Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 202225
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
525 PM CDT SAT SEP 20 2014

.MESOSCALE DISCUSSION...503 PM CDT

WIDESPREAD THREAT OF SEVERE STORMS APPEARS TO BE WINDING DOWN LATE
THIS AFTERNOON...AS MAIN LINE OF STRONGEST STORMS SLOWLY EXITS
SOUTHEAST OF THE BENTON COUNTY INDIANA AREA. AM MONITORING SOME
ADDITIONAL ISOLATED SHOWER/THUNDERSTORM DEVELOPMENT ALONG
SOUTHWARD MOVING SURFACE BOUNDARY BEHIND THE MAIN LINE OF
THUNDERSTORMS...FROM SOUTHERN LA SALLE EAST TO LAKE/JASPER
COUNTIES IN INDIANA. THIS WILL LIKELY PERSIST OVER THE NEXT COUPLE
OF HOURS AS IT CONTINUES TO DRIFT TO THE SOUTH/SOUTHEAST BUT WITH
WEAKENING LOW LEVEL LAPSE RATES AND OVERALL INSTABILITY
LOWERING...WOULD EXPECT ANY FURTHER DEVELOPMENT TO REMAIN
SUB SEVERE. HAVE DROPPED SOME COUNTIES FROM THE SEVERE
THUNDERSTORM WATCH...AND WILL LIKELY CONTINUE THIS TREND AS THIS
BOUNDARY/STORMS COMPLETELY EXIT THE WATCH AREA.

RODRIGUEZ

&&

.DISCUSSION...

329 PM...MAIN FORECAST CONCERNS ARE SEVERE POTENTIAL THROUGH
EARLY THIS EVENING THEN COOLER TEMPERATURES WITH RAIN SHOWERS FOR
SUNDAY.

LINE OF THUNDERSTORMS FROM NORTHWEST INDIANA BACK THROUGH WEST
CENTRAL IL MOVING INTO RATHER MOIST AND UNSTABLE AIR AND THIS WILL
BE THE BEST LOCATION...SOUTHERN/SOUTHEASTERN THIRD OF THE CWA...
FOR SEVERE WEATHER INTO EARLY THIS EVENING. FURTHER NORTH...PRECIP
IS MORE SHOWERY WITH EMBEDDED THUNDER AND THE BACK EDGE OF THIS
PRECIP SHOULD BE THROUGH MUCH OF THE NORTHERN HALF/TWO THIRDS OF
THE CWA BY EARLY EVENING.

AN UPPER WAVE MOVING SOUTHEAST ACROSS THE UPPER MIDWEST WILL MOVE
ACROSS THE WESTERN LAKES LATER THIS EVENING WITH PRECIP WITH THIS
FEATURE LIKELY REMAINING MAINLY NORTH OF THE CWA BUT SOME SHOWERS
OR AN ISOLATED THUNDERSTORM IS STILL POSSIBLE LATER THIS EVENING.

A STRONG COLD FRONT WILL THEN MOVE SOUTH ACROSS THE LAKES REGION
OVERNIGHT REACHING NORTHERN IL SUNDAY MORNING. THIS WILL SHIFT THE
WINDS NORTH/NORTHEAST BY AFTERNOON WITH A PERIOD OF SHOWERS
POSSIBLE FROM MID MORNING THROUGH MID/LATE AFTERNOON. SOME
UNCERTAINTY REGARDING COVERAGE BUT POTENTIAL IS HIGH ENOUGH FOR
CHANCE POPS FOR MUCH OF THE DAY. PRECIP AND CLOUD COVER ALONG WITH
COLDER AIR SPREADING INTO THE REGION WILL KEEP TEMPS COOLER AND
ONLY HAVE HIGHS IN THE 60S.

AS HIGH PRESSURE MOVES ACROSS THE AREA SUNDAY AND MONDAY...LIGHT
WINDS WILL LIKELY ALLOW TEMPS TO COOL TO THE DEWPOINTS WITH FOG
POSSIBLE. THE REST OF THE PERIOD IS EXPECTED TO BE DRY WITH TEMPS
STILL IN THE 60S MONDAY...THEN WARMING A FEW DEGREES THROUGH THE
70S EACH DAY THROUGH THE END OF THE WEEK. CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22+Z...

* WINDS SHIFTING TO WEST LATER THIS EVENING...THEN NORTHWEST EARLY SUNDAY
  MORNING AND NORTH SUNDAY AFTERNOON. GUSTS INTO THE MID 20S
  POSSIBLE SUNDAY.

* ADDITIONAL SHRA POSSIBLE LATE THIS EVENING.

* ANOTHER ROUND OF SHOWERS LATE SUNDAY MORNING THROUGH MID
  AFTERNOON. MVFR CIGS POSSIBLE.

MDB/KMD

//DISCUSSION...UPDATED 22Z...

SHRA AND EMBEDDED TSRA HAVE PUSHED SE OF THE TERMINALS. ADDITIONAL
TS MAY SNEAK BACK INTO RFD LATE THIS EVENING...WITH A FEW SHOWERS
POSSIBLE WITH THE TROUGH PASSAGE AS WELL FARTHER SOUTH AND WEST.
BEST BET WOULD BE IN THE 5Z-8Z TIME FRAME. A MIX OF VFR AND MVFR
HAS BEEN SEEN UPSTREAM WITH THIS SHOWER ACTIVITY. KMD

FROM 18Z....

SHRA/TSRA HAS BEGUN TO DEVELOP TOWARD RPJ/DKB/VYS IN CONJUNCTION
WITH A BOUNDARY FROM EARLIER CONVECTION AND INCREASING UPPER
FORCING. EXPECT THIS ACTIVITY TO CONTINUE TO GRADUALLY INCREASE IN
COVERAGE THROUGH THE AFTERNOON BUT IT APPEARS THAT THE MORE
EXTENSIVE COVERAGE MAY END UP BEING SOUTH OF THE TERMINALS.
DESPITE THIS EXPECTATION DO EXPECT ORD/MDW/DPA TO BE IMPACTED IN
THE NEXT FEW HOURS...WITH GYY SEEING A BETTER CHANCE GOING INTO
LATE AFTERNOON. THERE ARE STILL SOME LIMITING FACTORS THAT MAY
KEEP COVERAGE ON THE LOW SIDE HOWEVER...SO CONFIDENCE IN COVERAGE
DETAILS IS STILL LIMITED. ANY STORMS THAT DO PASS DIRECTLY OVER
THE TERMINALS WILL BRING HEAVY DOWNPOURS AND POTENTIALLY BRIEF IFR
VSBY. LESS INTENSE SHRA ACTIVITY MAY PERSIST THROUGH LATE
AFTERNOON. SOUTHWEST WINDS WILL CONTINUE BUT TURN WESTERLY LATE
THIS AFTERNOON AND EARLY THIS EVENING.

ANOTHER UPPER TROUGH WILL SWING SOUTHEAST AND EAST ACROSS
WISCONSIN LATER THIS EVENING AND MAY BRING A BAND OF SHOWERS
ACROSS THE TERMINALS TOWARD/JUST AFTER 06Z. HAVE NOT INCLUDED ANY
MENTION IN THE TAF AS IT MAY BE BRIEF AND REMAIN NORTH OF THE
AREA. WINDS MAY ALSO SHIFT BACK TO THE SOUTHWEST FOR A SHORT TIME
AS THE WAVE PASSES. WINDS WILL TURN NORTHWEST LATER SUNDAY MORNING
WITH ANOTHER UPPER TROUGH CROSSING DURING THE LATE MORNING AND
EARLY AFTERNOON. HAVE BETTER CONFIDENCE THAT SHRA WILL OCCUR WITH
THIS ACTIVITY. MVFR CIGS ALSO LOOK TO OCCUR...AT LEAST
INITIALLY...BUT MAY LIFT TO LOWER END VFR THROUGH THE AFTERNOON.
WINDS WILL TURN NORTH AND POSSIBLY NORTH-NORTHEAST LATER IN THE
AFTERNOON. AM SEEING MIXED SIGNALS WITH REGARD TO WIND SPEEDS
THROUGH THE DAY BUT EXPECT STRONGEST WINDS FROM LATE MORNING
THROUGH THE AFTERNOON WITH GUSTS TO AROUND 25 KT. SPEEDS MAY EASE
A BIT AS WINDS TURN NORTH.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH CONFIDENCE IN WIND TRENDS...MEDIUM CONFIDENCE IN TIMING OF
  SHIFTS.

* LOW CONFIDENCE THAT SHRA WILL OCCUR LATE THIS EVENING.

* MEDIUM-HIGH CONFIDENCE IN SHRA SUNDAY. MEDIUM CONFIDENCE IN MVFR
  CIGS.

MDB/KMD

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

SUNDAY NIGHT...MAINLY VFR. PATCHY MVFR CIGS EARLY IN THE EVENING.
BREEZY NORTHWEST WINDS.

MONDAY...VFR. LIGHT WEST WINDS.

TUESDAY...VFR. NORTHEAST WINDS.

WEDNESDAY THROUGH FRIDAY...VFR. GENERALLY SOUTHEAST TO SOUTH WINDS.

BEACHLER

&&

.MARINE...
123 PM CDT

FRONT THROUGH THE MIDDLE MISSISSIPPI VALLEY.  THE FIRST ROUND GALES
HAS SUBSIDED AND THE STRONGER...SMALL CRAFT ADVISORY LEVEL WINDS
OVER THE NEARSHORE WATERS ARE SUBSIDING AS WELL AS THE FRONTAL
TROUGH APPROACHES THE LAKE AND THE GRADIENT WEAKENS.  AS THE LOW
LIFTS TO THE NORTHEAST THROUGH QUEBEC...IT WILL DRAG A COLD FRONT
ACROSS THE LAKE...TURNING WINDS NWLY AND THEN NLY BY MID DAY
SUNDAY.  THE STRONGEST PUSH OF COLD ADVECTION SHOULD BE OVER THE
SOUTHERN PORTIONS OF THE LAKE...SO...THERE IS STILL A CHANCE FOR
MARGINAL NLY GALES OVER THE SOUTHERN PORTIONS OF THE LAKE.  WILL
MAINTAIN THE GOING GALE WATCH FOR SUNDAY AND NOT UPGRADE TO A GALE
WARNING JUST YET SINCE THERE IS STILL SOME UNCERTAINTY AS TO THE
TIMING...DURATION AND EXTENT OF GALES.  THE FRONT WILL FINALLY PUSH
SOUTH OF THE LAKE BY MID DAY SUNDAY WITH HIGH PRESSURE BUILDING OVER
THE CENTRAL PLAINS...MAINTAINING NLY WINDS THROUGH SUNDAY NIGHT OR
EARLY MONDAY MORNING.  BY MONDAY AFTERNOON...THE CENTER OF THE HIGH
WILL SLIDE JUST SOUTH OF THE LAKE AND THEN MOVE TO THE EASTERN GREAT
LAKES TUESDAY...ALLOWING WINDS TO TURN SOUTHERLY AGAIN.
HOWEVER...DO NOT EXPECT THE SLY WINDS TO GET TOO STRONG...PERHAPS
10-15KT...SINCE THE AREAL EXTEND OF THE HIGH WILL SPREAD FROM THE
EAST COAST TO THE MIDDLE MISSISSIPPI VALLEY...SETTING UP A WEAK SLY
GRADIENT.  THE NEXT UPSTREAM TROUGH DEVELOPING IN THE LEE OF THE
ROCKIES THURSDAY AND FRIDAY IS NOT EXPECTED TO MAKE MUCH EWD
PROGRESS UNTIL SATURDAY NIGHT OR SUNDAY...SO THE LIGHT SLY WINDS
SHOULD PREVAIL OVER THE LAKE THROUGH THE WEEKEND.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...7 AM SUNDAY TO 10
     AM MONDAY.

     GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ743-
     LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-
     LMZ876-LMZ878...9 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

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