Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 301928
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
228 PM CDT SAT MAY 30 2015

.UPDATE...
930 AM CDT

STRONG LAKE ENHANCED COLD FRONT WILL CONTINUE TO ACCELERATE SOUTH
DOWN THE LAKE THIS MORNING RESULTING IN A DRAMATIC DROP IN
TEMPERATURES...PARTICULARLY ALONG THE LAKE WITH A NEARLY INSTANT
DROP OF 20F IN TEMPS BEHIND THE FRONT ALONG THE LAKE. COULD BE
BRIEF PERIOD OF SOME DENSE FOG NEAR THE LAKE AS MARINE LAYER
ENCOUNTERS THE 60F+ DEWPOINTS...THOUGH THINKING RAIN WILL
HOPEFULLY KEEP THE DENSE FOG THREAT LOW AND MAINLY BRIEF.

OTHERWISE GOING FORECAST LARGELY IN GOOD SHAPE. DID REMOVE THUNDER
FOR NORTHWEST 2/3RDS OF THE CWA WHERE WEAK LAPSE RATES AND LITTLE
TO NO INSTABILITY SHOULD KEEP THUNDER THREAT EXTREMELY LOW. AS SFC
LOW OVER SOUTHERN MISSOURI LIFTS NORTHEAST INTO THE CENTRAL
ILLINOIS LATER THIS AFTERNOON THE THREAT OF THUNDER WILL RAMP UP
OVER OUR SOUTHEASTERN CWA WHERE DESPITE WEAK LAPSE RATES...SOME
MODEST BOUNDARY LAYER HEATING SHOULD RESULT IN A SEVERAL HUNDRED
J/KG OF CAPE. MODEST DEEP LAYER SHEAR OF 30-35KT COULD ALLOW FOR
SOME STORM SCALE ORGANIZATION AND PERHAPS A LOCAL WIND DAMAGE
THREAT WITH ANY MORE ROBUST CONVECTION THAT MANAGES TO DEVELOP.
THE BETTER THREAT LOOKS TO BE SOUTHEAST OF OUR CWA WHERE SUNSHINE
SHOULD ALLOW FOR STRONGER DESTABILIZATION...BUT CAN`T RULE OUT
MORE ROBUST STORM IN FAR SE CORNER OF CWA.

IZZI

&&

.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 18Z...

* STRONG NORTHEAST WINDS THROUGH MUCH OF SUNDAY

* IFR TO OCCASIONAL LIFR THIS AFTERNOON THROUGH THIS EVENING.

* LIGHT SHOWERS BECOMING MODERATE RAIN LATE AFTERNOON.

* LOW LEVEL WIND SHEAR THIS AFTERNOON AND EARLY EVENING.

MM

//DISCUSSION...UPDATED 18Z...

COLD FRONT WORKING ITS WAY ACROSS NORTHERN ILLINOIS HAS ALREADY
DROPPED THE CHICAGO AREA TO 500 FOOT CEILINGS WITH NNE WINDS. AS
COLD AND DENSE AIR WORKS ITS WAY DOWN THE LAKE TO REINFORCE THE
COLD FRONT...WIND SPEEDS AND GUSTS WILL CONSIDERABLY INCREASE
GENERALLY FROM 22Z ONWARD. THESE GUSTS WILL REMAIN IN PLACE
THROUGH TONIGHT AS AN ALREADY TIGHT PRESSURE GRADIENT IS AIDED BY
FLOW OFF OF LAKE MICHIGAN. THIS COMBINATION WILL KEEP GUSTS IN THE
25 TO 30KT RANGE THROUGH TONIGHT. JUST OFF THE DECK...WINDS WILL
BE EVEN GREATER SO DID MENTION LLWS IN THE TAF FOR 50KT OF FLOW
FROM THE NORTHEAST THROUGH EARLY EVENING.

INTO TONIGHT...WINDS BECOME MORE UNIFORM AND ONLY SLIGHTLY
SLACKEN. CONTINUED FLOW OFF THE LAKE WILL KEEP THE NE WINDS IN
PLACE...BUT THE LOW LEVELS WILL START TO DRY OUT MIDDAY SUNDAY.
THERE MAY BE SOME MVFR CEILINGS LINGERING DAYTIME SUNDAY AND THE
CHANCE FOR PRECIPITATION IS TOO LOW TO MENTION IN TAFS AT THIS
TIME. ISOLATED SHOWERS ARE NOT OUT OF THE QUESTION SUNDAY.

MM

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN WIND SPEEDS AND MEDIUM-HIGH IN WIND SPEEDS

* HIGH CONFIDENCE IN IFR THROUGH THIS EVENING. MEDIUM CONFIDENCE
  IN CEILINGS TONIGHT.

* MEDIUM HIGH CONFIDENCE IN TIMING OF HEAVIER RAIN.

* MEDIUM HIGH CONFIDENCE IN LOW LEVEL WIND SHEAR.

MM

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

* SUNDAY NIGHT AND MONDAY...DRY/VFR. NORTHEAST WINDS.
* TUESDAY...DRY/VFR. EAST WINDS.
* WEDNESDAY AND THURSDAY..DRY/VFR. SOUTHEAST WINDS.
* FRIDAY...CHANCE OF TSRA. SOUTHWEST WINDS.

&&

.MARINE...
228 PM CDT

NORTH-NORTHEAST WINDS WILL CONTINUE TO REINFORCE ABNORMALLY COOL AIR
ACROSS LAKE MICHIGAN THROUGH THE REMAINDER OF THE WEEKEND. GALE
FORCE GUSTS HAVE BEEN OBSERVED AT WAUKEGAN HARBOR EARLY THIS
AFTERNOON AND EXPECT TO SEE AN INCREASE IN FREQUENCY. GALE FORCE
GUSTS ARE LIKELY THROUGH THE EVENING AND EVEN INTO AT LEAST EARLY
OVERNIGHT ACROSS THE SOUTHERN PART OF THE LAKE INCLUDING THE
ILLINOIS AND INDIANA NEARSHORE AREAS. WAVES WILL BUILD RAPIDLY INTO
THIS EVENING ACROSS THE CENTRAL AND SOUTHERN PART OF THE LAKE
INCLUDING THE ILLINOIS AND INDIANA NEARSHORES...WHICH SHOULD REALIZE
SOME OF THE HIGHEST WAVES OF 8 TO 12 FEET...PEAKING FROM MID-EVENING
THROUGH OVERNIGHT. A VERY SLOW SUBSIDING IS EXPECTED ON SUNDAY WITH
CONTINUED BUT GRADUALLY DIMINISHING NORTHEAST WINDS.

BEYOND THE WEEKEND ACTION...CONDITIONS LOOK RELATIVELY QUIET ON THE
LAKE THIS UPCOMING WORK WEEK. AFTER A RIDGE AXIS PASSES ON
TUESDAY...WINDS WILL TURN SOUTHERLY FOR THE LATTER HALF OF THE WEEK
PRIOR TO A COLD FRONT PASSAGE SOMETIME LATE IN THE WEEK INTO EARLY
NEXT WEEKEND.


MTF

&&

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

     LAKESHORE FLOOD ADVISORY...ILZ006-ILZ014 UNTIL 4 AM SUNDAY.

IN...BEACH HAZARDS STATEMENT...INZ001-INZ002 UNTIL 10 PM SUNDAY.

     LAKESHORE FLOOD ADVISORY...INZ001-INZ002 UNTIL 4 AM SUNDAY.

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

&&

$$

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