FXUS64 KLCH 220534
AFDLCH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAKE CHARLES LA
1134 PM CST MON DEC 21 2009
.AVIATION...
LITTLE CHANGE TO THE AVIATION FORECAST. ADVECTION STRATUS WILL
FORM AND SPREAD THROUGH SOUTHEAST TEXAS JUST AFTER DAWN...AND
ACROSS THE REMAINDER OF SOUTHWEST LOUISIANA DURING THE MORNING
HOURS. VRF CEILINGS ARE EXPECTED...DENSE FOG IS NOT.
&&
.PREV DISCUSSION... /ISSUED 928 PM CST MON DEC 21 2009/
UPDATE...
LATEST SURFACE OBS THIS EVENING SHOW TEMPERATURES HAVE FALLEN
RAPIDLY UNDER MOSTLY CLEAR SKIES AND LIGHT TO CALM WINDS...WITH
QUITE A TEMPERATURE GRADIENT ACROSS THE AREA AS OAKDALE IS DOWN
TO 36 DEGREES BUT JASPER STILL AT 52 DEGREES. WITH TEMPERATURES
ALREADY WELL BELOW FORECAST LOWS FOR TONIGHT IN MOST AREAS HAVE
LOWERED TEMPS FOR THE REMAINDER OF THE NIGHT...IN SOME PLACES
SIGNIFICANTLY. HOWEVER...WIDESPREAD CIRRUS CLOUDS CONTINUE TO
SPREAD INTO THE FORECAST AREA FROM THE WEST...WITH MID LEVELS
CLOUDS DEVELOPING ALONG THE TEXAS COAST AND SPREADING
NORTHEASTWARD. IN ADDITION...GFS AND NAM TIME HEIGHT TRENDS
INDICATE SUBSTANTIAL CLOUD COVER WILL SPREAD EASTWARD INTO THE
AREA AFTER MIDNIGHT AS THE LLJ CONTINUES TO STRENGTHEN OVER THE
REGION. THUS TEMPERATURES WILL LIKELY REACH MINS EARLY TONIGHT
BEFORE BECOMING STEADY OR SLOWLY RISING BY MORNING...PARTICULARLY
IN WESTERN ZONES. AS FAR AS FOG POTENTIAL TONIGHT...STRENGTHENING
WINDS IN THE BOUNDARY LAYER COMBINED WITH AN INCREASE IN CLOUD
COVER FROM WEST TO EAST MEANS FOG IS UNLIKELY IN SOUTHEAST TEXAS
AND HAVE REMOVED MENTION FROM ZONES. HOWEVER...STILL COULD SEE
SOME PATCHY FOG IN WESTERN LOUISIANA WITH FOG MUCH MORE LIKELY IN
EASTERN ZONES WHERE WINDS WILL BE LIGHTER AND CLOUD COVER DELAYED
UNTIL AFTER SUNRISE...AND CANNOT RULE OUT SOME PATCHY DENSE FOG
ALONG AND EAST OF THE I-49 CORRIDOR.
SHAMBURGER
PREV DISCUSSION... /ISSUED 525 PM CST MON DEC 21 2009/
AVIATION...
A COLD DOME OF HIGH PRESSURE SITUATED JUST WEST OF APPLACHICOLA WILL
CONTINUE ITS EASTWARD DRIFT...REACHING JACKSONVILLE BY DUSK TUESDAY
EVENING. A LIGHT GULF RETURN FLOW WILL SET-UP ACROSS THE WESTERN
UPPER GULF COAST STATES...ON THE OUTER WESTERN PERIPHERY OF THE COLD
DOME. ASSOCIATED ADVECTION STRATUS WILL FORM JUST BEFORE DAWN
TUESDAY. DENSE FOG SEEMS LESS LIKELY...AS SOUTHERLY WINDS WILL KEEP
THE NOCTURNAL BOUNDARY LAYER WELL STIRRED.
PREV DISCUSSION... /ISSUED 520 PM CST MON DEC 21 2009/
DISCUSSION...
PRIMARY CONCERN FOR THIS FORECAST PACKAGE CONTINUES TO BE MID WEEK
STORM SYSTEM AND ASSOCIATED SEVERE WEATHER THREAT.
SOUTHERLY WINDS HAVE RETURNED TO THE AREA TODAY AS HIGH PRESSURE
AT THE SURFACE HAS SHIFTED EAST OVER THE NORTH CENTRAL GULF COAST.
THIS ONSHORE FETCH IS FORECAST TO BEGIN STRENGTHENING
TONIGHT...WHICH WILL CONTINUE TO DRAW GULF MOISTURE BACK INTO THE
AREA. THE HIGH WILL STILL BE CLOSE ENOUGH...AND WINDS LIGHT
ENOUGH...TO WARRANT AT LEAST SOME CONCERN FOR RADIATION FOG
FORMATION LATER TONIGHT. WHILE I DO NOT ANTICIPATE A REPEAT FROM
THIS MORNING...FELT IT PRUDENT TO INCLUDE PATCHY FOG INTO THE
FORECAST. THE AREA AT MOST RISK OF SEEING FOG WOULD BE EAST AND
SOUTH CENTRAL LOUISIANA...NEAREST THE PROXIMITY OF THE HIGH.
TUESDAY LOOKS TO BE GENERALLY A NICE DAY...WITH TEMPS WARMING TO
NEAR 70...AND SOUTHERLY WINDS BECOMING A LITTLE BREEZY BY THE
AFTERNOON. RAIN CHANCES WILL START TO INCREASE AS AN ACTIVE
SOUTHERN STREAM JET BEGINS TO NOSE INTO THE AREA...ESPECIALLY BY
TUESDAY NIGHT AS SYNOPTIC SCALE LIFT INCREASES WITH THE FLOW
BECOMING DIVERGENT AND THE AREA FALLING UNDER THE FAVORABLE LFQ
RAIN CHANCES WILL INCREASE FURTHER ON WEDNESDAY AS SCATTERED TO
NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED AMID AN
INCREASING LLJ. OF SOME CONCERN TUESDAY NIGHT HEADING INTO
WEDNESDAY WILL BE THE POTENTIAL FOR SEA FOG FORMATION AS 60 PLUS
DEWPOINT AIR IS ADVECTED OVER THE COOLER SEA SURFACE TEMPERATURES
OF THE GULF SHELF WATERS. INSERTED PATCHY FOG WORDING FOR THE
NEARSHORE WATERS AND COASTAL COUNTIES/PARISHES...WITH A LOW CLOUD
DECK BECOMING MORE LIKELY FARTHER INLAND. PENDING WHAT
TRANSPIRES...THIS MAY NEED TO BE EXTENDED FURTHER IN TIME AND/OR
THE INTENSITY BEEFED UP.
BY LATE WEDNESDAY NIGHT...WITH THE MID/UPPER LEVEL LOW ENTERING
THE RED RIVER VALLEY BECOMING MORE NEGATIVELY TILTED...THE SFC FRONT IS
EXPECTED TO EXTEND N-S THROUGH EAST TEXAS. FORCING ALONG THE FRONT
IS FORECAST TO BECOME QUITE STRONG...WITH THUNDERSTORMS EXPECTED
TO FILL IN ALONG THE FRONT...AND SUBSEQUENTLY RACE EASTWARD
THROUGH THE AREA AS A SQUALL LINE. LOOKING AT SEVERAL SEVERE
WEATHER KINEMATIC AND THERMODYNAMIC PARAMETERS...IT APPEARS THAT
ALL MODES OF SEVERE WEATHER WILL BE POSSIBLE...THOUGH AT LEAST ONE
OVERALL HINDERING FACTOR WILL BE THE SOMEWHAT LIMITED INSTABILITY.
I SHOULD NOTE THAT THE TIMING OF EVENTS...THOUGH WITHIN ABOUT 6
HOURS AMONG ALL OF THE MODELS...IS STILL UNCERTAIN. THE MOST
GLARING DIFFERENCE BEING BETWEEN THE SLOWER NAM AND FASTER
GFS/ECMWF. USED A BLEND OF THE LATTER TWO FOR THIS FORECAST
PACKAGE...BUT WILL CONTINUE TO MONITOR TRENDS.
IN THE WAKE OF THE FRONTAL PASSAGE ON THURSDAY...COOLER AIR DRIER
AIR IS EXPECTED FOR THE CHRISTMAS HOLIDAY AND THROUGH THE WEEKEND.
MARINE...
LIGHT ONSHORE FLOW WILL PERSIST TONIGHT AND BEGIN TO INCREASE ON
TUESDAY...AS THE PRESSURE GRADIENT BETWEEN A DEPARTING HIGH AND A
DEVELOPING LOW OVER THE SOUTHERN PLAINS BRINGS STRENGTHENING WINDS
AND BUILDING SEAS. A COLD FRONT WITH SHOWERS AND THUNDERSTORMS
WILL ADVANCE ACROSS THE GULF WATERS ON THURSDAY WITH A STRONG
OFFSHORE FLOW DEVELOPING IN ITS WAKE.
&&
.PRELIMINARY POINT TEMPS/POPS...
KLCH 43 70 61 70 63 / 0 10 40 60 70
KBPT 46 70 62 71 59 / 0 20 40 60 60
KAEX 41 68 58 68 61 / 0 20 50 70 80
KLFT 42 69 59 70 63 / 0 10 40 50 60
&&
.LCH WATCHES/WARNINGS/ADVISORIES...
LA...NONE.
TX...NONE.
GM...NONE.
&&
$$
