Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 281724
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1224 PM CDT FRI AUG 28 2015

.SHORT TERM...
344 AM CDT

THROUGH SATURDAY NIGHT...

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH PRECIP TRENDS LATER
TODAY INTO TONIGHT...AND INTO THE WEEKEND.

LATEST SATELLITE IMAGERY DEPICTING UPPER LEVEL WITH SEVERAL VORT
LOBES ROUNDING THE BASE...PROGRESSING EAST THROUGH THE NORTHERN
PLAINS EARLY THIS MORNING. ALTHOUGH ASSOCIATED PRECIP REMAINS WELL
WEST OF THE CWA AT THIS TIME...FAIRLY DENSE MID/HIGH LEVEL CLOUD
COVER ALREADY STRETCHING EAST INTO NORTHERN ILLINOIS. RADAR
IMAGERY SHOWING SOME WEAK RETURNS AT THIS TIME...HOWEVER...THIS IS
PICKING UP THESE CLOUDS WITH ANY PRECIP LIKELY NOT MAKING IT TO
THE SURFACE. HAVE MAINTAINED A DRY FORECAST EARLY THIS MORNING
THROUGH MIDDAY FOR THE ENTIRE CWA AS STRONGEST FORCING WITH THE
FIRST WAVE LIFTING EAST/NORTHEAST STAYING TO THE WEST/NORTHWEST.
SOME GUIDANCE IS TRYING TO HINT AT SOME STRAY LIGHT SHOWERS OVER
PORTIONS OF NORTHERN ILLINOIS THIS MORNING BUT WITH RATHER DRY LOW
LEVELS IN PLACE THIS MORNING...PER 00Z OBSERVED SOUNDINGS AND
LATEST FORECAST SOUNDINGS...THINK ANY FORCING OWING TO WEAK WAA
WILL NOT BE ABLE TO OVERCOME THIS DRIER AIR. DO BRING SLIGHT
CHANCE TO CHANCE POPS OVER FAR NORTHERN ILLINOIS BY MID TO LATE
AFTERNOON TODAY AS THIS MID/UPPER LEVEL TROUGH AND ASSOCIATED
ENERGY MOVE CLOSER TO THE CWA...BUT ONCE AGAIN FEEL THAT THE BEST
FORCING WILL STILL BE TO THE NORTH AND NORTHWEST. HAVE MAINTAINED
SHOWERS AND DID NOT INCLUDE THUNDER...WITH INSTABILITY STAYING TO
THE WEST OF THE CWA. HIGH TEMPERATURES WILL BE LIMITED TODAY DUE
TO THE MID/HIGH CLOUDS IN THE 70S...AND DID LOWER THEM SLIGHTLY TO
THE LOW/MID 70S ACROSS NORTHERN ILLINOIS WHERE MORE DENSE CLOUDS
AND PRECIP WILL LIKELY BE LOCATED.

HIGHER CHANCES FOR PRECIP WILL ARRIVE LATER THIS EVENING AND
ESPECIALLY OVERNIGHT TONIGHT FOR MOST OF NORTHERN ILLINOIS...AS
SHORTWAVE ENERGY ON THE BACKSIDE OF THIS TROUGH AND ATTENDANT
SURFACE REFLECTION WILL PUSH INTO NORTHERN ILLINOIS. DID MAINTAIN
SLIGHT CHANCE FOR THUNDER WITH THE LIKELY/CAT POPS OVER NORTHERN
ILLINOIS TONIGHT...DESPITE LACKING INSTABILITY. STRENGTHENING LLJ
AND STRONGER FORCING COULD OFFSET THIS LACKING INSTABILITY AND
ALLOW THUNDER...SIMILAR TO WHAT IS OCCURRING NOW OVER IOWA. EAST
CENTRAL ILLINOIS AND NORTHWEST INDIANA WONT OBSERVE THE HIGHER
CHANCES FOR SHOWERS/THUNDER UNTIL SATURDAY MORNING AND SATURDAY AS
THIS TROUGH PUSHES THROUGH. CONFIDENCE WITH OVERALL PRECIP TRENDS
ON SATURDAY AND SATURDAY NIGHT DOES LOWER WITH GUIDANCE VARYING TO
THE EXTENT AND LOCATION OF BEST FORCING. DID MAINTAIN HIGH CHANCE
POPS FOR SHOWERS ACROSS MUCH OF THE CWA SATURDAY AND THEN TOOK
THESE CHANCE POPS EASTWARD THROUGH TIME DURING SATURDAY NIGHT.
INSTABILITY WILL TRY TO INCREASE ON SATURDAY...BUT STILL THINK IT
WONT BE HIGH ENOUGH TO WARRANT ANY WORDING OTHER THAN SLIGHT
CHANCE.

RODRIGUEZ

&&

.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 18Z...

* 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 18Z...

* 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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