549
FXUS63 KDMX 240952
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
452 AM CDT Tue Jun 24 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms throughout today with
  greatest areal coverage in the afternoon and evening. Heavy
  rainfall and gusty winds are the main concern with today.

- More widespread showers and storms expected overnight tonight
  into Wednesday morning, then continuing over northern Iowa
  Wednesday afternoon. Heavy rainfall and gusty winds still the
  main concern.

- Heavy rainfall overnight last night and continued heavy
  rainfall throughout this week may lead to localized flash
  flooding and will cause rises on area rivers.

&&

.UPDATE...
Issued at 349 AM CDT Tue Jun 24 2025

Most of the precipitation which originated along the surface
boundary yesterday afternoon and evening has generally
dissipated early this morning as they`ve become detached from
the main synoptic boundary and main moisture axis. Observed
rainfall amounts from last night`s convection were generally
around 2 to 4 inches within the heaviest band over south central
into east central Iowa. This band fell in a fortunate spot by
avoiding the river basins most susceptible to flooding and
keeping outside of any larger metro areas which would have been
more prone to flash flooding. That said, we are just getting
started with the active period this week, with shower and
thunderstorm chances continuing intermittently through much of
the week.

Our next round of rainfall has come as the result of moisture
continuing to stream into the area and broad ascent allowing
showers and thunderstorms to fester overnight into the morning
hours. Currently, we are seeing two areas of slow moving storms
moving into central Iowa, the first being over northern
Missouri and southern Iowa, then the second in eastern Nebraska
into western Iowa. With PWAT values near or exceeding 2" still
overhead and slow storm motions, these storms will likely
produce some efficient rainfall. Will be monitoring the
rainfall rates and amounts closely, especially as this moves
into areas that already saw heavy rainfall last night. Severe
weather is unlikely with any of this morning activity (shear is
generally less than 30 kts and instability values are less than
1000 J/kg).

As we get into the day today, the overall expectation hasn`t changed
much with isolated to scattered showers and storms continuing
throughout the day as the moist environment remains in place
overhead and weak theta-e advection continues into the area.
Although fairly washed out from the convection last night, a weak
stationary boundary/trough still remains in place from west to east
today, which could become an additional forcing mechanism for
more convection today. The main concern today will still be
heavy rainfall, especially if the slow moving storms continue to
fall over similar areas to last night. The severe risk looks
fairly limited, and would be contingent on getting some clearing
and destabilization of the air mass as the boundary layer mixes
out. This may be difficult to come by if storms continue to
fester through the morning hours, leaving convective debris over
the area. However, if we do clear out and destabilize, could
certainly see some gusty winds produced by rain falling into the
dry mixed layer below. Small hail would also be possible, but
severe hail will be limited given the lack of any deep layer
shear and warm, saturated profiles. Therefore, it will be
limited and somewhat conditional, but the severe threat does
still exist and would be diurnally driven.

Progressing into the night tonight and into Wednesday, the steady
stream of moisture continues, allowing showers and storms to fester
into the evening. A shortwave lifting to our west will bring
better forcing and slightly better flow in the low levels. More
widespread convection will develop as a result of this, which
will be fueled by a modest 30 to 35 kt low level jet nosed into
southwestern Iowa. As of right now, most of this convection
appears broad and disorganized on model reflectivity output,
but the environment does show an instability maximum developing
over eastern Nebraska into western Iowa. This instability axis
could serve as fuel for convection along the nose of the low
level jet. Still, shear will be marginal and it may be a heavy
lift to expect the 20 to 30 kts of deep layer shear and the 10
to 20 kts of 0-3 km shear ahead of the jet to keep storms
organized or cold pools in balance, but with a slightly more
prominent jet nearby it`s something worth keeping an eye on.
Aside from that, heavy rainfall remains a threat overnight into
Wednesday as our prolonged period of showers and storms
continues.

Convection continues through the day Wednesday. This will be
primarily over northern Iowa, where we`ll see more diurnally
driven thunderstorm chances in the afternoon. These storms will
have slightly better phasing of shear and instability, at least
in the far northern and northeastern portions of the state,
suggesting a chance for better organized convection and a
slightly better chance for some severe storms. Wind still
appears to be the main threat, but better organized updrafts
could help produce a better hail environment as well. High
resolution models also depict a more linear feature developing
out of this convection in northern Iowa, but this is occurring
towards the end of the current high resolution window so will
continue to monitor how this feature evolves in the coming days.

&&

.DISCUSSION...
Issued at 248 PM CDT Mon Jun 23 2025

Another active week has begun with shower/storm development having
already occurred over northern into north central Iowa early this
afternoon near to just south of the surface boundary that is a main
driver of our storms today, and will continue to be a driver over
the next several days as it stalls out and wobbles north to south
and back with time through much of the upcoming week. Although
temperatures to the north of this boundary in northwest Iowa are
only in the 70s, temperatures have warmed again into the 80s or 90s
with near widespread dewpoints in the 70s. Although in the short
term this means another very warm day is ongoing in much of southern
to eastern Iowa with heat indices near to over 100, it also means
the environment is becoming increasingly unstable with anywhere from
1000-2500 J/kg of MLCAPE, and up to another 1000 J/kg more than that
at the surface per 18Z SPC Mesoanalysis. Although shear remains
lackluster south of the boundary in the warm sector with profiles
largely unidirectional, still expecting storms to continue to
develop as H700 temperatures decrease and in turn inhibition
continues to weaken over the next several hours and into this
evening. The strongest storms/biggest severe threat will be with the
initial storms that develop this afternoon into evening. Can`t
fully rule out some hail or a brief tornado with these initial
storms or any storm mergers near/along the boundary prior to
having to compete with other updrafts, but these are generally
less likely threats with any cold pools in the warm sector
likely struggling to stay in balance, as noted in the previous
update. Thus, the main threat remains strong wind gusts as
storms pulse up and then collapse down, with gusty winds also
possible along storm outflows, or if storms can actually
organize into some kind of line. If this later threat occurs,
the wind threat could continue later into the evening, as
starting to be noted by some of the CAMs in far southern Iowa,
and will continue to be monitored closely.

With the unidirectional flow previously mentioned, the boundary
remains largely parallel to the mean flow which will also allow
for storms to train over the same area increasing the hydro
threat with time. Although not overly robust, the LLJ redevelops
overnight allowing the rain to continue through much of the
night leading to rain totals of 1-3" over portions of central
into southern Iowa with localized higher totals certainly
possible. Rain totals to the north remain on the lower side, but
could near up to 2" by 7 AM Tuesday per the HREF localized
probability matched mean. With the large bulk of this QPF
through these first 24 hours of our active week in southern Iowa
that has more hydro capacity, did not pursue a flood watch for
flash flooding at this time, but for any of these larger QPF
values that fall in an urban area, flash flooding is certainly
possible. Ponding in any poor drainage or low lying areas is
expected and conditions will be monitored closely. See the hydro
discussion for additional information on the hydro threat.

Depending on any MCV activity and associated outflow that may/may
not develop tonight, the surface boundary stays stalled out in the
area, as noted above, allowing for additional storm development
tomorrow afternoon and evening once the morning activity moves out.
At this time, activity looks largely isolated but with additional
diurnal instability developing, more strong to severe storms are not
out of the question near the boundary or any other lingering
features. Exactly where this occurs is somewhat dependent on how
things play out tonight into tomorrow morning, but with shear still
not overly robust, main threat would once again be gusty winds with
activity not overly organized but should that occur, then maybe some
hail.

By overnight into Wednesday morning, additional rain or storms move
in along a shortwave with additional afternoon/evening storm
development possible as well. Each event will continue heighten the
hydro threat from a flooding stand point (again, see hydro
discussion) with the severe threat in time and place dependent each
day on the day before and the location of the lingering boundary
with this active weather continuing through the work week though not
necessarily at every time step as noted by the extended NBM
forecast. Will continue to refine PoPs with time through the week.
Although warm in the 80s to 90s, the daily precipitation/storm
chances will keep heat indicies lower this week.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1231 AM CDT Tue Jun 24 2025

Showers and isolated thunder continue over roughly the
southeastern third of the state, currently KALO and KOTM.
Expecting this first area of showers to continue drifting
southeast out of the area through the morning hours, but
additional development has begun over eastern Nebraska and
southwestern Iowa which will begin to move into Iowa through
the next few hours. Therefore, sporadic shower and occasional
thunder chances linger through the night at all sites. In
addition to showers/storms, ceilings down to MVFR and
potentially IFR heights will develop. Precipitation trends
through tomorrow remain tricky given the scattered shower/storm
chances over the entire area through the day. Therefore, have
used PROB30 to indicate most likely windows, but updates and
amendments will be needed.

&&

.HYDROLOGY...
Potentially wet conditions this week will lead to above average
hydrologic concerns involving both flash flooding and river
flooding. There has been a persistent signal of heavy rainfall
however there is uncertainty in terms of amounts and location. See
the above sections for the meteorological aspects. The hydrologic
response will depend heavily on the meteorological activity. In
terms of short term hydrologic response, flash flooding will be a
possibility through at least the middle to late part of this week.
Although soil moisture values are near to above normal, the heavy
rainfall this week has the potential to still generate flash
flooding due to either its intensity or the sheer volume of
rainfall.

In terms of longer term hydrologic response, present thinking is the
most likely scenario will be significant rises on many streams--with
potential flooding--especially across the northern half of the CWA.
Right now the river basins of most concern include the
Cedar/Winnebago/Shell Rock, Iowa, Skunk, Des Moines and Raccoon
rivers. We are also concerned that QPF going into our river model
guidance may be underdone, thus the true flooding threat may be
higher than indicated by our current river forecast guidance such as
HEFS and the NWM. The primary QPF inputs into HEFS and NWM are GEFS
and GFS respectively. In higher-end rainfall events the QPF tends to
be underdone which is our concern this week. Thus our partners and
users are strongly encouraged to follow subsequent watches, warnings
and advisories from our office and not necessarily take the online
river forecast guidance at face value.

&&

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

&&

$$

UPDATE...Dodson
DISCUSSION...05
AVIATION...Dodson
HYDROLOGY...Zogg