343 PM CDT
FOR THE REMAINDER OF THE AFTERNOON AND EVENING...THE MAIN CONCERN
WILL FOCUS ON THE AREA OF SHOWERS THAT FORMED ALONG THE MISSISSIPPI
RIVER. THE AREA OF SHOWERS HAS BEEN MAKING SOME SLOW EWD PROGRESS
AND EXPECT THAT SCT SHOWERS MAY MOVE INTO THE I-39 CORRIDOR DURG THE
EARLY EVENING HOURS. THE SHOWERS SHOULD CONTINUE EWD THROUGH THE
EVENING...BUT WILL LIKELY DISSIPATE AS THEY APPROACH THE FOX
VALLEY. WITH INCREASING LOW LEVEL MOISTURE OVER THE AREA UNDER
PERSISTENT SOUTHERLY FLOW...THE AREA HAS SEEN INCREASING LOW AND MID
CLOUD. HOWEVER...MUCH OF THIS CLOUDINESS IS DIURNAL IN NATURE AND
MUCH OF THE CLOUDINESS OVER THE ERN PORTIONS OF THE CWA SHOULD
DISSIPATE AT SUNSET. WITH THE INCREASING CLOUD COVER OVER THE WRN
PORTIONS OF THE CWA...EXPECT THAT AREA TO SEE LOWS ONLY DROP INTO
THE UPPER 50S...WHILE ERN PORTIONS OF THE CWA SHOULD RADIATE A
BIT...AND DROP INTO THE LOWER 50S...WITH THE EXCEPTION OF DOWNTOWN
CHICAGO...WHICH SHOULD REMAIN WARMER...ONLY DROPPING TO ARND 60
DEGREES.
FOR WEDNESDAY THROUGH FRIDAY...THE MAIN FORECAST CONCERN WILL BE
TIMING THE ONSET OF PCPN ASSOCIATED WITH AN APPROACHING UPPER TROUGH
AND ASSOCIATED SFC COLD FRONT...AS WELL AS...THE SPEED OF
PROGRESSION OF THE SYSTEM THROUGH THE AREA. THE LATEST MODEL
GUIDANCE IS RATHER CONSISTENT WITH RECENT RUNS WITH THE SYNOPTIC
SCALE PATTERN. THE ONLY REAL ADJUSTMENT TO THE FORECAST IS TO DELAY
THE PROGRESSION OF THE MAIN PCPN AREA ACROSS THE REGION. THE
ONGOING PCPN OVER THE WRN PORTIONS OF THE CWA IS ACTUALLY NOT PART
OF THE SYNOPTIC UPPER TROUGH AND COLD FRONT...BUT RATHER...IS
ASSOCIATED WITH A LOW LEVEL CONVERGENCE ZONE BETWEEN THE
TROUGH...CURRENTLY LOCATED OVER THE WRN PLAINS...AND A SFC LOW OVER
THE SERN CONUS. EVENTUALLY...BY TOMORROW MORNING...THE CONVERGENCE
ZONE WILL BE ABSORBED INTO THE SYNOPTIC TROUGH. EXPECT THAT
ORGANIZED PCPN WILL APPROACH THE I-39 CORRIDOR BY ARND NOON TOMORROW
AND SLOWLY PROGRESS EWD ACROSS THE CWA...LIKELY NOT REACHING ERN
IL/NWRN IN...INCLUDING THE CHICAGO METRO AREA UNTIL THE EVENING RUSH
HOURS. THERE WILL STILL BE A CHANCE FOR SOME ISOLD/EMBEDDED THUNDER
WITH THE SYSTEM...BUT EXPECT THAT ANY THUNDER SHOULD BE CONFINED TO
THE SFC FRONTAL ZONE. LOW LEVEL INSTABILITY IS RATHER MODEST...BUT
PERSISTENT WARM ADVECTION AND ISENTROPIC LIFT SHOULD BE CONDUCIVE TO
A LEAST SOME THUNDER. TEMPERATURES TOMORROW WILL REMAIN
UNSEASONABLY WARM...BUT WITH INCREASING CLOUD COVER AND EXPECTED
PCPN...HIGHS WEDNESDAY WILL BE LOWER THAN RECENT DAYS...TOPPING OUT
IN THE LOWER 70S. AS MODEST COLD ADVECTION SETS UP BEHIND THE
FRONT...TEMPERATURES WILL DROP OFF INTO THE MIDDLE 60S FOR
THURSDAY. THE COLD ADVECTION WILL INCREASE FOR THURSDAY NIGHT AND
FRIDAY...WITH LOWS BY FRIDAY MORNING DROPPING INTO THE MIDDLE TO
UPPER 40S. THE URBANIZED AREAS OF THE CHICAGO METRO AREA WILL
REMAIN A BIT WARMER...REMAINING IN THE 50S. THE COOLING TREND WILL
CONTINUE INTO FRIDAY AND FRIDAY NIGHT AS AN UPPER TROUGH MOVES
THROUGH THE GREAT LAKES REGION.
FOR THE LONG TERM FORECAST PERIOD...SATURDAY THROUGH TUESDAY...THERE
IS REASONABLY GOOD CONFIDENCE IN A WARMING TREND FOR THE WEEKEND AS
UPPER RIDGING BUILDS OVER THE WRN CONUS AND HEIGHTS RISE OVER THE
CNTRL CONUS AS THE UPPER TROUGH EJECTS OUT TO THE EAST.
HOWEVER...THROUGH THE WEEKEND...THE 12Z GFS AND THE OLDER 00Z RUN OF
THE ECMWF HAD BEGUN TO SHOW SIGNIFICANT TIMING DIFFERENCES LATE IN
THE PERIOD. HOWEVER...THE OVERALL TREND THROUGH THE EXTENDED PERIOD
SHOULD BE FOR TEMPERATURES TO BE NEAR SEASONAL NORMAL LEVELS. THE
LONG RANGE GUIDANCE IS SUGGESTING SURGE OF SIGNIFICANTLY COLDER AIR
TO DROP OUT OF CANADA. BY THE MIDDLE OF NEXT WEEK...BOTH THE GFS
AND ECMWF ARE ADVERTISING 850MB TEMPERATURES IN THE -2C TO
-6C...WHICH WOULD SUGGEST HIGHS IN THE 40S AND LOWS IN THE 30S.
KREIN
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 20Z...
* WIND DIRECTION THIS AFTERNOON AND EVENING WITH POTENTIAL LAKE
BREEZE PASSAGE.
LENNING
//DISCUSSION...UPDATED 18Z...
A VERY SLOW MOVING LINE OF SHOWERS HAS MADE ITS WAY TO THE WESTERN
EDGE OF ILLINOIS BUT DOES NOT APPEAR TO BE HOLDING TOGETHER VERY
WELL THIS AFTERNOON. EXTRAPOLATED FORWARD PROGRESSION WOULD HAVE
THEM INTO THE ORD-MDW AREA BY 11Z TOMORROW...BUT MORE LIKELY
CHANCES FOR SHOWERS WOULD COME TOMORROW AFTERNOON. THE PRIMARY
WEATHER MAKER THIS WEEK IS A COLD FRONT EXPECTED TO CROSS THE AREA
ON THURSDAY...BUT AHEAD OF THE FRONT THERE ARE SOME POCKETS OF
ENERGY MOVING THROUGH THE MID AND UPPER LEVELS OF THE ATMOSPHERE.
THESE WILL SUPPORT INCREASED CLOUDINESS AND SPOTTY SHOWERS THROUGH
THE NEXT DAY OR SO BEFORE THE MAIN SYSTEM ARRIVES ON THURSDAY.
THROUGH THIS SAME PERIOD WINDS GENERALLY REMAIN LIGHT...OUT OF THE
SOUTHEAST...VARYING FROM EAST TO SOUTH.
LENNING
//ORD AND MDW CONFIDENCE...UPDATED 20Z...
* HIGH CONFIDENCE ON ALL FORECAST ELEMENTS FOR REMAINDER OF THE
DAY EXCEPT FOR EXACT WIND DIRECTION...POSSIBLY VARIABLE BETWEEN
SOUTH AND EAST.
LENNING
//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...
* WEDNESDAY NIGHT AND THURSDAY...OCCASIONAL SHRA WITH MVFR OR EVEN
BRIEF IFR POSSIBLE ESPECIALLY WED NGT/THURS MORNING.
* FRIDAY AND SATURDAY...SLGT CHC SHRA FRI...OTHERWISE VFR.
* SUNDAY AND MONDAY...SLGT CHC SHRA WITH MVFR CIGS.
SHEA
&&
.MARINE...
152 PM CDT
THE MAIN CONCERN DURING THE PERIOD CONTINUES TO REVOLVE AROUND THE
STRONG AUTUMN STORM SYSTEM THAT IS EXPECTED TO PUSH ACROSS LAKE
MICHIGAN LATE THURSDAY INTO FRIDAY. LOW PRESSURE NOW TAKING SHAPE
ACROSS THE FRONT RANGE OF THE CANADIAN ROCKIES...WILL PUSH
SOUTHEASTWARD OVER NEXT FEW DAYS. THIS WILL MAINTAIN A SOUTH TO
SOUTHEASTERLY WIND ACROSS THE LAKE INTO THURSDAY. AS THE LOW MOVES
ACROSS THE LAKE INTO FRIDAY MORNING...THE SURFACE LOW IS EXPECTED TO
DEEPEN. THIS WILL LIKELY PRODUCE A HEALTHY PRESSURE GRADIENT ACROSS
THE WESTERN GREAT LAKES AS A SURFACE RIDGE OF HIGH PRESSURE BUILDS
IN ACROSS THE PLAINS BEHIND THIS SYSTEM. THEREFORE...A PERIOD OF
GALES APPEAR TO BE A GOOD BET ON FRIDAY AS THE SYSTEM INTENSIFIES
AND A MUCH COLD AIRMASS OVERRIDES THE LAKE.
KJB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
