Area Forecast Discussion
Issued by NWS Charleston, SC

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000
FXUS62 KCHS 301727
AFDCHS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
127 PM EDT SAT APR 30 2016

.SYNOPSIS...
HIGH PRESSURE WILL EXTEND ACROSS THE AREA TODAY AND TONIGHT AS A
STATIONARY FRONT TO THE NORTH TODAY LIFTS NORTH TONIGHT. LOW
PRESSURE WILL PASS FAR TO THE NORTH SUNDAY AND MONDAY AND BE
FOLLOWED BY A DEVELOPING LOW OVER OR NEAR THE AREA TOWARDS THE
MIDDLE OF NEXT WEEK. HIGH PRESSURE WILL BUILD INTO THE AREA
TOWARDS THE END OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
DEEP LAYERED LOW PRESSURE WILL SPIN IN THE CENTRAL PLAINS WHILE
DOWNSTREAM RIDGING WILL PREVAIL ACROSS MUCH OF THE EAST AND
SE...INCLUDING THE LOCAL CWFA. THIS DEFLECTS ANY SHORT WAVES TO
OUR NW AND NORTH AND THERE IS NO LARGE SCALE FEATURES TO INITIATE
CONVECTION. WITH SOME LOW LEVEL CONVERGENCE ALONG WITH WHAT
APPEARS TO BE A SHARP DIFFERENTIAL HEATING BOUNDARY FROM THE
MORNING FOG/STRATUS INTERACTING WITH THE SEA BREEZE AND THE
PROXIMITY TO THE FRONT TO THE NORTH...WE HAVE SMALL POPS MAINLY
NEAR AND NORTH OF I-26 IN CHARLESTON...BERKELEY AND DORCHESTER
COUNTIES THIS AFTERNOON. WHILE SEVERE WEATHER LOOKS ALMOST NON-
EXISTENT...GIVEN DCAPES IN EXCESS OF 900 J/KG THERE COULD BE SOME
STRONG DOWNBURSTS IF UPDRAFTS ARE ABLE TO OBTAIN ANY APPRECIABLE
HEIGHT.

HIGH PRESSURE HUGGING THE COAST OF NEW JERSEY AND NEW ENGLAND
WILL WEDGE INTO NC AND THE UPSTATE OF SC...WHILE AN OSCILLATING
FRONT IS SLIDING A LITTLE SOUTH OVER THE ATLANTIC OFF THE
CHARLESTON COUNTY COAST. THE HIGH TO THE NORTH WILL BRIDGE ACROSS
THE FRONT AND THAT ALONG WITH SEA BREEZE CIRCULATIONS WILL RESULT
IN AN EAST AND SE SYNOPTIC FLOW LOCALLY. THIS ALONG WITH VARYING
AMOUNTS OF MAINLY TRANSLUCENT CIRRUS CLOUDS FROM UPSTREAM
CONVECTION WILL PREVENT MOST TEMPS FROM GETTING QUITE AS HOT AS
YESTERDAY...BUT STILL UNSEASONABLY WARM IN THE UPPER 80S AND LOWER
90S MOST COMMUNITIES NEAR AND WEST OF US-17. HIGHEST TEMPS WILL
OCCUR FROM NORTHERN ALLENDALE COUNTY TO TATTNALL COUNTY. SHORELINE
LOCALES WILL BE HELD IN CHECK BY THE ONSHORE FETCH AND WILL PEAK
IN THE MID 70S NORTH TO THE LOWER TO MIDDLE 80S CENTRAL AND SOUTH.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
TONIGHT...THE DEEP LAYERED RIDGE WILL FINALLY BEGIN TO RETREAT
TONIGHT AS THE UPPER LOW OVER THE PLAINS FINALLY KICKS OUT IN
RESPONSE TO ANOTHER POWERFUL LOW DEVELOPING OVER THE FOUR CORNERS
REGION. THE PRIMARY LOW-LEVEL JET AXIS AND ASSOCIATED CORRIDOR OF
WARM AIR ADVECTION LOOK TO REMAIN DISPLACED TO THE WEST AND
NORTHWEST OVERNIGHT AS SHORTWAVE ENERGY PASSES TO THE NORTH. THERE
MAY BE JUST ENOUGH LIFT TO SUPPORT AN ISOLATED SHOWER/TSTM ACROSS
THE FAR INTERIOR AREAS OVERNIGHT, BUT CONFIDENCE IN THIS SCENARIO
IS QUITE LOW GIVEN THE DISCREPANCIES NOTED IN THE VARIOUS 30/00Z
GLOBAL MODEL SUITE. GENERALLY FAVORED THE DRIER NAM AND ECMWF
SOLUTIONS WHILE DISCOUNTING THE WETTER GFS. WILL HIGHLIGHT SLIGHT
CHANCE POPS ACROSS THE INTERIOR WITH DRY CONDITIONS AT THE COAST.
FURTHER REFINEMENTS WILL BE NEEDED AS MORE DATA ARE RECEIVED AND
EVALUATED. LOWS WILL RANGE FROM THE UPPER 60S INLAND TO THE LOWER
70S AT THE COAST.

SUNDAY THROUGH MONDAY...LOW PRESSURE ALOFT WILL TRACK THROUGH THE
CENTRAL PLAINS INTO THE UPPER MIDWEST ON SUNDAY...THEN BECOMES
ABSORBED BY NORTHERN STREAM ENERGY ON MONDAY. THE MEAN TROUGH
POSITION WILL REMAIN FAR TO THE NORTH/NW EARLY NEXT WEEK...WITH
GENERALLY A ZONAL FLOW TO PREVAIL LOCALLY. AT THE SURFACE WEAK LOW
PRESSURE WILL SHIFT THROUGH THE OHIO VALLEY SUNDAY...THEN PASSES OFF
THE DELMARVA AND TO THE SOUTH OF NEW ENGLAND MONDAY. HIGH PRESSURE
CENTERED BETWEEN BERMUDA AND THE MID ATLANTIC COAST SUNDAY WILL BE
FORCED EAST AS THIS OCCURS...BUT IT/S ANTICYCLONIC FLOW ATTEMPTS TO
HOLD ON LOCALLY. A COLD FRONT TRAILING FROM THE LOW WILL STRUGGLE TO
MOVE EAST SUNDAY...MAKING IT TO NEAR THE APPALACHIANS MONDAY AS THE
ATLANTIC RIDGE HOLDS ON. BOTH DAYS WILL EXPERIENCE A CONTINUATION OF
UNUSUALLY WARM WEATHER WITH 850 MB TEMPS SOME 2 STANDARD DEVIATIONS
ABOVE NORMAL. WE HAVE MID AND UPPER 80S FOR HIGHS AND MID AND UPPER
60S FOR LOWS.

WHILE THERE ARE SUBTLE MID LEVEL IMPULSES THAT TRAVERSE THE
REGION...OVERALL FORCING FOR ASCENT IS MISSING OUTSIDE OF THE SEA
BREEZE AND MESO-SCALE BOUNDARIES THAT ARE ABLE TO FORM. AN INCREASE
IN INSTABILITY AND CAPE...MODEST UPWARD VERTICAL VELOCITIES AND
ADEQUATE LAPSE RATES WILL SUPPORT AN INCREASED RISK FOR MAINLY
DIURNALLY INDUCED SHOWERS AND T-STORMS. WE/LL CAP POPS IN THE CHANCE
RANGE BUT WITH PWATS AROUND 2 STANDARD DEVIATIONS GREATER THAN
NORMAL THERE COULD BE A LOCALLY HEAVY RAIN RISK.

THE SEVERE CHANCES ARE VERY LOW BUT NON-ZERO WITH DCAPES OF 1000-
1200 J/KG SUGGESTING A STRONG WIND THREAT. PLUS 500 MB TEMPS ARE AS
COLD AS -11/-12C AND CAPE IN THE HAIL GROWTH ZONE IS ALSO FAVORABLE
FOR AT LEAST MARGINALLY SEVERE HAIL. PROBABILITIES REMAIN LOW ENOUGH
WHERE THERE IS NO NEED TO INCLUDE IN THE HAZARDOUS WEATHER OUTLOOK
AT THIS STAGE.

TUESDAY...A STRENGTHENING TROUGH WILL BE OVER THE EAST COAST. AT THE
SURFACE...A WEAK HIGH SHOULD BE OVER OR NEAR THE NORTHEASTERN STATES
WHILE A BROAD AREA OF HIGH PRESSURE WILL BE CENTERED OVER TEXAS.
MEANWHILE...BROAD LOW PRESSURE WILL BE DEVELOPING OVER OR NEAR OUR
AREA. THE MODELS HAVE DIFFERING SOLUTIONS REGARDING THE INTERACTION
OF ALL OF THESE FEATURES AND WHERE THE RESULTING LOW DEVELOPS. THE
MODEL CONSENSUS SEEMS TO HAVE THE LOW DEVELOPING/MOVING TO THE NORTH
DURING THE DAY. THE END RESULT WILL BE UNSETTLED CONDITIONS FOR OUR
AREA. HIGH-END CHANCE POPS ARE IN THE FORECAST. THE SEVERE THREAT
REMAINS VERY LOW. SURFACE AND MID-LEVEL INSTABILITY IS LOWER THAN
THE PREVIOUS TWO DAYS AND SHEAR IS LACKING. HIGHS WILL BE NEAR
NORMAL.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
THERE IS STILL A FAIR AMOUNT OF DISAGREEMENT WITH THE MODELS TUESDAY
NIGHT ONWARD. THE 00Z GFS HAS WEAK LOW PRESSURE HOVERING OVER OR
NEAR US TUESDAY NIGHT INTO WEDNESDAY...THEN MOVING TO THE NORTHEAST
WEDNESDAY NIGHT FOLLOWED BY BUILDING HIGH PRESSURE THURSDAY. THE 00Z
ECMWF HAS A MUCH STRONGER/STRENGTHENING LOW DURING THIS SAME TIMER
PERIOD. HOWEVER...WRAP AROUND SHOWERS WILL PERSIST INTO THURSDAY
BEFORE HIGH PRESSURE BUILDS THURSDAY NIGHT INTO FRIDAY. THE 00Z
CANADIAN SEEMS TO BE IN THE MIDDLE OF THESE TWO...EXCEPT IT BRINGS
THE HIGH PRESSURE IN WEDNESDAY NIGHT. GIVEN ALL THE DIFFERENT
SOLUTIONS AND A GENERAL TROUGH OVER THE EAST COAST...OPTED TO KEEP
CHANCE POPS TUESDAY NIGHT INTO WEDNESDAY...FOLLOWED BY POPS TRENDING
DOWNWARD TO SLIGHT CHANCE WEDNESDAY NIGHT INTO THURSDAY. BUILDING
HIGH PRESSURE WILL BRING DRY CONDITIONS ON FRIDAY WITH BELOW NORMAL
TEMPERATURES.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
VFR INTO EARLY TONIGHT...EXCEPT FOR A BRIEF POTENTIAL FOR A LOW
END CHANCE OF A STRAY SHRA AT KCHS THIS AFTERNOON.

CONDITIONS WILL DETERIORATE TO MVFR OR PERHAPS IFR AT BOTH
TERMINALS OVERNIGHT INTO SUNDAY MORNING...AS BOUNDARY LAYER
MOISTURE INCREASES WITHIN A SE/SOUTH FLOW AND THE NOCTURNAL
INVERSION DEVELOPS. WE HAVE SHOWN CEILINGS DEVELOPING AROUND 1500
FT BY 05-06Z AND LASTING THROUGH 13-14Z SUNDAY...BUT THE SREF DOES
SHOW 30-40 PERCENT PROBABILITIES OF IFR CONDITIONS. FOR NOW WE
HAVE A SCATTERED DECK AT 900 FT...JUST TO IMPLY THAT THE RISK OF
IFR COULD OCCUR. SURFACE VISIBILITIES SHOULD REMAIN 6SM OR GREATER
WITH TOO MUCH WIND WITHIN THE BOUNDARY LAYER...THUS LIMITING THE
FOG POTENTIAL.

VFR WEATHER WILL RETURN AGAIN THE SECOND HALF OF SUNDAY MORNING
AND EARLY AFTERNOON.

EXTENDED AVIATION OUTLOOK...UNSETTLED CONDITIONS FOR THE EARLY AND
MIDDLE PART OF NEXT WEEK WILL RESULT IN PERIODIC FLIGHT RESTRICTIONS
IN SHRA/TSRA AT THE LOCAL TERMINALS.

&&

.MARINE...
THIS AFTERNOON...HIGH PRESSURE TO THE DISTANT NORTH WILL STRETCH
OVERHEAD AS AN UNDULATING FRONT NOT FAR TO THE NORTH ATTEMPTS TO
SLIDE SOUTH AND NEVER QUITE GETS INTO OUR COASTAL WATERS. THE
RESULT WILL BE FOR EAST AND SE WINDS AT SPEEDS GENERALLY NO HIGHER
THAN ABOUT 10 OR 15 KT...DESPITE SEA BREEZE INFLUENCES. NOT MUCH
HEIGHT TO THE SEAS...HOLDING AT 2 FT OR LESS THROUGH THE PERIOD.

TONIGHT...NOT MUCH CHANGE WILL OCCUR TONIGHT WITH SOUTHERLY WINDS
PREVAILING. WINDS LOOK TO NUDGE UP JUST SLIGHTLY TO 10-15 KT WITH
SEAS BUILDING 2-4 FT.

SUNDAY THROUGH THURSDAY...HIGH PRESSURE WILL BE THE MAIN LARGE
SCALE FEATURE THAT PREVAILS INTO EARLY NEXT WEEK...BEFORE AN AREA
OF LOW PRESSURE IMPACTS THE WATERS BY THE MIDDLE OF THE WEEK.
OUTSIDE OF CONVECTION THERE ARE NO REAL CONCERNS IN REGARDS TO
WINDS AND SEAS...WITH NO ADVISORY CONDITIONS EXPECTED. EVEN WITH
SOME BOOST OF SEA BREEZE CIRCULATIONS WINDS WILL REMAIN AT OR
BELOW 12-18 KT AND SEAS WON/T GET ANY HIGHER THAN 3 OR 4 FT.
HOWEVER...MARINERS ARE ADVISED THAT CHANCES OF SHOWERS AND
T-STORMS WILL BE ON THE RISE EARLY NEXT WEEK...PEAKING IN THE
CHANCE RANGE LATER MONDAY OR TUESDAY THROUGH WEDNESDAY.

&&

.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...
EQUIPMENT...



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