Severe Thunderstorm Warning 166, NWS Des Moines, IA

Area Forecast Discussion
National Weather Service Des Moines IA
1149 PM CDT Sun Jun 16 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Strong to severe storms with damaging winds, heavy rain and
  hail the primary threats. Locally heavy rainfall possible,
  but the highest amounts look to remain north of the state at
  this time.

- Continued above average temperatures with heat indices in the
  mid to upper 90s to start the week.

- Storm chances return Tuesday night with rain chances lingering
  through the remainder of the week. Storms Tuesday night could
  be strong to severe and produce heavy rain.

&&

.DISCUSSION...
Issued at 247 PM CDT Sun Jun 16 2024

Earlier this morning, an MCV progressed across the south,
bringing with it clouds and some precipitation in the southeast.
Temperatures have since then mostly recovered, with far
southeastern areas such as Ottumwa likely having highs limited
into the 80s this afternoon. Visible satellite imagery has a
front tailing from an area of low pressure located in western
MN. This front extends down into northwest Iowa and further
southwest into Nebraska and Kansas. Connected on the other end
of the front is a developing surface low off the Rockies. This
low will be pulled to the northeast, placing the connecting
boundary near the IA-MN border. At this time, expecting CI to
hold off until near or after sunset as the column cools. The
limiting factor for daytime convection is 700mb temperatures
nearing 12 degrees C. A 50kt+ LLJ will enhance moisture return
in the northwest part of the state and assist in rain production
towards the end of the night. With CAPE in excess of 2000 J/kg,
storms could be strong to severe with damaging winds and hail.
Better deep layer shear will be closer to the parent upper low,
but the jet from the southwest will provide sufficient shear for
organization in the lowest 3km. Given the noticeable moisture
in the air, the more obvious concern would be heavy rain. The
latest HREF suite keeps the H85 front, thus the highest amounts
of precipitation, in southern Minnesota. Still, due to the
aforementioned nocturnal jet, northwest Iowa could see rainfall
amounts up to 1.5 inches from rain.

The boundary will sag into Iowa Monday, but the environment looks
capped at this time. Cooler air will be ushered in behind it and
with the combination of lingering clouds, high temperatures in the
north will be held into the 80s. Highs may underperform elsewhere
for a couple of other factors: 1) The thermal ridge is being pulled
further north, remaining more to the west of the area 2) Speaking to
the noticeable amount of moisture in the atmosphere, the specific
heat capacity of water is very high. Consequently, a moist airmass
such as this will have a very difficult time pushing well into the
90s. The mugginess will not help the comfortability factor,
however. Winds on Monday will be breezy, especially beneath the
enhanced flow over the west. Soundings have mean ML winds
exceeding 30kts in the afternoon there in the late afternoon
hours.

Southwest flow will push the boundary back into Minnesota Monday
afternoon and keep Monday night dry, but also mild, with lows once
again in the 70s. Temperatures will have the same struggles as
Monday. Breezy conditions coat more of the state. PWAT values
pushing 2 inches will build into the state Tuesday as the
constrained low driving the muggy pattern finally is allowed to move
east. Its trailing cold front will move across the state Tuesday
evening and overnight, giving the state another chance at severe
weather and heavy rain.

In the long term, the upper level ridge will build into the region
more, stalling the aforementioned boundary somewhere nearby and
shoving back northwest. As it retreats, Iowa will be back in the
warm sector at some point near the end of the work week. As long as
this boundary remains somewhere nearby, rain will be in the forecast
for parts of the state, especially the north.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1149 PM CDT Sun Jun 16 2024

Thunderstorms will move across South Dakota and Minnesota
overnight but remain largely north of Iowa. Toward Monday
morning, however, some storms may bleed into northern Iowa and
impact MCW at times with MVFR ceilings/visibilities, so have
included a mention there. Otherwise, VFR conditions will prevail
through the TAF period and beyond.

&&

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

&&

DISCUSSION...Jimenez
AVIATION...Lee

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