005
FXUS62 KCHS 241519
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1019 AM EST MON FEB 24 2020
SYNOPSIS
A DEVELOPING WARM FRONT WILL LIFT NORTH OF THE REGION TONIGHT,
FOLLOWED BY A PAIR OF COLD FRONTS DURING THE MIDDLE OF THE
WEEK. HIGH PRESSURE RETURNS THURSDAY AND FRIDAY, WITH A WEAK
COLD FRONT EXPECTED SATURDAY.
NEAR TERM /THROUGH TONIGHT/
AS OF 1015 AM: KCLX INDICATED SEVERAL PATCHES OF 10-20 DBZ
RETURNS ACROSS THE FORECAST AREA. THESE LIGHT RETURNS WERE
LIKELY ASSOCIATED SCATTERED AREAS OF SPRINKLES. I WILL UPDATE
THE FORECAST TO ADD A MENTION OF SPRINKLES AND INCREASED CLOUD
COVER TO THE FORECAST LATE THIS MORNING. FOR THIS AFTERNOON,
LIGHT SHOWERS WILL INCREASE IN COVERAGE FROM THE WEST. THE
SHOWERS MAY PRODUCE AROUND A TENTH OF AN INCH OF RAINFALL BY
LATE THIS AFTERNOON.
PREVIOUS DISCUSSION:
TODAY: MID LEVEL FLOW WILL SLOWLY BACK TODAY, WELL AHEAD OF A
STORM SYSTEM EJECTING OUT OF CENTRAL PLAINS. A WARM FRONT IS
FORECAST TO TAKE SHAPE LATER THIS MORNING ACROSS SOUTH GA AND
GRADUALLY LIFT TOWARD THE SAVANNAH RIVER LATE IN THE DAY. MODELS
INDICATE FAIRLY DEEP MOISTURE IN THE 850 MB TO 500 MB LAYERS
WILL SPREAD WEST TO EAST TO THE NORTH OF I-16 TODAY AND CHANCES
FOR LIGHTER RAINS WILL GENERALLY INCREASE FROM SOUTH TO NORTH
AND FROM EAST TO WEST LATER TODAY. WE HAVE POPS RANGING FROM
20/30 TO THE SOUTH OF I-16 TO LIKELY RIGHT ALONG OUR FAR NW
CORRIDOR WITH LESSER CHANCES FOR SOME LIGHT MEASURABLE RAINS
ALONG COASTAL SC PRIOR TO SUNSET. CLOUDS AND ANY PRECIP WILL
TEMPER HOW WARM IT COULD GET TODAY IF OUR REGION WERE TO SEE
MORE IN THE WAY OF SUNSHINE (WHICH IS UNLIKELY). WE MAINTAINED
HIGHS IN THE MID 60S NORTH TO THE WARMEST READINGS POSSIBLY IN
THE LOWER 70S INLAND AND SOUTH OF SAVANNAH.
TONIGHT: THE WARM AIR ADVECTION PATTERN WILL CONTINUE TO
STRENGTHEN AS THE WARM FRONT LIFTS NORTH OF THE REGION AFTER
MIDNIGHT. MODELS REMAIN CONSISTENT ON STRONG MOISTURE TRANSPORT
AND BUILDING UPPER DIFLUENCE AS RAINS INCREASE IN COVERAGE AND
INTENSITY. STEERING FLOW LOOKS PROGRESSIVE ENOUGH TO KEEP MOST
OF THE CONVECTIVE ELEMENTS PROGRESSIVE OVERNIGHT AND WE KEPT
QPF AMOUNTS MOSTLY 1/2 INCH OR SO, ALTHOUGH HEAVIER BANDS OF
SHOWERS COULD STILL RESULT IN SOME 1 INCH BANDS INLAND FROM
I-95. SOUTHWEST WINDS WILL INCREASE ALONG COASTAL ZONES
OVERNIGHT AS TEMPS WARM FROM THE MID TO UPPER 50S DURING THE
EVENING HOURS TO THE LOWER TO MID 60S MANY AREAS AFTER
MIDNIGHT.
SHORT TERM /TUESDAY THROUGH THURSDAY/
TUESDAY: AN AMPLIFYING AND LARGE SCALE MID AND UPPER TROUGH WILL
COVER MUCH OF THE CENTRAL AND EASTERN CONUS, AS A STRONG RIDGE ALOFT
EXISTS OVER THE CARIBBEAN. AT THE SURFACE, AN OCCLUDED LOW WILL LIFT
SLOWLY INTO THE OHIO VALLEY, WITH A TRAILING COLD FRONT TO SLOWLY
APPROACH THE LOCAL AREA. BUT THE FRONT STALLS OUT AS IT BECOMES MORE
PARALLEL WITH THE FLOW ALOFT. WIDESPREAD CONVECTIVE RAINS WILL BE
ONGOING AT DAYBREAK IN ASSOCIATION WITH A POTENT SOUTHERN STREAM
UPPER LEVEL JET. BUT FORCING DIMINISHES DURING THE AFTERNOON, SO
RAIN CHANCES DROP FROM 90-100% IN THE MORNING DOWN TO 50-70% IN THE
AFTERNOON. POOR LAPSE RATES AND CONSIDERABLE CLOUD COVER WILL BE
PRESENT, BUT A SWATH OF MLCAPE AS GREAT AS 300-500 J/KG IS FORECAST
TO DEVELOP AHEAD OF THE COLD FRONT DURING THE AFTERNOON. THIS MAY BE
ENOUGH FOR ISOLATED T-STORMS, MAINLY NEAR AND WEST OF I-95. DESPITE
THE EXTENSIVE CLOUD COVER, WARM ADVECTION WILL PREVAIL, AS 850 MB
TEMPS REACH 11-13C. THIS WILL ALLOW FOR MAX TEMPS TO CLIMB TO 70F OR
GREATER INLAND FROM US-17. THE RISK OF T-STORMS ENDS BY SUNSET, BUT
SCATTERED TO WIDESPREAD SHOWERS WILL CONTINUE THROUGH THE NIGHT
WITHIN A DEEP FEED OF SUB-TROPICAL MOISTURE AND FORCING FROM THE
UPPER JET AND VARIOUS MID LEVEL IMPULSES. TEMPS WILL BE ABOUT 15-20F
ABOVE CLIMO. ADDITIONAL QPF FOR TUESDAY AND TUESDAY NIGHT WILL
AVERAGE 1/4 TO 1/3 INCHES. THESE RAINS, PLUS THOSE OF TODAY AND
TONIGHT, WILL MAINTAIN THE FLOODING OF ALL MAJOR RIVERS IN OUR
FORECAST AREA.
WEDNESDAY: A DEEP TROUGH ALOFT WILL SWEEP EAST TOWARD THE
APPALACHIANS, SENDING A SECONDARY COLD FRONT THROUGH THE LOCAL AREA
LATE DAY OR EARLY AT NIGHT. THE MAIN DEEP LAYERED MOISTURE AXIS WILL
SHIFT OFFSHORE AS THIS OCCURS, ALLOWING FOR DECREASING RAIN CHANCES
THROUGHOUT THE DAY. THERE ISN'T ANY COLD ADVECTION UNTIL WEDNESDAY
NIGHT, SO MAX TEMPS WILL AGAIN BE WELL ABOVE NORMAL, BEFORE DROPPING
SOME 30F BY THURSDAY MORNING AS THE SYNOPTIC FLOW VEERS TO THE WEST-
NORTHWEST. THIS INFLUX OF COLDER AIR, PLUS STEADY AND LARGE
ISALLOBARIC PRESSURE RISES COULD PRODUCE A LAKE WIND ADVISORY ACROSS
LAKE MOULTRIE WEDNESDAY NIGHT INTO THURSDAY.
THURSDAY: AN ENORMOUS MID AND UPPER TROUGH COVERS A LARGE PART OF
THE CONUS, INCLUDING THE LOCAL VICINITY, AS COLDER HIGH PRESSURE AT
THE SURFACE BUILDS IN FROM THE WEST. THE 850 MB 0C ISOTHERM
PENETRATES FAR OFFSHORE AND EVEN INTO NORTHERN FLORIDA, LEAVING US
WITH A MUCH COLDER DAY, DESPITE PLENTY OF INSOLATION.
LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/
COLDER WEATHER WILL PREVAIL FOR THE END OF FEBRUARY AND START OF
MARCH, AS A BROAD AND DEEP TROUGH PERSISTS OVER THE AREA. FOR THE
MOST PART HIGH PRESSURE WILL DOMINATE AT THE SURFACE AND IN THE
LOWER LEVELS. WITHIN A DEEP OFFSHORE FLOW, MOISTURE WILL BE
SIGNIFICANTLY LIMITED, SO THERE IS LITTLE IF ANY CHANCE OF PRECIP
DURING THIS TIME. THE EXCEPTION MIGHT BE SATURDAY WHEN A DECENT
SHORT WAVE MOVES THROUGH, AND COULD RESULT IN A FEW SHOWERS. FOR NOW
WE HAVE CAPPED POP AT LESS THAN 15%, SO NO MENTION IN THE FORECAST.
ALSO, CONDITIONS FAR INLAND COULD FAVOR A POTENTIAL FOR ONE OR TWO
LATE NIGHT/EARLY MORNING FREEZES.
AVIATION /15Z MONDAY THROUGH FRIDAY/
VFR CONDITIONS ANTICIPATED TODAY WITH THE BULK OF THE CLOUD-LAYER
MOISTURE ABOVE 3 KFT. TONIGHT, A WARM FRONT WILL MOVE THROUGH
AND EVENTUALLY NORTH OF THE TERMINALS. INCREASING CHANCES FOR
LOWER CIGS BY LATE EVENING WITH RAIN CHANCES ALSO WILL BE ON THE
RISE FOR THE OVERNIGHT. SURFACE WINDS WILL GENERALLY BE LIGHT
TODAY, THEN INCREASE FROM SOUTHERLY DIRECTIONS LATE TONIGHT AS
TEMPS RISE ALONG THE COASTAL CORRIDOR.
EXTENDED AVIATION OUTLOOK: A PAIR OF COLD FRONTS WILL BRING FLIGHT
RESTRICTIONS TUESDAY THROUGH EARLY WEDNESDAY. VFR WITH BREEZY
CONDITIONS ARE EXPECTED BEHIND THE SECOND COLD FRONT INTO
THURSDAY.
MARINE
TODAY: RELATIVELY TRANQUIL CONDITIONS MUCH OF TODAY AS THE PRESSURE
PATTERN REMAINS WEAK AHEAD OF A DEVELOPING WARM FRONT ACROSS SOUTH
GA. THERE WILL BE LINGERING 2-3 FT SWELLS OFFSHORE BUT WINDS WILL
REMAIN VERY LIGHT EARLY ON AND LESS THAN 15 KT PRIOR TO DUSK.
AS THE WARM FRONT LIFTS NORTH TONIGHT, SOUTH FLOW WILL INCREASE
AND SEAS WILL GRADUALLY BUILD AFTER MIDNIGHT. THERE IS POTENTIAL
FOR BOTH GUSTS TO 25 KT AND 6 FT SEAS DEVELOPING ACROSS OUTER
GA WATERS CLOSER TO THE GULF STREAM BUT GIVEN TRICKY MIXING
PROFILES, WE OPTED TO WAIT ON THE SCA ISSUANCE, STILL LIKELY TO
BE ISSUED LATER TODAY FOR AMZ374.
TUESDAY THROUGH SATURDAY: CHANGEABLE CONDITIONS ACROSS THE MARITIME
COMMUNITY DURING THE MID AND LATE WEEK PERIOD. HIGH PRESSURE TO THE
EAST AND SOUTHEAST ON TUESDAY WILL GIVE WAY TO A PAIR OF COLD FRONTS
THAT MOVE THROUGH LATE WEDNESDAY OR WEDNESDAY NIGHT. THIS IS
FOLLOWED BY HIGH PRESSURE BUILDING FROM THE WEST ON THURSDAY AND
FRIDAY. CONDITIONS IN ADVANCE OF THE COLD FRONT FAVOR SMALL CRAFT
ADVISORIES OVER AT LEAST AMZ350 AND AMZ374. BEHIND THE FRONTS THERE
WILL BE THE NEED FOR ADDITIONAL ADVISORIES AT TIMES OVER ALL WATERS,
INCLUDING CHARLESTON HARBOR. THERE IS EVEN A LOW END CHANCE FOR
MARGINAL GALES WEDNESDAY NIGHT INTO EARLY THURSDAY OVER THE OUTER
GEORGIA WATERS, WHERE THE GREATEST MIXING OF THE COLD AIR WILL
OCCUR.
BOTH THE NAM AND SREF DEPICT SOME POTENTIAL FOR SEA FOG TUESDAY
NIGHT INTO WEDNESDAY, BUT CONDITIONS DON'T APPEAR FAVORABLE FOR SUCH
AN OCCURRENCE. IF ANY REDUCTION IN VISIBILITY WERE TO OCCUR IT WOULD
BE DUE TO LOW STRATUS. SO WE HAVE NO MENTION IN THE GRIDS OR COASTAL
WATERS FORECAST.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...NONE.
NEAR TERM...NED
SHORT TERM...33
LONG TERM...33
AVIATION...
MARINE...
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