717
FXUS63 KDMX 272000
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
300 PM CDT Thu Jun 27 2024

.KEY MESSAGES...

-On and off showers, with a few non-severe storms possible this
evening into Friday

-Severe weather possible Friday afternoon to evening, but remaining
conditional due to potential lingering clouds

- Quiet and pleasant weekend with dry conditions, especially Sunday
with cooler and less humid weather

- Signal remains for more active pattern with multiple chances
  for on and off showers and storms

&&

.DISCUSSION...
Issued at 259 PM CDT Thu Jun 27 2024

Satellite imagery this afternoon shows mid-level clouds streaming
eastward over Iowa, with mostly cloudy skies across much of the
area. Radar returns have overall increased across much of western
and northern Iowa throughout the day, though surface observations
indicate very little if any rainfall associated with this activity
into Iowa, thanks to low level dry air that has been stubborn to
depart. Model guidance depicts increasing southwesterly flow and
moisture return to the region into the evening with a strengthening
low level jet ahead of the circulating low pressure system slowly
entering into the Dakotas, which is expected to increase rain
chances as the front passes through into Friday. Further analysis of
model soundings over the region this evening into Friday shows CAPE
values generally under 1000 J/kg, along with limited shear and mid-
level lapse rates. A few stronger storms cannot be ruled out, though
largely expecting storms to remain below severe limits this evening
into Friday. Uncertainty remains on the overall coverage of this
activity, as the CAMS show mainly scattered activity along a line
pushing eastward across the state, though models such as the Euro
and NAM have more widespread coverage of showers and storms.
Regardless, some heavy showers are possible with rainfall amounts
generally under an inch expected.

Lingering shower activity is expected throughout the morning Friday,
with non-severe storms possible as the front continues to track
eastward. With the pressure gradient tightening, winds out of the
south/southwest are expected to increase, turning breezy by late
morning through the afternoon with gusts up to 30-35 mph, especially
over the northern portions of the state. The big question remains in
how much cloud cover will remain through the day. Models such as the
NAM and GFS are trending with more clouds throughout the day, though
the HRRR is more optimistic on cloud cover diminishing later into
the afternoon after the initial wave of showers and storms push
through the state. If clearing does occur later in the day, then the
chance for showers and storms will be higher. Overall, guidance per
model soundings show more appreciable CAPE values in the 2000-3000
J/kg range, along with 35-40 knots of shear and mid-level lapse
rates around 7-7.5 C/km, which would be favorable for strong to
severe storms later on Friday afternoon to evening. Damaging winds
and large hail would be possible if conditions do become favorable,
along with the potential for a tornado or two. Will be closely
monitoring for any changes, which will be most important tonight
into Friday in terms of how cloud cover plays out. On the side of
heavy rain potential, conditions are still on the more favorable end
with PWATS around 2 inches and deep warm cloud depths overhead, as
surface dewpoints increase into the low 70s. With the better
potential further south into Missouri however, not anticipating any
major impacts at this time, with values generally around an inch or
less expected, especially south. Will continue to keep a close eye,
especially given the remaining river impacts over northern Iowa.

As the cold front departs the state into Saturday, drying conditions
with high pressure sliding into the Midwest region will lead to dry
and quiet weather through the weekend. Highs are generally expected
in the upper 70s to 80s Saturday, with cooler conditions Sunday in
the 70s. The signal per long term guidance remains as more active
with a series of waves within the larger scale flow passing through
the region, and low level flow opens up more consistently from the
south, bringing in warm and more humid conditions back into the
region. This looks to result in on and off chances for showers and
storms throughout much of the next week, though specific details on
exact impacts are limited and will be better defined as more
information becomes available. Temperatures gradually warm back into
the upper 80s to low 90s Tuesday and through the next few days as
well.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1245 PM CDT Thu Jun 27 2024

Mainly dry with VFR conditions this afternoon, as mid-level
clouds continue to stream eastward across Iowa. As low level
saturation increases this evening, expecting to see rain shower
activity increase from west to east and continue into Friday.
Some weak storms may occur later tonight into Friday morning,
though confidence is not high enough to include in the TAFs
specifically and will continue to monitor. Scattered shower and
storm chances continue through Friday, with periods of MVFR
conditions possible by mid to late morning. Winds will increase
out of the south Friday, with gusts upwards of 20-30 knots.

&&

.HYDROLOGY...
Issued at 333 AM CDT Thu Jun 27 2024

Major to record flooding continues on the West Fork of the Des
Moines River early this morning. It looks like both Estherville
and Emmetsburg have reached their final crest and while they may
remain there for a bit, should start to see a slow fall in the
next day or two. Humboldt and Fort Dodge are cresting now or
will be later today. The remainder of the rivers in northern
Iowa, including the East Fork Des Moines, Cedar, Winnebago,
Shell Rock, and Iowa Rivers are all in recession. Both Dakota
City and Shell Rock are forecast to fall below flood stage
within the next 12 hours or so based on current forecasts. The
only rise is on the mainstem Des Moines at Stratford as the
water works its way down towards Saylorville Reservoir, which
should reach its peak around 875 feet around the Fourth of July
and remain there for a period of time.

The next chance for rainfall will be later today through Friday
night. The flash flood risk in this time period is less likely
given lower rainfall amounts as well as lower areal coverage in
higher amounts, which may top out around 2 to 3 inches in a few
locations for the event. As for possible infiltration, northern
Iowa north of Highway 20 has shown a slight improvement with
the roughly top 4 inches of relative soil moisture (RSM) showing
a 2 to 4% drying compared to this time yesterday. The 4 to 16
inch layer RSM continues to show 60% or higher values over this
same area so while the top layer has shown a bit of drying,
these areas will continue to be prone to saturation and more
rapid runoff response. Elsewhere in Iowa, the rainfall from
Tuesday has lowered capacity in southern Iowa with streaks of
60% RSM. Thus, there may be isolated areas that may see more
runoff response. However, in this part of the state USGS
streamflows are generally at the normal percentile at both the
daily and 7 day average. While there is more rainfall forecasted
early next week, there should be some time for soil moisture and
infiltration capacity recovery, but will need to monitor QPF
amounts as the event approaches given the favorable heavy
rainfall parameters.

On the river flooding, the plan is to use just 24 hours of QPF
today. Thus, the first part of this late week rain event
through 7am Friday will make it into today`s river forecasts.
For areas that are not currently experiencing or forecast to go
above flood stage, namely central and southern Iowa, the
experimental Hydrologic Ensemble Forecasting Service (HEFS)
based on GEFS 10 day QPF continues to paint within bank rises at
the 30% chance exceedance level. The 10th exceedance level
would bring a few locations on the Iowa, Raccoon, and Des Moines
into at least flood stage. However, this would require the
higher end rainfall. For northern Iowa and rivers with above
action stage conditions (Des Moines above Saylorville, Cedar,
Shell Rock, and Winnebago), the rainfall Thursday night into
Friday as well as early next week may slow the recession and
prolong above action stage flows.

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...Bury
AVIATION...Bury
HYDROLOGY...Ansorge