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Area Forecast Discussion

498
FXUS62 KCHS 011402
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1002 AM EDT SUN MAY 1 2016

.SYNOPSIS...
LOW PRESSURE WILL PASS FAR TO THE NORTH TODAY AND MONDAY. ANOTHER
AREA OF LOW PRESSURE IS EXPECTED TO DEVELOP JUST NORTH OF THE AREA
TUESDAY AND WEDNESDAY. HIGH PRESSURE WILL BUILD INTO THE REGION BY
THE END OF THE WEEK.

&&

.NEAR TERM /THROUGH 6 PM/...
AN ENORMOUS AND POSITIVELY TILTED LARGE SCALE TROUGH WILL PREVAIL
FROM SE CANADA AND THE GREAT LAKES THROUGH THE CENTRAL PLAINS TO
THE WEST/SW STATES. EMBEDDED WITHIN THIS FEATURE ARE TWO MID/UPPER
LEVEL CYCLONES...ONE THAT IS OPENING IN IOWA AND A SECOND THAT IS
SITUATED IN THE FOUR CORNERS. DOWNSTREAM FROM THIS IS A BROAD
RIDGE FROM CENTRAL AMERICA TO THE SW ATLANTIC...WHILE WE REMAIN IN
A QUASI-ZONAL WEST/SW FLOW ALLOWING FOR A FEED OF SUB-TROPICAL
MOISTURE WHERE PWATS ARE CLOSE TO 1.5 INCHES.

ONE SHORT WAVE IS PULLING EAST/NE INTO SOUTHERN NC THIS
MORNING...WITH THE TAIL END MOVING THROUGH THE EAST/SE CWA. THIS
WILL CAUSE ISOLATED AND BRIEF SHOWERS WITH ONLY MINIMAL QPF TO
OCCUR. MOST PLACES THOUGH WILL STAY RAINFREE THIS MORNING.

A NOTED DRY SLOT WITH NVA AS DEPICTED ON WATER VAPOR IS MAKING
HEADWAY TOWARD THE FORECAST DISTRICT THROUGH THE SC UPSTATE AND
MUCH OF GA...IN RESPONSE TO VERY SUBTLE AND TEMPORARY SHORT WAVE
RIDGING. THIS WILL FIGHT AGAINST THE FORMATION OF A QUICKLY
EXPANDING CUMULUS FIELD GIVEN THE MOIST AND UNSTABLE ENVIRONMENT.
BUT WITH WARM ADVECTION AND AT LEAST PARTIAL INSOLATION THIS WILL
SUPPORT MAX TEMPS AT LEAST SEVERAL DEGREES ABOVE NORMAL. WARMEST
LOCALES WILL BE OVER INTERIOR SE GA WHERE UPPER 80S WILL BE
COMMON. A MODEST SOUTHERLY FLOW ACROSS THE MORE STABLE OCEAN WILL
LIMIT MAX TEMPS TO THE UPPER 70S AND LOWER 80S ALONG THE COASTAL
CORRIDOR.

A SECOND SHORT WAVE ACROSS THE LOWER MS VALLEY THIS MORNING WILL
TREK EASTWARD AND WILL ARRIVE IN WESTERN GA BY EVENING. THIS ALONG
WITH ASSOCIATED UPPER DIVERGENCE WITH THE LEFT EXIT REGION OF THE
SUB-TROPICAL JET WILL PROVIDE THE NECESSARY FORCING...IN SYNC WITH
LOW LEVEL CONVERGENCE AND INSTABILITY. THIS WILL ALLOW FOR AT
SCATTERED SHOWERS AND T-STORMS TO OCCUR INLAND AFTER 1 OR 2 PM.
SLIGHTLY LESS CHANCES ARE ANTICIPATED CLOSER TO THE COAST WITHIN
A LESS UNSTABLE ATMOSPHERE.

MODIFIED 12Z SOUNDINGS DEPICT A WORST CASE SCENARIO OF SBCAPE
REACHING AS HIGH AS 2500-3000 J/KG INLAND AND LIFTED INDICES AS
LOW AS -8C. THERE IS QUITE A BIT OF 0-3KM CAPE/ 150-250 J/KG/
NOTED WEST OF THE I-95 CORRIDOR WHICH SUGGESTS STORMS COULD GO UP
WITH SOME FEROCITY ONCE INITIATION OCCURS. THE APPROACHING DRY
SLOT WILL SUPPORT A RISK FOR DAMAGING WINDS WITH DCAPE VALUES
REACHING AS HIGH AS 900-1200 J/KG AND INDEX IN EXCESS OF 55 KT.
HIGH CAPE VALUES IN THE -10 TO -30C LAYER AND WBZ HEIGHTS AROUND
9.5-10K FT WILL ALSO SUPPORT A RISK FOR MARGINALLY SEVERE HAIL.
DESPITE STRONG INSTABILITY...THE WEAK SHEAR PROFILES OF 15-25 KT
SUGGEST THE FORMATION OF ANY ORGANIZED SEVERE WEATHER IS LOW.
HOWEVER, ISOLATED SEVERE THUNDERSTORMS WILL BE
POSSIBLE...ESPECIALLY WHERE LOW-LEVEL FORCING IS SUPPLEMENTED BY
MESOSCALE BOUNDARY COLLISIONS. THE RISK FOR SEVERE THUNDERSTORMS
WILL BE THE GREATEST NORTH OF I-16 AND WEST OF I-95 AND IS
HIGHLIGHTED IN THE HAZARDOUS WEATHER OUTLOOK.

&&

.SHORT TERM /TONIGHT THROUGH WEDNESDAY/...
TONIGHT...CONVECTION WILL GRADUALLY WIND DOWN DURING THE EARLY
EVENING AS INSTABILITY WANES AND SHORTWAVE ENERGY PUSHES OFF TO
THE NORTHEAST AWAY FROM THE AREA. COULD SEE AN ISOLATED SHOWER
BRUSH THE CENTRAL/UPPER CHARLESTON COUNTY COAST EARLY MONDAY
MORNING AS NOCTURNAL SHOWER/TSTM ACTIVITY DEVELOPS OVER THE
COASTAL WATERS, BUT CONFIDENCE IN THIS SCENARIO IS STILL RATHER
LOW. IT WILL BE ANOTHER WARM/HUMID NIGHT WITH LOWS ONLY DROPPING
INTO THE UPPER 60S INLAND TO THE LOWER 70S AT THE COAST.

IT IS POSSIBLE THAT NEW RECORD HIGH MINIMUMS COULD BE SET AT ALL
THREE CLIMATE SITES TODAY. MUCH WILL DEPEND ON HOW MUCH CONVECTION
IMPACTS THE SITES PRIOR TO 1 AM MONDAY.

MONDAY...AN UNSETTLED PATTERN EXPECTED THROUGH THIS PERIOD. A
BROAD...POSITIVELY TILTED UPPER LEVEL TROUGH...WILL REMAIN OVER
THE NORTH- CENTRAL PORTION OF THE COUNTRY. THIS WILL KEEP OUR
REGION ON THE SOUTHEAST PERIPHERY OF THE UPPER TROUGH...WITH
PERIODIC WEAK UPPER IMPULSES EXPECTED TO MOVE ACROSS THE REGION
MONDAY. GIVEN THE WEAKNESS OF THE UPPER FEATURES...TIMING OF
CONVECTION IS CHALLENGING. MONDAY STARTS OUT DRY WITH POPS
INCREASING TO CHANCE FROM WEST TO EAST AS THE DAY PROGRESSES. THE
BEST CHANCES WILL BE DURING THE AFTERNOON COINCIDENT WITH MAXIMUM
HEATING. CAPE VALUES ARE MODERATE IN THE 1000-1500 J/KG
RANGE...BUT WEAK BULK SHEARS WILL MEAN ANY THUNDERSTORM ACTIVITY
SHOULD REMAIN BELOW SEVERE LIMITS AND LACK ORGANIZATION. THE
MODELS STILL INDICATE HIGH POPS MONDAY NIGHT. THIS SEEMS TO BE A
LITTLE OVERDONE GIVEN THE LOCATION OF THE SYNOPTIC FEATURES. KEPT
CHANCE POPS...BUT HAVE THEM TRENDING DOWNWARD AS THE NIGHT
PROGRESSES.

TUESDAY...THE TROUGH REMAINS OVER THE EAST COAST WHILE A SHORT WAVE
ROUNDS THE BASE OF THE TROUGH DURING THE DAY...MOVING INTO THE
MIDDLE MISSISSIPPI VALLEY. AT THE SURFACE...A BROAD AREA OF WEAK LOW
PRESSURE WILL BE SPREAD ACROSS THE MID-ATLANTIC STATES WITH A COLD
FRONT STRETCHED DOWN NEAR THE FLORIDA PANHANDLE. OUR AREA WILL BE IN
THE WARM/UNSTABLE SECTOR OF THE SYNOPTIC PATTERN.
PLENTIFUL MOISTURE ACROSS THE AREA...PWATS EXCEEDING 1.5
INCHES...COMBINED WITH GOOD LIFT DUE TO THE TROUGH AND THE
APPROACHING COLD FRONT WILL LEAD TO SHOWERS AND THUNDERSTORMS.
RAISED POPS TO ACCOUNT FOR THIS. THE INGREDIENTS ARE COMING TOGETHER
FOR SOME OF THESE STORMS TO BE STRONG OR MAYBE SEVERE.
ALONG WITH THE AFOREMENTIONED LIFT AND MOISTURE THERE WILL BE A JET
STREAK APPROACHING FROM THE WEST. THERE WILL ALSO BE PLENTY OF
INSTABILITY AT THE SURFACE. THE QUESTION IS DO ALL OF THE
INGREDIENTS COME TOGETHER AT THE RIGHT TIME? IF THEY DO THEN THE
GREATEST THREAT WOULD BE DAMAGING WINDS AND HAIL. GIVEN THERE IS
STILL SOME UNCERTAINTY IN THE FEATURES COMING TOGETHER AT THE RIGHT
TIME...ESPECIALLY THE COLD FRONT WHICH MAY CROSS THROUGH THE AREA
TUESDAY NIGHT. WE STILL DO NOT HAVE SEVERE IN THE FORECAST AND ARE
HIGHLIGHTING IT IN THE HWO. THIS WILL BE UPDATED IN THE UPCOMING
FORECAST PACKAGES.

WEDNESDAY...THE TROUGH IS STILL OVER THE EAST COAST WHILE THE SHORT
WAVE ROUNDS THE EASTERN PERIPHERY OF IT...MOVING INTO THE MID-
ATLANTIC STATES. AT THE SURFACE A COLD FRONT WILL BE JUST OFFSHORE
IN THE MORNING...MOVING AWAY DURING THE DAY. SOME REMNANT LIGHT
SHOWERS ARE POSSIBLE...ESPECIALLY IN THE MORNING. POPS WILL
GRADUALLY DECREASE DURING THE DAY AS HIGH PRESSURE BUILDS INTO THE
REGION...ALLOWING FOR DRYING CONDITIONS. HIGH WILL BE A FEW DEGREES
BELOW NORMAL...IN THE UPPER 70S.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
MODELS ARE NOW IN FAIRLY GOOD AGREEMENT SHOWING WEAK HIGH PRESSURE
OVER THE AREA WEDNESDAY NIGHT WHILE A STORM SYSTEM IMPACTS THE
NORTHEASTERN STATES. A DRY COLD FRONT IS FORECAST TO MOVE THROUGH ON
THURSDAY...BRINGING COOLER TEMPERATURES FOR FRIDAY. DESPITE A TROUGH
REMAINING OVER THE EAST COAST DURING THIS ENTIRE TIME PERIOD...POPS
ARE LOW BECAUSE HIGH PRESSURE WILL BE SPREAD ACROSS OR NEAR THE
SOUTHEAST STATES FRIDAY AND SATURDAY.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
MOSTLY VFR AT THE TERMINALS. A BRIEF SHOWER COULD IMPACT KSAV
PRIOR TO 15Z...BUT MAJOR IMPACTS ARE NOT ANTICIPATED. TSTM
CHANCES WILL INCREASE THIS AFTERNOON...ESPECIALLY AT KSAV. WILL
MAINTAIN A TEMPO GROUP FROM ROUGHLY 20-23Z FOR MARGINAL MVFR
CONDITIONS IN TSRA. FURTHER ADJUSTMENTS WILL LIKELY BE NEEDED AS
THE CONVECTIVE PATTERN BECOMES MORE CERTAIN.

EXTENDED AVIATION OUTLOOK...PERIODIC FLIGHT RESTRICTIONS WITHIN
SCATTERED SHOWERS/THUNDERSTORMS...MONDAY THROUGH TUESDAY NIGHT.

&&

.MARINE...
TODAY...HIGH PRESSURE SANDWICHED BETWEEN BERMUDA AND THE EASTERN
SEABOARD WILL BE THE MAIN INFLUENCE ON OUR WEATHER. SEA BREEZE
CIRCULATIONS WILL HELP IN BOOSTING SOUTHERLY WINDS UP NEAR 15 KT
AT TIMES...WITH SEAS TO HOLD BETWEEN 2 AND 4 FT. ISOLATED TO
SCATTERED SHOWERS AND T-STORMS WILL OCCUR...ESPECIALLY THIS
AFTERNOON AND MAINLY WITHIN 10 NM OF THE COAST AND OUT NEAR THE
WESTERN WALL OF THE GULF STREAM.

TONIGHT...A SOUTHERLY FLOW WILL PERSIST TODAY AS HIGH PRESSURE
REMAINS WELL OFFSHORE. WINDS WILL REMAIN AROUND 10 KT WITH SEAS
2-4 FT THROUGH THE PERIOD.

MONDAY THROUGH THURSDAY...NO HIGHLIGHTS ARE EXPECTED THROUGH THE
PERIOD. IN GENERAL...THE WATERS WILL SIT BETWEEN ATLANTIC HIGH
PRESSURE WELL ENE OF THE AREA AND LOWER PRESSURE OVER THE MID
ATLANTIC AND CAROLINAS. THIS WILL RESULT IN SOUTH-SOUTHWEST WINDS
OF 15 KNOTS OR LESS AND SEAS 3 FEET OR LESS. UNSETTLE CONDITIONS
ARE LIKELY WITH SCATTERED SHOWER AND THUNDERSTORMS...ESPECIALLY
MONDAY AND TUESDAY.

&&

.CLIMATE...
RECORD HIGH MINIMUMS FOR 1 MAY...
KCHS 70/1989...
KCXM 73/2012...
KSAV 73/1953...

&&

.EQUIPMENT...
THE CHARLESTON HARBOR NOS TIDE GAUGE HAS STOPPED REPORTING ALL
METEOROLOGICAL AND TIDE DATA. THE NATIONAL OCEAN SERVICE IS
INVESTIGATING THE CAUSE OF THE OUTAGE. AN ESTIMATED TIME FOR DATA
RESTORATION IS UNKNOWN AT THIS TIME.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
CLIMATE...
EQUIPMENT...



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