951
FXUS62 KRAH 210825
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
322 AM EST SAT NOV 21 2009
SYNOPSIS
HIGH PRESSURE TO OUR NORTH WILL BRING NORTHEAST FLOW TO NORTH
CAROLINA INTO SUNDAY. THE NEXT STORM SYSTEM WILL MOVE INTO THE
REGION FROM THE SOUTHWEST AND BRING CLOUDS AND RAIN FOR SUNDAY AND
SUNDAY NIGHT.
NEAR TERM /THROUGH TONIGHT/
AS OF 315 AM...
SURFACE HIGH PRESSURE NORTH OF NORTH CAROLINA WILL KEEP NORTHEAST
FLOW OVER CENTRAL NORTH CAROLINA INTO TONIGHT. EXPECTING ENOUGH
SUNSHINE THROUGH THE MID AND HIGH CLOUDS TO BRING TEMPERATURES TO
JUST SHORT OF FULL SUN VALUES FOR NORTHEAST FLOW. AFTERNOON HIGHS
UPPER 50S TO LOWER 60S NORTH... AND 62 TO 65 SOUTH.
AN UPPER LEVEL SYSTEM DROPPING INTO TEXAS IS GENERATING SURFACE
LOW PRESSURE IN THE NORTHWEST GULF OF MEXICO AT THIS TIME. BOTH
THESE LOWS FORECAST TO ROUGHLY MOVE EAST NORTHEAST INTO SUNDAY.
THE NAM 700 MILLIBAR PRESSURE FIELD IS PERHAPS TOO WEAK AND PREFER
THE STRONGER MID LEVEL FRONT OF THE CANADIAN AND GFS MODELS. THE
GFS AND CANADIAN DEPICT A 700 MILLIBAR WARM FRONT... BARELY
LIFTING NORTH INTO NORTH CAROLINA BY SUNRISE SUNDAY. ISENTROPIC
LIFT IS QUITE WEAK BELOW THIS FRONT SO ANY RAINFALL SHOULD BE
LATE... WELL UNDER ONE TENTH INCH AND NOT STRAY TOO FAR NORTH BY
SUNRISE. INCREASED LOWER CLOUDINESS AND MORE OF A BREEZE THAN
FRIDAY NIGHT SHOULD YIELD LOW TEMPERATURES IN THE MID TO UPPER
40S.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/
AS OF 315 AM...
A 700 MILLIBAR WARM FRONT NEAR THE SOUTH CAROLINA BORDER SUNRISE
SUNDAY WILL EXIT TO THE NORTH AFTER SUNSET. GIVEN THE EXPECTED
NORTHWARD PROGRESS OF THE FRONT AND MODERATE TO WEAK ISENTROPIC
LIFT NEAR 850 MILLIBARS... AT LEAST THE SOUTHWEST THREE QUARTERS
SHOULD SEE MEASURABLE RAIN BEFORE SUNSET SUNDAY.
AS THE UPPER SYSTEM LIFTS NORTHEAST THROUGH THE MOUNTAINS SUNDAY
NIGHT... LOW PRESSURE DEVELOPMENT OFF THE CAROLINAS OCCURS AND
BECOMES THE DOMINATE SURFACE LOW. GOOD MID LEVEL ISENTROPIC LIFT
IN THE MID LEVELS SHOULD KEEP RAIN CHANCES HIGH INTO SUNDAY NIGHT.
MOST MODELS DAMP OUT THE PARENT LOW PRESSURE TROUGH AS IT MOVES
NORTHEAST AND KEEP THE SURFACE LOW WEAKER THAN THE CANADIAN AS IT
APPROACHES CAPE HATTERAS. RAINFALL PERHAPS TWO TENTHS INCH
NORTHWEST TO FOUR TENTHS SOUTHEAST SUNDAY NIGHT.
WINDS WEAKEN LATE SUNDAY NIGHT INTO MONDAY AND HEAVIER
PRECIPITATION MAY MISS US TO THE EAST MONDAY. PRECIPITATION MAY
LINGER LONGEST IN THE NORTHEAST WITH THE EXITING SURFACE LOW BUT
RAINFALL AMOUNTS OF ONE TENTH INCH OR LESS EAST... AND MUCH LESS
TO THE WEST. OF COURSE IF THE LOW TRACKS CLOSER TO THE COAST...
THESE AMOUNTS ARE UNDERDONE. ONLY A SLIGHT RAIN CHANCE IN THE
NORTHEAST WITH THE EXITING LOW MONDAY NIGHT.
OVERNIGHT LOWS 45 TO 50 SUNDAY NIGHT... AND MOSTLY MID 40S TUESDAY
NIGHT. SUNDAY HIGH TEMPERATURES NEAR 50 NORTHWEST TO UPPER 50S
SOUTHEAST. IF A COLD AIR MASS DAMMING WEDGE SETS UP AS EXPECTED
MONDAY...A LOW OVERCAST WITH LIGHT RAIN OR DRIZZLE POSSIBLE. THE
CURRENT FORECAST TEN DEGREE DIURNAL RISE TO MONDAY AFTERNOON WOULD
NEED TO BE DROPPED TO THREE TO SIX DEGREES IF CLOUDS ARE ABLE TO
PERSIST INTO EARLY MONDAY EVENING.
LONG TERM /TUESDAY THROUGH FRIDAY/
AS OF 315 AM FRIDAY...
ANY LIGHT PRECIP LINGERING INTO MONDAY NIGHT SHOULD BE GONE BY
TUESDAY MORNING...AS SOUTHWESTERLY MID LEVEL FLOW USHERS IN DRIER
AIR ABOVE THE REMAINING CAD AIRMASS. THE POSSIBILITY LINGERING LOW
CLOUDS COULD COMPLICATE THE TEMPERATURE FORECAST ON TUESDAY AS SOME
MOISTURE REMAINS BELOW A SUBSIDENCE INVERSION BENEATH DEVELOPING
SHORTWAVE RIDGING ALOFT. WILL STICK WITH MOS VALUES WITH HIGHS
64-70.
THE FORECAST GETS QUITE A BIT MORE COMPLICATED BEYOND TUESDAY...WITH
THE HANDLING OF A SHORTWAVE EXPECTED TO ENTER THE PACIFIC NORTHWEST
ON MONDAY AND EMERGE OVER THE NORTH CENTRAL PLAINS BY WED. THE
GENERAL TREND IS FOR THE DEVELOPMENT OF A HIGH AMPLITUDE LONGWAVE
TROUGH BY THE END OF THE WEEK...AND WHILE BOTH THE GFS AND ECMWF
RESOLVE SUCH A SOLUTION...THEY CURRENTLY GET THE SIMILAR ANSWER
THROUGH SOMEWHAT DIFFERENT SCENARIOS. THE GFS SENDS THE
AFOREMENTIONED SHORTWAVE ACROSS THE UPPER MIDWEST AND THE LIFTS THE
SYSTEM INTO ONTARIO BY THURSDAY...PUSHING A DRY COLD FRONT INTO
CENTRAL NC WED NIGHT. THIS IS FOLLOWED BY A SECOND SHORTWAVE THAT
DIVES SOUTH THROUGH THE MIDWEST...BUT WITH NO MORE TO WORK
WITH....POINTS EAST OF THE MOUNTAINS STAY DRY EVEN AS A SURFACE WAVE
IS INDUCED OFFSHORE THURSDAY MORNING. THE ECMWF ON THE OTHER HAND
IS MUCH SLOWER WITH THE FIRST SHORTWAVE...ALLOWING MORE MOISTURE TO
BE PULLED NORTH OVER A PERSISTENT SURFACE RIDGE ALONG THE EASTERN
SEABOARD. CYCLOGENESIS ALONG THE COAST SUBSEQUENTLY OCCURS CLOSER
TO THE COAST THURSDAY MORNING WITH LESS EASTWARD PROGRESSION OF THE
SURFACE FRONT...AND THUS THE ECMWF PRODUCES PRECIP OVER THE EASTERN
THIRD OF NC. GIVEN THESE CONTINUED MODEL INCONSISTENCIES...FEEL THE
BEST COURSE OF ACTION IS TO SHOW BELOW NORMAL TEMPS FOR THE END OF
THE WEEK...CONTINUING WITH HIGHER SLIGHT CHANCE POPS IN THE EAST
UNTIL SOME SORT OF MODEL CONVERGENCE BEGINS.
AVIATION /08Z SATURDAY THROUGH WEDNESDAY/
AS OF 1245 AM SATURDAY...
OTHER THAN PERIODS OF LIMITED VSBYS AT KRWI WHERE LINGERING LOW
LEVEL MOISTURE IS ALREADY CAUSING SOME SHALLOW FOG...VFR CONDITIONS
ARE GENERALLY EXPECTED ACROSS CENTRAL NC THROUGH THE CURRENT TAF
PERIOD. HIGH PRESSURE OVER THE OHIO VALLEY REGION WILL DRIFT SLOWLY
NORTHEAST TODAY...AND SETTLE OVER NEW ENGLAND TONIGHT...KEEPING
SURFACE WINDS PREDOMINATELY OUT OF THE NE. A DEVELOPING SYSTEM
OVER THE WESTERN GULF COAST WILL BEGIN TO LIFT NORTH AND EASTWARD
TODAY...WITH PERIODS OF CIRRUS DRIFTING OVER CENTRAL NC FROM THE
SOUTHWEST. CEILINGS WILL EVENTUALLY BEGIN TO LOWER LATE TONIGHT AND
INTO SUNDAY MORNING AS THE PRECIPITATION SHIELD ASSOCIATED WITH THE
GULF COAST STORM SYSTEM SPREADS TO TOWARDS THE AREA...BUT ALL SITES
SHOULD REMAIN VFR AND PRECIP FREE THROUGH 06Z.
LOOKING BEYOND 00Z SUNDAY: A STORM SYSTEM WILL APPROACH FROM THE
SOUTHWEST SUNDAY MORNING AND MAY BRING MVFR OR IFR CONDITIONS TO THE
REGION FOR SUNDAY THROUGH MONDAY. LOW CIGS ARE EXPECTED TO CLEAR OUT
BY MONDAY AFTERNOON BUT AREAS OF IFR/LIFR FOG MAY DEVELOP LATE
MONDAY NIGHT/TUESDAY MORNING. VFR CONDITIONS ARE ANTICIPATED TUESDAY
MORNING THROUGH WEDNESDAY WITH HIGH PRESSURE BUILDING IN FROM THE
SOUTHWEST.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
LONG TERM...SMITH
AVIATION...SMITH
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