Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 262024 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 320 PM EST WED NOV 26 2014 .SYNOPSIS...SURFACE LOW PRESSURE JUST OFF THE NORTHERN OUTER BANKS WILL CONTINUE MOVING NORTHWARD AWAY FROM THE REGION THIS EVENING. A STRONG UPPER LEVEL DISTURBANCE WILL QUICKLY CROSS THE REGION LATE TONIGHT THROUGH EARLY THURSDAY. HIGH PRESSURE WILL BUILD OVER THE CAROLINAS FRIDAY THROUGH THE REST OF THE HOLIDAY WEEKEND. && .NEAR TERM /THROUGH THURSDAY/... AS OF 315 PM WEDNESDAY... THE COASTAL LOW CURRENTLY SITS JUST OFF THE NRN OUTER BANKS OF NC... MOVING STEADILY NORTHWARD. THE MID LEVEL VORTICITY MAX RIDING NE ON THE SW SIDE OF THE BROAD RIDGE ALOFT CONTINUES TO SHEAR AND WEAKEN AS IT MOVES THROUGH CENTRAL NC/VA... AND THIS DWINDLING FORCING FOR ASCENT COUPLED WITH WANING UPPER DIVERGENCE AND LOWER PW FROM WEST TO EAST ARE RESPONSIBLE FOR THE DOWNTURN IN BOTH COVERAGE AND INTENSITY OF RAINFALL... AS WELL AS THE INCREASING SUNSHINE ACROSS THE WRN AND SRN CWA. THIS TREND SHOULD CONTINUE... WITH RAIN CHANCES DECREASING RAPIDLY OVER THE NEXT FEW HOURS... YIELDING LITTLE OR NO RAIN CHANCES IN CENTRAL NC AFTER 6 PM OR 7 PM OR SO. BUT ATTENTION IMMEDIATELY TURNS TO THE POTENT SHORTWAVE TROUGH NOW MOVING RAPIDLY THROUGH THE MID MISS VALLEY... EXPECTED TO MOVE EAST THROUGH THE CAROLINAS TONIGHT THROUGH MIDDAY THU... ACCOMPANIED BY SURFACE LOW PRESSURE EXPECTED TO MOVE EASTWARD ACROSS CENTRAL/SRN NC. LATEST SHORT-RANGE HI-RES MODEL GUIDANCE HAS SPED UP THE ONSET OF LIGHT RAIN OVER OUR FORECAST AREA... AND BASED ON EXTRAPOLATION OF UPSTREAM PRECIP... THIS LOOKS VERY REASONABLE. WILL BRING IN SLIGHT CHANCES OF LIGHT SHOWERS OVER THE WRN PIEDMONT BY MID-LATE EVENING... THEN FOLLOWING THE CONSENSUS OF LATEST MODEL OUTPUT... WILL SPREAD 20-50% RAIN CHANCES ACROSS THE NRN PIEDMONT AND NRN COASTAL PLAIN LATER TONIGHT... CONTINUING THROUGH THU MORNING... FOLLOWED BY AN EXIT OF THE PRECIP OUT OF THE NORTHEAST CWA DURING THE EARLY AFTERNOON HOURS. THIS PRECIP SHOULD BE MOSTLY SHOWERY IN NATURE... GIVEN THE POTENTIAL FOR WEAK INSTABILITY ALOFT AS 850-500 MB LAPSE RATES ARE STILL PROJECTED TO BE 7.0-7.5 C/KM. AS SUCH... WOULDN`T BE SURPRISED TO SEE A FEW LIGHTNING STRIKES... ESPECIALLY GIVEN THE DYNAMIC CONTRIBUTION TO LIFT FROM THE INCOMING VORTICITY MAX AND IMPROVING UPPER DIVERGENCE DUE TO WIND ACCELERATION OVER SC AND SRN NC. TOTAL RAINFALL AMOUNTS WITH THIS SYSTEM SHOULD BE SMALL... GENERALLY A TENTH OF AN INCH OR LESS... ALTHOUGH TRENDS WOULD SUGGEST THAT THE VA BORDER COUNTIES COULD SEE A COUPLE TENTHS... AS FORECAST SOUNDINGS SHOW GREATER SATURATION IN THE LOW LEVELS AS COMPARED TO YESTERDAY. CONSENSUS OF STATISTICAL GUIDANCE SUPPORTS LOWS TONIGHT OF 34-37. THERE IS STILL A SMALL CHANCE THAT WE COULD SEE A FEW WET SNOWFLAKES LATE TONIGHT INTO THU MORNING MAINLY NEAR THE VA BORDER... BUT FORECAST SOUNDINGS AND SREF PLUMES AT DANVILLE SUGGEST A THREAT TOO LOW TO MENTION... AND ANYTHING THAT FELL WOULD GENERATE NO IMPACT. EXPECT IMPROVING SUNSHINE LATE IN THE DAY... WITH MORE OVERALL INSOLATION SOUTH THAN NORTH... BUT STILL ANTICIPATE COOL HIGHS RANGING FROM 48 NORTH TO 55 FAR SOUTH. -GIH && .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... AS OF 320 PM WEDNESDAY... THU NIGHT: THE VORTICITY MAX AND ACCOMPANYING SURFACE LOW SHOULD BE HEADING EAST OFF THE COAST BY THU EVENING... AS HIGH PRESSURE BEGINS TO BUILD IN FROM THE WEST... WITH GRADUALLY RISING HEIGHTS OVERNIGHT AS THE SHORTWAVE TROUGH LIFTS OUT. EXPECT CLEARING SKIES EARLY WITH DECREASING WINDS. LOWS AT THE MID RANGE OF GUIDANCE... 25-30... WITH GOOD RADIATIONAL COOLING CONDITIONS EXPECTED. -GIH FRIDAY AND FRIDAY NIGHT: SURFACE HIGH PRESSURE WILL BUILD IN FROM THE DEEP SOUTH ON FRIDAY AS THE UPPER LEVEL TROUGH MOVES OFF OF THE COAST. FOR THE FIRST PART OF THE DAY...CENTRAL NC WILL REMAIN ON THE EAST SIDE OF THE HIGH...IN WEAK NORTHERLY FLOW BUT BY LATE AFTERNOON THE HIGH WILL MOVE DIRECTLY OVERHEAD...CALMING ANY REMAINING WIND. CLOUD COVER LEFT OVER FROM THE DEPARTING SYSTEM WILL FILTER OUT TO THE NORTHEAST. THUS EXPECT LOWEST TEMPS IN THE NE AND HIGHEST IN THE SW. COOLEST DAY OF THE WEEK WITH HIGHS IN THE MID 40S TO NEAR 50 DEGREES. FRIDAY NIGHT WILL SEE TEMPERATURES DROP INTO THE MID TO UPPER 20S WITH FEW CLOUDS AND CALM WINDS. -ELLIS && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 245 PM WEDNESDAY... SATURDAY THROUGH MONDAY NIGHT: THE FIRST PART OF THE LONG TERM WILL FEATURE A SIGNIFICANT WARMING TREND AS SURFACE HIGH PRESSURE MOVES EAST OF THE AREA SETTING UP RETURN FLOW OVER CENTRAL NC. THIS WILL BE THE MAIN DRIVER AS UPPER LEVEL FLOW REMAINS VERY ZONAL. ALTHOUGH BOTH THE GFS AND THE ECMWF AGREE THAT IT WILL BE WARMER...THE QUESTION REMAINS HOW MUCH? WITH FEW TO SCATTERED CLOUDS OVER THE AREA...RISING THICKNESSES AND WARM AIR ADVECTION THROUGH SOUTHWESTERLY FLOW...CANT SEE HOW TEMPERATURES WONT RISE SIGNIFICANTLY. THEREFORE HAVE GONE TO THE HIGH SIDE OF GUIDANCE WHICH IN THIS CASE IS MORE IN LINE WITH THE LONG RANGE ECMWF NUMBERS FOR MAX TEMPS THROUGH MONDAY. SPECIFICALLY MID TO UPPER 50S SATURDAY...MID TO UPPER 60S SUNDAY...AND UPPER 60S TO LOWER 70S MONDAY. LOWS WILL ALSO WARM THROUGH THE WEEKEND BUT MORE MODESTLY...UPPER 30S INCREASING TO MID 40S SUNDAY NIGHT BEFORE FALLING SLIGHTLY BACK INTO THE LOWER 40S ON TUESDAY AHEAD OF A COLD FRONT DRAPED TO OUR NORTHWEST. TUESDAY THROUGH WEDNESDAY: THE LAST PART OF THE LONG TERM INTRODUCES A FAIR AMOUNT OF UNCERTAINTY IN THE HANDLING OF THE AFOREMENTIONED COLD FRONT AS THE PARENT LOW IS IS QUICKLY HAULED AWAY TO THE NORTHEAST BY THE NORTHERN STREAM JET...LEAVING A WEAKLY DEFINED FRONTAL ZONE JUST TO THE NORTHWEST OF THE CWA. ANY PRECIPITATION ASSOCIATED WITH TEH FRONT SHOULD HOLD OFF UNTIL TUESDAY MORNING WHEN A FAIRLY STRONG 1040 MB HIGH PRESSURE SYSTEM MOVES THROUGH QUEBEC. THIS LOCATION IS FURTHER NORTH THAN THE PREVIOUS MODEL RUNS AND IS NOT QUITE AS IDEAL FOR A CLASSICAL/HYBRID COLD AIR DAMMING EVENT AS IT WAS YESTERDAY. STILL THINK SOME FORM OF A WEAK CAD IS POSSIBLE AND THUS KEEPING HIGHS ON TUESDAY FAIRLY LOW AS WE SHOULD BE OVERCAST WITH NORTHEASTERLY WINDS. MAX TEMPS IN THE LOW TO UPPER 50S BUT STILL COULD BE LOWER IN THE TRIAD IF WEDGE DEVELOPS. THIS HIGH WILL NOT REMAIN IN PLACE FOR VERY LONG AS IT IS QUICKLY MOVES OUT TO SEA BY A DEVELOPING LOW OVER NORTHERN ONTARIO AND A DEEPENING UPPER LEVEL TROUGH OVER THE MIDWEST. THIS WILL SET UP A SLIGHTLY WARMER DAY ON WEDNESDAY IN THE WARM AIR ADVECTION REGIME AHEAD OF THE FRONT AS LONG AS THE WEDGE DISSIPATES. MID 50S TO MID 60S NW TO SE. PRECIP CHANCES AND AMOUNTS STILL FAIRLY UNCERTAIN AT THIS POINT BUT WILL CARRY SLIGHT CHANCE POPS TUESDAY AND WEDNESDAY. LOWS DURING THIS TIME IN THE UPPER 30S TO LOWER 40S. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 1220 PM WEDNESDAY... EXPECTED AVIATION CONDITIONS: POOR THROUGH THIS AFTERNOON... BECOME FAIR TO GOOD THIS EVENING... BRIEFLY POOR AT NORTHERN SITES LATE TONIGHT THROUGH THU MORNING... THEN GOOD BY EARLY THU AFTERNOON. PRIMARY AVIATION CONCERNS: LOW CIGS THROUGH THIS AFTERNOON AND AGAIN LATER TONIGHT. CURRENT MVFR CIGS AT CENTRAL NC TERMINALS (EXCEPT BRIEFLY IFR ESPECIALLY AT GSO/RDU) WILL PERSIST FOR ANOTHER FEW HOURS. AREAS OF RAIN CONTINUE BUT THE HEAVIEST RAIN HAS DEPARTED... THUS VSBYS ARE NOW MOSTLY VFR. CIGS WILL IMPROVE TO VFR FROM SW TO NE BETWEEN 19Z AND 23Z AS A POTENT UPPER LEVEL DISTURBANCE NOW OVER THE FAR WRN PIEDMONT OF NC TRACKS QUICKLY TO THE NE AND MOVES AWAY FROM NC LATER TODAY. BRIEF MAINLY VFR CONDITIONS ARE EXPECTED THIS EVENING... THEN ANOTHER DISTURBANCE AND SURFACE LOW WILL QUICKLY CROSS THE REGION... TRACKING ROUGHLY ALONG THE NC/VA BORDER... FROM LATE TONIGHT THROUGH THU MORNING. IFR/LIFR CIGS ARE EXPECTED AT GSO/INT AFTER MIDNIGHT TONIGHT UNTIL LATE MORNING THU... AND MVFR CIGS ARE POSSIBLE AT RDU/RWI THU MORNING THROUGH THE END OF THE TAF VALID PERIOD. BRISK WINDS MAINLY FROM THE NORTH WILL BE OF CONCERN AT ALL SITES THROUGH 21Z TONIGHT... THEN WINDS WILL BE LIGHT THIS EVENING THROUGH TONIGHT. WEST WINDS UP TO 8-12 KTS POSSIBLE THU MORNING INTO AFTERNOON. LOOKING BEYOND 18Z THU... VFR CONDITIONS ARE EXPECTED TO LAST THROUGH MON... AS HIGH PRESSURE BUILDS IN FROM THE WEST OVER THE WEEKEND BEFORE SHIFTING TO OUR EAST ON MONDAY. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...HARTFIELD/ELLIS LONG TERM...ELLIS AVIATION...HARTFIELD

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