Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 011721
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
121 PM 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 /UNTIL 6 PM THIS EVENING/...
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.

VARIOUS BOUNDARIES ARE EVIDENT ON SATELLITE AND RADAR THIS
AFTERNOON...ALL OF WHICH ARE CAUSING AN INCREASE IN CONVECTION NOW
THAT WE HAVE REACHED OUR CONVECTIVE TEMP IN THE LOWER 80S. ONE IS
MOVING THROUGH SOUTHERN NC WITH ITS ASSOCIATED TAIL SWINGING
THROUGH. ANOTHER SHORT WAVE IS IN THE LOWER MS VALLEY AND WESTERN
AL AND HEADING EAST. DESPITE NVA AND DRY AIR BETWEEN BOTH FEATURES
AS SHOWN IN WATER VAPOR SATELLITE...INSTABILITY IS STRONG ENOUGH
TO MAKE UP FOR THIS. THERE IS ALSO SOME DIFFERENTIAL HEATING
BOUNDARIES AND THE SEA BREEZE. SUFFICE TO STAY PLENTY OF FEATURES
FOR CONVECTION TO CONTINUE INITIATING.

SPC MESO-ANALYSIS DEPICTING MLCAPES GREATER THAN 1000
J/KG...SBCAPES IN EXCESS OF 2500 J/KG AND LIFTED INDICES OF -4 TO
-6C. BUT MID LEVEL LAPSE RATES HAVE ACTUALLY DECREASED SOME SINCE
THIS MORNING AND EVEN THE LOW LEVEL LAPSE RATES DUE TO EXTENSIVE
CLOUD COVER ARE NOT THAT IMPRESSIVE. WITH AN EARLY START TO
CONVECTION THIS MAY PUT A DAMPER SOMEWHAT ON SEVERE WEATHER. BUT
WITH DCAPES STILL FORECAST TO REACH 800-1200 J/KG AND TOTAL TOTALS
NEAR 50 WE HAVE MAINTAINED THE RISK OF ISOLATED SEVERE STORMS
AFTER 2 PM MAINLY NEAR AND WEST OF I-95. MAIN HAZARDS WOULD BE
STRONG DOWNBURSTS OF WIND AND MARGINALLY SEVERE HAIL WITH CAPE IN
THE -10C TO -30C HAIL LAYER GREATER THAN 500 J/KG AND WET BULBS
NEAR 9.5-10K FT.

THERE IS ALSO A RISK FOR LOCALLY HEAVY RAINS WITH THE STORM MOTION
LESS THAN 10-15 MPH AND RECENT RADAR PATTERNS STARTING TO SHOW
SIGNS OF TRAINING TO POTENTIALLY OCCUR. HIGH TIDE IS DURING THE
MID TO LATE AFTERNOON AND BEARS WATCHING IF SOME PERSISTENT CELLS
START IMPACTING THE COASTAL SECTIONS.

MINOR ADJUSTMENTS HAVE BEEN MADE IN THE GRIDS TO ACCOUNT FOR MORE
CLOUD COVER AND TEMP TRENDS...BUT STILL BANKING ON MOSTLY CLOUDY
SKIES AND MAX TEMPS SEVERAL DEGREES ABOVE NORMAL.

&&

.SHORT TERM /6 PM THIS EVENING 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 /18Z SUNDAY THROUGH THURSDAY/...
MAINLY VFR AT THE TERMINALS. BUT PERIODIC FLIGHT RESTRICTIONS
COULD OCCUR AT BOTH SITES AS SCATTERED SHRA/TSRA OCCURS INTO THIS
EVENING. WHILE CONVECTION WILL FADE EARLY TONIGHT...THERE IS THE
RISK FOR SOME LATE NIGHT/EARLY MORNING STRATUS AND PERHAPS A
LITTLE GROUND FOG AND PERIODIC MVFR OR IFR CONDITIONS TO OCCUR.

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

&&

.MARINE...
THIS AFTERNOON...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.

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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