FXUS62 KRAH 111442
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
945 AM EST FRI DEC 11 2009
.SYNOPSIS...
COLD HIGH PRESSURE WILL BUILD INTO THE REGION TODAY... AND LINGER
THROUGH SATURDAY. A LOW PRESSURE SYSTEM WILL MOVE UP THE SOUTHEAST
COAST SATURDAY NIGHT AND SUNDAY.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 945 AM FRIDAY...
A RATHER COLD START TO THE DAY AS MIN TEMPERATURES THIS MORNING WERE
IN MID 20S ACROSS MUCH OF THE FORECAST AREA. THE EXCEPTION WAS ACROSS
THE SE TIER WHERE GREATER CLOUD COVER AND A STEADY 6 TO 10 KT WIND
KEPT TEMPERATURES IN THE LOWER 30S. WHATS EVEN MORE IMPRESSIVE IS THE
SINGLE DIGIT DEWPOINTS ACROSS THE AREA...A TRUER SIGN OF THE POLAR
AIRMASS IN PLACE.
ONLY QUESTION FOR TODAY IS WHETHER THESE THICK MILKY HIGH CLOUDS
WILL STAY AROUND LONG ENOUGH TO INHIBIT ANY MEANINGFUL INSOLATION.
FORECAST MODELS WOULD SUGGEST THAT THEY CERTAINLY WILL AS THE
CAROLINAS REMAIN UNDER THE INFLUENCE STRONG 160 KT SUBTROPICAL JET.
TEMPERATURES HAVE YET TO CLIMB ABOVE FREEZING ACROSS THE CENTRAL
AND WESTERN PIEDMONT. WITH THICKNESSES STARTING OUT AT 1265M...
IN-HOUSE TEMP SCHEME WOULD SUGGEST CURRENT FORECAST HIGHS OF LOWER
40S NORTH TO MID 40S SOUTH ARE A CATEGORY TOO WARM. COMBINED WITH
THE OBSERVED TEMP TREND...DIFFICULT TO IGNORE THESE SIGNALS...SO WILL
LOWER HIGHS TODAY...WITH UPPER 30S NORTHWEST TO LOWER TO MID 40S
SE.
SURFACE HIGH PRESSURE SETTLES OVER NORTH CAROLINA TONIGHT AND THE
AIR MASS WILL BE QUITE DRY. CALM WINDS OVERNIGHT WITH A BRIEF
REPRIEVE IN THE HIGH CLOUDS WILL SUPPORT A COLDER NIGHT COMPARED
TO LAST NIGHT. MIN TEMPERATURES RANGING FROM 20 TO 25...WITH SOME
TEENS POSSIBLE IN NON-URBAN AREAS.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY/...
AS OF 325 AM FRIDAY...
SATURDAY CONTINUES TO BE FORECAST DRY WITH RELATIVELY WEAK WEST FLOW
OVER CENTRAL NORTH CAROLINA AND DEVELOPING ISENTROPIC LIFT
SUPPRESSED TO OUR SOUTH.
MID LEVEL HIGH PRESSURE OFFSHORE SATURDAY NIGHT SLOWLY EXITS TO THE
EAST WHILE SURFACE HIGH PRESSURE ALSO EDGES EAST... BUT CONTINUING
INITIALLY TO NOSE SOUTHEAST INTO THE FOOTHILLS. RAIN IS EXPECTED
BEFORE MIDNIGHT IN THE SOUTH AS WINDS OF 30 TO 40 KNOTS OVERRUN THE
SURFACE DRY AIR MASS. BY SUNRISE SUNDAY EVERYONE SHOULD HAVE
MEASURABLE RAIN... THOUGH SOME AREAS NEAR THE VIRGINIA BORDER MAY
SOMEHOW ESCAPE RAIN OVERNIGHT.
PRECIPITATION STILL FORECAST TO BE RAIN. THE AIR MASS WILL SATURATE
FROM THE TOP DOWN AND A VERY DRY SURFACE AIR MASS WILL ALLOW
TEMPERATURES TO FALL TO NEAR FREEZING IN PARTS OF THE NORTH DUE
TO EVAPORATIVE COOLING. WARMING ALOFT WILL BE UNDERWAY BUT IT IS
NOT IMPOSSIBLE FOR FREEZING RAIN TO DEVELOP BRIEFLY IN THE
NORTHWEST PIEDMONT... OR EVEN A FEW FLAKES OF SNOW. HOWEVER 32
DEGREES IS ALSO THE MELTING POINT AND DO NOT EXPECT AIR
TEMPERATURES TO DROP LOWER AS LATENT HEAT RELEASE KEEPS
TEMPERATURES IN THE LOWER 30S IN THIS AREA. AIR TEMPERATURES WILL
HAVE BEEN ABOVE FREEZING FOR TWELVE HOURS OR SO. AT THIS TIME DO
NOT SEE ANY ACCUMULATION OF ICE... EVEN IN THE GRASS OR TREES. AS
WARMING ALOFT CONTINUES... TEMPERATURES IN THE NORTH WILL RISE TO
THE MID 30S BEFORE DAWN WITH TEMPERATURES AT 3000 FEET APPROACHING
THE MID 40S. IF FREEZING RAIN WERE TO BRIEFLY OCCUR IT WOULD BE IN
NAME ONLY WITH ACTUAL ICE ACCUMULATION DIFFICULT TO IMPOSSIBLE TO
FIND. HOWEVER AS ALWAYS... STAY TUNED TO THE LATEST FORECASTS AND
THINKING AS THIS EVENT APPROACHES.
RAIN TO CONTINUE INTO THE AFTERNOON SUNDAY... NOT ENDING UNTIL
EVENING APPROACHES IN THE EAST.
AFTERNOON HIGHS 45 TO 50 SATURDAY AND MID 40S NORTHWEST TO MID 50S
EXTREME SOUTHEAST ON SUNDAY. LOW TEMPERATURES SATURDAY NIGHT
OCCURRING BEFORE MIDNIGHT... 33 NORTHWEST TO NEAR 40 SOUTHEAST.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 255 AM FRIDAY...
THE COASTAL LOW... DEEP CLOUD COVER... AND PRECIPITATION CHANCES
SHOULD PULL AWAY FROM THE MID ATLANTIC COAST SUNDAY NIGHT. THE
EXPECTED CLEARING SKIES AND LIGHT STEERING FLOW (ASSOCIATED WITH A
WEAK SURFACE RIDGE) MAY PROMOTE THE DEVELOPMENT OF PATCHY FOG OR LOW
STRATUS BY MONDAY MORNING. LOWS GENERALLY 35 TO 40 DEGREES.
MONDAY THROUGH THURSDAY: EXPECT A BRIEF WARM UP MONDAY AHEAD OF THE
NEXT TROUGH ALOFT... ATTENDANT SURFACE COLD FRONT... AND CHANCE OF
SHOWERS PROJECTED TO CROSS CENTRAL NC TUESDAY OR TUESDAY NIGHT. THE
MILDER TEMPERATURES IN THE UPPER 50S TO LOWER 60S MONDAY (AND
PERHAPS AGAIN TUESDAY PENDING THE FRONTAL PASSAGE TIMING) WILL
TURN COOLER BEHIND THE FRONT... WITH HIGHS IN THE MIDDLE 40S TO
LOWER 50S EXPECTED ON WEDNESDAY AND THURSDAY.
&&
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
AS OF 625 AM FRIDAY...
HIGH PRESSURE AND VFR CONDITIONS EXPECTED THROUGH THE 12Z TAF
PERIOD. NORTHWEST TO WEST SURFACE WINDS BETWEEN 6 AND 11 KTS (WITH
OCCASIONAL 15-20 GUSTS) TODAY... WILL BECOME CALM AS THE RIDGE AXIS
SETTLES DIRECTLY OVERHEAD TONIGHT.
VFR WILL PREVAIL OWING TO CONTINUED HIGH PRESSURE RIDGING THROUGH
SATURDAY. INITIALLY HIGH-MID LEVEL CEILINGS WILL LOWER TO LIFR/IFR
RANGE SATURDAY NIGHT AND CONTINUE THROUGH SUNDAY... IN RESPONSE TO
THE DEVELOPMENT AND PASSAGE OF A RAIN-PRODUCING LOW PRESSURE SYSTEM
ALONG THE SOUTHEAST US COAST. WHILE THE RAIN AND CEILINGS SHOULD
EXIT BY SUNDAY NIGHT... A LIGHT WIND AND FRESHLY SATURATED SOIL
COULD LEAD TO THE DEVELOPMENT OF FOG OR LOW STRATUS LATE SUNDAY
NIGHT AND MONDAY MORNING. HIGH PRESSURE AND VFR CONDITIONS EXPECTED
AGAIN FOR THE EARLY PART OF THE UPCOMING WEEK.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...CBL
NEAR TERM...CBL
SHORT TERM...RLH
LONG TERM...MWS
AVIATION...MWS
