000 FXUS62 KCHS 240229 AFDCHS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHARLESTON SC 929 PM EST MON NOV 23 2009 .SYNOPSIS... A WEDGE OF HIGH PRESSURE OVER THE INLAND CAROLINAS WILL WEAKEN BY TUESDAY NIGHT...THEN LOW PRESSURE WILL MOVE UP THE EASTERN UNITED STATES COAST WEDNESDAY. A DRY FRONT WILL MOVE THROUGH THURSDAY MORNING...THEN A LARGE RIDGE OF HIGH PRESSURE WILL BUILD IN THROUGH THE WEEKEND. ANOTHER SYSTEM COULD APPROACH FROM THE WEST EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... OUR HIGH PRESSURE WEDGE WILL PERSIST ACROSS THE REGION AGAIN TONIGHT...KEEPING ABUNDANT MOISTURE TRAPPED BENEATH THE INVERSION WHICH GETS LOWER AND STRONGER THROUGH THE NIGHT. THIS WILL CONTINUE TO RESULT IN OVERCAST SKIES...WITH AREAS OF FOG AND OCCASIONAL DRIZZLE THROUGH THE NIGHT. THE MAIN PROBLEM IS THE POTENTIAL FOR DENSE FOG. THE FOG STABILITY INDEX IS IN THE TEENS...OUR 1000 MB GEOSTROPHIC WINDS ARE LESS TONIGHT THAN LAST NIGHT...MANY AREAS HAVE OR WILL BECOME CALM AND MUCH OF THE REGION WILL EXPERIENCE GOOD RADIATIONAL EFFECTS WITH DRY AIR ALOFT. PLUS WITH THE LOWERING OF STRATUS BECOMING MORE SURFACE BASED...WE ANTICIPATE SURFACE VISIBILITIES TO ALSO DROP THROUGH THE NIGHT. ON THE FLIP SIDE...THE RIGHT REAR QUAD OF THE 90 KT UPPER LEVEL JET WILL ALLOW FOR CIRRUS TO OVERSPREAD AT LEAST THE SOUTHERN CWA...LIMITING THE EFFECTS OF RADIATION AND THE POTENTIAL FOR DENSE FOG. ALSO...EVEN THOUGH THE GEOSTROPHIC WINDS ARE LESS THAN LAST NIGHT...THEY STILL ARE A LITTLE HIGH AT 10 KT OR GREATER AFTER MIDNIGHT. WE WILL CONTINUE MENTION OF AREAS OF FOG IN THE FORECAST FOR THE ENTIRE AREA...AND SOME OF THE FOG WILL BE LOCALLY DENSE. BUT AS MENTIONED...SINCE THERE ARE STILL A COUPLE OF NEGATIVES FOR ITS FORMATION WE WILL HOLD OFF ON ANY DENSE FOG ADVISORY AT THIS TIME. STILL...IT IS CERTAINLY POSSIBLE THAT ONE MAY BE REQUIRED OVERNIGHT ONCE WE BETTER SEE HOW VISIBILITIES RESPOND TO THE LOWERING STRATUS CLOUDS. TEMPS TONIGHT WILL BE MODERATED BY THE CLOUD COVER...RESULTING IN ONLY A SMALL DROP OF TEMPS THROUGH THE NIGHT. LOWEST VALUES WILL RANGE FROM THE UPPER 40S AND LOWER 50S INLAND TO THE MID 50S NEAR THE COAST. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... THE HIGH PRESSURE WEDGE WILL REMAIN ENTRENCHED THROUGH THE DAY TUE...ALTHOUGH MOISTURE WILL BEGIN TO SURGE UP FROM THE SW IN ADVANCE OF GOMEX LOW PRES CYCLOGENESIS. WITH LOW MOISTURE CONTINUING TO REMAIN UNDER THE WEDGE...LOW CLOUDS...PATCHY DRIZZLE AND AREAS OF FOG WILL BE COMMONPLACE THROUGH AT LEAST THE FIRST HALF OF THE DAY. CONDITIONS WILL SLOWLY IMPROVE THROUGH THE DAY AS THE WEDGE TRIES TO ERODE TO THE NE...BUT AT LEAST MOSTLY CLOUDY CONDITIONS WILL PREVAIL. HAVE KEPT POPS OUT OF THE FORECAST SINCE MEASURABLE PRECIP IS NOT EXPECTED...BUT A FEW PASSING PATCHES OF DRIZZLE CANNOT BE RULED OUT. TEMPS WILL AGAIN REMAIN COOL...ESP OVER THE NRN HALF OF THE CWFA WHERE THE WEDGE WILL HAVE ITS GREATEST EFFECT. WILL LOOK FOR MAX TEMPS IN THE UPR 50S FOR FAR NRN PORTIONS OF THE CHS CWFA WHILE HIGHS WILL REACH THE MID 60S NEAR THE ALTAMAHA RIVER. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... WITH ANOTHER SHORTWAVE DIGGING INTO THE MISSISSIPPI VALLEY LATE TUESDAY...THE COASTAL TROUGH OFF THE SC/GA COAST SHOULD DEEPEN AND HELP TO REINFORCE THE COOL WEDGE THROUGH WEDNESDAY. EXTENSIVE CLOUD COVER WILL PROBABLY PERSIST THROUGH WEDNESDAY NIGHT BEFORE WE START TO SEE SOME CLEARING ON THURSDAY AFTER A DRY COLD FRONT SWINGS THROUGH FROM THE WEST. THE BRUNT OF THE MOISTURE CONVERGENCE ASSOCIATED WITH THE COASTAL TROUGH SHOULD REMAIN OVER THE COASTAL WATERS...BUT SCATTERED SHOWERS WILL BE POSSIBLE FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY NIGHT ACROSS THE EASTERN TWO- THIRDS OF THE AREA. MADE ONLY SMALL TWEAKS TO ONGOING POPS...MAINLY TO TRIM INLAND POPS BACK TO LESS THAN 15%. LOWS WILL REMAIN ABOVE NORMAL DUE TO THE PERSISTENT CLOUDS WHILE HIGHS ON WEDNESDAY WILL CONTINUE BELOW NORMAL IN THE LOWER 60S. A DRY FRONT LOOKS TO SWING THROUGH THURSDAY MORNING FOLLOWED BY EXPANSIVE HIGH PRESSURE THROUGH SUNDAY. ONE OF THE COLDEST AIR MASSES OF THE SEASON WILL ENSUE. THE COLDEST MORNING LOOKS TO BE SATURDAY MORNING DUE TO CLEAR SKIES...LIGHT WINDS...AND THE LOWEST THICKNESSES IN PLACE. THERE IS A CHANCE WE WILL FLIRT WITH THE FREEZING MARK ACROSS FAR INLAND AREAS...BUT AT A MINIMUM FROST COULD BE A CONCERN. ISSUES POSSIBLE FRI MORNING AND SUN MORNING BUT CHANCES NOT LOOKING AS HIGH. WILL CONTINUE MENTION OF FROST/FREEZE IN THE HAZARDOUS WEATHER OUTLOOK. MODERATING TEMPERATURES EXPECTED MONDAY AS SURFACE HIGH PRESSURE PUSHES OFF THE COAST AND AN ONSHORE FLOW DEVELOPS. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... THERE IS ABUNDANT MOISTURE IN THE BOUNDARY LAYER THAT WILL REMAIN TRAPPED BENEATH THE INVERSION TONIGHT AND TUESDAY...WITH LOW STRATUS AND LIGHT FOG EVENTUALLY LOWERING TO WHERE IT BECOMES MORE SURFACE BASED WITH THE POTENTIAL FOR DENSE FOG. WE HAVE CARRIED IFR OR LIFR CONDITIONS AT BOTH TERMINALS THROUGH 18Z...AND ALTHOUGH THE 00Z TAFS DO NOT INDICATE...THERE CERTAINLY COULD BE SEVERAL HOURS OF 1/4SM OR LESS WITH VERTICAL VSBYS ZERO OVERNIGHT/TUESDAY MORNING. THE INVERSION LIFTS ENOUGH TUESDAY AFTERNOON WHERE A RETURN TO MVFR WEATHER WILL OCCUR. SOME GUIDANCE SUGGESTS THERE MAY BE A FEW HOURS OF VFR CIGS LATE TUESDAY...BUT SOUNDINGS DO NOT SUPPORT THIS SCENARIO...AND WITH A LIGHT NORTHERLY SYNOPTIC FLOW WE HAVE OPTED TO REMAIN PESSIMISTIC BY KEEPING MVFR WEATHER FROM 18-24Z TUESDAY. EXTENDED AVIATION OUTLOOK...MVFR/IFR CEILINGS AND POSSIBLY VISIBILITIES ARE LIKELY TUESDAY NIGHT THROUGH THURSDAY MORNING. VFR CONDITIONS THEREAFTER. && .MARINE... THE HIGH PRESSURE WEDGE WILL REMAIN FIRMLY IN PLACE ACROSS THE SE TONIGHT...KEEPING MOSTLY GENTLE BREEZES /WMO CLASSIFICATION ON THE BEAUFORT WIND SCALE/ IN PLACE ACROSS THE LOCAL WATERS. THERE IS SUBTLE PINCHING OF THE PRESSURE GRADIENT LATE TONIGHT...BUT OVERALL WIND SPEEDS TONIGHT WILL REMAIN AT 10-12 KT OR LESS. SEAS ARE AND WILL CONTINUE TO BE MOSTLY IN THE FORM OF AN EASTERLY SWELL AT 2-4 FT EVERY 8 SECONDS. THE MAIN ISSUE FOR TONIGHT WILL BE THE POTENTIAL FOR DENSE FOG. WITH THE WIDESPREAD STRATUS TO LOWER FURTHER THROUGH THE NIGHT...WE WILL SEE VISIBILITIES DROP AS WELL...MOSTLY IN THE RANGE OF 1-3NM. HOWEVER...SOME VISIBILITIES WILL FALL TO 1/2 NM OR LESS AT TIMES AFTER MIDNIGHT INTO TUESDAY MORNING...ESPECIALLY WITHIN 5-10 NM OF THE COAST...IN CHARLESTON HARBOR AND THE INTRACOASTAL. A MARINE WEATHER STATEMENT HAS BEEN ISSUED TO ADDRESS THESE CONCERNS...AND THE COASTAL WATERS FORECAST ALREADY HAS MENTION OF FOG. THE INLAND WEDGE OF HIGH PRESSURE WILL MAINTAIN THE NORTHERLY FLOW OVER THE WATERS TUE. THE WEDGE WILL EXPAND A BIT OVER THE WATERS...HELPING KEEP SPEEDS LESS THAN 15 KT AND SEAS LESS THAN 4 FT. A STRENGTHENING OFFSHORE FLOW WILL DEVELOP THURSDAY NIGHT THROUGH SATURDAY AS STRONG HIGH PRESSURE BUILDS IN WITH SIGNIFICANTLY COLDER AIR. SMALL CRAFT ADVISORIES MAY EVENTUALLY BE NEEDED FOR THE OFFSHORE WATERS WHERE BETTER MIXING OCCURS AND SEAS ARE ABLE TO BUILD TO 6 FT. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...NONE. SC...NONE. MARINE...NONE. && $$ 33