FXUS62 KRAH 010303
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1003 PM EST MON NOV 30 2009
.SYNOPSIS...
HIGH PRESSURE WILL BUILD IN FROM THE SOUTHWEST TONIGHT AND SETTLE
OVERHEAD. 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 TUESDAY/...
AS OF 1003 PM MONDAY...
IT WAS QUITE AN ACTIVE EVENING THANKS TO THE DEVELOPMENT OF A NARROW
COLD FRONTAL RAINBAND (NCFR) NORTHWEST OF THE TRIANGLE. THE NCFR WAS
FORCED PRESUMABLY BY 1) DEEP AND STRONGLY-SLOPED FRONTOGENESIS... 2)
REARWARD-SLOPED FRONT-RELATIVE FLOW (IE. THE STRONG SOUTHWESTERLY
FLOW AT H85-925 WAS UNDERCUT BY THE SOUTHEASTWARD-SURGING SURFACE
FRONT THAT IN TURN INDUCED ISENTROPIC ASCENT/ANAFRONTAL RAIN)... AND
3) 60-100 METER/12 HOUR HEIGHT FALLS AT H5 ASSOCIATED WITH A POTENT
S/W TROUGH NOW CROSSING THE REGION. THE NCFR THEN PRODUCED NUMEROUS
MEASURED WIND GUSTS IN EXCESS OF 30 MPH.... AND A FEW IN EXCESS OF
40 MPH. THE STRONGEST MEASURED WINDS WERE LED BY RCZ (43 KTS)... FAY
(42 KTS)... FBG (37 KTS)... GSO (32 KTS)... POB (31 KTS)... AND HFF
(30 KTS). SIGNIFICANT MSL PRESSURE RISES ON THE ORDER OF 2-3 MB IN 1
HOUR IMMEDIATELY POST-FRONTAL AND ~6 MB/6 HR HAVE BEEN OBSERVED THIS
EVENING... WHICH CONTRIBUTED TO BOTH THE AFOREMENTIONED STRONGEST
GUSTY WINDS WITH THE FRONT AS WELL AS FREQUENT GUSTS UP TO 25 KTS
FOR A FEW HOURS BEHIND THE FRONT. THE WIND SHOULD CONTINUE TO ABATE
FROM NW TO SE AS THE STRONGEST PRESSURE RISES ALSO MOVE EAST.
WHILE THE COLD FRONT HAD ALMOST MADE IT TO THE SOUTHEASTERN NC
COAST... THE ANAFRONTAL RAIN AND CLOUDS LAGGED AS FAR WEST AS THE
RAH COASTAL PLAIN COUNTIES... BUT SHOULD MOVE FULLY EAST OF THE RAH
CWA... WITH CLEAR SKIES AREA WIDE BY 11 PM.
TEMPERATURES AND DEWPOINTS ALSO FELL SOME 10 DEGREES IN ONE HOUR...
AND HAD FALLEN TO AROUND 40 OVER 30... RESPECTIVELY IN THE TRIAD AT
10 PM. EXPECT THIS MUCH COOLER AND DRIER AIR TO CONTINUE TO SPILL
THROUGH THE REMAINDER OF CENTRAL NC THROUGHOUT THE NIGHT... COURTESY
OF AN INCOMING ~1022 MB SURFACE HIGH CENTERED OVER NORTHERN MS AT 10
PM. WE ARE WELL ON OUR WAY TO LOWS BY MORNING IN THE LOWER TO MIDDLE
30S NORTHWEST PIEDMONT TO AROUND 40 DEGREES IN THE SOUTHERN COASTAL
PLAIN. -MWS
TUESDAY...S/W RIDGE AND ASSOCIATED SURFACE HIGH PRESSURE WILL
PROVIDE OUR REGION WITH PLENTY OF SUNSHINE. LOW LEVEL THICKNESSES
SUPPORT MAX TEMPS IN THE MID/UPPER 50S IN THE PIEDMONT/NORTHERN
COASTAL PLAIN TO AROUND 60 IN THE SE.
&&
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
AS OF 245 PM MONDAY...
A SIGNIFICANT STORM SYSTEM WILL AFFECT THE REGION WEDNESDAY THROUGH
WEDNESDAY NIGHT... BRINGING WIDESPREAD MODERATE TO HEAVY RAIN
RAINSHOWERS... BLUSTERY CONDITIONS... AND A THREAT FOR LOCALLY
DAMAGING WIND.
FOR TUESDAY NIGHT: THE ANOMALOUSLY STRONG (HEIGHTS 4-5 STANDARD
DEVIATIONS BELOW NORMAL) MID LEVEL VORTEX WOBBLES ACROSS TX WITH
SURFACE CYCLOGENESIS UNDERWAY OVER THE NORTHWEST GULF. THIS LOW
SHIFTS NORTHWARD INTO SOUTHERN MS/AL BY WEDNESDAY MORNING... AS
THE SURFACE HIGH CENTERED OVERHEAD EARLY TUESDAY NIGHT IS PUSHED
QUICKLY NORTHEAST AND OFFSHORE BY THE INCOMING STORM SYSTEM. THE NAM
AND CANADIAN HAVE QUICKENED CONSIDERABLY SINCE SUNDAY'S RUNS... AS
MUCH AS 6-9 HOURS IN THE CASE OF THE NAM... AND THEIR SOLUTIONS ARE
COMING MORE IN LINE WITH THE GFS/ECMWF WHICH BEGIN TO SPREAD RAIN
OVER THE CWA SOUTHWEST TO NORTHEAST AROUND SUNRISE WEDNESDAY.
CURRENT FORECAST SHOWS THIS TREND WELL WITH JUST SLIGHT CHANCE POPS
VERY LATE TUESDAY NIGHT IN THE FAR SOUTHWEST... REASONABLE WHEN
FACTORING IN THE TIME IT WILL TAKE TO SATURATE THE LOW LEVELS... AND
ANY ADJUSTMENTS WILL BE MINOR. EXPECT CONSIDERABLE HIGH CLOUDINESS
TO THICKEN IN THE EVENING WITH OVERRUNNING STRATOCUMULUS DEVELOPING
TOWARD MORNING. GIVEN THE DRY CHARACTER OF THIS INCOMING HIGH (DEW
POINTS BENEATH IT ARE CURRENTLY AS LOW AS 20-25)... WE SHOULD SEE
LOWS IN THE MID 30S TO AROUND 40.
FOR WEDNESDAY/WEDNESDAY NIGHT: RAIN AND WIND WITH POSSIBLE SEVERE
STORMS WILL BE THE STORY HERE. THE LATEST MODEL GUIDANCE CONTINUES
TO INDICATE A MILLER "A" TYPE CYCLOGENESIS EVENT WITH THE SURFACE
LOW TRACKING FROM SOUTHERN MS/AL ACROSS EASTERN TN TO WESTERN NY BY
SUNRISE THURSDAY. DURING THIS TIME THE UPPER LOW SHOOTS RAPIDLY FROM
TX THROUGH THE MEMPHIS AREA TO WESTERN PA/NY. THE ROUGHLY 1025 MB
SURFACE HIGH SITTING OFF THE MIDATLANTIC COAST SHIFTS FURTHER EAST
BUT APPEARS LIKELY TO LEAVE BEHIND A WEAK SURFACE BASED STABLE POOL
OVER THE NORTHERN PIEDMONT WELL INTO WEDNESDAY... WHICH SHOULD
RESULT IN A WEAK/VULNERABLE WEDGE FRONT OVER THE NORTHERN PIEDMONT
AS THE SURFACE-925 MB WARM FRONT HEADS NORTHWARD INTO NC WEDNESDAY
MORNING. AN AREA OF ABOVE NORMAL PRECIPITABLE WATER NOW NOTED ON
BLENDED TPW PRODUCTS OVER THE NORTHWEST GULF SPREADS OVER CENTRAL NC
SOUTH TO NORTH... AND WITH THESE PW VALUES NEARLY 300% OF NORMAL AND
STRENGTHENING SOUTHEASTERLY 850 MB FLOW OFF THE ATLANTIC... MOISTURE
SHOULD BE PLENTIFUL THROUGH THE COLUMN. AND FORCING FOR ASCENT
INTENSIFIES WITH INCREASING UPPER DIVERGENCE AS THE 130+ KT JET CORE
TO OUR WEST SHIFTS EASTWARD INTO NC... AND IMPROVING DPVA AS THE
SHORTWAVE TROUGH (ALBEIT DEAMPLIFYING) SWINGS NORTHEAST THROUGH NC.
FOLLOWING THE TIMING OF THE CONSISTENT ECMWF... WILL HAVE
CATEGORICAL POPS EVERYWHERE FROM NOON THROUGH JUST PAST MIDNIGHT
FOLLOWED BY A QUICK TAPERING OFF. EXPECT WIDESPREAD RAINFALL AMOUNTS
OF 1.5-3.0 INCHES. DESPITE THE RAIN... WITH STRONG LOW LEVEL WARM
ADVECTION AND IN LOOKING AT THE TROPICAL SOURCE REGION... TEMPS
SHOULD BE ABLE TO REACH THE MID 60S OVER THE EAST SANDHILLS AND MUCH
OF THE COASTAL PLAIN... ALTHOUGH HIGHS 54-60 SHOULD HOLD OVER THE
PIEDMONT WITH THE COOLEST READINGS IN THE TRIAD. THE STRONG WARM
ADVECTION STRETCHES THROUGH WEDNESDAY NIGHT... AND WILL HOLD ONTO
CURRENT FORECAST OF TEMPS SLOWLY RISING WEDNESDAY NIGHT THROUGH THE
60S.
NOW ONTO THE SEVERE RISK WEDNESDAY/WEDNESDAY NIGHT: A HIGHLY DYNAMIC
SYSTEM WITH HIGH SHEAR (BOTH LOW LEVEL AND DEEP LAYER) BUT MARGINAL
TO LOW INSTABILITY IS STILL ANTICIPATED. DEEP LAYER SHEAR INCREASES
RAPIDLY FROM 50-60 KTS TO 70-80 KTS OVERNIGHT... AND LOW LEVEL SHEAR
GOES THROUGH THE ROOF WITH 0-1 KM HELICITY VALUES OF 500-800
M2/S2... HIGHEST NORTHWEST NEAR THE DISSIPATING WEDGE BOUNDARY...
WHILE 850 MB WINDS ARE EXPECTED TO INCREASE TO 55-70 KTS STARTING
WEDNESDAY AFTERNOON. INSTABILITY IS THE LIMITING FACTOR HERE... WITH
GFS/ECMWF INDICATING MUCAPE UNDER 300 J/KG... MAXIMIZED 21Z-04Z. THE
SATURATED COLUMN AND STEADY PRECIPITATION WILL ALSO LIMIT
INSTABILITY. ONE INTERESTING NOTE: THE CIPS ANALOG GUIDANCE TOOL
(AVAILABLE ONLINE) BASED ON THE GFS INDICATES A HIGH CORRELATION OF
THIS EVENT WITH JANUARY 13-14 OF 1992... WHEN THERE WERE JUST TWO
F-1 TORNADOES REPORTED... BUT WIDESPREAD WIND DAMAGE OCCURRED OVER
THE DEEP SOUTH UP THROUGH THE MIDATLANTIC. HOWEVER IN THAT EVENT THE
DEPARTING SURFACE HIGH WAS WEAKER... AND THUS THE RETREATING COOL
AIR POOL WAS LIKELY GONE... AS WAS THE SOURCE OF RICH LOW LEVEL
VORTICITY TYPICALLY ASSOCIATED WITH A WEAKENING WEDGE FRONT IN THIS
SORT OF REGIME. BASED ON THIS... THE CONFIDENCE IN SOME SEVERE
WEATHER IS BUOYED... AND IF THERE IS INDEED A RETREATING WEDGE FRONT
WITH SUFFICIENT INSTABILITY... THE RISK OF ISOLATED TORNADOES MAY BE
GREATER THAN WAS POSED IN THE 1992 CASE. BUT THE BACKGROUND WIND
FIELD ALONE BRINGS CONCERN... ESPECIALLY AFTER THE RAIN HELPS LOOSEN
UP TREE ROOT SYSTEMS. ONCE WE FULLY MIX IN THE VERTICAL LATE
WEDNESDAY INTO WEDNESDAY NIGHT... SUSTAINED SURFACE WINDS OF 15-20
MPH ARE LIKELY WITH GUSTS FREQUENTLY EXCEEDING 30 MPH. A WIND
ADVISORY MAY BE NEEDED FOR THIS TIME FRAME IN LATER FORECASTS. WILL
CONTINUE TO HIGHLIGHT IN THE HAZARDOUS WEATHER OUTLOOK THE OVERALL
RISK OF STRONG WINDS POSSIBLY PRODUCING DAMAGING GUSTS ALONG WITH
THE THREAT OF AN ISOLATED TORNADO OR TWO. IT LOOKS LIKE THE GREATEST
THREAT WILL BE MID AFTERNOON TO SHORTLY AFTER MIDNIGHT... 20Z TO
06Z... BOTH ALONG THE NORTHWARD-MOVING WARM FRONT AND WITH THE COLD
FRONT AS IT PASSES EAST TO WEST DURING THE LATE EVENING TO EARLY
OVERNIGHT HOURS.
FOR THURSDAY: WITH LOW LEVEL COLD ADVECTION CAPPED OFF BY A
PROMINENT WARM/DRY LAYER CENTERED AT 700-800 MB... EXPECT FAIR TO
MOSTLY CLEAR SKIES WITH FLAT AFTERNOON STRATOCUMULUS. SURFACE WINDS
SHIFT FROM WEST TO NORTHWEST... ALTHOUGH THE COLDEST AIR WITH THE
INCOMING SURFACE HIGH BUILDING IN FROM THE WEST IS LIKELY TO HOLD
WEST OF THE MOUNTAINS. THICKNESSES SLOWLY FALL THROUGH THE DAY BUT
REMAIN SEASONABLE TO MILD... AND STILL EXPECT HIGHS OF 56-64. -GIH
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
AS OF 300 PM MONDAY...
FOR THURSDAY NIGHT/FRIDAY: A MID LEVEL POLAR LOW DIGS OVER EASTERN
ONTARIO AND THE UPPER MIDWEST AND MI THROUGH FRIDAY WITH DEEP
LONGWAVE TROUGHING COVERING CENTRAL AND EASTERN NOAM. THE SURFACE
FRONT SHOULD BE EASING OUT TO SEA BY THURSDAY NIGHT ALTHOUGH A
TRAILING SURFACE TROUGH IS LIKELY TO LINGER BACK ALONG THE NC/SC
BORDER... AND WILL LIKELY LEAVE AREAS OF CLOUDS OVER THE SOUTHERN
AND EASTERN CWA THURSDAY NIGHT WITH DOWNSLOPE LOW LEVEL FLOW
GENERATING SOME CLEARING OVER THE PIEDMONT OVERNIGHT. LOWS 35-41.
LOW LEVEL THICKNESSES HOLD BELOW NORMAL FRIDAY WITH COLD AIR
ADVECTION AS ARCTIC HIGH PRESSURE STARTS TO BUILD IN FROM THE WEST.
EXPECT GENTLY SINKING AIR THROUGH THE DAY BUT THE FAST SOUTHWEST
FLOW IN THE MID-UPPER LEVELS SHOULD KEEP THICK HIGH CLOUDS STREAMING
OVERHEAD. THE RIGHT ENTRANCE REGION OF THE STRONG UPPER JET PASSES
OVER EASTERN NC... AND THIS LIFT ATOP THE PRE-EXISTING BAROCLINIC
ZONE JUST OFFSHORE (AND OVER THE WARM GULF STREAM) MAY INDUCE
CYCLOGENESIS ALONG THE FRONT. IF THIS OCCURS... SURFACE WINDS OVER
CENTRAL NC MAY BECOME MORE NORTHEASTERLY DRAGGING MOIST ATLANTIC LOW
LEVEL AIR INTO THE AREA... LEADING TO GREATER AMOUNTS OF STRATUS.
WILL LEAN IN THIS DIRECTION AND BEEF UP FRIDAY CLOUD COVER. HIGHS
49-55... 1-2 CATEGORIES BELOW NORMAL.
FOR FRIDAY NIGHT/SATURDAY: THE STRONG (140+ KTS ON THE GFS AND 160+
KTS ON THE ECMWF) UPPER JET CORE SITS OVER NC SATURDAY WITH BOTH THE
ECMWF AND GFS SHOWING SURFACE LOW DEVELOPMENT JUST OFF THE NC COAST.
THE GFS IN PARTICULAR DEPICTS ENOUGH DEEPENING TO THROW QUITE A BIT
OF ATLANTIC MOISTURE BACK INTO NC (ESPECIALLY NORTHERN SECTIONS)...
AND CONSIDERING ITS LIFT MECHANISMS (MID LEVEL DPVA THAT IS ALSO
SEEN ON THE ECMWF AND UPPER JET DYNAMICS)... MEASURABLE PRECIP COULD
INDEED FALL ESPECIALLY OVER THE NORTHERN PIEDMONT AND COASTAL PLAIN.
THE 12Z GFS HINTS THAT THERE WILL BE ENOUGH COLD AIR IN PLACE
THROUGH THE COLUMN AND ENOUGH SATURATION IN THE -12C TO -20C LAYER
FOR PRECIP TO BE A RAIN/SNOW MIX. BUT THIS IS THE FIRST GFS RUN TO
INDICATE THIS SCENARIO... THE 00Z ECMWF DOES NOT SUPPORT THIS DEEP A
LOW... AND THE AMOUNT OF MOISTURE AVAILABILITY IN THE LOW LEVELS IS
IN QUESTION. FOR NOW WILL INDICATE A SLIGHT CHANCE OF RAIN OVER THE
NORTHEAST CWA SATURDAY. LOWS IN THE UPPER 20S TO LOWER 30S...
AND HIGHS 45-51.
FOR SATURDAY NIGHT THROUGH MONDAY: THE CHILLY SURFACE HIGH CONTINUES
TO BUILD INTO AND OVER THE AREA. THE ECMWF SHOWS THE MID LEVEL
TROUGH AXIS SHIFTING OVERHEAD LATE SUNDAY WHICH WOULD YIELD ANOTHER
ROUND OF CONSIDERABLE CLOUDINESS FOR VA/NC... ALTHOUGH THE GFS LIFTS
THIS TROUGH AXIS MUCH FARTHER NORTH WITH MINIMAL IMPACT ON NC. WILL
KEEP THE FORECAST DRY AND PARTLY CLOUDY WITH BELOW NORMAL
TEMPERATURES. THE MODELS SHOW LONGWAVE TROUGHING STARTING TO DIG
OVER THE NORTHERN ROCKIES TO CA BY MONDAY... KEEPING A FAST AND FLAT
ZONAL FLOW ACROSS THE GULF STATES/MIDSOUTH/SOUTHEAST/MIDATLANTIC...
WITH SURFACE HIGH PRESSURE DRIFTING OVER THE CAROLINAS. EXPECT
CONTINUED FAIR SKIES... DRY WEATHER... AND BELOW NORMAL TEMPS INTO
MONDAY. -GIH
&&
AVIATION /00Z TUESDAY THROUGH SATURDAY/...
AS OF 710 PM MONDAY...
A BAND OF SHOWERS ASSOCIATED WITH AN COLD FRONT IS CURRENTLY RACING
ACROSS CENTRAL NORTH CAROLINA THIS EVENING. THE LINE HAS ALREADY
MOVE SOUTH AND EAST OF ALL THE TERMINALS EXCEPT KFAY. GUSTY WINDS OF
UP TO 30 TO 35 MPH OUT OF THE NORTHWEST AND MVFR/IFR CIGS AND VISBYS
WILL BE POSSIBLE WITH THE BAND/LINE OF SHOWERS AS IT MOVES THROUGH
THE AREA. SHOWERS WILL LINGER FOR A FEW HOURS ACROSS THE AREA BEHIND
THE FRONT. HOWEVER... WITH DRY AIR SURGING INTO THE AREA IN THE
LOWER LAYERS OF THE ATMOSPHERE EXPECT SHOWERS TO END AND SKIES TO
GENERALLY CLEAR BY 06Z ACROSS THE ENTIRE AREA. THUS... EXPECT VFR
CONDITIONS TO RETURN TO THE ENTIRE AREA BY 06Z... WITH NORTH TO
NORTH-NORTHWEST WINDS REMAINING BETWEEN 5 TO 10 KTS OVERNIGHT.
HIGH PRESSURE WILL MOVE ACROSS THE AREA TUESDAY AFTERNOON ALLOWING
WINDS TO BECOME LIGHT AND VARIABLE... WITH CONTINUED VFR CONDITIONS
AND MOSTLY SUNNY SKIES.
A STRONG LOW PRESSURE SYSTEM OVER THE GULF COAST STATES WILL MOVE NE
TOWARD THE CAROLINAS WEDNESDAY AND AFFECT THE REGION LATE WEDNESDAY
THROUGH WEDNESDAY NIGHT. WIDESPREAD SHOWERS...IFR TO LIFR
CEILING/VISIBILITY RESTRICTIONS...AND STRONG TURBULENCE WILL
ACCOMPANY THIS WEATHER FEATURE. POTENTIAL FOR LOW LEVEL WIND SHEAR
BY EARLY WEDNESDAY MORNING AS WINDS JUST ABOVE THE SURFACE INCREASE
SUBSTANTIALLY OUT OF THE SE WHILE NEAR SURFACE WINDS WILL BE LIGHT
AND VARIABLE. THESE CONDITIONS MAY PERSIST WELL INTO WEDNESDAY
AFTERNOON.
THE MOST ADVERSE WEATHER CONDITIONS ASSOCIATED WITH THE AREA OF LOW
PRESSURE SHOULD OCCUR FROM MID DAY WEDNESDAY THROUGH LATE WEDNESDAY
NIGHT. EXPECT WIDESPREAD IFR/MVFR CEILINGS AND VISIBILITIES WITH
RAIN WEDNESDAY MORNING INTO WEDNESDAY AFTERNOON TRANSITIONING TO
SHOWERS AND ISOLATED THUNDERSTORMS WEDNESDAY NIGHT.
THE AREA OF LOW PRESSURE WILL EXIT CENTRAL NORTH CAROLINA EARLY
THURSDAY...ALLOWING HIGH PRESSURE TO BUILD IN FROM THE WEST. A
FAIRLY TIGHT PRESSURE GRADIENT WILL RESULT IN BLUSTERY CONDITIONS
THURSDAY...SUBSIDING BY LATE AFTERNOON.
VFR CONDITIONS EXPECTED FRIDAY THROUGH SATURDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...LEP
NEAR TERM...MWS/WSS
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...BSD/WSS
