FXUS62 KRAH 160229
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
927 PM EST TUE DEC 15 2009

.SYNOPSIS...

A COLD FRONT WHICH WILL DROP SOUTHEAST THROUGH THE STATE THIS 
EVENING. COLD HIGH PRESSURE OVER THE UPPER MIDWEST WILL BUILD 
SOUTHEAST INTO OUR REGION TONIGHT THROUGH THURSDAY NIGHT. A LOW 
PRESSURE SYSTEM WILL SKIRT BY JUST TO OUR SOUTH AND EAST FRIDAY INTO 
THE WEEKEND.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
AS OF 925 PM TUESDAY...

A DRY COLD FRONT IS CURRENTLY CROSSING CENTRAL NORTH CAROLINA THIS 
EVENING... USHERING IN DRIER AIR AND EVENTUALLY COOLER AIR. THE GOOD 
CAA APPEARS TO BE LAGGING A BIT AS IT USUALLY THE CASE WITH FRONTS 
MOVING INTO THE AREA THIS TIME OF DAY... THANKS TO THE MOUNTAINS. 
THUS... TEMPERATURES IN THE TRIAD ARE STILL IN THE UPPER 40S TO 
LOWER 50S... WITH THE ACTUAL FRONT (AS OF 9 PM) LOCATED JUST TO THE 
SOUTH AND EAST OR RALEIGH (ROUGHLY ALONG A LINE EXTENDING FROM 
WADESBORO, NC TO WILSON, NC). GIVEN THE BOUNDARY LAYER SHOULD REMAIN 
MIXED AS THE FRONT MOVES THROUGH THE AREA AND SEVERAL HOURS 
THEREAFTER... AND ALONG WITH AMPLE MID AND HIGH LEVEL MOISTURE STILL 
PRESENT VIA THE STRONG JET ALOFT (WITH LOW LEVEL MOISTURE STILL 
PRESENT AHEAD OF THE LOW LEVEL FRONT) WILL SHOW A SLOWER DECLINE OF 
TEMPERATURES THIS EVENING IN THE FORECAST... AND INCREASE LOW TEMPS 
BY A COUPLE OF DEGREES. EXPECT SKIES TO BECOME MOSTLY CLEAR TO 
PARTLY CLOUDY ACROSS THE AREA BY 06Z WEDNESDAY AS THE 500 MB TROUGH 
SWINGS THROUGH THE CWA... ALLOWING FOR MID LEVEL MOISTURE TO MOVE 
EAST AND SOUTH OF THE AREA. BY MORNING EXPECT SKIES TO GENERALLY BE 
MOSTLY CLEAR ACROSS THE AREA... WITH ONLY SCATTERING OF HIGH CLOUDS 
STILL AROUND... AND TEMPS BOTTOMING OUT ACROSS THE IN THE MID 30S IN 
THE NORTHWEST TO THE LOWER 40S IN THE SOUTHEAST.

COLD HIGH PRESSURE WILL BUILD INTO THE AREA FROM THE WEST ON 
WEDNESDAY... WITH A WNW FLOW ALOFT. GIVEN LOW LEVEL THICKNESS VALUES 
AREA EXPECT ONLY TO WARM TO NEAR 1300 TO 1305 METERS OR SO... EXPECT 
HIGH TEMPS TO BE CONSIDERABLE COOLER THAN TODAY. HOWEVER... WITH 
MOSTLY SUNNY SKIES AND A DRY ADIABATIC PROFILE UP TO AROUND 900 
MB... IN HOUSE THICKNESS TEMPERATURE SCHEME INDICATES TEMPS TOPPING 
OUT IN THE UPPER 40S ACROSS THE NORTH TO THE LOWER TO MID 50S ACROSS 
THE SOUTH... WHICH SEEMS REASONABLE AND BLENDS WELL WITH MOS 
STATISTICAL GUIDANCE. 

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
AS OF 230 PM TUESDAY...

FOR WEDNESDAY NIGHT THROUGH THURSDAY: COLD AND DRY WEATHER WILL 
DOMINATE... ALTHOUGH SKIES BEGIN TO CLOUD UP HEADING INTO THURSDAY 
NIGHT THANKS TO A SOUTHERN STREAM WAVE (NOW DROPPING THROUGH THE 
WEST TEXAS HILL COUNTRY) AND A WEAK NORTHERN WAVE THAT DROPS THROUGH 
THE UPPER MIDWEST ON THURSDAY AND ATTEMPTS TO GRAB THE SOUTHERN WAVE 
AND KICK IT EASTWARD... RESULTING IN NEARLY PHASED TROUGHING OVER
THE MIDSOUTH AND GULF STATES. A RIDGE OF ARCTIC SURFACE HIGH
PRESSURE CENTERED OVER WISCONSIN AND LOWER MICHIGAN WEDNESDAY
EVENING (WITH A SMALLER PORTION CENTERED OVER THE OHIO VALLEY AND
WEST VIRGINIA) EDGES SLOWLY TO THE EAST NORTHEAST THROUGH FRIDAY
WHILE EXTENDING SOUTH INTO NORTH CAROLINA. MID LEVEL FLOW REMAINS
OUT OF THE WEST NORTHWEST AND THE VERTICAL THERMAL STRUCTURE OVER
NORTH CAROLINA BASED ON FORECAST SOUNDINGS SUGGESTS THAT WE MAY
SEE SOME OROGRAPHICALLY ENHANCED HIGH CLOUDINESS LATE WEDNESDAY
NIGHT... HOWEVER ANY SUCH CLOUDS WOULD BE THIN AND DO LITTLE TO
IMPEDE SUNSHINE ON THURSDAY. THE COLUMN REMAINS DRY... INCLUDING
NEAR THE GROUND... THUS FOG WILL NOT BE AN ISSUE. WITH WINDS
BECOMING VERY LIGHT WEDNESDAY NIGHT BENEATH AN ANOMALOUSLY CHILLY
AIR MASS... EXPECT LOWS TO BE JUST UNDER STATISTICAL GUIDANCE...
24 TO 29. LOW LEVEL THICKNESSES AS WELL AS ADJUSTED HIGHS SHOWN BY
THE LOCAL DRY ADIABATIC MAXIMUM TEMPERATURE TOOL INDICATE HIGHS OF
47 TO 52... ROUGHLY A CATEGORY BELOW NORMAL.

FOR THURSDAY NIGHT AND FRIDAY: BY LATE WEEK WE START TO SEE SIGNS
OF A POTENTIALLY VERY ACTIVE WEEKEND SETTING UP. AS THE SOUTHERN
STREAM WAVE EMERGES OFF THE TEXAS COAST AND SHIFTS SOUTH OF
LOUISIANA AND MISSISSIPPI THURSDAY NIGHT WITH THE NORTHERN WAVE
AMPLIFYING NOT TOO FAR TO ITS NORTHWEST... UPPER DIVERGENCE
GENERATED BY IDEALLY JUXTAPOSED JETS (OVER THE CENTRAL GULF AND
EXTENDING FROM NEW JERSEY AND NEW YORK CITY EAST OVER THE
ATLANTIC) STRENGTHENS OVER THE CAROLINAS AND SOUTHEAST. WITH THE
ARCTIC SURFACE RIDGE LEADING TO AN EXTENSIVE COLD AIR OUTBREAK
OVER THE GULF COAST... IT IS NOT SURPRISING THAT THE MODELS ARE
INDICATING SURFACE CYCLOGENESIS OVER THE NORTHWEST GULF LATE
THURSDAY WHICH DEEPENS WHILE CROSSING INTO NORTHERN FL ON FRIDAY.
THE EASTWARD SHIFTING SURFACE RIDGE COMBINED WITH THIS LOW SHOULD
SERVE TO SLOWLY INCREASE LOW LEVEL ATLANTIC MOISTURE INFLUX OVER
SOUTHERN NORTH CAROLINA BY LATE FRIDAY... IN TANDEM WITH THE
DEEPENING MID AND HIGH LEVEL MOISTURE WITH THE APPROACHING MID
LEVEL TROUGH. BUT THE SURFACE RIDGING PERSISTS OVER NORTHERN NORTH
CAROLINA... REFLECTED WELL IN NAM FORECAST SOUNDINGS SHOWING A
RATHER DRY SUBCLOUD LAYER. WILL INCLUDE JUST A SLIGHT CHANCE OF
RAIN ACROSS THE SOUTH ON FRIDAY. LOWS THURSDAY NIGHT 27 TO 32
WITH SKIES BECOMING PARTLY CLOUDY. HIGHS FRIDAY 46 TO 50 WITH
INCREASING CLOUDINESS AND THICKNESSES HOLDING BELOW NORMAL. -GIH

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
AS OF 245 PM TUESDAY...

     SOUTHEAST COASTAL STORM IS POSSIBLE EARLY IN THE WEEKEND...

FOR FRIDAY NIGHT THROUGH SUNDAY: AS PREVIOUS SHIFTS HAVE NOTED... A 
CONTINUATION OF A POSITIVE PNA AND NEGATIVE NAO PATTERN IS EXPECTED 
INTO THE MEDIUM RANGE... FAVORING GENERALLY COOL AND STORMY WEATHER 
FOR THE SOUTHEAST. UNFORTUNATELY THE LATEST ROUND OF OPERATIONAL 
MODELS DOES NOT BUOY CONFIDENCE IN THE DETAILS OF THIS STORM SYSTEM. 
THEY AGREE ON THE SURFACE LOW EXITING THE NORTHEAST FL COAST TO JUST 
OFF THE SOUTHEAST COAST FRIDAY NIGHT... BUT THEN THEIR SOLUTIONS 
DIVERGE MARKEDLY. THE GFS... WHICH HAS NOT DONE TOO WELL LATELY 
HANDLING MID LEVEL POTENTIAL VORTICITY MAXIMA PRODUCED BY GULF COAST 
CONVECTION... IS AMONG THE WETTEST OF THE OPERATIONAL MODELS OVER
WESTERN NORTH CAROLINA FRIDAY NIGHT AND SATURDAY AND THIS 12Z RUN
IS MUCH WETTER THAN ITS 06Z RUN. THE 12Z CANADIAN HAS A MORE
POSITIVELY TILTED MID LEVEL TROUGH COMPARED TO ITS MORE UPRIGHT
00Z RUN AND AS A RESULT IT SHOOTS THE SURFACE LOW AWAY FROM THE
COAST INSTEAD OF DEEPENING IT ALONG THE MID ATLANTIC COAST AS ITS
00Z RUN SHOWED. AND THE ECMWF... WHOSE 00Z RUN BOMBED OUT THE
SURFACE LOW ALONG THE NORTH CAROLINA COAST SATURDAY NIGHT AND SUNDAY
AND THREW PRECIPITATION WEST OVER THE ENTIRE CWA... IS NOW EVEN
DEEPER BUT FASTER WITH THE SURFACE LOW... AND EERILY RESEMBLES THE
12Z GFS TRACKING A STRONG LOW UP THE NORTH CAROLINA COAST. THE 12Z
GEFS MEAN... HOWEVER... SUPPORTS THE SURFACE LOW MOVING AWAY FROM
THE CAROLINA COAST BY MIDDAY SATURDAY. WITH RATHER POOR RUN-TO-RUN
CONSISTENCY AND LIMITED AGREEMENT AMONG THE MODELS... DO NOT WANT
TO JUMP TOO QUICKLY INTO A MAJOR COASTAL STORM... BUT THESE LATEST
MODEL TRENDS DO NECESSITATE BRINGING IN AT LEAST GOOD CHANCE POPS
IN THE SOUTHEAST HALF OF THE CWA WITH SLIGHT CHANCES IN THE
NORTHWEST... MAINLY LATE FRIDAY NIGHT THROUGH SATURDAY EVENING.
FURTHER COMPLICATING THE FORECAST ARE THE PARTIAL THICKNESSES FROM
THE 00Z/12Z ECMWF AND 12Z GFS WHICH SUGGEST A POSSIBLE WINTRY MIX
DOMINATED BY--OR TRANSITIONING TO--A BAND OF WET SNOW ON THE
WESTERN AND NORTHERN SIDES OF THE PRECIPITATION SHIELD. AS THIS IS
DAY 4 OF THE FORECAST AND CONFIDENCE IN THE DETAILS IS BELOW
NORMAL... WILL KEEP THE FORECAST ALL LIQUID FOR NOW... AS THERE IS
PLENTY OF TIME FOR THE MODEL SOLUTIONS TO CONVERGE. BUT... GIVEN
THE RECENT OPERATIONAL MODEL TRENDS... THE PREVAILING CIRCULATION
PATTERN... AND THE VERY COLD NATURE OF THE AIR MASS... THERE IS A
RISK OF SIGNIFICANT WINTRY PRECIPITATION OVER NORTH CAROLINA WITH
THIS SYSTEM... AND PEOPLE SHOULD CERTAINLY CHECK BACK WITH LATER
FORECASTS IN THE ENSUING DAYS. EXPECT LOWS OF 32 TO 37 FRIDAY
NIGHT AND SATURDAY NIGHT. HIGHS SATURDAY 38 TO 45... AND EVEN
THIS MAY NOT BE COOL ENOUGH IF THERE IS GREATER PRECIPITATION
COVERAGE. WILL INDICATE A SLOW CLEARING SATURDAY NIGHT AS THE
MID LEVEL TROUGH AXIS SHIFTS OVERHEAD AND TO OUR EAST WITH
NORTHWEST SURFACE FLOW THROUGH SUNDAY. HIGHS SUNDAY 40 TO 47 WITH
GFS/ECMWF THICKNESSES WELL BELOW SEASONAL NORMALS.

FOR SUNDAY NIGHT THROUGH TUESDAY: WILL HAVE DRY AND COLD CONDITIONS 
FOR THE FIRST PART OF NEXT WEEK. DEEP POLAR TROUGHING COVERS ALL OF 
EASTERN NORTH CAROLINA WITH A STORM TRACK STRAIGHT OUT OF THE
YUKON. EXPECT A FAST WESTERLY MID LEVEL FLOW OVER NORTH CAROLINA
WITH CHILLY HIGH PRESSURE TRYING TO BUILD INTO NORTH CAROLINA FROM
THE WEST. LOWS IN THE LOWER TO MID 20S AND HIGHS IN THE LOW TO MID
40S. -GIH

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
AS OF 650 PM...

SOME VFR CEILINGS NEAR 6000 FEET IN THE SOUTHEAST WILL DISSIPATE
LATER THIS EVENING... THEN VFR THROUGH THE TAF PERIOD. STEADY
NORTHWEST TO NORTH WINDS THROUGH THE TAF PERIOD WITH SOME BRIEF
GUSTINESS IN THE IMMEDIATE VICINITY OF A COLD FRONT WHICH WILL
PASS THROUGH CENTRAL NORTH CAROLINA TONIGHT.

VFR CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THURSDAY NIGHT.
 
THE NEXT CHANCE FOR ADVERSE AVIATION CONDITIONS WITH IFR TO LIFR
CEILINGS AND VISIBILITIES AT TIMES WILL ARRIVE PERHAPS AS EARLY
AS FRIDAY AND PERSIST INTO SATURDAY. VFR CONDITIONS BY SUNDAY
MORNING. 

&&

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

&&

$$

NEAR TERM...BSD
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD