333
FXUS63 KDMX 021047
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
547 AM CDT Tue Jul 2 2024

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

.KEY MESSAGES...

- Threat for severe and flash flooding continues today
- Break on the way for Wednesday
- More spotty showers/storms from Friday through Monday.
  Rainfall not expected to be significant, but outdoor
  activities may be impacted from time to time.

&&

.DISCUSSION...
Issued at 330 AM CDT Tue Jul 2 2024

.Short Term /Today through Wednesday/...

Confidence Short Term:  Medium to High

Everything reaching the peak from early morning through around 02z
this evening; including early morning heavy rainfall and potential
for some flash flooding. Then this afternoon, the continued risk of
severe storms and more heavy rainfall and potentially some flash
flooding, rises in rivers and areal flooding.

Late evening synoptic surface map shows two pronounced areas of warm
air advection tied to weak lows and two warm fronts pushing north
into Iowa/Minnesota. A trough of low pressure through the eastern
Dakotas will eventually pass east later today and exit the region.
The northern most low over southern North Dakota has a warm front
over northern Iowa/southeast Minnesota. This has been responsible
for the first round of moderate to heavy rainfall that has already
lifted northeast over our border counties into southeast Minnesota
this morning. The southern most low is situated over southeast
Nebraska with a warm front extending southeast over northeast Kansas
and into southwest Missouri. This has been the overachiever early
this morning with a stronger cluster of storms in southeast
Nebraska. This has already dropped 3 to 5 inches of rainfall
and is edging east into southwest/western Iowa. Though most of
the storms have been lessening in intensity the past few hours,
rainfall efficiency will likely remain high through around 12 to
15z. The current HRRR runs suggest a more southerly propagation
of the cluster to our west and due to that have added Madison
Co to the early day FF.A. Since the low level jet is driving
much of the overnight convection, this should begin to weaken
this morning with lingering efficient showers/iso storms into
the late morning hours. As we move into the afternoon hours, the
southern low will to track toward southern Iowa with the warm
front edging into or tracking near the border. With PWATS still
running 2 to 2.5 inches this afternoon and evening over the
east, warm cloud depths still over 4kft and ample support from
the low and low level jet, heavy rainfall will again be
possible. Severe storms will also be possible over the south and
we again have a similar SPC forecast for slight/enhanced risk
of storms over the southeast two thirds. The greatest risk will
be wind nearer the Iowa Missouri border with hail and a smaller
risk of a few tornadoes. Though rainfall has not been as
prolific over the southeast, east and up toward the Waterloo
area in the most recent past, there is still some signal that
these areas may see amounts of 2 to 3 inches today with locally
higher rainfall. Have added another Flash Flood Watch over the
southeast third of the area today from 20z to 03z. Most of the
convection will have exited the region by 01 to 02z, but some
lingering hydro issues may still be ongoing. Today will see
highs in the mid to upper 70s north with lower to mid 80s in the
south. Tonight the low and boundary will scour out the moisture
and bring cooler air into the region. Mins will dip to the
lower 60s north to the upper 60s south. Tomorrow will be
pleasant as a ridge of high pressure builds in behind the system
and brings milder air back to the area. Highs will be warmer
with readings in the mid to upper 80s.

.Long Term /Wednesday Night through Monday/...

Confidence: Medium to High

There is reasonable confidence moving forward. Little has changed in
the forecast. By Wednesday night, another lee side trough will
approach the region with showers and storms edging into southern and
western Iowa toward sunrise the 4th. There is some agreement with
the GFS and EC in terms of the initial morning convection
diminishing toward midday, but the GFS is tending to hold onto the
afternoon convection into the evening across the east slightly
longer than the Euro. Depending on the timing of the later day
storms, some holiday festivities Thursday evening may be delayed
east of I35. Will need to wait and see. Though there are breaks from
time to time from Thursday night through Monday, a shift to
northwest flow will bring several waves and weak fronts southeast
through the region. Brief periods of showers and some thunderstorms
can be expected each day. Spotty quarter to half inch rains may
occur with the passing systems and should not really add much to our
current hydro situation, but the passing showers and occasional
storms will likely interfere with a few outdoor plans.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 546 AM CDT Tue Jul 2 2024

Main issues today will be periods of storms and lower cigs/vsby.
Winds not much of an issue through 18z, but aft 18z some of the
storms may bring VRB25G45kts or higher to DSM/OTM. We continue
with potential for locally heavy rainfall which may impact
runway conditions. Area of moderate/heavy rain passing over DSM
now and another round of storms may impact most sites with a
period of heavy rainfall for 1 or so hours aft 15z north and
over the south aft 20z. /rev

&&

.HYDROLOGY...
Issued at 330 AM CDT Tue Jul 2 2024

A Flood Watch is in effect for parts of central and north central
Iowa to noon today which covers both the potential for flash
flooding and new or renewed river flooding.  We have added a second
Flood Watch for both the potential of flash flooding and a possible
impacts on rivers. The second watch begins at 20z and goes through
03z in the east/southeast.

The current river forecasts, which includes 48 hrs of forecast
precipitation, do slow the fall along the West Fork Des Moines
river. Rises are forecast across most other basins including the
East Fork Des Moines, Des Moines, Winnebago, Shell Rock, Cedar and
Iowa River basins including a return to Minor Flood stage at Mason
City, Shell Rock, Cedar Falls and Waterloo, Stratford and Des
Moines at SE 6th. Heavy rain is currently drifting east northeast
from near I80 in western Iowa and may set up this morning across
the area between I80 and US30, west of I35. This may bring additional
impacts to these areas including the Saylorville Lake storage,
which is currently forecast to reach 880 ft by the Corps of
Engineers.

This afternoons area of heavy rainfall is expected over south
central to southeast Iowa, over to around Highway 63. Note, the QPF
utilized by the RFCs for these forecasts may be on the low end and
shifted to far northwest which may lead to some locations forecast
being underdone. Rivers/streams and soil moisture in that part of
the state are in better shape and can handle heavy rainfall compared
to the recently impacted north. At this time, no streams are
forecast to reach flood stage. However, there will still be a threat
for some localized flash flooding, urban flooding and if enough rain
falls, some areal flooding later today.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Flood Watch until noon CDT today for IAZ005>007-015>017-
023>026-033>037-044>048-057>060-070>072.
Flood Watch from 3 PM CDT this afternoon through this evening
for IAZ038-039-049-050-061-062-073>075-083>086-094>097.

&&

$$

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