FXUS63 KLSX 291117
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
517 AM CST SUN NOV 29 2009

.DISCUSSION...
/312 AM CST SUN NOV 29 2009/

THERE CONTINUES TO BE TWO MAIN FEATURES OF INTEREST FOR THIS
FORECAST PACKAGE. FIRST THE NRN STREAM TROF EXTENDING THROUGH THE
NORTHERN PLAINS AND ASSOCIATED CDFNT DRAPPED ACROSS NW MO...AND
SECOND THE UPPER LOW IN EXTREME SRN CA.

THE MODELS ARE GENERALLY IN GOOD AGREEMENT THROUGH THE FIRST 72H
SHOWING THE NRN PLAINS TROF DIGGING SEWD AND AMPLIFYING WITH 500 MB
HEIGHTS ACROSS THE AREA FALLING ON THE ORDER OF 120M BY MIDNIGHT.
THE CDFNT WILL BE ON THE DOORSTEP OF THE FAR NW CORNER OF THE CWA
AT DAYBREAK AND PROGRESS SEWD INTO SRN IL AND THE ERN OZARKS BY
EARLY EVENING. GOOD CAA IN THE WAKE OF THE FRONT ALONG WITH A
DECENT AMOUNT OF CLOUDINESS SHOULD RESULT IN FALLING TEMPS IN THE
WAKE OF THE FRONT THROUGH THE DAY. AHEAD OF THE FRONT THERE IS
STILL A QUESTION REGARDING THE COVERAGE AND THREAT OF PCPN.
MOISTURE RETURN IS STILL IN PROGRESS AND WILL CONTINUE TO STEADILY
INCREASE IN ADVANCE OF THE FRONT TODAY. LARGE SCALE LIFT IS WEAK
BUT THERE APPEARS TO BE DECENT FRONTOGENETICAL FORCING. AND BOTH
THE GFS AND NAM ARE SHOWING MODESTLY STEEP MID LEVEL LAPSE RATES
AND AN ELEVATED UNSTABLE LAYER ALOFT. WHAT THIS ALL TRANSLATES TO
IS THE PERSISTENT IDEA THAT THE HIGHEST POPS WILL BE ACROSS THE SE
THIRD OF THE CWA. HAVE ALSO ADDED THE MENTION OF THUNDER GIVEN THE
PRESENCE OF THE UNSTABLE LAYER. THE CHANCE OF PCPN TONIGHT WILL BE
CONFINED TO THIS EVENING ALONG AND AHEAD OF THE FRONT...ACROSS THE
ERN OZARKS INTO SRN IL. ELSEWHERE COLD AIR WILL CONTINUE TO DEEPEN
ACROSS THE AREA. THE LONGEVITY OF THE COLD WILL BE BRIEF HOWEVER.
THE POST-FRONTAL SFC RDG IS FORECAST TO MOVE SWD MORE QUICKLY THAN
PREVIOUS MODEL RUNS...AND BY MIDDAY MON...THE SFC FLOW IS ALREADY
BACKING AND WAA IS COMMENCING. THE WAA PERSISTS ON MONDAY NIGHT
AND BY TUESDAY WE ARE LOOKING AT ANOTHER DAY OF ABOVE NORMAL
TEMPS. DON'T THINK IT WILL BE NEARLY AS WARM AS SATURDAY...BUT DO
BELIEVE THE MOS GUIDANCE IS TOO COOL AND HAVE BOOSTED HIGHS
CONSERVATIVELY ANYWHERE FROM 2-5 DEGS.

AS MENTIONED THE SECOND FEATURE OF INTEREST IS THE UPPER LOW NOW
IN EXTREME SOUTHERN CA. THE MODELS ARE IN DECENT AGREEMENT THRU
DAYBREAK WED MOVING THE LOW THROUGH NRN MEXICO AND INTO CENTRAL
TX. THEREAFTER THE GUIDANCE CONTS TO DIVERGE ON THE TRACK/TIMING
WED AND WED NIGHT AS THE LOW MOVES ACROSS THE LOWER MS VLY. THE
GFS REMAINS THE MOST SRN TRACK AND THE CMC GEM THE MOST NORTHERN
WITH THE NEW 00Z ECMWF NOW SHIFTING A BIT FURTHER SOUTH AND
INBTWN. THROWING OUT THE MODEL QPFS WHICH HAVE THE LEAST SKILL OF
THE MODEL FIELDS AT THESE RANGES AND JUST KEYING ON SOME OF THE
MORE SIGNIFICANT MASS FIELDS...IE THE H85 LOW AND MID/UPPER
LOW...WOULD SUGGEST THAT ANY PCPN THREAT WILL BE CONFINED TO THE
ERN OZARKS AND SRN IL...AND THIS IS FOLLOWING THE MOST NRN CMC
GEM. ACCORDINGLY I HAVE ADJUSTED THE POPS A BIT SOUTH. I HAVE
CONTINUED THE MENTION OF RAIN/SNOW ALTHO IT APPEARS THE DEEPER
COLD AIR FROM THE NORTH WON'T GET PULLED INTO THIS SYSTEM UNTIL
NEAR THE LATER STAGES OF ITS IMPACT. WILL HAVE TO CONTINUE TO
MONITOR THIS SYSTEM CLOSELY OVER THE COMING DAYS.

GLASS

&&

.AVIATION...
/449 AM CST SUN NOV 29 2009/

FOR THE 12Z TAFS...CDFNT WAS POISED TO MOVE THRU UIN ARND 13Z
SUN...THRU COU ARND 14Z SUN...AND THRU STL/SUS ARND 17Z SUN. SWLY
SFC WNDS WILL VEER AROUND TO A NWLY DIRECTION AFTER FROPA. MVFR
CLOUD COVER...2500-3000 FT WILL DEVELOP AND ADVECT E-NEWD INTO
COU...STL AND SUS EARLY THIS MRNG ALONG AND AHEAD OF THIS
FRONT...WITH EVEN LOWER LEVEL CLOUDS ADVECTING INTO THE TAF SITES
LATER THIS MRNG BEHIND THE CDFNT. CIG HGTS WILL LIKELY DROP DOWN
TO 1000-2000 FT LATER THIS MRNG. RAIN WILL DEVELOP ALONG AND JUST
BEHIND THIS FRONT AS IT BEGINS TO INTERCEPT BETTER LOW LEVEL
MOISTURE WITH LIGHT RAIN EXPECTED IN COU DURING THE LATE MRNG
HOURS AROUND 15-18Z SUN AND EVENTUALLY IN STL/SUS AROUND 17-21Z SUN.
DRIER AND COLDER AIR WILL ADVECT SEWD INTO THE AREA WELL BEHIND
THE CDFNT WITH THE LOW LEVEL CLOUD COVER CLEARING OUT IN UIN AND
COU THIS EVNG AND IN STL/SUS AROUND 06Z MON.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...NONE.
IL...NONE.
&&

$$

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