FXUS63 KLSX 061742
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1242 PM CDT SAT SEP 6 2008

.UPDATE...
/552 AM CDT SAT SEP 6 2008/

HAVE ISSUED DENSE FOG ADVISORY FOR WIDESPREAD THICK FOG THAT HAS
FORMED OVER NERN MO AND A SLIVER OF W CNTRL IL. ELSEWHERE...FOG IS
STILL PATCHY IN COVERAGE AND LARGELY RESTRICTED TO FAVORED LOW
LYING SPOTS AND BODIES OF WATER.

TES

&&

.DISCUSSION...
/430 AM CDT SAT SEP 6 2008/

MODELS CONTINUE THEIR CONSENSUS ON THE MAJOR FEATURES...WITH BROAD
TROF OVER THE N CNTRL CONUS TO GRADUALLY SHIFT EWD TO THE GRTLKS
REGION AND RETREAT TO THE N SOME. A SERIES OF SHORTWAVES WILL
ROTATE AROUND THE BASE OF THIS TROF OVER THE NEXT 48HRS...AND IT
IS ON THESE FEATURES THAT NWP MODELS HAVE COME CONSIDERABLY INTO
BETTER AGREEMENT FROM RUNS 24HRS AGO. THE FIRST SHORTWAVE WILL
PUSH THRU LATE THIS AFTERNOON AND TONIGHT AND PERHAPS INTO SUNDAY
MORNING OVER THE NRN FA...WITH A SECOND SHORTWAVE ALSO IMPACTING
THE NRN FA BUT ON MONDAY AND MONDAY EVENING. AT THE SFC...HI PRES
OVERHEAD TODAY AND TONIGHT WILL GIVE WAY TO A CDFNT TO PUSH INTO
THE NRN/CNTRL FA LATE SUNDAY AFTERNOON AND SUNDAY NIGHT...THEN
BECOME STATIONARY ON MONDAY BEFORE RESUMING ITS PUSH SEWD THRU THE
REMAINDER OF THE FA BY MONDAY EVENING. A 1025MB HI PRES WILL THEN
BE ON DECK TO PRODUCE THE WX FOR MID WEEK.

IN THE NEAR-TERM...PATCHY DENSE FOG HAS FORMED OVER MUCH OF THE
FA...NOTABLY IN THE RIVER VALLEYS WHERE STEAM FOG PROCESSES
DOMINATE WITH COOL AIR TEMPS VERSUS WARM WATER TEMPS. RADIATIONAL
FOG NOT TO BE COMPLETELY OUTDONE...HOWEVER...AND HAS TAKEN BETTER
SHAPE OVER PARTS OF NERN/CNTRL MO IN THE PAST COUPLE HRS. LOOK FOR
THIS TO QUICKLY DISSIPATE DURING MID MORNING...ALTHOUGH RAPIDLY
EXPANDING CLOUDS FROM THE SYSTEM IN THE W MAY DELAY THINGS A TAD
OVER THE WRN FA.

SYSTEM OVER SRN KS TAKING ADVANTAGE OF WAA AND FRONTOGENETICAL
FORCING AND THIS FORCING VERY SLOW TO MOVE EWD...ALTHOUGH IMPETUS
FOR PCPN TO DO SO. SHOULD SEE PCPN LARGELY OUTRUN THE FORCING AND
WEAKEN THRU THIS MORNING...WITH APPROACH OF MORE NLY SHORTWAVE
THIS AFTERNOON EXPANDING PCPN CHCS INTO NERN/CNTRL MO AND W CNTRL
IL. THICK HI CLOUDS RAPIDLY EXPANDING FROM KS AND WILL IMPACT
TEMPS ESPECIALLY IN THE WRN FA. WENT AOB MOS TEMPS IN THE WRN
FA...AND LEANED WARM IN THE ERN FA.

THE NLY SHORTWAVE WILL THEN PASS THRU LARGELY DURING TONIGHT AND
MAINTAIN THE BEST PCPN CHCS OVER THE NRN FA. A NEW MCS WILL FORM
JUST A TAD E FROM WHERE THE TSRA COMPLEX IS OVER SRN KS ATTM AND
SHOULD STAY E OF THE FA...BUT HAVE TOKEN CHC POPS IN CNTRL MO.
THIS FEATURE WILL THEN WEAKEN AS IT HEADS E TOWARDS THE SWRN FA.

AFTER THESE RELATIVELY LOW CHCS FOR PCPN...THINGS LOOK MORE
SUBSTANTIAL FOR SUNDAY NIGHT THRU MONDAY NIGHT...WHERE DEEP
FORCING FROM THE SECOND SHORTWAVE AND A SYNOPTIC FRONTAL BOUNDARY
WILL WORK TOGETHER TO CREATE MUCH HIGHER RAIN CHANCES FOR PARTS OF
THE NRN FA WITH RESPECTABLE QPF. HAVE BUMPED POPS TO LIKELY IN THE
N...AND TAPERED HEADING S.

TES

&&

.AVIATION...
/1157 AM CDT SAT SEP 6 2008/
FOR THE 18Z TAFS...WKNG MRNG CONVECTION MOVG EWD THRU SWRN MO
ATTM. MAY GET A BRIEF LGT SHRA IN COU THIS AFTN. DIURNAL CUMULUS
CLOUDS HAVE DVLPD UNDERNEATH CIRRUS CLOUD SHIELD. THESE CUMULUS
CLOUDS SHOULD SLOWLY RISE IN HGT DURING THE AFTN HRS WITH CONTD HTG
AND MIXING OF THE BNDRY LYR. SHRTWV TROF IS FCST TO MOVE EWD THRU
NRN MO THIS EVNG. THIS FEATURE ALONG WITH INCRSG LOW-MID LVL WAA
SHOULD BRING MID LVL CLOUDINESS TO THE CWA LT THIS AFTN AND THIS
EVNG. AT LEAST SCT SHRA SHOULD DVLP FM UIN TO COU THIS EVNG
SPREADING SEWD THRU THE STL METRO AREA LT TGT. MAY INCLUDE A TEMPO
GRP OF SHRA IN UIN AND COU THIS EVNG...AND A PROB30 GRP OF SHRA IN
STL/SUS LT TGT. LOOKING AT MDL RH FCSTS AND MOS CLOUD HGT FCSTS
THE CLOUD CEILING SHOULD LWR THRU THE NGT POSSIBLY DROPPING INTO
THE MVFR CATAGORY. LGT FOG IS ALSO POSSIBLE LT TGT AND EARLY SUN
MRNG WITH A CONTD LGT SFC WND FIELD ALTHOUGH THE CLOUD CVR SHOULD
LIMIT NOCTURNAL COOLING AND THE DEVELOPMENT OF ANY DENSE FOG.

GKS

&&

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

$$

WFO LSX



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