FXUS63 KLOT 291203
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
603 AM CST SUN NOV 29 2009
.DISCUSSION...
228 AM CST
AS ANTICIPATED...INCREASING CLOUDINESS IS OVERSPREADING THE MS VLY
AND GREAT LAKES REGION AHEAD OF AN APPROACHING COLD FRONT. THIS
FRONT STRETCHED FROM CENTRAL LAKE MICHIGAN SW THRU THE MILWAUKEE
AREA TO TOPEKA KANSAS AROUND MIDNIGHT. SOUTH WINDS AHEAD OF THIS
FRONT ARE KEEPING DEWPTS IN THE 30S WITH UPR 30S PROMPTING SOME
DENSER FOG SOUTH OF I-88 THIS EARLY MORNING. THE DENSER FOG IS
PRESENTLY QUITE PATCHY WITH VISIBILITIES VARYING FROM A QUARTER
MILE TO 3 MILES IN ANY GIVEN LOCATION. TIME WILL TELL HOW
WIDESPREAD THE DENSE FOG BECOMES...AND WHETHER A DENSE FOG
ADVISORY IS NEEDED.
THE NATIONAL RADAR MOSAIC INDICATES RAIN DEVELOPMENT IS POST
FRONTAL...PHASING WITH A MID LVL TROF ADVECTING ACROSS THE PLAINS
AND INTO THE MS VLY THIS MRNG. SFC FRONTAL PASSAGE IS EXPECTED SOON
AT ROCKFORD AND NEAR SUNUP IN THE CHICAGO AREA AND BY NOONTIME
THROUGH NORTHWEST INDIANA. WITH THE APPROACH OF THE MID LVL
TROF...RAIN IS PROBABLY AT A MINIMAL CHANCE BY NOONTIME ACROSS
NORTHERN IL AND NW INDIANA...BEING RATHER LIGHT AND SHORTLIVED.
THIS IS A FAIRLY PROGRESSIVE UPR TROF AND DRYING SHUD BE
FORTHCOMING THIS EVENING AS TEMPERATURES FALL. FCST SOUNDINGS
INDICATE NO HIGH RH IN THE CRYSTAL FORMING TEMPS...SO A RAIN AND
SNOW MIXTURE IS PROBABLY NOT LIKELY AS PCPN ENDS THIS EVENING.
SFC HIGH PRESSURE BUILDING ACROSS THE PLAINS AND INTO THE MIDWEST
LATE TONIGHT AND MONDAY WILL PUSH ANTICYCLONIC FLOW OVER THE AREA
AND HELP CLEAR SKIES AS THE UPR TROF SWINGS THRU. HOWEVER A SHORT
TURNABOUT WILL CLOUD UP SKIES AGAIN FOR THE LATE AFTN AND EVENING ON
MONDAY AS ANOTHER SFC LOW WORKS EAST ACROSS SRN CANADA INTO ONTARIO.
ANY PCPN HOWEVER SHUD REMAIN NORTH OF ILLINOIS AS HIGH PRESSURE
STRETCHED ACROSS OUR SOUTH GUIDES ACTIVITY AROUND THE FORECAST AREA.
RIDGING IN FACT RETURNS THE CLEARING LATE MON NGT...RESTORING
ANTICYCLONIC FLOW TO THE FORECAST AREA. A RETURN OF SLY FLOW
ALOFT SUGGESTS THAT HIGHS TUESDAY WILL BE APPROACHING THE 50 MARK
AGAIN.
MODELS VARY A BIT MORE SIGNIFICANTLY AFTER MONDAY NIGHT THOUGH. A
TWO STREAM ENVIRONMENT TO THE NORTH AND SOUTH OF ILLINOIS GIVES
MODELS A LOT OF OPTIONS IN DEVELOPING A CONSISTENT AND...
SUBSEQUENTLY ASSUMED...AN ACCURATE SCENARIO THAT WE CAN HANG A HAT
ON.
A NORTHERN STREAM LOW MAKING LANDFALL IN THE PACIFIC NORTHWEST IS
EXPECTED TO GLIDE EAST ACROSS THE NRN CONUS TUESDAY THRU WEDNESDAY.
THE SRN STREAM EJECTS A CLOSED LOW OUT OF THE BAJA MON NIGHT AND
ACROSS TEXAS TUESDAY AND INTO THE LOWER MS VLY TUES NGT INTO
WEDNESDAY. THE TRAJECTORY OF THIS SFC LOW TO THE SOUTH WILL
DETERMINE HOW MUCH COLD AIR IS PULLED DOWN INTO ILLINOIS WHILE
WRAPPING GULF MSTR INTO THIS COLD REGIME. A MORE NORTHERLY TRACK
WILL MAKE FOR A SNOWIER FORECAST FOR ILLINOIS AND INDIANA THAN A
NORTHEAST TRACK THRU THE TN AND OHIO VALLEYS TO OUR SOUTHEAST.
CURRENT LEANINGS IN THE EXTENDED FORECAST FAVOR THE SLIGHTLY NORTHERLY
TRACK. FURTHER MODELS RUNS SHOULD RESOLVE THE INCONSISTENCIES.
RLB
&&
.AVIATION...
1200 UTC TAFS...WEAK COLD IS MOVING SLOWLY ACROSS THE AREA AND IS
ACCOMPANIED BY A VERY WEAK PRESSURE GRADIENT. WINDS ACROSS THE
AREA ARE GENERALLY CALM OR LGT/VRBL. PATCHY MVFR VIS HAS BEEN
MOVING IN AND OUT OVERNIGHT AND SHOULD CONTINUE FOR A FEW MORE
HOURS AFTER SUNRISE. LATEST SATELLITE IMAGERY INDICATES INCREASING
MID AND HIGH CLOUD COVERAGE...WHICH SHOULD HELP LIMIT THE VIS
RESTRICTION TO MVFR. FOLLOWING THE FRONTAL PASSAGE...CIGS SHOULD
GRADUALLY LOWER TO AT LEAST LOWER END MVFR. LATEST OBS STILL
INDICATING SOME IFR CIGS OVER IOWA BEHIND THE FRONT AND HAVE SOME
CONCERN FOR TIMING OF THESE IFR CIGS MOVING OVER THE LOCAL
TERMINALS. BASED ON THE SLOW PROGRESSION OF THE FRONT...HAVE
PUSHED BACK THE ONSET OF IFR AND CONFINED IT TO A TEMPO GROUP AS
SOME DAYTIME WARMING SHOULD OCCUR BY THE TIME THE FRONT TRAVERSES
THE AREA. PCPN AMOUNT AND COVERAGE IS ANOTHER CONCERN. THE LATEST
MODEL RUNS SHOW THAT THE PCPN SHOULD DEVELOP OVER THE NERN IL/NWRN
IN AND BYPASS THE RFD TERMINAL. SINCE THERE IS ONLY VERY WEAK
FORCING ASSOCIATED WITH THIS SYSTEM...PCPN SHOULD GENERALLY BE
LIGHT AND SCATTERED. DO NOT EXPECT SGFNT IMPROVEMENT IN CIGS UNTIL
LATE TONIGHT AS THE POST FRONTAL CLOUD IS RATHER EXTENSIVE AND THE
SYSTEM VERY SLOWLY PROGRESSIVE. HOWEVER...THE BACK EDGE OF THE
CLOUD IS RATHER SHARP AND THE IMPROVEMENT WILL BE QUICK.
KREIN
&&
.MARINE...
400 AM CST
A WEAK COLD FRONT STRETCHES FROM LAKE HURON SOUTHWEST THROUGH
NORTHWEST ILLINOIS...TO CENTRAL TEXAS...WITH A WEAK LOW PRESSURE
CENTER NEAR ST. LOUIS. THIS FRONT WILL MOVE SLOWLY SOUTHEAST AS
THE WEAK LOW TRACKS NORTHEAST INTO LOWER MICHIGAN BY SUNDAY
AFTERNOON. FOLLOWING THE PASSAGE OF THE COLD FRONT...COOLER AIR
WILL OVERSPREAD THE LAKE AND WINDS WILL BECOME WLY-NWLY AND
INCREASE TO 15-25KT. EXPECT SMALL CRAFT ADVISORY CONDITIONS TO
DEVELOP BY LATE THIS AFTERNOON AND PERSIST THROUGH TUESDAY
MORNING. A LARGE RIDGE OF HIGH PRESSURE OVER THE ROCKIES WILL
SPREAD EAST ACROSS THE PLAINS SUNDAY AND INTO THE MISSISSIPPI
VALLEY SUNDAY NIGHT AND MONDAY. THE RIDGE WILL BUILD ACROSS THE
LAKE LATE TUESDAY ALLOWING WINDS AND WAVES TO SUBSIDE.
KREIN
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...3 PM SUNDAY TO 9 AM TUESDAY.
&&
$$
