Severe Thunderstorm Warning 285, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
632 AM CDT Wed Jul 31 2024

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Early morning storms across central Iowa with large hail,
  damaging winds, and heavy rain

- Heat into the afternoon, extent highly dependent on convective
trends.

- Additional round of storms this evening with severe and heavy
  rain threat.

&&

.DISCUSSION...
Issued at 238 AM CDT Wed Jul 31 2024

Storms are passing across central Iowa early this morning, following
along the 850 mb moisture gradient. So far storms have produced
brief periods of quarter to half dollar sized hail, along with
longer lasting dime to penny sized hail. Winds have been reported
mostly in the 30 to 40 mph range but a few stronger gusts over 50
mph have occurred with downbursts. CAMs have struggled significantly
with the evolution of convection the past several days and tonight
is no different. Even so, we expect that the general trend of
training storms along this boundary (which CAMs have shown, even if
timing and placement has been incorrect) will occur with storms
tonight. In the last 60-90 minutes storms have generally produced 1-
1.5 inches of rain. We're near flash flood guidance on this, so will
monitor closely for hydro problems through the rest of the morning.
The good news here is that back building further east has slowed at
this time, which may help reduce more enhanced training storm
concerns. Of course placement will also be in play, as metro areas
will be more susceptible.

Storms are expected to push out of the area by mid morning with a
lull through the daytime. This should allow for temperatures to warm
substantially. Uncertainty in just how high temperatures (and heat
index, with high humidity in place) is high. Should storms and cloud
cover linger later into the day, temperatures will be kept down. As
such, have kept the heat advisory unchanged from the previous shift.
If clearing occurs with optimal warming into the afternoon, this
could be expanded north and/or upgraded to a heat warning as the
potential for extreme heat is there.

Our attention then turns to the next round of convection. This round
is more synoptically driven by a shortwave passing across the area,
which lends towards a least a little more confidence in evolution
compared to the past several nights. Storms will fire across the
plains in the late afternoon, moving into Iowa by late this evening.
By this time it is expected that they will have grown upscale.
Storms will persist through the overnight with damaging winds and
large hail the main hazards. Heavy rain will also be a concern with
this final round, especially in area that receive heavy rain this
morning (and that received it yesterday).

Into this weekend less active with temperatures more seasonal in the
upper 80s to low 90s with heat index only a degree or 2 over
that.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 632 AM CDT Wed Jul 31 2024

Early morning storms continue to move east, impacting KOTM for
the next few hours. Otherwise, VFR conditions for much of the
TAF period. By this evening storms will move into the area and
continue form east to west overnight. Have included -TSRA across
all sites, though further adjustments for wind and visibility
may be needed as storms develop.

&&

.HYDROLOGY...
Issued at 347 PM CDT Tue Jul 30 2024

Once again flash flooding will be possible from this afternoon into
at least Wednesday. In spite of maturing crops (which usually limit
flash flood potential this time of year), recent heavy rainfall has
led to elevated soil moisture values (and thus elevated flash flood
concerns) across much of the CWA. Right now the NASA SPoRT 4-inch
soil moisture as well as CREST and SAC-SMA upper-level soil moisture
parameters all agree on elevated soil moisture values roughly north
of a line from Sioux City to Winterset to Centerville. While soil
moisture values are elevated across much of the CWA north of this
line, the most elevated values are roughly within a 75-mile band
north of that line. In this area the soil moisture values are
elevated such that flash flooding concern is significantly higher
than normal.

With this aforementioned 75-mile wide band, it will take
significantly less rainfall than typical for this time of year to
produce flash flooding. Flash flood guidance values within this
region are as low as 1.7 inches over three hours which could easily
be achieved and exceeded with the potential rainfall through
Wednesday. Even outside this 75-mile band if the rain is heavy
enough then flash flooding would be possible elsewhere across the
CWA especially within a 125-mile band north of the aforementioned
line. Of course urban flooding will be a concern as well regardless
of location with the heavy rainfall amounts that are possible.

In terms of potential river flooding, it would be heavily dependent
on the amount, location and timing of the heavy rainfall. Although
the rivers in the area of most concern through Wednesday have
recovered significantly from the high stages associated with the
flooding last month into the early part of this month, much of the
Des Moines, Skunk and Cedar/Iowa River basins are still reporting
above (76 to 90th percentile) to much above normal (greater than
90th percentile) flows for this time of year. Right now the most
likely scenario according to QPF hydrograph ensemble and HEFS
guidance is that there would be minor to moderate rises on area
rivers with isolated moderate to significant rises possible in
isolated areas.

Make sure to stay up to date on the latest forecasts and river
information, avoid flooded areas and rivers, and never drive around
barricades or through flooded areas.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM this afternoon to 7 PM CDT this
evening for IAZ033>035-044>048-057>061-070>075-081>086-092>097.
Flood Watch until 7 AM CDT this morning for IAZ034>036-045>049-
058>062-072>075-085-086-097.

&&

DISCUSSION...Hagenhoff
AVIATION...Hagenhoff
HYDROLOGY...Zogg

Hazardous Weather Outlook
National Weather Service Des Moines IA
440 AM CDT Wed Jul 31 2024

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-010945-
Emmet-Kossuth-Winnebago-Worth-Palo Alto-Hancock-Cerro Gordo-
Pocahontas-Humboldt-Wright-Franklin-Butler-Bremer-Sac-Calhoun-
Webster-Hamilton-Hardin-Grundy-Black Hawk-Crawford-Carroll-Greene-
Boone-Story-Marshall-Tama-Audubon-Guthrie-Dallas-Polk-Jasper-
Poweshiek-Cass-Adair-Madison-Warren-Marion-Mahaska-Adams-Union-
Clarke-Lucas-Monroe-Wapello-Taylor-Ringgold-Decatur-Wayne-
Appanoose-Davis-
440 AM CDT Wed Jul 31 2024

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

A Flood Watch and Severe Thunderstorm Watch are in effect for the
area. Please refer to the National Weather Service website at
weather.gov/desmoines for further details.

A Heat Advisory is in effect for the area this afternoon. Please
refer to the National Weather Service website at
weather.gov/desmoines for further details.

Additional thunderstorms will arrive late this evening from the
west and move across the state overnight. Damaging winds and large
hail will be the primary threats. Heavy rain is also a concern
for areas that will have received the most rain so far this week.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

A few non-severe thunderstorms may linger into Thursday.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed today through Thursday morning. Rainfall
amount reports are also appreciated.

Hagenhoff

<!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>

<!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>