Flash Flood Warning 4, NWS Des Moines, IA

300 
WGUS73 KDMX 021510
FFSDMX

Flash Flood Statement
National Weather Service Des Moines IA
1010 AM CDT Wed Aug 2 2023

IAC029-021520-
/O.CAN.KDMX.FF.W.0004.000000T0000Z-230802T1630Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Cass IA-
1010 AM CDT Wed Aug 2 2023

...FLASH FLOOD WARNING IS CANCELLED FOR CENTRAL CASS COUNTY...

The heavy rain has diminished. Flooding is no longer expected to 
pose a threat. Please continue to heed remaining road closures.

LAT...LON 4148 9516 4137 9470 4132 9470 4125 9470
      4124 9470 4118 9470 4128 9516 4129 9516
      4132 9516 4133 9516 4135 9516 4136 9516
      4137 9516 4139 9515

$$

Zogg

Area Forecast Discussion
National Weather Service Des Moines IA
253 AM CDT Wed Aug 2 2023

.DISCUSSION.../Today through Tuesday/
Issued at 247 AM CDT Wed Aug 2 2023

Take Home Points:

* Heavy rain potential through this morning across portions of
  southern Iowa, isolated strong to severe possible
* Lingering shower/thunder activity into Wednesday overnight as
  shortwave impulses slide through
* Additional shower/thunder chances into/through the weekend
* Seasonable to seasonably cool temperatures

Discussion:

As generally expected, thunderstorm activity quickly ramped up this
evening, around/after 06z, in conjunction with a modest LLJ and mid-
level boundary/baroclinic zone. Hi-res guidance, namely the HRRR,
has struggled mightily with initiation timing and area as compared
to reality, leading to some wholesale adjustments to the near-term
forecast. Additionally, an area/gradient of elevated MUCAPE values
across SW Iowa around/in excess of 2000-3000 J/kg has raised some
concern for a few storms to flirt with severe criteria. Current SPC
mesoanalysis does not co-locate supportive effective shear with
current activity, supported by radar analysis, and should result in
a more pulsey severe threat for hail and damaging winds. The main
threat, though, looks to continue to revolve around efficient heavy
rainfall with warm cloud layer depths to around 4km, Pwats in excess
of 2 inches, persistent moisture advection into the
boundary/baroclinic zone, and some training activity given mean wind
orientation to initiation areas. Hi-res guidance depictions of
localized potential for 5 inches or more will be possible. Best
opportunity for such rainfall amounts will reside in areas south
of Interstate 80. RFC FFG of around 3 inches will be most
appropriate for urban areas, whereas rural areas and agriculture
fields commonly handle 3+ inch rainfalls with minimal issue during
the growing season. This should be especially true with the
predominantly dry antecedent conditions. Should we start to see
training activity result in more widespread areas approaching 4 to
5+ inches, flash flood products will become increasingly
likely/necessary.

This activity will ease through the morning as the LLJ subsides, but
additional shower/storm activity appears likely by late morning into
the afternoon as a shortwave trough slides in from Nebraska. While
more progressive in nature, the potential for an additional 1 to 2
inches may be possible. Location appears to be a bit further
north than the earlier activity.

Through the remainder of the work week, upper level ridging flattens
with shortwave activity to the west, helping keep conditions
seasonable in the 80s. Remains somewhat difficult to hammer down
additional shower/storm details given the variance in timing,
track, and strength depicted in guidance. Friday into Saturday may
be the next best opportunity for showers/storm as a boundary
oozes southward from larger trough moving across Canada and a few
shortwaves move across the area. Into Sunday, guidance continues
to show a stronger shortwave trough moving across the region and
an attendant cool front. This may provide another round of
activity before seasonably cool conditions next week in the upper
70s to low 80s.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1149 PM CDT Tue Aug 1 2023

Showers with embedded lightning continue to impact mainly KDSM and
KOTM late this evening, which are expected to push out over the
next hour or two. A boundary kicking off showers and storms is
then expected to bring more active weather after 06-09z into
Wednesday, though still generally affecting central and southern
Iowa per most recent guidance. Could see periods of thunderstorms
with this activity, though heavy rain looks to be a concern,
especially over the far south. Low ceilings and possible reduced
visibilities allowing for MVFR and possible brief IFR conditions
at times are expected. Additional shower and storm chances are
expected later in the day but overall uncertainty is pretty high
at this time. Close monitoring on how things play out through this
forecast period will continue.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

DISCUSSION...Curtis
AVIATION...Bury

Hazardous Weather Outlook
National Weather Service Des Moines IA
349 AM CDT Wed Aug 2 2023

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-030900-
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-
349 AM CDT Wed Aug 2 2023

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...Today and tonight

Additional showers and thunderstorms are likely later today
across portions of central and southern Iowa. While the severe
threat is low, the strongest of storms may produce damaging hail
and gusty winds in addition to heavy rain.

Locally high rainfall amounts are possible, especially in the far
south.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

Additional chances for showers and thunderstorms are possible
Friday and through the weekend. Severe threat appears on the lower
end, though details remain uncertain.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated.

Special Weather Statement
National Weather Service Des Moines IA
203 AM CDT Wed Aug 2 2023

IAZ070-020745-
Cass IA-
203 AM CDT Wed Aug 2 2023

...A strong thunderstorm will impact portions of western Cass County
through 245 AM CDT...

At 202 AM CDT, Doppler radar was tracking a strong thunderstorm near
Walnut, or 9 miles west of Atlantic, moving east at 25 mph.

HAZARD...Nickel size hail and rainfall up to one and half inches.

SOURCE...Radar indicated.

IMPACT...Minor damage to outdoor objects is possible. Ponding of
         water on roadways, low visibilities, and rises in small
         streams and creeks.

Locations impacted include...
  Atlantic.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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

&&

LAT...LON 4148 9515 4149 9490 4119 9497 4126 9516
TIME...MOT...LOC 0702Z 282DEG 20KT 4142 9520

MAX HAIL SIZE...0.88 IN
MAX WIND GUST...<30 MPH

Ansorge