FXUS62 KCHS 262337
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
637 PM EST SAT DEC 26 2009
.SYNOPSIS...
HIGH PRESSURE WILL REMAIN IN PLACE THROUGH EARLY NEXT WEEK. A GULF
LOW PRESSURE SYSTEM COULD AFFECT THE REGION WEDNESDAY THROUGH
FRIDAY.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
AN UPPER TROUGH WILL BUILD INTO THE OHIO VALLEY TONIGHT WHILE
SURFACE HIGH PRESSURE EXTENDS INTO THE SOUTHEAST STATES. MOST OF
THE JET-INDUCED CIRRUS IS PROGGED TO BE MOVING OFF THE COAST BY
06Z WHILE SURFACE WINDS SHOULD DECOUPLE LATE. CONDITIONS ARE RIPE
FOR FREEZING TEMPERATURES ACROSS THE INLAND THIRD OF THE FORECAST
AREA WHERE THERE WILL BE A LONGER PERIOD OF CLEAR SKIES AND WINDS
WILL DECOUPLE EARLIER. WE INCLUDED PATCHY FROST WEST OF I-95 IN GA
AND US-17 IN SC WHERE LOWS WILL DROP INTO THE MIDDLE 30S BY LATE
TONIGHT.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
MODEL TIME-HEIGHTS SHOW A PARCHED AIRMASS IN PLACE ON SUNDAY.
DESPITE A CONSIDERABLE JET STREAK OVERHEAD...UPPER-LEVEL MOISTURE
SHOULD BE WELL ENOUGH OFFSHORE TO PREVENT THE FORMATION OF MUCH
CLOUD COVER. AS A NEUTRAL-TILT UPPER LEVEL TROUGH SHIFTS SLOWLY
EAST DURING THE DAY...A SLUG OF 700 MB MOISTURE FROM THE NORTHERN
GULF MAY SKIRT PAST DURING THE LATTER HALF OF THE AFTERNOON. THIS
COULD BRING IN SOME MID CLOUDS. OTHERWISE WE EXPECT A DRY DAY WITH
HIGHS NEAR NORMAL IN THE 58-60F RANGE.
&&
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
OVERALL....A DIFFICULT FORECAST THROUGH THE EXTENDED PERIOD. MODELS
CONTINUE TO DIFFER ON THE TIMING OF SYSTEMS WITHIN A STRONG SOUTHERN
STREAM/SUB TROPICAL JET FLOW. A DEEP UPPER LEVEL LOW WITH A BROAD
TROF EXTENDING DOWN THE ENTIRE EASTERN 1/3 OF THE U.S. WILL START
OFF THE PERIOD. THIS TROF WILL MOVE EASTWARD...BEING REPLACED BY A
DEEP LAYER RIDGE MONDAY THROUGH TUESDAY. THE RIDGING BREAKS DOWN ON
WEDNESDAY AS ANOTHER BROAD UPPER TROF BUILDS OVER THE CENTRAL U.S..
IT IS THE PRESENCE OF THIS STRONG SOUTHERN STREAM AND EMBEDDED UPPER
SHORT WAVES THAT WILL CONTINUE TO BE THE FORECAST CHALLENGE LATER
WEDNESDAY THROUGH AT LEAST EARLY FRIDAY.
MONDAY THROUGH TUESDAY...A MODERATELY STRONG SURFACE RIDGE WILL
REMAIN CENTERED NW OF THE REGION WITH GENERALLY WNW LOW LEVEL FLOW.
ALTHOUGH THIS PERIOD WILL BE THE DRIEST /MOST SUN/...AFTERNOON HIGHS
ARE STILL NOT EXPECTED TO GET OUT OF THE LOWER TO MID 50S WITH LOWS
IN THE LOWER TO MID 30S. GUIDANCE IS STILL HINTING THAT TUESDAY
MORNING WILL BE THE COLDEST MORNING...BUT CONFIDENCE THAT THIS WILL
BE TRUE IS ACTUALLY GOING DOWN A BIT SINCE LOW LEVEL WINDS ARE NOW
BEING PROGD TO REMAIN IN THE 3-5 KT RANGE MUCH OF THE NIGHT.
MAINTAINED SIMILAR TEMPS FROM PREVIOUS FORECAST FOR NOW...BUT THEY
MAY NEED TO BE ADJUSTED UPWARDS WITH LATER GUIDANCE.
WEDNESDAY...THIS DAY /IN MY OPINION/ IS THE PIVOTAL DAY FOR THE
ENTIRE EXTENDED PERIOD. THE UPPER FLOW TURNS SW AS ANOTHER TROF
FORMS OVER THE CENTRAL U.S. MODELS NOW IN FAIR AGREEMENT WITH THE
GENERAL SCENARIO OF THE NEXT SFC LOW THAT HAS BEEN FORECAST TO FORM
WITHIN THE SOUTHERN STREAM OF THIS UPPER TROF. RIGHT NOW...IT
LOOKS LIKE THE FIRST PART OF WEDNESDAY MAY START OF DRY...BUT DEEP
LAYER MOISTURE RAPIDLY INCREASES FROM THE SW DURING THE DAY. HAVE
PLACED THE HIGHEST POPS FOR LATER WEDNESDAY AND WEDNESDAY NIGHT.
THIS IS BASED ON A COMPOSITE SOLUTION OF THE ECMWF...GFS AND THE
CANADIAN MODELS...WHICH WOULD SHOW A SURFACE LOW OVER THE NORTHERN
GULF OF MEXICO WEDNESDAY NIGHT...THEN AN ELONGATED CENTER MOVING
INTO THE ATLANTIC BY EARLY FRIDAY. THE MODELS VARY GREATLY WITH
THE STRENGTH AND EXACT TIMING OF THIS LOW. FOR EXAMPLE...THE GFS
SHOWS MULTIPLE SFC CENTERS/WAVES...WITH THE LOW MOVING GENERALLY
ACROSS THE EXTREME SOUTHERN FORECAST AREA...WHILE THE ECMWF SHOWS
A STRONGER AND MORE CONSOLIDATED CENTER MOVING FURTHER NORTH
ACROSS THE SC MIDLANDS BY LATER THURSDAY NIGHT. AS HAS BEEN STATED
IN THE PAST SEVERAL AFDS...CONFIDENCE ON THE TIMING AND STRENGTH
OF THIS SYSTEM CONTINUES TO BE LOW. HAVE OPTED TO GO WITH A MORE
SOUTHERN TRACK LOW...EXPECTING THE SFC WEDGE OF HIGH PRESSURE MAY
HANG IN LONGER THAN MOST MODELS INDICATE. BIGGEST THREAT WITH THIS
SYSTEM AT THE CURRENT TIME LOOKS TO BE POTENTIAL FOR WIDESPREAD
RAINFALL /POSSIBLY HEAVY/. HOWEVER...IF A MORE NORTHERN AND
WESTERN TRACK OCCURS WITH THE SFC LOW...THE THREAT MAY LEAN MORE
TOWARD SEVERE WEATHER. STAY TUNED TO THE LATEST FORECASTS AND
DISCUSSIONS CONCERNING THIS TIME PERIOD.
FRIDAY AND SATURDAY...HAVE GONE WITH A SOLUTION OF PUSHING THE SFC
LOW OFFSHORE AS A STRONG UPPER TROF OVER THE EASTERN U.S. MOVES
THROUGH THE REGION. STRONG SFC HIGH PRESSURE WILL BUILD THROUGH THE
PERIOD WITH POTENTIALLY THE COLDEST AIR OF THE SEASON. HOWEVER...
GIVEN THE OVERALL UNCERTAINTY OF THIS FORECAST...CONFIDENCE ON THE
MAGNITUDE OF THE COLD AIR IS SUSPECT...ESPECIALLY GIVEN THAT THERE
HAVE BEEN SEVERAL FORECASTS IN THE PAST FEW WEEKS THAT HAVE SHOWN
SIMILAR COLD OUTBREAKS THAT NEVER REALLY GOT AS COLD AS ORIGINALLY
PREDICTED BY THE MODELS.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
VFR CONDITIONS ARE EXPECTED FOR THE NEXT 24 HOURS AT BOTH CHS AND
SAV TERMINALS. LIGHT WEST WINDS WILL BECOME NORTHWEST BY DAYBREAK
SUNDAY AT BOTH TERMINALS. NORTHWEST WINDS AT OR BELOW 10 KNOTS WILL
THEN BECOME SOUTHWEST SUNDAY AFTERNOON.
EXTENDED AVIATION OUTLOOK...EXPECT MAINLY VFR CONDITIONS SUNDAY
NIGHT THROUGH EARLY WEDNESDAY. ANOTHER AREA OF LOW PRESSURE IS
EXPECTED TO APPROACH THE AREA FROM THE SOUTHWEST LATER WEDNESDAY
THROUGH THURSDAY. FOR NOW...HAVE GONE WITH A SOLUTION THAT MOVES
THE LOW ACROSS THE SOUTHERN AREA WEDNESDAY NIGHT AND THURSDAY.
THIS WOULD IMPLY MVFR OR LOWER CONDITIONS WOULD BE POSSIBLE BY
LATER WEDNESDAY AND THURSDAY AS RAIN AND LOWER CIGS SPREAD ACROSS
THE AREA. HOWEVER...CONFIDENCE IN THIS FORECAST IS STILL LOW GIVEN
THE UNCERTAINTY IN MODEL SOLUTIONS REGARDING THE TIMING...STRENGTH
AND TRACK OF THIS LOW.
&&
.MARINE...
QUIET CONDITIONS WILL CONTINUE THROUGH SUNDAY AS SURFACE HIGH
PRESSURE BUILDS ACROSS THE WATERS AND A FAIRLY WEAK OFFSHORE FLOW
ALLOWS SEAS TO DIMINISH.
STRONG HIGH PRESSURE WILL BUILD INTO THE REGION MONDAY THROUGH
TUESDAY NIGHT. EXPECT SCA CONDITIONS OVER AT LEAST THE OFFSHORE
WATERS FOR MONDAY THROUGH MONDAY NIGHT/EARLY TUESDAY. HIGH PRESSURE
MOVES NE OF THE REGION BY WEDNESDAY WITH A WEAKER PRESSURE GRADIENT
AND DECREASING WINDS/SEAS. ANOTHER AREA OF LOW PRESSURE IS EXPECTED
TO APPROACH THE AREA FROM THE SOUTHWEST LATER WEDNESDAY THROUGH
THURSDAY. FOR NOW...HAVE GONE WITH A SOLUTION THAT MOVES THE LOW
ACROSS THE SOUTHERN WATERS WEDNESDAY NIGHT AND THURSDAY. THIS
SOLUTION WILL KEEP GENERALLY EASTERLY WINDS BELOW HIGHLIGHT LEVELS
WEDNESDAY THROUGH THURSDAY. HOWEVER...CONFIDENCE IN THIS FORECAST IS
STILL LOW GIVEN THE UNCERTAINTY IN MODEL SOLUTIONS REGARDING THE
TIMING...STRENGTH AND TRACK OF THIS LOW.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.
&&
$$
