FXUS62 KRAH 171936
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
230 PM EST THU JAN 17 2008

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL TRACK NORTHEAST ALONG THE SOUTHEAST COAST 
TODAY.  WEAK HIGH PRESSURE WILL MOVE ACROSS CENTRAL NORTH CAROLINA 
FRIDAY.  ANOTHER LOW PRESSURE SYSTEM FROM THE GULF OF MEXICO WILL 
MOVE UP THE SOUTHEAST COAST SATURDAY.  HIGH PRESSURE WITH MUCH 
COLDER AIR WILL EXPAND INTO THE AREA FROM THE WEST SUNDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
AS OF NOON THURSDAY...
WINTER WEATHER ADVISORY HAS NOW EXPIRED FOR THE NW PIEDMONT AND
PERSON COUNTY. WHATEVER SLIGHT FREEZING RAIN REMAINS IN THE FAR NW
CORNER OF THE CWA SHOULD HAVE NEGLIGIBLE ADDITIONAL ACCRUAL.

STRONG LOW LEVEL FLOW VEERING WITH HEIGHT FROM NE TO SE IS
EVIDENT ON THE RADAR VWP NETWORK ACROSS THE REGION. SATELLITE
IMAGERY SHOW A SHORT WAVE CONTINUING TO MOVE ENE ACROSS THE UPPER
SAVANNAH BASIN WITH WIDESPREAD RAIN OVER CENTRAL NC EXPECTED
THROUGH EARLY AFTERNOON.

CONTINUED SATURATION IN THE LOWEST LAYERS AND LACK OF PUSH OF ANY
DRIER AIR INTO THE REGION IS LIKELY TO RESULT IN LINGERING
CLOUDINESS AND POSSIBLY FOG INTO THE NIGHTTIME HOURS. TEMPERATURES
WILL FALL SLOWLY AND SHOULD HOLD AT OR ABOVE FREEZING MOST OF THE
NIGHT. NEAR DAYBREAK...PARTIAL CLEARING COULD LEAD TO SURFACE
COOLING AND A BRIEF PERIOD OF BLACK ICE POTENTIAL MAINLY IN THE
WEST. -RFG

AS OF 330 AM THURSDAY...
FRIDAY...HIGH CLOUDINESS IS EXPECTED TO REMAIN ACROSS THE AREA.
HIGH TEMPS WILL RANGE FROM NEAR 50 IN THE NW PIEDMONT TO THE MID
50S IN THE COASTAL PLAIN. -VINCENT
&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...

AS OF 200 PM THURSDAY...
MID AND HIGH CLOUDINESS WILL SPREAD NORTHEAST RAPIDLY AHEAD OF THE 
DEVELOPING LOW OVER THE NORTHERN GULF OF MEXICO. WILL HAVE VERY 
RAPID MOISTURE ADVECTION IN DEEP SOUTHWEST FLOW...WITH A CHANCE OF 
RAIN REACHING THE SOUTHERN TIER AFTER MIDNIGHT AND OVERSPREADING THE 
CWFA DURING THE MORNING. AT THE ONSET...SURFACE TEMPS WILL BE AROUND 
FREEZING AND THE VERTICAL TEMP PROFILE SUPPORTS A MIX OF RAIN AND 
SNOW ACROSS THE NORTHERN TIER.

THE GFS HANDLED THE PAST SYSTEM QUITE WELL AND IS SUPPORTED BY THE 
ECMWF...SO WILL LEAN TOWARDS THEIR SOLUTION...WHICH HAS THE MILLER A 
LOW RACING UP THE COAST ON A MORE OFFSHORE TRAJECTORY. THIS LOOKS 
QUITE PLAUSIBLE CONSIDERING THE VERY COLD AIRMASS WHICH WILL BE 
NOSING INTO PLACE AS THE UPPER TROF ROTATES RAPIDLY ACROSS THE GREAT 
LAKES. 

CLIMATOLOGICALLY...WE HAVE VERY LITTLE ICING ASSOCIATED WITH MILLER 
A LOWS...AS WE HAVE A NARROW TRANSITION ZONE...OR RAIN-SNOW LINE. 
THE POSITION AND TIMING OF THIS TRANSITION ZONE AS IT SHIFTS EAST 
WILL BE THE MAJOR PROBLEM. IF THE COLD AIR FLOWS IN BEFORE THE RAIN 
ASSOCIATED WITH THE COASTAL LOW LIFTS OUT...THIS EARLY CHANGEOVER TO 
SNOW COULD PRODUCE ADVISORY OR PERHAPS EVEN WARNING CRITERA 
SNOWFALL. PINNING THE FINE DETAILS DOWN AT THIS TIME WOULD LIKELY 
RESULT IN A FLIP-FLOPPING FORECAST...THUS WILL OPT FOR A MORE 
CONSERVATIVE APPROACH...WITH A RAIN/SNOW MIX IN THE NORTH/NORTHWEST 
IN THE MORNING...WITH THE RAIN MIXING WITH SNOW EASTWARD AS THE DAY 
PROGRESSES. HIGHS WILL TOP OUT MOSTLY IN THE 30S...WITH SOME LOWER 
40S IN THE SOUTHEAST...DUE TO EXTENSIVE CLOUDINESS AND EVAPORATIVE 
COOLING. 

PRECIP WILL CUT OFF QUICKLY IN THE EVENING AS THE STRONG DRY...COLD 
AIR ADVECTION REALLY KICKS IN AFTER 00Z. WILL END PRECIP BY 03Z IN 
THE EAST WITH RAPID CLEARING. CRASHING THICKNESS VALUES SUPPORT LOWS 
IN THE TEENS IN THE WEST TO LOWER 20S EAST. NO RECOVER ON TAP 
SUNDAY...WITH COLD AIR CONTINUING TO SETTLE INTO PLACE...DESPITE 
SUNNY SKIES...HIGHS WILL TOP OUT IN THE 30 TO 35 DEGREE RANGE.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...

AS OF 1100 AM THURSDAY...

SUNDAY NIGHT AND MONDAY: LOOK FOR COLDEST NIGHT DURING THIS ARCTIC 
OUTBREAK TO OCCUR SUNDAY NIGHT/MONDAY MORNING...WITH MODEL CONSENSUS 
INDICATING OPTIMAL RADIATIONAL CONDITIONS AS COLD SURFACE HIGH 
BUILDS DIRECTLY OVER THE AREA...BEFORE PUSHING OFFSHORE DURING THE 
DAY ON MONDAY. MINS MONDAY MORNING IN THE LOWER TO MID TEENS. THEN 
THE MODERATION OF THE FRIGID CONDITIONS BEGIN DURING THE DAY ON 
MONDAY FROM RISING HEIGHTS ALOFT AND THE ONSET ON SWLY LOW-LEVEL 
WAA. HIGHS 40 TO 45.  

TUESDAY THROUGH THURSDAY: MID AND UPPER FLOW FLOW IS EXPECTED TO 
BECOME NEARLY ZONAL ACROSS MUCH OF THE CONUS THROUGH THE PERIOD WITH 
MODERATION CONTINUING AS RETURN FLOW CIRCULATING AROUND THE 
ANTICYCLONE OFF THE SOUTHEAST COAST...MARKING THE RETURN OF NEAR 
NORMAL CONDITIONS. 

OF LESS UNCERTAINTY ARE RAIN CHANCES AND MOISTURE AVAILABILITY DURING
THE LATTER PART OF THE PERIOD AS MODEL DISCREPANCIES EVOLVE 
REGARDING THE DEPARTURE OF A CLOSED LOW OVER THE NW PACIFIC/SW 
CONUS. THE GFS AND ECMWF ARE THE FASTEST WITH THIS SYSTEM'S EASTWARD 
PROGRESSION...WHILE THE CANADIAN/UKMET/NOGAPS DEPICT SLOWER TIMING. 
OBVIOUS FORCING/LIFT IS ABSENT...WITH THE GFS DEPICTION OF 
ISENTROPIC LIFT OVER THE REGION LATE TUESDAY AND WEDNESDAY IN 
QUESTION WITH UNCERTAINTY IN THE EJECTION OF THE  SW CLOSED LOW.
GIVEN THE LOW PREDICTABILITY OF THESE SMALL SCALE FEATURES...WILL 
KEEP POPS IN THE SLIGHT TO LOW CHANCE CATEGORY THROUGH THURSDAY. 

CBL

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 1240 PM THURSDAY... LOW PRESSURE WILL RIDE UP THE NC COAST 
THIS EVENING.  IN ITS WAKE...WEAK FLOW PATTERN ALLOWS SATURATED AIR 
TO LINGER IN THE COOL SURFACE BASED LAYER OVERNIGHT.  FREQUENT IFR 
CONDITIONS IN RAIN AND DRIZZLE THIS AFTERNOON WILL CONTINUE WITH IFR 
AND LIFR MAINLY CAUSED BY LOW STRATUS OVERCAST.  MODELS SHOW AN 850 
MB TROUGH CROSSING THE MTNS BETWEEN 06Z AND 12Z.  THIS SHOULD ALLOW 
A SURGE OF DRIER AIR TO INFILTRATE THE AREA FROM HIGH PRESSURE TO 
THE WEST AROUND DAYBREAK.  IN THE PIEDMONT TERMINALS AT KINT...KGSO 
...AND KRDU...A SUDDEN CLEARING OF THE CLOUDS AROUND DAYBREAK MAY 
LEAD TO BLACK ICE FROM RESIDUAL MOISTURE ON PAVED SURFACES.

WEAK HIGH PRESSURE WILL MAINTAIN VFR CONDITIONS OVER CENTRAL NC ON 
FRI INTO FRI NIGHT.

ANOTHER AREA OF LOW PRESSURE WILL DEVELOP OVER THE GULF OF MEXICO BY 
SAT MORNING AND RIDE UP THE SOUTHEAST U.S. COAST ON SAT.  THIS IS 
EXPECTED TO LOWER CIGS AND VSBY TO MVFR AND IFR IN STRATUS AND 
PRECIPITATION DURING THE DAY.  PRECIPITATION MAY TAKE THE FORM OF 
RAIN OR SNOW...WITH THE GREATEST CHANCES OF SNOW OR MIXED RAIN AND 
SNOW NORTHWEST AT KINT...KGSO...AND LESSER CHANCES SOUTHEAST AT 
KRDU...KFAY...AND KRWI.  

VERY COLD AIR WITH LONG DURATION SUBFREEZING SURFACE TEMPERATURES 
ARE EXPECTED FOR SAT NIGHT-MON NIGHT.  OTHERWISE HIGH PRESSURE AND A 
DRY AIRMASS SHOULD MAINTAIN VFR CONDITIONS.  

FOR TUE...MOIST SWLY FLOW AND INCREASING MOISTURE MAY LEAD TO 
LOWERING STRATOCUMULUS CLOUD BASES AND POSSIBLE MVFR CONDITIONS.
-RFG

&&

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

&&

$$
SYNOPSIS...RFG
NEAR TERM...RFG
SHORT TERM...VINCENT/MWS
LONG TERM...CBL
AVIATION...RFG