FXUS62 KRAH 060802
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
300 AM EST SUN DEC 6 2009

.SYNOPSIS...
COLD HIGH PRESSURE WILL DRIFT ACROSS THE REGION TODAY... AND MOVE 
OFFSHORE TONIGHT. A WEAK COLD FRONT WILL APPROACH THE AREA ON MONDAY 
MORNING... AND CROSS THE REGION ON LATE MONDAY AFTERNOON INTO THE 
EVENING. 

&&

.NEAR TERM /THROUGH TONIGHT/... 
AS OF 240 AM SUNDAY...

COLD HIGH PRESSURE IS BUILDING INTO THE AREA FROM THE WEST THIS 
MORNING. DEWPOINTS ACROSS THE NORTHWEST PIEDMONT HAVE ALREADY 
DROPPED INTO THE LOWER TO MID 20S... WHICH COMBINED WITH LIGHT AND 
VARIABLE WINDS AND CLEAR SKIES... HAS LED TO TEMPERATURES DROPPING 
INTO THE UPPER 20S AND LOWER 30S. THIS DRY AIR MASS WILL CONTINUE TO 
ADVECT INTO CENTRAL NORTH CAROLINA THIS MORNING... WITH A GOOD 
PORTIONS OF THE THE AREA POTENTIALLY SEEING SOME PATCHY BLACK ICE... 
AS TEMPS FALL BELOW FREEZING. THUS... WILL CONTINUE THE SPS FOR THE 
WESTERN TWO THIRDS OF THE CWA FOR THE POTENTIAL FOR PATCHY BLACK ICE.

SURFACE HIGH PRESSURE WILL SETTLE ACROSS THE REGION LATE THIS 
MORNING INTO THE AFTERNOON. THIS SHOULD PROVIDE THE AREA WITH A DRY 
COLD AIR MASS. IN FACT... DEWPOINTS IN THE TEENS ARE CURRENTLY BEING 
OBSERVED WITH THE AIR MASS ACROSS PORTIONS OF TN/KY/VA/WV. THUS... 
EXPECT SKIES TO BE SUNNY TO MOSTLY SUNNY TODAY... WITH ONLY A FEW TO 
SCATTERED HIGH CIRRUS TRAVERSING THE AREA IN THE WSW'ERLY FLOW 
ALOFT. AFTERNOON LOW LEVEL THICKNESS VALUES ARE EXPECTED TO BE IN 
THE 1300 TO 1310 METER RANGE. LOCAL IN HOUSE LOW LEVEL THICKNESS 
EQUATION/TOOL YIELDS HIGH TEMPS IN THE MID TO UPPER 40S ACROSS 
(PERHAPS TOUCHING 50 ACROSS THE FAR SOUTH) THE AREA WITH THESE 
THICKNESS VALUES. THIS SOUNDS REASONABLE... THUS WILL SHOW HIGH 
TEMPS RANGING FROM 44 TO 50 DEGREES FROM NORTH TO SOUTH ACROSS THE 
CWA... WHICH IS ON THE COOL SIDE OF GUIDANCE.

THE SURFACE HIGH IS EXPECTED TO SHIFT OFFSHORE TONIGHT... ALLOWING 
FOR THE AIR MASS TO RECOVER A BIT. MOSTLY CLEAR SKIES THIS 
EVENING... SHOULD BECOME PARTLY TO MOSTLY CLOUDY ACROSS THE AREA 
OVERNIGHT (ESPECIALLY ACROSS THE SOUTH)... AS ISENTROPIC UPGLIDE ON 
THE 285K AND 290K SURFACE KICKS IN. GIVEN THE EXPECTED DRY AIR MASS 
IN PLACE ACROSS THE AREA THIS EVENING... EXPECT GENERALLY DRY 
CONDITIONS... WITH ANY POTENTIAL PRECIP FALLING FROM RESULT OF THE 
WAA/ISENTROPIC LIFT FALLING AFTER 12Z MONDAY. THIS INCREASE IN CLOUD 
COVER AND MOISTENING IN THE LOWER LAYERS SHOULD HELP PREVENT TEMPS 
FROM FALLING TOO LOW. THUS... EXPECT LOW TEMPS TONIGHT TO BE IN THE 
UPPER 20S ACROSS THE NORTH TO LOWER 30S ACROSS THE SOUTH.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
AS OF 245 AM SUNDAY...

FOR MONDAY/MONDAY NIGHT: THE MID LEVEL FLOW INTO NC REMAINS RATHER 
FLAT... HOWEVER A SEEMINGLY MINOR PERTURBATION NOW OVER NORTHERN 
MEXICO PASSES QUICKLY THROUGH THE MIDSOUTH AND SHIFTS OFF THE 
SOUTHEAST COAST MONDAY MORNING. WITH THE CHILLY SURFACE HIGH 
CENTERED OFF THE MIDATLANTIC COAST ALREADY FACILITATING DEVELOPMENT 
OF A BAROCLINIC ZONE OVER THE GULF STREAM... THIS WAVE SHOULD HELP 
LOWER SURFACE PRESSURES ENOUGH FOR A DEFINED INVERTED SURFACE TROUGH 
ALONG THE SOUTHEAST COAST... AND THE NAM/GFS/ECMWF/CANADIAN AGREE 
FAIRLY WELL ON THIS. AN 850 MB THETA-E RIDGE NOSES NORTHWESTWARD 
THROUGH CENTRAL AND EASTERN NC DURING THE DAY AHEAD OF AN 850 MB 
SHORTWAVE MOVING NORTHEAST FROM THE GULF THROUGH NC... AND THIS 
BRINGS A SLUG OF ISENTROPIC UPGLIDE AT 285-295K WHICH SHOULD BE DEEP 
AND STRONG ENOUGH TO KICK OFF LIGHT RAIN OVER THE CENTRAL AND 
EASTERN CWA AS THE INVERTED TROUGH EASES BRIEFLY INLAND. WILL EXPAND 
POPS A BIT FARTHER WEST AND INCREASE COASTAL PLAIN AND SANDHILLS 
POPS TO CHANCE... HOWEVER AMOUNTS SHOULD BE LOW... AROUND A TENTH OF 
AN INCH OR LESS BASED ON THE WEAK MID LEVEL FORCING. THE ASSOCIATED 
CLOUDS AND LOW LEVEL STABILITY DUE TO THE RAIN WILL KEEP TEMPS 
CHILLY... AND EXPECT MUCH OF THE PIEDMONT TO HOLD UNDER 50 DURING 
THE DAY. HAVE NUDGED HIGHS DOWN SLIGHTLY TO 46-55. THE UPGLIDE 
SHIFTS OFFSHORE MONDAY EVENING AS THE 850 MB TROUGH EXITS... AND 
WILL TREND OUT POPS EARLY. WE SHOULD SEE A SHORT PERIOD OF 
CLEARING... BUT THEN THE NAM/GFS SHOW A BATCH OF MID LEVEL MOISTURE 
AHEAD OF A WEAK 700 MB SHORTWAVE PASSING BY OVERNIGHT... SO WILL 
KEEP SKIES PARTLY CLOUDY... WHICH SHOULD KEEP TEMPS FROM DROPPING 
TOO MUCH. LOWS 33-40. 

FOR TUESDAY: HIGH PRESSURE BUILDS OVER THE MIDATLANTIC REGION... 
WEAKLY RIDGING SOUTHWARD INTO NC. THIS HIGH IS AN OFFSHOOT OF A 
LARGER POLAR HIGH NOW OVER WESTERN CANADA WITH DEW POINTS OF ZERO TO 
-20F. BASED ON THE WEAKNESS AND MODIFICATION OF THIS OFFSHOOT 
HIGH... IT SHOULD NOT POSSESS AIR QUITE THIS DRY/COLD... BUT IT DOES 
STRENGTHEN A BIT TO NEAR 1027 MB AS IT BECOMES CENTERED OVER THE ST 
LAWRENCE VALLEY AND STARTS TO TAP INTO THIS COLDER AIR... AND THIS 
WILL HAVE RAMIFICATIONS ON THE PIEDMONT AIR MASS ONCE PRECIP STARTS. 
MEANWHILE... THE MID LEVEL VORTEX NOW OVER SOUTHERN OR AND NORTHERN 
CA EJECTS EASTWARD ACROSS THE ROCKIES INTO THE PLAINS TUESDAY... AND 
THE RESULTING BROAD CYCLONIC FLOW HELPS TO PULL ABUNDANT DEEP 
MOISTURE... NOW OVER MEXICO AND OFF ITS PACIFIC COAST AND OVER THE 
NORTHWEST GULF (PW OVER 1.5 IN.)... RAPIDLY NORTHEASTWARD. AN 850 MB 
WARM FRONT APPROACHES FROM THE SOUTH LATE TUESDAY... BUT DOESN'T 
QUITE GET INTO THE CWA UNTIL AROUND 00Z. THE INCREASE IN 925 MB 
MOISTURE TRANSPORT IS SIMILARLY DELAYED UNTIL AFTER DARK... WHEN THE 
UPPER DIVERGENCE -- MAXIMIZED BENEATH THE IDEALLY JUXTAPOSED RIGHT 
ENTRANCE REGION OF THE JET OFF NEW ENGLAND AND LEFT EXIT REGION OF 
THE JET STRETCHING FROM AZ/NM TO AR/TN -- ALSO RAMPS UP QUICKLY OVER 
NC. WILL INCLUDE A SMALL POP OVER THE SOUTHWEST CWA LATE IN THE 
DAY... AFTER 2 PM. BUT MID AND HIGH CLOUDS SHOULD BE PLENTIFUL 
AREAWIDE WITH LOWER CLOUDS ARRIVING IN THE AFTERNOON. FACTORING IN 
THICKNESSES AND CLOUDS... EXPECT HIGHS OF 47-54... WITH THE 50S ONCE 
AGAIN CONFINED TO THE SOUTHEAST CWA. 

FOR TUESDAY NIGHT/WEDNESDAY: YET ANOTHER SIGNIFICANT STORM SYSTEM 
AFFECTS THE REGION. STRONG FORCING FOR ASCENT THROUGH THE COLUMN... 
INDUCED BY UPPER DIVERGENCE / MID LEVEL DPVA / DEEP MOIST UPGLIDE... 
ALONG WITH INCOMING PW NEARLY 300% OF NORMAL MAKES PRECIP IN NC A 
NEAR CERTAINTY. THE NAM/GFS ARE IN REMARKABLY GOOD AGREEMENT ON AN 
INTENSE PRIMARY SURFACE LOW TRACKING UP THROUGH IL/IN TUESDAY NIGHT 
WHILE IN NC... THE COASTAL FRONT SURGES INLAND INTO THE EASTERN 
PIEDMONT WHERE A SECONDARY SURFACE LOW FORMS ALONG THE EDGE OF 
DAMMING WEDGE THAT APPEARS LIKELY TO SET UP IN THE CLIMATOLOGICALLY 
FAVORED AREA OF THE NORTHWEST PIEDMONT BACK INTO THE FOOTHILLS. THE 
ECMWF/CANADIAN ARE LESS DEFINED WITH A SECONDARY LOW ALONG THE WEDGE 
FRONT BUT SHOW A SIMILAR PATTERN... PUSHING CONFIDENCE IN THIS 
SCENARIO ABOVE NORMAL. WILL CONTINUE CATEGORICAL POPS CWA-WIDE 
TUESDAY NIGHT THROUGH WEDNESDAY MORNING. RAINFALL AMOUNTS ARE TOUGH 
TO PINPOINT AT THIS RANGE BUT THE HIGH MOISTURE... DEEP WARM LAYER 
OVER EASTERN NC... AND STRONG FORCING SUGGEST AN INCH OR TWO OF RAIN 
IS POSSIBLE. FORTUNATELY... THE CHANCE FOR A LITTLE ICING IN THE 
NORTHWEST PIEDMONT AT ONSET IS LOOKING VERY LOW BASED ON TRIAD 
FORECAST SOUNDINGS SHOWING ABOVE-FREEZING AIR AT THE SURFACE. THE 
POTENTIAL FOR A SIGNIFICANT SEVERE WEATHER EPISODE REMAINS... WITH 
VERY STRONG KINEMATICS EXPECTED... HOWEVER AS WAS THE CASE WITH THIS 
PAST WEDNESDAY NIGHT... THE LOW INSTABILITY MAY BE THE LIMITING 
FACTOR HERE. MODELS AGREE QUITE WELL ON AN INCOMING 50-60 KT 850 MB 
JET NOSING INTO CENTRAL NC FROM THE SOUTHWEST OVERNIGHT... AND DEEP 
LAYER SHEAR NEAR 70 KTS IS MORE THAN ENOUGH FOR ORGANIZED 
CONVECTION... PLUS THE UPPER DIVERGENCE STRENGTHENS AS THE NOSE OF 
THE 120+ KT JET TO OUR WEST ARRIVES. BUT FORECAST SOUNDINGS SHOW 
RELATIVELY STABLE AIR BELOW 700 MB EVEN IN THE WARM SECTOR... AND 
EVEN ELEVATED CONVECTION LOOKS UNLIKELY. BUT GIVEN THIS PATTERN WE 
COULD STILL SEE BOWING SEGMENTS PRODUCING STRONG DAMAGING WINDS... 
AS WELL AS ISOLATED TORNADOES ALONG THE WEDGE FRONT WHERE LOW LEVEL 
VORTICITY WILL BE ENHANCED. EXPECT TEMPS TO HOLD STEADY IN THE 
NORTHWEST PIEDMONT OVERNIGHT AND RISE SLOWLY ELSEWHERE. ON 
WEDNESDAY... ONCE THE LOW LEVEL JET HEADS TO OUR EAST... THE MID 
LEVEL TROUGH AXIS MOVES TO OUR NORTHEAST... AND THE UPPER JET CORE 
SHIFTS NORTH... LIFT WILL DIMINISH AS THE MID AND UPPER LEVEL DRY 
AIR PUNCHES FROM THE WEST-SOUTHWEST. WILL TAPER OFF POPS THROUGH THE 
AFTERNOON. THE COLD FRONT IS NOT EXPECTED TO PASS THROUGH CENTRAL NC 
UNTIL AFTER SUNDOWN... SO ONCE THE AREA SEES A LITTLE SUN IN THE 
AFTERNOON WITH THICKNESSES STILL HOLDING WELL ABOVE NORMAL AT 
1360-1375 M AHEAD OF THE FRONT... TEMPS SHOULD EASILY WARM INTO THE 
MID 50S TO UPPER 60S. -GIH

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
AS OF 255 AM SUNDAY...

LITTLE CHANGE TO EXISTING FORECAST. A CHILLY SURFACE HIGH BUILDS IN 
FROM THE WEST-SOUTHWEST WEDNESDAY NIGHT THROUGH FRIDAY... YIELDING 
PARTLY TO MOSTLY SUNNY SKIES... WITH A STABLE/DRY COLUMN AND LITTLE 
MORE THAN HIGH THIN CLOUDS... AND BELOW NORMAL TEMPS FOLLOWING THE 
LOW LEVEL THICKNESSES. THE GFS/ECMWF AGREE ON BROADLY CYCLONIC FLOW 
COVERING THE CONUS INTO THE WEEKEND. A MID LEVEL PERTURBATION 
APPROACHES FROM THE SOUTHWEST FRIDAY NIGHT/SATURDAY... WITH THE GFS 
REMAINING MUCH FASTER BRINGING THIS FEATURE IN AS COMPARED TO THE 
ECMWF. WILL HOLD ONTO CHANCE POPS SPREADING IN FROM THE SOUTHWEST 
LATE FRIDAY NIGHT INTO SATURDAY... AND WAIT FOR BETTER MODEL 
AGREEMENT ON TIMING BEFORE INCREASING POPS. -GIH

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
AS OF 1240 AM SUNDAY...

DRY COLD HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE AREA THIS 
MORNING. LINGERING LOW LEVEL MOISTURE ACROSS THE EASTERN TAF SITES 
(KRDU... KFAY... AND KRWI) COULD PRODUCE A BRIEF PERIOD OF MVFR 
VSBYS OR CIGS THROUGH 10Z. OTHERWISE... VFR CONDITIONS ARE EXPECTED 
FOR THE ENTIRE TAF FORECAST PERIOD... AS HIGH PRESSURE MOVES ACROSS 
THE REGION. NORTHERLY WINDS TONIGHT... WILL BECOME LIGHT AND 
VARIABLE ACROSS THE AREA BY AFTERNOON AS THE SURFACE HIGH CROSSES 
THE AREA. SKIES SHOULD BE MOSTLY CLEAR TODAY... WITH ONLY A FEW TO 
SCATTERED HIGH CIRRUS CLOUDS TRAVERSING THE SKIES OF CENTRAL NORTH 
CAROLINA IN THE AFTERNOON AND EVENING.

LOOKING BEYOND 06Z MONDAY... THERE WILL BE ANOTHER CHANCE OF MVFR 
CONDITIONS AND A LITTLE LIGHT RAIN AND/OR DRIZZLE... MAINLY AT 
EASTERN TERMINALS... AHEAD OF A WEAKER STORM SYSTEM ON MONDAY. AFTER 
A RETURN TO VFR FOR MONDAY NIGHT AND TUESDAY... EXPECT LIFR/IFR 
CONDITIONS AND A COLD RAIN ASSOCIATED WITH A STRONGER STORM SYSTEM 
TUESDAY NIGHT AND WEDNESDAY.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...BSD
NEAR TERM...BSD
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...BSD/KR