Severe Thunderstorm Warning 86, NWS Chicago, IL

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1005 AM CDT Sun Jul 19 2020

.MESOSCALE DISCUSSION...
1005 AM CDT

Currently, a compact bowing line of storms (and associated MCV)
is moving across Henry, Bureau, Stark, and northern Marshall
counties. The bow is being driven by a strong 80-85kt RIJ seen
nicely on our radar, with reports from NWS Quad Cities confirming
severe winds are reaching the surface. Given the storm is moving
into an airmass into which heavy rain and hence cool air has been
falling over the past few hours, and the low-level shear is not
optimally strong to balance such a strong surging RIJ/cold pool,
confidence in the damaging winds continuing to plow into La Salle
county is not high even though a reservoir of plentiful
instability exists downstream from the cluster. So, while the bow
may continue eastward through northern Illinois, the highest winds
may remain elevated and hence limit the severe weather threat to
an isolated basis. We touched base with SPC and they agree
- though if damage continues into La Salle county, we will have to
entertain the idea of a Severe Thunderstorm Watch through a small
portion of northern Illinois.

Borchardt

&&

.SHORT TERM...
245 AM CDT

Through Today...

Upstream convection has failed to materialize early this morning
across Iowa and and has been quite slow to develop southward
through western Wisconsin. As of 230am CT, convection has reached
only as far south as near La Crosse. The lack of convection has
prevented any development of a surging cold pool that was
originally expected to spread a line of thunderstorms
southeastward into at least the northern CWA prior to daybreak.
While some widely isolated showers have attempted to develop
across southwest Wisconsin and northwest Illinois in association
with an axis of weak sub- 850 hPa WAA, it appears capping with an
EML originally present on the 00Z DVN RAOB and additional warming
around 750 hPa has been enough to prevent convection in the
absence of any other appreciable forcing. Additionally, rather dry
air within the EML up to at least 500 hPa is eroding any weaker
updrafts that develop. At this time, it appears any convection
that develops will be tied to or just ahead of the surface cold
front currently bifurcating Iowa from NE to SW. A sheared out mid-
level wave within weakly cyclonic flow in the vicinity of the
front may provide enough lift to erode some of the capping.

Putting together everything above, have made substantial delays
to the arrival of any potential thunderstorms to after daybreak
for all but the north-central CWA. Coverage will likely be lower
given the lack of any upstream cold pool, so am not expecting
anything more than a loosely broken line of showers and storms
drifting across northern Illinois through mid-morning. The cold
front will gradually become more W to E oriented while shifting
south across the remainder of the CWA, eventually stalling just
south of the CWA by this evening. Scattered thunderstorms will be
possible at any point in the warm and humid airmass ahead of the
front, with the greatest coverage/chance confined to the far
southern CWA late this afternoon. Any thunderstorm today will have
the potential to produce damaging wind gusts given 40 knot flow
as low as 1.5kft this morning and a dry column this afternoon.

A break from the humidity is expected as much drier air arrives
behind the cold front. If no congealed outflow boundaries develop
and surge southeast this morning, the combination of temps rising
to near 90F and dew points still in the mid 70s will allow heat
index values to rise to around 100F for areas south and east of a
Pontiac to Kankakee to Valparaiso line.

Kluber

&&

.LONG TERM...
302 AM CDT

Tonight through Saturday...

Quieter and a bit more pleasant conditions are still expected for
Monday following todays cold front. A surface ridge of high
pressure will shift over the area for Monday bringing with it some
lower humidity and more seasonable temperatures in the mid 80s.
Slight cooler conditions are likely along the lakeshore due to
the likelihood for an afternoon lake breeze. Any shower and
thunderstorm activity on Monday is expected to remain well south
of the area in closer proximity to the surface boundary.

The threat for some showers and thunderstorms will return to the
area late Monday night and especially on Tuesday as the surface
boundary to our south begins to lift back northward across the
area. Several convectively enhanced impulses are likely to drive
bouts of convection in the viscid of the frontal boundary through
midweek. So as this boundary shifts back northward over the area
on Tuesday we will have a decent shot at having a period or two
showers and storms through Midweek.

The chances for convection look to be lower over our area for the
later half of the week and into the weekend as upper level
heights look to build across the central CONUS. The main story
with these building upper level heights will be the potential for
a return to a period of dangerous heat and humidity next weekend.
This potential will need to be monitored.

KJB

&&

.AVIATION...
For the 12Z TAFs...

Scattered thunderstorms continue to develop along a narrow band
from KPIA to KMDW at press time. With each cell, drops in
visibility to 1SM and wind gusts to 30 kt are likely with the
strongest perhaps producing wind gust in excess of 40 kt. With
time, the band should shift south and east. Additional scattered
thunderstorms may develop this morning ahead of a southward-
drifting front (currently inching into far northwestern
Illinois), and along the front itself. The strategy with the
outgoing TAF package is to offer VCTS at most terminals with a
targeted TEMPO with the expected frontal passage along which a
higher coverage of storms is possible. AMDs will be offered if
thunderstorm cells target individual TAF sites.

In the wake of the front, the TAFs become more trivial with
initially gusty but with time relaxing northwest winds and
scattered cloud cover.

Borchardt

&&

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

Visit us at weather.gov/chicago

Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSChicago
www.twitter.com/NWSChicago
www.youtube.com/NWSChicago

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

Special Weather Statement
National Weather Service Chicago/Romeoville
1115 AM CDT Sun Jul 19 2020

ILZ013-104>108-INZ001-002-191700-
Eastern Will IL-Southern Cook IL-DuPage IL-Southern Will IL-
Central Cook IL-Northern Will IL-Porter IN-Lake IN-
1115 AM CDT Sun Jul 19 2020

...SIGNIFICANT WEATHER ADVISORY FOR EASTERN WILL...SOUTHEASTERN
DUPAGE...SOUTHEASTERN COOK...SOUTHWESTERN PORTER AND LAKE COUNTIES
UNTIL NOON CDT...

At 1114 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Lemont to near Peotone. Movement was east
at 65 mph.

Wind gusts of 50 to 55 mph will be possible with these storms. Winds
were reported at 52 mph at Shorewood, and 48 mph at Romeoville.
Winds of this magnitude can damage small tree limbs and power poles.

Locations impacted include...
Chicago, Hammond, Gary, Orland Park, Tinley Park, Oak Lawn, Downers
Grove, Calumet City, Portage, Merrillville, Woodridge, Chicago
Heights, Englewood, Chicago Lawn, South Shore, Roseland, Midway
Airport, East Chicago, Schererville and Hobart.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

A Severe Thunderstorm Watch remains in effect until 600 PM CDT for
northeastern Illinois...and northwestern Indiana.

LAT...LON 4129 8793 4175 8802 4183 8760 4175 8753
      4171 8753 4167 8747 4168 8743 4164 8743
      4162 8729 4163 8720 4132 8707
TIME...MOT...LOC 1614Z 256DEG 55KT 4170 8795 4134 8784

Donofrio

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
1130 AM CDT SUN JUL 19 2020

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

1119 AM     TSTM WND DMG     LOCKPORT                41.58N 88.06W
07/19/2020                   WILL               IL   PUBLIC

            TRANSFORMER BLOWN DOWN FROM POWER POLE
            REPORTED AT DIVISION & HAMILTON ST.

&&

MTF

Special Weather Statement
National Weather Service Chicago/Romeoville
1142 AM CDT Sun Jul 19 2020

ILZ023-033-039-INZ010-011-019-191715-
Iroquois IL-Kankakee IL-Ford IL-Newton IN-Jasper IN-Benton IN-
1142 AM CDT Sun Jul 19 2020

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN KANKAKEE...
SOUTHEASTERN FORD...IROQUOIS...BENTON...NEWTON AND JASPER COUNTIES
UNTIL 1215 PM CDT/115 PM EDT/...

At 1142 AM CDT/1242 PM EDT/, Doppler radar was tracking strong
thunderstorms along a line extending from near DeMotte to Earl Park
to near Gifford. Movement was east at 60 mph.

Wind gusts of 50 to 55 mph will be possible with these storms.

Locations impacted include...
Rensselaer, Watseka, Paxton, Fowler, Kentland, Milford, Otterbein,
Remington, Morocco, Lake Village, Roselawn, Oxford, Sheldon,
Goodland, Brook, Cissna Park, Boswell, Hopkins Park, Buckley and
Martinton.

Including the following interstates...
 I-57 between mile markers 258 and 274.
 Indiana I-65 between mile markers 200 and 231.

This includes...  US 41 Dragway.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

A Severe Thunderstorm Watch remains in effect until 600 PM CDT/700 PM
EDT/ for northeastern and east central Illinois...and northwestern
Indiana.

LAT...LON 4091 8699 4084 8699 4084 8710 4048 8709
      4049 8794 4040 8793 4040 8819 4079 8794
      4117 8748 4118 8736 4112 8693 4091 8693
TIME...MOT...LOC 1642Z 282DEG 55KT 4116 8722 4069 8743 4039 8799

Donofrio

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE CHICAGO IL
1142 AM CDT SUN JUL 19 2020

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

1138 AM     TSTM WND GST     MIDWAY AIRPORT          41.78N 87.75W
07/19/2020  M55 MPH          COOK               IL   ASOS

&&

MTF