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000
FXUS63 KLOT 152105
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
405 PM CDT SAT JUN 15 2013

.MESOSCALE DISCUSSION...

CONTINUING TO MONITOR CONVECTIVE TRENDS EARLY THIS AFTERNOON.
STILL PLENTY OF UNCERTAINTY REGARDING EXTENT OF SEVERE THREAT BUT
CURRENT SATELLITE AND SURFACE OBS AND MESOANALYSIS GIVE SOME HINT
AT HOW THINGS MIGHT PLAY OUT. MCV ASSOCIATED WITH LATE MORNING
COMPLEX CURRENTLY PIVOTING SOUTHEAST FROM EASTERN CWA...WITH
BREAKS IN CLOUDS DEVELOPING ON BACK SIDE OF MCV. EASTERN HALF OF
CWA IS QUITE STABLE INITIALLY...BUT RECOVERY OF DEWPOINTS INTO MID
AND UPPER 60S INTO WEST AND SOUTHWEST CWA...ALONG WITH
TEMPERATURES ALREADY WARMING INTO UPPER 70S TO AROUND 80 HAS
RENEWED DESTABILIZATION PROCESS FOR THESE AREAS. RAP IS MOST
BULLISH/LIKELY TOO BULLISH ON MLCAPE VALUES BY LATE
AFTERNOON...BUT EVEN NAM SUPPORTS MLCAPES OF ABOUT 1000-1500 J/KG
BY LATE AFTERNOON OVER THE WESTERN CWA...WITH MINIMAL TO NO
CAPPING BY THEN AND ONLY MINIMAL CAPPING RETURNING BY EARLY
EVENING.

EXPECT THE COMPLEX OVER WEST CENTRAL ILLINOIS TO BE STEERED SOUTH OF
THE CWA...WITH THE LIKELY FOCUS FOR ROBUST DEVELOPMENT IN THE
LATE AFTERNOON INTO THE EVENING TO BE THE WAVE NOTED ON W/V AND
RADAR OVER NORTH CENTRAL IOWA. HI RES MODELS SUCH AS SPC-WRF NMM
AND HRRR SEEM TO HAVE A DECENT HANDLE ON TRENDS AND SHOW CLUSTER
OR CLUSTERS DEVELOPING SOUTH OF THE CURRENTLY WEAKENING
CONVECTION OVER NORTH CENTRAL IOWA OVER EASTERN IOWA AND NORTHERN
MO. THESE THEN FOLLOW THE 850-300 MB THICKNESS LINES EAST OR
EAST-SOUTHEAST FROM WESTERN ILLINOIS BY THE LATE AFTERNOON AND
EARLY EVENING (23Z-01Z) TO NORTHEAST IL AND NORTHWEST INDIANA A
FEW HOURS LATER (02-04Z).

0-6 KM BULK SHEAR STRENGTHENING TO 40 TO AS MUCH AS 50 KT BY EARLY
EVENING WILL SUPPORT ORGANIZATION...AND INCREASING LOW LEVEL JET/0-3
KM SHEAR COULD RESULT IN DAMAGING WIND THREAT. ALSO...MID LEVEL
LAPSE RATES STEEPENING FROM THE WEST WITH APPROACH OF WAVE COULD
PRESENT A SEVERE HAIL THREAT...MAINLY FOR NORTH CENTRAL IL AND
POINTS WEST. THINK THAT COMPLEX WILL BE ON WEAKENING TREND AS IT
HEADS EAST INTO NORTHEAST IL AND NW INDIANA DUE TO LOWER AND
DIMINISHING INSTABILITY BY THAT TIME...BUT STILL CAN FORESEE
LIGHTNING AND GUSTY WINDS AFFECTING OUTDOOR EVENTS OVER THESE AREAS.
IN ADDITION...MORE INTENSE STORMS TODAY OVER REGION HAVE PRODUCED
VERY HEAVY RAINFALL WITH PWAT OVER 1.5 INCHES AND WITH 850 MB
MOISTURE TRANSPORT INCREASING THIS EVENING...IMPRESSIVE RAINFALL
RATES AND LOCALIZED FLASH FLOODING ARE CERTAINLY POSSIBLE.
FINALLY...SOME CONCERN THAT THE INCREASING 850 MB MOISTURE TRANSPORT
AND FLOW COULD ALSO MAINTAIN SEVERE THREAT FARTHER EAST THAN
CURRENTLY EXPECTED...SO WILL CONTINUE TO MONITOR THIS POSSIBILITY
AS WELL. THIS IS SOMETHING THAT THE LATEST 17Z HRRR SHOWS.

RC

&&

.DISCUSSION...
306 PM CDT

THIS EVENING AND TONIGHT...
FOR A SPECIFIC DISCUSSION OF THE FORECAST THROUGH EARLY THIS EVENING
SEE THE MESOSCALE DISCUSSION ABOVE.

THE WEAKENING LINE OF STORMS WILL CONTINUE TO MOVE ESE THROUGH THE
EVENING AND OVERNIGHT.  HEAVY RAIN AND LIGHTNING WILL BE THE PRIMARY
THREATS LATER THIS EVENING WITH GUSTY WINDS PSBL.  FLASH FLOODING
WILL ALSO NOT BE OUTSIDE OF THE REALM OF POSSIBILITY.

DESPITE THE LINE OF SHOWERS AND STORMS MOVING THROUGH...STILL
LOOKING LIKE A SOUPY NIGHT WITH TEMPS IN THE MID TO UPPER 60S AND
DEWPOINTS ABOUT THE SAME.  PUT AREAS OF FOG IN THE FORECAST BEHIND
THE RAIN...BUT NOT EXPECTING WIDESPREAD FOG DEVELOPMENT.

SUNDAY AND MONDAY...
THE CLOSED UPPER LEVEL LOW CURRENTLY OVER SASKATCHEWAN WEAKENS AND
MOVES INTO NORTH DAKOTA SUNDAY EVENING.  IT THEN BECOMES ABSORBED BY
A STRONGER TROUGH OVER JAMES BAY SUNDAY NIGHT...AND THE TROUGH AXIS
PASSES OVERHEAD MONDAY NIGHT.  AT THE SURFACE...THE LOW ALSO OVER
SASKATCHEWAN EXPANDS OVER THE GREAT LAKES AND THEN CONTINUES
EASTWARD MOVING OVER NEW ENGLAND BY LATE SUNDAY NIGHT.

THINKING THERE MAY BE A FEW LINGERING SHOWERS...SO HAVE SLIGHT
CHANCE TO CHANCE POPS FOR AREAS SOUTH OF A GARY TO STREATOR LINE.
THE SHOWERS SHOULD EXIT TO THE SOUTHEAST DURING THE DAY AS THE
SHORTWAVE SHIFTS EAST.  THEN EXPECTING SHOWERS AND THUNDERSTORMS TO
FORM OVER THE NORTH END OF LAKE MICHIGAN SUNDAY AFTN/EVENING AS THE
LOW EXPANDS.  THINKING SHOWERS AND STORMS WILL NOT REACH NORTHERN
IL/IN UNTIL MONDAY.  HAVE CHANCE POPS BEGINNING MONDAY MORNING...BUT
CONFIDENCE IS LOW IN EXACT TIMING.  THINKING SHOWERS AND TS COULD
POSSIBLY BE A BIT DELAYED AND NOT ARRIVE UNTIL THE MORNING/EARLY
AFTN.  THE SYSTEM KEEPS PUSHING SOUTH WITH SHOWERS AND STORMS SOUTH
OF THE CWA LATE MONDAY NIGHT. PWATS WILL BE AROUND AN INCH
THROUGHOUT THE EVENT SO A DECENT SOAKING RAIN IS VERY POSSIBLE...BUT
HEAVY RAIN LIKE WE HAVE EXPERIENCED WITH THE PAST FEW SYSTEMS IS NOT
LIKELY.

FOR TEMPS...DID NOT MAKE TOO MANY ADJUSTMENTS TO THE PREVIOUS HIGH
TEMPS FOR SUNDAY.  NOT SURE HOW QUICKLY THE SKIES WILL CLEAR
TOMORROW WITH HIGHER TEMPS EXPECTED IF WE CLEAR QUICKER THAN
INDICATED.  LOW TO MID 80S ARE EXPECTED AT LEAST...WITH OVERNIGHT
LOWS IN THE 60S.  LOWS WILL BE WARMER DOWNTOWN AND SOUTH OF I-80.
HIGH TEMPS ON MONDAY WILL GET INTO THE LOW TO MID 80S AGAIN BUT
EXPECTING A SIGNIFICANT COOLING TREND MONDAY NIGHT AS THE LOW PUSHES
SOUTH.  LOW TEMPS MONDAY NIGHT WILL DROP TO AROUND 60...WITH CLEAR
SKIES HELPING THE COOLING ALONG.

EXTENDED...TUESDAY THROUGH FRIDAY...

HIGH PRESSURE OVER THE NORTHERN GREAT LAKES EXPANDS SOUTHWARD
DOMINATING THE PATTERN THROUGH THE EXTENDED.  A WEAK SHORTWAVE
WEAKENS AS IT APPROACHES NW IL TUESDAY...BUT KEPT TUESDAY DRY.  DRY
WEATHER SETTLES IN THROUGH AT LEAST FRIDAY.  THE RIDGE BEGINS TO
FLATTEN AND THE ZONAL FLOW ALLOWS A SHORTWAVE TROUGH AND SURFACE LOW
TO MOVE NORTH OF THE CWA BRINGING SHOWERS AND TS TO THE REGION
FRIDAY. FOR TEMPS...TEMPS WARM UNDER THE RIDGE TO NEAR NORMAL BY
THURSDAY AND PERHAPS INTO THE MID TO UPPER 80S BY THE END OF THE
WEEK.

JEE

&&

.AVIATION...

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

* TIMING...MAGNITUDE...AND DURATION OF TSRA THIS EVENING.

* POSSIBLE LAKE BREEZE PASSAGE THIS AFTERNOON.

LENNING

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

CONFIDENCE IN CONVECTIVE TRENDS TODAY AND THIS EVENING IS
INCREASING SOMEWHAT...WITH THE BASIC IDEA SIMILAR TO WHAT WAS
ALREADY BEING CONVEYED IN EARLIER FCST PRODUCTS. FACTORS THAT WERE
RESPONSIBLE FOR LAST NIGHTS CONVECTION OVER THE IA/MO/IL
INTERSECTION ARE DEPICTED TO OCCUR AGAIN TONIGHT...AND WITH
GREATER INTENSITY...ACROSS NORTHEAST ILLINOIS.

THE THOUGHT IS THAT EXISTING ACTIVITY TO THE SOUTHWEST OF THE
AREA...FROM MLI TO SPI...WILL ERODE FROM NORTH TO SOUTH AS IT
SLIDES EAST OR SOUTHEAST AND STAYS OUT OF THE LOCAL AREA. ACTIVITY
OVER NORTHERN IOWA ALSO IS BEGINNING TO FADE. NEW ACTIVITY IS
EXPECTED TO DEVELOP IN THE MOIST AND DESTABILIZING AIR OVER SOUTH
CENTRAL IOWA AND EVEN MORE SO ACROSS NORTHERN MISSOURI. THIS NEW
DEVELOPMENT WOULD WORK INTO THE CHICAGO TERMINALS TOWARD THE END
OF THE EVENING RUSH...SOMEWHERE IN THE 02Z TIMEFRAME.

OVERNIGHT THE FOCUS FOR THIS CONVECTION IS DEPICTED TO PUSH
THROUGH THE TERMINALS OVER A 2-3 HOUR PERIOD AND THEN EVENTUALLY DROP
SOUTH BY MORNING.

LENNING

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

* MEDIUM CONFIDENCE ON TIMING OF CONVECTION. COULD ARRIVE AN
  HOUR...POSSIBLY TWO HOURS...EARLIER THAN DEPICTED IN TAFS. LOWER
  CONFIDENCE IN MAGNITUDE OF WINDS AND REDUCED VSBYS.

* MEDIUM TO HIGH CONFIDENCE THAT OVERNIGHT CONVECTION WILL PUSH
  WELL SOUTH OF TERMINALS BY MORNING.

* LOW CONFIDENCE IN WHETHER LAKE BREEZE MIGHT PASS THIS
  AFTERNOON...AND WHEN THAT MIGHT OCCUR. ELECTED TO LEAVE OUT OF
  TAFS FOR NOW.

LENNING

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

SUNDAY NIGHT...VFR.

MONDAY...CHANCE OF PM TSRA...OTHERWISE VFR.

TUESDAY THROUGH THURSDAY...VFR.

FRIDAY...CHANCE OF SHRA/TSRA.

IZZI

&&

.MARINE...
404 PM CDT

LARGE HIGH PRESSURE OVER THE EASTERN UNITED STATES WILL SLOWLY
CONTINUE EAST WHILE A TROUGH OF LOW PRESSURE AND FRONTAL BOUNDARY
OVER THE UPPER MISSISSIPPI VALLEY SHIFT EAST ACROSS THE LAKE
TONIGHT. WITH THIS IN PLACE...EXPECT GENERALLY SOUTHERLY FLOW TO
SPAN THE LAKE BEFORE WINDS TURN MORE TO THE SOUTHWEST OVERNIGHT.
WEAK HIGH PRESSURE WILL THEN BUILD EAST ACROSS THE SOUTHERN GREAT
LAKES ON SUNDAY...WITH A TROUGH OF LOW PRESSURE EXTENDING FROM
SOUTHERN QUEBEC WEST TO SOUTHERN ONTARIO. THIS TROUGH OF LOW
PRESSURE WILL SLOWLY SHIFT SOUTH DOWN THE LAKE SUNDAY NIGHT INTO
MONDAY. WESTERLY WINDS WILL TURN TO THE NORTHWEST AND NORTH AS
THIS TROUGH AND ASSOCIATED BOUNDARY WORK DOWN THE LAKE. WINDS AND
WAVES WILL INCREASE BEHIND THIS TROUGH/BOUNDARY...BUT STILL
REMAINING AT 10 TO 20 KT. HIGH PRESSURE WILL THEN MOVE SOUTHEAST
FROM THE CANADIAN PRAIRIES INTO THE GREAT LAKES BEHIND THIS FRONT
BY MIDWEEK.

RODRIGUEZ

&&

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

$$

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