FXUS62 KRAH 261125
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
625 AM EST THU NOV 26 2009
.SYNOPSIS...
A POTENT UPPER LEVEL DISTURBANCE AND ASSOCIATED COLD FRONT WILL
CROSS THE REGION THIS EVENING. BLUSTERY...CHILLY CONDITIONS FOLLOW
ON FRIDAY. HIGH PRESSURE BUILDS OVERHEAD SATURDAY INTO THE
WEEKEND...WITH MODERATING TEMPERATURES BY SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 300 AM THURSDAY...
HIGH CLOUDS CONTINUED TO DEPART CENTRAL NORTH CAROLINA EARLY THIS
MORNING AS MID-LEVEL DRY AIR WAS SPREADING QUICKLY INTO THE AREA
FROM THE SOUTHWEST. WITH THE THINNING CLOUDS AND CLEARING...AREAS OF
FOG DEVELOPED RAPIDLY AROUND 1 AM...SPREADING EAST. OBSERVATIONS
AND AREA TRAFFIC CAMERAS SHOWED NUMEROUS AREAS OF FOG...WITH THE
THICKEST FOG IN RURAL AREAS. AS OF THIS WRITING...A VERY LIGHT WIND
AND REMAINING CLOUDS HAVE KEPT AREAS OF FOG AT BAY TOWARD KFAY AND
KCTZ...BUT WITH CLEARING EXPECTED AREAS OF DENSE FOG SHOULD OCCUR
THERE AS WELL. THE DENSE FOG ADVISORY CONTINUES FOR ALL OF CENTRAL
NORTH CAROLINA.
00Z UPPER-AIR DATA SHOWED A LARGE AREA WITH A GOOD DEPTH OF DRY AIR
AHEAD OF THE UPPER TROUGH DIGGING ACROSS THE MID-MISSISSIPPI VALLEY.
FOR MUCH OF THE DAY...AFTER FOG LIFTS...CONSIDERABLE SUNSHINE SHOULD
OCCUR WITH HIGHS REACHING THE LOWER TO MID 60S. LATE THIS AFTERNOON
AND TONIGHT...CONDITIONS SHOULD BEGIN TO DETERIORATE SOME WITH THE
APPROACH OF THE UPPER TROUGH.
THE GFS AND THE NAM ARE CONSISTENT IN SHOWING STRONG PVA PUSHING
ACROSS CENTRAL NORTH CAROLINA MAINLY BETWEEN 00Z AND 06Z...WITH THE
GFS SLIGHTLY FASTER THAN THE NAM. THE TROUGH ALREADY IS FAIRLY
DYNAMIC...WITH TEMPERATURES FALLING TO -13C AT 700MB AND AROUND -30C
AT 500MB AT UPPER-AIR SITES IN VICINITY OF THE TROUGH AT 00Z. IN
FACT...PRESSURES ON THE 300K SURFACE ARE FORECAST TO FALL OVER 200MB
IN RESPONSE TO THE APPROACH OF THE TROUGH FROM THIS MORNING THROUGH
06Z TONIGHT. AS THE LEFT EXIT REGION OF A 500MB JET OF 80-90KT
AFFECTS CENTRAL NORTH CAROLINA TONIGHT...WEAK TROUGHINESS AND
PRESSURE FALLS AT THE SURFACE SHOULD PROVIDE FOR ENOUGH CONVERGENCE
ASSOCIATED WITH THE STRONG LIFT OF THE UPPER TROUGH TO RESULT IN AT
LEAST SCATTERED SHOWERS FOR CENTRAL NORTH CAROLINA MAINLY BETWEEN
ABOUT 00Z AND 06Z...POSSIBLY STARTING A LITTLE EARLIER IN THE FAR
WESTERN PIEDMONT AND ENDING A LITTLE LATER IN THE NORTHERN COASTAL
PLAIN. HIGHEST POPS...HIGH CHANCE FOR NOW...WILL BE MAINLY ALONG AND
NORTH OF U.S. 64 AND EAST OF THE TRIAD WHERE MOISTURE IS DEEPEST ON
BOTH THE NAM AND GFS. SUBSIDENCE FOLLOWS QUICKLY OVERNIGHT WITH
DIMINISHING 850MB THETA-E AND DEEP DRYING EVIDENT ON BOTH GFS AND
NAM BUFR SOUNDINGS. ANTICIPATE A FEW GUSTS OF WIND TO 20 TO 30 MPH
OR SO ASSOCIATED WITH THE UPPER TROUGH PASSAGE OVERNIGHT. WILL JUST
MENTION THAT THE DEPTH OF THE ABOVE FREEZING AIR ON MODEL SOUNDINGS
SUPPORTS ALL LIQUID DESPITE COOL TEMPERATURES WITH THE TROUGH ALOFT
AND LOWERING 850-700MB THICKNESSES. OVERNIGHT LOWS WILL MAINLY BE IN
THE UPPER 30S.
&&
.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
AS OF 240 AM THURSDAY...
FRIDAY AND FRIDAY NIGHT: STRONG SUBSIDENCE BEHIND THE NEGATIVELY
TILTED TROUGH AXIS -- WHICH WILL BE FURTHER CARVED BY ONE FINAL
PIECE OF SHORTWAVE ENERGY CENTERED OVER WESTERN ONTARIO THIS
MORNING -- WILL OVERSPREAD NC THIS PERIOD. A TIGHT MSL PRESSURE
GRADIENT BETWEEN AN ASSOCIATED SURFACE RIDGE AND A BOMBING COASTAL
STORM OFF THE NEW ENGLAND COAST WILL LEAD TO BREEZY CONDITIONS
THROUGHOUT THE DAY. FORECAST SOUNDINGS CONTINUE TO INDICATE UPWARDS
OF 30 TO 35 KTS OF WIND IN A DEEP... WELL-MIXED BOUNDARY LAYER
(BETWEEN 5 AND 6 THSD FT)... AND THESE WINDS SHOULD YIELD WNW
SURFACE WIND GUSTS BETWEEN 25 AND 30 KTS. DRY ADIABATIC MIXING OF
CONSENSUS H85 TEMPERATURES AT 18Z SUGGESTS HIGH TEMPERATURES OF
AROUND 51 TO 57 DEGREES. COLD TEMPERATURES WITH A DIMINISHED BUT
STILL PRESENT WNW WIND (~3-7 KTS) OVERNIGHT... WITH LOWS GENERALLY
IN THE LOWER 30S.
SATURDAY THROUGH SUNDAY NIGHT: SURFACE HIGH PRESSURE... BENEATH
BUILDING HEIGHTS ALOFT... WILL CREST OVER THE SOUTHEASTERN CONUS
EARLY THIS WEEKEND AND SHIFT OFFSHORE BY SUNDAY. DESPITE A SUNNY
SKY... SATURDAY SHOULD BE THE COOLEST DAY OF THE WEEKEND (55 TO 60
DEGREES)... BEFORE TEMPERATURES MODERATE SUNDAY WITH RETURN FLOW
AROUND THE DEPARTING RIDGE. IT STILL APPEARS THAT THE PASSAGE OF A
SOUTHERN STREAM TROUGH ALOFT -- AN AMALGAMATION OF A COUPLE OF OF
WELL DEFINED S/W TROUGHS ALONG THE SOUTHERN CA COAST AND OFF THE
BAJA AT 07Z -- WILL SPREAD THE NORTHERN PERIPHERY OF A CIRRUS SHIELD
ACROSS AT LEAST SOUTHERN NC SATURDAY NIGHT. THE COMBINATION OF
INCREASING HIGH CLOUDS AND A LIGHT SW STIRRING (NOW THAT IT APPEARS
THE SURFACE HIGH AND CALM WIND WILL BE A BIT FURTHER SOUTH THAN
EARLIER PROGGED) MAY HOLD TEMPERATURES A COUPLE OF DEGREES WARMER
THAN PREVIOUSLY THOUGHT... WITH MAINLY MIDDLE 30S EXPECTED.
TEMPERATURES SUNDAY AND SUNDAY NIGHT IN THE MIDDLE 60S AND UPPER 30S
TO LOWER 40S... RESPECTIVELY... GIVEN THE DEVELOPING RETURN FLOW.
&&
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 310 AM THURSDAY...
MONDAY THROUGH WEDNESDAY: THE 00Z/26TH OPERATIONAL MEDIUM RANGE NWP
MODELS HAVE COME INTO REMARKABLY GOOD AGREEMENT WRT THE EVOLUTION OF
A POSITIVELY-TILTED TROUGH ALOFT FROM THE GREAT LAKES TO THE BAJA
EARLY NEXT WEEK. THE SOUTHERN PORTION OF THE TROUGH IS NOW PROGGED
TO FULLY SEPARATE FROM THE NORTHERN STREAM... AND SUCH A SCENARIO
WOULD LEAD TO A PAIR OF PRECIPITATION EVENTS FOR CENTRAL NC EARLY TO
MID NEXT WEEK... THE FIRST OF WHICH WOULD BE RELATIVELY LIGHT
OWING TO A DOMINANT NORTHERN STREAM TROUGH THAT WOULD ONLY GRAZE NC.
WARM CONVEYOR BELT CLOUDS AND PRECIPITATION AHEAD OF THE NORTHERN
STREAM TROUGH SHOULD EASE INTO CENTRAL NC LATE MONDAY INTO MONDAY
NIGHT... BUT GULF MOISTURE ENTRAINMENT SHOULD BE RELATIVELY LIMITED
OWING TO THE POSITIVE TILT OF THE UPPER TROUGH. THERE SHOULD THEN BE
A LULL WITH CLEARING SKIES AND SURFACE RIDGING TUESDAY AND TUESDAY
NIGHT... AS THE LOW LEVEL FRONTAL ZONE SHIFTS OFFSHORE BEHIND THE
NORTHERN STREAM. HOWEVER... THERE IS GOOD MODEL AGREEMENT THAT THE
LAGGING SOUTHERN PORTION OF THE TROUGH ALOFT WILL THEN GET KICKED
NORTHEASTWARD THROUGH THE LOWER MS... TN... AND OH VALLEYS BY
WEDNESDAY AND WEDNESDAY NIGHT... AND PROMOTE STRONG ISENTROPIC LIFT
AHEAD OF A DEVELOPING SURFACE WAVE OVER THE WESTERN GULF OF MEXICO
AND ATOP THE ASSOCIATED PRECEDING... RETREATING FRONTAL ZONE. THIS
SYSTEM HAS THE POTENTIAL TO PRODUCE A COLD... WIDESPREAD SOAKING
RAIN FOR OUR AREA WEDNESDAY.
&&
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
AS OF 625 AM THURSDAY...
EARLY MORNING AVIATION CONCERN CONTINUED TO BE LIFR/VLIFR CONDITIONS
IN DENSE FOG. AVAILABLE AMDAR SOUNDINGS AT KGSO SHOWED A LOW
INVERSION...AND WITH NO CLOUDS ABOVE THE FOG...THINK LIFR/VLIFR
CONDITIONS WILL IMPROVE GRADUALLY GIVEN THE LIGHT GRADIENT...BUT
PERSISTENTLY AFTER SUNRISE. SOME OF THE LATEST STATISTICAL GUIDANCE
HOLDS ONTO THE FOG AND LOW CLOUDS THROUGH THE MORNING...HOWEVER.
ANTICIPATE VFR CONDITIONS THROUGHOUT CENTRAL NORTH CAROLINA BY LATE
MORNING...CONTINUING THROUGH THE REST OF THE 12Z VALID TAF PERIOD.
WITH A STRONG UPPER-LEVEL TROUGH MOVING THROUGH VERY LATE THIS
AFTERNOON AND TONIGHT...BROKEN VFR CEILINGS ARE EXPECTED TO DEVELOP
WITH ENOUGH LIFT FOR SCATTERED SHOWERS. WITH TROUGH PASSAGE...WINDS
SHOULD VEER TO WEST-NORTHWEST OR NORTHWEST AND GUST INTO THE 20S KTS
FOR A PERIOD. WINDS AROUND 900MB ACTUALLY INCREASE TO JUST OVER 30KT
LATE TONIGHT. DRY AIR AND SUBSIDENCE BEHIND THE TROUGH DRIES
CONDITIONS FOR THE LATE NIGHT PERIOD.
BREEZY CONDITIONS PERSIST FRIDAY. VFR CONDITIONS OCCUR FRIDAY
THROUGH THE DAY MONDAY. A COLD FRONT BEGINS TO APPROACH FROM THE
NORTHWEST LATE MONDAY...WITH CHANCES FOR SHOWERS RETURNING THEN.
&&
.CLIMATE...
THROUGH NOVEMBER 25...THE TOTAL MONTHLY RAINFALL AT KGSO WAS 7.66
INCHES. THIS PLACES KGSO THIRD SO FAR FOR WETTEST NOVEMBERS...BEHIND
THE 8.26 INCHES IN 1985 AND THE 7.72 INCHES IN 1948. AT KRDU...THE
6.66 INCHES TOTALLED THROUGH NOVEMBER 25 ARE STILL BELOW THE TOP
FIVE...BEHIND THE 7.06 INCHES IN 1963.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY FOR ALL OF CENTRAL NORTH CAROLINA UNTIL 9 AM.
&&
$$
SYNOPSIS...DJF
NEAR TERM...DJF
SHORT TERM...MWS
LONG TERM...MWS
AVIATION...DJF
CLIMATE...DJF
