Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 281958
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
258 PM CDT TUE JUL 28 2015

.SHORT TERM...
246 PM CDT

THROUGH TONIGHT...

FOR THE REMAINDER OF THE AFTERNOON...FOCUS WILL BE ON TEMPERATURES
OVER THE ERN PORTIONS OF THE CWA AND PCPN TRENDS FOR THE REMAINDER
OF THE AFTERNOON.  A DECAYING MCS CONTINUES TO PUSH THROUGH
NWRN/NCNTRL IL.  THE ONLY ACTIVE TS ARE APPROACHING WRN LA SALLE AND
LIVINGSTON COUNTIES WITH SOME TRAILING SCT SHRA TO THE NORTH AND
WEST. LATEST RADAR TRENDS INDICATE THAT THE RESIDUAL STRATIFORM RAIN
OVER FAR NWRN IL IS DIMINISHING AND EVEN THE LEADING SHRA/TSRA ARE
ON A WANING TREND AS THE ACTIVITY MOVES TO THE SOUTHEAST THROUGH THE
FAVORABLE AREA OF UPPER DIFFLUENCE...BUT IS AT THE SAME
TIME...MOVING AWAY FROM THE MAIN SHORTWAVE WHICH IS LIFTING NEWD
INTO THE UPPER GREAT LAKES. AT THIS POINT...IT IS UNLIKELY THAT ANY
RESIDUAL SHOWERS WILL REACH THE CHICAGO METRO AREA. TEMPERATURE
TRENDS ARE GENERALLY ON TRACK WITH TEMPERATURES IN THE UPPER 80S
INLAND OF A PESKY LAKE BREEZE NERN IL AND AWAY FROM THE RAIN COOLED
AIR OVER NWRN IL.  SOUTH OF THE ILLINOIS AND KANKAKEE RIVERS...WHERE
TEMPS IN THE UPPER 80S AND DEWPOINTS IN THE MID 70S HAVE COMBINED TO
PRODUCE HEAT INDICES AT OR SLIGHTLY ABOVE 100F.

FOR TONIGHT...CONCERN WILL SHIFT TO THUNDERSTORMS EXPECTED TO
DEVELOP IN ASSOCIATION WITH A COLD FRONT APPROACHING FROM THE WEST.
AS OF ARND 2PM CDT...THE COLD FRONT EXTENDED FROM DEEP LOW PRESSURE
OVER SRN SASKATCHEWAN...THROUGH THE UPPER MISSOURI VALLEY AND THEN
BACK INTO THE TX PANHANDLE.  A QUASI-STATIONARY FRONT WAVING ACROSS
CNTRL IOWA...THROUGH CNTRL IL/IN IS ALSO ACTING AS A LIFTING
MECHANISM FOR AN EAST-WEST ORIENTED BAND OF TS OVER CNTRL IOWA...AND
SUSPECT THAT THIS BOUNDARY IS HELPING TO MAINTAIN SOME TS OVER CNTRL
IL...IN THE BLOOMINGTON AREA.  WHILE THE ENVIRONMENT OVER ERN
IA/NWRN IL IS CURRENTLY WORKED OVER FROM EARLIER CONVECTION...EXPECT
THAT THE ENVIRONMENT WILL BECOME MORE CONDUCIVE TO TS AGAIN THROUGH
THE EVENING AS THE COLD FRONT BEGINS TO MOVE FROM NW TO SE ACROSS
THE CWA.  WHILE THE REGION REMAINS IN THE WARM SECTOR AHEAD OF THE
COLD FRONT...THE REGION WILL REMAIN UNDER A VERY MOIST
AIRMASS...WITH DEWPOINTS REMAINING IN THE LOWER TO MIDDLE 70S.  THE
QUASI-STATIONARY SHOULD BE THE INITIAL FOCUSING MECHANISM FOR SOME
ELEVATED TS...BUT THE COLD FRONT SHOULD QUICKLY TAKE OVER AS THE
MAIN FOCUSING MECHANISM FOR MORE SFC BASED CONVECTION.  THE WILD
CARD IN THE DECK IS THE QUASI-STATIONARY FRONT OVER CNTRL IL.  THE
INTERACTION OF THIS BOUNDARY WITH THE COLD FRONT COULD ADD SOME
ENHANCED SFC FOCUSING TO THE CONVERGENCE ASSOCIATED WITH THE COLD
FRONT...LEADING TO THE POTENTIAL FOR SOME STRONGER...AND POSSIBLE
SEVERE THUNDERSTORMS OVER THE FAR SOUTHERN PORTIONS OF THE CWA.  THE
OTHER THREAT WILL BE SOME LOCALLY HEAVY RAINFALL WITH THE POTENTIAL
FOR ECHO TRAINING ALONG THE EAST-WEST ORIENTED BOUNDARY.  CONFIDENCE
IS NOT VERY HIGH ON THE LOCATION OF ANY POTENTIAL ECHO
TRAINING...BUT SHOULD IT DEVELOP...THE POTENTIAL WILL EXIST FOR SOME
LOCALIZED FLOODING OR FLASH FLOODING.

KREIN

&&

.LONG TERM...
252 PM CDT

WEDNESDAY THROUGH TUESDAY...

AS THE DEEP SUMMERTIME LOW PROGRESSES ACROSS ONTARIO ON WEDNESDAY
THE FRONT WILL ADVANCE THROUGH THE FORECAST AREA IN THE MORNING. AT
LEAST ONGOING SCATTERED SHOWERS AND POSSIBLY SOME STORMS ARE
EXPECTED AT DAYBREAK WITHIN THE PRE-TROUGH DEEP MOIST PLUME AND
GLANCING UPPER FORCING. THAT SAID...THE TREND LAST NIGHT WAS FOR
REGIONAL CONVECTION TO BE FURTHER SOUTH THAN HIGH-RES GUIDANCE HAD
INDICATED AND ALREADY SEEING THAT TREND TODAY...SO IT IS CERTAINLY
POSSIBLE THAN ANY MORNING ACTIVITY IS MAINLY SOUTH OF I-80.
CONFIDENCE REMAINS HIGH THAT THE BOUNDARY WILL BE SOUTH OF THE AREA
BY PEAK HEATING AND CONVECTIVE REGENERATION TIME ON WEDNESDAY
AFTERNOON...SO CONTINUE TO DROP POPS OFF FAIRLY QUICKLY DURING THE
LATE MORNING...KEEPING ONLY A SMALL CHANCE IN THE FAR SOUTHEAST IN
THE AFTERNOON.

WITH THE PARENT LOW WELL TO THE NORTH ON WEDNESDAY...THE 850-925MB
THERMAL RIDGE BECOMES ELONGATED OVER THE AREA AND NOT SHUNTED
SOUTHWARD AT AS GREAT OF SPEED AS THE SURFACE FRONT. GIVEN CLEARING
BY EARLY WEDNESDAY AFTERNOON AND VERY MILD STARTING POINT TO
TEMPERATURES TO START THE DAY...HIGHS SHOULD REACH MID TO UPPER 80S
WITH 90 POSSIBLE...ESPECIALLY IF DEW POINTS CAN DROP SOME.

HIGH PRESSURE FROM THE NORTHERN PLAINS THROUGH THE LOWER OHIO VALLEY
ON THURSDAY SHOULD PROVIDE QUIET WEATHER WITH A WEST-NORTHWEST WIND
CONTINUING TO NOT ALLOW MUCH OF OR ANY LAKE BREEZE. A WEAK NORTHERN
STREAM COOL FRONT IS FORECAST BY THE SUITE OF AVAILABLE GUIDANCE TO
INCH SOUTHWARD THROUGH THE GREAT LAKES REGION ON FRIDAY...WITH A
SLIGHTLY BETTER DEFINED FRONTAL BOUNDARY LATER IN THE WEEKEND OR
EARLY NEXT WEEK. DEW POINTS SHOULD GRADUALLY CLIMB THROUGH THE 60S
INTO THE WEEKEND AND MAY ALLOW THAT SECOND BOUNDARY A BETTER CHANCE
TO GENERATE SOME STORMS. TEMPERATURES LOOK TO REMAIN SLIGHTLY ABOVE
NORMAL LATE THIS WEEK AND MORE AT NORMAL THIS WEEKEND.

MTF

&&

.AVIATION...

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

* LAKE BREEZE NEARING ORD/MDW...BUT SHOULD REMAIN JUST EAST OF
  ORD/MDW.

* POSSIBLE SHOWERS NEARING ORD/MDW AFT 22Z...WITH INSTABILITY
  INCREASING AND THUNDERSTORMS POSSIBLE AFT 3Z. BEST TIMING FOR
  COVERAGE CONTINUES TO BE AFT 5Z THRU ABOUT 9Z.

* WINDS WILL TURN SOUTH THEN WEST BY DAYBREAK WED...THEN TURN
  NORTHWEST WITH GUSTS DEVELOPING WED MORNING TO 18KT.

BEACHLER

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

AREA OF CUMULUS CLOUDS HAVE DEVELOPED WITH MINIMAL VERTICAL GROWTH
EARLY THIS AFTERNOON ACROSS NORTHEAST IL/NORTHWEST IN...FURTHER
WEST THICKER CLOUD COVER FROM EARLY MORNING CONVECTION CONTINUES
TO MOVE EAST. REGIONAL RADAR INDICATES SOME AREAS OF
SHOWERS/THUNDERSTORMS LINGERING AND DRIFTING EAST. BEST TIMING IS
FOR THE LEADING EDGE TO NEAR RFD ARND 22Z...THEN MAY NOT ARRIVE AT
ORD/MDW UNTIL CLOSER TO 00Z. FORECAST GUIDANCE HAS NOT HANDLED
PLACEMENT OR TIMING VERY WELL...SO IT IS POSSIBLE THE TIMING FOR
ORD/MDW MAY NEED TO BE ADJUSTED EARLIER AS THE AFTERNOON
PROGRESSES. A LAKE BREEZE WAS ON THE DOORSTEPS OF MDW AT TAF
ISSUANCE...AND IS EXPECTED TO PUSH ACROSS MDW THEN ORD BY 19Z.
SPEEDS CONTINUE TO BE BETWEEN 8-10KT.

ANTICIPATE THE BETTER COVERAGE FOR RAIN/THUNDERSTORMS WILL BE AFT
3Z...BUT AS THE EVENING PROGRESSES THUNDERSTORM COVERAGE MAY
LOWER. HAVE ADJUSTED THE PROB30 GROUP TO EARLIER...BUT CONFIDENCE
HAS NOT BEEN HIGH ENOUGH TO TRANSITION TO A TEMPO YET. FRONTAL
BOUNDARY WILL CONTINUE TO MOVE SOUTHEAST ACROSS NORTHWEST IL
JUST PRIOR TO DAYBREAK WED...THEN CLEARING NORTHWEST IN BY MID-
MORNING WED. WINDS WILL THEN SHIFT WEST TO NORTHWEST AND BECOME
GUSTY.

BEACHLER

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

* MEDIUM CONFIDENCE IN WIND DIR THRU 20Z...HIGH CONFIDENCE IN
  WINDS AFTER 20Z.

* MEDIUM CONFIDENCE IN RAIN TIMING/COVERAGE BEFORE 00Z...LOW
  CONFIDENCE IN TIMING/COVERAGE AFT 00Z. HIGH CONFIDENCE THAT
  THUNDERSTORMS WILL OCCUR MAINLY AFT 00Z.

* HIGH CONFIDENCE IN CIGS FORECAST.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT THROUGH SATURDAY...DRY/VFR. WESTERLY WINDS.
* SUNDAY...CHANCE OF TSRA. SOUTHWEST WINDS.
* MONDAY...CHANCE OF TSRA. LAKE BREEZE POSSIBLE.

&&

.MARINE...
255 PM CDT

A MAINLY QUIET SUMMERTIME PATTERN WILL PERSIST OVER LAKE
MICHIGAN...THOUGH A LITTLE MORE CONSISTENT FLOW TO 20 KT WILL BE
SEEN THROUGH MID TO LATE WEEK WITH A DEEP LOW OVER WESTERN ONTARIO
WEDNESDAY MORNING SLOWLY MOVING NORTHEAST. A WEAK COOL FRONT IS
EXPECTED TO MOVE SOUTH DOWN THE LAKE ON FRIDAY AND FRIDAY
EVENING...WITH ANOTHER SLIGHTLY BETTER DEFINED ONE LATE IN THE
WEEKEND.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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