Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 251403
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
903 AM CDT FRI JUL 25 2014

.DISCUSSION...
324 AM CDT

SYNOPSIS...A TRICKY UNSETTLED FORECAST IS EXPECTED TODAY THROUGH
SUNDAY. THEN THINGS QUIET DOWN FOR THE BEGINNING OF THE WORK WEEK.
SATURDAY WILL BE THE WARMEST DAY IN THE FORECAST WITH HIGHS NEAR
90.  TEMPS THEN FALL TO BELOW NORMAL SUNDAY AND SLOWLY BEGIN TO
CLIMB BACK TO NEAR 80 BY LATE NEXT WEEK.

TODAY AND TONIGHT...
AN UPPER LEVEL HIGH IS OVER THE SOUTHWEST U.S. AND SOUTHERN PLAINS
WHILE LOW PRESSURE IS OVER THE ALBERTA/SASKATCHEWAN BORDER.  THE
HIGH WILL SLOWLY RETROGRADE THROUGH MONDAY AFTERNOON TO OVER THE SW
U.S. WHILE THE LOW PASSES OVER LAKE MICHIGAN SUNDAY EVENING.  AT THE
SURFACE HIGH PRESSURE IS OVER THE OHIO RIVER VALLEY AND IT WILL MOVE
OFF THE ATLANTIC COAST TONIGHT.  THERE ARE TWO SURFACE LOWS...ONE
OVER THE NORTHERN PLAINS AND THE SECOND CO-LOCATED WITH THE UPPER
LEVEL LOW OVER THE ALBERTA/SASKATCHEWAN BORDER.

CONVECTION IS ONGOING OVER WEST CENTRAL MINNESOTA AND IOWA VERY
EARLY THIS MORNING. THE STORMS WILL BE MOVING INTO A MORE STABLE
ENVIRONMENT AND THE LOW LEVEL JET WILL ALSO BE WEAKENING AS IT
PUSHES EAST. THERE IS HIGH CONFIDENCE THAT THE STORMS OVER IOWA WILL
WEAKEN AS THEY APPROACH THE CWA...BUT EXPECTING SHOWERS AND A COUPLE
OF STORMS TO REACH THE I-39 CORRIDOR BY MID MORNING. SOME GUIDANCE
MEMBERS SUGGEST SHOWERS AND STORMS COULD LINGER INTO THE MID
AFTERNOON HOURS BUT THINKING THEY WILL DISSIPATE BY THE EARLY
AFTERNOON.

HIGH CLOUDS WILL BE OVERHEAD AND MAY LIMIT HEATING A BIT...AS SUCH
LEFT HIGH TEMPS TODAY IN THE UPPER 70S.

MULTIPLE ROUNDS OF STORMS ARE EXPECTED WITH THE SECOND ROUND
SPREADING SOUTH THIS EVENING. THE LOW OVER THE PLAINS WILL WEAKEN AS
IT PUSHES EAST AND FORM AN OPEN TROUGH. THE LOWS WARM FRONT WILL
APPROACH THE REGION TONIGHT AND EXPECTING STORMS AHEAD OF IT. THE
NOSE OF THE LOW LEVEL JET WILL ALSO BE OVER NORTHWEST IL THIS
EVENING PROVIDING ADDITIONAL LIFT.  CAPE WILL BE LIMITED WITH
MODEL SOUNDINGS SHOWING SHALLOW AREAS OF CAPE AT 1000 J/KG OR LESS.
PWAT VALUES WILL BE AROUND 1.9 INCHES SO TORRENTIAL DOWNPOURS ARE
THE MOST LIKELY HAZARD.

SATURDAY...
THE PLAINS LOW/TROUGH MOVES OVER THE MIDWEST WITH SATURDAY
HAVING THE BEST CHANCE FOR SEVERE WEATHER ESPECIALLY SOUTH OF I-88.
PWAT VALUES REMAIN HIGH AROUND 1.8 INCHES IN THE MORNING AND THEN
INCREASE TO 2-2.3 INCHES SOUTH OF I-80 SATURDAY AFTERNOON.  CAPE
VALUES WILL BE MUCH MORE HEALTHY IN THE 3000 J/KG RANGE ESPECIALLY
ALONG AND SOUTH OF THE I-80 CORRIDOR.  EXPECTING STORMS TO FIRE
ALONG THE LOWS COLD FRONT SATURDAY AFTERNOON AND EVENING WITH THE
CHANCES OF SHOWERS AND STORMS INCREASING AS YOU HEAD SOUTH.  SOME OF
THESE STORMS MAY BE SEVERE WITH TORRENTIAL DOWNPOURS.  HAIL AND WIND
LOOK TO BE THE MAIN SEVERE THREATS.

SATURDAY WILL FEEL UNPLEASANT TO MANY WITH HIGHS IN THE UPPER 80S
AND HIGH DEWPOINTS.  MAX HEAT INDICES WILL BE IN THE 90S...WITH MID
TO UPPER 90 HEAT INDICES EXPECTED SOUTH OF I-80.

SUNDAY...
THE LOW OVER CANADA DRIFTS SOUTHEAST MOVING OVER WISCONSIN SUNDAY.
ADDITIONAL THUNDERSTORMS ARE POSSIBLE NORTH OF THE I-80
CORRIDOR...WITH THE BEST CHANCES ALONG THE IL/WI STATE LINE. THE
STORMS PUSH EAST OF THE CWA IN THE EVENING. COOLER AIR ASSOCIATED
WITH THE LOW ALSO SPREAD SOUTH WITH HIGHS ON SUNDAY ONLY EXPECTED TO
GET INTO THE LOW TO MID 80S.  OVERNIGHT LOWS WILL BE AROUND
60...EXCEPT FOR DOWNTOWN WHICH WILL BE IN THE LOW 60S.

MONDAY THROUGH THURSDAY...
WE REMAIN UNDER THE UPPER LEVEL TROUGH THROUGH NEXT WEEK WITH A
SURFACE HIGH MOVING OVER THE REGION BY MID WEEK.  THERE ARE
OCCASIONAL CHANCES OF SHOWERS AND STORMS BUT NONE OF THOSE CHANCES
LOOK ALL THAT IMPRESSIVE AT THIS POINT.  THE BIGGER STORY WILL BE
ANOTHER EXTENDED PERIOD OF BELOW NORMAL TEMPS...ALTHOUGH
TEMPERATURES WILL BE SLOWLY RISING THROUGH THE END OF THE FORECAST
PERIOD.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* CHANCE FOR SCATTERED MAINLY LIGHT SHRA TODAY AND EARLY THIS EVE.

* CHANCE FOR TSRA...MAINLY TONIGHT.

//DISCUSSION...UPDATED 12Z...

MOIST ADVECTION ALOFT ACROSS IA/NW IL/WI CONTINUES TO SPRING
SCATTERED SHOWERS WITH A FEW STORMS EARLY THIS MORNING. THE MAIN
DRIVING UPPER DISTURBANCE IS IN CENTRAL IA AND WILL CONTINUE TO
MOVE SOUTHEAST. IMMEDIATELY EAST OF THIS SHOULD BE THE MORE
WIDESPREAD SHOWER/STORM ACTIVITY...WITH ONLY ISOLATED/SCATTERED
FURTHER NORTHEAST NEAR THE CHICAGOLAND TAF SITES.

WHILE THE UPPER DISTURBANCE MOVES BEYOND THE AREA IN THE
AFTERNOON...THERE WILL STILL BE MOIST ADVECTION ALONG WITH THE
APPROACH OF A SURFACE TROUGH...SO CANNOT RULE OUT SOME SHRA/TSRA
ACTIVITY. HOWEVER OVERALL SUPPORT IS LOW AND THUS HAVE TAFS MAINLY
DRY IN THE AFTERNOON. THE MORE FAVORABLE CHANCES FOR PRECIP WILL
ARRIVE AFTER DARK AS THE NEXT UPPER DISTURBANCE MOVES ACROSS THE
AREA AND INTO A VERY MOIST ENVIRONMENT. CONTINUE TO MENTION
PROB30S FOR TSRA DURING THE MID/LATE EVE INTO EARLY OVERNIGHT.
SOME GUIDANCE DOES INDICATE MVFR CONDITIONS IN THE IMMEDIATE WAKE
OF THIS AND BELIEVE IF IT DOES RAIN WITH DIMINISHING FLOW LATE
TONIGHT THEN THERE COULD VERY WELL BE SOME LOWERED VISBYS/CIGS
INTO EARLY SATURDAY MORNING.

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* LOW IN ANY RAIN AT THE AIRPORTS TODAY...HOWEVER IF IT OCCURS IT
  WOULD BE LIGHT AND VFR.

* MEDIUM IN WINDS.

* LOW IN TSRA OCCURRING TONIGHT. MEDIUM IN TIMING IF IT WERE TO
  OCCUR.


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

SATURDAY NIGHT...SMALL CHANCE OF TSRA.
SUNDAY...CHANCE OF TSRA.
MONDAY...VFR LIKELY. STRONG NORTH-NORTHEAST WINDS.
TUESDAY...VFR.
WEDNESDAY-THURSDAY...SLIGHT CHANCE OF TSRA.

MTF

&&

.MARINE...
228 AM CDT

SOUTHERLY FLOW WILL INCREASE OVER THE LAKE TODAY AS HIGH PRESSURE
SCOOTS EASTWARD FROM THE OHIO RIVER VALLEY. THE SURFACE TROUGH
LEADING TO THE INCREASE IN WINDS WILL ARRIVE EARLY
SATURDAY...HOWEVER WEAKEN TO THE POINT WHERE IT WILL NOT SHIFT THE
WINDS MUCH IF ANY FROM THE SOUTH-SOUTHWEST. THE LOW PRESSURE
DRIVING THIS TROUGH WILL EVOLVE OVER THE LAKE ON SUNDAY TURNING
WINDS NORTHERLY AND DRIVING A SHARP INCREASE IN SPEEDS SUNDAY
NIGHT AND PERSISTING INTO MONDAY. FOR JULY STANDARDS THESE WIND
SPEEDS ONCE AGAIN WILL BE QUITE STRONG WITH EVEN POSSIBLY SOME
GALE FORCE NORTHERLY GUSTS LATE SUNDAY NIGHT INTO MONDAY MORNING.
WITH ONCE AGAIN A LONG FETCH WAVES SHOULD REACH HEIGHTS OF OVER 6
FT OVER MUCH OF THE LAKE WITH EVEN POSSIBLY UP TO 10 FT AGAIN
ACROSS THE FAR SOUTH...PRIMARILY NEAR THE INDIANA SHORE.

MTF

&&

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

$$

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