Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 281950
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
250 PM CDT FRI AUG 28 2015

.SHORT TERM...

TONIGHT AND SATURDAY...

250 PM...FORECAST CONCERNS INCLUDE PRECIP COVERAGE/TIMING AND
RAINFALL AMOUNTS.

LOW PRESSURE OVER WESTERN IOWA WILL SLOWLY MOVE EAST TONIGHT AND
EVENTUALLY DISSIPATE OVER NORTHERN ILLINOIS SATURDAY. FIRST WAVE OF
PRECIP IS GENERALLY LIFTING NORTHEAST INTO SOUTHERN WISCONSIN AND
THE MODELS SEEM TO HAVE THIS HANDLED FAIRLY WELL WITH THE HRRR ALSO
SHOWING JUST ISOLATED SHOWERS/SPRINKLES INTO EARLY THIS EVENING AND
MAINLY ACROSS NORTHWEST AND NORTHERN IL. ADDITIONAL PRECIP IS
EXPECTED TO DEVELOP LATER THIS EVENING AND SPREAD NORTHEAST
OVERNIGHT INTO SATURDAY MORNING. THIS PRECIP WILL ALSO BE FOCUSED
ACROSS NORTHWEST/NORTHERN IL...INTO SOUTHERN WI. MODEL QPF AMOUNTS
NEAR THE IL/WI STATE LINE ARE IN THE 1 TO 1.5 INCH RANGE. THESE
AMOUNTS HAVE BEEN CONSISTENT BETWEEN RUNS AND VARIOUS MODELS SO IT
IS LIKELY SOME AREAS WILL SEE OVER AN INCH OF RAIN. HOWEVER...THESE
AMOUNTS APPEAR TO DROP OFF QUICKLY BETWEEN I-88 AND I-80 WITH MUCH
OF THE SOUTHEAST THIRD OR HALF OF THE CWA POSSIBLY STAYING DRY INTO
SATURDAY MORNING. INSTABILITY IS LIMITED AND LIGHTNING HAS BEEN
CONFINED TO THE STRONGEST STORMS/CONVECTION. THUNDER IS CERTAINLY
POSSIBLE TONIGHT BUT OVERALL COVERAGE SHOULD BE LIMITED AND HELD
SLIGHT CHANCE MENTION OF THUNDER TO HIGHER POP AREAS.

AFTER THE MAIN AREA OF RAIN MOVES NORTHEAST SATURDAY MORNING...
PRECIP ACROSS THE REST OF THE CWA WILL BE MORE SCATTERED...OR
ISOLATED...INTO THE LATE MORNING/EARLY AFTERNOON. APPEARS THERE
COULD BE NEW DEVELOPMENT IN THE EARLY/MID AFTERNOON BUT COVERAGE
POSSIBLY STILL JUST SCATTERED. THUS DIDN/T MAKE TOO MANY CHANGES
FROM CURRENT POPS IN THE 40-50 PERCENT RANGE.

TEMPS WILL ONLY SLOWLY FALL INTO THE LOWER/MID 60S TONIGHT AND HIGHS
ON SATURDAY WILL BE DEPENDENT ON PRECIP COVERAGE AND CLOUD COVER.
CURRENT FORECAST OF MID 70S NORTH TO LOWER 80S SOUTHEAST WILL
NEED SOME SUN TO OCCUR. SOUTHEASTERLY WINDS WILL KEEP THE IL SHORE
A BIT COOLER. CMS

&&

.LONG TERM...
344 AM CDT

SUNDAY THROUGH THURSDAY...

END OF THE WEEKEND INTO THE START OF NEXT WEEK WILL SEE THIS
MID/UPPER TROUGH SLOWLY EXITING TO THE EAST...WITH CLOUDS AND
PRECIP CHANCES LIKEWISE EXITING DURING THE DAY SUNDAY. GUIDANCE
VARIES TO THE EVOLUTION OF THIS EXITING SYSTEM BUT LIKELY SCENARIO
FOR OUR AREA WILL BE FOR UPPER LEVEL RIDGING WITH WEAKER FLOW
ALOFT. CONDITIONS WILL LIKELY BE ON THE DRY SIDE THROUGH EARLY
NEXT WEEK...OUTSIDE OF SOME POSSIBLE AFTERNOON THUNDERSTORMS ON
TUESDAY DUE TO INCREASING MOISTURE/INSTABILITY...WHILE A WARMING
TREND CONTINUES.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* WIND SHIFT TO EAST-SOUTHEASTERLY LIKELY EARLY THIS EVENING.
* CHANCE OF SHRA/SLIGHT CHANCE OF TS TONIGHT INTO SAT MORNING.
  SLIGHTLY BETTER CHANCE OF THUNDER SATURDAY AFTERNOON.

KJB

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

AN ATMOSPHERIC DISTURBANCE...CURRENTLY DRIVING AN AREA OF SHOWERS
AND EMBEDDED STORMS OVER IOWA...WILL GRADUALLY SHIFT EASTWARD
TONIGHT. HOWEVER...IT APPEARS THE MAIN FOCUS FOR SHOWERS AND ANY
STORMS MAY LARGELY REMAIN NORTH OF THE EASTERN TERMINALS...ACROSS
FAR NORTHERN ILLINOIS AND INTO WISCONSIN. BETTER CHANCES OF MORE
SUBSTANTIAL SHOWERS LOOKS TO ENTER THE PICTURE AFTER DAYBREAK
SATURDAY...AND CONTINUING AT TIMES INTO THE AFTERNOON. IT APPEARS
THE THUNDER THREAT WILL BE LOW WITH MUCH OF THIS ACTIVITY.
HOWEVER...THERE WILL BE A SLIGHT BETTER CHANCE OF THUNDER SUNDAY
AFTERNOON AS A FRONTAL ZONE SAGS SOUTHEASTWARD OVER THE AREA.
GIVEN THIS...I HAVE OPTED TO ADD A PROB30 FOR A PERIOD OF THUNDER
LATER SATURDAY AFTERNOON AT THE END OF THE 30 HOUR ORD TAF.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH WITH WIND SHIFT TO SOUTHEAST THIS EVENING...LOW WITH PRECISE
  SPEEDS AND TIMING.
* MEDIUM WITH PRECIP CHANCES/TIMING...ESPECIALLY SATURDAY
  MORNING/EARLY AFTERNOON.
* LOW WITH THREAT OF THUNDER DURING THE PERIOD.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

KJB

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

SATURDAY NIGHT...SLIGHT CHANCE OF TSRA...OTHERWISE VFR.

SUNDAY...VFR. NORTHEAST WINDS.

MONDAY THROUGH THURSDAY...VFR. SOUTHERLY WINDS...POSSIBLE
AFTERNOON WIND SHIFTS TO EASTERLY WITH LAKE BREEZES EACH
AFTERNOON.

IZZI

&&

.MARINE...
157 AM CDT

FAIRLY TYPICAL SUMMER PATTERN LIKELY TO PERSIST THROUGH THE
UPCOMING WEEK WITH GENERALLY NO SIGNIFICANT WINDS/WAVES
ANTICIPATED. WEAK SURFACE LOW OVER THE CORN BELT WILL TRACK SLOWLY
EAST INTO NORTHERN ILLINOIS/SOUTHERN WISCONSIN THROUGH SATURDAY
BEFORE DISSIPATING. THE MAIN RESULT WILL BE A BACKING OF WINDS TO
EASTERLY OVER SOUTHERN PORTIONS OF THE LAKE LATER TODAY INTO THIS
EVENING BEFORE VEERING SOUTHERLY AGAIN LATE TONIGHT AND FRESHENING
UP JUST A BIT...BUT LIKELY LESS THAN 20KT.

IZZI

&&

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

$$

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