Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 300919
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
419 AM CDT SAT MAY 30 2015

.SHORT TERM...
336 AM CDT

THROUGH SUNDAY...

THERE IS A SOMEWHAT COMPLICATED PATTERN ALOFT EARLY THIS MORNING AS
A POSITIVELY TILTED TROUGH CONTINUES EASTWARD FROM THE CENTRAL
PLAINS AND SLOWLY MOVES INTO IOWA THROUGH THE AFTERNOON. ITS
EASTWARD PROGRESS IS SLOWED BY A NEGATIVELY TILTED AND MORE
DYNAMIC SYSTEM IN THE ARKLATEX REGION AND EXTENDING NORTH TO THE
THE OZARKS OF MISSOURI. BROAD SW FLOW EXISTS AHEAD OF THESE TWO
FEATURES IN A MOIST LOW LEVEL AIRMASS CHARACTERIZED BY HIGH
PRECIPITABLE WATER VALUES...AND GIVEN THE SLOW PROGRESSION OF
THESE SYSTEMS...A SLOW MOVING PRECIPITATION SHIELD. WE DO STILL
HAVE INSTABILITY PRESENT...BUT MID LEVEL LAPSE RATES ARE STILL
SUBPAR OVER THE LOCAL AREA WHICH WILL LIMIT THUNDER POTENTIAL
UNTIL STRONGER LIFT ARRIVES TO TAP INTO GETTING PARCELS
HIGHER...WHICH IS WHAT IS HAPPENING DOWNSTATE. A STRONG UPPER
TROUGH ALSO EXISTS OVER SOUTH CENTRAL CANADA. MEANWHILE AT THE
SURFACE... A LOW PRESSURE TROUGHS DRAPED TO OUR NORTH AND
EXTENDING NORTHEAST INTO ONTARIO. A COLD FRONT EXISTS AHEAD OF
STRONG HIGH PRESSURE PUSHING SOUTHWARD OUT OF THE CANADIAN
PRAIRIES BEHIND THE DEPARTING CANADIAN TROUGH. IT IS THIS FRONT
THAT WILL PLAY A BIG ROLE IN THE CHANGING WEATHER PATTERN TODAY.

IN THE NEAR TERM...SHOWERS ARE INCREASING ACROSS NE ILLINOIS
EARLY THIS MORNING...MOST NOTABLY SOUTH AND WEST. MODEST RAINFALL
RATES ARE OCCURRING WITH THIS ACTIVITY...WITH .33" IN A HOUR AT
BLOOMINGTON (BMI). THERE HAS BEEN SOME LIGHTNING WITH THIS
RAIN...BUT MORE FREQUENT LIGHTNING IS STILL FOUND FARTHER SOUTH
AND EAST CLOSER TO THE BETTER UPPER LEVEL FORCING. STILL EXPECT
SHOWERS TO INCREASE OVER THE REMAINDER OF THE AREA THROUGH THE
MORNING...WITH EMBEDDED THUNDER. 1.7/1.8 INCH PRECIPITABLE WATER
VALUES ARE CREEPING INTO OUR AREA AS WELL...SO EXPECT GOOD
RAINFALL RATES...WITH LOCALLY HIGHER AMOUNTS IN THUNDERSTORMS. THE
WEAKEST FORCING WITH THIS INITIAL RAINFALL WILL BE IN FAR NE IL
AND NW WHERE MORE SCATTERED ACTIVITY IS EXPECTED.

THE SURFACE LOW TO THE NORTH WILL CONTINUE EAST TODAY...BUT WITH THE
STRONGER FORCING TO OUR SOUTH LIFTING NORTHWARD...THE SURFACE LOW
OVER SOUTHERN MISSOURI WILL SLOWLY MOVE NORTH AND EAST
TODAY...REACHING SOUTH CENTRAL ILLINOIS THIS AFTERNOON. THE RESULT
OF THIS IS TO SLOW A SEASONABLY STRONG COLD FRONT TO THE NORTH FROM
PASSING THROUGH NE IL/NW IN.  THE COLD FRONT WILL COME MARCHING
SOUTHWARD THROUGH THE MORNING. EXPECT WINDS TO QUICKLY RAMP UP AS
THIS OCCURS AND TEMPERATURES TO PLUMMET. WAVES WILL ALSO QUICKLY
BUILD TO NEAR 10 FT ALONG THE LAKEFRONT WHERE A LAKESHORE FLOOD
ADVISORY REMAINS IN EFFECT. IN COLLABORATION WITH ALL OF OUR
SOUTHERN LAKE MICHIGAN NEIGHBORS...WE HAVE ISSUED A BEACH HAZARDS
STATEMENT FOR A VERY HIGH SWIM RISK. FOR ANYONE WHO WOULD VENTURE
TO THE BEACHES...SWIM CONDITIONS WILL BE EXTREMELY HAZARDOUS.

THE IMPACT OF THE SLOWER MOVEMENT OF THE FRONT WILL ALLOW THE HIGH
PW AIRMASS TO LINGER OVER THE AREA MUCH OF THE DAY. COUPLED FORCING
FROM THE NORTHWARD MOVING TROUGH COMBINED WITH STRONG LOW TO MID
LEVEL FRONTOGENESIS WILL LEAD TO SOME MODERATE TO HEAVY RAINFALL
EVEN IN THE STRATIFORM PRECIPITATION LATER TODAY AFTER A POSSIBLE LULL
IN THE ACTIVITY LATER THIS MORNING. WE WILL ALSO NEED TO WATCH
AREAS TO THE SOUTH AND EAST WHERE THE AIRMASS WILL REMAIN SOUTH OF
THE COLD FRONT AND WILL LIKELY BE WEAKLY UNSTABLE WITH A DEEP WARM
LAYER IN PLACE. GLOBAL MODELS ARE HITTING FAR EASTERN ILLINOIS AND
NORTHWEST INDIANA WITH SOME IMPRESSIVE RAINFALL TOTALS...SO HAVE
SOME HEAVY RAIN WORDING IN THESE AREAS. LOCAL FLOODING WOULD
EASILY BE A CONCERN IF THESE HIGHER AMOUNTS COME TO FRUITION.

THE SLOW MOVING TROUGHS MERGE TO SOME DEGREE TONIGHT BEFORE EXITING
TO THE EAST SUNDAY MORNING. THIS WILL KEEP AREAS SOUTH AND EAST WET
THROUGH AT LEAST THE EVENING. POSSIBLY LINGERING INTO NW INDIANA
THROUGH DAYBREAK SUNDAY....AND EVEN INTO THE MORNING BASED ON SOME
OF THE GLOBAL MODELS WHICH HAVE SLOWED DOWN CONSIDERABLY. BRIEF
RIDGING ENSUES BEHIND THE DEPARTING TROUGH SUNDAY LATE MORNING AND
AFTERNOON. THE IMPACTS OF THIS SLOWER PROGRESSION WILL BE THAT
CLOUDS WILL LINGER A BIT MORE INTO SUNDAY...ESPECIALLY ALONG AND
EAST OF I-57. THE THEME REMAINS THE SAME...MUCH COLDER THAN NORMAL
TO START METEOROLOGICAL SUMMER.

KMD

&&

.LONG TERM...
336 AM CDT

SUNDAY NIGHT THROUGH FRIDAY...

MUCH OF THE EXTENDED PERIOD WILL FEATURE DRY WEATHER...WITH JUST
SOME SMALL CHANCES FOR A SHOWER OR THUNDERSTORM LATER IN THE WEEK.
MONDAY LOOKS TO BE CONTINUED COOL WITH ONSHORE FLOW ACROSS THE AREA
AND LIMITED WARMING. TUESDAY AND ESPECIALLY WEDNESDAY FEATURE A
STRENGTHENING UPPER LEVEL RIDGE WHICH WILL ALLOW THE SURFACE HIGH TO
SHIFT EAST RESULT IN WINDS BECOMING MORE SOUTHEASTERLY. WEAK
DISTURBANCES RIDING/BREAKING INTO THE RIDGE AXIS WILL ATTEMPT TO
TRIGGER AN AFTERNOON SHOWER/STORM. MOST AREAS WILL BE BACK IN TO THE
80S BY THURSDAY...WITH LAKE BREEZES CONTINUING KEEPING LAKESHORE
AREAS A BIT COOLER. BETTER CHANCES FOR PRECIP COMES FRIDAY INTO THE
WEEKEND.

KMD

&&

.AVIATION...

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

* WIND SHIFT TO NORTH/NORTHEAST MID MORNING.
* STRONG/GUSTY NORTH/NORTHEAST WINDS FROM MID/LATE MORNING THRU
  THE REMAINDER OF THE PERIOD.
* SHRA EARLY THIS MORNING...RAIN LATER THIS MORNING INTO THIS
  AFTERNOON.
* IFR/LIFR FROM MID MORNING THRU THIS EVENING. CMS

//DISCUSSION...UPDATED 06Z...

A STRONG COLD FRONT WILL MOVE ACROSS THE AREA LATER THIS MORNING.
SOUTHWESTERLY WINDS GENERALLY UNDER 10KTS WILL TURN MORE WESTERLY
BY MORNING WITH SPEEDS DIMINISHING JUST A BIT. WINDS WILL SLOWLY
TURN NORTHWEST JUST AHEAD OF A COLD FRONT WHICH WILL SHIFT WINDS
TO THE NORTH/NORTHEAST. INITIALLY SPEEDS WILL INCREASE INTO THE
12-16KT RANGE WITH GUSTS INTO THE LOWER/MID 20KT RANGE. BUT THESE
SPEEDS AND GUSTS WILL INCREASE THRU THE DAY WITH 20G30KT EXPECTED
BY LATE AFTERNOON INTO THIS EVENING.

SCATTERED SHOWERS WILL BE POSSIBLE FOR THE NEXT FEW HOURS WITH A
PERIOD OF SHOWERS/RAIN TOWARD DAY BREAK ASSOCIATED WITH THE
ACTIVITY NOW OVER CENTRAL IL. THERE COULD BE A LULL MID MORNING
BUT OVERALL...EXPECT PERIODS OF SHOWERS AND RAIN...POSSIBLY HEAVY
AT TIMES FOR MOST OF TODAY...SLOWLY ENDING INTO THIS EVENING.
INSTABILITY LOOKS RATHER MARGINAL FOR THUNDER ACROSS THE
TERMINALS. COULD BE A FEW THUNDERSTORMS WITH THE ACTIVITY EXPECTED
AROUND DAYBREAK...BUT POTENTIAL TOO LOW TO MENTION IN THE TAFS.
COULD BE THUNDERSTORMS JUST SOUTH OF THE TERMINALS LATER THIS
AFTERNOON HOWEVER.

AS RAIN SATURATES THE INCREASINGLY COLDER AIR SPREADING IN BEHIND
THE FRONT...CIGS SHOULD STEADILY LOWER TO IFR LATER THIS MORNING
WITH A PERIOD OF LIFR POSSIBLE. SOME UNCERTAINTY REGARDING HOW
LONG THESE LOWER CIGS WILL PERSIST BUT SHOULD SEE SOME IMPROVEMENT
BACK INTO IFR LATER THIS AFTERNOON AND INTO MVFR THIS EVENING. CMS

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

* HIGH FOR WINDS THRU THE PERIOD...MEDIUM FOR COLD FRONT/WIND
  SHIFT TIMING.
* HIGH FOR SHOWERS/RAIN.
* HIGH FOR IFR/LIFR. MEDIUM FOR TIMING/DURATION. CMS

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

SUNDAY AND MONDAY...VFR. NORTHEAST WINDS.

TUESDAY...VFR. EAST WINDS.

WEDNESDAY...VFR. EAST-SOUTHEAST WINDS.

THURSDAY...VFR. SOUTH WINDS.

RATZER

&&

.MARINE...

326 AM...A STRONG COLD FRONT WILL MOVE SOUTH ACROSS LAKE MICHIGAN
THIS MORNING AS STRONG HIGH PRESSURE BUILDS ACROSS THE NORTHERN
PLAINS AND UPPER MIDWEST. THIS WILL TIGHTEN THE GRADIENT BEHIND
THE FRONT AND NORTHERLY WINDS WILL INCREASE TO 30 KT BEHIND THE
FRONT WITH GALES LIKELY OVER THE SOUTHERN PART OF THE LAKE. IN
ADDITION...WEAK LOW PRESSURE WILL DEVELOP OVER INDIANA AND OHIO
TONIGHT...AND THIS WILL MAINTAIN THE STRONG GRADIENT INTO SUNDAY
MORNING. AS THIS LOW DEPARTS...THE GRADIENT WILL SLOWLY WEAKEN
SUNDAY AFTERNOON INTO SUNDAY NIGHT. THE HIGH OVER THE UPPER
MIDWEST WILL MOVE ACROSS THE NORTHERN LAKES AND ONTARIO SUNDAY
THEN INTO QUEBEC MONDAY...WITH WEAKER RIDGING EXTENDING BACK
ACROSS THE LAKES REGION THROUGH TUESDAY. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...BEACH HAZARDS STATEMENT...ILZ006-ILZ014...10 AM SATURDAY TO 10
     PM SUNDAY.

     LAKESHORE FLOOD ADVISORY...ILZ006-ILZ014...1 PM SATURDAY TO 4 AM
     SUNDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002...10 AM SATURDAY TO 10
     PM SUNDAY.

     LAKESHORE FLOOD ADVISORY...INZ001-INZ002...1 PM SATURDAY TO 4 AM
     SUNDAY.

LM...GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-
     LMZ779...9 AM SATURDAY TO 10 PM SATURDAY.

&&

$$

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