Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270345 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1045 PM EST WED NOV 26 2014 .SYNOPSIS...
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AN UPPER LEVEL DISTURBANCE AND ATTENDANT SURFACE LOW PRESSURE SYSTEM WILL TRACK EAST ACROSS THE REGION THROUGH EARLY THU. DRY HIGH PRESSURE WILL BUILD INTO THE CAROLINAS FROM THE WEST LATER THU THROUGH FRI.
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&& .NEAR TERM /THROUGH THURSDAY/...
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AS OF 1040 PM WEDNESDAY... REMARKABLE CHANGES OF THE THERMODYNAMIC PROFILE OBSERVED AT KGSO DURING THE PAST 12 HOURS...SUCH THAT THE DEEP NEAR FREEZING ISOTHERMAL LAYER FROM THE SURFACE TO 550 MB THIS MORNING HAS BEEN REPLACED BY MUCH STEEPER LAPSE RATES IN THE SAME LAYER THIS EVENING...INCLUDING A 12 HR 500 MB CHANGE OF 15 DEGREES. LAPSE RATES WILL CONTINUE TO STEEPEN OVERNIGHT...MOST NOTABLY ACROSS THE NORTHERN PIEDMONT...AS A SERIES OF MID-UPPER LEVEL VORTICITY MAXIMA AND ASSOCIATED COLDER TEMPERATURES ALOFT - INCLUDING MINUS 30 C AT KBNA AT 00Z - ROUND THE BASE OF A MEAN TROUGH AND CROSS NC. THE STEEPENING OF THE LAPSE RATES...AND RE-MOISTENING/RE-SATURATION OF THE LOWEST 3-4 KM OWING TO THE APPROACH AND PASSAGE OF STRONG QG- FORCING ACCOMPANYING BOTH THE VORTICITY MAXIMA ALOFT AND A BRIEF LOW LEVEL WAA REGIME IN ASSOCIATION WITH ELONGATED 850 MB LOW PRESSURE FROM THE MID-MS VALLEY TO THE SOUTHERN APPALACHIANS...WILL CAUSE AN AREA OF MIXED CHARACTER RAIN/SHOWERS TO FURTHER BLOSSOM IN THE LEE OFF THE APPALACHIANS...AND ACROSS THE NORTHERN NC PIEDMONT... TONIGHT. ALTHOUGH TEMPERATURES HAVE RADIATIONALLY COOLED BRIEFLY TO NEAR FREEZING OVER PORTIONS OF THE PIEDMONT...THE INCREASING CLOUDINESS ACCOMPANYING THE INCOMING PRECIPITATION WILL CAUSE SURFACE TEMPERATURES TO CREEP UP (FROM DOWNWARD L/W RADIATION) INTO THE MIDDLE TO UPPER 30S - SIMILAR TO WHAT WAS OBSERVED AT KBUY AND K5W8 FROM 02-03Z - SUCH THAT ALL RAIN IS EXPECTED. IN FACT...RECENT AMDAR DATA FROM RDU INDICATES A WARM LAYER WITH A MAXIMUM TEMPERATURE OF AROUND 5 DEGREES IS PRESENT BETWEEN A 3-5 THOUSAND FT FREEZING LEVEL...AND THE AFOREMENTIONED NEAR FREEZING TEMPERATURE RIGHT AT THE SURFACE - MUCH TOO DEEP AND WARM FOR SNOW. WHILE IT IS POSSIBLE FOR A FEW LIGHTNING STRIKES TO OCCUR WITH THE PRECIPITATION TONIGHT...OVER THE NW PIEDMONT WHERE LAPSE RATES WILL BE STEEPEST AND TOTAL TOTALS AND K-INDICES ARE FORECAST TO PEAK AROUND 55 AND NEAR 30 C...RESPECTIVELY...THE RELATIVE BETTER (BUT STILL LOW PROBABILITY) WILL BE WITH DIURNAL HEATING/BENEATH THE COLD POOL ALOFT ON THU. -MWS PREVIOUS DISCUSSION THROUGH THU FOLLOWS: 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
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&& .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 /00Z THURSDAY THROUGH MONDAY/... AS OF 700 PM WEDNESDAY... 24-HR TAF PERIOD: VFR CONDITIONS HAVE RETURNED TO THE MAJORITY OF CENTRAL NC AS OF 00Z THIS EVENING. HOWEVER...A POTENT UPPER LEVEL DISTURBANCE AND ASSOCIATED SFC LOW PRESSURE SYSTEM WILL RAPIDLY APPROACH FROM THE WEST THIS EVENING...PROGRESSING EAST ACROSS NORTHERN NC AND SOUTHERN VA OVERNIGHT/EARLY THU MORNING. A PERIOD OF SHOWERS AND MVFR/IFR CEILINGS CAN BE EXPECTED BETWEEN 06-12Z THU AT THE INT/GSO TERMINALS. THOUGH PRECIPITATION WILL BE LESS LIKELY AT THE RDU/RWI TERMINALS...MVFR/IFR CEILINGS ARE EXPECTED BETWEEN 09- 15Z THU. FURTHER SOUTH OF THE APPROACHING DISTURBANCE AT THE FAY TERMINAL...VFR CONDITIONS ARE EXPECTED TO PREVAIL. CALM OR LIGHT/ VARIABLE WINDS AT ALL TERMINALS OVERNIGHT WILL BECOME WNW/NW AT 10- 15 KT BETWEEN 15-18Z THU AS THE DISTURBANCE MOVES OFFSHORE AND HIGH PRESSURE BUILDS INTO THE REGION FROM THE WEST. LOOKING AHEAD: VFR CONDITIONS WILL PREVAIL THU AFTERNOON THROUGH SAT NIGHT AS DRY HIGH PRESSURE SETTLES OVER THE REGION. EXPECT AN INCREASING POTENTIAL FOR ADVERSE AVIATION CONDITIONS SUN NIGHT THROUGH EARLY NEXT WEEK AS HIGH PRESSURE MOVES OFFSHORE AND THE NEXT IN A SERIES OF UPPER LEVEL DISTURBANCES APPROACHES THE REGION FROM THE WEST. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT/MWS NEAR TERM...MWS/HARTFIELD SHORT TERM...HARTFIELD/ELLIS LONG TERM...ELLIS AVIATION...VINCENT

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