FXUS62 KRAH 301956
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
255 PM EST MON NOV 30 2009

.SYNOPSIS...
A COLD FRONT WILL SWEEP EAST THROUGH THE REGION LATE THIS AFTERNOON 
THROUGH EARLY EVENING. HIGH PRESSURE WILL BUILD BRIEFLY OVER THE 
AREA TONIGHT THROUGH TUESDAY. A STRONG LOW PRESSURE SYSTEM OVER THE 
GULF COAST WILL MOVE NORTHEAST ACROSS THE REGION... BRINGING 
WIDESPREAD RAIN AND BLUSTERY WINDS WEDNESDAY AFTERNOON THROUGH 
WEDNESDAY NIGHT.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 210 PM MONDAY...

TONIGHT...SURFACE COLD FRONT WILL BE CROSSING THE FORECAST AREA 
BETWEEN 21Z-02Z. OVERALL PRECIP INTENSITY HAS DECREASED AHEAD AND 
ALONG THIS FEATURE...INDICATIVE OF MARGINAL LIFT AND MOISTURE. HAVE 
NOTED BAND OF HEAVIER PRECIP OCCURRING ALONG AND IMMEDIATELY WEST OF 
THE MOUNTAINS. THIS BAND OF PRECIP APPEARS TO BE OCCURRING ALONG THE 
850MB TROUGH. THIS FEATURE PROGGED TO SWEEP THROUGH THE AREA BETWEEN 
00Z-03Z. WHILE PRECIP AMOUNTS ARE EXPECTED TO BE LIGHT...STILL 
EXPECT TO SEE MEASURABLE RAIN AT MOST SITE LATE THIS AFTERNOON AND 
EARLY EVENING. THUS WILL MAINTAIN LOW END CATEGORICAL POPS IN THE NW 
PIEDMONT AND LIKELY POPS ELSEWHERE AS THE SURFACE AND 850MB TROUGH 
CROSS THE REGION. 

CLEARING IN THE WESTERN TN VALLEY AT 18Z ALIGNS WELL WITH THE 700MB 
TROUGH AXIS. THIS MID LEVEL TROUGH WILL ENTER THE REGION AFTER 
00Z AND SHOULD EXIT THE COASTAL PLAIN SHORTLY AFTER 06Z. 

COLD AIR ADVECTION WILL RESULT IN A PERIOD OF BLUSTERY CONDITIONS 
WITH THE PASSAGE OF THE FRONT. MAY SEE INFREQUENT WIND GUSTS OUT OF 
THE N-NW BETWEEN 20-25KTS WITHIN 3-4 HOURS OF FRONTAL PASSAGE.

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 /18Z MONDAY THROUGH SATURDAY/...
AS OF 1215 PM MONDAY...

A COLD FRONT WILL AFFECT CENTRAL NC LATE THIS AFTERNOON AND THIS 
EVENING WITH NUMEROUS SHOWERS EXPECTED IN VICINITY OF THE FRONT 
ALONG WITH A PERIOD OF 3-5 HOURS OF MVFR CEILINGS. THE SURFACE FRONT 
SHOULD CROSS THE PIEDMONT COUNTIES INCLUDING KINT...KGSO AND 
KRDU...BETWEEN 21Z-00Z...AND THE SANDHILLS AND COASTAL PLAIN 
INCLUDING KFAY AND KRWI BETWEEN 23Z-02Z. WINDS WILL BE GUSTY AHEAD 
AND BEHIND THE FRONT WITH FREQUENT GUSTS BETWEEN 20-25KT. STRONG 
SUBSIDENCE BEHIND THE 850MB TROUGH THE CROSSES THE AREA BETWEEN 
00Z-06Z WILL AID IN THE RAPID DISSIPATION OF CLOUD COVERAGE FROM 
WEST-TO-EAST AFTER 00Z WITH MOST OF CENTRAL NC CLEAR BY 07Z. 

HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE WEST OVERNIGHT AND 
SCOOT ACROSS THE STATE ON TUESDAY. THIS WEATHER SYSTEM WILL PROVIDE 
VFR CONDITIONS THROUGH TUESDAY NIGHT. 

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...HARTFIELD
NEAR TERM...WSS
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...WSS