818
FXUS62 KCHS 231812
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
112 PM EST SUN FEB 23 2020
SYNOPSIS
HIGH PRESSURE WILL PERSIST THROUGH TONIGHT. A WARM FRONT WILL
LIFT NORTH OF THE REGION ON MONDAY, FOLLOWED BY A PAIR OF COLD
FRONTS DURING THE MIDDLE OF THE WEEK. HIGH PRESSURE RETURNS
THURSDAY AND FRIDAY, WITH ANOTHER COLD FRONT EXPECTED ON
SATURDAY.
NEAR TERM /THROUGH TONIGHT/
AS OF 1 PM: CIRRUS CLOUDS HAVE INCREASED ACROSS THE FORECAST
AREA SINCE THE LAST UPDATE. I WILL UPDATE THE FORECAST TO
INCREASE CLOUD COVER THROUGH THIS AFTERNOON. IN ADDITION, I WILL
LOWER THE AFTERNOON RH VALUES BASED ON RECENT OBSERVATIONS.
AS OF 10 AM: SATELLITE IMAGES AND VIEW OUT THE WINDOW INDICATED
THIN CIRRUS PASSING OVER THE FORECAST AREA THIS MORNING. I WILL
MAKE MINOR EDITS TO THE HOURLY TEMPERATURES, MAINLY TO BETTER
ALIGN WITH TRENDS IN OBSERVED VALUES. OTHERWISE, THE CURRENT
FORECAST APPEARS ON TRACK.
PREVIOUS DISCUSSION:
TODAY: TEMPERATURES WILL CONTINUE TO MODERATE AS THE SURFACE
HIGH PRESSURE BREAKS DOWN AND TRANSITIONS OFF MID ATLANTIC COAST
LATE. LOW LEVEL THICKNESS VALUES AND WEAK AFTERNOON RETURN FLOW
IN THE BOUNDARY LAYER SUGGEST MOST AREAS SHOULD HAVE NO TROUBLE
REACHING THE 60S; LOWER 60S NORTH TO THE MID 60S SOUTH. WE
SHOULD SEE PLENTY OF SUNSHINE THIS MORNING BUT MODELS INDICATE
HIGH CLOUDS WILL TEND TO BECOME THICKER AND MORE WIDESPREAD
TOWARD LATE AFTERNOON. A WEAK PRESSURE PATTERN OVER THE REGION
IN THE LOW LEVELS WILL RESULT IN LIGHT WINDS ALL AREAS TODAY.
TONIGHT: WARM AIR ADVECTION PROCESSES ALOFT, INCREASING LAYERED
CLOUDS, AND ELEVATED LOW LEVEL DEW POINTS WILL RESULT IN MUCH
MILDER TEMPS OVERNIGHT ACROSS THE AREA. MOST OF THE MOISTURE
INITIALLY WILL BE MID AND HIGH CLOUDS AND WE HAVE DRY WEATHER
AND SOME LOW SILENT POPS UNTIL LATE NIGHT. THERE COULD BE A FEW
SHOWERS BREAKING OUT ACROSS EAST CENTRAL GA ACROSS THE SAVANNAH
RIVER TO THE SC MIDLANDS LATE NIGHT, WE MAINTAINED SOME 20/30
POPS ADJACENT TO THESE AREAS AROUND DAYBREAK. THERE COULD BE
SOME PATCHY FOG IN A FEW SPOTS LATE TONIGHT, NOT ENOUGH
CERTAINTY TO INSERT INTO OUR FORECAST AT THIS TIME.
SHORT TERM /MONDAY THROUGH WEDNESDAY/
MONDAY: HIGH PRESSURE THAT COVERS THE WESTERN ATLANTIC WILL PULL A
LITTLE FURTHER OFFSHORE. THIS ALLOWS FOR A WARM FRONT TO LIFT NORTH
OF THE LOCAL AREA IN RESPONSE TO A SURFACE LOW AND ASSOCIATED SHORT
WAVE TROUGH MOVING FROM THE CENTRAL AND SOUTHERN GREAT PLAINS TOWARD
THE LOWER AND MIDDLE MISSISSIPPI VALLEY. STRENGTHENING ISENTROPIC
ASCENT ALONG WITH MID LEVEL PERTURBATIONS AND A DEEP FLOW ALOFT OUT
OF THE GULF OF MEXICO WILL SUPPORT SCATTERED POP NORTH AND
NORTHWEST, WITH ISOLATED TO LOW END CHANCE POP SOUTH AND SOUTHEAST.
QPF IS NO MORE THAN 1/10 TO 2/10 INCHES. EXPECT A LARGE RANGE OF
TEMPS DEPENDENT UPON THE TIMING OF THE WARM FRONT LIFTING THROUGH,
FOR NOW WE HAVE 60-63F NORTH AND NORTHWEST, MID 60S TO LOWER 70S
ELSEWHERE.
MONDAY NIGHT: A CONTINUED FEED OF RICH TROPICAL-LIKE MOISTURE OUT OF
THE GULF WILL PREVAIL IN ADVANCE OF A COLD FRONT WITHIN A DEEP
SOUTHWEST FLOW ALOFT. PWAT CLIMBS NEAR 1.5 INCHES, OR CLOSE TO THE
CLIMATOLOGICAL MAX FOR FEBRUARY OVER THE AREA. THERE IS LARGE SCALE
FORCING FOR ASCENT WITH A NEARBY 135-145 KT UPPER LEVEL JET, SUPPORTING
WIDESPREAD RAINS SPREADING IN FROM THE WEST AND SOUTHWEST. WE HAVE
CATEGORICAL POP AS A RESULT. AFTER COORDINATION WITH WPC WE HAVE
OPTED TO EXPAND THE "MARGINAL RISK" OF EXCESSIVE RAINFALL INTO
MOST OF OUR COUNTIES INLAND FROM I-95. QPF WILL REACH AT LEAST
1/2 TO 1 INCH, WITH LOCALLY HIGHER AMOUNTS. GIVEN THE RECENT HEAVY
RAIN EVENT IN SOME AREAS, THERE COULD BE A NEED FOR A FLASH
FLOOD WATCH AT A LATER TIME. TEMPS WILL BE CONSIDERABLY WARMER
THAN RECENT NIGHTS WITHIN A STRONG WARM ADVECTION PATTERN.
EXPECT TEMPS TO HOLD FAIRLY STEADY OR EVEN RISE DURING THE
OVERNIGHT PERIOD.
TUESDAY: A COLD FRONT THAT TRAILS FROM LOW PRESSURE LIFTING INTO THE
OHIO VALLEY, WILL STALL OVER THE LOCAL AREA AS IT BECOMES ALIGNED TO
THE FLOW ALOFT. MODELS DIFFER SLIGHTLY ON WHERE THE MAIN MOISTURE
AXIS BECOMES SITUATED IN RELATION TO SOUTH CAROLINA AND GEORGIA. BUT
GIVEN MID LEVEL IMPULSES PASSING THROUGH AND LARGE SCALE FORCING
FOR ASCENT DUE TO THE PRESENCE OF THE 140-150 KT UPPER JET, WE
MAINTAINED 70-80% POP. WE ADDED MENTION OF ISOLATED T-STORMS GIVEN
SOME INSTABILITY AND CAPE AND A MID LEVEL JET NEARBY. TEMPS WILL BE
SEVERAL DEGREES ABOVE CLIMO GIVEN THE WARM ADVECTION REGIME IN
PLACE.
WEDNESDAY: A SECONDARY AND STRONGER COLD FRONT WILL SWEEP THROUGH IN
RESPONSE TO A ROBUST SHORT WAVE TROUGH SHIFTING INTO THE EAST. THIS
SHUNTS THE DEEP PLUME OF MOISTURE FURTHER OFFSHORE, AND CONVECTIVE
RAIN CHANCES WILL DIMINISH THROUGHOUT THE DAY. GIVEN GOOD QG FORCING
WE DID HOLD ONTO CHANCE POP, BUT SOUNDINGS AND TIME CROSS-SECTIONS
DO SHOW CONSIDERABLE DRIER AIR WORKING IT'S WAY IN BEHIND THE SECOND
COLD FRONT. THE COLD ADVECTION IS RATHER SLUGGISH IN ARRIVING, THUS
WE STILL HAVE TEMPS WELL ABOVE CLIMO.
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
A HIGHLY AMPLIFIED MID AND UPPER PATTERN WILL COVER THE LOWER 48
STATES, SHOWING A BROAD TROUGH OVER THE EASTERN HALF OF THE COUNTRY
AND RIDGING OUT WEST DURING MOST OF THE PERIOD. AT THE SURFACE, HIGH
PRESSURE WILL DOMINATE INTO FRIDAY, FOLLOWED BY A COLD FRONT NEXT
SATURDAY. AS OF THIS TIME THE FRONT LOOKS TO BE MOISTURE STARVED, SO
WE DON'T HAVE ANY MENTION OF POP. CONFIDENCE IS EXCELLENT THAT GIVEN
THE LOW HEIGHTS ALOFT AND 850 MB TEMPS THAT ARE AS AS MUCH AS
SEVERAL DEGREES BELOW 0C, THAT THE END OF FEBRUARY WILL BE WELL
BELOW CLIMO.
LAKE WINDS: COLDER AIR MOVING ATOP THE RELATIVELY WARMER WATERS OF
LAKE MOULTRIE WILL LIKELY RESULT IN THE ISSUANCE OF A LAKE WIND
ADVISORY WEDNESDAY NIGHT INTO THURSDAY NIGHT.
AVIATION /18Z SUNDAY THROUGH FRIDAY/
VFR THROUGH 24/12Z AT BOTH KSAV/KCHS. SLIGHT CHANCE OF SOME LOW
CIGS AT KSAV TOWARD DAYBREAK ON MON.
EXTENDED AVIATION OUTLOOK: A WARM FRONT WILL LIFT NORTH OF THE AREA
MONDAY, FOLLOWED BY A PAIR OF COLD FRONTS INTO WEDNESDAY. THIS WILL
RESULT IN PERIODS OF SHOWERS AND MAYBE EVEN A FEW T-STORMS, ALONG
WITH AT LEAST PERIODIC FLIGHT RESTRICTIONS. VFR ALONG WITH BREEZY TO
WINDY CONDITIONS WILL THEN PREVAIL BEHIND THE SECOND COLD FRONT INTO
THURSDAY.
MARINE
THROUGH TONIGHT: A WEAK PRESSURE PATTERN ACROSS THE WATERS AS
HIGH PRESSURE WEAKENS ALONG THE COAST TODAY THEN SETS UP OFF THE
MID ATLANTIC COAST TONIGHT. WIND SPEEDS WILL MAINLY BE LESS THAN
10 KT WITH VARIABLE DIRECTIONS, BECOMING ONSHORE. WEAK FLOW WILL
THEN BECOME SE TO S LATE TONIGHT. SEAS CONTINUE TO SLOWLY SUBSIDE.
WE HAVE 6 FT SEAS WELL OFFSHORE NEAR THE GULF STREAM OVER THE
20-60 NM GA WATERS THIS MORNING AND THEN SUSPECT THAT THE SCA
IN THAT MARINE LEG WILL COME DOWN FOR THIS AFTERNOON.
MONDAY: A WARM FRONT WILL PASS NORTH OF THE LOCAL WATERS, WITH HIGH
PRESSURE ANCHORED WEST OF BERMUDA. EVEN THOUGH WIND FIELDS ARE
LIMITED, SEAS ARE SOMEWHAT ELEVATED DUE TO CONTINUED SWELLS
IMPACTING THE AREA.
MONDAY NIGHT THROUGH WEDNESDAY: ONE COLD FRONT WILL APPROACH ON
TUESDAY AND STALLS OUT OVER OR NEAR THE LOCAL VICINITY, BEFORE A
SECOND AND STRONGER COLD FRONT MOVES THROUGH WEDNESDAY. WINDS WILL
TURN S AND SW AND INCREASE, ALLOWING FOR SEAS TO ALSO CLIMB. WE
COULD NEED SMALL CRAFT ADVISORIES AT A LATER TIME ON AT LEAST SOME
OF THE MARINE ZONES. CONVECTIVE RAINS WILL OCCUR DURING MUCH OF THE
TIME, ALONG WITH SOME POTENTIAL FOR T-STORMS. THERE ARE HINTS OF SEA
FOG PER MODEL GUIDANCE, BUT THE CONDITIONS OVERALL DON'T APPEAR
HIGHLY FAVORABLE FOR IT TO OCCUR AS OF THIS TIME.
WEDNESDAY NIGHT THROUGH FRIDAY: STRONG HIGH PRESSURE BUILDS IN FROM
THE WEST, AND WITH VARYING DEGREES OF COLD ADVECTION AND STEADY
ISALLOBARIC PRESSURE RISES, WE ANTICIPATE THE NEED FOR ADDITIONAL
SMALL CRAFT ADVISORIES.
CHS WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
MARINE...NONE.
NEAR TERM...NED
SHORT TERM...33
LONG TERM...33
AVIATION...RAD
MARINE...
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