDIRECTIONAL DEEP LAYER FLOW...AFTER THE EARLY MORNING WARM FRONTAL PASSAGE...WILL SUPPORT A CONDITIONAL RISK OF SEVERE WEATHER IN THE COASTAL PLAIN. IN ADDITION...MIXING OF THE STRONG LLJ WILL RESULT IN A VERY BREEZY SW WIND...SUSTAINED AROUND 20 MPH...WITH GUSTS BETWEEN 30 AND 40 MPH PROBABLE PER ~35 KT MIXED LAYER WIND FORECASTS. HIGHS GENERALLY IN THE LOWER TO MIDDLE 70S. AFTER PERHAPS A LINGERING SHOWER IN THE COASTAL PLAIN DURING THE EVENING...COLD AND DRY ADVECTION...AND CLEARING...WILL DEVELOP EASTWARD AND RESULT IN LOWS RANGING FROM AROUND 40 WEST TO LOWER 50S EAST. -MWS
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 350 PM SATURDAY... TUE-WED: 1025 MB SURFACE HIGH PRESSURE WILL BUILD SOUTHEAST ACROSS THE HIGH PLAINS TUE...THEN EASTWARD INTO THE MIDDLE ATLANTIC STATES TUE NIGHT. MEANWHILE...THE APPROACH OF A POSITIVELY-TILTED TROUGH ALOFT FROM THE MS VALLEY WILL INDUCE COASTAL CYCLOGENESIS...ALONG AN OLD FRONTAL ZONE OFF THE SOUTH EAST...REFERENCED IN THE SHORT TERM DISCUSSION ABOVE. THERE REMAINS CONSIDERABLE MODEL SPREAD WITH THE DEVELOPMENT AND TRACK OF THIS COASTAL LOW AS IT LIFTS UP THE SOUTHEAST AND MIDDLE ATLANTIC COASTS THROUGH MID WEEK...RANGING FROM THE WELL OFFSHORE AND TOTALLY DRY-FOR-CENTRAL-NC CANADIAN SOLUTIONS OF RECENT DAYS...TO THE CLOUDY AND WET SOLUTIONS DEPICTED BY THE PAST FEW ECMWF AND GFS RUNS. GIVEN THE POSITIVE TILT AND ONLY SLOW EASTWARD PROGRESSION OF THE TROUGH ALOFT...THE MORE WESTWARD (AND WET) SOLUTIONS OF THE OFFSHORE FRONT AND INCIPIENT COASTAL LOW ARE FAVORED...WITH A LOW TRACK MOST PROBABLE ALONG THE WESTERN WALL OF THE GULF STREAM. THE RESULT WOULD BE RAIN DEVELOPING FROM THE SOUTH LATE TUE AND ESPECIALLY TUE NIGHT...WITH A COLD RAIN LIKELY AND TEMPERATURES IN THE UPPER 30S TO MIDDLE 40S...ON WED. THOUGH THE AFOREMENTIONED PARENT POLAR HIGH IS FORECAST TO BE RELATIVELY WEAK (AROUND 1025 MB) AND POSITIONED FARTHER SOUTH (OVER THE MIDDLE ATLANTIC STATES) THAN IS TYPICAL FOR SNOW IN CENTRAL NC...THE TRACK OF THE COASTAL LOW AND RESULTANT PARTIAL THICKNESSES ON THE WEST/NW SIDE SUGGEST AT LEAST A THREAT OF A LITTLE WEST SNOW MIXING IN WITH THE RAIN OVER THE PIEDMONT. GIVEN THE MARGINALLY COLD THERMODYNAMIC PROFILES...AND FREEZING LEVELS AROUND 1000 FT OVER THE PIEDMONT PER GFS BUFR FORECAST SOUNDINGS...ANY SUCH SNOW WOULD LIKELY BE DRIVEN BY PRECIPITATION RATES...AND THE EXCEPTION RATHER THAN THE RULE. WED NIGHT-SAT: MEDIUM RANGE GUIDANCE HAS COME INTO SOMEWHAT BETTER AGREEMENT (THAN RECENT DAYS) REGARDING THE DEVELOPMENT OF A BROAD TROUGH ALOFT FROM NORTH-CENTRAL CANADA TO THE MIDDLE ATLANTIC COAST LATE WEEK INTO NEXT WEEKEND. SUCH A PATTERN 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)...AND MILDER/MORE MODIFIED HIGH PRESSURE OVER THE SOUTHEAST STATES. THIS PATTERN OF NW TO WNW FLOW ALOFT WOULD RESULT IN DRY AND COOL CONDITIONS OVER CENTRAL NC. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... AS OF 1255 AM SUNDAY... VFR CONDITIONS ARE EXPECTED TO GENERALLY CONTINUE ACROSS MOST OF THE AREA THROUGH THE PRE-DAWN HOURS THIS MORNING AS HIGH PRESSURE REMAINS OFFSHORE AND EXTENDING BACK INTO CENTRAL NC. HOWEVER...RETURN FLOW ON THE BACK SIDE OF THE DEPARTING HIGH (ESPECIALLY ACROSS THE WESTERN PORTIONS OF NC) MAY BRING SOME STRATUS ACROSS THE TRIAD LATE TONIGHT...BUT CONFIDENCE IN THIS OCCURRENCE IS STILL LOW. IN ADDITION... SOME LIGHT RAIN AND/OR SPRINKLES MAY MOVE INTO THE AREA WITH A LEADING BAND OF PRECIP MORNING NORTHWARD OUT OF GA/SC EARLY THIS MORNING. HOWEVER... GIVEN THE AMOUNT OF DRY AIR IN PLACE IN THE MID LEVELS OF THE ATMO EXPECT ONLY LIGHT RAIN AT BEST (VFR CONDITIONS). ANY SUB VFR CONDITIONS THAT MAY DEVELOP WILL IMPROVE BY MID-MORNING. HOWEVER...THESE VFR CONDITIONS WILL BE SHORT LIVED AS AVIATION CONDITIONS DETERIORATE FROM THE SOUTH/WEST TO NORTH/EAST AS A LOW PRESSURE SYSTEM APPROACHES FROM THE SOUTHWEST. CIGS/VSBYS WILL GRADUALLY FALL INTO THE IFR RANGE THROUGH THE AFTERNOON HOURS...AS PRECIP OVERSPREADS THE AREA FROM SOUTH TO NORTH... WITH LIFR CONDITIONS POSSIBLE BY THIS EVENING... WITH POSSIBLE LLWS (ESPECIALLY AT KGSO/KINT) AS LOW LEVEL FLOW ATOP AN INITIAL COOL STABLE AIRMASS AT THE SURFACE INCREASINGS TO AROUND 50 KTS AT AROUND 2 KFT OUT OF THE SOUTH. OUTLOOK...ADVERSE AVIATION CONDITIONS WILL CONTINUE TONIGHT AS RAIN...HEAVY AT TIMES...IMPACTS THE AREA. A STRONG 50-60KT LOW LEVEL JET MAY CAUSE SOME CONTINUED LOW-LEVEL WIND SHEAR...ESPECIALLY AT KGSO/KINT...WHILE SOME 30-40KT WIND GUSTS MAY BE POSSIBLE OVER EASTERN NC WHERE THUNDERSTORMS DEVELOP. CONDITIONS WILL IMPROVE SOME ON MONDAY AS DRIER AIR ALOFT MOVES IN FROM THE WEST...THOUGH LOW CEILINGS MAY LINGER AT EASTERN TERMINALS. THERE MAY ALSO BE SOME GUSTY SOUTHWESTERLY WINDS (GUSTS UP TO 35-40 MPH) MONDAY AFTERNOON AHEAD OF A COLD FRONT. BEYOND MONDAY..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...BSD SHORT TERM...VINCENT/MWS LONG TERM...MWS AVIATION...BSD/KRD

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