354
FXUS63 KDMX 230912
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
412 AM CDT Sun Jun 23 2024

.KEY MESSAGES...

- Dry Sunday with low chance thunderstorms west late tonight.

- Heat Advisory in effect for the west Monday afternoon with
  severe chances ramping up later that evening. Wind and hail
  are the primary threats.

- Additional severe weather chances Tuesday evening with
  similar threats. Storms will continue into the overnight
  hours.

- Additional rain and storm chances return to the region
  Thursday.

&&

.DISCUSSION...
Issued at 408 AM CDT Sun Jun 23 2024

Overnight surface analysis showed a surface high across Nebraska and
a series of weak boundaries dropping southeast across Iowa. The
surface high will preserve the drier air today, keeping
precipitation out of the forecast for the day and making it feel
less muggy outside. Highs will be in the 80s with some temperatures
approaching 90 in the southwest. A shortwave will develop off
of the northern High Plains and move into the upper Midwest
through the day. A few thunderstorms will form on the back side
of the departing high tonight as the LLJ angles in the western
part of the state. CAPE values over 1500 J/kg will be available,
but with weak flow. Models aren`t keen on precipitation
primarily because of the questionable amount of available
moisture. Soundings look relatively dry save for the midlevels.
Have added in some precipitation mentions across the west and
central through the night to cover the non-zero possibility of
enough moisture being present.

A thermal ridge will approach from the west on Monday. A front
originating from the cyclone in the Dakotas will be positioned
somewhere across the state. The EML will blanket at least the
western half of the state by Monday afternoon with the cap
inhibiting CI until the column cools in the evening. With H850
temperatures over 25C filling in the western half of the state and
dew point values in the 70s, muggy conditions will resume, this time
with higher confidence in warmer temperatures, driving up the heat
indices. Currently expecting heat indices across far western Iowa
behind the front to meet and exceed 105 degrees F. In coordination
with neighboring offices, have issued a Heat Advisory Monday
afternoon to cover the heat concerns for the afternoon. Adjustments
possible in upcoming issuances depending on the progression of the
thermal ridge.

The nocturnal jet initiates an MCS somewhere in Nebraska that
evening, moving into southern Iowa through the night. Some
initiation is possible along the cold front later on in the
night in the northeast. Better shear can be found closer to the
main upper level feature near Canada with profiles across the
state fairly unidirectional. Still, with ample MUCAPE available,
cannot rule out severe winds and hail with storms along the
front. The MCS will have DCAPE values near 1000 J/kg to work
with, but will quickly become outflow dominant in an environment
with weak shear. A boundary will stall somewhere across the
northern part of the state Tuesday with cause for concern for
more severe weather, again primarily with severe winds and hail.
Soundings have an inverted-v PBL and CAPE in excess of 2000
J/kg, but again with relatively weak flow. South of the
boundary, heat indices may reach the 100s once again, but will
be dependent on the aftermath of the MCS. Trends for Tuesday
will be monitored.

High pressure behind the departing system will keep temperatures
lower and conditions dry, but upcoming will be another wide open
Gulf moisture plume into the Midwest region (and possibly into Iowa)
late Thursday and into Friday. There is consensus among ensemble
members of there being 99th percentile to climatological max values
of precipitable water in the state. To give an idea for what values
look like in that percentile, operational GFS has PWAT values of
2.3"+. GEFS QPF M-climate percentiles for 24 hours are in the upper
90s for Friday. Of course, details can change this far out, but
given the recent heavy rain the state has experienced, it`s worth
keeping an eye on trends for rain at the end of this week.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1249 AM CDT Sun Jun 23 2024

MVFR to locally IFR stratus to affect KMCW and KALO for the next
6 to 8 hours, lifting to VFR after sunrise. Low confidence fog
possible at KFOD, but have left out of TAF due to low confidence
at this time. VFR conditions to prevail for much of the daytime
and evening hours tomorrow.

&&

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

Heavy rainfall in northeastern Iowa last night has led to flooding
on multiple area rivers, primarily along the Des Moines River and
Cedar River basins. As of right now, hydrographs are either on track
or slightly less than what was expected yesterday.

Those that have fallen below the forecasted rises are mainly along
the Cedar/Winnebago Rivers which missed out on some of the heavier
rainfall that was previously expected through that basin. This is
most notable at MCWI4, which will see a significant downward trend
from the previous forecasted crest of major flood stage to a now
forecasted moderate flood stage. That being said, precipitation
fallen in the basins and water routing down from Minnesota along the
Cedar River, will still result in moderate to major flooding in
areas along the Cedar River, notably at CCYI4, JANI4, and CEDI4,
among other sites also seeing minor flooding on the Cedar River and
it`s tributaries.

Further west, river forecasts are mostly on track, with major
flooding already ongoing at ESVI4 on the West Fork Des Moines River.
Rises at ESVI4 have slowed some, but not expecting much improvement
at this time with more water upstream still to be routed down.
Forecasted crests of moderate and major flooding downstream at EMTI4
and HBTI4, respectively. HBTI4 is also forecasted to near and exceed
the flood of record of 15.4ft. Flooding is also ongoing along the
East Fork Des Moines River, with moderate flooding at AGNI4 and
minor flooding forecasted at DAKI4. Consequently, flooding is likely
along the main stem of the Des Moines River north of Des Moines as
water routes downstream. This will lead to significant rises at
Saylorville Lake, with an estimated lake elevation of just over 870
ft.

Additional showers and thunderstorms are expected over portions of
northeast Iowa this evening, which may slightly delay improvement on
rivers. Those along the Cedar River basins will be most affected by
any rainfall tonight, while those further west should mostly get a
break. That being said, more rainfall is forecast at the beginning
of next week so will continue to monitor the impacts these may have
on area rivers.

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...Jimenez
AVIATION...Jimenez
HYDROLOGY...Dodson