FXUS64 KLCH 111558
AFDLCH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAKE CHARLES LA
958 AM CST FRI DEC 11 2009
.DISCUSSION...
TRAVELING SUBTROPICAL PACIFIC SHORTWAVES ARE IMPINGING UPON THE
SIERRA MADRE ORIENTAL RANGE...GENERATING STRETCHING VORTICITY
DOWNWASH OVER THE MOUTH OF THE RIO GRANDE.
THIS LEESIDE FORCING WILL SPIN-UP THE FRONTAL WAVE CYCLONE...
CURRENTLY POSITIONED JUST NORTHWEST OF MOORED BUOY 42002 (25.12N
94.4W) WITH A CENTRAL PRESSURE AROUND 1014 MB.
THE OVERNIGHT GFS GUIDANCE COMPUTES THE POSITION OF THE EVOLVING
CYCLONE FURTHER WEST...CLOSER TO JUST OFFSHORE BROWNSVILLE. ITS
SUBSEQUENT NORTHWARD JOURNEY PLACES ITS LANDFALL FURTHER WEST...
NEAR HOUSTON. THIS WESTWARD CORRECTION...IF CORRECT...WOULD CAUSE
A LARGER AMOUNT OF RAINFALL THAN PREVIOUSLY THOUGHT.
FOR NOW...THE ZONE PACKAGE IS ON TARGET. WILL NEED TO EXAMINE THE
MORNING GFS RUN (THE PRIMARY SYNOPTIC RUN).
&&
.PREV DISCUSSION... /ISSUED 422 AM CST FRI DEC 11 2009/
DISCUSSION...
LATEST WATER VAPOR IMAGERY SHOWS A FAST AND MOIST SOUTHERN JET
FLOWING FROM THE EAST PACIFIC ACROSS NORTHERN OLD MEXICO AND
ACROSS THE GULF COAST STATES. THIS IS HELPING TO PROVIDE MID AND
UPPER LEVEL CLOUDINESS ACROSS THE FORECAST AREA. LATEST RADAR
IMAGES DO SHOW SOME RETURNS OVER THE COASTAL WATERS.
HOWEVER...THIS IS LIKELY VIRGA AND RAIN NOT REACHING THE GROUND AS
STILL SOME DRY AIR NOTED ON THE LATEST SOUNDING. AT THE
SURFACE...HIGH PRESSURE IS CENTERED OVER TENNESSEE HELPING TO
PROVIDE A NORTHEAST FLOW WITH COOL CONTINENTAL CONDITIONS.
OVER THE NEXT 24 HOURS...CONDITIONS SHOULD REMAIN COOL AND
BECOMING INCREASINGLY WET. SURFACE HIGH PRESSURE WILL SETTLE OVER
THE APPALACHIANS. MEANWHILE...DISTURBANCES IN THE ACTIVE SOUTHERN
JET SHOULD INDUCE LOW PRESSURE TO DEVELOP OFF THE LOWER TEXAS
COAST. THE GRADIENT BETWEEN THESE TWO SYSTEMS WILL PROVIDE STRONG
EASTERLY FLOW OVER THE AREA WITH A COASTAL TROF DEVELOPING...KEEPING
MAINLY A COOL CONTINENTAL AIRMASS OVER THE FORECAST AREA.
STRENGTHENING SOUTHERLY FLOW ALOFT AS UPPER LEVEL DISTURBANCE
APPROACHES WITH HELP LIFT MOISTURE ABOVE THE COOLER LOW LEVELS.
LIGHT RAIN WILL BEGIN LATER THIS MORNING...THEN SPREAD NORTHWARD
DURING THE AFTERNOON AS ISENTROPIC SURFACES SHOW CONDENSATION
PRESSURE DEFICITS BECOMING SATURATED IN THE LOW LEVELS.
THE ISENTROPIC RAINS WILL CONTINUE TO INCREASE DURING THE NIGHT
AS MOISTURE SURGES OVER THE FORECAST AREA. PRECIPITABLE WATER
VALUES ARE PROGGED TO RANGE FROM 1.25 TO 1.5 INCHES...THIS IS OVER
150 PERCENT OF NORMAL FOR DECEMBER...WITH MEAN RH VALUES OVER 80
PERCENT. LIFT WILL ALSO INCREASE DURING THE NIGHT AS LOW LEVEL
CONVERGENCE INCREASES AS SURFACE WAVE OF LOW PRESSURE RIDES UP THE
COASTAL TROF...ALONG WITH GOOD 85H CONVERGENCE FURTHER INLAND.
ALSO...REGION WILL COME UNDER THE RIGHT ENTRANCE REGION OF STRONG
UPPER LEVEL JET. 85H PROGGS ALSO SHOW ENOUGH CAPE AND LOW
SHOWALTER VALUES THAT A FEW ELEVATED STORMS COULD ALSO DEVELOP.
HEAVIEST RAINFALL STILL LOOKS TO OCCUR BETWEEN MIDNIGHT AND 6 AM.
RAINS SHOULD TAPER OFF FROM WEST TO EAST DURING THE DAY ON
SATURDAY AS UPPER LEVEL JET STREAK MOVES OFF TO THE EAST...AND
SURFACE WAVE WEAKENS...THUS DECREASING UPGLIDE AND ISENTROPIC
LIFT. RAINFALL AMOUNTS ACROSS THE FORECAST AREA ARE EXPECTED TO
AVERAGE FROM 0.75 TO 1.25 INCHES...WITH LOCALLY HIGHER AMOUNTS
BEFORE THE RAINS END.
SUNDAY LOOKS TO BE WARMER AS SURFACE WINDS BEGIN TO COME OUT OF
THE SOUTH AS NEXT FRONTAL SYSTEM BEGINS TO FORM OUT WEST.
THIS COLD FRONT IS EXPECTED TO REACH THE FORECAST AREA MONDAY
NIGHT AND MOVE THROUGH THE FORECAST AREA EARLY ON TUESDAY. EXPECT
SHOWERS AND A FEW THUNDERSTORMS TO DEVELOP AHEAD OF THIS SYSTEM.
MUCH COOLER AND DRIER CONDITIONS ARE THEN EXPECTED BEHIND THIS
FRONT WITH MAINLY BELOW NORMAL TEMPERATURES PREVAILING FOR THE
REMAINDER OF NEXT WEEK.
RUA
MARINE...
STRONG NORTHEAST...BECOMING EASTERLY...FLOW IS EXPECTED OVER THE
COASTAL WATERS FOR THE NEXT 24 HOURS AS GRADIENT TIGHTENS BETWEEN
HIGH PRESSURE OVER THE APPALACHIANS AND DEVELOPING LOW PRESSURE
OFF THE LOWER TEXAS COAST. SMALL CRAFT ADVISORY CONDITIONS WILL BE
IN EFFECT THROUGH EARLY SATURDAY MORNING.
WITH THE STRONG EASTERLY FLOW...TIDES WILL RUN UP TO ONE FOOT
ABOVE PREDICTED LEVELS...AS WATER PILING OCCURS ALONG THE COAST.
THE GRADIENT WILL LESSEN ON SATURDAY AS THE LOW PRESSURE SYSTEM WEAKENS.
A COLD FRONT IS EXPECTED TO MOVE ACROSS THE COASTAL WATERS EARLY
TUESDAY. STRONG NORTH WINDS WILL DEVELOP AGAIN IN THE WAKE OF THIS FRONT.
RUA
&&
.PRELIMINARY POINT TEMPS/POPS...
KLCH 50 48 61 54 70 / 50 80 50 20 10
KBPT 50 48 60 52 70 / 50 80 40 20 10
KAEX 48 43 53 48 70 / 40 80 70 20 10
KLFT 52 47 60 55 70 / 50 80 70 20 10
&&
.LCH WATCHES/WARNINGS/ADVISORIES...
LA...NONE.
TX...NONE.
GM...SMALL CRAFT ADVISORY UNTIL 6 AM CST SATURDAY FOR THE FOLLOWING
ZONES: COASTAL WATERS FROM CAMERON, LA TO HIGH ISLAND, TX
OUT 20 NM...COASTAL WATERS FROM INTRACOASTAL CITY TO
CAMERON, LA OUT 20 NM...COASTAL WATERS FROM LOWER
ATCHAFALAYA RIVER TO INTRACOASTAL CITY, LA OUT 20 NM...
WATERS FROM CAMERON, LA TO HIGH ISLAND, TX EXTENDING FROM
20 NM TO 60 NM...WATERS FROM INTRACOASTAL CITY, LA TO
CAMERON, LA EXTENDING FROM 20 NM TO 60 NM...WATERS FROM
LOWER ATCHAFALAYA RIVER TO INTRACOASTAL CITY, LA EXTENDING
FROM 20 NM TO 60 NM.
&&
$$
