FXUS62 KRAH 012019
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
320 PM EST TUE DEC 01 2009
.SYNOPSIS...
HIGH PRESSURE WILL DRIFT 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 /THROUGH TONIGHT/...
AS OF 230 PM TUESDAY...
TONIGHT...SURFACE HIGH OVER CENTRAL NC SHIFTS OFFSHORE EARLY THIS
EVENING. EXPECT TEMPS TO INITIALLY TUMBLE IN THE DRY AIR MASS THEN
STABILIZE AROUND MIDNIGHT AS MID/HIGH LEVEL CLOUDS BEGIN TO THICKEN
FROM THE SW AHEAD OF STRONG UPPER LEVEL LOW OVER TX. THIS WILL LEAD
TO THE COOLEST MIN TEMPS IN THE FAR NORTHERN PIEDMONT/NORTHERN
COASTAL PLAIN. MINS RANGING MID 40S SOUTH TO MID/UPPER 30S NE.
INCREASING ISENTROPIC LIFT TOWARD DAYBREAK WILL LIKELY LEAD TO THE
DEVELOPMENT OF SPOTTY LIGHT RAIN. DUE TO THE DRY SUB CLOUD
LAYER...INITIAL FIVE HUNDREDTHS OR SO OF MODEL PRECIP WILL GO TO
MOISTENING THE COLUMN. BEST CHANCE FOR MEASURABLE RAIN WILL BE OVER
THE SW COUNTIES. PLAN TO INCREASE POPS TO CHANCE BY 09Z IN THE SW
AND EXTEND THE SLIGHT CHANCE POP NORTHWARD INTO THE
TRIAD...LILLINGTON AND NEWTON GROVE AREAS PRIOR TO DAYBREAK.
&&
.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
AS OF 245 PM TUESDAY...
STILL APPEARS THERE IS A THREAT FOR SEVERE WEATHER LATE WED
WEDNESDAY NIGHT ALONG WITH MODERATE TO HEAVY RAIN THAT COULD LEAD TO
FLASH FLOODING.
MODEL GUIDANCE STILL QUITE IMPRESSIVE WITH THE KINEMATICS AS UPPER
LEVEL DIVERGENCE INCREASES LATE WED/WED NIGHT SUPPLIED BY A DUAL JET
CONFIGURATION. MEANWHILE SE FLOW ABOVE THE SURFACE WILL INCREASE TO
35-40KTS BY EARLY WEDNESDAY. THIS SET-UP WILL LEAD TO ENHANCE
RAINFALL POTENTIAL ALONG OUR WESTERN/NW BORDER DUE TO UPSLOPE
COMPONENT OF WIND. EXPECT RAIN TO BECOME WIDESPREAD DURING THE
MORNING HOURS WITH MODERATE TO LOCALLY HEAVY RAIN PROBABLE IN THE
AFOREMENTIONED WEST-NW. RAIN FALLING THROUGH THE DRY AIR MASS AT
ONSET WILL LIKELY INITIATE A SHORT LIVE INSITU DAMMING EVENT IN THE
PIEDMONT. THIS AIR MASS EXPECTED TO BE RATHER SHALLOW. AS PRECIP
INTENSITY INCREASES...PRECIP DRAG SHOULD PULL WARMER AIR ALOFT TO
THE SURFACE...HELPING TO DIMINISH/DISSIPATE CAD AIR MASS. EXPECT
THIS PROCESS TO BE COMPLETED BY MID AFTERNOON. TEMPS BY LATE WED
SHOULD RANGE FROM LOWER 50S NW TO LOWER 60S SE.
MAY SEE A BRIEF LULL IN PRECIP OVER THE FAR SOUTHERN-SE COUNTIES
AFTER 18Z PERSISTING INTO THE EARLY EVENING AS BEST LIFT OCCURS N-W
OF THIS REGION. AS WARMER AIR MASS TAKES HOLD...EXPECT TO SEE PRECIP
TYPE TRANSITION FROM STRATIFORM RAIN TO SHOWERS.
WEDNESDAY NIGHT...LOW LEVEL JET 60-65KTS PROGGED TO CROSS REGION
DURING THE EVENING AS STRONG UPPER LOW LIFT RAPIDLY NE THROUGH THE
TN/OH VALLEYS...GAINING A NEGATIVE TILT. THIS SHOULD INCREASE MID
LEVEL LAPSE RATES TO NEAR 6 DEG C KM. MEANWHILE NEAR SURFACE SLY
FLOW WILL PULL WARMER/SLIGHT UNSTABLE AIR INTO THE REGION. TEMPS
WILL LIKELY RISE THROUGH THE EVENING HOURS WITH CALENDER DAY HIGHS
OCCURRING AROUND MIDNIGHT. MODELS STILL DISAGREE AS TO THE
EXTENT/MAGNITUDE OF LOW LEVEL INSTABILITY. DURING THE PAST 24
HOURS...NAM DEPICTS BETTER INSTABILITY OVER THE SANDHILLS/COASTAL
PLAIN WITH MLCAPE RANGING FROM 300 J/KG TO NEAR 700 J/KG SOUTH.
MEANHWILE GFS (WHICH STILL IS A FAST OUTLIER) AND THE LATEST
CANADIAN FAVOR THE AREAS EAST OF OUR FORECAST AREA FOR BETTER LOW
LEVEL INSTABILITY. CONSIDERING THAT THE MODELS ARE DEPICTING MORE
INSTABILITY THAN BEFORE (THOUGH STILL MODEST)...APPEARS THAT SEVERE
WEATHER RISK INCREASING OVER THE AREA...ESPECIALLY FOR LOCALES ALONG
AND EAST OF HIGHWAY ONE. MAIN SEVERE WEATHER THREAT APPEARS TO BE
DAMAGING STRAIGHT LINE WINDS ASSOCIATED WITH BANDS OF STRING
CONVECTION EXPECTED TO OCCUR AHEAD OF 850MB TROUGH THAT CROSSES AREA
BY 06Z. DUE TO LACK OF LOW LEVEL INSTABILITY NOT OVERLY CONCERNED BY
TORNADO THREAT BUT IF ISOLATED CELLS OCCUR AHEAD OF LINE...WEAK
SHORT LIVED TORNADOES POSSIBLE.
EXPECT SHOWERS/ISOLATED STORMS TO END IN THE WEST ARID MIDNIGHT WITH
TREND CONTINUING EAST BY 4 AM AS MID/UPPER LEVEL SCOOT QUICKLY NE
INTO WESTERN NEW ENGLAND BY 7 AM THU..
THE DEPARTING LOW PRESSURE (~990MB) SHOULD BE INVOF OF NEW ENGLAND
BY 12Z THURSDAY...WITH ONLY A SLIGHT CHANCE OF A LINGERING SHOWER AS
THE SURFACE FRONT PASSES THROUGH THE COASTAL PLAIN. WITH A DECENT
PRESSURE GRADIENT OVER CENTRAL NC IN THE WAKE OF THE SYSTEM....W-SW
WINDS MAY STAY UP IN THE 10-15KT RANGE WITH GUSTS TO 25KT IN THE NE
DURING THE FIRST HALF OF THE DAY BEFORE TURNING TO NWRLY AND
RELAXING. OTHERWISE THURSDAY LOOKS TO BE A NICE DAY...ALTHOUGH COLD
ADVECTION WILL KEEP TEMPS FROM REBOUNDING TOO MUCH...AND MOS
GUIDANCE CONSISTENT WITH UPPER 50S TO LOWER 60S.
COOL...WEAK SURFACE HIGH PRESSURE RIDGE LINGERS OVER THE MID
ATLANTIC ON FRIDAY...WHILE SHORTWAVE ENERGY (AND THE DRIVING FORCE
FOR THE WEEKENDS WEATHER) DIVES SOUTH AROUND THE BACK SIDE OF THE
LONG WAVE TROUGH EXPECTED TO DEVELOP OVER THE EASTERN 2/3 OF THE
COUNTRY. HIGHS FRIDAY A BIT COOLER THAN THURSDAY...ALTHOUGH THE
COLDEST AIR WILL LIKELY HOLD TO OUR WEST UNTIL SATURDAY. HIGHS
SHOULD HOLD IN THE LOW TO MID 50S...ALTHOUGH SOME UPPER 40S QUITE
POSSIBLE...ESPECIALLY AS HIGH CLOUDS INCREASE AHEAD OF THE NEXT
SYSTEM. -BLS
&&
.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
AS OF 245 PM TUESDAY...
PRECIPITATION CHANCES INCREASE FRIDAY NIGHT INTO SATURDAY...AS THE
AFOREMENTIONED SHORTWAVE DIVES THROUGH THE DEEP SOUTH AND SPINS UP A
SURFACE LOW OVER THE EASTERN GULF OF MEXICO AND EVENTUALLY ALONG THE
SE COAST. SPREAD AMONG MODELS INCREASES AS THE SHORTWAVE EJECTS OUT
OF THE BASE OF THE TROUGH AND BECOMES NEGATIVELY TILTED. RECENT
RUNS OF THE GFS HAVE WAVERED A BIT ON THE LOCATION OF THE SURFACE
LOW AND AMPLITUDE OF THE SHORTWAVE...WITH THE MOST RECENT 12Z RUN
WEAK AND FURTHER OFFSHORE WITH THE LOW...AND THE SHORTWAVE SLIGHTLY
MORE SHEARED. WILL SHOW BEST CHANCES STARTING FRIDAY NIGHT IN THE
EAST...WITH A CHANCE EVERYWHERE SATURDAY. THE HIGHEST CHANCES WILL
BE IN THE EAST...BUT THE POTENTIAL REMAINS FOR THE IMPACT OF SOME
WRAP AROUND PRECIP IN THE WEST WITH MODEST HEIGHT FALLS EXPECTED.
ALTHOUGH MODELS DONT REALLY PRODUCE MORE THAN A COUPLE TENTHS OF AN
INCH WEST OF I-95 AT THE MOMENT...GOOD BACKING WIND PROFILES AND
COLD ADVECTION WITH AN ARCTIC AIRMASS ON THE WEST OF THE MOUNTAINS
CREATE A CONCERN FOR HOW QUICKLY COLD AIR CAN REACH THE WESTERN
PIEDMONT BEFORE PRECIP ENDS. MID LEVEL TEMPS COOL RAPIDLY FRI NIGHT
WITH H85-H7 THICKNESSES CALLING TO 1520M BY 12Z SAT MORN...BUT
H10-H85 THICKNESSES HOLD ABOVE 1305M UNTIL SAT NIGHT....WHEN THE
FAST MOVING SYSTEM IS EXPECTED TO BE DEPARTING. HOW QUICKLY THE
COLD AIR CAN MAKE IT ACROSS THE MOUNTAINS CAN BE A TROUBLE SPOT FOR
THE MEDIUM RANGE MODELS...SO WHILE THE POTENTIAL FOR A CHANGEOVER TO
SNOW EXISTS...SEEMS TOO EARLY AND QUESTIONABLE STILL FOR ANY MENTION
IN THE FORECAST. HIGHS SATURDAY OBVIOUSLY DEPENDENT ON PRECIP...BUT
WITH THICKNESSES FALLING BY LATE AFTERNOON...LOW TO MID 40S MAY EVEN
BE TOUGH TO OBTAIN.
THE UPPER LEVEL VORTEX OVER THE GREAT LAKES AND WESTERN CANADA
SHIFTS FURTHER NORTH THROUGH THEN END OF THE PERIOD...AND THE MID
AND UPPER LEVEL FLOW DAMPENS TO MORE ZONAL AS CHILLY HIGH PRESSURE
BUILDS ACROSS THE APPALACHIANS AND SETTLES OVER THE MID ATLANTIC.
STILL QUESTIONABLE AS TO HOW MODIFIED THIS AIRMASS WILL BE BY
SUNDAY...BUT GIVEN GFS ENSEMBLE MOS GUIDANCE GIVES A LOW OF 23 FOR
GSO ON SUNDAY MORNING... MID TO UPPER 20S SEEMS REASONABLE AT THIS
POINT. WITH HIGH PRESSURE IN CONTROL AND NO REAL FORCING FOR
PRECIP...HIGHS WILL SLOWLY REBOUND INTO THE LOW 50S THROUGH THE
BEGINNING OF THE WEEK.
&&
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...
FLASH FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH WEDNESDAY EVENING
FOR NCZ021>023-038-039-073-074-083-084.
&&
$$
SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...WSS/SMITH
LONG TERM...SMITH
AVIATION...WSS
