Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 210605
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
105 AM CDT SUN SEP 21 2014

.DISCUSSION...
936 PM CDT

LATEST RADAR IMAGERY DEPICTING SCATTERED SHOWER AND THUNDERSTORM
DEVELOPMENT PERSISTING MAINLY ACROSS THE FAR SOUTHERN PORTIONS OF
THE CWA...WHILE ISOLATED DEVELOPMENT CONTINUES ELSEWHERE. THIS
LINE OF SHOWERS/THUNDERSTORMS ARE DEVELOPING ALONG LOW LEVEL
CONVERGENT AXIS STRETCHED ACROSS CENTRAL ILLINOIS WITHIN MODERATE
INSTABILITY...WHILE ISOLATED DEVELOPMENT IS FORMING NEAR ANY
BETTER LOW LEVEL CONVERGENCE. HEIGHTS OF THESE STORMS HAVE NOT
BEEN OVERLY GREAT...LIKELY DUE TO LACK OF ANY STEEP LAPSE RATES.
WILL LIKELY OBSERVE A SOUTHWARD TREND WITH THIS PRECIP OVER THE
NEXT COUPLE OF HOURS...WITH ISOLATED SMALL HAIL OR GUSTY WINDS
STILL NOT OUT OF THE QUESTION WITH ANY STRONGER STORMS. LARGE VORT
MAX WILL CONTINUE TO SWING EAST/SOUTHEAST ACROSS THE UPPER MIDWEST
AND GREAT LAKES REGION TONIGHT...WHILE COLD FRONT/SURFACE TROUGH
SHIFT SOUTHEAST THROUGH THE CWA. CURRENT PRECIP OVER SOUTHWEST
WISCONSIN WILL SHIFT SOUTHEAST THROUGH THE NORTHERN THIRD OF THE
CWA ALONG THESE FEATURES...BUT DO EXPECT BEST DEVELOPMENT TO
REMAIN IN WISCONSIN. A THUNDERSTORM OR TWO WILL BE POSSIBLE BUT
DONT EXPECT COVERAGE TO BE OVERLY GREAT...AS INSTABILITY AXIS WILL
SHIFT SOUTHEAST WITH TIME THROUGH EARLY SUNDAY MORNING.

RODRIGUEZ

//PREV 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 06Z...

* ISOLATED TSRA ENDING BY 7Z.

* WEST WINDS VEERING NORTHWEST BY DAYBREAK. SPEEDS GENERALLY ARND
  10-14KT WITH GUSTS DEVELOPING AFT DAYBREAK TO 20-24KT.

* MVFR CIGS DEVELOPING ARND 10Z AND LIKELY PERSISTING THRU EARLY
  AFTN.

BEACHLER

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

LINE OF SHOWERS AND THUNDERSTORMS MOVING THRU AT TAF TIME...SHUD
QUICKLY END BY 630Z FOR ORD/MDW...GYY WILL BE CLOSER TO 7Z.
ELSEWHERE STORMS HAVE MOVED TO THE EAST WITH MAINLY VFR CIGS
PUSHING IN. HOWEVER FURTHER NORTH ACROSS WISCONSIN MVFR CIGS HAVE
DEVELOPED AND WILL CONTINUE TO SLIDE SOUTHEAST TOWARDS NORTHERN IL
AIRFIELDS...BUT HOLD OFF UNTIL ARND DAYBREAK. WINDS HAVE MAINLY
BECOME WESTERLY WITH SPEEDS ARND 10-14KT...AND AS DAYBREAK NEARS
GUSTS WILL BE DEVELOPING TO NEAR 20-24KT. GUIDANCE INDICATES THAT
WITH THE MID-LVL SYSTEM DROPPING SOUTHEAST TOWARDS THE TAF
SITES...MVFR CIGS WILL BE DEVELOPING AND LIKELY PERSIST THUR EARLY
AFTN. IN ADDITION IT APPEARS SOME VCSH OR LGT SHRA WILL ACCOMPANY
THE LOW CIGS LATER THIS MORNING THRU EARLY AFTN. WINDS WILL ALSO
BE TURNING NORTHWEST THEN NORTH BY THIS AFTN. THEN DRIER AIR WILL
ARRIVE AND SCOUR THE LOW CLOUDS BY SUNSET.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH CONFIDENCE IN WIND DIR/SPEED/GUSTS.

* MEDIUM CONFIDENCE IN PRECISE TIMING OF CIGS...HIGH CONFIDENCE IN
  MVFR CIGS DEVELOPING THOUGH.

* MEDIUM CONFIDENCE IN TIMING AND PLACEMENT OF SHRA LATER TODAY.

BEACHLER

//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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