Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 301927
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
227 PM CDT THU JUL 30 2015

.SHORT TERM...
226 PM CDT

THROUGH FRIDAY...

FORECAST PERIOD WILL REMAIN RELATIVELY QUIET...WITH DRY
CONDITIONS EXPECTED. INCREASING WESTERLY WINDS AT THIS TIME WILL
LIKELY REACH THEIR PEAK OVER THE NEXT COUPLE OF HOURS WITH A
DIMINISHING TREND THEN EXPECTED INTO THE EARLY EVENING. A FEW CU
HAVE DEVELOPED THIS AFTERNOON BUT THESE WILL QUICKLY ERODE WITH
CLEAR SKIES EXPECTED ONCE AGAIN TONIGHT. GUIDANCE IS HINTING AT
SOME PASSING MID/HIGH LEVEL CLOUD COVER LATE TONIGHT INTO FRIDAY
MORNING. HOWEVER...FEEL IT MAY BE A BIT AGGRESSIVE AND DONT THINK
IT WILL AMOUNT TO MUCH BEYOND A WINDOW OF PARTLY CLOUDY SKIES.
SUNNY SKIES WILL HELP TEMPS ACROSS THE AREA TO BE SOMEWHAT OF A
MIRROR OF TODAY...WITH OFFSHORE FLOW KEEPING ANY LAKE COOLING
LIMITED ACROSS PORTIONS OF NORTHWEST INDIANA. DEWPOINTS WILL TRY
TO INCREASE THROUGHOUT THE DAY BUT SHOULD BE LIMITED TO THE LOWER
60S BEFORE DAYTIME MIXING ALLOWS DRIER AIR TO MIX DOWN...WITH THIS
LOWER DEWPOINT AIR ALSO LIMITING HEAT INDICES. WAS A LITTLE
CONCERNED THAT PREVIOUS RUNS OF GUIDANCE WERE NOT QUITE HANDLING
PRECIP POTENTIAL FRIDAY AFTERNOON QUITE WELL BUT 12Z GUIDANCE
TODAY HAS CONTINUED A SIMILAR TREND...KEEPING ANY DEVELOPMENT OUT
AHEAD OF APPROACHING TROUGH/BOUNDARY OUTSIDE OF THE CWA. WITH LOW
TO MID LEVEL FLOW ALREADY WEST TO NORTHWEST ON FRIDAY...LOW/MID
LEVEL CONVERGENCE WILL REMAIN RATHER WEAK. ALSO...SUPPORT ALOFT
APPEARS TO BE LACKING. SO HAVE BACKED AWAY ON THUNDERSTORM CHANCES
FRIDAY AFTERNOON FOR THE CWA BUT IF ANY BRIEF/ISOLATED DEVELOPMENT
WERE TO OCCUR...IT WOULD BE ALONG THE FORD/IROQUOIS TO BENTON
COUNTY LINE.

RODRIGUEZ

&&

.LONG TERM...
356 AM CDT

MONDAY THROUGH WEDNESDAY...

GUIDANCE IN GOOD AGREEMENT IN A SHORT WAVE DIGGING ACROSS THE
GREAT LAKES EARLY IN THE PERIOD THAT REINFORCES TROUGH OVER THE
GREAT LAKES. WEAK SURFACE LOW AND ANOTHER COLD FRONT LOOK TO SAG
ACROSS THE AREA MONDAY AFTERNOON/NIGHT...AGAIN WITH A CHANCE OF
PRECIP. WEAK HEIGHT RISES THEN DEVELOP BEHIND THE DEPARTING MID-
LEVEL TROUGH AXIS TUESDAY ALLOWING SURFACE HIGH PRESSURE RIDGE TO
DEVELOP FROM THE UPPER MISSISSIPPI VALLEY ACROSS IL/WI/MI BY
TUESDAY NIGHT. ECMWF THEN WEAKENS SOUTHWESTERN CONUS UPPER RIDGE
MORE THAN THE GFS BY MID-WEEK...ALLOWING ANOTHER MID-LEVEL WAVE TO
PROPAGATE INTO THE MID-MISSISSIPPI VALLEY LATE TUESDAY NIGHT INTO
WEDNESDAY AND THUS BRINGS PRECIP THREAT ACROSS MO/IA AND WESTERN
IL TUES NIGHT AND INTO THE WFO LOT FORECAST AREA ON WEDNESDAY.

HIGH PRESSURE BUILDING ACROSS THE NORTHERN LAKES IN THE WAKE OF
THE COLD FRONT LATE MONDAY DOES RESULT IN A BIT OF A COOL DOWN AS
LOW LEVEL FLOW BECOMES MORE NORTH-NORTHEASTERLY TUE-WED...WITH
HIGHS AROUND 80/LOWER 80S AND COOLER 70S OFF OF THE LAKE.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* WEST TO NORTHWEST WINDS GUSTING AROUND 25 KT THROUGH THE EARLY
  EVENING.

* GUSTY WEST WINDS FRIDAY WITH GUSTS UP TO 20 KT.

JEE

//DISCUSSION...UPDATED 18Z...

HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH FRIDAY EVENING.
 WEST TO NW WINDS WILL BE GUSTING INTO THE MID 20 KT RANGE AND
THEN DIMINISH TO LESS THAN 10 KT THIS EVENING. WEST WINDS THEN
BEGIN GUSTING AGAIN INTO THE LOW 20 KT RANGE MID FRIDAY MORNING
THROUGH THE AFTN. OTHERWISE VFR CONDITIONS ARE EXPECTED.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

JEE

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

* FRIDAY NIGHT AND SATURDAY...DRY/VFR. WESTERLY WINDS.
* SUNDAY...CHANCE OF TSRA. SOUTHWEST WINDS.
* MONDAY...SLIGHT CHANCE OF TSRA. NORTHWEST WINDS.
* TUESDAY...DRY/VFR. NORTHEAST WINDS.
* WEDNESDAY...CHANCE OF TSRA. EASTERLY WINDS.

&&

.MARINE...
226 PM CDT

OVERALL FLOW OVER THE LAKE HAS DIMINISHED TODAY...BUT WITH
WESTERLY WINDS ALONG THE NEARSHORE IN ILLINOIS INCREASING AT THIS
TIME. THESE INCREASING WESTERLY WINDS WILL LIKELY REACH THEIR PEAK
OVER THE NEXT COUPLE OF HOURS WITH A DIMINISHING TREND THEN
EXPECTED INTO THE EARLY EVENING...WITH THE CURRENT SMALL CRAFT
ADVISORY END TIME STILL ON TRACK TODAY. WESTERLY WINDS OF 10 TO 20
KT WILL LIKELY REMAIN THE GENERAL TREND TONIGHT INTO FRIDAY OVER
THE LAKE...WHILE A TROUGH/FRONTAL BOUNDARY APPROACH ON FRIDAY. OUT
AHEAD OF THESE FEATURES...WEST/NORTHWEST WINDS WILL LIKELY
INCREASE TO THE 20-25KT RANGE BY EARLY FRIDAY AFTERNOON...WITH
HAZARDOUS CONDITIONS FOR SMALL CRAFT BECOMING LIKELY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 7 PM
     THURSDAY.

&&

$$

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