FXUS62 KRAH 231524
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1024 AM EST WED DEC 23 2009
.SYNOPSIS...
HIGH PRESSURE WILL EXTEND ACROSS THE REGION THROUGH
THURSDAY...BRINGING SEASONABLY COOL AND DRY CONDITIONS. A STORM
SYSTEM WILL APPROACH FROM THE SOUTHWEST LATE THURSDAY AND AFFECT THE
AREA CHRISTMAS EVE THROUGH CHRISTMAS DAY.
&&
.NEAR TERM /THROUGH THURSDAY/...
AS OF 1025 AM...
LITTLE CHANGE. CIRRUS ADVANCING INTO CENTRAL NORTH CAROLINA FROM THE
WEST BUT OVERALL EXPECTED TO BE THIN ENOUGH DURING MOST OF THE DAY
TO HAVE LITTLE IMPACT ON TEMPERATURES. MIXING HEIGHTS ARE QUITE
LOW AND LOCAL THICKNESS SCHEMES TOO WARM. CURRENT MID 40S TO LOWER
50S FOR HIGH TEMPERATURE ACCEPTED.
AS MENTIONED BY PREVIOUS SHIFT... SOME WEAK WARM ADVECTION IN THE
WEST TONIGHT WITH GFS FORECAST SOUNDINGS CERTAINLY INDICATING A
POSSIBILITY FOR LOW STRATUS. WEAK WINDS AND SUCH A THIN SURFACE
BASED MOIST LAYER MAY PRECLUDE CLOUD FORMATION. WILL EVALUATE FOR
THE AFTERNOON FORECAST.
THURSDAY LOOKS SIMILAR TO TODAY WITH THE EXCEPTION OF THE
SOUTHWEST... WHERE LOWERING CLOUDS WILL LIKELY CLIP A FEW DEGREES
OFF THE POTENTIAL FULL SUN HIGH TEMPERATURES. AFTERNOON
TEMPERATURES MOSTLY MID 40S WEST AND NORTH...RISING TO MID 50S
EXTREME SOUTHEAST.
&&
.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 230 AM WEDNESDAY...
..A THREAT OF SEVERAL HOURS OF LIGHT FREEZING RAIN AT THE ONSET OF
PRECIPITATION OVER THE NORTHWEST PIEDMONT LATE THURSDAY NIGHT...
BEFORE A TRANSITION TO ALL LIQUID BY FRIDAY MORNING...
THURSDAY NIGHT (CHRISTMAS EVE): THE 1038 MILLIBAR SURFACE HIGH
WILL BE CENTERED NORTH OF THE GREAT LAKES EXTENDING SOUTH DOWN THE
EAST COAST WITH A COLD AIR DAMMING WEDGE IN PLACE THURSDAY
EVENING. GIVEN THE NORTHWEST DISPLACEMENT OF THE SURFACE HIGH DO
NOT EXPECT THE AIR IN THE LOW LEVELS TO BE PARTICULARLY DRY WITH
DEWPOINTS MAINLY IN THE MIDDLE 20S PRIOR TO ONSET OF
PRECIPITATION. MODEL WET BULB ZERO FOR 06 TO 12Z FRIDAY REMAINS
OVER THE NORTHWEST PIEDMONT AND VIRGINIA BORDER COUNTIES
SUGGESTING THE POTENTIAL FOR THE PRECIPITATION TO BEGIN AS PERIOD OF
LIGHT FREEZING RAIN AFTER MIDNIGHT THURSDAY NIGHT/FRIDAY MORNING.
BEST ISENTROPIC LIFT DOES NOT GET GOING WITH THE INCREASING 40 KNOT
LOW LEVEL FLOW UNTIL 06Z AND LATER. WILL KEEP A MENTION OF LIGHT
FREEZING RAIN EARLY OVER THE TRIAD AND WELL NORTH OF RALEIGH WHERE
THERE IS A POTENTIAL FOR A LIGHT GLAZE PRODUCED BY THE FIRST TENTH
OF AN INCH OF PRECIPITATION. ALL MODELS SUGGEST A TRANSITION OVER
TO ALL LIQUID BY AROUND DAYBREAK AS THE SURFACE LOW LIFTS NORTH
TOWARD OUR REGION AND A COASTAL FRONT PUSHES INTO THE COASTAL
PLAIN. A WINTER WEATHER ADVISORY MAY BE NEEDED FOR THE NORTHWEST
PIEDMONT COUNTIES EARLY FRIDAY MORNING. LOWS FROM A DEGREE OR
TWO BELOW FREEZING NORTHWEST... TO AROUND 40 DEGREES OR SO SE...
WITH A GRADUAL RISE IN TEMPERATURES EXPECTED OVERNIGHT.
FRIDAY AND FRIDAY NIGHT (CHRISTMAS): EXPECT THE DEEP ISENTROPIC
LIFT TO PROVIDE WIDESPREAD RAINFALL SPREADING IN FROM THE
SOUTHWEST TO NORTHEAST ACROSS ALL OF CENTRAL NORTH CAROLINA. WILL
KEEP CATEGORICAL CHANCE OF SHOWERS ON FRIDAY. MODELS TRACK THE
SURFACE MILLER-B TYPE LOW INLAND JUST EAST OF THE INTERSTATE 95
CORRIDOR. THIS FOCUS WILL ALLOW FOR LONG PERIODS OF MODERATE
RAINFALL WITH QPF AMOUNTS AROUND TO JUST OVER ONE INCH ACROSS MOST
OF THE AREA. WHILE MARITIME TROPICAL LOW LEVEL THETA-E AND
ASSOCIATED SUFFICIENT SURFACE BASED INSTABILITY SHOULD REMAIN
OFFSHORE GIVEN THE EXPECTED TRACK OF THE TRIPLE POINT THERE IS
SOME CONCERN FOR ELEVATED CONVECTION. THE PATTERN WILL BE
SUPPORTIVE OF POTENTIAL (CONVECTIVE) INSTABILITY...OWING TO THE
OVERRUNNING OF THE MID LEVEL DRY SLOT ATOP UNSTABLE PARCELS
ORIGINATING IN SOUTHEASTERLY FLOW AROUND 850 MILLIBARS. THE ONLY
LACKING ELEMENT IS STRONG UPPER DYNAMICS AS THE BEST UPPER SUPPORT
FOR CONVECTION REMAINS NE OF THE AREA. WILL MAINTAIN ISOLATED
THUNDER OVER ROUGHLY THE EASTERN THIRD OF THE CWA (ALONG THE AXIS
OF THE SOUTHEASTERLY 850 MILLIBAR JET. HIGHS FRIDAY COULD RANGE
DRAMATICALLY WITH COOL AIR LOCKED IN THE TRIAD AND WARMER MARITIME
AIR REACHING INTO THE SANDHILLS AND COASTAL PLAIN. HIGHS IN THE
MID 40S OVER THE RESIDUALLY WEDGED NORTHWEST PIEDMONT TO NEAR 60
EAST OF THE WEDGE FRONT WARM SECTORED SE.
DRYING... COOLING... AND CLEARING FRIDAY NIGHT... AS THE SYSTEM
PIVOTS NORTHEASTWARD AND AWAY FROM CENTRAL NORTH CAROLINA. LOWS IN
THE MIDDLE 30S WEST TO MIDDLE 40S EAST WITH LINGERING CLOUD
COVER ESPECIALLY IN THE EAST.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
AS OF 230 AM WEDNESDAY...
SATURDAY THROUGH TUESDAY: THIS PERIOD WILL BE DOMINATED BY A COLD
POLAR VORTEX OVER THE GREAT LAKES AND NEW ENGLAND. ANY
PRECIPITATION IS EXPECTED TO REMAIN CONFINED TO UPSLOPE REGIONS IN
THE CENTRAL APPALACHIANS... THOUGH WE WILL NEED TO MONITOR THE
MAGNITUDE OF SHORT WAVE TROUGHS THAT MAY PIVOT AROUND THE BASE OF
THE VORTEX ON SUNDAY AND ESPECIALLY MONDAY WHEN THE BEST DYNAMICS
WITH THE UPPER LOW MOVE THROUGH. SOME FLURRIES OR LIGHT SNOW COULD
DEVELOP MONDAY BUT WILL DEPEND ON THE AMOUNT OF MOISTURE AVAILABLE
IN THE NORTHWEST FLOW. HIGHS AND LOWS IN THE 40S AND 20S
RESPECTIVELY... ABOUT A CATEGORY BELOW NORMAL.
&&
.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
AS OF 620 PM WEDNESDAY...
VFR CONDITIONS WILL GENERALLY CONTINUE THROUGH THE 24 TAF PERIOD...
WITH POSSIBLY SOME MVFR CIGS AND/OR VISBYS IN THE NORTHWEST PIEDMONT
NEAR SUNRISE ON THURSDAY.
HIGH PRESSURE LOCATED OVER SOUTHERN ONTARIO AND THE GREAT LAKES
REGION... WILL CONTINUE TO EXTEND INTO CENTRAL NORTH CAROLINA TODAY.
THE ACCOMPANYING DRY AIR MASS WILL ENSURE VFR CONDITIONS TODAY
THROUGH AT LEAST 06Z THURSDAY. OTHERWISE... SCATTERED TO AT TIMES
BROKEN HIGH CLOUDS WILL STREAM INTO THE AREA IN THE WESTERLY FLOW
ALOFT TODAY AND TONIGHT... WITH CALM WINDS THIS MORNING BECOMING
LIGHT NORTHEASTERLY BY 15Z OR SO.
WE MAY SEE SOME STRATUS DEVELOP THURSDAY MORNING AS 925MB EASTERLY
FLOW JUST ABOVE THE SURFACE WILL OVERSPREAD SOME ATLANTIC MARITIME
AIR INTO THE STATE. HOWEVER... WILL ONLY INTRODUCE A TEMPO GROUP AT
KGSO AND KINT FOR THE POTENTIAL FOR MVFR CIGS AND/OR VISBYS AFTER
08Z THURSDAY... AS THE FLOW REMAINS FAIRLY WEAK (NW TAF SITES LOOKS
TO STAND THE BEST CHANCE GIVEN THE AID FROM UPSLOPE FLOW).
A STORM SYSTEM WILL APPROACH NORTH CAROLINA FROM THE WEST-SOUTHWEST AND BRING
MVFR/IFR CONDITIONS THURSDAY NIGHT AND INTO FRIDAY. THERE IS ALSO
THE POTENTIAL FOR LOW LEVEL WIND SHEAR CONDITIONS THURSDAY
NIGHT/FRIDAY MORNING FROM A 40 TO 45KT SELY LLJ. VFR CONDITIONS ARE
EXPECTED TO RETURN ON SATURDAY AS THE STORM SYSTEM EXITS THE AREA.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...JO
NEAR TERM...
SHORT TERM...JO
LONG TERM...JO
AVIATION...BSD
