000
FXUS62 KRAH 061144
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
640 AM EST TUE JAN 6 2009
.SYNOPSIS...
A BACKDOOR COLD FRONT WILL MOVE SOUTH INTO CENTRAL NORTH CAROLINA
THIS MORNING... THEN STALL OVER THE SOUTHERN SECTIONS OF THE STATE
TODAY. A STORM SYSTEM DEVELOPING OVER THE MID MISSISSIPPI VALLEY
REGION WILL MOVE NORTHEAST... AND PULL THE FRONT BACK NORTHWARD AS A
WARM FRONT... INTO THE EASTERN PIEDMONT BY THIS EVENING. A STRONG
COLD FRONT WILL PUSH EAST ACROSS THE STATE WEDNESDAY.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 640 AM TUESDAY...
RECENTLY UPDATED FORECAST TO REFLECT SWD SURGE OF SURFACE FRONT
THROUGH THE COASTAL PLAIN AND INTO/THROUGH THE NORTHERN PIEDMONT. AT
1130Z...SURFACE FRONT CLOSE TO A GSB-SANFORD TO LEXINGTON LINE AND
CONTINUES TO MOVE SWD. RECENT ACAR AIRCRAFT SOUNDING FROM RDU
REVEALS THAT COOL AIR QUITE SHALLOW...2000FT THICK AT THE MOST.
PRESENT INDICATIONS ARE THAT THE FRONT WILL LIKELY IN VICINITY OF
THE SOUTH CAROLINA STATE LINE...COMPARABLE TO THE NAM-WRF SCENARIO.
UPDATES MAY BE NEEDED LATER THIS MORNING IF FRONT SURGES PAST FAY
AND ALBEMARLE.-WSS
REMAINDER OF DISCUSSION FROM 305 AM...
COMPLEX WEATHER PATTERN TO AFFECT CENTRAL NC THROUGH THIS PERIOD.
MAIN FORECAST CHALLENGES ARE TEMPERATURES AND THE NEED FOR A FLOOD
WATCH FOR SECTIONS OF THE PIEDMONT.
SURFACE COLD FRONT MARKING THE LEADING EDGE OF COOLER AIR WORKING
ITS WAY S-SW ACROSS THE NORTHERN COASTAL PLAIN AND FAR NE PIEDMONT
AT 07Z. KRZZ AND KHNZ. MEANWHILE SOUTH OF THE FRONT...TEMPS REMAIN
IN THE MILD 50S WITH LOWER 60S IN THE EXTREME SOUTH. MODEL
GUIDANCE VARIES ON HOW FAR SOUTH SURFACE FRONT WILL GET BEFORE
STALLING. NAM-WRF SUGGEST THAT FRONT WILL MAKE IT INTO THE
SANDHILLS AND SOUTHERN COASTAL PLAIN BY 18Z WHILE THE GFS STALLS
IT CLOSER TO HIGHWAY 64. THE TRUTH IS LIKELY IN THE MIDDLE BUT
HAVING DOUBTS THAT THE FRONT WILL MAKE IT TO GSB OR FAY AS PARENT
HIGH DRIVING THE FRONT RELATIVELY WEAK (SUB1020MB). ONE THING THAT
IT DOES HAVE GOING FOR IT IS IT`S POCKET OF COOL DRY AIR WITH
DEWPOINTS IN THE TEENS/SINGLE DIGITS. THUS...WHERE THE COOLER AIR
MASS DOES GET A FOOTHOLD AND MAINTAINS SOME CONNECT TO THE PARENT
HIGH...THE RAIN FALLING THROUGH THIS COOL STABLE LAYER WILL HELP
TO LOCK IN/SOLIDIFY THIS CAD AIR MASS. NEEDLESS TO SAY....TEMP
FORECAST WILL BE TRICKY...ESPECIALLY IN VICINITY OF THE FRONT. WILL
LIKELY SEE TEMP VARIANCES OF 10-15 DEGREES ACROSS SOME
COUNTIES...DEPENDING UPON WHICH SIDE OF THE FRONT THEY ARE ON.
UPSTAIRS...A SERIES OF DISTURBANCES IN THE FAST W-SW FLOW ALOFT
WILL HELP TO ENHANCE THE SLY LOW LEVEL FLOW...CAUSING WIDESPREAD
RAIN TO OCCUR ACROSS THE REGION. THE GFS SHUTS OFF THIS FAVORABLE
ISENTROPIC LIFT PATTERN A LITTLE SOONER (BY 18Z TUE) COMPARED T
THE NAM. CONSIDERING THAT THE CORE OF 850MB WINDS WILL REMAIN TO
OUR SW TODAY AND WATER VAPOR IMAGERY DEPICTING A SERIES OF
PERTURBATIONS EXTENDING TO THE MS RIVER...FAVOR NAM SCENARIO FOR
NOW. THUS EXPECT WIDESPREAD THIS MORNING WITH RAIN GRADUALLY
DIMINISHING FROM THE SOUTH THIS AFTERNOON.
TONIGHT...GFS AND NAM DIFFER IN THE EROSION OF THE CAD AIRMASS
OVER THE NORTHERN PIEDMONT. GFS QUICKLY SCOURS OUT THE COOL STABLE
AIR FROM ALOFT DUE TO INCREASING SLY JET (60-65KT). NAM-WRF
DEPICTS A SLOW EROSION FROM THE SOUTH AND EAST BUT SUGGEST
THROUGH ITS LIFTED INDICES FIELD THAT THE CAD AIRMASS WILL
PERSIST THROUGH THE NIGHT OVER THE NW PIEDMONT INTO THE NE
PIEDMONT. FORECAST EXPERIENCE FAVORS THE LATER SCENARIO. WILL
CONTINUE FORECAST TREND OF STEADY TEMPS IN THE CAD AIRMASS WITH
TEMPS SLOWLY RISING OVER THE REMAINDER OF THE CWA OVERNIGHT.
AM A BIT CONCERN THAT PERSISTENT LIGHT-MODERATE RAIN MAY LEAD TO
SOME URBAN FLOODING PROBLEMS IN THE NORTHERN PIEDMONT...ESPECIALLY
THE TRIAD. BOTH NAM AND GFS DEPICT STRONG MOISTURE TRANSPORT IN
THE 925-850MB LAYER OFF THE EASTERN GULF...SUGGESTING EFFICIENT
RAIN PRODUCTION. HOWEVER BEST LIFT ASSOCIATED WITH STRONG UPPER
LEVEL JET WILL BE TO OUR NW...PLACING GREATER EMPHASIS FOR LIFT
FOR AREAS WEST AND NORTH OF THE TRIAD. FOR NOW WILL HOLD OFF ON
WATCH BUT WILL HIGHLIGHT URBAN FLOOD THREAT IN THE HWO.
FINALLY ON WEDNESDAY...STRONG COD FRONT ASSOCIATED WITH DEEPENING
UPPER LEVEL WAVE WILL CROSS CENTRAL NC WED MORNING/EARLY AFTERNOON.
850-500MB LAPSE RATES DO HOVER AROUND 6 DEG C/KM IN THE EAST THROUGH
18Z AND BOTH NAM AND GFS HINT AT NARROW RIBBON OF INSTABILITY OVER
THE EASTERN COUNTIES. WILL INTRODUCE A ISOLATED THUNDER INT HE EAST
WITH FROPA. TIMING OF FROPA SUGGEST RAIN CHANCES DWINDLING
WEST-TO-EAST AFTER 16Z-18Z...ENDING IN THE COASTAL PLAIN BY 21-22Z.
WINDS BEHIND THE FRONT EXPECTED TO BE STRONG WITH SUSTAINED SPEEDS
15-20 MPH AND GUSTS 30-35MPH. DUE TO SATURATED TOP SOIL...THIS MAY
LEAD TO SOME SPORADIC POWER OUTAGES DUE TO DOWNED TREES/POWER POLES.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 435 AM TUESDAY
WEDNESDAY NIGHT INTO THURSDAY...BLUSTERY CONDITIONS EXPECTED IN CAA
REGIME. MIXING WED NIGHT INTO EARLY THU WILL PREVENT AIR MASS NEAR
SURFACE FROM REALIZING FULL COOLING POTENTIAL. WILL LIKELY SEE GUSTS
20-25 MPH WEDNESDAY EVENING BEFORE GUSTS SUBSIDE DURING OVERNIGHT
PERIOD. FOR THU...STRONG NW FLOW WILL SEND A SERIES OF VORT MAXIMA
TOWARD THE CAROLINAS. THE GFS DEPICTS AN INTERESTING SCENARIO
TRAVERSING ONE VORT MAX TO OUR NORTH WHILE ANOTHER CROSSES WELL
SOUTH. THE 00Z/6TH ECMWF SUGGEST A SOMEWHAT WEAKER VORTICITY MAX
CROSSING NEAR OR JUST NORTH OF OUR FORECAST AREA. 00Z GFS DOES
DEPICT A DECENT MOIST LAYER BETWEEN 3000-10000FT OVER THE NORTHERN
COUNTIES THU MORNING BUT CROSS SECTIONS DEPICT THE BEST LIFT IN THE
LOWER LAYERS OF THE ATMOSPHERE...BELOW THE FAVORED DENDRITE GROWTH
AREA. IF PRECIP WERE TO OCCUR...SNOW SHOWERS OR RAIN SHOWERS MIXED
WITH SNOW WOULD BE THE MOST LIKELY P-TYPE AS FREEZING LEVEL WILL BE
JUST ABOVE THE SURFACE. FOR THU MORNING...WILL ENHANCE CLOUD
COVERAGE BUT REFRAIN FROM MENTION OF SCATTERED SNOW SHOWERS AT THIS
TIME....HOPING A BETTER MODEL CONSENSUS. WILL NEED TO MONITOR
UPSTREAM CONDITIONS WED AFTERNOON-WED NIGHT.
OTHERWISE WINDS WILL REMAIN BLUSTERY THU...ESPECIALLY IN THE
MORNING. CLOUD COVERAGE WILL DIMINISH THE AMOUNT OF INSOLATION WHICH
MAY PREVENT US FROM MIXING STRONGER WINDS ALOFT DOWN TOWARD THE
SURFACE. DAY CREW YESTERDAY BROUGHT UP A GOOD POINT ABOUT THE STRONG
DOWNWARD MOMENTUM TRANSFER WHICH MAY BE ABLE TO COMPENSATE FOR LACK
OF SOLAR INDUCED MIXING. WILL FORECAST WINDS SPEEDS 15-20 MPH WITH
GUSTS AROUND 30 MPH.
THURSDAY NIGHT INTO FRIDAY...A MORE TRANQUIL WEATHER REGIME ACROSS
THE AREA THU NIGHT THROUGH FRIDAY NIGHT AS HIGH PRESSURE NEAR
SURFACE DRIFTS OVERHEAD. THIS HIGH WILL AID TO SUBSIDE WINDS THU
NIGHT. IF SKIES REMAIN CLEAR/MOSTLY CLEAR...THEN AIR MASS WILL BE
ABLE TO REACH MAXIMUM COOLING...RESULTING IN MIN TEMPS IN THE MID TO
UPPER 20S. DECENT DISPLAY OF SUNSHINE FRIDAY WILL ALLOW AIR MASS TO
MODERATE. AFTERNOON TEMPS IN THE UPPER 40S TO LOWER 50S EXPECTED.
AS THE HIGH DRIFTS OFFSHORE FRIDAY NIGHT...SOME MODERATION OF AIR
MASS WILL CONTINUE. THIS WILL RESULT IN MIN TEMPS A COUPLE OF
DEGREES WARMER THAN THU NIGHT.
&&
.LONG TERM /SATURDAY THROUGH MONDAY/...
AS OF 340 AM TUESDAY...
A TREND TOWARD BELOW NORMAL TEMPERATURES APPEARS LIKELY AS WE HEAD
SUNDAY INTO MONDAY. MODELS GENERALLY AGREE IN A COLD FRONTAL PASSAGE
AROUND SATURDAY NIGHT AND EARLY SUNDAY. IT APPEARS FROM THE LATEST
MODELS RUNS THAT THE MOISTURE MAY BE MORE LIMITED WITH THIS FRONT
THAN IN PREVIOUS MODEL RUNS. THE ECMWF CONTINUED TO BE THE MOST
ROBUST WITH THE MOISTURE... BUT EVEN THAT MODEL HAD CUT BACK ON THE
MOISTURE SINCE THE PREVIOUS FORECAST. THE ECMWF WAS MORE SUPPRESSED
WITH A POTENTIAL SOUTHERN WAVE DEVELOPMENT SUNDAY INTO SUNDAY NIGHT
THAN IN THE PREVIOUS RUNS... AND THIS WILL HAVE TO BE WATCHED. THE
GFS WAS ALSO MORE SUPPRESSED SOUTHWARD TOWARD THE GULF. WE WILL GO
WITH A SLIGHT CHANCE OF RAIN SATURDAY AFTERNOON INTO SUNDAY MORNING
WITH THE PASSAGE OF THE FRONT... THEN NO POP SUNDAY AFTERNOON INTO
MONDAY FOR NOW... LEANING TOWARD THE MORE SUPPRESSED MODELS WITH THE
POTENTIAL SOUTHERN WAVE.
THE SURFACE HIGH EXPECTED TO BUILD IN FROM THE WSW BEHIND THE FRONT
SUNDAY AFTERNOON/NIGHT IS OF YUKON ORIGIN BUT SHOULD HAVE HAD THE
OPPORTUNITY TO MODIFY SOMEWHAT ONCE IT ARRIVES. IT WILL STILL BE
MILD TO WARM AHEAD OF THE FRONT SATURDAY... WITH HIGHS 55-63 AND
LOWS SATURDAY NIGHT TO 35-42. EXPECT MUCH COOLER TEMPERATURES SUNDAY
INTO MONDAY WITH HIGHS IN THE 40S (LOWER 50S SE)... AND LOWS IN THE
20S.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
AS OF 630 AM TUESDAY...
THIS WILL BE A PROBLEMATIC FORECAST FOR AVIATION PURPOSES THROUGH
WEDNESDAY... AS WE WILL HAVE LOW CIGS/VSBYS AND RAIN TO DEAL WITH.
IN ADDITION... THERE MAY BE LOW LEVEL WIND SHEAR JUST NORTH OF THE
WARM FRONT TONIGHT.
THROUGH NOON... EXPECT A LOWERING OF CIGS AND VSBYS AS LARGE AREAS
OF RAIN MOVE ACROSS THE REGION. ALL AREAS SHOULD SEE IFR/LIFR
CIGS/VSBYS THROUGH 18Z. THE LOW LEVEL COLD FRONT SHOULD STALL
SOMEWHERE AROUND KFAY... AND THIS WILL KEEP THE TERMINALS TO THE
NORTH AND WEST SOCKED IN MUCH OF THE DAY... BOTH CIGS AND VSBYS.
THERE IS A CHANCE THAT KFAY WILL BREAK OUT INTO MVFR OR HIGHER CIGS
AND UNLIMITED VSBYS LATER TODAY... AS THE WARM FRONT TRIES TO PUSH
NORTH OF OF THEM. MOST MODELS SUGGEST THAT THE WARM FRONT WILL PUSH
INTO THE KRWI AREA BETWEEN 00Z/03Z... ALLOWING A WIND SHIFT TO THE
SSW AND A RISE IN VSBYS AND CIGS. KRDU SHOULD BE THE BATTLE ZONE AND
MAY NOT HAVE A WARM FRONTAL PASSAGE (PER THE 00Z/06 NAM). HOWEVER...
THE OTHER MODELS SHOW THE WARM FRONT PUSHING JUST NW OF KRDU BETWEEN
AROUND OR BEFORE 06Z/07.
THE DEVELOPING HYBRID CAD EVENT OVER THE NORTHERN COUNTIES INTO THE
KINT/KGSO/KRDU AREAS WILL BE HARD TO OVERCOME AND THE WARM FRONT MAY
STALL OVER THE EASTERN PIEDMONT PER THE NAM. A STRONG LOW LEVEL JET
(40-50 KT AT 2 KFT) IS FORECAST TO DEVELOP OVERNIGHT...WHICH MAY
LEAD TO LOW LEVEL WIND SHEAR BEGINNING SOMEWHERE BETWEEN 00-03Z
WEDNESDAY...AND LASTING THROUGH AT LEAST 12Z WEDNESDAY MORNING.
WEDNESDAY THROUGH THURSDAY:
A STRONG COLD FRONTAL PASSAGE IS EXPECTED DURING THE DAY WED...AND
ADVERSE AVIATION CONDITIONS IN THE FORM OF WIDESPREAD SHOWERS AND
GUSTY WEST SOUTHWESTERLY WINDS ARE EXPECTED THROUGHOUT THE
DAY...WITH THE FRONT EXITING EAST OF THE AREA BY AROUND SUNSET WED
EVENING. ALTHOUGH ISOLATED THUNDERSTORMS CANNOT BE COMPLETELY RULED
OUT IN ASSOCIATION WITH THE COLD FRONTAL PASSAGE...INSTABILITY WILL
BE VERY MARGINAL...AND THE PROBABILITY THAT CONVECTION WILL DEVELOP
IS QUITE LOW. VFR CONDITIONS WITH GUSTY WESTERLY WINDS ARE EXPECTED
ON THURSDAY BEHIND THE FRONT. A LIGHTER WIND REGIME AND VFR CONDS
EXPECTED ON FRIDAY WITH A SFC HIGH IN OUR VICINITY.
-VINCENT/MWS/BADGETT
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...BADGETT
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...BADGETT
AVIATION...BADGETT
