412
FXUS62 KRAH 040804
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
305 AM EST WED NOV 4 2009
SYNOPSIS
HIGH PRESSURE WILL BUILD ACROSS THE AREA TODAY...AS AN UPPER LEVEL
DISTURBANCE APPROACHES FROM THE NORTHWEST. THE UPPER DISTURBANCE
WILL BRING A FEW CLOUDS AND A CHANCE FOR SPRINKLES TONIGHT.
THEN...COLD HIGH PRESSURE WILL BUILD EAST OVER THE REGION FOR THE
REMAINDER OF THE WEEK.
NEAR TERM /THROUGH TONIGHT/
AS OF 300 AM WEDNESDAY...
..FROST ADVISORY FOR THE NORTHERN AND CENTRAL PIEDMONT
THE SURFACE COLD FRONT HAS PUSHED EAST OF THE AREA THIS
MORNING...WITH HIGH PRESSURE BUILDING EAST ACROSS THE OHIO VALLEY
REGION. TEMPS HAVE BEEN SOMEWHAT SLOW TO FALL THROUGH MIDNIGHT AS
WINDS HAVE HELD UP...BUT WITH DEWPOINTS FALLING INTO THE UPPER 20S
TO LOWER 30S OVER MUCH OF THE AREA...AND THE INITIAL COLD SURGE
THROUGH THE CWA...EXPECT WINDS WILL BEGIN TO DIE DOWN. A FROST
ADVISORY REMAINS IN EFFECT THIS MORNING FOR MAINLY THE NW PIEDMONT
AND NORTHERN COASTAL PLAIN...WHERE SHOULD WINDS GO CALM...MANY
LOCATIONS WILL SEE LOWS IN THE MID 30S.
TODAY...A SHORTWAVE TROUGH...CURRENTLY MOVING THROUGH THE UPPER
MIDWEST...WILL DIVE SE TOWARD THE CAROLINAS...BECOMING MORE
AMPLIFIED AS IT BEGINS TO PHASE WITH A SECOND AREA OF ENERGY ON ITS
HEELS DROPPING SOUTH OUT OF CANADA. MODELS HAVE BEEN CONSISTENT IN
WITH THIS WAVE...SHOWING ITS ASSOCIATED POTENT VORT CENTER CROSSING
THE MOUNTAINS AFTER 00Z THIS EVENING. AHEAD OF THE
DISTURBANCE...SURFACE WINDS WILL SHIFT AROUND TO SOUTHERLY AS A WEAK
SURFACE TROUGH DEVELOPS OVER THE AREA. LATEST MODEL GUIDANCE AND
MOS STATISTICS SHOW A FAIRLY DECENT RETURN OF MOISTURE IN THE
COASTAL PLAIN (GIVEN THE CURRENT AIRMASS)..WITH DEWPOINTS RISING
INTO THE UPPER 40S TO EVEN LOWER 50S BY LATE THIS AFTERNOON. THIS
WOULD ALLOW FOR THE DEVELOPMENT OF A FEW HUNDRED J/KG OF MLCAPE THIS
EVENING AS COOLING ALOFT COMMENCES WITH THE SHORTWAVE. GIVEN THE
STRENGTH OF THE DYNAMICS AND THE POTENTIAL FOR A LITTLE MORE LOW
LEVEL MOISTURE THAN WAS THE CASE IN PREVIOUS MODELS RUNS...HAVE
ELECTED TO PUT A SLIGHT CHANCE OF A SHOWER IN THE NE...WHERE THE
UPPER COLD POOL WILL BEST PHASE WITH BETTER MOISTURE. ISOLATED
SPRINKLES REMAIN POSSIBLE AS FAR SW AS THE TRIANGLE.
CLOUD COVER WILL HOLD OFF UNTIL THIS EVENING...AND FULL INSOLATION
WITH THICKNESSES REACHING UP TO AROUND 1350M WOULD YIELD HIGHS
RANGING FROM 62-69 NW TO SE...CONSISTENT WITH MOS GUIDANCE.
OVERNIGHT LOWS WILL SOMEWHAT DEPEND ON THE AMOUNT OF PASSING CLOUD
COVER THAT DEVELOPS WITH THE SHORTWAVE. WILL ADJUST CURRENT
FORECAST ONLY TO SHOW LOWS A LITTLE WARM IN THE NE WHERE CLOUD COVER
MAY INHIBIT COOLING THE MOST....40-46.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
AS OF 300 AM WEDNESDAY...
FOR THURSDAY: LATEST MODEL GUIDANCE SUPPORTS A TIMING SIMILAR TO THE
CURRENT FORECAST... WITH THE UPPER LEVEL JET STREAK OVER EASTERN
NC HEADING QUICKLY TO THE NORTHEAST AND THE MID LEVEL VORTICITY
MAXIMUM OVER SOUTH-CENTRAL NC AROUND 12Z ALSO EXITING RAPIDLY. WILL
LEAVE IN A COUPLE OF HOURS OF POTENTIAL SPRINKLES OVER THE NORTHEAST
CWA UNTIL MID MORNING THURSDAY. THE SUBSIDENCE BEHIND THIS SHORTWAVE
IS STRONG BUT LARGELY CONFINED TO THE MID LEVELS WELL INTO THE
AFTERNOON... AND FORECAST SOUNDINGS BEAR THIS OUT WITH STEADY
WARMING AND DRYING FROM ABOVE 800 MB UP THROUGH 400 MB WHILE LAPSE
RATES IN THE SURFACE-800 MB LAYER STEEPEN. WITH A LAYER OF MOISTURE
TRAPPED BENEATH THE SUBSIDENCE INVERSION ALOFT... SOME FLAT
HIGH-BASED AFTERNOON CUMULUS IS POSSIBLE GIVEN THIS GOOD LOW LEVEL
MIXING. AS THE SHORTWAVE TROUGH MOVES OFFSHORE... SURFACE LOW
PRESSURE INTENSIFIES OFF THE MIDATLANTIC COAST... HOWEVER THE BETTER
MSL PRESSURE GRADIENT DOESN'T SET UP OVER NC UNTIL LATE IN THE
DAY... WHEN THE SURFACE HIGH MOVES TO BE CENTERED OVER MEMPHIS...
AND WHEN A POLAR VORTICITY MAXIMUM THAT IS LOCATED OVER MI EARLY
THURSDAY DROPS SOUTHEAST ACROSS NJ/DELMARVA LATE. IT IS THIS SECOND
WAVE THAT SERVES TO LOWER MSL PRESSURES JUST OFF THE MIDATLANTIC
COAST FURTHER LEADING TO AN INCREASED PRESSURE GRADIENT AND HENCE
INCREASED SURFACE WINDS AND GUSTS OVER CENTRAL NC. WINDS AT THE TOP
OF THE MIXED LAYER APPEAR TO HOLD UNDER 20 KTS UNTIL AROUND
MIDAFTERNOON WHEN THEY RISE TO 25-30 KT... THUS WILL CONFINE THE
MOST PROMINENT GUSTS OF 25-30 MPH TO AFTER 18Z. TEMPS ARE TRICKY
CONSIDERING THAT THE DROP IN LOW LEVEL THICKNESSES WAITS UNTIL AFTER
THE SECOND VORTICITY MAXIMUM PASSES BY TO OUR NORTHEAST ALLOWING
MORE SUBSTANTIAL COLD AIR ADVECTION. WILL HOLD NEAR CURRENT FORECAST
HIGHS OF 60-67 WHICH IS UNDER STATISTICAL GUIDANCE BUT A BIT HIGHER
THAN WHAT THE LOW LEVEL THICKNESS TECHNIQUE INDICATES BASED ON THE
DELAY IN THE COOLER AIR.
FOR THURSDAY NIGHT THROUGH FRIDAY NIGHT: A MID LEVEL VORTEX CLOSES
OFF JUST OFF THE NORTHEAST COAST THURSDAY NIGHT... PRODUCING FAST
NORTHWEST FLOW ALOFT OVER NC. WITH DEEPENING SUBSIDENCE AND LOW
LEVEL COLD AND DRY AIR ADVECTION THURSDAY NIGHT WITH A STILL-TIGHT
MSLP GRADIENT... THE LOWEST 0.5-1 KM SHOULD REMAIN SUFFICIENTLY
STIRRED TO CUT DOWN ON RADIATIONAL COOLING AND LIMIT THE POTENTIAL
FOR FROST... ALTHOUGH LOWS OVER THE PIEDMONT UNDER CLEAR SKIES
SHOULD BE IN THE MID-UPPER 30S... AND WILL NEED TO KEEP AN EYE OUT
FOR PATCHY FROST IN THE OUTLYING AREAS. VERY DRY (PRECIPITABLE WATER
OF 0.25-0.30 IN.) AND SINKING AIR AS SURFACE HIGH PRESSURE BUILDS
OVERHEAD FROM THE WEST SHOULD ALLOW FOR PLENTY OF SUNSHINE FRIDAY.
THICKNESSES SUGGEST HIGHS SOME 10 DEGREES BELOW NORMAL ALTHOUGH THE
SUN SHOULD HELP TAKE THE EDGE OFF THIS COLD AIR. EXPECT HIGHS OF
54-61... COOLER NORTHEAST THAN SOUTHWEST. THE SURFACE HIGH SHIFTS
OVERHEAD FRIDAY NIGHT AND THIS MAY BE OUR COOLEST NIGHT OF THIS
STRETCH AS OVERNIGHT WINDS GO CALM... BRINGING ON A RISK OF
WIDESPREAD FROST/FREEZE CONDITIONS. WILL HAVE LOWS OF 31-35 UNDER
CLEAR SKIES. -GIH
LONG TERM /SATURDAY THROUGH TUESDAY/
AS OF 255 AM WEDNESDAY...
STILL LOOKS LIKE QUIET AND WARM WEATHER THROUGH THE WEEKEND INTO
MONDAY. MID LEVEL RIDGING COVERING THE GULF STATES SHIFTS EAST OVER
THE SOUTHEAST STATES WITH THE HIGH PRESSURE RIDGE HOLDING FIRM AT
THE SURFACE. BOTH THE GFS AND ECMWF SHOW PLENTY OF DEEP DRY AIR OVER
NC SATURDAY INTO MONDAY. LOW LEVEL THICKNESSES START OUT NEAR NORMAL
SATURDAY MORNING THEN RISE TO 10-20 M ABOVE NORMAL INTO MONDAY...
WHICH YIELDS HIGHS OF 63-67 SATURDAY RISING TO 69-74 SUNDAY/MONDAY.
BY MONDAY NIGHT/TUESDAY THE MID LEVEL TROUGH THAT SITS OVER
NORTHWEST MEXICO OVER THE WEEKEND OPENS UP AND HEADS NORTHEAST WHILE
THE SURFACE HIGH OVER THE CAROLINAS MOVES NORTHEAST ALLOWING AN
ATLANTIC RETURN FLOW INTO THE SOUTHEAST US. AS THE MID LEVEL RIDGE
SHIFTS TO OUR EAST WITH INCREASINGLY CYCLONIC FLOW ALOFT... BOTH
HIGH CLOUDS AND LOW CLOUDS WILL BEGIN TO SPREAD OVER THE REGION...
AND EXPECT SKIES TO BECOME PARTLY CLOUDY. WITH INCREASING MOISTURE
ESPECIALLY OVER SOUTHERN AND WESTERN NC AND IMPROVING FORCING FOR
ASCENT WITHIN THE RIGHT ENTRANCE REGION OF THE UPPER JET OVER THE
EASTERN GREAT LAKES/ST LAWRENCE... LOW CHANCE POPS FOR MONDAY
NIGHT/TUESDAY ARE WARRANTED. HIGHS 68-74. -GIH
AVIATION /06Z WEDNESDAY THROUGH SUNDAY/
AS OF 1250 AM WEDNESDAY...
VFR CONDITIONS THROUGH THE TAF FORECAST PERIOD. LIGHT WEST TO
NORTHWEST WINDS WILL SHIFT TO NORTH THIS MORNING WITH PERIODS OF
LIGHT TO CALM WINDS BY DAYBREAK...AS THE SURFACE COLD FRONT PUSHES
EAST TO THE COAST. SURFACE WINDS WILL SWING AROUND TO SOUTHERLY
TODAY...AHEAD OF AN APPROACHING UPPER LEVEL DISTURBANCE EXPECTED TO
CROSS THE AREA TONIGHT. WITH THE BOUNDARY LAYER REMAINING QUITE
DRY... ONLY EXPECT A PERIOD OF BROKEN HIGH BASED STRATOCU AT OR
ABOVE 8K FT AND A FEW SPRINKLES ACROSS THE NORTHERN HALF OF THE AREA
AS THE UPPER DISTURBANCE PASSES.
VFR CONDITIONS ARE EXPECTED FOR THE REMAINDER OF THE WEEK...AS
HIGH PRESSURE WILL FOR THE MOST PART DOMINATE THE WEATHER PATTERN
OVER CENTRAL NORTH CAROLINA.
RAH WATCHES/WARNINGS/ADVISORIES
FROST ADVISORY FROM 4 AM TO 9 AM EST WEDNESDAY FOR
NCZ007>010-021>026-038>041.
SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...SMITH
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