FXUS62 KRAH 231958 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 258 PM EST MON NOV 23 2009 .SYNOPSIS... LOW PRESSURE DEVELOPING OFF THE SOUTH CAROLINA COAST WILL TRACK SLOWLY NORTHEAST ALONG THE NORTH CAROLINA COAST THROUGH TUESDAY... KEEPING CONSIDERABLE CLOUDINESS AND COOL TEMPERATURES OVER THE REGION. READINGS WILL HEAD BACK TOWARD NORMAL BY WEDNESDAY...THEN A COLD FRONT THURSDAY NIGHT WILL BRING A SHOT OF COLDER AIR FOR FRIDAY AND SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 215 PM MONDAY... 15Z SURFACE ANALYSIS SHOWS A 1036MB SURFACE HIGH CENTERED OVER MAINE...WITH A RIDGE OF HIGH PRESSURE EXTENDING TO THE SOUTHWEST THROUGH THE CAROLINAS. AN UPPER LOW WILL CONTINUE TO LIFT NORTHEAST ACROSS THE TN VALLEY REGION...WITH WEAK LOW PRESSURE LOCATED OFF THE CAROLINA COAST. PRECIPITATION HAS DECREASED THIS AFTERNOON AS DRIER AIR ALOFT CONTINUES TO FILTER INTO THE REGION AND ISENTROPIC LIFT CONTINUES TO GRADUALLY DECREASES. HOWEVER...RECENT RADAR TRENDS SHOW RAIN SHOWERS MOVING INLAND ACROSS THE COASTAL COUNTIES OF NORTH CAROLINA AND THIS WRAP AROUND PRECIP MAY MOVE INTO THE NORTHERN PORTION OF THE CWA LATER THIS AFTERNOON AS THE COASTAL LOW SLOWLY MOVES TO THE NORTHEAST. AS A RESULT...WILL CONTINUE WITH SLIGHT CHANCE POPS ACROSS MOST OF THE AREA...EXCEPT FOR THE EXTREME SOUTHWEST CWA...UNTIL EARLY EVENING. THEN ANY LINGERING PATCHY DRIZZLE SHOULD COME TO AN END AFTER MIDNIGHT TONIGHT AS THE WEAK ISENTROPIC LIFT DIMINISHES. A SATURATED BOUNDARY LAYER/WET GROUND WILL LEAD TO FOG DEVELOPMENT ACROSS MOST OF THE CWA OVERNIGHT. HOWEVER...EXTENSIVE CLOUD COVER AND A LIGHT BREEZE DUE TO THE PRESSURE GRADIENT ON THE BACK SIDE OF THE DEPARTING COASTAL LOW...SHOULD KEEP WIDESPREAD DENSE FOG FROM DEVELOPING. OVERNIGHT LOWS WILL BE ABOVE NORMAL DUE TO THE THICK CLOUD COVER AND DAMP CONDITIONS...WITH VALUES GENERALLY RANGING FROM 46 TO 49 DEGREES. && .SHORT TERM /TUESDAY THROUGH THURSDAY/... AS OF 240 PM MONDAY... FOR TUESDAY: WEAK LOW PRESSURE SITS JUST OFF THE NORTHERN OUTER BANKS TUESDAY MORNING AND IS EXPECTED TO DRIFT NORTHEAST ALONG THE OFFSHORE BAROCLINIC ZONE THROUGH WEDNESDAY... LEAVING A VERY WEAK HIGH PRESSURE RIDGE AT THE SURFACE WITH LINGERING WEAK TROUGHS AT 925-850 MB. WITH THE RESULTANT WEAK AND LIGHTLY DIFFLUENT SURFACE WINDS AND SATURATED LOW LEVELS AS NOTED ON FORECAST SOUNDINGS... PATCHY LIGHT DRIZZLE AND AREAS OF FOG SHOULD HOLD THROUGH TUESDAY MORNING. PROFOUND WARM CAPPING AT 850-700 MB SHOULD HELP INHIBIT VERTICAL MIXING INTO THE SURFACE-BASED LAYER... AND THE NAM WITH ITS LIGHTER WINDS THROUGH THE LOWEST 1 KM HOLDS ONTO A NEARLY SATURATED LAYER THROUGH THE DAY. BUT THE GFS'S SLIGHTLY STRONGER WINDS ABOVE 950 MB ENCOURAGE HORIZONTAL MIXING RESULTING IN WEAKER STABILITY WITHIN WEDGE AIR MASS OVER CENTRAL NC. HEATING FROM ABOVE AND SOME MIXING-IN OF THE DRY AIR IN THE CAPPED LAYER MAY START TO SLOWLY BURN OFF THE UPPER PORTION OF THE SURFACE-BASED LAYER... HOWEVER THE MORE STUBBORN RESIDUAL STABLE POOL OF THE NAM IS PREFERRED BASED ON ITS BETTER TERRAIN DEPICTION AND MODEL AGREEMENT ON LINGERING WEAK MOISTURE ADVECTION IN THE NORTHEAST FLOW AT 925 MB. WITH CLOUDY SKIES... STILL EXPECT HIGHS OF 54-59. FOR TUESDAY NIGHT/WEDNESDAY: VERY WEAK RIDGING AT THE SURFACE AND WEAK TROUGHING AT 925 MB BOTH LINGER OVER NC OVERNIGHT. WITH A STEADY FEED OF LOW LEVEL ATLANTIC AIR AND NO MECHANISMS VIA WHICH THIS STABLE SURFACE POOL COULD DISPERSE... EXPECT A STEADY STATE TUESDAY NIGHT WITH CLOUDY SKIES. THE THICK BLANKET OF CLOUDS SHOULD LIMIT THE DIURNAL DROP. LOWS 47-51. A MID LEVEL LOW NEAR CHICAGO TRACKS NORTHEAST ACROSS MI AS THE NEXT STRONGER VORTEX DROPS SOUTHEAST TOWARD IA... WHICH KEEPS A BROAD CYCLONIC SOUTHWEST MID LEVEL FLOW OVER THE SOUTHEAST STATES. THE BAROCLINIC ZONE HOLDS JUST OFF THE COAST WITH THE MODELS INDICATING WEAK AREAS OF LOW PRESSURE TRACKING ALONG IT. THE GFS PULLS PRECIP BACK ACROSS SOUTHEAST NC WHEREAS THE NAM KEEPS THE BULK OF THE LIFT AND PRECIP OFFSHORE. GIVEN THAT THE GFS FEATURES SEVERAL SPURIOUS STRONG VORTICITY MAXIMA THAT APPEAR TO BE INDUCED BY EARLIER GULF CONVECTION... FAVOR THE DRIER NAM AND WILL KEEP IT DRY THROUGH WEDNESDAY. OTHERWISE THE LOW LEVEL COL ZONE WITH WEAK/VARIABLE WINDS LOOKS TO PERSIST THROUGH THE MORNING... ALTHOUGH THE RESIDUAL WEDGE AIR MASS WILL LIKELY BE QUITE VULNERABLE BY THIS POINT... WITH THE HIGHER TERRAIN AS THE ONLY REMAINING BLOCKADE RESTRICTING DRAINAGE. WITH THE NORTHWARD PASSAGE OF A WEAK 850 MB TROUGH THROUGH THE AREA... LOW LEVEL WINDS FINALLY SWING AROUND TO SOUTHWEST AND WEST AND SCOUR OUT THE LOW LEVELS. EXPECT TO FINALLY SEE SOME SUNSHINE BREAK OUT IN THE AFTERNOON... ALTHOUGH WITH THE AMOUNT OF LEFTOVER LOW LEVEL MOISTURE... WOULD EXPECT TO SEE ANY HOLES IN THE SKY COVER TO FILL IT WITH FLAT CUMULUS. HAVE LEANED TOWARD THE COOLER NAM STATISTICAL GUIDANCE AND SHAVED A DEGREE OR TWO OFF HIGHS... TO 58-63... CLOSE TO SEASONAL NORMALS. FOR WEDNESDAY NIGHT THROUGH THURSDAY NIGHT: THE WEATHER LOOKS LARGELY QUIET FOR MUCH OF THANKSGIVING DAY... BUT AN INTENSE STORM SYSTEM WILL BRING INCREASING WINDS... A FEW SPRINKLES OR SHOWERS... AND A SHOT OF COLDER AIR STARTING IN THE EVENING. THE MID LEVEL VORTEX SWINGS ACROSS NORTHERN IL AND ALONG THE MI/OH BORDER THROUGH THURSDAY. WITH MINOR TIMING DIFFERENCES THE MODELS ARE PRETTY CLOSE IN SWEEPING THE TAIL END OF A SHEARED LOBE OF VORTICITY AT 500 MB THROUGH WESTERN NC AND VA BY THURSDAY MORNING... ALTHOUGH THE PROJECTED MOISTURE PROFILES WOULD SUGGEST FEW IMPACTS ON OUR SENSIBLE WEATHER OTHER THAN ENHANCED HIGH/MID CLOUDS. SURFACE WINDS REMAIN LIGHT WEDNESDAY NIGHT AND WE SHOULD SEE AT LEAST PATCHY FOG THROUGH DAYBREAK. THE NAM/GFS/CANADIAN/ECMWF ALL INDICATE 850 MB COLD AIR ADVECTION BEGINNING LATE THURSDAY AFTERNOON AS THE NEXT STRONG MID LEVEL VORTICITY LOBE AND TROUGH AXIS SWING EAST THEN NORTHEAST TOWARD THE AREA. BUT THE COOLER AIR AT THE SURFACE WILL REMAIN HELD UP ON THE WEST SIDE OF THE MOUNTAINS THROUGH SUNSET... RESULTING IN STEEPENING LOW LEVEL LAPSE RATES THURSDAY AFTERNOON. EXPECT PARTIAL CLEARING AS ANY MORNING FOG AND STRATUS MIX OUT... THEN CLOUDS SHOULD INCREASE AGAIN IN THE AFTERNOON WITH THE DEVELOPING SHALLOW INSTABILITY... INCOMING DPVA... AND RAPIDLY INCREASING UPPER DIVERGENCE IN THE LEFT EXIT REGION OF THE STRENGTHENING (TO OVER 130 KTS) SUBTROPICAL JET OVER GA/AL... ALL PRODUCING RAPID PRESSURE FALLS AT THE SURFACE WITH A LOW FORMING JUST NORTH OF THE NC/VA BORDER. THE NAM/CANADIAN/ECMWF SHOW THE MID LEVEL TROUGH TAKING ON A NEGATIVE TILT HEADING NORTHEAST THROUGH VA... AND THIS MORE INTENSE SOLUTION IS PREFERRED OVER THE GFS WHICH KEEPS A MORE WRAPPED SYSTEM WITH A NEUTRAL TO POSITIVE TILT. THE MOISTURE ATTENDING THIS TROUGH IS LIMITED WITH NO OPPORTUNITY TO ADVECT ANY MOISTURE IN... HOWEVER IF THE DYNAMIC LIFT IS STRONG ENOUGH IT COULD CONDENSE SUFFICIENTLY FOR A FEW SHOWERS ACROSS THE NORTHERN COUNTIES. THE POTENTIAL ALSO REMAINS FOR A STRATOSPHERIC INTRUSION IN THIS TYPE OF DYNAMICALLY VIGOROUS PATTERN WITH 500 MB WINDS INCREASING TO AROUND 80 KTS... HOWEVER IT APPEARS FROM FORECAST SOUNDINGS THAT THE MIXED LAYER MIGHT NOT DEEPEN TO MORE THAN 2 KM SO THIS IS APPEARS UNLIKELY. REGARDLESS THOUGH... THE LOW LEVEL HEIGHT FALLS AND TIGHTENING PRESSURE GRADIENT WILL RESULT IN QUICKLY INCREASING SURFACE WINDS AND GUSTS LATE THURSDAY AFTERNOON THROUGH THURSDAY NIGHT. EXPECT SUSTAINED WINDS AROUND 15 MPH WITH FREQUENT GUSTS OVER 25 MPH... BUT WITH WINDS OF 25-35 KTS THROUGH THE MIXED LAYER THURSDAY NIGHT INTO FRIDAY... WOULD NOT BE SURPRISED TO SEE OCCASIONAL GUSTS APPROACH 40 MPH. LOWS WEDNESDAY NIGHT 40-46. HIGHS THURSDAY OF 60-66 STILL AGREE WELL WITH MODEL THICKNESSES TRENDS. LOWS 36-43 THURSDAY NIGHT WITH DECREASING CLOUDS TOWARD MORNING. -GIH && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 255 PM MONDAY... FOR FRIDAY/FRIDAY NIGHT: EXPECT CONTINUED BRISK AND GUSTY NORTHWEST WINDS WITHIN THE MIXED LAYER THROUGH FRIDAY AS THE MID LEVEL VORTEX SHIFTS EAST ACROSS THE MIDATLANTIC COASTAL AREA TOWARD NEW ENGLAND. WE SHOULD SEE JUST SCATTERED CLOUDS AT MOST WITH A DRY COLUMN AND DOWNSLOPE FLOW. LOW LEVEL THICKNESSES ARE NEARLY 25 M BELOW NORMAL WITH COLD ADVECTION THROUGH THE DAY. WILL HAVE HIGHS 51-57. LOWS IN THE LOWER-MID 30S FRIDAY NIGHT WITH WINDS DIMINISHING AS SURFACE HIGH PRESSURE STARTS TO BUILD IN FROM THE WEST-SOUTHWEST. FOR SATURDAY THROUGH MONDAY: QUIET WEATHER OVER THE WEEKEND WITH SURFACE HIGH PRESSURE BUILDING INTO AND OVER THE AREA WITH RIDGING ALOFT OVER THE SOUTHEAST. LOW LEVEL THICKNESSES RECOVER BACK TOWARD NORMAL. HIGHS 54-59 SATURDAY AND 57-63 SUNDAY WITH LOWS IN THE LOWER-MID 30S. THE NEXT STORM SYSTEM DIGS THROUGH THE SOUTHERN ROCKIES LATE SUNDAY AND SHIFTS INTO THE PLAINS MONDAY. GRADUALLY INCREASING OVERRUNNING SHOULD BRING INCREASING CLOUDS OVER NC MONDAY... BUT WITH THIS SYSTEM STILL WELL TO OUR WEST... WILL KEEP IT DRY FOR NOW. HIGHS AGAIN 57-63. -GIH && .AVIATION /18Z MONDAY THROUGH FRIDAY/... AS OF 1230 PM MONDAY... LIFR TO IFR CEILINGS ARE EXPECTED THROUGH THE TAF PERIOD AS LOW PRESSURE OFF THE CAROLINA COAST CONTINUES TO PUMP IN ATLANTIC MOISTURE. LIGHT RAIN ACROSS THE REGION IS BEGINNING TO TRANSITION TO DRIZZLE AND THIS WIDESPREAD DRIZZLE IS EXPECTED TO PERSIST THROUGH THE EARLY EVENING HOURS. OVERNIGHT...AREAS OF FOG AND LIGHT DRIZZLE WILL MAINTAIN IFR/LIFR CONDITIONS THROUGH AT LEAST THE MID MORNING HOURS ON TUESDAY. CAD WEDGE WILL LIKELY PERSIST ACROSS CENTRAL NC THROUGH A GOOD PORTION OF THE PERIOD...RESULTING IN A PERSISTENT PERIOD OF MVFR/IFR CONDITIONS WITH PERIODS OF FOG/LIGHT DRIZZLE THROUGH TUES AND POSSIBLY WED. SOME IMPROVEMENT IS POSSIBLE ON WED OR THU AS A COLD FRONT APPROACHES THE REGION AND THE INCREASING PRESSURE GRADIENT WILL RESULT IN BREEZY/GUSTY CONDITIONS BY THE END OF THE PERIOD. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...KRR SHORT TERM...HARTFIELD LONG TERM...HARTFIELD AVIATION...KRR