-- Discussion containing changed information from previous version are highlighted. --
386
FXUS63 KDMX 232344
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
644 PM CDT Sun Jun 23 2024

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

.KEY MESSAGES...

- Temperatures in the upper 80s to low 90s tomorrow and Tuesday.
  Heat index values near 100 to 105 F possible west on Monday.

- Chance for a few strong to severe storms on Monday, wind and
  hail being the main concerns.

- More shower and thunderstorm chances expected on Tuesday.
  Primary severe threats would be wind and hail, with locally
  heavy rainfall possible.

&&

.DISCUSSION...
Issued at 332 PM CDT Sun Jun 23 2024

>> Quiet Today then Hot Tomorrow

Surface high pressure has dictated weather conditions today,
resulting in a calm and clear day across Iowa. In the upper levels,
ridging continues to build over the southwest CONUS, which will
begin to influence our temperatures as the surface high departs
tonight and southerly flow takes over through tomorrow. In addition
to the increasing warm air advection, 850hPa temperatures will be
quite warm in the low 20s celsius, which will help boost
temperatures mixed down to the surface. However, surface moisture
will be increasing as well as 70+ dew points return to the area and
help to mitigate the mixing and, ultimately, the hotter
temperatures. This is especially true in areas over northern Iowa,
where a good amount of moisture has fallen over the weekend.
Therefore, temperatures will teeter on the balance between the high
850 hPa temperatures and the moist low levels. For that reason, have
nudged Mondays temperatures up slightly from previous forecasts,
but maintained the current area for the heat advisory over the
western and southwestern portions of the area where 105 F heat
indices are most likely.


>> Shower and Thunderstorm Chances Tomorrow

With the 500 hPa ridge in place to our southwest, we will reside in
a roughly northwest to zonal flow pattern for much of the week,
bringing us a few rain chances as shortwaves and weak troughs pass
through the area. The first of these chances will be tomorrow, as
the surface low pressure brings more warm moist air into the state
and a weak trough provides forcing across our north and west. With
the warm temperatures, instability values will be quite high in the
3000 to 4000 J/kg range. That being said, a strong EML will also be
present overhead for much of the day tomorrow, which will greatly
hinder displaced parcels. If temperatures over-perform, we
could see this convective inhibition reduce to greater than -100
J/kg, but even then, relatively weak shear of less than 30 kts
will make it difficult to get organized storms if convection
occurs. Therefore, the main severe threats would be a quick
burst of hail with any initial updrafts and/or brief downdraft
winds as a storm pulses up and back down.


>> Severe Weather Chances on Tuesday

As we get into Tuesday, a cold front to our northwest will be
dragged south and provide forcing for more showers and
thunderstorms. The severe threat looks a bit better on Tuesday, as
temperatures remain warm in the upper 80s to low 90s and CAPE values
again climb into the 3000 to 4000 J/kg range, this time with
slightly better shear along and north of the surface boundary. Of
course, the caveat with this is that any stronger storms will need
to be along or behind the boundary where the better shear resides,
while storms in the warm sector south of/ahead of the boundary will
be in a lower shear environment and lack the wind profiles to become
organized.  Therefore, the severe threat will again be somewhat
limited by the wind fields, but certainly more favorable than Monday
given the better forcing and diminishing EML along the cold front.
Hail and wind will be the primary concerns, while tornadoes would
rely on stretching and vorticity along a boundary. Locally heavy
rainfall will also be possible, especially with PWATs nearing 2 and
storm motions roughly parallel to the boundary. However, the front
will be progressive enough to limit training storms over one area
for a long period of time and mitigate any extreme rainfall amounts.
SPC has issued a day 3 slight risk for severe weather over much of
central, southern, and eastern Iowa. Beyond Tuesday, we get a brief
break from the heat and storms through mid week, before another
round of showers and thunderstorms moves through Thursday night into
Friday.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
-- Changed Discussion --
Issued at 644 PM CDT Sun Jun 23 2024

SCT-BKN mid clouds were in place across portions of northern IA
at 00z with nothing beyond that expected across the entire area
through the period. There is high confidence in VFR conditions
through Monday afternoon with breezy south winds by that time.
-- End Changed Discussion --

&&

.HYDROLOGY...
Issued at 346 PM CDT Sat Jun 22 2024

Major to historic flooding continues along portions of the Des
Moines River above Saylorville Lake. River observations today have
trended slightly higher than forecasts, which has resulted in an
increase in expected crests at multiple sites. This includes ESVI4,
EMTI4, and HBTI4, which are all either currently exceeding or
forecasted to exceed their record crests. Consequently, with the
greater volume of water coming downstream, we are now anticipating
greater impacts to areas along the main stem of the Des Moines River
above Saylorville, with FODI4 now forecast to crest at 19.5 ft which
is the 3rd highest crest on record for that site. Likewise, the
forecasted lake elevation at Saylorville Lake is now just over 875
ft.

Looking ahead to potential rainfall through the week, the most
immediate concern for heavier rainfall will be Tuesday, as most of
the rainfall on Monday is expected to avoid our forecast area.
Fortunately for those being impacted by river flooding in northern
Iowa, the higher QPFs currently favor southern Iowa, and even if
heavier rainfall develops north, it will quickly drop south with the
front. That being said, any heavy rainfall could still delay
improvement to flood conditions, if only briefly. Additional shower
and thunderstorm chances are expected again Thursday night into
Friday with more details provided on this in the coming days.

Make sure to stay up to date on the latest forecasts and river
information, and use extreme caution in flooded areas.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM to 8 PM CDT Monday for IAZ033-044-045-
057-070-071-081-082-092-093.

&&

$$

DISCUSSION...Dodson
AVIATION...Small
HYDROLOGY...Dodson