Area Forecast Discussion
Issued by NWS Greer, SC

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000
FXUS62 KGSP 260241
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
941 PM EST SUN JAN 25 2015

.SYNOPSIS...
LOW PRESSURE WILL TRACK ACROSS THE CENTRAL APPALACHIANS
TONIGHT...THEN INTENSIFY INTO A STRONG EAST COAST LOW MONDAY THROUGH
TUESDAY. DRY HIGH PRESSURE BUILDS IN FROM THE WEST ON
WEDNESDAY...THEN A COLD FRONT WILL CROSS THE REGION LATE THURSDAY.

&&

.NEAR TERM /THROUGH MONDAY/...
930 PM UPDATE...BAND OF LIGHT DRIZZLE OR SPRINKLES MADE ITS WAY
ACRS THE MTNS AND WILL CONTINUE TO PROGRESS EWD THRU THE CWFA OVER
THE NEXT COUPLE HRS. STILL WATCHING WEAKLY CONVECTIVE SHOWER
ACTIVITY OVER EAST TN AND NW GA BENEATH CORE OF THE APPROACHING
SHORTWAVE. SOME OF THIS ACTIVITY WILL MOVE INTO OUR WRNMOST MTNS
BEFORE MIDNIGHT. LATEST MODEL RUNS SUGGEST THAT THE FIRST CHANCE
AT MEASURABLE POPS IN THE MTNS WILL COME WITH THESE
SHOWERS...WHICH MAY FIZZLE OR MOVE OUT BEFORE THE NW FLOW RAMPS
UP. VAD PROFILES FROM KMRX RADAR INDICATE MOSTLY SW FLOW
ALOFT...WHICH NAM THINKS WILL NOT LINE UP FOR GOOD UPSLOPING UNTIL
NEAR DAYBREAK. IN LIGHT OF THIS...REVISED POP AND QPF TRENDS IN
THE MTNS TO FOCUS MORE ON THE MRNG ACTIVITY AND LIMITED THE
NUMBERS OVERNIGHT. ALSO...REVISED TEMP TRENDS BASED ON THOSE FROM
OUR SHORT TERM CONSENSUS PRODUCT WHICH HAS VERIFIED WELL LATELY.
THE WARMER NUMBERS AND LOWER QPF LEAD TO LESS SNOW. I WILL UPDATE
THE WSW TEXT FOR THE LATEST THINKING BUT NOT EXPAND IT TO ANY
ADDITIONAL ZONES.

AS OF 240 PM...ANOTHER TRICKY FORECAST AS A STRONG UPPER LOW WITH A
STRONG LEAD SHORT WAVE ROTATING AROUND THE LOW MOVE INTO THE AREA
TONIGHT THEN EAST OF THE AREA MONDAY AS CHANNELED VORTICITY MOVES IN
MON AFTERNOON IN THE NWLY FLOW BEHIND THE DEPARTING LOW. THE
ASSOCIATED SFC LOW MOVES NORTH OF THE AREA TONIGHT DRAGGING A COLD
FRONT ACROSS THE CWFA. THE LOW THEN REFORMS NEAR THE NC/VA COAST
LATE IN THE DAY. THERE WILL BE WAA FLOW...ISENTROPIC LIFT AHEAD OF
THE SYSTEM WITH DEVELOPING DEEP MOISTURE...BUT LITTLE IN THE WAY OF
UPPER DIVERGENCE TONIGHT. THE BEST DEEP LAYER FORCING WILL BE
TONIGHT WITH THE LEAD SHORT WAVE. BOTH THE FORCING AND MOISTURE WILL
BE A QUICK SHOT...SO WHILE THERE IS A CHC OF RAIN OUTSIDE OF THE
MTNS...QPF WILL BE VERY LIGHT. THE MOISTURE AND FORCING WILL BE
BETTER ACROSS THE MTNS...SO HAVE RETAINED CAT POP ALONG THE TN
BORDER. TEMPS FALL ENUF THE PRECIP WILL QUICKLY CHANGE TO SNOW
ACROSS THE HIGHER ELEVATIONS...BUT MAY ONLY MIX WITH SNOW ACROSS THE
VALLEYS. TEMPS MAY DROP ENUF FOR SOME SNOW TO FALL ACROSS THE NC
FOOTHILLS AND THE MTNS OF THE UPSTATE AND NE GA. HOWEVER...THE
BOUNDARY LAYER REMAINS QUITE WARM...LIMITING THE AMOUNT OF SNOW THAT
CAN SURVIVE TO THE SFC.

THE UPPER LEVEL COLD POOL ASSOCIATED WITH THE UPPER LOW SLIDES
ACROSS THE AREA MONDAY...KEEPING A CHC OF PRECIP ACROSS THE NC
FOOTHILLS AND PIEDMONT...AND THE ERN UPSTATE. AGAIN...ANY PRECIP
WOULD BE VERY LIGHT. ALTHOUGH THERE IS SOME LOW LEVEL INSTABILITY...
THE BOUNDARY LAYER REMAINS RELATIVELY WARM. THIS AGAIN WILL LIMIT
ANY SNOW OR GRAUPEL THAT COULD FORM IN THIS REGION...LEADING TO
MAINLY RAIN.

ACROSS THE MTNS...COPIOUS LOW LEVEL MOISTURE...DEVELOPING NWLY FLOW
AND LOW LEVEL INSTABILITY WILL KEEP ELEVATION DEPENDENT RAIN/SNOW
GOING THRU THE MORNING. THE PRECIP WILL TAPER OFF IN THE AFTERNOON.
LITTLE TO NO SNOW WILL MIX WITH THE RAIN ACROSS THE NE GA/UPSTATE
MTNS. HOWEVER...SNOW WILL CONTINUE ACROSS THE HIGH ELEVATIONS OF THE
NC MTNS WITH SOME SNOW MIX ACROSS THE VALLEYS. GIVEN THE FORECAST
QPF...TEMPS AND PRECIP DURATION...LOOKS LIKE THE HIGH ELEVATIONS
ALONG THE TN BORDER FROM HAYWOOD SOUTH COULD SEE ADVISORY LEVEL
ACCUMS. THE HIGH ELEVATIONS FROM MADISON NORTH COULD APPROACH ADV
LEVEL...BUT THE BULK OF THE AREA SHUD REMAIN BELOW. THEREFORE...WILL
ISSUE A WINTER WX ADV FOR THE SRN PORTION ABOVE 3500 FEET.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 PM SUNDAY...FOR MONDAY NIGHT THRU TUESDAY...THE CWFA WILL
BE WITHIN THE NWLY BACKSIDE OF THE DEEP NOREASTER THAT WILL BE
TRACKING NE UP ALONG THE COAST. THE 12Z NAM AND GFS HAVE TRENDED A
LITTLE LESS BULLISH ON MOISTURE AND SNOW POTENTIAL ALONG THE TN
BORDER. HOWEVER...STILL LOOKS LIKE AT LEAST PERIODS OF SCATTERED TO
NUMEROUS SNOW SHWRS WILL EXIST DURING THESE TWO PERIODS. AN
ADDITIONAL 1 TO 2" OF SNOW CAN BE EXPECTED IN THE USUAL FAVORED
SPOTS...WHICH MAY APPROACH LOW-END ADVISORY CRITERIA. WILL CONTINUE
TO MENTION IN THE HWO. OTHERWISE...GRADUAL CLEARING IS EXPECTED EAST
OF THE MTNS...WITH MORE CLOUDS LINGERING EAST OF I-77 CLOSER TO THE
COASTAL LOW. TEMPS WILL BE NEAR NORMAL OVERNIGHT...THEN STAY A
CATEGORY OR TWO BELOW NORMAL ON TUESDAY.

TUESDAY NIGHT AND WEDNESDAY...AS THE NOREASTER PULLS AWAY...DRY HIGH
PRES WILL BUILD FROM THE WEST...WITH THE SFC RIDGE AXIS CROSSING THE
AREA WEDNESDAY AFTN. FCST SNDGS SHOW VERY DRY AIR ATOP THE BL...SO
EXPECT TEMPS TO DIP BELOW NORMAL TUESDAY NIGHT. ON WEDNESDAY...TEMPS
REBOUND A CATEGORY OR TWO...ESP IN THE HIGH TERRAIN. MAY SEE NEAR
CRITICAL RH FOR FIRE WX CONCERNS...BUT WINDS WILL BE LIGHT. POPS
SHUD TAPER OFF ALONG THE TN BORDER BY AROUND MIDNIGHT...WITH DRY
WX/SUNNY SKIES FOR WEDNESDAY.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 145 PM EST SUNDAY...SOME MEASURE OF SPREAD IN THE HANDLING OF
THE 500 MB PATTERN SHOWS UP ON THURSDAY. THE GFS AND GEFS MEAN
DEPICT A SERIES OF FAIRLY WEAK CLIPPERS CROSSING THE CENTRAL
APPALACHIANS THU INTO FRI. THE 00Z RUN OF THE ECMWF HAS A MORE
AMPLIFIED SYSTEM DIGGING THROUGH THE OH VALLEY LATE IN THE
WEEK...WHICH SHOWED DECENT CONSISTENCY OVER THE PAST FEW RUNS. BOTH
MODELS FEATURE A RELATIVELY NARROW BAND OF MOISTURE AHEAD OF THE
WAVES ALONG A COLD FRONT FOR THU...BUT WITH BETTER MOISTURE
ACCOMPANYING THE MORE AMPLIFIED WAVE IN THE COLD ADVECTION FLOW ON
THE ECMWF THU NIGHT INTO FRI. THE AMPLIFIED...BUT SLIGHTLY MORE
MUTED...12Z ECMWF SOLUTION LOOKS TO BE A REASONABLE COMPROMISE. THIS
WILL KEEP CONTINUED MTN PRECIP CHANCES THU NIGHT INTO FRI...MAINLY
AS LIGHT SNOW DURING THE BEST COLD ADVECTION.

ONCE THE LATE WEEK WAVES MOVE EAST...THE SOLUTIONS SURPRISINGLY
APPEAR MORE CONSISTENT FOR THE WEEKEND...WITH AN ACTIVE NRN STREAM
BRINGING A WEAK CLIPPER TYPE WAVE THROUGH THE APPALACHIANS SAT
NIGHT...WHILE A STRONG SW SYSTEM NEAR THE BAJA PENINSULA STALLS
THROUGH THE WEEKEND. SOME MOISTURE SHOULD WORK BACK INTO THE
FORECAST AREA FROM THE WEST ON THE SHEARED FLOW BETWEEN THESE
SYSTEMS ON SATURDAY...BUT DEEP MOISTURE AND FORCING LOOK UNLIKELY AT
PRESENT. THIS WILL YIELD MAINLY CHC RAIN/SNOW POPS PRIMARILY ACROSS
THE WRN MOUNTAINS THROUGH THE LATTER HALF OF THE WEEKEND. ALSO
EXPECT A TIGHT PRESSURE GRADIENT TO SET UP IN THE NW FLOW ACROSS THE
SRN APPALACHIANS ON SUNDAY...WITH WINDY MOUNTAIN CONDITIONS AND
DOWNSLOPE DRYING EAST OF THE MTNS THROUGH LATE WEEKEND. EXPECT NEAR
CLIMO MINS BUT BELOW CLIMO MAXES THROUGH THE MEDIUM RANGE PERIOD.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
AT KCLT...CIGS WILL FORM THIS EVENING AND LOWER THRU THE
MIDLEVELS TONIGHT IN ADVANCE OF A SHORTWAVE TROUGH. THE PEAK IN
FORCING FROM THE TROUGH WILL COME IN THE WEE HRS MONDAY MRNG AND
SUFFICIENT MOISTURE WILL BE PRESENT FOR A LOW CHC OF RA. WINDS WILL
PREVAIL SOUTHERLY AHEAD OF THE WAVE...VEERING TO NW IN ITS WAKE.
DOWNSLOPING ACCORDINGLY IS EXPECTED TO LIMIT THE COVERAGE OF ANY
PRECIP. GLOBAL MODELS SUCH AS THE GFS...ALONG WITH ITS DERIVATIVE
THE LAMP...PREDICT WIDESPREAD LOW MVFR TO IFR CIGS AND MVFR VSBY
WITH RAIN. IF RAIN DOES OCCUR THERE IS A GOOD CHANCE SUCH A CIG
WOULD FORM. HOWEVER THE NAM FAMILY OF GUIDANCE SUGGESTS ONLY SPOTTY
PRECIP AND NO RESTRICTIONS AT THE FIELD. PROB30 IS USED TO HANDLE
THE THREAT. THOUGH THE WAVE APPEARS UNLIKELY TO BE ABLE TO FORCE
PRECIP ON ITS OWN DURING THE DAY MONDAY...MID-UPPER LAPSE RATES WILL
CONTINUE TO BE APPRECIABLE WITH TROUGHY UPPER PATTERN STILL
OVERHEAD. CAN/T RULE OUT A FEW CONVECTIVE SHRA AROUND MIDDAY BUT CHC
TOO LOW TO MENTION.

ELSEWHERE...TRENDS SIMILAR TO KCLT...THOUGH OVER THE SC SITES IFR IS
NOT PROGGED BY ANY GUIDANCE AND PRECIP CHANCES APPEAR EVEN LESS.
THUS OMITTED ANY MENTION THEREOF...BUT STILL KEPT A HIGHER MVFR
MENTION. THE MTNS ARE EXPECTED TO SEE A DECENT NW FLOW FORCED PRECIP
EVENT WITH SNOW ACCUMS IN THE HIGHER ELEVATIONS. CHANCES OF PRECIP
ARE HIGH ENOUGH OVERNIGHT TO MENTION AT KAVL...BUT TEMPS WILL
SUPPORT -RA THERE. THOUGH THE CHANCES TAPER OFF A MVFR CIG WILL
LINGER INTO AFTN. LOW END GUSTS WILL OCCUR AROUND THE AREA BY MIDDAY
AND CONTINUE THRU THE AFTN.

OUTLOOK...A SERIES OF CLIPPER SYSTEMS WILL BRING PERIODIC CHANCES
FOR SNOW SHOWERS...MAINLY TO THE MOUNTAINS THROUGH THE WEEK. MOST OF
THESE SNOW SHOWERS WILL REMAIN WEST AND NORTH OF KAVL...BUT BRIEF
PERIODS OF RESTRICTIONS AND SNOW SHOWERS CANNOT BE RULED OUT THERE.
OTHERWISE...MAINLY VFR CONDITIONS ARE EXPECTED.

CONFIDENCE TABLE...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       HIGH 100%     HIGH  83%     MED   67%     HIGH 100%
KGSP       HIGH 100%     MED   63%     HIGH 100%     HIGH 100%
KAVL       HIGH  91%     LOW   52%     MED   66%     HIGH 100%
KHKY       HIGH 100%     MED   69%     MED   77%     HIGH 100%
KGMU       HIGH 100%     LOW   54%     HIGH 100%     HIGH 100%
KAND       HIGH 100%     MED   62%     HIGH 100%     HIGH 100%

THE PERCENTAGE REFLECTS THE NUMBER OF GUIDANCE MEMBERS AGREEING
WITH THE SCHEDULED TAF ISSUANCE FLIGHT RULE CATEGORY. COMPLETE HOURLY
EXPERIMENTAL AVIATION FORECAST CONSISTENCY TABLES AND ENSEMBLE FORECASTS
ARE AVAILABLE AT THE FOLLOWING LINK: (MUST BE LOWER CASE)

WWW.WEATHER.GOV/GSP/AVIATION_TABLES

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...WINTER WEATHER ADVISORY UNTIL NOON EST MONDAY FOR NCZ051-052-
     058-059.
SC...NONE.

&&

$$
SYNOPSIS...ARK
NEAR TERM...RWH/WIMBERLEY
SHORT TERM...ARK
LONG TERM...HG
AVIATION...WIMBERLEY


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