Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 161852 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 252 PM EDT THU APR 16 2015 .SYNOPSIS...SURFACE HIGH PRESSURE TO THE NORTH WILL MOVE OFF OF THE MID-ATLANTIC COAST TONIGHT AS A LOW CONTINUES TO DEVELOP ALONG THE SOUTH CAROLINA COAST. COLD AIR DAMMING SCENARIO WILL BREAK DOWN FRIDAY CREATING WARMER AND DRIER CONDITIONS ACROSS THE AREA. && .NEAR TERM /THROUGH TONIGHT/... AS OF 250 PM THURSDAY... A LOT OF INTERESTING SURFACE FEATURES CONTRIBUTING THE A WIDE ARRAY OF CONDITIONS ACROSS THE CWA THIS AFTERNOON. FIRST IS THE WEDGE FRONT ANCHORED IN ACROSS THE WESTERN PIEDMONT AS A RESULT OF THE HYBRID COLD AIR DAMMING SCENARIO PRESENT BECAUSE OF HIGH PRESSURE NOW OFF OF THE NY/NEW ENGLAND COAST. THERE IS ALSO WARMER AIR BEING ADVECTED IN FROM THE EAST AS A COASTAL LOW DEVELOPS OFF OF THE SC/GA COASTLINE. THE COMBINATION OF THE TWO FEATURES HAS LED TO A VERY SHARP TEMPERATURE GRADIENT ACROSS THE CWA. IN THE WEST...LOWER CEILINGS REMAINED LOCKED IN WHEREAS IN THE EAST SOME SCATTERING HAS OCCURRED AND ALLOWED MAX TEMPERATURES TO TAKE OFF. EXPECTED HIGHS FOR TODAY WILL END UP IN THE LOW TO MID 50S ACROSS THE NW PIEDMONT TO THE LOWER 70S EAST OF I-95. LOOKING AT THE PRECIPITATION THREAT FOR THE REST OF THE DAY...THERE IS A MORE FOCUSED AXIS ALONG US HIGHWAY 1 AT THE MOMENT AS A RESULT OF LOW LEVEL CONVERGENCE BETWEEN THE WARM AIR ADVANCING FROM THE EAST (EVIDENT IN SURFACE OBSERVATIONS) AND THE MORE NORTHERLY FLOW ASSOCIATED WITH THE CAD TO THE WEST. CONVECTIVE ALLOWING MODELS HAVE PICKED UP ON THIS OVER THE LAST COUPLE OF HOURS AND HAVE IT DYING OFF AROUND 00Z WITH SOME PATCHY DRIZZLE THEREAFTER BUT A GENERAL DRYING TREND. OVERNIGHT TONIGHT EXPECT LOWER CEILINGS TO CREEP IN ONCE AGAIN WHICH WILL HELP TO EVEN OUT THE TEMPERATURE GRADIENT AND KEEP LOW TEMPS MODERATED OVERNIGHT. THEREFORE NOT TOO MUCH OF A DROP AT ALL IN THE WEST...WITH AN ALMOST 20 DROP IN THE EAST. FINAL LOWS SHOULD BOTTOM OUT LOWER 50S WEST TO MIDDLE 50S EAST. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... AS OF 250 PM THURSDAY... FRIDAY AND FRIDAY NIGHT: FRIDAY WILL SEE A DRIER AND WARMER DAY THAN THE LAST COUPLE AS WEAK ZONAL FLOW ALOFT KEEPS THE PATTERN FAIRLY MUNDANE. AT THE SURFACE...THE CAD WEDGE WILL BREAK DOWN AS THE SURFACE HIGH GETS PUSHED OUT TO SHORE AND SETTLES OVER THE WESTERN ATLANTIC. THE COASTAL LOW WILL MOVE NORTH AND CREATE A CONVERGENCE ZONE WITH RETURN FLOW FROM THE HIGH THAT WILL REMAIN OFFSHORE...THUS KEEPING US DRY. THE ONLY THING REALLY TO WATCH OUT FOR WILL BE A WEAK SURFACE FRONT ASSOCIATED WITH A NORTHERN STREAM LOW PRESSURE SYSTEM OVER EASTERN CANADA. THIS WILL CAUSE SOME WEAK INSTABILITY...PARTICULARLY IN THE NORTHWEST PIEDMONT LATER IN THE DAY ON FRIDAY. CAMS ARE PICKING UP ON THIS AND HAVE A LITTLE BIT OF CONVECTIVE SHOWER ACTIVITY...MAINLY WEST OF THE TRIAD BUT NOT STRONG AT ALL AS SB CAPE VALUES ONLY REACH 300 J/KG OR SO AND NO REAL KINEMATICS TO SPEAK OF WITH SHEAR VALUES LESS THAN 20. RESIDUAL CAD CLOUD DECKS MAY TAKE A LITTLE TIME TO SCOUR OUT BUT ONCE THEY DO ALL AREAS SHOULD SEE HIGHS IN THE 70S WITH LOW TO MID 70S NW TO UPPER 70S IN THE SE. CONDITIONS DRY OUT FRIDAY NIGHT AND NO FOG OR LOW STRATUS IS EXPECTED WITH VERY LIGHT NWLY FLOW. LOW TEMPERATURES IN THE MID 50S TO NEAR 60 DEGREES. -ELLIS SAT/SAT NIGHT: EXPECT DRY WEATHER AND PLENTY OF SUNSHINE SAT. A WEAK BACKDOOR FRONT WILL DROP THROUGH NC IN THE MORNING... OTHERWISE WE`LL HAVE SURFACE HIGH PRESSURE OVER THE REGION AND A DRY/SUBSIDING COLUMN BENEATH MID LEVEL RIDGING. WE MAY GET WARM AND MOIST ENOUGH IN THE SOUTHEAST FOR POTENTIAL INLAND-MOVING SEA BREEZE CONVECTION... SO WILL RETAIN THE EXISTING ISOLATED MENTION FOR THE AFTERNOON. WITH THICKNESSES LIKELY NEARING 20 M ABOVE NORMAL AND GOOD MIXING EXPECTED... HIGHS IN THE UPPER 70S TO LOWER 80S APPEAR ATTAINABLE. A STRONG VORTICITY MAX AND WAVE CROSSING NRN NEW ENGLAND SAT WILL HELP PROPEL A MORE PRONOUNCED BACKDOOR FRONT SOUTHWARD TO NEAR THE VA/NC BORDER LATE SAT NIGHT... PUSHED BY COOL DENSE HIGH PRESSURE CENTERED OVER WRN QUEBEC. MODELS DIFFER REGARDING HOW FAR (IF AT ALL) THE FRONT GETS INTO NE NC... WITH THE GFS A BIT FARTHER SSW THAN THE NAM/ECMWF. GIVEN THE STRENGTH OF THE PARENT HIGH AND INTENSITY OF THE NEW ENGLAND WAVE... THINK WE`LL SEE ENOUGH PENETRATION INTO OUR CWA FOR BRIEFLY LOWER DEWPOINTS AND TEMPS INTO THE NE CWA. EXPECT LOWS IN THE UPPER 50S TO LOWER 60S EXCEPT MID 50S FAR NE. THE STRONG LOW CLOSING OFF OVER SASK/MANITOBA AND ATTENDING TROUGH THROUGH THE DAKOTAS ULTIMATELY PICK UP THE SRN STREAM LOW OVER THE CENTRAL PLAINS... CULMINATING IN DEEP MID LEVEL TROUGHING THROUGH CENTRAL NOAM BY DAWN SUNDAY. WHILE WE`RE LIKELY TO SEE INCREASING CLOUDS FROM THE SW SAT NIGHT WITH ENCROACHING DPVA ALOFT AND IMPROVING MOIST INFLOW IN THE LOWER LEVELS... ANY LIFT IS TOO WEAK AND THE COLUMN STILL TOO DRY OVERALL TO SUPPORT ANY PRECIP THROUGH DAWN SUNDAY. -GIH && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 245 PM THURSDAY... SUN-MON NIGHT: A WET AND POTENTIALLY STORMY PERIOD. MID LEVEL FLOW OVER OUR REGION BECOMES INCREASINGLY CYCLONIC AS THE SLIGHTLY POSITIVELY TILTED BUT SLOWLY DAMPENING LARGE SCALE TROUGH APPROACHES FROM THE WSW. AT THE SURFACE... THE ASSOCIATED FRONTAL SYSTEM WILL OCCLUDE OVER THE UPPER MIDWEST AND GREAT LAKES SUN/SUN NIGHT... WITH THE BACKDOOR FRONT AROUND THE NC/VA BORDER SLOWLY RETREATING BACK TO THE NNE AS A WARM FRONT... WHILE THE PRIMARY COLD FRONT EXTENDS FROM A TRIPLE POINT LOW OVER LOWER MICH DOWN THROUGH THE MID/LOWER MISS VALLEY. MECHANISMS TO FORCE ASCENT SUCH AS MID LEVEL DPVA... UPPER DIVERGENCE... AND LOWER LEVEL (850-925 MB) MASS CONVERGENCE WILL BE STRENGTHENING (ESPECIALLY OVER WRN NC/SW VA) LATE SUN... PERSISTING THROUGH SUN EVENING AND INTO THE NIGHT... AND MOISTURE WILL BE ABUNDANT WITH AN INFLUX OF PW VALUES OVER 1.5"... OR WELL OVER 200% OF NORMAL. GIVEN THIS PLENTIFUL WATER CONTENT AND GOOD LIFT... TRAINING BANDS OF MODERATE RAIN COULD BRING LOCALIZED FLOODING PROBLEMS. MODELS CONTINUE TO SLOW DOWN THE ARRIVAL OF THE MID LEVEL TROUGH AND ITS ACCOMPANYING PRECIP... 6-9 HRS SLOWER THAN YESTERDAY MORNING`S RUNS... AND WILL CONTINUE TO REFLECT THIS IN THE FORECAST. WILL RAMP UP POPS TO LIKELY WEST/SMALL CHANCE EAST SUN MORNING... THEN GO TO CATEGORICAL WEST/GOOD CHANCE EAST SUN AFTERNOON... BEFORE GOING CATEGORICAL AREAWIDE SUN EVENING/NIGHT. WHILE THE LARGE SCALE MODELS DON`T DEPICT MUCH INSTABILITY AT ALL SUNDAY WITH PRIMARILY MOIST ADIABATIC FORECAST PROFILES... I DO HAVE SOME CONCERN ABOUT POCKETS OF CONVECTION AND AN ISOLATED THREAT OF A QUICK WEAK SPIN-UP IN OUR FAR NORTHWEST LATE SUNDAY INTO SUNDAY NIGHT... ESPECIALLY NEAR A WEAK ALONG-FRONT LOW THAT THE GFS/ECMWF DEVELOP OVER SOUTH CENTRAL VA. UPPER DIVERGENCE REACHES A HEFTY MAXIMUM OVER THE SRN APPALACHIANS SUN EVENING... WITH A 40-50 KT 850 MB JETLET FROM THE SSE... AND THE RETREATING BACKDOOR FRONTAL ZONE AND AFOREMENTIONED LOW COULD PROVIDE A SOURCE FOR ENHANCED LOW LEVEL VORTICITY WITH FORECAST SOUNDINGS SHOWING A STRONGLY CURVED HODOGRAPH. WILL CONTINUE TO MONITOR. TOTAL RAINFALL IS LIKELY TO REACH AT LEAST ONE INCH IN MOST SPOTS THROUGH SUN NIGHT... AND WITH A DEEP WARM LAYER (LCL TO 0C) NEAR 3.5 KM FAVORING WARM RAIN PROCESSES... LOCALLY HIGHER TOTALS ARE POSSIBLE. WILL TAPER POPS DOWN MON MORNING WEST TO EAST AS THE MID LEVEL TROUGH AXIS AND CONVEYOR BELT OF PEAK MOISTURE PUSHES TO OUR NORTHEAST... PLACING US FULLY IN THE WARM SECTOR WITH A PUNCH OF MID LEVEL DRY AIR ARRIVING FROM THE SW. ANY HEATING AT ALL WILL PUSH UP MUCAPE TO 1500-2000 J/KG (AS THE GFS SUGGESTS) MON AFTERNOON WITH 25-30 KT WSW 850 MB WINDS AND BULK SHEAR NEAR 30-35 KTS. THE SLOWLY LOWERING DYNAMIC FORCING FOR ASCENT MAY LIMIT THE THREAT OF SEVERE STORMS... BUT STILL EXPECT AT LEAST A FEW STRONG CELLS... ESPECIALLY IF WE DO INDEED GET SOME HEATING AHEAD OF THE COLD FRONT. AFTER A DOWNWARD TREND TO RAIN WEST TO EAST IN THE MORNING... WILL REBOUND WITH SCATTERED SHOWERS AND STORMS MON AFTERNOON INTO EARLY EVENING. A FEW OF THESE COULD PRODUCE STRONG GUSTY STRAIGHT LINE WINDS GIVEN INDICATIONS OF A STRAIGHT LINE HODOGRAPH. HIGHS FROM AROUND 70 NW TO THE MID 70S SE. LOWS AROUND 60 TO THE MID 60S WITH THE FRONT LIKELY NOT COMING THROUGH UNTIL LATE. TUE-THU: FAIRLY QUIET AND DRY WITH SURFACE HIGH PRESSURE BUILDING IN FROM THE WEST. LARGE/DEEP MID LEVEL LOW PRESSURE CENTERED OVER AND NORTH OF THE NRN GREAT LAKES WILL COVER MUCH OF CENTRAL AND EASTERN NOAM... BRINGING SEASONABLY COOL TEMPS AS IT SITS AND SPINS THROUGH MID WEEK. WE COULD SEE A QUICK SHOT OF LIGHT PRECIP WITH A FRONT APPROACHING FROM THE NW WED NIGHT OR THU... HOWEVER OUR MOISTURE SOURCES WILL REMAIN UNTAPPED AND LIFT APPEARS WEAK... SO THIS SHOULD AMOUNT TO ONLY LIGHT PRECIP AT MOST... AND WILL KEEP POPS WED NIGHT/THU BELOW CLIMATOLOGY. TEMPS SHOULD HOLD NEAR OR JUST BELOW NORMAL THROUGH THE PERIOD. -GIH && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 205 PM THURSDAY... 24 HOUR TAF PERIOD: VARIABLE CONDITIONS ACROSS THE CWA RIGHT NOW AS PREDOMINANTLY IFR CEILINGS AND MVFR VISIBILITIES HAVE OVERSPREAD THE SOUTHWESTERN COUNTIES...MVFR CONDITIONS OVER THE NW PIEDMONT ARE SETTLING BACK IN AND VFR TO THE EAST. WHILE CONDITIONS WILL VARY THIS AFTERNOON BASED ON CLOUD COVER AND PLACEMENT OF PRECIPITATION THERE WILL BE AN OVERALL TREND OF IMPROVING IN THE EAST THIS AFTERNOON AND HOLDING STEADY IN THE WEST WHERE THE CAD WEDGE HAS MORE INFLUENCE. OVERNIGHT TONIGHT EXPECT CEILINGS TO GO DOWN TO AT LEAST IFR LEVELS IN MOST LOCATIONS. THIS WILL HAPPEN EARLIER IN THE WEST AND LATER IN EAST. CONVERSELY...AFTER SUNRISE FRIDAY EXPECT EASTERN SITES TO RECOVER TO VFR FASTER THAN WESTERN SITES WHICH COULD HOLD MVFR THROUGH THE END OF THE TAF PERIOD. MOSTLY NNE WINDS AT THIS TIME AT 5-10 KTS BUT AS COASTAL LOW DEVELOPS OFF OF NC...BIGGER EASTWARD COMPONENT COMING IN...CURRENTLY NOTED AT KRWI. BIGGEST THREAT TO CEILINGS OVERNIGHT WILL BE LOW CEILINGS WITH VISIBILITIES SECONDARY. RAIN SHOULD TAPER OFF AFTER SUNSET. ONCE THAT HAPPENS SHOULD BE DRY THROUGH THE END OF THE TAF PERIOD. LONG TERM: RETURN TO MAINLY VFR CONDITIONS FRIDAY AFTERNOON THROUGH SATURDAY. CHANCE FOR ADVERSE CONDITIONS WITH A COLD FRONT SUNDAY INTO MONDAY AND THEN IMPROVING CONDITIONS FOR MIDWEEK NEXT WEEK. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...ELLIS NEAR TERM...ELLIS SHORT TERM...ELLIS/HARTFIELD LONG TERM...HARTFIELD AVIATION...ELLIS

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