FXUS62 KRAH 011726
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1225 PM EST TUE DEC 01 2009
.SYNOPSIS...
HIGH PRESSURE WILL EXTEND ACROSS THE AREA THIS AFTERNOON...AND THEN
MOVE OFFSHORE TONIGHT. A STRONG LOW PRESSURE SYSTEM OVER THE GULF
COAST REGION WILL MOVE NORTHEAST LATE WEDNESDAY AND WEDNESDAY
NIGHT...BRINGING WIDESPREAD RAIN AND GUSTY WINDS.
&&
.NEAR TERM /TODAY AND TONIGHT/...
AS OF 1110 AM TUESDAY...
THIS AFTERNOON...
SURFACE RIDGE AXIS EXTENDING SW-NE ACROSS THE FORECAST AT 10 AM WILL
DRIFT SLOWLY EAST THIS AFTERNOON. STARTED OUT MUCH COOLER THAN
ANTICIPATED WITH MANY LOCALES IN THE UPPER 20S TO LOWER 30S. WHILE
BULK OF COLD AIR WILL REMAIN TO OUR NORTH...MODEST COLD AIR
ADVECTION IN THE LOWEST 5000FT WILL RESULT IN MAX TEMPS A TAD COOLER
THAN EARLIER FORECAST. MID 50S NW-FAR NORTH TO NEAR 60 FAR SE. -WSS
TONIGHT...
SURFACE HIGH SHIFTS OFFSHORE LATER THIS EVENING. MEANWHILE...THE
VIGOROUS CLOSED CYCLONE OVER TEXAS WILL INDUCE SFC CYCLOGENESIS OVER
THE NW GULF OF MEXICO. AS THE SURFACE WAVE LIFTS NORTH INTO
AL/MS...MOISTURE AND OVERRUNNING PRECIP WILL SPREAD NORTH FROM THE
GULF COAST STATES...ACROSS THE SAVANNAH RIVER VALLEY...AND ON UP
INTO THE CAROLINAS THROUGH DAYBREAK WEDNESDAY. SOUTHERN PORTIONS OF
CENTRAL NC WILL REMAIN ON THE FAR NORTHERN PERIPHERY OF THIS
EXPANSIVE RAIN SHIELD WITH RESIDUAL LOW-LEVEL CONTINENTAL DRY
AIRMASS REQUIRING ADDITIONAL TIME TO SATURATE AND SUPPORT MEASURABLE
RAINFALL. WILL KEEP SLIGHT CHANCE POPS PRIOR TO 12Z WEDNESDAY
CONFINED TO SOUTHERN PIEDMONT AND SANDHILLS. OTHERWISE...A FEW
SPRINKLES POSSIBLE WITH CONSIDERABLE MID AND HIGH CLOUD THICKENING
OVERNIGHT WITH OVERRUNNING STRATOCUMULUS DEVELOPING TOWARDS
DAYBREAK. LOWS IN THE MID 30S TO AROUND 40...COOLEST IN THE NE WHERE
LATER ARRIVAL OF THICKER CLOUD SHIELD WILL ALLOW FOR BETTER
RADIATIONAL COOLING THIS EVENING.
&&
.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
AS OF 300 AM TUESDAY...
A SIGNIFICANT STORM SYSTEM WILL AFFECT THE REGION WEDNESDAY THROUGH
WEDNESDAY NIGHT... BRINGING WIDESPREAD MODERATE TO HEAVY RAIN
RAINSHOWERS... BLUSTERY CONDITIONS... AND A SEVERE WEATHER THREAT.
FOR WEDNESDAY/WEDNESDAY NIGHT:
OVERVIEW...
THE LATEST MODEL GUIDANCE CONTINUES TO INDICATE A MILLER "A" TYPE
CYCLOGENESIS EVENT WITH THE SURFACE LOW TRACKING NE IN CONJUNCTION
WITH THE DAMPENING BUT NEGATIVE TILED KICKER SHORTWAVE TROUGH
THROUGH THE LOWER MS VALLEY AND EASTERN TN ON WEDNESDAY. THE STORM
SYSTEM BEGINS TO ACCELERATE WEDNESDAY EVENING AND OVERNIGHT...RACING
NE INTO WESTERN NY BY DAYBREAK THURSDAY AS IT GETS PICKED BY THE
DIGGING NORTHERN STREAM ENERGY OVER THE NORTHERN AND CENTRAL PLAINS.
MODEL DIFFERENCES...
IT IS WITH THIS PHASING THAT MODEL DIFFERENCES BEGIN TO ARISE...WITH
THE GFS A FAST OUTLIER...DRY SLOTTING THE REGION AS EARLY AS 00Z
THU...WITH THE SLOWER ENVELOPE OF MODELS OF THE NAM AND EC SOME 6 TO
9 HOURS SLOWER. DESPITE THE GFS BEING AS OUTLIER...THE FASTER
SOLUTION IS CERTAINLY PLAUSIBLE GIVEN THE STRENGTH/AMPLITUDE
OF THE UPSTREAM STREAM. BUT FOR NOW WILL CONTINUE WITH THE
SLOWER TIMING...BUT THIS TIMING DISCREPANCY WILL NEED TO BE
EVALUATED AND SCRUTINIZED FURTHER WITH THE UPCOMING 12Z/01 MODEL RUN
AS THE POTENTIAL FOR A HIGH IMPACT/SEVERE WEATHER EVENT IS POSSIBLE
DURING THIS IMPORTANT TIME PERIOD.
IMPACTS...
A 60 TO 70KT WARM AIR CONVEYOR BELT WILL DELUGE THE REGION WITH
TROPICAL MARITIME AIR ON WEDNESDAY. RESIDUAL LOW-LEVEL DRY AIR
FORMERLY DEPOSITED BY THE OFFSHORE SURFACE HIGH WILL UNDERGO
COOLING AS IT PRECIPITATES INTO THE AIRMASS...ESTABLISHING A
VERY SHALLOW IN-SITU CAD AIRMASS ACROSS CENTRAL NC. DUE TO THE
STRONG WAA OF TROPICAL AIRMASS AND THE SHALLOW RESIDUAL COOL
POOL...TEMPERATURES SHOULD STILL BE ABLE TO RISE DURING THE
DAYTIME HOURS...BUT MUCH SLOWER IN THE NW PIEDMONT.
AFTERNOON TEMPS IN THE LOWER TO MID 50S NW TO MID 60S SE.
STRONGER/DEEPER LAYER ASCENT SPREADS ACROSS THE AREA LATE
WEDNESDAY AFTERNOON AND INTO THE EVENING AS DAMPENING
S/W TROUGH LIFTS ACROSS THE AREA...WITH MODELS OFFERING
SOME SIGNALS OF DUAL UPPER JET JUXTAPOSITION ATTEMPTING
TO CONGLOMERATE ACROSS SE NC. COMBINED WITH A CONVECTIVE
MODE OF PRECIP AS LOW-LEVEL FORCING ARRIVES WITH SURFACE
COLD FRONT PASSAGE...MUCH OF CENTRAL NC COULD SEE RAINFALL AMOUNTS
OF 1 TO 2 INCHES.
AS WEDGE BOUNDARY LIFTS NORTH INTO VA...TEMPS AND DEWPOINTS RISE
WELL INTO THE 60S WITH ALL OF CENTRAL NC WELL IN THE WARM SECTOR. IT
IS AT THIS TIME PERIOD THAT THE AFOREMENTIONED MODEL DIFFERENCES ARE
CRITICAL...AS THE SLOWER NAM SOLUTION ALLOWS A LONGER PERIOD TO
ADVECT A TRUE MARITIME TROPICAL AIRMASS WITH SFC BASED INSTABILITY
OF 500 TO 700 J/KG INTO CENTRAL AND EASTERN NC....WHILE THE GFS AND
EC KEEP THE SFC BASED INSTABILITY OFFSHORE. IF THE SFC BASE
INSTABILITY CAN DEVELOP...THE STRONG KINEMATICS WITH GOOD LOW-LEVEL
VEERING WILL RESULT IN A THREAT OF STRONG DAMAGING WINDS(WITHIN
A CONVECTIVE LINE SEGMENT) AND ISOLATED TORNADOES (WITH DISCRETE
SUPERCELLS). TIMING REMAINS DIFFICULT GIVEN THE MODEL DIFFERENCES.
THE FASTER GFS WOULD SUGGEST A SEVERE THREAT FROM NOON TO
TO 8PM...WITH THE SLOWER NAM FAVORING 6PM TO 2AM.
FOR THURSDAY: ANY LINGERING SHOWERS SHOULD QUICKLY EXIT BY
DAYBREAK. BRIEF GRADIENT W-NW GUSTINESS POSSIBLE FIRST HALF OF THE
DAY AS HIGH BUILDS INTO THE AREA FROM THE WEST. HIGHS NEAR 60 NW TO
MID 60S SE.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 245 AM TUESDAY...
THURSDAY NIGHT THROUGH FRIDAY NIGHT: AS A MID LEVEL POLAR LOW DIGS
ACROSS THE UPPER MIDWEST THROUGH FRIDAY...A LARGE TROUGH WILL BE
LOCATED ACROSS MUCH OF THE EASTERN 2/3RDS OF THE COUNTRY. AS SURFACE
HIGH PRESSURE BUILDS IN FROM THE WEST...THE SURFACE FRONT WILL
CONTINUE TO MOVE OFFSHORE THURSDAY NIGHT. WITH INCREASING
SUBSIDENCE/DOWN SLOPE LOW LEVEL FLOW IN PLACE...CLOUDS SHOULD
GRADUALLY CLEAR OUT AND ALLOW OVERNIGHT LOWS TO FALL INTO THE MID
30S TO UPPER 40S. CONTINUED COLD AIR ADVECTION ON FRIDAY WILL RESULT
IN THICKNESS VALUES RANGING FROM 1315-1325M. ALSO...AMPLE HIGH
CLOUDS WILL BE IN PLACE ACROSS THE REGION AS A STRONG JET REMAINS
OVER THE REGION. AS A RESULT...TEMPS WILL BE ON THE COOL SIDE ON
FRIDAY...GENERALLY IN THE 50S AREAWIDE.
SATURDAY THROUGH SATURDAY NIGHT: AS A SHORT WAVE ROUNDS THE BASE OF
THE BROAD TROUGH THAT IS IN PLACE ACROSS THE EASTERN UNITED
STATES...BOTH THE ECMWF AND GFS ARE SHOWING A SURFACE LOW DEVELOPING
OFF THE NORTH CAROLINA COAST. GFS SHOWS A DEEPER LOW DEVELOPING AND
THEREFORE RESULTS IN SIGNIFICANTLY MORE ATLANTIC MOISTURE MOVING
INTO CENTRAL NORTH CAROLINA...ESPECIALLY THE NORTHERN PORTIONS OF
THE CWA. AM A LITTLE SKEPTICAL ABOUT THE AMOUNT OF QPF THE GFS
GENERATES ACROSS THE REGION...GIVEN THE LOCATION OF THE LOW BEING AS
FAR OFFSHORE AS THE MODEL PROGS IT TO BE. NEVERTHELESS...GIVEN THE
SURFACE LOW AND STRONG UPPER SUPPORT (STRONG UPPER JET CORE REMAINS
OVER THE REGION THROUGH AT LEAST SATURDAY AFTERNOON)...MEASURABLE
PRECIP WILL BE POSSIBLE ESPECIALLY OVER THE NORTHERN PIEDMONT AND
COASTAL PLAIN. ON ANOTHER NOTE...PRELIMINARY SOUNDINGS/THICKNESS
VALUES WOULD INDICATE A CHANCE FOR WET SNOW ACROSS THE FAR NORTHWEST
PORTION OF THE CWA. HOWEVER...GIVEN THE GFS HAS ONLY RECENTLY BEGUN
TO HINT AT THIS SCENARIO AND THE ECMWF HAS BEEN FAIRLY CONSISTENT
WITH NOT DEEPENING THE LOW AS MUCH AND ALSO THAT THIS IS THE DAY 5
TIME FRAME...WILL MAINTAIN A SLIGHT CHANCE OF RAIN OVER THE
EAST/NORTHWEST CWA SATURDAY. THIS WILL HAVE TO BE MONITORED CLOSELY
BY FUTURE SHIFTS. LOWS WILL GENERALLY BE IN THE UPPER 20S TO LOWER
30S... AND HIGHS IN THE MID 40S TO LOWER 50S.
SUNDAY THROUGH MONDAY: A CHILLY SURFACE HIGH WILL DOMINATE THROUGH
THIS PART OF THE FORECAST...WITH DRY AND PARTLY CLOUDY CONDITIONS
EXPECTED...AS WELL AS BELOW NORMAL TEMPERATURES.
&&
AVIATION /18Z TUESDAY THROUGH SUNDAY/...
AS OF 1220 PM TUESDAY...
HIGH PRESSURE EXTENDING WEST-TO-EAST ACROSS THE AREA THIS AFTERNOON
WILL DRIFT EAST TONIGHT. NEAR SURFACE FLOW WILL BE LIGHT AND
VARIABLE THIS AFTERNOON...BECOMING S-SE LESS THAN 10KTS TOWARD
MIDNIGHT.
AFTER MIDNIGHT...SE FLOW JUST ABOVE THE SURFACE WILL INCREASE AS
PRESSURE PATTERN TIGHTENS BETWEEN THE HIGH AND AN ABNORMALLY STRONG
LOW PRESSURE THAT WILL LIFT NE ACROSS THE LOWER MS VALLEY. THIS SE
FLOW WILL ADVECT ATLANTIC MOISTURE INTO CENTRAL NC AFTER
05Z...RESULTING IN WIDESPREAD IFR/LIFR CEILING PRIOR TO 6 AM WITH
PATCHES OF LIGHT RAIN OCCURRING OVER THE SANDHILLS AND THE
SOUTHERN/WESTERN PIEDMONT AROUND DAYBREAK. LOW LEVEL WIND SHEAR WILL
EXIST AS SURFACE FLOW WILL BE E-NE AT 10KTS OR LESS WHILE THE FLOW
BETWEEN 1000-2000FT WILL BE SE 35-40KTS. THE LOW LEVEL WIND SHEAR
WILL PERSIST THROUGH 18Z WEDNESDAY...LIKELY THROUGH 22Z WEDNESDAY AT
KINT AND KGSO.
RAIN WILL BECOME WIDESPREAD ACROSS THE SE HALF OF CENTRAL NC
WEDNESDAY MORNING AND OVER THE ENTIRE AREA DURING THE AFTERNOON AS
VERY MOIST AND WARM AIR IS LIFTED OVER THE SHALLOW STABLE LAYER NEAR
THE SURFACE. RAIN MAY BE HEAVY AT TIMES IN VICINITY OF KINT AND KGSO
IN THE AFTERNOON DUE TO THE UPSLOPE COMPONENT OF THE LOW LEVEL WIND.
THE STRONG LOW PRESSURE SYSTEM WILL LIFT RAPIDLY NE ACROSS THE TN
AND OH VALLEYS WEDNESDAY NIGHT. THIS SYSTEM WILL CONTINUE TO SPREAD
MOIST AND SLIGHTLY UNSTABLE AIR INTO CENTRAL NC WED NIGHT. NEAR
SURFACE WINDS WILL BECOME SLY AND INCREASE TO AROUND 20 MPH WITH
GUSTS 35 MPH PROBABLE. THE PRECIP TYPE WILL BECOME MORE SHOWERY WITH
A BAND OF HEAVY SHOWERS AND ISOLATED STRONG/SEVERE THUNDERSTORMS
CROSSING THE REGION BETWEEN 7 PM AND 2 AM. WIND GUSTS WITHIN THIS
LINE MAY EXCEED 60 MPH.
THE LOW PRESSURE SYSTEM WILL EXIT THE REGION EARLY THU. STRONG
SUBSIDENCE ON THE BACK SIDE OF THE LOW WILL INDUCE RAPID CLEARING
FROM SOUTHWEST-TO-NORTHEAST TOWARD DAYBREAK THU. VFR CONDITIONS WILL
RETURN THU WITH BLUSTERY WLY WINDS LIKELY THU MORNING.
VFR CONDITIONS WILL PERSIST THU NIGHT THROUGH FRI NIGHT. A
DEVELOPING AREA OF LOW PRESSURE OFFSHORE SATURDAY WILL SPREAD MVFR
CEILINGS INTO THE VICINITY OF KRDU AND KRWI. OTHERWISE VFR EXPECTED
SATURDAY INTO SUNDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...CBL
NEAR TERM...WSS/CBL
SHORT TERM...CBL
LONG TERM...KRR
AVIATION...WSS
