Special Weather Statement, NWS Chicago, IL

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
111 PM CDT Sun Jul 23 2017

.SHORT TERM...
1248 PM CDT

Compact and digging upper trough over the upper great lakes will
continue southeast tonight. Height falls on the back side of the
trough will provide enough forcing ahead of a cold frontal
boundary to trigger scattered showers and thunderstorms during the
peak heating period this afternoon/early evening. Surface
convergence is weaker, possibly aided by the lake breeze, thus
scattered coverage seems appropriate. The parameter space of
instability/shear of approaching around 1000 j/kg and 30kt
respectively, with hail growth and downdraft cape at respectable
levels, places a marginal risk of damaging winds and large hail,
consistent with the SPC outlook.

The thunderstorm concerns will end quickly this evening as these
combined factors all shift southeast with the arrival of the
cooler and drier airmass behind the frontal boundary and
increased surface pressure ahead of large high pressure across
the upper midwest.

Behind the front in MN and across lake superior there is an area
of lower clouds. Some of these clouds will likely move southward
behind The front later tonight into early monday in our area as
well and Linger a bit in the morning. Breezy northeast winds will
also be in place through the remainder of the day providing some
natural air conditioning to the region after the recent muggy
period, with 70s for highs most areas.

&&

.LONG TERM...
111 PM CDT

Monday night through Sunday...

Model guidance is in pretty good agreement that the upcoming week
into next weekend will generally be much drier, both in terms of
precipitation amounts and dewpoints.

Tuesday should feature sunshine and seasonably warm temps and
comfortable humidity levels with an afternoon lake breeze knocking
temps lakeside down a bit. Temps and humidity will begin to creep
back upward Wednesday as southerly flow becomes established in
advance of the next shortwave and associated cold front.

Generally pretty good agreement between the GFS/GEM/ECMWF with
respect to timing of midweek cold frontal passage, which looks to
be in the later Wed night into Thursday morning time frame. Fairly
stout trough with plenty of moisture around would suggest a still
respectable chance of showers/storms despite the unfavorable
frontal timing. If timing of front slows in later model runs, then
chances for convection would likely end up being a bit higher.
Regardless of the timing, all indications are that this will be a
progressive trough and front, not one that looks overly concerning
at this distance for a major rain event that would have a big
impact on already swollen rivers.

In the wake of that front, all indications are that next weekend
will feature some really fantastic mid-summer weather with fairly
seasonable temps (maybe a bit below average), afternoon lake
breezes, comfortable humidity, and sunshine.

- Izzi

&&

.AVIATION...
For the 18Z TAFs...

Scattered showers and thunderstorms this afternoon are the main
concern for the tafs. We are seeing development across WI, and we
continue to work on destabilization across IL ahead of an upper
level shortwave/. The window will be fairly narrow for any one
location. Convergence ahead of the upper wave is somewhat weak,
Though could be aided by any lake breeze this afternoon. Therefore
scattered coverage seems appropriate. Some gusty/erratic winds or
even some hail are possible. The lake breeze will also push
inland, but confidence on how quickly it reaches ORD/MDW is not
super high given any potential modulation due to convection.
Eventually winds will settle NNE.

Behind the front in MN and across Lake Superior there was an area
of Mvfr/local ifr conditions this morning. Some MVFR ceilings may
filter southward behind the front later tonight into early monday
in our area as well and linger a bit in the morning. Breezy
northeast Winds will also be in place through the remainder of the
taf period.

KMD

&&

.MARINE...
111 PM CDT

Fairly typical summer pattern over the lake with high pressure
resulting in primarily land/lake breeze circulation winds Tuesday
before the high moves east Tuesday night allowing for a period of
more defined southerly winds midweek. Cold front will move down the
lake Wednesday night with a shower and thunderstorm potential
followed by a wind shift to northerly in the wake of the front.
Does look like a period of fresh northerlies Thursday into Thursday
evening before high pressure settles into the western Lakes region
allowing for a return to primarily a land/lake breeze regime next
weekend.

- Izzi

&&

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

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

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>

Special Weather Statement
National Weather Service Chicago/Romeoville Il
217 PM CDT SUN JUL 23 2017

ILZ005-006-231930-
Lake IL-McHenry IL-
217 PM CDT SUN JUL 23 2017

...SIGNIFICANT WEATHER ADVISORY FOR WEST CENTRAL LAKE AND EAST
CENTRAL MCHENRY COUNTIES UNTIL 230 PM CDT...

At 217 PM CDT, Doppler radar was tracking a strong thunderstorm over
Johnsburg, or over McHenry, moving southeast at 20 mph.

Nickel size hail and winds in excess of 40 mph will be possible with
this storm.

This strong thunderstorm will be near...
  Prairie Grove around 220 PM CDT.
  Lakemoor and Volo around 225 PM CDT.
  Round Lake, Island Lake and Holiday Hills around 230 PM CDT.

LAT...LON 4236 8834 4241 8829 4234 8813 4226 8823
TIME...MOT...LOC 1917Z 311DEG 18KT 4235 8826

IZZI

<!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 Il
234 PM CDT SUN JUL 23 2017

ILZ006-232000-
Lake IL-
234 PM CDT SUN JUL 23 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHWESTERN LAKE COUNTY UNTIL
300 PM CDT...

At 234 PM CDT, Doppler radar was tracking a strong thunderstorm over
Wauconda, moving southeast at 20 mph.

Nickel size hail and winds in excess of 40 mph will be possible with
this storm.

This strong thunderstorm will be near...
  Tower Lakes around 240 PM CDT.
  Lake Zurich and Hawthorn Woods around 250 PM CDT.
  Mundelein around 300 PM CDT.

Other locations impacted by this storm include North Barrington and
Lake Barrington.

LAT...LON 4226 8801 4219 8814 4228 8820 4230 8820
      4232 8815
TIME...MOT...LOC 1934Z 311DEG 18KT 4229 8816

IZZI

<!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>