Area Forecast Discussion
Issued by NWS Greer, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KGSP 121501
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
1001 AM EST FRI FEB 12 2016

.SYNOPSIS...
A FAST MOVING UPPER LEVEL DISTURBANCE WILL BRING A BRIEF CHANCE OF
PRECIPITATION TO MUCH OF THE AREA TODAY. A STRONG DOME OF CANADIAN
HIGH PRESSURE WILL SETTLE IN OVER THE WEEKEND...USHERING IN ANOTHER
PERIOD OF COLD TEMPERATURES. THIS WILL BE FOLLOWED BY ANOTHER
WEATHER SYSTEM WHICH WILL PRODUCE A BETTER CHANCE OF PRECIPITATION
EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
1500 UTC UPDATE...POPS HAVE BEEN ADJUSTED TO ACCOUNT FOR LIGHT SNOW
MOVING ACROSS UPSTATE NC. WINDS WERE UPDATED TO INCLUDE THE LATEST
NAM GUIDANCE...WITH GUSTS INCREASING AT HIGHER MC MOUNTAIN ELEVATIONS
LATER TODAY. ONLY MINOR ADJUSTMENTS WERE MADE TO MAXIMUM
TEMPERATURES.

AS OF 650 AM...THE MODELS SEEM TO BE LATCHING ONTO MORE MOISTURE OR
BETTER LLVL LIFT EAST OF THE MTNS. THE 6Z GFS AND THE LATEST RAP AND
HRRR NOW HAVE HIGHER POP/MORE COVERAGE OF SNOW SHOWERS ACROSS THE
PIEDMONT. IT LOOKS LIKE A BAND MAY SET UP SOMEWHERE ACROSS THE
UPSTATE. HOWEVER...CONFIDENCE IS STILL LOW. POPS MAY NEED TO BE
ADJUSTED UPWARD IF TRENDS ON RADAR LOOK TO BE LINING UP WITH THE
HRRR. OTHERWISE...FCST LOOKS ON TRACK.

AS OF 315 AM...A VIGOROUS SHORT WAVE CAN BE SEEN ON WATER VAPOR
IMAGERY DIVING INTO THE OHIO VALLEY TOWARD THE BASE OF A LONG WAVE
TROF ALONG THE EAST COAST. THIS WAVE WILL CROSS THE CWFA JUST AFTER
DAYBREAK...AND WILL BE ACCOMPANIED BY A 130 KT 300 MB JET. THIS WILL
RESULT IN STRONG MID AND UPPER LEVEL FORCING FROM ABOUT 12Z TO 18Z
TODAY. AT THE SFC...A WEAK ALBERTA CLIPPER WAS ANALYZED OVER
MO...AND WILL STREAK JUST SOUTH OF THE CWFA DURING THE DAY. LLVL FLOW
IS BACKING OUT OF THE WSW...BUT STRUGGLING TO TAP INTO MUCH MOISTURE.

SO THE FORECAST CHALLENGE FOR TODAY WILL BE HOW MUCH QPF WILL
ACCOMPANY THE SYSTEM...AS THE OP MODELS SHOW SOME SPREAD ON COVERAGE
AND AMOUNTS. THE 00Z NAM KEEPS THE PIEDMONT DRY...WHILE THE
OTHER OP MODELS HAVE SOME LIGHT AMOUNTS. I LIKE THE AGREEMENT OF THE
CAMS ON THE SIMULATED REFLECTIVITY...SHOWING LIGHT PRECIP BREAKING
OUT ACRS THE MTNS RIGHT AROUND DAYBREAK...THEN QUICKLY SPREADING
EAST ACROSS THE PIEDMONT DURING THE LATE MORNING HOURS. BY EARLY
AFTN...THE MODELS SHOW PRECIP CONFINED TO WESTERLY UPSLOPE AREAS
ALONG THE TN BORDER. I THINK MUCH OF WHAT THE CAMS ARE SHOWING WOULD
BE VIRGA...GIVEN THE MOISTURE MAINLY IN THE MID LEVELS. SO POPS SHOW
LIKELY IN THE MTNS...ESP NEAR THE TN BORDER...WHILE ONLY SLIGHT
CHANCE TO LOW-END CHANCE EAST. FCST PROFILES SHOW THAT THIS WOULD BE
A RAIN/SNOW EVENT...WITH WET-BULB EFFECTS ALLOWING FOR LIGHT SNOW
SHOWERS AND/OR FLURRIES JUST ABOUT ANYWHERE THIS MORNING. ACCUMS
THRU THE DAY WILL BE IN THE MTNS...WITH NOTHING MORE THAN A DUSTING
EXPECTED ELSEWHERE. TEMPS SHOULD BE ABOUT 10-15 DEGREES BELOW NORMAL
UNDER MOSTLY CLOUDY SKIES AND SPOTTY PRECIP.

TONIGHT...THE CLIPPER SYSTEM WILL ALREADY BE DEVELOPING A NEW LOW
OUT OVER THE ATLANTIC JUST EAST OF THE OUTER BANKS BY EARLY
EVENING...WHILE A STRONG ARCTIC HIGH (PRESSURE AROUND 1044 MB)
BUILDS IN ACROSS THE PLAINS TO THE SOUTHEAST STATES. THE SFC
PRESSURE GRADIENT NEVER GETS THAT IMPRESSIVE ATOP THE CWFA.
HOWEVER...THE 850 MB FLOW RAMPS UP OUT OF THE NW TO 40-55 KT ACROSS
THE NC MTNS WITH VERY STRONG CAA. THIS WILL RESULT IN A DOWN RIGHT
COLD AND BLUSTERY NIGHT IN THE MTNS...WITH THE ADDITION OF LINGERING
MOISTURE FOR NW FLOW SNOW SHOWERS. IN FACT...THE COLD AIR AND NEAR
PERFECT ORTHOGOTHAL DIRECTION COULD MAKE FOR EFFICIENT SNOW
PRODUCING SHOWERS ALONG THE TN LINE. THE EXPECTED SNOW WITH THE
CLIPPER ALONG WITH THE NW FLOW SNOW SHOULD RESULT IN TOTAL ACCUMS OF
2-4" ACROSS THE USUAL NW FLOW UPSLOPE AREAS. THIS ALONG WITH WINDS
IN THE 25-40 MPH RANGE AND GUSTS IN THE 40-55 MPH RANGE SEEMS TO
WARRANT A WINTER WEATHER ADVISORY. I WILL START IT AT NOON TO
EMCOMPASS THE SNOW ACCUMS EXPECTED TODAY...AND GO THRU 6 AM SATURDAY
(WHEN SNOW SHOWER ACTIVITY WILL TAPER OFF). IN ADDITION...TEMPS WILL
BE PLUMMETING INTO THE TEENS TO SINGLE DIGITS...SO WIND CHILLS WILL
BE IN THE -5 TO -15 F RANGE FOR MOST LOCATIONS ABOVE 3500 FT. A WIND
CHILL ADVISORY WILL BE ISSUED STARTING AT MIDNIGHT...ALTHOUGH SOME
LOCATIONS ABOVE 5000 FT OR SO MAY START SEEING DANGEROUS WIND CHILLS
EARLIER IN THE EVENING. THE REST OF THE CWFA SHOULD SEE CLEARING
SKIES AND LINGERING WINDS WITH CHILLY TEMPS ABOUT 8-15 DEGREES BELOW
NORMAL.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
AS OF 300 AM EST FRIDAY...A BROAD TROUGH OF LOW PRESSURE WILL EXTEND
SOUTHWARD ACROSS THE EASTERN UNITED STATES SATURDAY FROM A LOW
CENTER OVER SOUTHERN QUEBEC. ISOLATED TO SCATTERED NW FLOW SNOW
SHOWERS COULD LINGER ACROSS THE NORTHERN MOUNTAINS EARLY
SATURDAY...BUT WITH MOISTURE DIMINISHING THROUGH THE DAY. COLD
MORNING TEMPERATURES AND BRISK NW FLOW WILL PERMIT BITTER WIND
CHILLS TO CONTINUE THROUGH SATURDAY MORNING ACROSS THE
MOUNTAINS...AND ON INTO SATURDAY NIGHT/SUNDAY MORNING ACROSS THE
NORTHERN MOUNTAINS. MEANWHILE...VERY COLD AIR WILL DIVE SOUTHEAST
FROM CANADA INTO THE REGION ON THE BACK SIDE OF THE TROUGH AS THE
ASSOCIATED ARCTIC HIGH PRESSURE MOVES ACROSS THE MIDWEST ON SATURDAY
AND REACHES THE EASTERN SEABOARD BY LATE SUNDAY. IN THE COLD
AIRMASS...MAX TEMPERATURES WILL RUN AT LEAST 20 DEGREES BELOW CLIMO
IN MOST AREAS...WHILE SUNDAY MORNING MINS WILL BE 10 TO 20 DEGREES
BELOW CLIMO. A WIND CHILL ADVISORY WILL CONTINUE UNTIL MID SUNDAY
MORNING ACROSS THE NORTHERN NC MOUNTAINS.

THE UPPER FLOW WILL FLATTEN SLIGHTLY OVER THE EAST ON SUNDAY AS A
NORTHERN STREAM SHORTWAVE DIGS INTO THE MIDWEST WHILE A SOUTHERN
STREAM SYSTEM TAKES SHAPE FROM THE FOUR CORNERS REGION TOWARD TX.
THE FIRST HINT OF MID LEVEL UPGLIDE MOISTURE WILL ARRIVE IN THE CWA
FROM THE WEST ON SUNDAY...BUT WITH DRY LOW LEVELS PRECLUDING ANY
PRECIPITATION FROM REACHING THE GROUND THROUGH LATE DAY.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
AS OF 300 AM EST FRIDAY...A WINTRY MIXED MAG OF PRECIPITATION IS
LOOKING LIKELY STARTING SUNDAY NIGHT INTO MONDAY GIVEN THE VERY COLD
AND DRY AIRMASS THAT WILL BE PRESENT OVER THE AREA BEFORE ONSET.
THERE IS GOOD MODEL CONSENSUS ON THE ENERGY WITH THE SOUTHERN STREAM
SYSTEM SHARPENING UP RAPIDLY OVER THE LOWER MS RIVER VALLEY SUNDAY
NIGHT INTO MONDAY. MEANWHILE...THE SURFACE HIGH CENTER TO THE NORTH
WILL RETREAT OFFSHORE. LOW LEVEL UPGLIDE MOISTURE WILL FILL IN
RAPIDLY ACROSS OUR AREA EARLY MONDAY...WITH THE 850 MB ZERO ISOTHERM
ALONG THE SOUTHERN FRINGE OF THE AREA AROUND DAYBREAK MOVING RAPIDLY
TOWARD THE NORTHERN FRINGE OF THE FORECAST AREA BY MID AFTERNOON.
EVEN THOUGH COLD AIR DAMMING IS VERY LIKELY...THE COLD AIR MAY ONLY
STAY DEEPLY ENTRENCHED EAST OF THE NORTHERN BLUE RIDGE GIVEN THE
INCREASINGLY OFFSHORE PARENT HIGH LOCATION. STILL...PROFILES ARE
PLENTY COLD FOR PRECIPITATION TO START AS SNOW THROUGHOUT BEFORE
DAYBREAK MONDAY...WITH A BLOSSOMING WARM NOSE THEN INVADING THE
SOUTHERN TIER OF THE FORECAST AREA MONDAY MORNING AND MOVING
NORTHWARD ACROSS THE REGION THROUGH THE DAY.

THE BEST UPPER FORCING ACTUALLY ARRIVES MONDAY NIGHT AS UPPER JET
DIVERGENCE BRIEFLY SETS UP AND DEEP LAYER Q VECTOR FORCING CROSSES
THE REGION AHEAD OF THE INCREASINGLY NEGATIVE TILT UPPER TROUGH.
FORCING AND MOISTURE WILL BE STRONGLY FOCUSED ON THE REGION LATE
MONDAY NIGHT/EARLY TUESDAY WITH THE SURFACE LOW CENTER LIKELY
TRACKING THROUGH THE CENTRAL CAROLINAS...THE CAD GETTING FURTHER
PINCHED OFF TO THE NORTH...AND THE HEAVIEST PRECIPITATION DURING THE
WARMEST PART OF THE EPISODE.

SO...THERE ARE PLENTY OF POTENTIAL HAZARDS. SIGNIFICANT ICE AND SNOW
ACCUMULATIONS WILL BE POSSIBLE...MAINLY OVER WESTERN NC AND
ESPECIALLY ALONG AND NORTH OF INTERSTATE 40. IN ADDITION...HEAVY QPF
COULD CREATE SOME HYDRO ISSUES MONDAY NIGHT INTO TUESDAY MORNING
WITH THE FRONTOGENESIS MAX WEST OF THE PASSING 850 MB LOW LIKELY
LINGERING OVER THE EASTERN SLOPES OF THE MOUNTAIN. THE HEAVY
RAINFALL ON TOP OF ACCUMULATED SNOW AND ICE COULD CREATE SOME LOCAL
ICE DAMMING PROBLEMS ON SHALLOW SLOPED ROOFS. FINALLY...SURFACE
BASED CAPE VALUES OF 200 TO 300 J/KG ARE POSSIBLE TOWARD DAYBREAK
TUESDAY IN THE LOWER PIEDMONT...WITH 850 TO 500 MB LAPSE RATES OF
6.5 TO 7.0 DEG C/KM...ALONG WITH BACKED 50 KT 850 MB FLOW. THIS
COULD CREATE A BRIEF SEVERE THUNDERSTORM THREAT FROM CHESTER TO
MONROE OR THEREABOUTS AROUND DAYBREAK TUESDAY. OTHERWISE...DRYING
WILL DEVELOP FROM THE SOUTHWEST THROUGH TUESDAY AFTERNOON...WITH
NORTHERN MOUNTAIN UPSLOPE MOISTURE BRIEFLY DRYING UP.

A REINFORCING CLIPPER MAY DIVE INTO THE MEAN EASTERN TROUGH TUESDAY
NIGHT...WITH THE GFS MORE AMPLIFIED THAN THE ECMWF...PRODUCING
MAINLY ADDITIONAL UPSLOPE SNOW SHOWER COVERAGE OVER THE WESTERN
MOUNTAINS. HEIGHTS WILL BUILD EASTWARD FROM THE BROAD WESTERN RIDGE
WEDNESDAY THROUGH THURSDAY...WITH ASSOCIATED WARMING AND DRYING.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
AT KCLT AND ELSEWHERE...THE 6Z GFS AND LATEST HRRR HAVE TRENDED MUCH
WETTER WITH THIS FAST-MOVING WEAK LOW PRESSURE SYSTEM TODAY. THEY
ARE SUGGESTING THAT THERE MAY BE ENUF MOISTURE AND LLVL SUPPORT FOR
A BAND OF SNOW SHOWERS SOMEWHERE ACROSS THE PIEDMONT. THE HRRR HAS
IT SETTING UP FROM KAND TO SOUTH OF KUZA AND KCLT. STILL HAVE THE
TEMPO FOR KCLT FOR 14-18Z...BUT WENT A LITTLE MORE PESSIMISTIC WITH
RESTRICTIONS DUE TO INCREASED CHANCE FOR A HEAVIER SNOW SHOWER.
STILL THINK ODDS ARE FOR MAINLY VIRGA AND FLURRIES FOR MOST OF THE
AREAS EAST OF THE MOUNTAINS. AT KAVL...STILL EXPECT VCSH FOR SNOW
SHOWERS. CIGS SHOULD BE MAINLY VFR...BUT THE PESSIMISTIC GFS HAS
SOME MVFR CIGS/VSBY DUE TO SNOW. THIS EVENING THRU THE
OVERNIGHT...NW FLOW BEHIND THE DEPARTING LOW WILL RAMP UP...SCOURING
OUT THE LOW CLOUDS AND MOISTURE EAST OF THE MTNS...BUT KEEPING A
CHANCE FOR MVFR OR LOW VFR STRATUS AND PERIODIC SNOW SHOWERS AT KAVL
WITH GUSTY NNW WINDS. WINDS EAST OF THE MTNS WILL FAVOR NE THRU
ABOUT MIDDAY OR EARLY AFTN...THEN SWITCH TO SW FOR THIS AFTN AND
EVENING. THEN SHIFT TO NW LATE EVENING.

OUTLOOK...AN ARCTIC AIR MASS WILL BUILD OVER THE REGION THIS
WEEKEND...WITH UPSLOPE CLOUDS ON THE WEST SIDE OF THE APPALACHIANS.
A SIGNIFICANT WINTER WEATHER SYSTEM IS POSSIBLE EARLY NEXT WEEK.

CONFIDENCE TABLE...

            14-20Z        20-02Z        02-08Z        08-12Z
KCLT       HIGH  91%     HIGH  90%     HIGH 100%     HIGH 100%
KGSP       HIGH 100%     HIGH 100%     HIGH 100%     HIGH 100%
KAVL       HIGH  95%     HIGH 100%     HIGH 100%     HIGH 100%
KHKY       HIGH  91%     HIGH 100%     HIGH 100%     HIGH 100%
KGMU       HIGH  98%     HIGH 100%     HIGH 100%     HIGH 100%
KAND       MED   78%     HIGH 100%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULE TAF ISSUANCE FLIGHT RULE CATEGORY.  COMPLET HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK:

WWW.WEATHER.GOV/GSP/AVIATION

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER WEATHER ADVISORY UNTIL 6 AM EST SATURDAY FOR NCZ033-
     048>052.
     WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EST SUNDAY
     FOR NCZ033-049-050.
     WIND CHILL ADVISORY FROM MIDNIGHT TONIGHT TO NOON EST SATURDAY
     FOR NCZ048-051-052-058-059.
SC...NONE.

&&

$$
SYNOPSIS...HG
NEAR TERM...ARK/JAT
SHORT TERM...HG
LONG TERM...HG
AVIATION...ARK


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.