667 FXUS62 KCHS 040510 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 1210 AM EST MON MAR 4 2013 .SYNOPSIS... HIGH PRESSURE WILL BUILD FROM THE WEST TONIGHT AND WILL PREVAIL THROUGH EARLY THIS WEEK. LOW PRESSURE AND ITS TRAILING COLD FRONT WILL IMPACT THE AREA TUESDAY NIGHT INTO EARLY WEDNESDAY...FOLLOWED AGAIN BY HIGH PRESSURE THROUGH LATE WEEK. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... NO MAJOR CHANGES WERE MADE FOR THE EARLY MORNING UPDATE. WATCHING CIRRUS MOVING IN FROM THE NORTHWEST. RAP 600MB RH PROGS SUGGEST MOST OF THIS WILL REMAIN TO THE NORTHWEST THROUGH DAYBREAK. UNDER CLEAR SKIES...TEMPERATURES BY DAYBREAK WILL FALL INTO THE MID TO UPPER 20S AT MOST LOCATIONS AWAY FROM THE IMMEDIATE COAST. A FEW OF THE COLDEST LOCATIONS WELL INLAND COULD BRIEFLY BOTTOM OUT IN THE LOWER 20S...AND TEMPERATURES CLOSE TO FREEZING WILL EVEN OCCUR ON THE SEA ISLANDS/BEACHES. THESE LOW TEMPERATURES WILL AVERAGE AS MUCH AS 15-20F BELOW AVERAGE FOR MARCH 4. AT KSAV...THE MARCH 4 RECORD LOW OF 26 DEGREES LAST SET IN 2009 COULD BE TIED OR EVEN ECLIPSED. && .SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/... MONDAY...THE ABNORMALLY DEEP TROUGH THAT IMPACTED THE AREA OVER THE WEEKEND WILL FINALLY LIFT OUT...AND BECOMES REPLACED BY A BUILDING RIDGE FROM THE WEST AND ITS ASSOCIATED RISING HEIGHTS. THE CYCLONIC FLOW OF RECENT DAYS THAT EXTENDS FAR TO THE SW FROM DEEP LOW PRESSURE NEAR THE COAST OF MAINE WILL GIVE WAY TO ANTICYCLONIC CURVATURE OF THE ISOBARS AS HIGH PRESSURE ARRIVES FROM THE WEST. ALTHOUGH THERE IS AN INCREASE IN JET STREAM CIRRIFORM CLOUDS IN THE LATE MORNING AND AFTERNOON...CROSS-SECTIONS AND SOUNDINGS INDICATE THAT THEY WILL BE MORE TRANSLUCENT RATHER THAN OPAQUE. THUS WITH DECENT INSOLATION...A 20-30 METER RISE IN LOW LEVEL THICKNESS VALUES AND A SOLID 8-10C CLIMB IN 850 MB TEMPS AND COLD ADVECTION WANING...WE LOOK TO REACH THE MID 50S NORTH TO AROUND 60 SOUTH. MONDAY NIGHT...THE SURFACE RIDGE SLIDES INTO THE ATLANTIC...THE SYNOPTIC FLOW BACKS AROUND TO THE WEST AND SW...AND THERE IS A STEADY INCREASE IN HIGHER LEVEL CLOUDS. THESE CLOUDS WILL THICKEN WITH TIME FROM WEST TO EAST IN ASSOCIATION WITH THE UPPER JET AND IN ADVANCE OF A LOW PRESSURE SYSTEM THAT ORGANIZES AS IT MOVES NE FROM THE ARKLATEX TO KENTUCKY. WE/LL EXPERIENCE SOME RADIATIONAL COOLING IN THE EVENING...BUT TEMPS WILL HOLD STEADY OR EVEN RISE LATE. BOTTOM LINE THOUGHT...WE WILL BE CONSIDERABLE WARMER THAN WE WILL BE 24 HOURS PRIOR. TUESDAY...A STRONG CUT OFF LOW WILL SHIFT FROM THE NORTHERN PLAINS TO ILLINOIS...WITH ITS ASSOCIATED SURFACE LOW TO TREK EASTWARD THROUGH THE OHIO VALLEY TOWARD THE CENTRAL APPALACHIANS. THE FORECAST ZONES WILL LIE IN THE WARM SECTOR REGIME...WITH A WARM FRONT FOUND IN NC AND A TRAILING COLD FRONT ORIENTED FROM NE TO SW TO CROSS THE SOUTHERN PORTION OF THE MOUNTAINS BY 00Z WEDNESDAY. WITH ONLY MINIMAL HEIGHT FALLS LATE AND THE BEST CONVERGENCE AND DEEPER MOISTURE TO REMAIN OFF TO OUR WEST AND NW...THE CHANCES FOR ANY RAIN BEFORE NIGHTFALL ARE SMALL. THERE IS A MOISTENING OF THE COLUMN...BUT THE LOW LEVELS REMAIN QUITE DRY WITH DEW POINT DEPRESSIONS AS MUCH AS 20-25 DEGREES IF NOT MORE. THUS WE/LL CARRY ONLY 20 POPS IN THE AFTERNOON NW OF A LINE FROM ABOUT JAMESTOWN TO SUMMERVILLE AND YEMASSEE IN SC...AND NW OF A LIN FROM ABOUT SHAWNEE TO CLAXTON AND REIDSVILLE IN GA. LATER FORECASTS MAY NEED TO ADJUST THESE POPS UP OR DOWN...DEPENDING UPON TIMING OF THE APPROACHING FRONT. DESPITE AN INCREASE IN CLOUD COVER...STRONG WARM ADVECTION WILL BOOST TEMPS TO THEIR HIGHEST LEVELS IN ABOUT A WEEK. AWAY FROM THE MUCH COOLER SHORELINE COMMUNITIES...UPPER 60S AND LOWER 70S WILL BE COMMON JUST ABOUT EVERYWHERE. A 30-40 KT LOW LEVEL JET WILL SHIFT THROUGH THE REGION...AND THAT ALONG WITH A TIGHTENING OF THE GRADIENT WILL ALLOW FOR BREEZY TO WINDY CONDITIONS TO DEVELOP. TUESDAY NIGHT...THE CUTOFF ALOFT MOVES THROUGH VIRGINIA AND NC...WHICH TRIGGERS A TRIPLE POINT SURFACE LOW FORMING JUST TO THE EAST OF THE FEATURE ALOFT. BETTER HEIGHTS FALLS LOCALLY WILL ACCOMPANY THE LOW...AND THIS WILL WILL DRIVE THE COLD FRONT FAIRLY QUICKLY THROUGH THE AREA FROM NW TO SE THROUGH THE NIGHT. POPS WILL EASILY REACH THE 60-70 PERCENTILE...BUT EVEN THESE MAY BE CONSERVATIVE AS REFINEMENTS WILL LIKELY BE REQUIRED ONCE THE EXACT TIMING DETAILS ARE HASHED OUT. THERE IS LITTLE IF ANY SURFACE BASED INSTABILITY...BUT SOME ELEVATED CAPE /200-300 J/KG/...SHOWALTERS LESS THAN ZERO AND 0-6 KM BULK SHEAR OF 50 KT OR MORE. THEREFORE WE CAN/T RULE OUT A LITTLE ELEVATED CONVECTION. THE QUICK PROGRESSION OF THE FRONT SHOULD LIMIT OUR QPF VALUES...MAINLY IN THE RANGE FROM 0.10 TO 0.30 INCHES. WINDS WILL FLUCTUATE THROUGH THE NIGHT...BUT ONCE THE FRONT MOVES THROUGH AND PRESSURES STEADILY RISE AND COLD ADVECTION ENSUES...THEY WILL REMAIN ELEVATED AND PERIODICALLY BREEZY OR EVEN WINDY. TEMPS WILL PLUNGE IN WAKE OF THE FRONT AND NOT FAR FROM TYPICAL MINIMAL LEVELS. WEDNESDAY...THE CUT OFF WILL FINALLY TRAP ITS SURFACE LOW UNDERNEATH NEAR THE MID-ATLANTIC COAST. WE/LL BE IN THE DRY SLOT BEHIND THE COLD FRONT THAT PULLS FAR AWAY THROUGH THE ATLANTIC...AND THE WRAP-AROUND MOISTURE ASSOCIATED WITH THE STACKED LOW. ALTHOUGH THERE ARE HINTS THAT SOME SHOWERS COULD MAKE A RUN FOR OUR FAR NORTHERN AND/OR NE SECTIONS LATE...WE CURRENTLY ANTICIPATE THAT THE DAY WILL BE FREE OF ANY PRECIPITATION. TEMPS WILL CERTAINLY BE COLDER THAN ON TUESDAY...BUT DOWNSLOPE FLOW AND A DECENT AMOUNT OF SUNSHINE WILL NEGATE SOME OF THE COLDER AIR IMPACTING THE REGION. EVEN SO...WE/RE LOOKING AT HIGHS AS MUCH AS 10-15 DEGREES COLDER THAN ON TUESDAY. A TIGHT PRESSURE GRADIENT ND THE PRESENCE OF A 25-35 KT LOW LEVEL JET WILL PRODUCE A WINDY DAY AREA WIDE. WE MIGHT EVEN FLIRT WITH A WIND ADVISORY IN SOME LOCALES...WITH WINDS OF 20-30 MPH SUSTAINED AND 35 OR 40 MPH IN GUSTS. LAKE WINDS...WINDS WILL APPROACH ADVISORY CRITERIA TUESDAY AFTERNOON AS A 30-40 KT LOW LEVEL JET PASSES OVER THE REGION. HOWEVER...MIXING WILL BE LIMITED WITHIN A WARM ADVECTION REGIME OVER THE COOLER LAKE WATERS. A BETTER CHANCE FOR LAKE WIND ADVISORY THRESHOLDS TO BE MET TUESDAY NIGHT THROUGH EARLY THURSDAY...AS A SIGNIFICANTLY TIGHTENED PRESSURE GRADIENT AND BOUTS OF STRONG COLD ADVECTION ENHANCES THE MIXING AND SUPPORTS 20 TO 25 KT AND GUSTY OVER LAKE MOULTRIE. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... AS THE POTENT LOW SYSTEM RAPIDLY TRACKS INTO THE ATLANTIC THROUGH THE LATE WEEK PERIOD...SURFACE HIGH PRESSURE AND UPPER LEVEL RIDGING WILL FOLLOW IN ITS WAKE. EXPECT DRY CONDITIONS TO THUS PREVAIL THURSDAY THROUGH THE WEEKEND. RISING HEIGHTS ALOFT WILL SUPPORT A GRADUAL WARMING TREND THROUGH THE PERIOD...WITH TEMPERATURES PEAKING IN THE LOW TO MID 60S THURSDAY AND FRIDAY...THEN POSSIBLY THE LOW 70S SATURDAY AND SUNDAY. LOW TEMPERATURES WILL ALSO MODERATE INTO THE UPPER 30S TO LOWER 40S BY LATE PERIOD. && .AVIATION /05Z MONDAY THROUGH FRIDAY/... VFR. EXTENDED AVIATION OUTLOOK...THERE IS A LOW TO MODERATE CHANCE OF REDUCED FLIGHT CONDITIONS AT TIMES TUESDAY NIGHT AS A COLD FRONT MOVES THROUGH THE AREA...ACCOMPANIED BY NUMEROUS SHRA. WINDY CONDITIONS WILL ALSO IMPACT THE TERMINALS TUESDAY AFTERNOON THROUGH THURSDAY. && .MARINE... MAINTAINED THE ONGOING SCA FOR AMZ354 AND 374 VALID UNTIL 10 AM MONDAY. SUNDAY EVENING...THE PRESSURE GRADIENT HAD RELAXED ACROSS SC WATERS IN RESPONSE TO AN INLAND SURFACE TROUGH N/W OF THE WATERS. AS A RESULT...WINDS HAD BACKED TOWARD THE SW AND HAD WEAKENED TO 15 KT OR LESS. HOWEVER...00Z GUIDANCE CONTINUES TO ADVERTISE LOW LEVEL WINDS VEERING TOWARD THE NW AND SURGING TO AS MUCH AS 20 KT ACROSS SC WATERS OVERNIGHT. ACROSS GA NEARSHORE AND OUTER WATERS... A TIGHTER SURFACE PRESSURE GRADIENT WILL MAINTAIN WINDS IN THE 20-25 KT RANGE...PERHAPS GUSTING NEAR 30 KT 40-60 NM OFFSHORE...WITH THE WIND DIRECTION VEERING FROM W TO NW OVERNIGHT. DUE TO THE OFFSHORE FETCH...SEAS SHOULD REMAIN 2-3 FT WITHIN 20 NM AND 4 TO 6 FT BEYOND 20 NM OVERNIGHT. MONDAY...AS COLD ADVECTION SHUTS OFF AND THE PRESSURE PATTERN FINALLY RELAXES AS HIGH PRESSURE BUILDS FROM THE WEST...WINDS AND SEAS WILL DECREASE THROUGH THE DAY. ONGOING SCA/S WILL END BY 15Z AND IMPROVING CONDITIONS WILL DEVELOP FOR THE BALANCE OF THE DAY. MONDAY NIGHT...HIGH PRESSURE WILL SITUATE ITSELF ATOP THE WATERS...RESULTING IN QUIET MARINE CONDITIONS. TUESDAY...HIGH PRESSURE ACROSS THE MARINE AREA EARLY WILL GIVE WAY TO AN AREA OF LOW PRESSURE AND ITS COLD FRONT THAT MOVES THROUGH THE SE QUADRANT OF THE NATION. THE PRESSURE GRADIENT WILL ONCE AGAIN BECOME ENHANCED AS THIS PATTERN TRANSPIRES. ALTHOUGH THE WARM ADVECTION WILL LIMIT MIXING...OUR WINDS AND SEAS WILL NONETHELESS BE ON A STEADY RISE. AND WE COULD BE LOOKING AT MARGINAL SMALL CRAFT ADVISORY CONDITIONS YET AGAIN. TUESDAY NIGHT THROUGH WEDNESDAY...STRONG LOW PRESSURE WILL MOVE EAST THROUGH THE MID ATLANTIC STATES...WITH ITS ASSOCIATED COLD FRONT TO SWEEP THROUGH THE COASTAL WATERS THE LATTER PART OF TUESDAY NIGHT. LARGE ISALLOBARIC PRESSURE FALLS WILL BE FOLLOWED BY LARGE ISALLOBARIC PRESSURE RISES. THAT ALONG WITH STRONG COLD ADVECTION DEVELOPING IN WAKE OF THE COLD FRONT WILL LEAD TO A HIGH PROBABILITY OF GALES OVER MOST IF NOT ALL WATERS. THESE CONDITIONS WILL THEN PERSIST THROUGH WEDNESDAY...POSSIBLY EVEN INTO WEDNESDAY NIGHT WITH ANOTHER SURGE OF COLD ADVECTION AND STEADY PRESSURE RISES AS THE SURFACE LOW MOVES INTO THE WESTERN ATLANTIC. MARINERS ARE ADVISED THAT A FEW T-STORMS COULD PRECEDE THE COLD FRONT TUESDAY NIGHT...PERHAPS ACCOMPANIED BY WINDS IN EXCESS OF 35 KT. THURSDAY AND FRIDAY...THE ATLANTIC LOW WILL EVENTUALLY MOVE AWAY AND GIVE WAY TO HIGH PRESSURE. IT/LL TAKE AWHILE...BUT IMPROVING CONDITIONS WILL ARRIVE DURING THIS TIME. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 10 AM EST THIS MORNING FOR AMZ354- 374. && $$ ST