Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 281947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
247 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...
257 AM CDT

WEDNESDAY NIGHT THROUGH MONDAY...

DRY AND WARM CONDITIONS EXPECTED THURSDAY-SATURDAY WITH COMFORTABLE
HUMIDITY LEVELS BY LATE JULY/EARLY AUGUST STANDARDS. WESTERLY
GRADIENT APPEARS LIKELY TO BE STRONG ENOUGH TO PREVENT ANY
APPRECIABLE LAKE BREEZES SENDING THE WARMTH RIGHT UP TO THE CHICAGO
BEACHES. WEAK COLD FRONT LOOKS LIKE IT COULD MAKE A RUN AT THE
REGION SUNDAY INTO MONDAY...THOUGH HIGH PRESSURE OVER THE SOUTHEAST
STATES PROMISES TO KEEP DEEP GULF MOISTURE AT BAY. DESPITE THE LACK
OF RETURN MOISTURE...CORN-FED DEWPOINTS ARE LIKELY TO CREEP UP OVER
THE WEEKEND AND POTENTIALLY POOL ALONG THE WEAK FRONT PROVIDING
ENOUGH MOISTURE AND INSTABILITY TO JUSTIFY AT LEAST CHANCES POPS AT
THIS DISTANCE.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* LAKE BREEZE NEARING ORD/MDW...WILL TURN WINDS FROM SOUTH TO
  SOUTHEAST WITH SPEEDS REMAINING ARND 8-10KT.

* 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 18Z...

* 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...

217 AM...HIGH PRESSURE OVER THE EASTERN LAKES WILL SLOWLY MOVE
EAST TODAY AND TONIGHT WHILE A LARGE TROUGH OF LOW PRESSURE OVER
THE WESTERN PLAINS CONSOLIDATES INTO A LOW IN SOUTHERN CANADA.
THIS LOW WILL THEN MOVE NORTHEAST TONIGHT REACHING HUDSON BAY
WEDNESDAY EVENING. A TRAILING COLD FRONT FROM THIS LOW WILL MOVE
ACROSS LAKE MICHIGAN WEDNESDAY. THE GRADIENT WILL TIGHTEN AHEAD
OF THIS FRONT LATER TONIGHT INTO WEDNESDAY MORNING WITH A PERIOD
OF 15-25 KTS STILL EXPECTED ACROSS NORTHERN PORTIONS OF THE LAKE.
WINDS WILL SHIFT WESTERLY WEDNESDAY AFTERNOON INTO WEDNESDAY
EVENING. ANOTHER COLD FRONT IS EXPECTED TO MOVE ACROSS THE LAKES
FRIDAY AFTERNOON INTO FRIDAY NIGHT. CMS

&&

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

$$

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