FXUS63 KLOT 201142
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
642 AM CDT SAT SEP 20 2008
.DISCUSSION...
307 AM CDT
SATLT LOOPS SHOW PERSISTENT WEAK UPR LOW OVR SRN/SERN MO. THIS
FEATURE IS FCST TO SLOWLY DSIPT OVR THE NEXT FEW DAYS AS UPR
RIDGING TAKES PLACE OVR MIDEWST/SRN GRTLKS. THICKER BAND OF HIGH
CLOUDS ASSD WITH DEFORMATION AXIS RUNS FROM SERN IA...S OF QUAD
CITIES...NEWD ACROSS WRN LWR MI. OTHER BANDS OF MID/HIGH
CLOUDINESS WILL PERSIST IN LIFTING NWD ACROSS IL/IN AND INTO SRN
PORTIONS OF FA. BASED ON THIS...WILL JUST GO PARTLY CLOUDY MOST
SECTIONS FOR CHARACTER OF THE DAY. OTHER FEATURE TO FOLLOW THRU NR
TERM OF FCST IS COLD FRONT APCHG FROM NW. AT 08Z...THIS FRONT
EXTENDED FROM A LOW OVR NRN QUEBEC...SWWD ACROSS THE UPR
GRTLKS...TO SD. ALTHOUGH SFC ANALYSIS SHOWS FAIRLY STG PRES RISES
TO N OF GRTLKS...ISALLOBARIC GRADIENT IS DIRECTED EWD ACROSS ONT
AND QUE...SO TRAILING PORTION OF FRONT IS ALREADY LOSING MOST OF
ITS SWD PUSH. INDEED...TIMING OF THIS FEATURE BASED ON MODEL GUID
HAS SLOWED SOMEWHAT FROM LAST NGTS RUNS. NONETHELESS...EXPECT
WINDSHIFT TO BACK DOOR INTO NERN IL LATE THIS AFTN AS MORE OF A LK
BREEZE...THAN SYNOPTIC FRONT...WITH WINDS TURNING NELY OVR ENTR FA
DURG EVENING AS INFLUENCE OF HI PRES BUILDING OVR ERN ONTARIO THIS
AFTN AND TNGT EVENTUALLY PUSHES FRONT SWD AS IT WASHES OUT. WITH
OVERALL SYNOPTIC PRES GRADIENT IN PRE FRONTAL AMS VERY WEAK TO
BEGIN WITH...AND FCST LAND/WATER AMBIENT AIR DELTA T'S PUSHING 20
F DEGREES THIS AFTN...EXPECT AT LEAST A WEAK LAKE BREEZE TO DVLP MID-
LATE AFTN. HOWEVER...EXPECT THIS WILL DVLP LATE ENUF FOR AREAS
ADJACENT TO LK MI TO HEAT UP DIURNALLY THRU MID AFTN.
THEREFORE...WITH ONLY A FEW BANDS OF HI CLOUDINESS TDY...TEMPS
SHOULD WARM INTO LWR 80S. THIS IS ALSO SUPPORTED BY LLVL PARCEL
TRAJECTORY. FCST LLVL MOISTURE FIELDS STILL HINT AT SOME MOISTURE
POOLING ALG BOUNDARY...BUT ANY LOWER BASED CONVECTIVE CLOUD DVLPMT
WILL BE GENLY ALG/JUST AFTER FROPA. AM A LTL CONCERNED ABOUT GFS
FCST SOUNDINGS ACROSS FA FOR THIS AFTN WHICH DO DVLP FAIRLY DECENT
CAPE OF NR 1400 J/KG...BUT WILL KEEP POPS BLO MENTION AS WIND AND
VERTICAL MOTION PROFILES ARE VERY WEAK AND WITH ARRIVAL OF SFC FNT
NOT EXPECTED TIL AFTER MAX HEATING...NOTHING REALLY APPARENT FOR
CONVECTION TO FOCUS ON. 
LTL WX CHG SUN THRU MON/MON NGT AS RGN WILL BE IN RELATIVELY DRY
SELY FLOW CIRCULATING AROUND RETREATING HI WELL OFF TO E. WITH
TIME...A SERIES OF SHRT WAVES ARE FCST TO DIG ACROSS NRN/CNTRL
RCKYS BY TUES. THIS WILL BACK FLOW ACROSS PLAINS STAS THRU PERIOD
SETTING UP ZONE OF ACTIVE WX/LLVL MOIST ADVECTION WELL TO W. EWD
PROGRESSION OF THIS MORE ACTIVE ZONE IS EXPECTED TO BE HELD AT BAY
AS H5 HGTS SLOWLY BUILD DOWNSTREAM...OVR GRTLKS.  
EVENTUALLY...THIS PATN IS FCST TO SHFT FAR ENUF E DURG MIDWEEK
PERIOD TO SUPPORT BETTER CHCS FOR PCPN E OF MS RVR.
MDL TRENDS THRU EXTENDED PERIOD SHOW WLYS DVLPG INTO HI INDEX PATN
WITH STORM TRACK WELL TO N OF RGN AS H5 RIDGE BUILDS NEWD ACROSS
MID MS VLY. THIS WOULD SUGGEST A DRY AND WARM PERIOD LATE NXT WEEK
AND INTO NXT WEEKEND. 
MERZLOCK
&&
.AVIATION...
12Z TAFS...FEW CHANGES FROM PREVIOUS FORECAST BUT CONFIDENCE
REGARDING WINDS...SPECIFICALLY FROPA THIS EVENING...IS DECREASING.
WINDS GENERALLY CALM ACROSS THE REGION THIS MORNING WITH MVFR FOG
AT MANY LOCATIONS AWAY FROM THE WARMER URBAN AREA. A FEW SPOTS
HAVE DIPPED LOWER BUT VIS WILL QUICKLY IMPROVE TO P6SM SOON AFTER
SUNRISE. WINDS WILL BECOME LIGHT WESTERLY THIS MORNING AND PERHAPS
TURN MORE SOUTHWESTERLY DURING THE AFTERNOON. HOWEVER...WITH WEAK
GRADIENT EXPECT A LAKE BREEZE TO DEVELOP BY EARLY AFTERNOON. THIS
LAKE BREEZE SHOULD MAKE IT THRU ORD/MDW BY MID/LATE AFTERNOON BUT
DIRECTION BEHIND IT A BIT UNCERTAIN AS WELL AS TIMING. PREVIOUSLY
HAD GONE WITH AN EASTERLY DIRECTION BUT LATEST GUIDANCE SUPPORTS
MORE OF A SOUTHEAST DIRECTION. PREVAILING SPEEDS HOWEVER WILL BE
LESS THAN 10 KNOTS.
COLD FRONT NOW PUSHING SOUTH ACROSS NORTHERN WI AND NORTHERN MI.
MODELS CONTINUE TO SLOW ITS PROGRESS SOUTH AS IT REACHES THE AREA
THIS EVENING. WHILE WINDS WILL PROBABLY BECOME NORTHEAST...TIMING
IS UNCERTAIN. SIMILAR TO THE LAKE BREEZE THOUGH...SPEEDS SHOULD BE
UNDER 10KTS.
SCT/BKN CIRRUS THRU THE PERIOD ALONG WITH A FEW CU THIS AFTERNOON.
ISOLATED SHOWERS POSSIBLE ALONG THE FRONT...NORTH OF THE TERMINALS
THIS AFTERNOON AND THESE SHOULD DISSIPATE WITH LOSS OF DAYTIME
HEATING BY THE TIME THE FRONT ARRIVES THIS EVENING. CONVECTION
ACROSS SE MO AND SOUTHERN IL ASSOCIATED WITH AN UPPER LOW WILL
CONTINUE TO SLOWLY LIFT NORTH TODAY...REMAINING SOUTH OF THE TAFS
BUT MAY BECOME A CONCERN BY SUNDAY AFTERNOON.
FOG POSSIBLE AGAIN LATER TONIGHT INTO SUNDAY MORNING. WITH
SLIGHTLY COOLER AIR WITH THE FRONT AND LITTLE CHANGE TO AIRMASS
IN TERMS OF MOISTURE...FOG MAY DROP VISIBILITIES LOWER THAN THIS
MORNING. BUT FOR NOW HAVE ONLY INCLUDED AT DPA. CMS
&&
.MARINE...
213 AM...COLD FRONT CURRENTLY PUSHING SOUTH ACROSS LAKE SUPERIOR
AND NORTHERN MN. THIS FRONT WILL CONTINUE PUSHING SOUTH ACROSS
LAKE MICHIGAN TODAY. AS HIGH PRESSURE SLIDES EAST ACROSS THE
NORTHERN LAKES AND SOUTHERN ONTARIO LATER TODAY AND TONIGHT...THE
GRADIENT WILL LIKELY SUPPORT 15-25 KNOTS THOUGH WINDS WILL LIKELY
BE DIMINISHING DURING THE NIGHT. AS THE FRONT PUSHES SOUTH ACROSS
SOUTHERN LAKE MICHIGAN THIS AFTERNOON INTO THE EVENING HRS...THE
MODELS HAVE SLOWED ITS PUSH SOUTH...PERHAPS TOO SLOW...BUT HAVE
SLOWED FROPA TIMING DOWN A BIT IN THE GRIDS...REACHING THE NE IL
SHORE AFTER 00Z. HOWEVER...WEAK GRADIENT AHEAD OF THE FRONT WITH
TEMPS PUSHING 80 TODAY WILL ALLOW A LAKE BREEZE TO DEVELOP BY
EARLY AFTERNOON...THUS WINDS WILL TURN ONSHORE ALONG THE IL AND
INDIANA SHORES PRIOR TO FROPA. AS THE HIGH OVER THE NORTHERN LAKES
SLOWLY MOVES EAST SUNDAY AND SUNDAY NIGHT...WINDS WILL TURN
EASTERLY...THEN SOUTHEASTERLY BY MONDAY MORNING. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$