Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 271407
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
907 AM CDT SUN JUL 27 2014

.DISCUSSION...
322 AM CDT

SYNOPSIS...ONE MORE DAY OF A DIFFICULT AND MESSY PATTERN THAT WILL
RESULT IN SHOWERS AND THUNDERSTORMS ACROSS THE REGION.  NO SEVERE
STORMS ARE EXPECTED.  TEMPERATURES FALL THIS AFTERNOON AND REMAIN
BELOW NORMAL THROUGH THE REST OF THE WEEK. WE DRY OUT MONDAY AND
THEN HAVE LOW CHANCES OF PRECIP TUESDAY THROUGH SATURDAY.

TODAY AND TONIGHT...
AN UPPER LEVEL LOW IS OVER NORTHERN MINNESOTA WHILE A LARGER LOW IS
OVER NORTHERN QUEBEC. A SHORTWAVE TROUGH IS ALSO OVER EASTERN IOWA
WITH CONVECTION OVER CENTRAL WI.  SPOTTY SHOWERS/SPRINKLES HAVE
SPROUTED OVER SOUTHEAST WI AND NOT EXPECTING MUCH ACTIVITY FROM
THOSE SPRINKLES.  ADDITIONAL MORE IMPRESSIVE CONVECTION HAS FIRED
ALONG A WEAK BOUNDARY OVER CENTRAL IL. MAY SEE A FEW STORMS SOUTH OF
A PERU TO RENSSELAER LINE EARLY THIS MORNING.

FOG IS PRESENT OVER MUCH OF THE FORECAST AREA THIS MORNING AS
WELL. CLOUD COVER IS EXPANDING FROM SOUTH TO NORTH AND VSBY
INCREASES AS THE CLOUDS MOVE OVERHEAD. AS SUCH WILL HOLD OFF ON A
DENSE FOG ADVISORY FOR NOW AND SEE HOW THE CLOUD COVER SPREADS
ACROSS THE REGION.

EXPECTING ADDITIONAL CONVECTION TO FIRE AHEAD OF THE SHORTWAVE THIS
MORNING AND MOVE INTO NORTH CENTRAL IL. INSTABILITY MAY BE
LIMITED...BUT SOME THUNDER SHOULD BE REALIZED BASED ON
OBSERVATIONAL TRENDS UPSTREAM. THE SHOWERS AND STORMS WILL PUSH
EAST INTO THE AFTERNOON AS THE SHORTWAVE MOVES THROUGH. A COLD
FRONT CURRENTLY ACROSS NW WI THROUGH CENTRAL IA WILL ALSO
TRANSVERSE THE REGION AHEAD OF THE UPPER LEVEL LOW. THE LOW WILL
SWING OVER THE LAKE THIS AFTERNOON AND EXPECTING ADDITIONAL
ISOLATED TO SCATTERED STORMS WITH THIS FEATURE. TODAY WILL NOT BE
A WASH OUT HOWEVER AND THERE SHOULD BE PLENTY OF DRY HOURS.
ISOLATED SHOWERS CONTINUE INTO THE EVENING AND THEN THE BACK SIDE
OF THE UPPER LEVEL TROUGH SLIDES SOUTH THROUGH THE REGION
OVERNIGHT CLEARING OUT THE CLOUDS.

GUSTY WINDS ARE EXPECTED...AT TIMES TO 30 MPH THIS AFTERNOON.
WITH THE STRONG WINDS OVER LAKE MICHIGAN ORIENTED PARALLEL TO THE
FETCH...WAVES WILL BUILD CONSIDERABLY TONIGHT AND PERSIST INTO
MONDAY...AND A BEACH HAZARDS STATEMENT WILL GO INTO EFFECT FOR ALL
LAKE ADJACENT COUNTIES IN THE FORECAST AREA.

CLOUD COVER SHOULD STAY WITH US MOST OF THE DAY LIMITING HOW WARM WE
GET AGAIN.  HIGHS WILL VARY FROM AROUND 80 NORTH TO THE MID 80S
SOUTH WHERE THERE COULD BE MORE SUNSHINE. TEMPS AND DEWPOINTS WILL
FALL THIS AFTERNOON THOUGH AS COOLER AIR MOVES IN BEHIND THE COLD
FRONT.

MONDAY...
THE UPPER LEVEL LOW WEAKENS TO AN OPEN TROUGH AND THEN MERGES WITH
THE STRONGER LOW OVER QUEBEC MONDAY NIGHT.  WE STAY STUCK IN AN
UPPER LEVEL PATTERN WITH A RIDGE TO THE WEST AND TROUGH TO THE
EAST. THE SURFACE LOW MOVES OVER NEW ENGLAND MONDAY MORNING AND
HIGH PRESSURE BUILDS OVER THE PLAINS. MONDAY LOOKS DRY WITH WEAK
VORTICITY STREAMERS PASSING BY OVERHEAD. HIGHS WILL BE WELL BELOW
NORMAL IN THE LOW TO MID 70S. ONSHORE FLOW WILL KEEP THE LAKEFRONT
NEAR 70. THEN A BEAUTIFUL NIGHT FOR SLEEPING IS IN STORE WITH LOWS
IN THE MID 50S...EXCEPT FOR AROUND 60 DOWNTOWN.

TUESDAY THROUGH SATURDAY...
WE REMAIN IN THE STAGNANT UPPER LEVEL PATTERN WITH A SURFACE HIGH
OVER THE PLAINS.  KEPT PERIODIC LOW CHANCES OF SHOWERS AND STORMS IN
THE EXTENDED FORECAST AS VORTICITY STREAMERS CONTINUE TO ROTATE
THROUGH THE REGION. MOISTURE IS NOT PLENTIFUL SO NOT EXPECTING MUCH
PRECIP AT THIS TIME.  TEMPERATURES ALSO REMAIN BELOW NORMAL IN THE
70S WITH A FEW SITES MAYBE REACHING 80.

JEE

&&

.AVIATION...

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

* SCATTERED TSRA 16Z-19Z.
* CHANCE OF SHRA THIS AFTERNOON INTO EARLY THIS EVENING.
* STRONG/GUSTY WEST/NORTHWEST WINDS LATE MORNING THRU THIS EVENING.
* NORTH/NORTHEAST WINDS MONDAY MORNING.
* POSSIBLE MVFR CIGS TONIGHT. CMS

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

HIGH MOISTURE VALUES OVER THE AREA WILL SUPPORT FOG/LOW CLOUDS
THROUGH 13Z-14Z AND MAYBE EVEN TO 15Z ACROSS THE REGION. WOULD NOT
EXPECT CONDITIONS TO GET WORSE AT TAF SITES AFTER 12Z GIVEN
DAYBREAK AND AN INCREASING WIND FLOW.

A STRONG UPPER LEVEL LOW PRESSURE MOVING INTO NORTHWEST WI AS OF
12Z WILL ROTATE SOUTHEASTWARD OVER CHICAGO BY MID-AFTERNOON. JUST
AHEAD OF THIS WILL EXIST A FAIR AMOUNT OF LIFT AND UPPER
SUPPORT...WHICH OVERRIDING A COLD FRONT WITH INSTABILITY ALONG IT
WILL LIKELY SUPPORT THE DEVELOPMENT OF A LINE OF SHRA/TSRA. HOW
FAR SOUTH THIS WILL EXTEND IS UNCERTAIN BUT AT THIS TIME BELIEVE
ENOUGH THAT IT WARRANTS INCLUSION INTO THE TAF. AS THE HEART OF
THE UPPER LOW MOVES OVER THE AREA DURING THE MID TO LATE
AFTERNOON...WOULD EXPECT SCATTERED SHOWERS WITH POSSIBLY ISOLATED
STORMS.

BEHIND THE COLD FRONTAL PASSAGE LATE THIS MORNING/EARLY
AFTERNOON...THERE WILL BE A SHARP INCREASE IN THE WIND SPEEDS
FROM THE WEST-NORTHWEST. OCCASIONAL GUSTS IN EXCESS OF 25 KT ARE
PROBABLE. A SECONDARY COLD FRONT DROPPING SOUTHWARD LATE THIS
AFTERNOON WILL LIKELY KEEP SOME GUSTS INTO THE EVENING PERIOD DUE
TO ITS COOL AIR ADVECTION. THIS FRONT WILL ALSO LIKELY PROVIDE
SOME FOCUS FOR MVFR OR NEAR-MVFR CLOUDS THIS EVENING INTO EARLY
OVERNIGHT.

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

* MEDIUM FOR TSRA 16Z-19Z.
* LOW FOR SHRA THIS AFTERNOON/EARLY EVENING.
* HIGH FOR WINDS THROUGH THIS AFTERNOON...MEDIUM TONIGHT/MONDAY.
* LOW FOR MVFR CIGS TONIGHT. CMS

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

MONDAY NIGHT...VFR.
TUESDAY...SLIGHT CHANCE OF AFTERNOON TSRA.
WEDNESDAY...SLIGHT CHANCE OF TSRA.
THURSDAY-SATURDAY...SLIGHT CHANCES OF TSRA. NORTHEAST WINDS.

MTF

&&

.MARINE...
300 AM CDT

AN ACTIVE AND ATYPICAL SUMMERTIME PATTERN WILL UNFOLD ACROSS THE
LAKE THIS AFTERNOON THROUGH MONDAY NIGHT. LOW PRESSURE OVER THE
MIDDLE OF LAKE MICHIGAN BY MID TO LATE MORNING WILL MOVE EASTWARD
AND SLOWLY DEEPEN THIS AFTERNOON INTO TONIGHT. AS THIS OCCURS...COOL
AIR ADVECTION ON ITS BACKSIDE WITHIN A TIGHTENING PRESSURE
GRADIENT WILL DRIVE STRONG NORTHERLY WINDS. THESE WINDS LOOK TO
COME UP QUICKLY LATE THIS AFTERNOON AND BE MAXIMIZED THIS EVENING
INTO EARLY OVERNIGHT AND IT IS THEN WHEN OCCASIONAL GALE FORCE
GUSTS COULD OCCUR...ESPECIALLY OVER THE CENTRAL AND SOUTHERN PART
OF THE LAKE AND INTO THE INDIANA NEARSHORE. WINDS WILL BE SLOW TO
DIMINISH DURING MONDAY BUT THEN QUICKLY DROP MONDAY NIGHT. GIVEN
THE LONG FETCH THAT WILL BE REALIZED WAVES WILL BE ON THE UPPER
END OF THE SPECTRUM FOR SUMMERTIME WITH 7 TO 10 AND OCCASIONAL
HIGHER WAVES IN THE CENTRAL AND SOUTHERN PART OF THE LAKE INTO THE
INDIANA AND POSSIBLY ILLINOIS NEARSHORE AREAS. STRONG CANADIAN
HIGH PRESSURE FOR MID-SUMMER OVER THE NORTHERN PLAINS ON MONDAY
WILL EVOLVE EASTWARD OVER LAKE MICHIGAN BY MIDWEEK.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ014...10 PM SUNDAY TO 4 AM TUESDAY.

     BEACH HAZARDS STATEMENT...ILZ006...10 PM SUNDAY TO 10 PM MONDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002...6 PM SUNDAY TO 4 AM
     TUESDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO NORTHERLY IS
     UNTIL 10 PM MONDAY.

     SMALL CRAFT ADVISORY...LMZ742-LMZ743 UNTIL 4 AM TUESDAY.

     SMALL CRAFT ADVISORY...LMZ744-LMZ745...3 PM SUNDAY TO 4 AM
     TUESDAY.

&&

$$

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