Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 210014
AFDLOT

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

.MESOSCALE DISCUSSION...
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 00Z...

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

* ADDITIONAL SHRA POSSIBLE LATE THIS EVENING.

* MVFR CIGS LATER TONIGHT INTO SUNDAY MORNING.

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

KMD

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

THE MAIN CONVECTIVE THREAT IN THE NEAR TERM IS LARGELY SOUTH AND
WEST OF THE TERMINALS THIS EVENING. LATER THIS EVENING AS THE
UPPER TROUGH IN SOUTHERN MN ROTATES EASTWARD...A BAND OF SHOWERS
MAY HOLD TOGETHER LONG ENOUGH LATE THIS EVENING. CURRENT TIMING
WOULD BE AROUND 4Z-6Z WEST AND 5Z-7Z IN THE CHICAGO TERMINALS.
INSTABILITY SHOULD BE WANING SUCH THAT ANYTHING THAT COMES THROUGH
WOULD GENERALLY BE VOID OF THUNDER. IT IS DURING THIS TIME THAT
THE FIRST MORE SIGNIFICANT WIND SHIFT TO WNW WILL OCCUR. EXPECT A
SURGE OF WIND WITH GUSTS TO 25 KT...POSSIBLY HIGHER WITH THE
INITIAL FRONT/TROUGH PASSAGE...THEN SETTLE INTO A MORE STEADY MID
TEENS SUSTAINED WINDS WITH GUSTS TO 20 KT OR SO.

A SECONDARY FRONT WILL BE POISED TO MOVE THROUGH LATER SUNDAY
MORNING. ALONG AND AHEAD OF THIS SECONDARY FRONT...GUIDANCE IS
SUGGESTING A PERIOD OF MVFR CIGS. NW WINDS WILL PICK UP WITH SOME
GUIDANCE SUGGESTING GUSTS AS HIGH AS 30 KT IN THE MORNING. THERE
MAY ALSO BE A FEW SHOWERS AROUND MIDDAY AS THIS FRONT MOVES
THROUGH AND SHIFTS WINDS TO NORTHERLY IN THE 19-21Z TIME
FRAME...POSSIBLY FLOPPING OVER TO AN 010-020 DIRECTION CLOSER TO
THE LAKE AND CONTINUED GUSTY. CIGS SHOULD BE TRENDING TOWARD VFR
DURING THIS TIME AS WELL. KMD

KMD


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

* HIGH CONFIDENCE IN WIND TRENDS...MEDIUM CONFIDENCE IN TIMING OF
  SHIFTS AND SPECIFIC SPEEDS.

* LOW CONFIDENCE THAT SHRA WILL OCCUR LATE THIS EVENING.

* MEDIUM CONFIDENCE IN MVFR CIGS SUNDAY MORNING.

* MEDIUM CONFIDENCE IN SHOWERS SUNDAY MIDDAY THOUGH LOW
  CONFIDENCE IN COVERAGE.

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

MONDAY AND TUESDAY...VFR.

WEDNESDAY THROUGH FRIDAY. VFR. SOUTHEAST WINDS.

KMD

&&

.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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