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Area Forecast Discussion

898
FXUS62 KGSP 292350
AFDGSP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREENVILLE-SPARTANBURG SC
750 PM EDT SUN MAR 29 2015

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE SOUTHEAST COAST TONIGHT. A LOW
PRESSURE CLIPPER SYSTEM AND ASSOCIATED COLD FRONT WILL THEN PASS
OVER THE AREA EARLY MONDAY MORNING. HIGH PRESSURE WILL RETURN FOR
MIDWEEK...WITH ANOTHER COLD FRONT APPROACHING THE REGION BY THE END
OF THE WORK WEEK.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 745 PM...NARROW BAND OF STRATOCU CONTINUES TO APPROACH THE
WESTERN ZONES AT MID-EVENING...WHILE CIRRUS IS BEGINNING TO SPILL
INTO THE NORTHERN ZONES. A GRADUAL INCREASE IN CLOUD COVER APPEARS
TO BE IN ORDER THROUGH THE REMAINDER OF THE EVENING. UPSTREAM...
SHOWERS ARE GRADUALLY FILLING IN FARTHER SOUTHWEST ALONG FRONTAL
ZONE ACROSS THE OHIO/MID-MISS VALLEY. THEREFORE...POPS LATER TONIGHT
STILL APPEAR TO BE IN GOOD SHAPE FOR OUR AREA...ALTHOUGH BASED UPON
THE LATEST OBS TRENDS...INCREASING POPS WERE DELAYED A COUPLE OF
HOURS.

AS OF 230 PM...DRY HIGH PRESSURE CURRENTLY OVER THE CAROLINA COASTAL
PLAIN WILL MOVE OFFSHORE THIS EVENING AS SFC/UPPER TROUGH BEGINS TO
DIG INTO THE OHIO VALLEY. A FAST MOVING BUT NOT ESPECIALLY
STRONG COLD FRONT WILL SWING THROUGH THE AREA MONDAY MORNING IN
ASSOCIATION WITH THE TROUGH.

WARM ADVECTION WILL GET UNDERWAY ALOFT BY THIS EVENING AHEAD OF THE
FRONT...REINTRODUCING CLOUD COVER AND ALSO CREATING A WARM NOSE OF
SORTS THAT WILL CAP THE COOL AND DRY AIRMASS ALREADY IN PLACE. UPPER
DYNAMIC FORCING COMES INTO PLAY AS THE TROUGH ARRIVES
09-12Z...CONCURRENT WITH MODEST FRONTOGENETIC FORCING IN THE LLVLS
AND WITH DEEP SATURATION. GUIDANCE IS VIRTUALLY UNANIMOUS IN
BRINGING A BAND OF QPF ACRS THE AREA AS A RESULT. TEMPS TONIGHT
AGAIN WILL BE BELOW NORMAL...BUT WARM ENOUGH OVER MOST OF THE
PIEDMONT AND MTN VALLEYS TO CONFIDENTLY FORECAST AN ALL RAIN EVENT.
HOWEVER...THE PRESENCE OF THE WARM NOSE AND THE INCUMBENT DRY AIR AT
THE SFC POSE A SMALL CHANCE THAT WINTRY PRECIP COULD OCCUR AT THE
ONSET OF PRECIP. WET BULB TEMPS ARE EXPECTED TO BE BELOW 0C
THROUGHOUT THE HIGHER ELEVATIONS OF THE MTNS UNTIL SUFFICIENT
MOISTURE RETURNS JUST PRIOR TO FROPA. THE STRENGTH OF THE WARM NOSE
WOULD SUGGEST NO NUCLEATION...AND FZRA RESULTING AT THE SFC IF THE
WET BULBS WERE TO COOL ENOUGH. THE MORE LIKELY SCENARIO IS THAT
PRECIP WILL NOT GET UNDERWAY UNTIL AFTER THE WET BULBS WARM ABOVE
0C. A FEW HIGH ELEVATION LOCATIONS DO GET A SNOW OR RA/SN MENTION
AROUND DAYBREAK...WHEN THE FRONT IS EXPECTED TO HAVE ERODED THE WARM
NOSE AND AIR TEMPS REMAIN JUST ABOVE FREEZING.

PEAK FORCING APPEARS TO OCCUR OVER THE PIEDMONT AROUND 12-14Z...AND
POPS SHOULD QUICKLY TRAIL OFF AS THE FRONT DEPARTS THRU THE REST OF
THE MRNG. WEAK UPSLOPE FORCING WILL PROLONG THE PRECIP CHANCES ALONG
THE TENN BORDER...BUT BY MID AFTN ALL PRECIP SHOULD HAVE COME TO AN
END. WINDS FLIPPING TO NWLY...AND THUS DOWNSLOPE...AS WELL AS
CLEARING SKIES SHOULD ALLOW TEMPS TO RISE TO NEAR NORMAL FOR AFTN
MAXES.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 230 PM EDT SUNDAY...SFC HIGH PRESSURE WILL BUILD BRIEFLY OVER
THE SRN APPALACHIANS MON NIGHT BEFORE MOVING OFF THE SE COAST
THROUGH TUE. RADIATIONAL COOLING CONDITIONS WILL LIKELY BECOME
FAVORABLE ENOUGH FOR NEAR FREEZING TEMPERATURES IN PARTS OF THE
CENTRAL AND SRN MOUNTAINS...WHERE THE FROST/FREEZE SEASON IS NOW
ACTIVE. AN HWO MENTION OF POTENTIAL FREEZING TEMPERATURES WILL BE
ADDED FOR TUESDAY MORNING IN THIS AREA. OTHERWISE...DEEP LAYER NW
FLOW WILL SET UP OVER THE REGION ON TUESDAY. MAX TEMPS WILL REBOUND
TO ABOUT A CATEGORY ABOVE CLIMO TUE AFTN.

A BACKDOOR COLD FRONT WILL PUSH SWD THROUGH THE VIRGINIAS TUESDAY
NIGHT AND ENTER THE NRN TIER OF THE FORECAST AREA ON WED. WEAK
UPGLIDE MOISTURE MAY SET UP FROM THE SW ON WED...BUT WILL PROBABLY
NOT PROVIDE ENOUGH QPF TO ALLOW ANY SHALLOW COLD AIR DAMMING TO GET
ESTABLISHED. ANY INSTABILITY WED AFTN SHOULD BE LIMITED TO THE SW
HALF IN THE BETTER DEWPOINT AIR...BUT NO THUNDER WILL BE FEATURED AT
THIS POINT. TEMPS WILL LIKELY RECOVER ANOTHER DEGREE ON TWO OVER TUE
VALUES...BUT THE NRN TIER COULD BE COOLER IF ANY CAD FORMS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AT 230 PM EDT SUNDAY...ON WEDNESDAY EVENING A LOW AMPLITUDE UPPER
RIDGE WILL BE OVER THE GREAT LAKES...WITH TROUGHS OVER THE WESTERN
ATLANTIC AND WESTERN USA. NEARLY ZONAL FLOW WILL EXIST OVER THE
SOUTHERN TIER OF STATES...WITH A SHORTWAVE CROSSING THE SOUTHERN MS
RIVER VALLEY. THE UPPER RIDGE MOVES TO THE EAST COAST LATE
THURSDAY...WHILE THE SOUTHERN STREAM SHORTWAVE CROSSES THE SOUTHERN
APPALACHIANS. ON FRIDAY THE TROUGH UPSTREAM MOVES TO THE CENTER OF
THE NATION...BUT UPPER FLOW REMAINS ZONAL ACROSS THE SOUTHERN TIER
OF STATES. THE NORTHERN STREAM TROUGH AMPLIFIES ALONG THE EAST COAST
ON SATURDAY...THEN MOVES OFF THE COAST ON SUNDAY WHILE A LOW
AMPLITUDE RIDGE CROSSES THE PLAINS.

AT THE SURFACE...ON THURSDAY HIGH PRESSURE WILL BE OFF THE EAST
COAST...WHILE A COLD FRONT MOVES ACROSS THE MS RIVER VALLEY. ROBUST
GULF INFLOW WILL SPREAD MOISTURE FROM THE GULF STATES TO THE OH
RIVER VALLEY...REACHING AS FAR EAST AS THE SOUTHERN APPALACHIANS. ON
FRIDAY...THE PROGRESSION OF THE NORTHERN STREAM TROUGH WILL LEAD TO
THE SURFACE FRONT BECOMING MORE NE TO SW ORIENTED...AND TO LESS OF A
PRESSURE GRADIENT OVER THE GULF. THIS MAY REDUCE GULF INFLOW
SOMEWHAT...BUT THE PROGRESSION OF THE SURFACE RIDGE OFF THE EAST
COAST WILL ALLOW MORE MOISTURE TO SPREAD INTO GA AND THE CAROLINAS.
THE RESULT IS THAT PRECIPITATION CHANCES ARE EXPECTED TO INCREASE
AHEAD OF THE FRONT. THE COLD FRONT WILL CROSS OUR AREA EARLY
SATURDAY...FOLLOWED BY SOME BRIEF NW FLOW SHOWERS IN THE NC
MOUNTAINS WHERE THICKNESS VALUES SUPPORT AN ALL RAIN EVENT. DRY HIGH
PRESSURE SPREAD OVER THE AREA FROM THE WEST ON SUNDAY. TEMPERATURES
WILL RUN ABOVE NORMAL AHEAD OF THE FRONT...AND SLIGHTLY BELOW NORMAL
IN ITS WAKE.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
AT KCLT AND ELSEWHERE...VFR CONDITIONS ARE EXPECTED THROUGH AT LEAST
THE REMAINDER OF THE EVENING...ALTHOUGH SOME VFR CLOUDS IN THE 045-
060 RANGE MAY APPROACH KAND/KAVL BY LATE EVENING. CHANCES FOR -RA
AND RESTRICTIONS WILL THEN INCREASE AFTER MIDNIGHT...AS A FAST-
MOVING COLD FRONT/UPPER AIR DISTURBANCE SWEEP ACROSS THE REGION.
GUIDANCE IS OFFERING MIXED SIGNALS AS TO HOW LOW CIGS WILL LOWER
MONDAY MORNING...BUT BASED UPON THE DRY AIR MASS CURRENTLY IN
PLACE...AND THE NATURE AND TIMING OF THE FRONT...IT SEEMS UNLIKELY
THAT THE IFR CIGS SUGGESTED BY SOME GUIDANCE MEMBERS FOR TOMORROW
MORNING WILL OCCUR. THEREFORE...HAVE MAINTAINED AN MVFR FORECAST
ALONG WITH A BRIEF PERIOD OF -RA AT MOST TERMINALS FROM AROUND
SUNRISE THROUGH MID-MORNING OR SO. CONDITIONS WILL THEN IMPROVE
RATHER QUICKLY...WITH VFR AND/OR SKC CONDITIONS EXPECTED AT MOST
TERMINALS BY AFTERNOON. LIGHT S/SW WINDS AT 5-10 ITS OVERNIGHT WILL
TURN TOWARD THE WEST BY MONDAY AFTERNOON AS THE COLD FRONT MOVES
OVER THE AREA...WITH NW WINDS POSSIBLE AT MOST TERMINALS BY THE END
OF THE PERIOD.

OUTLOOK...VFR UNTIL AT LEAST EARLY WED. A WEAK LOW PRESSURE SYSTEM
PASSING TO THE NORTH OF THE REGION MAY BRING SOME LIGHT PRECIP EARLY
WED...PERHAPS WITH A FEW RESTRICTIONS OVER THE MTNS. AN APPROACHING
WARM FRONT AND RESULTANT MOISTURE RETURN WILL BRING BETTER CHANCES
FOR PRECIP/RESTRICTIONS ACROSS THE AREA LATER IN THE WEEK.

CONFIDENCE TABLE...

            00-06Z        06-12Z        12-18Z        18-00Z
KCLT       HIGH 100%     HIGH 100%     MED   78%     HIGH  93%
KGSP       HIGH 100%     HIGH 100%     HIGH  86%     HIGH 100%
KAVL       HIGH 100%     HIGH  92%     MED   74%     HIGH 100%
KHKY       HIGH 100%     HIGH 100%     HIGH  88%     HIGH 100%
KGMU       HIGH 100%     HIGH  92%     MED   79%     HIGH 100%
KAND       HIGH 100%     HIGH  95%     HIGH  88%     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

&&

.FIRE WEATHER...
A DRY POLAR AIRMASS WILL REMAIN IN PLACE OVER THE AREA THIS
AFTERNOON AHEAD OF THE RETURN OF SOUTHERLY FLOW OVERNIGHT. RH
VALUES HAVE ALREADY DIPPED INTO THE TEENS OVER MUCH OF THE AREA.
WINDS WILL BE RATHER LIGHT BUT WITH OCCASIONAL LOW GUSTS. ENHANCED
FIRE DANGER EXISTS HOWEVER DUE TO DRY FUELS. IN COORDINATION WITH
GA LAND MANAGERS...A FIRE DANGER STATEMENT REMAINS IN EFFECT FOR
NORTHEAST GA THRU 7 PM.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
NC...NONE.
SC...NONE.

&&

$$
SYNOPSIS...JPT
NEAR TERM...JDL/WIMBERLEY
SHORT TERM...HG
LONG TERM...JAT
AVIATION...JDL
FIRE WEATHER...



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