Severe Thunderstorm Warning 224, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
619 PM CDT Sun Jul 7 2024

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Scattered showers/storms Nearly Every Day this week. Some with
  locally heavy rainfall this evening; marginal severe this
  evening
- Seasonal Temps Through Next Friday
- Western Ridge Builds East Late in Period with temperatures heating
  up into the 90s by Saturday

&&

.DISCUSSION...
Issued at 202 PM CDT Sun Jul 7 2024

.Short Term /Tonight through Monday Night/...

Confidence Short Term:  Medium to High

Relatively weak flow continues with tropical airmass in place. We
continue to see a slowly moving large surface trough over the
Northern Plains with an upper level reflection stretching from the
Northern Plains south into the Southern Plains. A large subtropical
high situated in the Antilles and stretching northeast into the
southeast US continues to provide a constant deep moisture plume of
+15C dewpoints north into Iowa. The northern extent of the +15C is
just at the border at 12z. Within the elongated upper level trough,
several weak short waves southwest of Iowa will track into the
region within the next 24 hours. This and an approaching cool front
will be enough to create another round of showers and storms late
this afternoon through tonight. PWATs over the southeast will
continue to range from 1.5 to 1.75 in later this afternoon and
tonight. Warm cloud depths are holding around 11kft. All combined,
we have another late afternoon and evening of tropical rain and with
relatively modest steering currents of 20 to 25 kts aloft, will be
susceptible to isolated, but locally heavy rainfall amounts in
excess of 2 to 3 inches. Though BWD is relatively weak early this
evening under 20kts, later in the night along the trailing boundary,
BWD increases to 30 to 35kts. This evening we will likely see some
pulse storms with wind and some hail potential and later in the
night, some organization is possible later in the evening for a
short period of time prior to 05z. After midnight, instability will
be weakening enough to allow storms to lessen in intensity. By
tomorrow evening, the main trough will be exiting the area. We will
still have some lingering showers and possible isolated storms mainly
east of I35 on Monday prior to 00z. Tomorrow night will quiet down
with partly cloudy skies and some fog expected. Tonight and Monday
night mins will be rather mild again with overnight lows around 60
northwest to the mid 60s southeast. Monday will be similar to today
with highs in the upper 70s to lower 80s.

.Long Term /Tuesday through Sunday/...

Confidence: Medium to High

By Tuesday we will be under the influence of weak high pressure. The
remnants of Beryl will be drifting north northeast into the mid
Mississippi River Valley. At this time, there is general consensus
that the old tropical system will remain far enough southeast of
Iowa to not directly influence our weather with any precipitation.
Though the GFS/GEFs suite is indicating otherwise, the bias of the
GFS suite is likely resulting in a suspect solution. The EPS/EC
system keeps the core of the ex-tropical tracking from northeast AR
to northeast Indiana by 18z Wednesday.  A widespread 2 to 4 inches
of rain is expected along its track and thankfully will not impact
our area with any more rainfall.  Despite this, the one thing that
will happen is a weak phasing of the old tropical system with a
lingering weak trough in the current northwest flow. As indicated by
some of the models, a subtle amount of falling heights Tuesday
afternoon, along with daytime heating and expected instability, may
be enough to produce a few showers/iso storms over northern Iowa.
Wednesday into Thursday a similar weak trough tracks along the
western fringes of old Beryl and across Iowa, bringing some airmass
showers and thunderstorms to the region during the afternoon and
early evening. At this time, it appears that the better chances will
be Wednesday with the stronger H500 trough. Thursday will be warm
and continued humid, but with lesser afternoon chances for any rain.
By Friday, the weak high we had hoped would keep us rain free the
previous few days will be moving east. Subtle warm air advection
will arrive later Friday afternoon. This will be enough to bring
some small thunder chances into the region once again. Highs during
the period Tuesday through Thursday will remain in the lower to mid
80s with lows in the lower to mid 60s.

Looking ahead to the weekend, the one consistent signal for Iowa
will be rapidly warming temperatures back to the 90s. There remains
a consistent signal for the western ridge to build east during the
period. h850 temperatures are forecast to rise into the lower to mid
20s. This will likely propel highs into the lower to mid 90s. Late
in the period a lazy east to west boundary will set up over northern
Iowa or southern Minnesota. South of the boundary will be capped
with H700 temperatures from 12 to 14C. At this time, the
GFS/GEFS/EPS solutions support the front remaining farther north
into southern to central Minnesota. This should keep the region dry
over the weekend with heat now becoming the main concern. Heat
indices should rise to the lower 90s east Saturday to mid to upper
90s central to west Saturday and to the mid 90s to around 100 on
Sunday.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 619 PM CDT Sun Jul 7 2024

Challenging period to nail down timing and any impacts to
terminals from first storms this evening that will exit
overnight and then second patchy fog that may develop toward
daybreak Monday. Storms are slowly becoming more numerous from
northern Iowa from DEH to MCW to SUX, around CBF/OMA, and now
CNC. Expect the showers and storms over western Iowa to be the
more widespread to our terminals as they move in this evening
and this is where the forecast groups have been focused. As the
storms move out, there will be a period where low level moisture
will remain high with light winds. This may allow fog to develop
and have highest confidence at MCW and ALO with lower
confidence/6SM BR at DSM and OTM. After any fog dissipates, VFR
conditions are shown to prevail, though there may be a few
showers or storms over northeastern Iowa Monday afternoon.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

DISCUSSION...REV
AVIATION...Ansorge

Hazardous Weather Outlook
National Weather Service Des Moines IA
220 PM CDT Sun Jul 7 2024

IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097-081930-
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-
220 PM CDT Sun Jul 7 2024

This Hazardous Weather Outlook is for portions of central Iowa.

.DAY ONE...This afternoon and tonight

Scattered thunderstorms are expected across much of the area late
this afternoon into evening. A few strong to severe storms with
wind and/or hail are possible, especially in portions of central
to southeast Iowa. Locally heavy rainfall may also occur.

.DAYS TWO THROUGH SEVEN...Monday through Saturday

Isolated to scattered showers or thunderstorms remain in the
forecast through the next several days, primarily during the
afternoon into early evening hours. The severe weather potential
remains low through at least Tuesday.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed briefly tonight.

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