Severe Thunderstorm Warning 66, NWS Chicago, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
312 PM CDT SAT JUN 21 2014

.DISCUSSION...
200 PM CDT

MAIN CONCERNS FOR TONIGHT WILL CONTINUE BE ON THE POTENTIAL FOR
ISOLATED THUNDERSTORMS ALONG WITH REDEVELOPING FOG.

NORTHERN IL/NORTHWEST IN HAVE BECOME UNSTABLE WITH GENERALLY MU-CAPE
VALUES BETWEEN 2000-3000J/KG...WITH A WEAK MID-LVL VORT SLIDING
EAST/SOUTHEAST ACROSS THE FORECAST AREA. THIS WILL SERVE AS THE
FOCAL POINT FOR SEEING ISOLATED STORMS...POSSIBLY SEVERE STORMS
BETWEEN 20-23Z THEN EXPECTED TO STEADILY DECREASE IN COVERAGE AND
INTENSITY BY 2Z. TEMPS WILL REMAIN MILD OVERNIGHT WITH LOWS
GENERALLY IN MID/UPR 60S AND A FEW LOCATIONS ONLY DIPPING TO ARND
70. THERE WILL REMAIN AN ISOLATED POTENTIAL FOR SHRA/TSRA
OVERNIGHT...HOWEVER THE FOCUS OVERNIGHT WILL BE ON FOG DEVELOPMENT.
WITH A VERY MOIST ENVIRONMENT LINGERING OVER THE REGION
TONIGHT...FOG DEVELOPMENT IS VERY FAVORABLE. HOWEVER THE CHALLENGE
WILL BE ON THE INTENSITY. AT THIS TIME WILL LEAN TOWARDS VSBY ONLY
DIPPING TO ARND 1-3SM...HOWEVER A FEW POCKETS OF PATCHY DENSE FOG
MAY OCCUR.

SUNDAY...
VERY WARM/MOIST ATMOSPHERE WILL LINGER THRU SUN AS WELL. NOT
PLANNING TO MAKE MANY CHANGES TO THE GOING FORECAST FOR SUN. STILL
LOOKS TO BE A GOOD CHC FOR SEEING SCATTERED STORMS REDEVELOP IN
THE MIDDAY THRU AFTN TIMEFRAME. GUIDANCE HAS BEEN INDICATING SOME
MID-LVL DIFFLUENCE RIDING ALONG A WEAK RIDGE FOR THE MIDDAY/AFTN
SUN TIMEFRAME. THIS COULD ACT AS AN INHIBITOR FOR CONVECTIVE
DEVELOPMENT. ALTHOUGH CONFIDENCE IN THE STRENGTH OF THIS IS
MINIMAL...SO HAVE OPTED TO KEEP THINGS AS IS FOR SUN AND MENTION
THE TSRA POTENTIAL.

WITH AN EXPECTED TURNING IN THE
WINDS...IT IS POSSIBLE THAT A LAKE BREEZE COULD PUSH INLAND AND KEEP
TEMPS COOLER FOR FAR NORTHEAST IL. AT THIS TIME THE THINKING IS THAT
WINDS WILL REMAIN SOUTHERLY FOR THE MOST PART.
PWAT VALUES WILL LINGER ARND 1.5-2"...WITH CONTINUED MOISTURE
CONVERGENCE IN THE LOW/MID LEVELS. SO WHATEVER STORMS ARE ABLE TO
DEVELOP...THEY WILL LIKELY BE ABLE TO EFFICIENTLY PRODUCE VERY HEAVY
RAINFALL.

BEACHLER

REMAINING FORECAST DISCUSSION WILL BE ISSUED SHORTLY...

&&

.AVIATION...

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

* SCATTERED TSRA THROUGH EARLY EVENING.
* ERRATIC/GUSTY WINDS FROM TSRA OUTFLOW BOUNDARIES.
* IFR/LIFR CIGS OVERNIGHT/SUNDAY MORNING.
* POSSIBLE FOG OVERNIGHT/SUNDAY MORNING. CMS

//DISCUSSION...UPDATED 20Z...

WITH A VERY MOIST AND UNSTABLE AIRMASS...ISOLATED TSRA POSSIBLE AT
ANY TIME BUT FOCUS SEEMS TO BE IN TWO AREAS FIRST FROM VPZ/JOT/PNT
AND THEN BACK FROM JVL/FEP/SFY. ITS THIS SECOND AREA OVER NORTHWEST
IL THAT MAY CONTINUE TO DEVELOP AND SPREAD EAST ACROSS THE
TERMINALS DURING THE LATE AFTERNOON...POSSIBLY LINGERING INTO EARLY
THIS EVENING. THE HEAVIEST STORMS WILL BRIEFLY REDUCE CIGS/VIS TO
IFR WITH VERY HEAVY RAINFALL. STRONG/GUSTY WINDS WILL ALSO
ACCOMPANY THE STRONGEST STORMS. IN ADDITION AS THESE WINDS MOVE
AWAY FROM THE STORMS...OUTFLOW BOUNDARIES MAY CAUSE WIND SHIFTS.
THERE IS A LAKE BREEZE NEAR THE LAKE BUT IS NOT MAKING MUCH
PROGRESS INLAND BUT WILL NEED TO BE MONITORED INTO THE EARLY
EVENING. CMS

PREVIOUS 18Z DISCUSSION...

VISIBLE IMAGERY THIS AFTN SHOWS MOST CLOUD COVER CONFINED TO NORTH
OF CENTRAL IL OVER THE TAF SITES...WITH SOME ENHANCEMENT BEGINNING
TO DEVELOP. RADAR RETURNS HAVE BEEN SHOWING ISO TSRA DEVELOPING
AND HAVE BEEN PRODUCING SOME LIGHTNING WITH EXPECTED CONTINUE
GROWTH IN SIZE AND INTENSITY OF THE THUNDERSTORMS. WINDS ARE
GENERALLY FROM THE SOUTHEAST ACROSS FAR NORTHEAST IL/NORTHWEST
IN...MEANWHILE JUST WEST OF THOSE SITES WINDS TURN TO
SOUTHWESTERLY OR SOUTHERLY. WITH THE LACK OF A GRADIENT...SPEEDS
HAVE HELD AROUND 8KT OR LESS WITH AN OCCASIONAL GUST TO 16KT. IF
TSRA CAN BECOME MORE ORGANIZED...THE POTENTIAL FOR WINDS TO BECOME
STRONGER IN AND ARND TSRA IS PROBABLE. THE BEST TIMING FOR
INCREASED COVERAGE IN TSRA WILL BE 20-23Z FOR NORTHERN IL...THEN
LINGERING TO JUST AFT 00Z ACROSS NORTHWEST IN. LATER THIS EVENING
THE POTENTIAL OF AN ISO TSRA CONTINUES...HOWEVER THE CONFIDENCE IN
COVERAGE AND PRECISE TIMING DECREASES. SO HAVE OPTED TO HOLD OFF
ON ANY MENTION OF ADDTL TSRA THIS EVE. OVERNIGHT WINDS BECOME LGT
AND VRB AGAIN...WITH THE POSSIBILITY OF FOG REDEVELOPING. AT THIS
TIME CONFIDENCE IS THAT THE DENSE FOG SHOULD BE CONFINED TO LAKE
MICHIGAN. ALTHOUGH THAT BEING SAID MOST TAF SITES WILL STILL SEE
VSBYS DROP TO ARND 2-3SM AND POSSIBLY RFD/DPA COULD DIP TO ARND
1SM OVERNIGHT.

BEACHLER

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

* MEDIUM FOR TSRA THROUGH EARLY EVENING.
* MEDIUM FOR PREVAILING WINDS THROUGH THE PERIOD.
* MEDIUM FOR IFR/LIFR CIGS OVERNIGHT/SUNDAY MORNING.
* MEDIUM FOR FOG OVERNIGHT/SUNDAY MORNING. CMS

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

SUNDAY NIGHT...CHANCE TSRA.

MONDAY...TSRA LIKELY.

TUESDAY THROUGH THURSDAY...PERIOD CHANCES FOR TSRA/SHRA.

THURSDAY NIGHT AND FRIDAY...VFR. WX NIL.

KREIN

&&

.MARINE...
234 PM CDT

GENERALLY LIGHT WIND REGIME OUTSIDE OF THUNDERSTORM INDUCED WINDS TO
CONTINUE THOUGH MONDAY NIGHT WHEN A COLD FRONT WILL SWEEP ACROSS THE
LAKE BRINGING DRYER CONDITIONS AND NORTHERLY FLOW BY TUESDAY.  UNTIL
THEN... EXPECT AREAS OF DENSE FOG TO PERSIST OVER THE LAKE WITH
WINDS GENERALLY REMAINING AT OR BELOW 20 KTS AND WAVES AT OR BELOW 3
FEET. WINDS AND WAVES WILL BE HIGHER NEAR THUNDERSTORMS.

A RIDGE OF HIGH PRESSURE FROM JAMES BAY TO THE CENTRAL GREAT LAKES
WILL REMAIN NEARLY STATIONARY TONIGHT AND THEN GRADUALLY DRIFT EAST
SUNDAY.  MEANWHILE WEAK LOW PRESSURE OVER WISCONSIN WILL SLIDE
SOUTHEAST ALONG A NEARLY STATIONARY FRONTAL BOUNDARY ACROSS NORTH
CENTRAL ILLINOIS TO SOUTHEAST ILLINOIS OVERNIGHT AND DISSIPATE.  WEAK
LOW PRESSURE OVER THE CENTRAL PLAINS WILL BECOME BETTER ORGANIZED AS
IT DOES AND MOVE EAST.  THIS LOW WILL REACH CENTRAL IOWA BY DAYBREAK
MONDAY AND MOVE TO THE EASTERN UPPER PENINSULA OF MICHIGAN BY
OVERNIGHT MONDAY INTO TUESDAY.

A WEAK COLD FRONT ASSOCIATED WITH THIS LOW WILL THEN SWEEP ACROSS THE
LAKE LATE MONDAY NIGHT INTO TUESDAY...TURNING WINDS FROM SOUTHERLY
TO NORTHERLY. BROAD HIGH PRESSURE WILL THEN BUILD INTO THE UPPER
GREAT LAKES WEDNESDAY LASTING INTO THURSDAY.

ED F

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...DENSE FOG ADVISORY...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-
     LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-
     LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 10 AM SUNDAY.

&&

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
208 PM CDT SAT JUN 21 2014

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0133 PM     HAIL             4 SE NEW LENOX          41.48N 87.93W
06/21/2014  E0.50 INCH       WILL               IL   COCORAHS

            SIZE - 1/4 TO 1/2 INCH.

0140 PM     HEAVY RAIN       4 SE NEW LENOX          41.48N 87.93W
06/21/2014  E0.59 INCH       WILL               IL   COCORAHS

            RAINFALL IN APPROX 13 MINUTES.

&&

BN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 PM CDT SAT JUN 21 2014

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0130 PM     HAIL             5 ENE MANHATTAN         41.45N 87.90W
06/21/2014  E0.25 INCH       WILL               IL   COCORAHS

&&

BN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
251 PM CDT SAT JUN 21 2014

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0150 PM     HAIL             3 SE MANHATTAN          41.40N 87.95W
06/21/2014  E0.25 INCH       WILL               IL   EMERGENCY MNGR

            AT US52 AND CEDAR RD.

0150 PM     TSTM WND DMG     3 SE MANHATTAN          41.40N 87.95W
06/21/2014                   WILL               IL   EMERGENCY MNGR

            AT US52 AND CEDAR RD - SEVERAL SMALL BRANCHES DOWN. ALSO
            MINOR STREET FLOODING SOUTHWARD INTO WILTON CENTER.

&&

BN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
310 PM CDT SAT JUN 21 2014

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0248 PM     TSTM WND GST     4 SW GARDNER            41.15N 88.37W
06/21/2014  E60 MPH          GRUNDY             IL   TRAINED SPOTTER

            PEA SIZE HAIL.

&&

BEACHLER