Ankeny, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

395
FXUS63 KDMX 182329
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
629 PM CDT Thu Jun 18 2026

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Low (20-40%) chances for showers and thunderstorms are
  forecast in the afternoon and evening both today and Friday.
  The threat of severe weather or widespread rainfall is low.

- More substantial (60-90%) and widespread rain and thunderstorm
  chances are forecast Saturday night and Sunday. There may be
  some risk of severe weather mainly in southern Iowa. There is
  also potential for heavy rain and localized flooding, mainly
  in the southern half of Iowa.

&&

.SHORT TERM /THROUGH SATURDAY/...
Issued at 212 PM CDT Thu Jun 18 2026

From this afternoon through Saturday, Iowa will reside beneath
relatively benign west northwesterly 500 MB steering flow. This
will translate into a fairly nebulous surface pattern, with
alternating weak troughs and ridges and generally light breezes
of varying direction. Temperatures will also remain pretty
steady from day to day, with highs in the mid-70s to lower 80s
each afternoon and lows in the 50s to lower 60s each morning.
The precipitation forecast is a bit more interesting, however.
Later this afternoon and evening a subtle shortwave impulse will
move overhead, focused more in northeastern Iowa and adjacent
states, and combined with the diurnal heating maximum should
provide sufficient impetus for convective initiation. The
coverage and latitudinal extent of any resulting showers and
thunderstorms is unclear, however. Earlier short-range model
runs depicted only isolated coverage mostly confined to our
northern and northeastern counties, however, new data this
morning has indicated more scattered coverage extending perhaps
all the way down to the Missouri border. In light of this, have
expanded 20-30% PoPs across most of our area for a few hours
later today, keeping only our southwestern and far southern
counties at 10% with no rain mention. In any event, weak low-
level flow and meager instability will preclude any severe
weather threat, so the only sensible impacts from any convection
that does occur will be brief rain and a few rumbles of
thunder.

After quiet and dry conditions overnight and Friday morning,
another, somewhat more energetic shortwave will approach our
area from the northwest later on Friday. Once again the approach
of this system will be coincident with maximum diurnal
heating/destabilization, but this time around the broad forcing
for ascent associated with the wave is somewhat more pronounced,
and atmospheric moisture is also much higher with forecast
soundings showing a few hours of near-saturation in the mid-
levels. In our northern counties this near-saturation extends
down to the surface, but in our central and southern counties it
may still be undercut by a dry layer in the lowest 5000 FT or
so. Nevertheless, the coverage and duration of rain chances will
be higher Friday afternoon and evening, and have
increased/expanded PoPs as a result with ~40% now included in
our north, and ~20% PoPs extending southward to the Missouri
border by Friday evening. Despite the expectation of higher
precipitation coverage/chances, instability will remain low and
severe weather again is not anticipated. Pockets of relatively
heavier rainfall could occur given the greater degree of
available atmospheric moisture, but not of sufficient magnitude
or area to prompt any hydrological concerns.

In wake of the late Friday system, we will experience another
brief dry and quiet weather period from late Friday night
through much of Saturday. By late in the day Saturday some
additional showers/storms could occur, but for the most part
these should hold off until Saturday night, as discussed in the
Long Term section below.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Issued at 212 PM CDT Thu Jun 18 2026

By Saturday afternoon, a 500 MB trough will be moving over the
Rockies and approaching the High Plains. The vorticity embedded
within this trough will be split into at least two distinct
shortwaves, the first of which will move across Nebraska and
northern Kansas Saturday night, and Iowa on Sunday. As this
system approaches on Saturday, broad surface low pressure will
develop over the southern High Plains, while a surface high
pressure ridge over the Upper Midwest steadily retreats
northeastward away from Iowa. By midnight Saturday night, the
surface trough will coalesce into a trough somewhere around
southwestern kansas, with an effective warm front extending east
northeastward along or near the Iowa/Missouri border. Deep and
persistent moisture transport ahead of the system will result in
significantly increasing PWAT values across the region, such
that by 12Z Sunday PWATs will approach 2" in far
southern/southwestern Iowa, which is well above normal for the
season. While there is some disagreement among various
deterministic models in the details of convective evolution, it
does appear likely that some type of thunderstorm complex will
form over southern Nebraska or far northern Kansas Saturday
evening, then spread eastward or east southeastward along the
frontal boundary. This complex may affect our southern counties
Saturday night, or may remain farther south across Kansas and
Missouri. Meanwhile, north of the boundary widespread rain will
develop across most or all of Iowa, as broad forcing for ascent
ahead of the approaching shortwave meets deep available moisture
and modest elevated instability in place across Iowa. By late
Saturday night and into Sunday the current forecast calls for
PoPs of around 60% in our north to near 100% in the south.

While rain is likely to a near certainty from late Saturday
night into Sunday, the associated threats are somewhat less
clear. Given the time of day, saturated atmospheric column, and
limited instability north of the aforementioned warm front, the
severe weather threat should be generally low across Iowa. An
exception to this is in far southern Iowa, where depending on
the location of the front and track of the associated
thunderstorm complex discussed above, there may be a threat of
strong winds if the forecast trends northward and sufficient
near-surface instability is introduced. Aside from severe
weather potential, the more growing concern at this time is the
possibility of heavy rainfall and localized flooding.
Deterministic guidance paints generally 1.5-3" or so of QPF
across the southern half of Iowa from midnight Saturday night
through the day Sunday. However, much of the deterministic
guidance is at the higher end of the ensemble envelopes. For
example, the deterministic NBM depicts 2.2" of QPF at Des
Moines and a maximum of 3.0" in Taylor County, however, it also
indicates only a 20% chance of exceeding 3.5" at Des Moines and
a 35% chance along the Iowa/Missouri border. This indicates that
while substantial rainfall is likely, very high or extreme
amounts are less likely than might otherwise be expected. In
addition, for most solutions within this general scenario, the
rain should be of a longer-duration, which those amounts (if
they even occur) falling over the course of 18 hours or so,
rather than in a short burst, which lowers the flash flooding
threat. The season also raises the bar for rainfall
intensity/amount needed to get a response, due to the peak state
of most crops and vegetation at providing capacity. Finally, in
terms of river flooding, if the heaviest rain does fall from
southwestern into southern Iowa, it will be near the state
divide an in smaller basins that quickly drain out of the area,
somewhat limiting the river flooding threat. All that being
said, these concerns will be closely monitored over the next
couple of days, as the forecast could easily shift more toward a
more northern and/or heavier rain solution, or toward a more
southern and/or less heavy rain solution. If the more
northern/heavier rain solution verifies, then we could see
heightened flooding/flash flooding concerns in some parts of our
southern and even into central areas.

The weekend rain/storm system will gradually push off to the
east later Sunday, after which forecast confidence decreases
rapidly. This is primarily due to the evolution of the second
shortwave within the larger 500 MB trough as mentioned earlier,
which long-range models are not handling well in terms of
consistency between models or from run to run. The result is
persistent low to moderate (10-50%) PoPs in the first half of
next week, with a continuation of near to a little below normal
temperatures. Looking into the way-out machine, it does appear a
large 500 MB high pressure area will become established over the
southwestern U.S. by the latter half of next week, with a ridge
extending up along the Rockies. If this ridge remains shunted
somewhat southward and Iowa lies beneath broad cyclonic flow to
its northeast, then seasonal temperatures and intermittent rain
chances would be likely to continue. On the other hand, if the
ridge exerts its influence farther northward, and the cyclonic
storm track is pushed northeast of Iowa, then it could favor
gradual warming and a somewhat drier forecast. We will see how
this plays out as we have several more pressing systems to get
through before then.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 617 PM CDT Thu Jun 18 2026
VFR conditions are expected to prevail through the end of this
TAF period. While an isolated shower is  possible this evening
across northern and central Iowa, confidence remains too low to
include PROB30s. Skies will clear out overnight with winds
turning light. As we near the end of this TAF period, clouds
will start to increase across Iowa with a few showers and storms
possible; however, forecast confidence is currently too low to
warrant a PROB30 mention.

&&

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


&&

$$

SHORT TERM...Lee
LONG TERM...Lee
AVIATION...Hagenhoff/TDR