Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 270037
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
737 PM CDT SAT JUL 26 2014

.DISCUSSION...
736 PM CDT

OVERALL THREAT OF SEVERE WEATHER HAS DIMINISHED IN THE NEAR TERM
AND FOR THE REMAINDER OF THE EVENING...WITH CHANCES APPEARING LOW
FOR ADDITIONAL THUNDERSTORM DEVELOPMENT OVERNIGHT.

LATEST RADAR IMAGERY DEPICTING REMAINING SHOWERY ACTIVITY EXITING
THE SOUTHEAST CWA AS COMPLEX OVER CENTRAL ILLINOIS AND INDIANA
CONTINUES TO PROGRESS TO THE EAST...LEAVING THE CWA AND MUCH OF
THE REGION TO THE NORTH AND NORTHWEST DRY AT THIS TIME. LACK OF
ANY REAL GOOD FOCUS THIS EVENING AND A STRONG CAP STILL IN PLACE
OVER LINGERING STATIONARY BOUNDARY WILL LIMIT FURTHER
STRONG/SEVERE THUNDERSTORM DEVELOPMENT FOR THE REST OF THE
EVENING. DID ADJUST POPS TO KEEP LOW CHANCE/SLIGHT CHANCE POPS FOR
SHOWERS AND THUNDERSTORMS MAINLY FOR THE SOUTHERN CWA WITH THIS
LINGERING BOUNDARY STILL IN PLACE...BUT WITH ANY FURTHER
DEVELOPMENT MORE THAN LIKELY REMAINING MORE SHOWERY. ALSO GOING TO
ADD A SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS ACROSS THE
NORTHERN CWA VERY LATE TONIGHT INTO EARLY SUNDAY MORNING. LARGE
VORT MAX ENTERING THE FAR NORTHERN PLAINS WILL SINK SOUTHEAST
THROUGH THE UPPER MIDWEST THROUGH SUNDAY MORNING. VORT LOBE OUT
AHEAD OF IT WILL SWING SOUTHEAST TO EASTERN IOWA AND SOUTHWEST
WISCONSIN AND COULD HELP THUNDERSTORM DEVELOPMENT IN THESE
AREAS...ESPECIALLY ALONG COLD FRONTAL BOUNDARY. CONFIDENCE OF
COVERAGE AND INTENSITY IS LOW AT THIS TIME BUT THERE IS A
POSSIBILITY FOR SOME OF THIS DEVELOPMENT TO REACH FAR NORTHERN
ILLINOIS BY VERY LATE TONIGHT AND EARLY SUNDAY MORNING. IF THIS
WERE TO OCCUR...WOULD EXPECT THAT HEAVY DOWNPOURS WOULD BE THE
MAIN THREAT.

VERY MOIST CONDITIONS IN A RELAXED SURFACE PATTERN WILL BE
CONDUCIVE FOR FOG DEVELOPMENT TONIGHT ESPECIALLY AS WINDS FURTHER
DIMINISH...AND SO HAVE ADDED MENTION OF FOG FOR THE ENTIRE CWA
TONIGHT.

RODRIGUEZ

&&

.PREV DISCUSSION...

246 PM...FORECAST CONCERN AND CHALLENGE REMAINS CONVECTIVE TRENDS
THROUGH SUNDAY MORNING.

18Z SOUNDINGS FROM ILX AND DVN THIS AFTERNOON SHOW STRONG CAPPING
IN PLACE ACROSS THE AREA. RADAR IMAGERY SHOWS LIGHT RETURNS WHICH
ARE LIKELY ELEVATED SHOWERS/WEAK CONVECTION ROOTED FROM 800MB...
ABOVE THE CAP. NOT EXPECTING MUCH ACTIVITY ACROSS NORTHERN IL WITH
THIS CAP IN PLACE BUT ISOLATED SHOWERS/SPRINKLES WILL BE POSSIBLE.

THUNDERSTORMS OVER NORTHERN MO CONTINUE MOVING EAST AND INCREASING
IN COVERAGE BUT NOT MUCH ORGANIZATION YET. AS THIS ACTIVITY MOVES
EAST INTO THE MORE CAPPED AIR...IT MAY CONTINUE TO STRUGGLE TO
ORGANIZE INTO A SEVERE LINE/COMPLEX. THUS CONFIDENCE REGARDING
CONVECTIVE TRENDS ACROSS THE SOUTHERN CWA/CENTRAL IL/CENTRAL
INDIANA ARE DECREASING AT THE MOMENT. BUT WITH THE WARM FRONTAL
BOUNDARY NEARBY AND MID 70S DEWPOINTS POOLING SOUTH OF THE
FRONT...HAVE NOT MADE ANY CHANGES TO COVERAGE/TIMING. AND WHILE
SEVERE POTENTIAL REMAINS UNCERTAIN...SHOULD STORMS BECOME SEVERE
EARLIER THOUGHTS REMAIN ON TRACK FOR WIDESPREAD DAMAGING WINDS TO
BE THE MAIN THREAT...MAINLY SOUTH OF THE KANKAKEE RIVER.

THE GRADIENT MAY BECOME WEAK ENOUGH FOR LIGHT/CALM WINDS OVERNIGHT
ESPECIALLY OVER THE SOUTHERN HALF OF THE CWA. WHILE PRECIP
COVERAGE REMAINS UNCERTAIN...LOW LEVELS WILL REMAIN QUITE MOIST
AND FOG WILL BE POSSIBLE...AND WHERE ANY RAIN DOES FALL...COULD
BECOME LOCALLY DENSE.

A COLD FRONT WILL MOVE ACROSS THE AREA SUNDAY MORNING...LIKELY
MOVING EAST OF THE CWA BY 18Z. COULD BE ISOLATED/SCATTERED
THUNDERSTORMS ALONG/AHEAD OF THIS FRONT DURING THE MID MORNING
HOURS BUT WILL BE SHORT-LIVED WITH A PERIOD OF DRY CONDITIONS
EXPECTED MIDDAY/EARLY AFTERNOON POST FRONTAL. AS COOLER AIR
SPREADS ACROSS THE AREA...DIURNAL SHOWERS AND PERHAPS A FEW
THUNDERSTORMS WILL BE POSSIBLE MID/LATE SUNDAY AFTERNOON AND THIS
WOULD BE MOST LIKELY ACROSS NORTHERN IL. AS THIS COOLER AND DRIER
AIR ADVECTS INTO THE AREA...LOW LEVEL MIXING WILL BECOME QUITE
EFFICIENT. FORECAST SOUNDINGS SHOW 25-30 KTS IN THE MIXED LAYER
BY LATE AFTERNOON...THUS WINDY CONDITIONS ARE EXPECTED SUNDAY
AFTERNOON WITH WIND GUSTS AS HIGH AS 35 MPH.

A SECONDARY COLD FRONT WILL MOVE SOUTH ACROSS THE AREA SUNDAY
NIGHT USHERING IN EVEN COOLER AIR WITH HIGHS ON MONDAY ONLY IN THE
LOWER/MID 70S. A LARGE UPPER TROUGH WILL THEN REMAIN ACROSS MUCH
OF THE GREAT LAKES REGION AND EASTERN U.S. THROUGH THE END OF NEXT
WEEK. HIGH TEMPS WILL REMAIN BELOW NORMAL...GENERALLY IN THE MID/
UPPER 70S THROUGH THE END OF NEXT WEEK. IN ADDITION THERE WILL BE
AFTERNOON/EARLY EVENING CHANCES FOR ISOLATED SHOWERS/THUNDERSTORMS
JUST ABOUT EVERYDAY. CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* SOME FOG POSSIBLE OVERNIGHT...MVFR VSBY PROBABLE WITH A CHANCE
  OF IFR VSBY
* GUSTY WNW WINDS DEVELOP SUNDAY AFTERNOON
* SLIGHT CHANCE OF ISOLD SHRA OR TSRA SUNDAY

IZZI

//DISCUSSION...UPDATED 00Z...

DIMINISHING WINDS...CLEARING SKIES...AND VERY MOIST AIR MASS
FILTERING INTO THE AREA WILL SET THE STAGE FOR GROUND FOG TO
DEVELOP TONIGHT. THE MOST DENSE FOG SHOULD BE IN OUTLYING AREAS
BUT IFR CONDITIONS OR LOWER ARE A POSSIBILITY EVEN IN THE URBAN
AREAS. STRONG UPPER TROUGH WILL DIG SOUTHEAST INTO THE GREAT LAKES
REGION SUNDAY MORNING WITH INCREASING WINDS AFTER SUNRISE QUICKLY
MIXING OUT ANY FOG/VSBY EARLY SUNDAY MORNING. WINDS WILL REALLY
RAMP UP BY LATE MORNING/EARLY AFTERNOON SUNDAY AS BEHIND COLD
FRONT MOVING THROUGH THE AREA...GUSTS OF 25-30KT LOOK LIKE A GOOD
BET DURING THE AFTERNOON. NOT OUT OF THE QUESTION THAT THERE
COULD BE ISOLD SHRA OR EVENING TSRA AROUND SUNDAY...BUT EVEN IF
ANY FORM COVERAGE SHOULD BE LOW AND DURATION BRIEF IN ANY GIVEN
LOCATION SO NO REASON TO INCLUDE IN TERMINAL FORECAST AT THIS
TIME.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* MEDIUM-HIGH CONFIDENCE IN VSBY RESTRICTIONS DUE TO FOG TONIGHT
  BUT LOW CONFIDENCE IN HOW LOW VSBYS DROP
* HIGH CONFIDENCE IN OTHER FORECAST ELEMENTS

IZZI

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

MONDAY...VFR. MODERATELY STRONG NORTH-NORTHEAST WINDS.

TUESDAY THROUGH FRIDAY...PREDOMINANTLY VFR THROUGH THE PERIOD.

IZZI

&&

.MARINE...
230 PM CDT

AN ACTIVE PERIOD OF WEATHER IS SETTING UP FOR LAKE MICHIGAN FOR
THE NEXT FEW DAYS. A DIFFUSE AREA OF LOW PRESSURE OVER THE LAKE
THIS AFTERNOON WILL KEEP WINDS RELATIVELY LIGHT AND VARIABLE...BUT
A DEEPENING LOW PRESSURE SYSTEM DROPPING THROUGH THE UPPER
MISSISSIPPI VALLEY WILL LEAD TO STRENGTHENING SOUTHERLY WINDS
OVERNIGHT TONIGHT. THE LOW IS EXPECTED TO TRACK ACROSS CENTRAL
LAKE MICHIGAN LATE TONIGHT OR EARLY SUNDAY MORNING...DRAGGING A
STRONG COLD FRONT ACROSS THE LAKE AND TURNING WINDS NORTHERLY.
WINDS SHOULD QUICKLY INCREASE TO ARND 30 KT FOLLOWING THE LOW
PASSAGE AND FROPA AND DURING THE PERIOD OF STRONGEST COLD
ADVECTION...THE SEVERAL HOURS AFTER THE PASSAGE OF THE LOW AND
COLD FRONT...OCCASIONAL GALE FORCE GUSTS WILL BE POSSIBLE. WILL
ISSUE A SMALL CRAFT ADVISORY FOR THE NEAR SHORE WATERS FOR SUNDAY
MORNING THROUGH LATE MONDAY NIGHT FOR THE ILLINOIS NEARSHORE
WATERS AND SUNDAY MORNING THROUGH EARLY TUESDAY MORNING FOR THE
INDIANA WATERS AS WINDS AND WAVES WILL BOTH EXCEED ADVISORY
CRITERIA...WITH WAVES IN THE INDIANA NEAR SHORE WATERS REACHING AS
HIGH AS 7 TO 10 FT WITH OCCASIONAL HIGHER WAVES. A NORTHWESTERLY
TO NORTHERLY FETCH OVER THE ILLINOIS WATERS WILL KEEP WAVES A BIT
LOWER...BUT SHOULD EXCEED 4-5 FT BY THE END OF THE 5NM NEARSHORE
FETCH. HIGH PRESSURE BUILDING ACROSS CENTRAL PLAINS TO THE WESTERN
GREAT LAKES BY MONDAY AFTERNOON AND EVENING SHOULD ALLOW WINDS
AND WAVES TO SUBSIDE OVER THE LAKE. AS THE HIGH SETTLES INTO THE
OHIO VALLEY TUESDAY NIGHT AND WEDNESDAY...ANOTHER LOW PRESSURE
SYSTEM DROPPING SOUTHEAST THROUGH ONTARIO DRAGGING ANOTHER COLD
FRONT DOWN THE LAKE. THIS COMBINATION SHOULD KEEP MODEST WEST TO
NORTHWEST WINDS OVER THE LAKE THROUGH MIDWEEK. ANOTHER AREA OF
SPRAWLING HIGH PRESSURE IS FORECAST TO SPREAD ACROSS THE WESTERN
GREAT LAKES REGION BY LATE IN THE WEEK...BRING BACK LIGHT AND
VARIABLE WINDS AND LOW WAVES FOR LATE IN THE WEEK AND POSSIBLY
INTO NEXT WEEKEND.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...BEACH HAZARDS STATEMENT...INZ001-INZ002...NOON SUNDAY TO 5 AM
     TUESDAY.

LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...NOON SUNDAY TO 11
     PM MONDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...NOON SUNDAY TO 5
     AM TUESDAY.

&&

$$

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