Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 252017
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 PM CDT MON AUG 25 2014

.DISCUSSION...
315 PM CDT

SHORT TERM...THROUGH EARLY TUESDAY MORNING...

FOR THE REMAINDER OF THE AFTERNOON...MAIN FOCUS WILL CONTINUE TO BE
2 LINES OF THUNDERSTORMS...ONE MOVING THROUGH NWRN IL AND ANOTHER
MOVING THROUGH NWRN IN AND ECNTRL IL.  THESE LINES ARE PRODUCING
STRONG TO OCNLY SVR TS...WITH THE PRIMARY THREAT BEING WIND GUSTS
TO 60 MPH AND TORRENTIAL DOWNPOURS.  THE TREND WITH TIME SHOULD BE
FOR THE  LINE OVER NWRN IL TO BEGIN TO WEAKEN AS IT MOVES INTO AN
AIRMASS OVER NERN IL WHICH HAS BEEN WORKED OVER BY EARLIER
CONVECTION.  THE LINE ACROSS NWRN IN INTO ECNTRL IL SHOULD MAINTAIN
SOME STRENGTH AS IT CONTINUES TO PUSH SEWD.  LATEST RADAR IMAGERY
SHOWS A DISTINCT OUTFLOW BOUNDARY EXTENDING WEST FROM KANKAKEE TO
PERU WHICH COULD YET BE THE FOCUS FOR SOME ADDITIONAL THUNDERSTORM
DEVELOPMENT INTO THE EARLY EVENING HOURS.  THUNDERSTORMS HAVE HAD A
HISTORY OF PRODUCING IN EXCESS OF 1 INCH IN 30 MINUTES...BUT SINCE
THEY HAVE BEEN PROGRESSIVE...SIGNIFICANT WIDESPREAD FLOODING IS NOT
ANTICIPATED...THOUGH LOCALLY HEAVY RAINFALL COULD PRODUCE URBAN ANS
SMALL STREAM TYPE FLOODING.  EXPECT THAT THE POTENTIAL FOR ORGANIZED
THUNDERSTORMS SHOULD DIMINISH INTO EARLY THIS EVENING WITH THE
SETTING SUN AND LARGER SCALE SUBSIDENCE MOVES OVER THE AREA AS WEAK
SHORT WAVE RIDGING MOVES OVER THE AREA TONIGHT.  AS THE THUNDERSTORM
ACTIVITY DIMINISHES THIS EVENING...PATCHY FOG AND WIDESPREAD
MISTY/MURKY CONDITIONS WILL SET UP.  WHILE WIDESPREAD DENSE FOG IS
NOT LIKELY DUE TO PERSISTENT DEBRIS CLOUD FROM EARLIER
CONVECTION...A VERY MOIST ENVIRONMENT WILL REMAIN IN PLACE...AND
COMBINED WITH LIGHT WINDS CONDITIONS WILL REMAIN MUGGY OVERNIGHT.

THE TEMPERATURE FORECAST FOR TODAY WAS DISRUPTED BY THE THUNDERSTORMS
AND EXTENSIVE CLOUD COVER OVER AREAS IMPACTED BY THE THUNDERSTORMS.
HOWEVER...LOCATIONS SOUTH OF A LINE FROM MIDWAY AIRPORT TO PERU
STILL SAW MAX HEAT INDICES IN EXCESS OF 100F WHILE LOCATIONS SOUTH
OF THE ILLINOIS/KANKAKEE RIVERS SAW HEAT INDICES APPROACH OR SLIGHTLY
EXCEED 110F.  TEMPERATURES AND DEWPOINTS SHOULD REMAIN IN THE LOWER
TO MIDDLE 70S OVERNIGHT AS THERE WILL BE NO SGFNT CHANGE IN
AIRMASS.  WITH OLD OUTFLOW BOUNDARIES HANGING AROUND THE AREA
OVERNIGHT...THERE WILL STILL BE SOME LOW CHANCES FOR ADDITIONAL
SHOWERS OR THUNDERSTORMS AS A WEAK COLD FRONT MOVES DOWN THE LAKE
AND INTO THE WARM...HUMID ENVIRONMENT.

KREIN

LONG TERM DISCUSSION COMING SOON...

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* WINDS TURNING NE ARND 10-12KT...WITH AN OCCASIONAL GUSTS TO
  20-25KT.

* WIND SPEEDS DIMINISH TO ARND 6-8KT LATE AFTN/EARLY EVE...THEN
  TURN W/NW.

* POSSIBLE ADDTL ISOLATED TSRA OVERNIGHT/EARLY TUE MORNING.

* PATCHY FOG DEVELOPING AFT 04Z...MAY REDUCE VSBYS TO ARND 2-4SM.
  WEST OF TAF SITES VSBYS COULD BE LOWER.

BEACHLER

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

SPOTTY SHOWERS AND THUNDERSTORMS HAVE CONTINUED TO DEVELOP ALONG
AN ORIGINAL OUTFLOW BOUNDARY ACROSS NORTHEAST IL. ADDTL SHRA/TSRA
HAVE DEVELOPED WEST OF TAF SITES...WITH A FEW STRONGER STORMS
CAPABLE OF PRODUCING WIND GUSTS TO 40KTS THIS AFTN. CONCERN IS
THAT A WEAK BOUNDARY SLIDING SOUTH AND A LACK OF A GRADIENT...WILL
ONLY PROLONG THE NORTHEAST WINDS AT ORD/MDW. MEANWHILE FURTHER
WEST AT RFD/DPA THE WINDS SHUD BE ABLE TO TURN NW/W ARND 20-21Z.
WILL CONTINUE TO MENTION VCTS THRU 23Z...AND IF ADDTL STORMS ARE
ABLE TO DEVELOP WE WILL LIKELY NEED TO ADJUST WITH A TEMPO BUT
COVERAGE IS NOT EXPECTED TO BE THERE. THEN LATE THIS EVENING
GUIDANCE IS SUGGESTING THE WINDS WILL BECOME LGT FROM THE NW ARND
5-8KT. THE CONCERN THEN WILL TURN TOWARDS THE LOW CIGS BUT ALSO
THE POTENTIAL FOR PATCHY FOG TO DEVELOP GIVEN HOW MOIST THE
ENVIRONMENT WILL REMAIN OVERNIGHT. FOG MAY BEGIN TO DISSIPATE AFT
DAYBREAK TUE...THEN GUIDANCE SUGGESTS THE WINDS WILL TRY TO TURN
NW WITH SPEEDS ARND 8-11KT.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN TSRA REMAINING ISOLATED...LOW CONFIDENCE IN
  PRECISE TIMING/INTENSITY AT TAF SITES.

* HIGH CONFIDENCE IN WINDS REMAINING NORTHEAST THRU 22Z...THEN LOW
  CONFIDENCE IN TIMING OF WINDS TURNING NW LATE AFTN/EARLY EVE.

* MEDIUM CONFIDENCE IN PATCHY FOG DEVELOPING.

BEACHLER

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

* TUESDAY NIGHT...TSRA LIKELY.
* WEDNESDAY THROUGH SUNDAY...CHANCE OF TSRA.

&&

.MARINE...

243 AM...LOW PRESSURE OVER SOUTHERN MANITOBA WILL MOVE ACROSS
NORTHERN ONTARIO TODAY AND TONIGHT REACHING JAMES BAY TUESDAY
MORNING. A TRAILING COLD FRONT WILL SLOWLY SAG SOUTHEAST ACROSS
THE WESTERN LAKES AND REACH NORTHERN LAKE MICHIGAN BY DAYBREAK
TUESDAY MORNING. THIS FRONT WILL THEN CONTINUE SOUTH ACROSS LAKE
MICHIGAN TUESDAY AND EVENTUALLY STALL NEAR OR JUST SOUTH OF THE
LAKE WEDNESDAY INTO THURSDAY. AHEAD OF THIS FRONT...SOUTH TO
SOUTHEAST WINDS 10-20KTS WILL GRADUALLY SHIFT MORE SOUTHWESTERLY
LATER TODAY AND THIS EVENING. A FEW HIGHER GUSTS ARE POSSIBLE BUT
THE TIGHTEST PORTION OF THE GRADIENT PASSES NORTH OF THE LAKE.
HIGH PRESSURE WILL BUILD ACROSS THE NORTHERN PLAINS ON TUESDAY
AND THEN MOVE ACROSS THE NORTHERN LAKES WEDNESDAY. THIS MAY
STRENGTHEN THE GRADIENT A BIT ON THE SOUTHERN END OF THE LAKE
WITH A PROLONGED NORTHEAST FLOW IN THE 10-20KT RANGE POSSIBLE.
CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...HEAT ADVISORY...ILZ010-ILZ019-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039
     UNTIL 10 PM MONDAY.

IN...NONE.
LM...NONE.
&&

$$

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