043
FXUS63 KDMX 291947
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
247 PM CDT Sat Jun 29 2024

.KEY MESSAGES...

- Quiet and dry Sunday.

- Storms return Monday into Monday night. Some severe storms
  possible west with primarily damaging winds. Heavy rain
  possible north and west.

- Additional severe storms and heavy rain possible Tuesday
  afternoon and overnight. Severe weather primarily in the
  southeast with heavy rain primarily east.

- Rain chances to return Thursday.

&&

.DISCUSSION...
Issued at 243 PM CDT Sat Jun 29 2024

The main upper level trough moved off to the east through the day
with remnant showers from a decaying MCS getting eroded by dry air
associated with high pressure and northwest flow. As the center of
high pressure sinks down this afternoon from the Dakotas, the
pressure gradient across the north will increase and lead to some
continued breezy conditions through the evening. Decoupling
will keep winds light overnight and high pressure overhead will
keep winds light Sunday. Skies will be mostly clear and highs
will only be in the 70s. We`ll get a reprieve from mugginess as
dew points drop into the 50s.

For early this week, the H850 high center will be slow to move
across the Great Lakes region, allowing for an available channel of
Gulf moisture to make its way into the Upper Midwest as a series of
upper level shortwaves move across Canada. PWATs will be in the 2-
2.3" range with warm cloud depths pushing 14kft. Precipitation is
anticipated to arrive late Monday beginning in the northwest as
isentropic ascent commences. This precipitation will increase in
intensity and coverage as the H850 jet forms along the nose of the
LLJ. Right now, this looks to be near the unfavored region of
southern MN/northern IA. Further to the west somewhere in Nebraska,
an MCS will form along the warm front and move towards Iowa. It`s
not certain this far out where exactly this MCS would move, but it
is certain that locations impacted by it will be subject to heavy
rain. There`s a nonzero chance of severe winds with is as well, but
the main instability axis will lag behind as it arrives into the
state, making that chance wane over time. The Marginal Risk for
severe weather in the west highlights this well. The QPF forecast
currently has up to 2 inches near the IA-MN state line, but
convective processes can easily push this amount higher in localized
spots. What can inhibit this is the aforementioned MCS that will
pass south of the main H850 front and track into western and central
Iowa. Depending on its pace, it will eat away at the instability
axis and moisture transport that would have otherwise continued to
be pushed farther north. Trends will be monitored. It`s still
important to note that the flash flood guidance for 3 hours near the
border is just below 2 inches. The mature corn crop osmosis will add
some buffer room to this value, but regardless, it will not take
much water to cause problems.

The main cold front will make its way into the state Tuesday and
will have plenty of deep layer shear and instability to work with in
at least the southeast, hence the Day 4 outline for this region.
There remains some uncertainty in warm sector placement as the cold
pool from the overnight MCS could be nearby. Aside from severe
weather, heavy rain will focus in the southeast which is an area
where basins can take on extra rain. The mean wind Tuesday evening
will be parallel to the cold front with low dew point depression at
low and mid levels. PWATs will still be well over 2 inches. The
highest precipitation looks to be in northeast Iowa with this round,
but much of eastern Iowa could see 1-2 inches. Beyond Tuesday night,
the boundary will stall somewhere in Missouri and block moisture
transport further north on Wednesday. The front tries to retreat
into the state Thursday ahead of the next trough. Accompanying the
trough may be another MCS, according to deterministic guidance.
Both subsystems translate to more chances for heavy rain nearby
near the end of the work week. Due to the lingering rain
chances and clouds hanging around this week, highs will largely
be held out of the 90s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1242 PM CDT Sat Jun 29 2024

VFR conditions expected to prevail with cloud deck right at
3kft arriving from the north. This should be SCT to FEW this
afternoon. 25kt gusts possible this afternoon for northern
terminals. Winds lighten after sunset and become northerly for
tomorrow.

&&

.HYDROLOGY...
Issued at 301 AM CDT Sat Jun 28 2024

Despite the rainfall over some of the region into early Friday,
little additional rain fell in the Winnebago and Shell Rock River
watersheds late this afternoon or evening. So far, the rivers have
not risen as quickly as forecast. We may see the Winnebago River
remain just below FS at Mason City while the Shell Rock River at
Shell Rock may yet just get to or slightly above flood stage this
afternoon.

In the longer term, a much bigger concern is QPF next week and its
potential impact on rivers. 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 2 to 2.5
inches over much of the region.

Our latest QPF ensemble hydrographs and Hydrologic Ensemble Forecast
System (HEFS) runs are latching on to this QPF. Unlike the rainfall
a week ago, the QPF next week will 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 Monday night and Tuesday night through 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...Jimenez
AVIATION...Jimenez
HYDROLOGY...Zogg