FXUS62 KRAH 120856
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
355 AM EST SAT DEC 12 2009
.SYNOPSIS...
COLD HIGH PRESSURE WILL LINGER OVER THE REGION TODAY. A LOW PRESSURE
SYSTEM WILL MOVE UP THE SOUTHEAST COAST TONIGHT AND SUNDAY.
&&
.NEAR TERM /THROUGH SUNDAY/...
AS OF 300 AM...
LITTLE CHANGE.
HIGH CLOUDINESS KEPT MOST OF CENTRAL NORTH CAROLINA IN THE 30S
FRIDAY. THE POTENTIAL IS THERE FOR A REPEAT... WITH THE THICKEST
CLOUDS OVER SOUTH PARTS. HAVE DROPPED AFTERNOON TEMPERATURES A FEW
DEGREES... ESPECIALLY IN THE SOUTH. STILL FORECASTING HIGH
TEMPERATURES IN THE LOW TO MID 40S... BUT 30S WILL RULE IN MANY
LOCATIONS THROUGH THE MORNING HOURS AFTER SUNRISE.
THE THINKING ON THE RAIN EVENT TONIGHT INTO SUNDAY IS UNCHANGED. THE
USUALLY COLD GFS CONTINUES TO WARM WITH ALMOST EVERY MODEL RUN. IT
STILL LOOKS LIKE EVAPORATIVE COOLING WILL DROP TEMPERATURES TO NEAR
FREEZING IN THE NORTHWEST PIEDMONT BEFORE MIDNIGHT... WITH A WARMING
TREND DURING THE PREDAWN HOURS. NO DEEP COLD SURFACE LAYER SO SLEET
ONLY POSSIBLE FROM EVAPORATIVE COOLING NEAR THE ONSET OF
PRECIPITATION IN THE NORTHWEST AND BRIEF IF IT OCCURS AT ALL.
OTHERWISE A RISK FOR WHAT WOULD BE FREEZING RAIN IN NAME ONLY IN
THE NORTHWEST AT PRECIPITATION ONSET BUT STILL BELIEVE NO GLAZE
WILL DEVELOP... EVEN ON TREES OR GRASS. TEMPERATURES WILL BE ABOVE
FREEZING FOR ABOUT TWELVE HOURS PRIOR TO PRECIPITATION AND SOME
SUNSHINE WILL WARM THE GROUND A BIT. STILL DO NOT SEE ANYTHING BUT
A BRIEF RISK FOR ANYTHING BUT RAIN... AND ONLY NEAR THE ONSET OF
PRECIPITATION IN THE NORTHWEST. WILL CONTINUE TO OMIT THE MENTION
OF ANYTHING BUT RAIN FROM THE FORECAST.
HAVE RAISED RAINFALL AMOUNTS FOR THE EVENT TO ONE TO ONE AND A HALF
INCHES WITH MODELS CONTINUING TO INCREASE LOW LEVEL WIND SPEEDS
(CURRENTLY TO 50 KNOTS IN THE GFS NEAR SUNRISE SUNDAY) WITH GOOD
ISENTROPIC LIFT ON THE LOW LEVEL ISENTROPIC SURFACES. NEARLY
EVERYONE SHOULD HAVE MEASURABLE RAIN BEFORE MIDNIGHT... WITH RAIN
NOT TAPERING OFF IN THE WEST UNTIL EARLY AFTERNOON SUNDAY... AND
RAIN ENDING ACROSS CENTRAL NORTH CAROLINA BEFORE SUNSET SUNDAY.
HIGH TEMPERATURES IN THE MID 40S TODAY... THOUGH THICKER MORE
PERSISTENT CLOUDS COULD MAKE FOR COOLER READINGS. LOW TEMPERATURES
TONIGHT FROM 33 NORTHWEST TO 43 SOUTHEAST. SUNDAY ANOTHER WARM FRONT
WILL PUSH INLAND FROM THE EAST AND ITS EXACT PUSH INLAND IS UNKNOWN.
CURRENTLY HAVE A HUGE SPREAD IN TEMPERATURES WITH LOW TO MID 40S IN
THE NORTHWEST... AND LOW 60S EAST OF INTERSTATE 95... WHICH MAY BE
TOO COOL.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/...
.
AS OF 315 AM...
LOTS OF MOISTURE ON THE GROUND SUNDAY NIGHT BUT THE AIR MASS
BECOMING QUITE DRY JUST OFF THE SURFACE IN NORTHWEST FLOW. ADMIT
TO BEING UNCERTAIN ABOUT THE POSSIBILITY OF FOG SUNDAY NIGHT.
MODEL SOUNDINGS SEEM TO SHOW DRYNESS ALMOST TO THE SURFACE SO WILL
OMIT ANY MENTION OF FOG AT THIS TIME... BUT THIS WILL HAVE TO BE
MONITORED.
OTHERWISE SOME HIGH CLOUDINESS MONDAY AND PERHAPS A FEW CUMULUS
DURING THE AFTERNOON.
LOW TEMPERATURES MID 30S NORTHWEST TO MID 40S SOUTHEAST. HIGH
TEMPERATURES MONDAY UPPER 50S TO MID 60S.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
AS OF 350 AM SATURDAY...
LITTLE CHANGE FROM PREVIOUS FORECAST RATIONALE THIS PERIOD.
MONDAY NIGHT THROUGH TUESDAY NIGHT: A POSITIVELY-TILTED TROUGH ALOFT
-- COMPRISED INITIALLY OF NORTHERN AND SOUTHERN STREAM S/W TROUGHS
-- WILL APPROACH AND CROSS THE REGION THROUGH EARLY WEDNESDAY.
THE ATTENDANT SURFACE COLD FRONT SHOULD CROSS CENTRAL NC DURING
THE DAY TUESDAY. THE ASSOCIATED WARM CONVEYOR BELT ALONG AND AHEAD
OF THE FRONT SHOULD PROVIDE CHANCE TO LIKELY SHOWERS FROM NORTHWEST
TO SOUTHEAST ON TUESDAY... PERHAPS LINGERING IN THE EAST TUESDAY
NIGHT. DESPITE DEWPOINTS INTO THE 50S AND RELATIVELY MILD WAA-DRIVEN
HIGH TEMPERATURES IN THE UPPER 50S TO MIDDLE 60S... PROJECTED
INSTABILITY (OR LACK THEREOF) AND RESULTANT THREAT OF THUNDER IS
MINIMAL.
WEDNESDAY THROUGH FRIDAY: A MODIFIED AND WEAKENED ARCTIC HIGH WILL
EXPAND ACROSS THE EASTERN CONUS THIS PERIOD. WHILE THE NWP MODELS
DEPICT THE STABLE AND DRY SURFACE RIDGE DOMINATING THIS PERIOD... WE
WILL HAVE TO MONITOR THE EVOLUTION OF A NORTHERN STREAM S/W TROUGH
ALOFT INTO THE TN/OH VALLEYS ON FRIDAY... AND POTENTIAL INTERACTION
WITH THE SOUTHERN PORTION OF THE AFOREMENTIONED POSITIVELY-TILTED
TROUGH FROM EARLY IN THE WEEK THAT MAY GET LEFT BEHIND OVER TX.
SOMETHING TO WATCH... BUT ANY ASSOCIATED CYCLOGENESIS LOOKS TO OCCUR
FAR ENOUGH OFFSHORE THE MID ATLANTIC/NEW ENGLAND COASTS TO AFFECT
CENTRAL NC WITH ANY PRECIPITATION. TEMPERATURES GENERALY IN THE
MIDDLE 40S TO AROUND 50 BY DAY... AND GENERALLY MIDDLE TO UPPER 20S
BY NIGHT.
&&
.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
AS OF 110 AM SATURDAY...
THE CONTINUED BUT DEPARTING PRESENCE OF COLD HIGH PRESSURE WILL
MAINTAIN VFR CONDITIONS TODAY. INITIALLY HIGH-MID LEVEL CEILINGS
TODAY WILL LOWER TO LIFR/IFR RANGE WITH OCCASIONAL RAIN AND MAINLY
MVFR VISIBILITY RESTRICTIONS AROUND THE END OF THE 06Z TAF PERIOD...
IN RESPONSE TO THE DEVELOPMENT AND PASSAGE OF A RAIN-PRODUCING LOW
PRESSURE SYSTEM ALONG THE SOUTHEAST US COAST.
OUTLOOK: THESE POOR AVIATION CONDITIONS WILL LIKELY PERSIST THROUGH
MOST OF THE DAY SUNDAY... BEFORE RAIN ENDS AND DEEP LAYER CLEARING
OVERSPREADS THE AREA BY SUNDAY EVENING. CLEARING SKIES... A LIGHT
WIND... AND LINGERING NEAR SURFACE MOISTURE (AUGMENTED BY THE
EXPECTED RAIN-SATURATED SOIL) MAY PROMOTE THE RE-DEVELOPMENT OR
PERSISTENCE OF FOG OR LIFR STRATUS LATE SUNDAY NIGHT AND MONDAY
MORNING. MVFR-IFR CONDITIONS AGAIN PROBABLE MONDAY NIGHT AND
TUESDAY... AHEAD OF THE NEXT FRONTAL SYSTEM EXPECTED TO AFFECT THE
REGION.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...MWS
AVIATION...MWS
