FXUS62 KRAH 052239
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
530 PM EST SAT DEC 5 2009
.SYNOPSIS...
LOW PRESSURE CENTERED OFF THE VIRGINIA COAST THIS EVENING WILL
INTENSIFY AND TRACK NORTHEASTWARD OFFSHORE THE NEW ENGLAND COAST
TONIGHT. MEANWHILE... COLD HIGH PRESSURE WILL BUILD IN FROM THE WEST
AND LINGER THROUGH SUNDAY NIGHT.
&&
.NEAR TERM /THROUGH SUNDAY NIGHT/...
AT 530 PM SATURDAY...
THE LATEST MOBILE MICRO RAIN RADARS (MRR) DATA FROM CHAPEL HILL AND
ASHEBORO INDICATE THE FREEZING LEVEL CONTINUED TO REMAIN WELL
ABOVE 5000K FEET AT 530 PM. LOCAL RADARS ALSO INDICATE ONE LAST AREA
OF LIGHT RAIN/DRIZZLE PUSHING EAST ACROSS THE NORTHERN PIEDMONT OF
NC. PRECIPITATION FALL VELOCITY INDICATED SATURATION CONTINUES TO
BE SHALLOW ON THE TAIL END OF THIS PRECIP EVENT... AND WILL NOT
EXTEND INTO DENDRITIC SNOW GROWTH ZONE BEFORE ENDING. SINCE THE
FREEZING LEVEL HAS ESSENTIALLY REMAINED UNCHANGED AND IS EXPECTED TO
FALL AFTER THE LIGHT PRECIPITATION EXITS OUR REGION... WE NO LONGER
EXPECT ANY MIXING OR CHANGE OVER TO LIGHT SNOW BEFORE ENDING. WE
WILL REMOVE THIS CHANCE FROM THE FORECAST.
THE DEW POINTS REMAIN 35+ EVEN IN THE WINSTON-SALEM AREA AT 500 PM.
RAPID CLEARING FROM THE WEST SHOULD ARRIVE IN THE NEXT FEW HOURS.
THE SURFACE WINDS WERE REMAINING UP NEAR 10KT THROUGHOUT THE REGION.
THE STREETS AND ROADS SHOULD HAVE PLENTY OF TIME TO DRY BEFORE THE
TEMPERATURES/DEW POINTS CRASH LATER THIS EVENING. AT THE CURRENT
TIME... A PROBLEM WITH BLACK ICE DEVELOPMENT IS NOT ANTICIPATED.
WE WILL UPDATE THE HAZARDOUS WEATHER OUTLOOK AS WELL.
NO OTHER CHANGES AT THIS TIME. -BADGETT
PREVIOUS DISCUSSION...
AS OF 255 PM SATURDAY...
WHILE SHALLOW SATURATION SHOULD MAINTAIN PERIODS OF LIGHT RAIN AND
DRIZZLE THROUGH THIS EVENING... IT APPEARS THAT THE ARRIVAL OF THE
MID LEVEL DRY AIR AND DEPARTING STRONGEST AND DEEPEST FORCING FOR
ASCENT MAY REDUCE THE THREAT OF A MIX OR CHANGEOVER TO SNOW. THE
THREAT IS NOT NON-EXISTENT... HOWEVER... MAINLY ALONG THE NC
COUNTIES ADJACENT TO THE VA BORDER. THAT WILL BE WHERE THE SATURATED
LAYER SHOULD BE DEEPEST/COLDEST ON THE SOUTHERN PERIPHERY OF THE
PROGRESSIVE DEFORMATION BAND OVER THE NORTHERN NC MOUNTAINS AND
FOOTHILLS... WHICH IS EXPECTED TO SLIDE EASTWARD ALONG THE VA
BORDER. LITTLE (ON GRASSY AND ELEVATED SURFACES SUCH AS CAR TOPS) TO
NO ACCUMULATION EXPECTED... IF ANY FLAKES FLY AT ALL... GIVEN THE
RELATIVELY UNFAVORABLE CLOUD MICROPHYSICS.
WITH COLDER TEMPERATURES SET TO ARRIVE OVERNIGHT... BLACK ICE WILL
BECOME A CONCERN. WILL COVER THIS THREAT IN THE HAZARDOUS WEATHER
OUTLOOK... AND DEFER TO THE EVENING SHIFT TO ASSESS THE POTENTIAL
FOR AN ADVISORY ONCE IT IS BETTER DETERMINED HOW MUCH LINGERING
MOISTURE REMAINS ON AREA ROADWAYS.
TONIGHT: CLEARING AND COLDER IN THE WAKE OF THE DEPARTING COASTAL
LOW... WITH CAA-DRIVEN OVERNIGHT LOWS BETWEEN 26 DEGREES TO AROUND
FREEZING... WARMEST SOUTHEAST.
SUNDAY AND SUNDAY NIGHT: CHILLY HIGH PRESSURE WILL SETTLE INTO THE
MID ATLANTIC STATES AND DOMINATE THIS PERIOD. HIGH TEMPERATURES
MAINLY IN THE MIDDLE TO UPPER 40S EXPECTED... OR ABOUT A DEGREE
COOLER THAN WHAT PROJECTED LOW LEVEL THICKNESSES IN THE 1300 TO 1310
METER RANGE WOULD SUGGEST GIVEN LOW MIXING HEIGHTS AND A WARM
SUBSIDENCE INVERSION ABOVE. (IE. THE THICKNESSES ARE INFLATED BY
UNATTAINABLE WARMTH WITHIN THE SUBSIDENCE INVERSION/ABOVE THE
BOUNDARY LAYER). AFTER A SUNNY START... CIRRUS OVER THE SOUTHERN AND
CENTRAL PLAINS STATES THIS AFTERNOON WILL STEADILY SPREAD EASTWARD
AND PROVIDE FOR PARTLY CLOUDY CONDITIONS BY SUNDAY NIGHT. WEAK
ISENTROPIC LIFT -- ATOP THE AFOREMENTIONED MID ATLANTIC SURFACE
RIDGE -- MAY YIELD MVFR STRATUS AND RESULTANT MOSTLY CLOUDY SKIES
OVER THE SOUTHERN COASTAL PLAIN AND SANDHILLS BY MONDAY MORNING.
TEMPERATURES SHOULD FALL QUICKLY AFTER SUNSET GIVEN INITIALLY GOOD
RADIATIONAL COOLING CONDITIONS (ASIDE FROM THE INCREASED CIRRUS)...
WITH OVERNIGHT LOWS IN GENERALLY IN THE UPPER 20S TO LOWER 30S.
TEMPERATURES MAY RISE A BIT TOWARD MORNING OWING TO DOWNWARD L/W IR
ASSOCIATED WITH THE POSSIBLE STRATUS.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
AS OF 220 PM...
MONDAY A MIDWEST LOW PRESSURE SYSTEM WILL APPROACH AND MOVE THROUGH
MICHIGAN WHILE SURFACE HIGH PRESSURE LINGERS OFF THE NORTH CAROLINA
COAST. THE GFS IS STRONGEST WITH THE PRESSURE GRADIENT ACROSS NORTH
CAROLINA MONDAY AND DEVELOPS A SIGNIFICANT 925 MILLIBAR TROUGH OVER
THE WESTERN PIEDMONT AT MIDDAY... MOVING IT TO THE COASTAL PLAIN AT
SUNSET WHILE RETAINING A LEE SIDE TROUGH IN THE FOOTHILLS.
ISENTROPIC LIFT IS QUITE IMPRESSIVE ON THE GFS. HOWEVER THERE IS
MINIMAL SUPPORT FROM THE ECMWF AND CANADIAN FOR THIS FEATURE. I HAVE
FOUND THE GFS TO BE FREQUENTLY OVERDONE IN LOW LEVEL WINDS... BUT
STILL SUPERIOR IN RELATION TO THE NAM MODEL. THUS WILL ADD A SLIGHT
CHANCE FOR MEASURABLE RAIN TO MONDAY. SHOULD DRIZZLE OR LIGHT RAIN
DEVELOP TEMPERATURES WILL BE DAMPENED A BIT AND HAVE DROPPED
AFTERNOON HIGHS A FEW DEGREES... TO 49 TO 53.
NORTH FLOW MONDAY NIGHT AROUND SURFACE HIGH PRESSURE WILL BEGIN TO
SHUNT LOW LEVEL MOISTURE TO THE SOUTH. NORTH PARTS WILL HAVE BEST
RADIATIONAL COOLING CONDITIONS AND AS MUCH AS A TEN DEGREE GRADIENT
IN TEMPERATURES NORTH TO SOUTH POSSIBLE... WITH MOST LOW
TEMPERATURES IN THE 30S.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
AS OF 220 PM...
A STRONG UPPER LEVEL SHORT WAVE WILL EXIT THE ROCKIES TUESDAY...
REACHING THE EASTERN PARTS OF THE OKLAHOMA PANHANDLE BY SUNSET. A
STRONG SURFACE LOW IN CLOSE PROXIMITY TO THE UPPER TROUGH WILL BRING
STRONG SOUTH RETURN FLOW AHEAD OF THE LOW INTO THE TENNESSEE VALLEY
AND THE SOUTHEAST. RIDGING OVER THE EAST COAST HOLDS STRONG AND
WINDS RELATIVELY LIGHT OVER NORTH CAROLINA TUESDAY. THUS MOISTURE
ADVECTION AND DYNAMICS SHOULD BE RELATIVELY WEAK AND WILL CONTINUE
TO LIMIT SLIGHT RAIN CHANCES TO THE WESTERN PIEDMONT TUESDAY.
AFTERNOON HIGHS 50 TO 55.
THE UPPER TROUGH IS FORECAST TO REACH MISSOURI MIDNIGHT TUESDAY
NIGHT AND OVERRUNNING SOUTH FLOW OVER THE WEAKENING AND RETREATING
SURFACE HIGH SHOULD GENERATE RAIN IN CENTRAL NORTH CAROLINA
OVERNIGHT. WARMING ALOFT MAY BE ABLE TO WORK TO THE SURFACE CAUSING
LOW TEMPERATURES TO OCCUR WELL BEFORE SUNRISE. LOW TEMPERATURES 38 TO
45. RAINFALL OF ONE QUARTER TO ONE HALF INCH POSSIBLE OVERNIGHT.
STRONG WARMING ALOFT DURING THIS EVENT AND AT THIS TIME
PRECIPITATION EXPECTED TO BE ALL RAIN. THE ONLY POSSIBLE RISK WOULD
BE FOR INITIAL RAINS TO COOL TEMPERATURES TO FREEZING FOR A BRIEF
PERIOD OF FREEZING RAIN OF LITTLE TO NO CONSEQUENCE. THIS IS NOT
EXPECTED... BUT NOT ENTIRELY IMPOSSIBLE.
THE GFS IS STRONGEST AT DEPICTING A WEAK MILLER B SECONDARY SURFACE
LOW DEVELOPMENT OVER NORTH CAROLINA OR OFF THE COAST OF VIRGINIA
LATE TUESDAY NIGHT OR WEDNESDAY MORNING... WITH THE INLAND LOW
REMAINING DOMINATE. GIVEN THE LOCATION OF THE UPPER TROUGH THIS IS
ACCEPTED. MODELS IN AGREEMENT IN PUSHING A STRONG DRY SLOT INTO
NORTH CAROLINA BY NOON WEDNESDAY...SHUTTING DOWN PRECIPITATION IN
SPITE OF THE SURFACE TROUGH STILL BEING OVER CENTRAL NORTH CAROLINA.
WEDNESDAY HIGH TEMPERATURES NEAR 50 NORTHWEST TO MID 60S SOUTHEAST.
SURFACE HIGH PRESSURE OVER THE MIDWEST WEDNESDAY NIGHT WILL ADVANCE
EAST ON STRONG UPPER LEVEL WEST FLOW... REACHING THE EAST COAST
FRIDAY. THE 12Z ECMWF AND THE LATEST GFS ARE IN AGREEMENT IN
BRINGING AN UPPER LEVEL SHORT WAVE INTO THE OHIO VALLEY
SATURDAY... BUT SURFACE FEATURES ARE SIGNIFICANTLY DIFFERENT...
THOUGH BOTH MANAGE TO GENERATE RAINFALL FRIDAY NIGHT AND SATURDAY.
ACCEPTING THIS SOLUTION FOR NOW... BUT WITH TIMING OF THE EVENT
SUSPECT THIS FAR OUT IN TIME IN A FAST FLOW PATTERN.
AFTERNOON HIGHS THURSDAY THROUGH FRIDAY IN THE UPPER 40S TO MID 50S.
LOW TEMPERATURES 35 TO 45 WEDNESDAY NIGHT. SURFACE HIGH PRESSURE AND
A DRY AIR MASS WITH THICKNESSES BELOW 1300 METERS WILL DROP LOW
TEMPERATURES INTO THE UPPER 20S TO LOW 30S THURSDAY NIGHT. CLOUDS
AND SOUTH RETURN FLOW WILL WARM LOW TEMPERATURES FRIDAY NIGHT TO
THE MID 30S TO LOWER 40S.
&&
.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
AS OF 100 PM SATURDAY...
THE PASSAGE OF AN UPPER LEVEL DISTURBANCE COMBINED WITH MOIST
SOUTHEASTERLY FLOW FROM THE ATLANTIC WILL RESULT IN IFR/LIFR
CONDITIONS AT ALL CENTRAL NORTH CAROLINA TERMINAL SITES THROUGH
THE EARLY TO MID AFTERNOON. AS COLD AIR RUSHES INTO THE REGION
THROUGH THE DEPTH OF THE ATMOSPHERE... THE RAIN MAY MIX WITH OR
CHANGE OVER TO SNOW (WITH ASSOCIATED REDUCED VISIBILITIES) FOR A
FEW HOURS (MAINLY AT TRIAD TERMINALS AND PERHAPS AS FAR EAST AS
RDU AND RWI). PRECIPITATION SHOULD END WITH A RETURN TO VFR FROM
SOUTHWEST TO NORTHEAST IN THE 22Z TO 04Z/5TH TIME FRAME... AS COLD
BUT DRY HIGH PRESSURE BUILDS INTO THE REGION FROM THE WEST TONIGHT
AND LINGERS THROUGH SUNDAY.
LOOKING BEYOND 18Z SUNDAY: THERE WILL BE ANOTHER CHANCE OF MVFR
CONDITIONS AND A LITTLE LIGHT RAIN OR DRIZZLE... MAINLY AT EASTERN
TERMINALS... AHEAD OF A WEAKER STORM SYSTEM ON MONDAY. AFTER A
RETURN TO VFR FOR MONDAY NIGHT AND TUESDAY... EXPECT LIFR/IFR
CONDITIONS AND A COLD RAIN ASSOCIATED WITH A STRONGER STORM SYSTEM
TUESDAY NIGHT AND WEDNESDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...BADGETT/MWS
NEAR TERM...BADGETT/MWS
SHORT TERM...RLH
LONG TERM...RLH
AVIATION...MWS
