Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 291727
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1227 PM CDT WED JUL 29 2015

.UPDATE...
1106 AM CDT

FOR MORNING UPDATE...

MID-MORNING SURFACE ANALYSIS DEPICTS COLD FRONT PUSHING THROUGH THE
EASTERN PORTION OF THE CWA...APPROXIMATELY ALONG OR JUST EAST OF A
BURNS HARBOR INDIANA TO CHAMPAIGN IL LINE AT 1530Z. SOME PATCHY
LOWER CLOUDS LINGER WITHIN AND JUST BEHIND THE FRONTAL ZONE...WITH
SURFACE DEW POINTS POOLED IN THE MID-70S...THOUGH HUMIDITY
DECREASING 75-100 MILES BEHIND THE FRONT WITH DEW POINTS DROPPING
INTO THE MID-UPPER 50S OVER NORTHWEST IL. THIS DRIER AIR MASS WILL
CONTINUE TO SPREAD INTO THE FORECAST AREA INTO THIS AFTERNOON...
MAKING FOR MORE COMFORTABLE CONDITIONS DESPITE AIR TEMPS STILL
EXPECTED TO RISE INTO THE MID-UPPER 80S UNDER MOSTLY SUNNY SKIES AND
BREEZY NORTHWEST WINDS 15-20 MPH.

ACROSS THE FAR SOUTHEAST TIER OF COUNTIES WHERE THE FRONT WILL
CONTINUE TO PUSH EAST-SOUTHEAST INTO THE EARLY AFTERNOON HOURS...
THERE IS STILL THE POTENTIAL FOR AN ISOLATED SHOWER OR THUNDERSTORM
WHERE MOIST LOW LEVELS PROMOTE DESTABILIZATION...THOUGH HAVE LOWERED
POPS TO 20 PERCENT OR LESS INTO EARLY AFTERNOON THEN TRENDED DRY AS
FRONT CLEARS THE AREA.

RATZER

&&

.SHORT TERM...
332 AM CDT

THROUGH TONIGHT...

ONGOING T-STORM ACTIVITY OVER EASTERN CWA ASSOCIATED WITH PRE
FRONTAL TROUGH SHOULD CLEAR THE AREA PRIOR TO SUNRISE. ATTENTION
FOR THE MORNING HOURS WILL TURN WEST TOWARD THE SYNOPTIC FRONT AND
THE POTENTIAL FOR ANY SHOWER AND POSSIBLE T-STORM ACTIVITY WITH
IT. DESPITE RATHER PALTRY APPEARANCE OF PRECIP WITH FRONT AT THIS
TIME...CERTAINLY LESS THAN GUIDANCE WOULD SUGGEST...AM STILL
CONCERNED THAT SOME DEVELOPMENT COULD TAKE PLACE GIVE THE
MAGNITUDE OF MOISTURE AND FORCING WITH FRONT. ANY SCTD SHOWERS AND
POSSIBLE THUNDER SHOULD CLEAR MAJORITY OF THE CWA BY NOON...BUT
SOME ACTIVITY COULD LINGER OR REDEVELOP SOUTH OF KANKAKEE RIVER IN
NW INDIANA EARLY THIS AFTERNOON.

IN WAKE OF THE FRONT DEWPOINTS WILL BEGIN TO TUMBLE...MOST
NOTICEABLY OVER NW HALF OF THE CWA THROUGH MID AFTERNOON WITH
NOTICEABLY LESS HUMID AIR ARRIVING IN CHICAGO METRO AREA BY MID-
LATE AFTERNOON AND IN NW INDIANA EARLY THIS EVENING. AIR MASS NOT
THAT MUCH COOLER BEHIND THE FRONT SO HIGHS SHOULD ONCE AGAIN CLIMB
WELL INTO THE 80S TO PERHAPS NEAR 90 IF THERE IS ENOUGH SUNSHINE.

IZZI

&&

.LONG TERM...
332 AM CDT

THURSDAY THROUGH TUESDAY...

SUNNY AND VERY WARM WEATHER IS ON TAP FOR THURSDAY WITH
COMFORTABLE HUMIDITY LEVELS BY LATE JULY STANDARDS. FRIDAY LOOKS
TO BE A CARBON COPY OF THURSDAY WITH PERHAPS JUST A FEW MORE
CLOUDS BUT STILL A LOT OF SUNSHINE. PROGGED 925MB TEMPS IN THE
LOW-MID 20S CELSIUS SUPPORTS HIGHS IN THE UPPER 80S TO LOWER 90S
AND GIVEN SUCH LOW DEWPOINTS AND AMPLE SUNSHINE HAVE LEANED CLOSER
TO WARMER GUIDANCE BOTH PERIOD.

WEAK COLD FRONT SLIDES THROUGH FRIDAY NIGHT AND CANNOT TOTALLY
RULE OUT SOME ISOLATED CONVECTION WITH IT...THE FACT ITS COMING
THROUGH AT DIURNALLY UNFAVORABLE TIME OF DAY AND WITH NO RETURN
MOISTURE WORK AGAINST INTRODUCING POPS AT THIS TIME. AFTER
COORDINATION WITH MKX IT WAS DECIDED TO KEEP POPS IN THE 10-15
PERCENT RANGE IN THE GRIDS...BELOW MENTIONABLE THRESHOLD IN THE
TEXT FORECAST FOR NOW. A COUPLE OF MORE WEAK NORTHWEST FLOW FRONT
ARE SLATED TO MOVE ACROSS THE CWA SUNDAY AFTERNOON AND TUESDAY
AFTERNOON...BOTH OF WHICH COULD BRING SOME SCATTERED STORMS BUT
NEITHER LOOKING LIKE BIG TIME WASHOUTS FROM WIDESPREAD RAIN
EITHER. FOR NOW HELD ONTO MODEL CONSENSUS LOWER END CHANCE POPS
FOR BOTH FRONTS. NO SIGNIFICANT COOL DOWNS EXPECTED WITH EITHER
FRONT AT THIS TIME.

IZZI

&&

.AVIATION...

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

* NW WINDS GUSTING TO ARND 20 KT THROUGH THE EARLY EVENING.

* NW WINDS GUSTING TO 20 TO 25 KT FROM MID MORNING THROUGH THE
  LATE AFTN THURSDAY.

JEE

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

HIGH PRESSURE CURRENTLY OVER THE PLAINS WILL SPREAD OVERHEAD
TONIGHT WITH CLEAR SKIES AND GUSTY NW WINDS DIMINISHING TO ARND
8 KT. CLEAR SKIES CONTINUE TOMORROW ALLOWING AMPLE MIXING TO TAKE
PLACE SO THINKING WE WILL SEE NW WINDS GUSTING AGAIN TO ARND 20-25
KT BY THE LATE MORNING. SOME GUIDANCE MEMBERS FEATURE SLIGHTLY
HIGHER WINDS...BUT THINKING WE WILL NOT MIX THAT MUCH.

JEE


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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

* THURSDAY NIGHT THROUGH SATURDAY...DRY/VFR. WESTERLY WINDS.
* SUNDAY AND MONDAY...CHANCE OF TSRA. WESTERLY WINDS.
* TUESDAY...SLIGHT CHANCE OF TSRA. NORTH/NORTHEAST WINDS.

&&

.MARINE...

233 AM...DEEP LOW PRESSURE OVER MANITOBA WILL MOVE NORTHEAST TO
HUDSON BAY THURSDAY AS A TRAILING COLD FRONT MOVES ACROSS THE LAKE
TODAY. SOUTHERLY WINDS 15-25 KTS OVER THE NORTHERN PORTION OF THE
LAKE WILL REMAIN AT THOSE SPEEDS BUT ONLY GRADUALLY TURN WESTERLY
BY THIS EVENING. THIS LOW WILL REMAIN OVER HUDSON BAY THROUGH THE
END OF THE WEEK...WHILE SLOWLY WEAKENING. HIGH PRESSURE WILL BUILD
ACROSS THE CENTRAL PLAINS TODAY AND TONIGHT AND GRADUALLY SPREAD
INTO THE OHIO VALLEY THURSDAY AND FRIDAY. THIS WILL MAINTAIN A
WESTERLY FLOW ACROSS LAKE MICHIGAN WITH PERIODS OF 15-25 KTS
POSSIBLE INTO THURSDAY. THE GRADIENT WILL THEN RELAX WITH SPEEDS
DIMINISHING. A WEAK TROUGH/FRONT WILL MOVE ACROSS THE LAKE FRIDAY
NIGHT...BRIEFLY TURNING WINDS TO THE NORTHWEST BEFORE TURNING BACK
TO THE SOUTHWEST SATURDAY. CMS

&&

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

$$

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