Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280943
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
443 AM 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 09Z...

* WIND SHIFT TO EASTERLY LIKELY LATE FRIDAY AFTERNOON
* CHANCE OF -SHRA/SLIGHT CHANCE OF TS FRIDAY NIGHT

IZZI

//DISCUSSION...UPDATED 09Z...

A FEW SPRINKLES BRIEF LIGHT SHRA COULD IMPACT MAINLY RFD DURING
PREDAWN HOURS.

IZZI

UPDATED 06Z...

VFR WITH LIGHT WINDS THROUGH FRIDAY MORNING AS SLOW MOVING STORM
SYSTEM OVER NEBRASKA/WESTERN IOWA SLOWLY MOVES TOWARD REGION.
PRESSURE FALLS IN ADVANCE OF THIS SYSTEM SHOULD CAUSE INITIALLY
SOUTH-SOUTHWEST WINDS FRIDAY TO BACK MORE EASTERLY WITH LAKE
INFLUENCE LIKELY RESULTING IN A MORE DRAMATIC SHIFT TO EASTERLY
FOR CHICAGO TERMINALS. CERTAINLY PLAUSIBLE THAT THERE COULD BE A
PERIOD OF 10-12KT EASTERLY WINDS...PARTICULARLY WITHIN AN HOUR OR
SO OF THE WIND SHIFT...BUT CLOUD COVER AND WEAKER THERMAL GRADIENT
LEAD ME TO BELIEVE THAT IF EASTERLY WINDS REACH PREVAILING 10KT IT
WON`T LAST LONG OR MORE LIKELY JUST A PERIOD OF A COUPLE HOURS OF
OCNL 10KT WINDS. THREAT OF SHOWERS AND PERHAPS ISOLATED TSRA WILL
SLOWLY INCREASE FROM THE WEST/NORTHWEST FRIDAY NIGHT.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE IN WIND SHIFT TO EAST LATE FRIDAY...LOW-MEDIUM
  CONFIDENCE IN SPEEDS AND PRECISE TIMING
* MEDIUM CONFIDENCE IN PRECIP CHANCES/TIMING
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

IZZI

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

SATURDAY...A FEW PERIODS OF SHRA PROBABLE AND ASSOCIATED VSBY
IMPACTS. SLIGHT CHANCE OF TSRA. VFR CIGS LIKELY.

SUNDAY...PRIMARILY VFR...SLIGHT CHANCE OF SHRA. NORTH TO NORTHEAST
WINDS.

MONDAY THROUGH WEDNESDAY...VFR. AFTERNOON WIND SHIFTS TO EAST-
SOUTHEAST POSSIBLE.

RC

&&

.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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