Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170324 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1124 PM EDT THU APR 16 2015 .SYNOPSIS...LOW PRESSURE WILL MOVE SLOWLY AWAY FROM THE SOUTHEAST US COAST THROUGH FRI NIGHT. HIGH PRESSURE WILL OTHERWISE EXTEND ACROSS THE MIDDLE ATLANTIC STATES THROUGH SAT. && .NEAR TERM /TONIGHT/... AS OF 1115 PM THURSDAY... REGIONAL RAOB DATA INDICATES A WEAKLY UNSTABLE AND SATURATED OR NEARLY SO LOWEST 10 K FT - SUPPORTIVE OF SCATTERED SHOWERS IN A WEAKENING REGIME OF ISENTROPIC UPGLIDE ATOP A WEAKENING INVERTED SFC TROUGH AXIS/WARM FRONT THAT HAS BISECTED CENTRAL NC FROM N-S DURING THE PAST DAY. ALOFT...WV IMAGERY INDICATED A LEAD SHORTWAVE TROUGH HAD CROSSED THE MIDDLE ATLANTIC STATES AND WAS MOVING AWAY FROM THE VA TIDEWATER...WHILE A TRAILING SHEAR AXIS ALOFT WAS MOVING EAST FROM THE CENTRAL APPALACHIANS. A MORE SIGNIFICANT IMPULSE WAS EVIDENT LIFTING NE FROM THE LOWER MS VALLEY. THE FORECAST TRACK OF BOTH THE LEAD SHEAR AXIS ALONG THE APPALACHIANS AND TRAILING AND MORE SIGNIFICANT IMPULSE FROM THE LOWER MS VALLEY WILL BE FOCUSED TO OUR NORTH/ACROSS VA...SUCH THAT THE RELATIVE BETTER FORCING FOR ASCENT AND ASSOCIATED CHANCE OF SHOWERS OVER THE NORTHERN NC PIEDMONT. RAISED LOW TEMPERATURES GIVEN THE STILL RELATIVELY MILD TEMPERATURES AROUND 60 DEGREES OR BETTER OVER THE COASTAL PLAIN...WHICH ARE FORECAST TO CHANGE VERY LITTLE DURING THE OVERNIGHT...WITH LOWS RANGING FROM THE LOWER 50S WEST TO AROUND 60S 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 SUN... AND MID 70S TO LOWER 80S MON. LOWS AROUND 60 TO THE MID 60S SUN NIGHT AND MID 50S TO LOWER 60S MON NIGHT... 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 /00Z FRIDAY THROUGH TUESDAY/... AS OF 806 PM THURSDAY... 24 HOUR TAF PERIOD: CONDITIONS ARE CURRENTLY VFR ACROSS THE EASTERN PART OF THE AREA (KRDU... KRWI... AND KFAY) AND IFR ACROSS THE WESTERN PART (KGSO AND KINT). LIGHT SHOWER ACTIVITY WILL CONTINUE TO DIMINISH ACROSS THE AREA OVERNIGHT. HIGH LOW LEVEL MOISTURE WILL RESULT IN LOWERING CIGS ACROSS THE AREA OVERNIGHT... AND ALL SITES WILL BE IFR BY 06Z AND REMAIN THERE UNTIL MID MORNING ON FRIDAY. CONDITIONS ARE EXPECTED TO GRADUALLY IMPROVE TOMORROW MORNING... WITH A RETURN TO VFR GENERALLY BETWEEN 15-18Z AT KRWI... KFAY... AND KRDU AND BETWEEN 21Z-00Z AT KINT AND KGSO. 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...RAH NEAR TERM...RAH SHORT TERM...ELLIS/HARTFIELD LONG TERM...HARTFIELD AVIATION...RAH/ELLIS

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