Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 040840
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
340 AM CDT FRI SEP 4 2015

.SHORT TERM...
338 AM CDT

TODAY AND TONIGHT...

MAIN CONCERNS ARE WITH CONTINUED VERY WARM TO HOT AND HUMID
CONDITIONS AND THUNDERSTORM POTENTIAL. MORNING W/V IMAGERY SHOWS A
WELL DEFINED UPPER LOW OVER SOUTHEAST WISCONSIN AND ANOTHER UPPER
LOW IN CLOSE PROXIMITY OVER LOWER MICHIGAN TRAPPED UNDER THE
PERSISTENT AND STRONG UPPER RIDGE THAT HAS BEEN BRINGING US JULY
IN SEPTEMBER. NONEXISTENT GRADIENT WILL EASILY ALLOW A LAKE BREEZE
TO PUSH INLAND TODAY...LIMITING HIGHS NEAR THE LAKE TO THE MID AND
UPPER 70S. SLIGHTLY COOLER 925 MB TEMPS THROUGH MID DAY NEAR THE
UPPER LOW WILL RESULT IN HIGHS INLAND NORTH OF I-80 TO THE MID AND
UPPER 80S...BUT WARMER 925 MB TEMPS SOUTH WILL YIELD ANOTHER DAY
IN THE UPPER 80S TO LOWER 90S. DEWPOINTS AROUND 70 WILL RESULT IN
AN UNSTABLE AND WEAKLY CAPPED ENVIRONMENT.

THE UPPER LOWS PIVOTING AROUND AND EVENTUALLY MERGING OVER
SOUTHERN LAKE MICHIGAN WILL PROVIDE SOME UPWARD MOTION...HOWEVER
LIFTING WILL BE COUNTERED BY GRADUAL HEIGHT RISES OVERALL. HI-RES
GUIDANCE ADMITTEDLY NOT TOO EXCITED WITH SHOWER/TSRA COVERAGE
TODAY...BUT GUIDANCE HONING IN ON FAIRLY ROBUST MOISTURE
CONVERGENCE INVOF LAKE BREEZE. THIS AND MINOR FORCING FROM THE
UPPER LOW APPEARS IT WILL BE THE IMPETUS FOR ISOLATED TO WIDELY
SCATTERED SHRA/TSRA DEVELOPMENT. HAVE KEPT POPS IN 20 TO 30
PERCENT RANGE...HIGHEST IN AFTERNOON NEAR THE INLAND PUSH OF THE
LAKE BREEZE. MANY AREAS ARE LIKELY TO STAY DRY TODAY...BUT GIVEN
WEAK FLOW ALOFT...ANY THUNDERSTORM WILL BE SLOW MOVING AND CAPABLE
OF HEAVY DOWNPOURS DUE TO MOIST AIRMASS. LOSS OF INSTABILITY WITH
NIGHTFALL THIS EVENING AND CONTINUED HEIGHT RISES WILL QUICKLY
SHUT OFF CONVECTION. CANNOT RULE OUT A VERY ISOLATED SHOWER OR
STORM LATE EVENING/OVERNIGHT...BUT HAVE GONE WITH A DRY FORECAST
DURING THIS TIME. IT WILL BE YET ANOTHER WARM AND MUGGY NIGHT...IN
THE UPPER 60S TO LOWER 70S.

RC

&&

.LONG TERM...

SATURDAY THROUGH THURSDAY...

TO BE ISSUED SHORTLY.

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS AND VSBYS IN THE AREA OVERNIGHT.

* LIGHT AND VARIABLE WINDS WITH FAVORED EASTERLY DIRECTION.

* ISOLATED TSRA FRIDAY AFTERNOON.

LENNING

//DISCUSSION...UPDATED 06Z...

A PRETTY TOUGH BUT HOPEFULLY LOW IMPACT FORECAST OVERNIGHT. MVFR
CIGS ARE BEING REPORTED AT SEVERAL UPSTREAM STATIONS AND
SATELLITE PICS SEEM TO SHOW THIS LOWER AREA OF CLOUDS SPREADING
TOWARD THE MDW/ORD TERMINALS. DESPITE MOSTLY CLEAR METAR AT TAF
TIME...WENT AHEAD AND INCLUDED A 3KT BKN CEILING. THIS CERTAINLY
WILL LOOK LIKE AN ODD DECISION IF TRENDS DO NOT PROGRESS AS
EXPECTED...BUT MAY ALSO BE TOO HIGH BASED ON A FEW POCKETS OF IFR
CIGS OUT THERE AS WELL. AS FOR VSBYS...OPTED TO DELAY THE LOWER
VALUES TILL AROUND SUNRISE SINCE TRENDS ARE NOT AS CLEAR AND FAR
FEWER OBS ARE HEADING THAT DIRECTION AT THIS HOUR.

FRIDAY AFTERNOON IS THE NEXT PERIOD OF CONCERN...WITH SUPPORT FOR
ISOLATED TSRA ACTIVITY...PERHAPS WITH A BIT MORE COVERAGE THAN
THURSDAY AFTERNOON BUT WITH LOW CONFIDENCE ON TIMING AND LOCATION.

LENNING

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* LOW CONFIDENCE ON CIGS AND VSBYS OVERNIGHT.

* HIGH CONFIDENCE REGARDING LIGHT WIND SPEEDS EARLY IN TAF PERIOD.

* LOW CONFIDENCE ON TIMING AND COVERAGE OF TSRA FRIDAY AFTERNOON.

LENNING

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...SLIGHT CHANCE OF TSRA IN THE AFTERNOON.

SUNDAY...SLIGHT CHANCE OF TSRA LATE.

MONDAY...CHANCE OF TSRA.

TUESDAY...CHANCE OF TSRA.

WEDNESDAY...CHANCE OF TSRA.

KREIN

&&

.MARINE...
325 AM CDT

QUIET WEATHER AND GENERALLY LIGHT WINDS PERSIST OVER THE LAKE FOR
MOST OF THE HOLIDAY WEEKEND. WAVES COULD GROW A BIT BY LATE SUNDAY
OR MONDAY ACROSS THE NORTH HALF WITH SUSTAINED SOUTHERLY
FLOW...BUT STABLE CONDITIONS WITH COOL WATER AND WARM AIR WILL NOT
SUPPORT SIGNIFICANT WAVE GROWTH. A COLD FRONT CROSSING THE LAKE
FROM WEST TO EAST EARLY NEXT WEEK WILL BRING A CHANGE TO THIS
PATTERN.

LENNING

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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