434
FXUS63 KDMX 301125
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
625 AM CDT Sun Jun 30 2024

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Much less humid and cooler today!
- Seasonal temperatures Monday through Friday with more active
  boundary nearly stationary near Iowa/Missouri through Tuesday
  and back into the area by Thursday.
- River Flooding continues with monitoring of evolution and
  location of upcoming rainfall beginning tomorrow.

&&

.DISCUSSION...
Issued at 250 AM CDT Sun Jun 30 2024

.Short Term /Today through Monday/...

Confidence Short Term:  Medium to High

Finally a break from the heat and humidity and rainfall. Every hour
of dry weather helps the rivers and flood areas recede for now, even
if only slowly. Expansive high pressure stretches from the Northern
Plains south into Nebraska and Iowa, south to Kansas. Yesterdays
boundary has worked south to southern Missouri and northern Arkansas
back to Colorado at the moment, then up to Wyoming where low
pressure sits across the western states. Surface moisture has really
dropped and most of the region sits with dewpoints in the  40s and
50s. Today will be very pleasant with light winds and afternoon
highs in the 70s with a few fair weather clouds through the day.
Aloft at H850, the deep moisture is really not that far away. Though
it has been pushed south, the northern edge of the expansive +15C
dewpoint pool still stretches from southeast Colorado across
southern Missouri, then through the Ohio River Valley. This extends
all the way to the eastern seaboard and south into the Gulf of
Mexico.  As we move into the late afternoon and evening, there will
be a return of weak warm air advection over western Iowa and eastern
Nebraska with some mid level clouds far west. Under partly cloudy
skies tonight, mins will not be as cool west where overnight lows
will generally touch the mid to upper 50s while the northeast sees
lower 50s. Late tonight into early Monday morning, a low level jet
of 30 to 40kts will develop over western Iowa/eastern Nebraska. This
should initiate an MCS between 06 to 12z which will track east
northeast into western Iowa. There is now better model consistency
between the GFS/EC deterministic runs. Per usual diurnal tendencies,
the MCS will reach its peak magnitude by 10 to 12z and then may
weaken somewhat into the day tomorrow as it edges northeast. The GFS
remains slightly slower in releasing the Great Lakes high eastward
tomorrow than the 12z EC and weakens the MCS more quickly than
the EC which holds it together most of Monday. Rainfall amounts
from this first round of rainfall will range from light amounts
to a half to inch through afternoon, depending on the
progression of the return moisture east northeast. With clouds
and lingering showers/storms Monday, highs will be held back
once again and remain mainly in the lower to mid 70s for the
day.

.Long Term /Monday Night through Saturday/...

Confidence: Medium

We continue to set the stage for an active period Monday night
through at least Thursday with periods of showers and storms;
including some strong to severe storms and locally heavy rainfall.
With an area of low pressure tracking into southern Canada by
Tuesday morning, a trailing trough will edge into Iowa during the
day Monday into Tuesday. This will pull a front south across
northwest into central Iowa Monday night into Tuesday morning.
Though shear and warm air advection will be enough to maintain storm
development and potentially efficient rainfall, instability is not
overly impressive. Similar PWAT and warm cloud depth forecasts are
in the offing for Monday night into Tuesday over the region which
will likely promote rainfall of 1 to 2 inches in some of the heavier
totals overnight mainly over north central to northeast Iowa. With
stronger warm air advection into Tuesday morning, overnight mins
will hold to 60 north to the mid to upper 60s south. Tuesday will be
stormy early as the first of two overnight impulses/LLJ moves
northeast into Wisconsin. There is a likelihood that any trailing
outflow from the overnight storms will help keep a boundary
sitting over central Iowa Tuesday. This makes for a low
confidence high temperature forecast; especially if showers and
a few thunderstorms are ongoing from time to time during the
day. The front should light up again in the afternoon as another
short wave tracks northeast through the region and daytime
heating aids in instability. This will result in another round
of showers and stronger thunderstorms with up to 1 to 2 inches
of rainfall mainly from central to southeast areas of the state.
Rainfall totals from Monday through Tuesday night will likely
range from 1 to +3 inches with a few locally higher totals over
our area. There is generally good agreement by Wednesday with
the upper level trough now east of the area and a weak area of
high pressure bringing a break from the rain all of Wednesday.
With H850 temperatures cooling back to the mid to upper teens,
highs should climb back to the lower to mid 80s. We continue to
see the front again lifting back north into Thursday morning
with additional showers and storms building back into at least
the southern half of the forecast area on the 4th. The EC
deterministic continues to advertise this with the GEFS also.
The deterministic GFS is still shading activity south into
Missouri. As the end of the period approaches, cooler northwest
flow will return to Iowa with some clouds and perhaps a few
showers. Highs should cool to the 70s to around 80 Friday with
temperatures warming a degree or so for Saturday.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 624 AM CDT Sun Jun 30 2024

Other than several wind shifts under 12kts, conditions remain
VFR. Approaching MCS aft 12z will bring some mid/high clouds
into region around 12z Monday DSM/FOD. /rev

&&

.HYDROLOGY...
Issued at 250 AM CDT Sun Jun 30 2024

We continue to see the impacts of last weeks rain in the current
river warnings, but a much bigger concern is QPF next week and its
potential renewed impact on river levels. Again, with our current
river forecasts taking into account 24 hrs of QPF they do not
include the QPF for next week. The last few meteorological model
runs have been trending higher in QPF especially across the
southeast two thirds of the state with mean ensemble values of 1.5
to 2 inches over much of the region in the EPS with the GEFS about a
half inch lower.

QPF ensemble hydrographs and Hydrologic Ensemble Forecast System
(HEFS) runs continue to show the impacts of this QPF. The QPF next
week will likely affect more of the state so additional river basins
may come in to play. The Cedar/Iowa River basins look to be the most
affected however our guidance is showing possible rises on
tributaries to those rivers as well as portions of the Des Moines
and Skunk River basins. At this point the most likely scenario will
be slowing the rate of fall of our area rivers, however some
ensemble members are suggesting the possibility of additional or new
crests with additional minor flooding. Some of the lower
probabilities are suggesting moderate to major flooding at some
locations. We cannot totally rule out these possibilities.
Ultimately the location, amount and timing of the rain next week
will be the biggest factor.

In addition to the river flooding, we will also need to monitor for
localized flash flood potential next week given the favorable heavy
rainfall parameters from Monday through Monday night and Tuesday
night. We do get a brief break now on Wednesday, but more rain is
forecast to return over southern Iowa by Thursday. Though this is a
rather broad overview for now, refinement of details will likely be
a 6 to 12 hour process at most and will be much better defined prior
to each potential event.

Make sure to stay up to date on the latest forecasts and river
information, avoid flooded areas and rivers, and never drive around
barricades or through flooded areas.

&&

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

&&

$$

DISCUSSION...REV
AVIATION...REV
HYDROLOGY...REV