Debris Flow in North Carolina, February 5, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
253 PM EST FRI FEB 5 2010

.SYNOPSIS...
A LOW PRESSURE SYSTEM WILL INTENSIFY AS IT MOVES NORTHEASTWARD OUT
OVER THE MID ATLANTIC COASTAL WATERS THROUGH SATURDAY.  AN AREA OF
HIGH PRESSURE WILL BUILD IN FROM THE NORTHWEST TO END THE WEEKEND
AND BEGIN THE UPCOMING WEEK. ANOTHER LOW PRESSURE SYSTEM AND FRONT
WILL APPROACH THE FORECAST AREA FROM THE WEST BY THE MIDDLE OF NEXT
WEEK.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
BACK EDGE OF PRECIP ASSOCIATED WITH WARM CONVEYOR BELT OF DEEPENING
COASTAL STORM IS MOVING RAPIDLY ACROSS THE CWFA ATTM. AS THE LOW
CONTINUES TO DEEPEN TO OUR EAST...THE BACK EDGE MAY SLOW...OR EVEN
PIVOT SLIGHTLY INTO EASTERN PORTIONS OF THE CWFA...SO WE WILL HOLD
ON TO HEALTHY POPS THERE THROUGH MID-EVENING.

FREEZING RAIN IS CURRENTLY CONFINED TO A NARROW SWATH ALONG THE
EASTERN ESCARPMENT THIS AFTERNOON...WHERE WIDESPREAD POWER OUTAGES
AND SIGNIFICANT ICING HAVE BEEN REPORTED. FORTUNATELY...THE HEAVY
PRECIP IS ALMOST OVER IN THESE AREAS. OUR CURRENT PLAN IS TO
DOWNGRADE ALL WARNINGS TO A FREEZING RAIN ADVISORY OVERNIGHT...AS
WRAP AROUND -FZRA/-FZDZ WILL REMAIN POSSIBLE THROUGH THE PERIOD.
ALTHOUGH THE WARM NOSE WILL BE REMOVED LATER TONIGHT...AS COLDER
LOW/MID LEVEL AIR WRAPS AROUND THE COASTAL STORM...DRYING ALOFT WILL
RESULT IN AN ABSENCE OF SATURATION IN THE DENDRITIC SNOW GROWTH
LAYER. IN OTHER WORDS...THE SOUNDINGS WILL STILL FAVOR FREEZING AS
OPPOSED TO FROZEN PRECIP. WE WILL ALSO CHANGE THE ADVISORY FOR
HAYWOOD/MADISON TO A FZRA ADVISORY AND EXTEND IT TO 6 AM...AS THESE
AREAS ARE LIKELY TO DIP BELOW FREEZING AFTER MIDNIGHT.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
AS OF 230 PM FRIDAY...MODELS STILL SUPPORT THE NOTION THAT OUR
TRANSITION TO A NW FLOW SNOW EVENT SHOULD BE COMPLETE. THE UPPER LOW
SHOULD BE CENTERED OVER THE MOUNTAINS AT 12Z SATURDAY WITH THE
STRONGEST VORT CENTER ROTATING ACROSS THE PIEDMONT. THIS BIT OF
UPPER FORCING SHOULD ALLOW SOME SHOWER ACTIVITY TO BREACH
CONTAINMENT AND MOVE OUT EAST OF THE MTNS SATURDAY MORNING. BY
AFTERNOON...THE UPPER SYSTEM MOVES OFF TO OUR EAST AND THICKNESS
CONTINUES TO FALL. THE INTERESTING PART OF THE FORECAST IS THE
TRAILING VORT CENTER THAT MOVES ACROSS THE REGION...WHICH IS
ACCOMPANIED BY SOME SLIGHTLY DEEPER MOISTURE. WE HAVE SEEN THIS
BEFORE WHERE SOME CONFLUENCE IN THE OTHERWISE NW FLOW IS LEFT BEHIND
AT LOW LEVELS WHICH FORCES CLOUD STREETS OR HORIZONTAL ROLLS WHICH
GROW LARGE ENOUGH TO SUPPORT A BAND OR TWO OF SHOWERS. IN THIS
CASE...MOST LIKELY A BAND OR TWO OF SNOW OR RAIN SHOWERS RUNNING NW
TO SE ACROSS THE NC FOOTHILLS...SRN PIEDMONT...AND NRN UPSTATE. WILL
INCLUDE A SLIGHT CHANCE OVER THE PIEDMONT AND NRN UPSTATE TO HANDLE
THIS POSSIBILITY. ANY ACCUM SHOULD BE MINIMAL. HIGH TEMPS WERE KEPT
BELOW GUIDANCE WITH THE COLD ADVECTION BEHIND THE UPPER LOW IN MIND.
MEANWHILE...SNOW SHOWERS WILL CONTINUE TO DEVELOP ON THE TN BORDER
THROUGH THE DAY...SO POP THERE WAS BUMPED TO CATEGORICAL. THE
SMOKIES MIGHT BE FAVORED A BIT MORE WITH THE FLOW CONTINUING TO VEER
AROUND TO MORE NORTHERLY BY THE EVENING...SO THE HIGHEST AMOUNTS
WERE PUT THERE. AS A WHOLE...THE FORECAST SUPPORTS THE ISSUANCE OF
AN ADVISORY MAINLY BECAUSE SNOW TO LIQUID RATIO IS NOT EXPECTED TO
BE THAT HIGH INITIALLY...AND THE WINDS BECOME INCREASINGLY NORTHERLY
WHICH IS NOT AS FAVORABLE. THE SNOW PRODUCTION SHOULD COME TO AN END
DURING THE EARLY MORNING HOURS ON SUNDAY AS THE MOISTURE DRIES UP.

THE REST OF THE SHORT TERM IS COMPARATIVELY BORING. A FLAT UPPER
RIDGE BETWEEN SYSTEMS BUILDS IN FOR THE EARLY PART OF NEXT WEEK.
THIS WILL SUPPORT HIGH PRESSURE TO OUR NORTH RIDGING DOWN ACROSS THE
REGION SUNDAY AND MONDAY. TEMPS WERE NUDGED TOWARD A GUIDANCE BLEND.

&&

.LONG TERM /MONDAY NIGHT THROUGH THURSDAY/...
AS OF 245 PM FRIDAY...MEDIUM RANGE MODELS HAVE CONTINUED THEIR TREND
OF BETTER AGREEMENT FOR THE MID WEEK SYSTEM. THEY SHOW PHASING OF
THE SPLIT STREAM FLOW OVER THE CENTRAL CONUS AT THE START OF THE
PERIOD. THE SRN STREAM SHORT WAVE WRAPS AROUND AND AHEAD OF THE
POLAR VORTEX AS IT DROPS INTO THE MID MS VALLEY. THE SHORT WAVE
MOVES ACROSS THE AREA LATE TUESDAY AS THE VORTEX MOVES ACROSS THE
LOWER GREAT LAKES THEN INTO THE MID ATLANTIC WED. THE VORTEX MOVES
OFF SHORE THU AS ZONAL FLOW DEVELOPS OVER THE SE. THE MODELS THAN
HAVE ANOTHER SYSTEM THREATENING THE AREA FRIDAY WITH THE GFS SHOWING
A RETURN TO SPLIT FLOW WITH NO PHASING AND BRINGS THE SRN STREAM
WAVE OVER THE SE...WHILE THE ECMWF PHASES THE FLOW AND BRINGS THE
RESULTANT SYSTEM ACROSS THE AREA.

WITH THE BETTER AGREEMENT...CONFIDENCE IS GROWING THAT A MILLER B
LOW PRESSURE SYSTEM APPROACHES THE AREA MON NITE AND CROSSES THE
AREA TUESDAY. WHAT REMAINS IN QUESTION IS THE P-TYPE. USING A MODEL
BLEND OF PARTIAL THICKNESSES...WE HAVE ANOTHER SCENARIO OF COLD LOW
LEVEL AIR AS CAD DEVELOPS WITH COLD MID LEVELS TO START THEN STRONG
WARM NOSE DEVELOPING DURING THE DAY TUESDAY. SFC TEMPS WARM DURING
THE DAY AS WELL SINCE THE HIGH IS WEAK AND THE CAD SHALLOW. THAT
SAID...EXPECT PRECIP TO START AS SNOW ACROSS THE NORTH AND RAIN OR
FREEZING RAIN ACROSS THE SOUTH DEPENDING ON LOW TEMPS. SLEET WILL
LIKELY BE MIXED IN AS WELL. PRECIP WILL CHANGE TO RAIN FROM THE
SOUTH AS WEST AS TEMPS WARM THRU THE DAY. PRECIP WILL CHANGE TO
SLEET AND FREEZING RAIN...THEN RAIN ACROSS THE NORTH AS THE WARM
NOSE MOVES IN AND TEMPS WARM FROM THE SOUTH. PRECIP ENDS DURING THE
EVENING AS THE LOW PULLS AWAY TAKING THE MOISTURE WITH IT. PRECIP
TEMPS COOL BACK DOWN AS COLD AIR MOVES IN BEHIND THIS SYSTEM. EXPECT
NW FLOW SNOW TO DEVELOP OVER THE MTNS AND CONTINUE THRU WED NITE AS
WRAP AROUND MOISTURE REMAINS IN PLACE. DRY ELSEWHERE. AS MENTIONED
ABOVE...MDLS SHOW A SYSTEM AFFECTING THE AREA FRIDAY. HOWEVER...
THERE IS QUITE A BIT OF UNCERTAINTY WITH IT AS THE WEAKER AND
UN-PHASED GFS KEEPS THE LOW WEAK SOUTH INTO THE GULF AND KEEPS OUR
AREA BASICALLY DRY. THE ECMWF IS STRONGER AND PHASED WITH A MILLER A
SYSTEM MOVING ALONG THE GULF COAST...SUGGESTING SNOW FOR THE ENTIRE
CWFA. WILL KEEP FCST DRY FOR NOW DUE TO THE DIFFERENCES. LOWS NEAR
NORMAL EARLY...THEN FALLING BELOW. HIGHS HIGHS NEARLY STEADY BELOW
NORMAL THRU THE PERIOD.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
AT KCLT AND ELSEWHERE...FROZEN/FREEZING PRECIP HAS CHANGED TO RAIN
AT ALL TERMINALS...AND OTHER THAN THE POTENTIAL FOR SOME -FZDZ AT
KAVL LATER TONIGHT (POSSIBLY KHKY AS WELL)...THE THREAT FOR WINTRY
PRECIP SHOULD BE OVER. WIDESPREAD MODERATE/HEAVY RAIN WILL TAPER OFF
GRADUALLY FROM WEST TO EAST ACROSS THE AREA THIS AFTERNOON...GIVING
WAY TO DRIZZLE/-RA BY THIS EVENING. LOW (IFR/LIFR) CIGS WILL PERSIST
THROUGH THE END OF THE PERIOD. VISBY IS EXPECTED TO IMPROVE SLIGHTLY
LATER THIS AFTERNOON...AS THE RAIN TAPERS OFF...BUT WILL LIKELY
REMAIN REDUCED THROUGH MUCH OF THE PERIOD...THANKS TO -DZ/-RA.

OUTLOOK...CIG/VSBY RESTRICTIONS LIKELY THRU SAT. HI PRES REBUILDS
FOR THE FIRST PART OF NEXT WEEK. ANOTHER STORM SYSTEM WILL BRING
PRECIPITATION...POSSIBLY VISBY/CIG RESTRICTIONS TUE INTO WED.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...FLOOD WATCH UNTIL 7 PM EST THIS EVENING FOR GAZ010-017-018-026-
     028-029.
NC...FLOOD WATCH UNTIL 7 PM EST THIS EVENING FOR NCZ057-062>065-
     068>072-082-507>510.
     WINTER WEATHER ADVISORY FROM 6 AM SATURDAY TO MIDNIGHT EST
     SATURDAY NIGHT FOR NCZ033-048>052-058.
     FREEZING RAIN ADVISORY UNTIL 6 AM EST SATURDAY FOR NCZ033-035-
     036-048>050-052-053-056-065-501>507-509.
SC...FLOOD WATCH UNTIL 7 PM EST THIS EVENING FOR SCZ001>014-019.

&&

SYNOPSIS...DEO
NEAR TERM...JDL
SHORT TERM...PM
LONG TERM...RWH
AVIATION...JDL

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