Ames, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

103
FXUS63 KDMX 281943
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
243 PM CDT Sat Jun 28 2025

.KEY MESSAGES...

- Shower and thunderstorms likely (60-80%) Sunday. A few storms
  may become strong-severe capable of damaging winds and heavy
  rain

- A few degrees cooler air mass and dry conditions for the
  first half of the week

- More storm chances (20-40%) and and seasonally warm
  temperatures (similar to today) return for Wednesday into the
  holiday week (not washouts)

&&

.DISCUSSION...
Issued at 243 PM CDT Sat Jun 28 2025

The one-day reprieve of higher humidity yesterday is a distant
memory as the high plains surface low advects a low-mid 70F
surface dew point air mass within the warm sector across the
state today. Aloft, the H3 jet core remains confined to
northern Minnesota, with mid-level shortwave energy riding thru
it`s southern periphery. At the surface, the warm front resides
in a similar area, extending back to the the high plains sfc
low. As such, the convective focus overnight will remain north
and northwest closer to better theta-e advection and forcing.
Similar to last night, all of the CAMs develop a MCS across the
Dakotas, sliding southeast in some form on Sunday morning. As
typical in relatively light mid/upper-flow situations, models
underachieve consensus regarding MCS sustainability and timing.
This time is no different. The HRRR is the most aggressive in
maintaining it the longest - well into Sunday morning across
northern & central portions of the CWA, which if it would occur,
would have impact on where and when/where storms initiate on Sunday
afternoon and evening. Alternatively, the majority of the other
model output weakens/dissipates the activity before
redeveloping storms across southern Iowa along a south moving
"cool" front in afternoon/evening. Although best deep-layer
shear lags the boundary near the jet, values of 25-30 knots
should be sufficient for the potential for a few strong/severe
storms once they do develop. Although initial updrafts may
present a brief hail threat, downdraft CAPE values in excess
1000 j/kg (due to mid- level dry air) points to damaging winds
as the primary threat, especially once convection congeals.
Also, 0-3 CAPE values remain above 150 j/kg which suggest at
least the potential for a few funnel clouds with LCLs near 1 km.
However tornadoes are not expected given the environment. Heavy
rain will be a good possibility as well, with precipitable
water values progd to be 1.5-2" statewide. More details can be
found in the Hydrology section below.

Storms should depart into Missouri Sunday night giving way to
slightly cooler and dry conditions for Monday & Tuesday.
The progressive pattern returns by mid-week which will bring
storm chances (20-40%) and above normal temperatures along with
it for the latter half of the week and into the holiday weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1237 PM CDT Sat Jun 28 2025

VFR conditions expected to prevail at area terminals through the
period as south winds of 5-10 knots persist across the state.
Thunderstorm chances will return to some terminals just beyond
this TAF cycle and will likely need to be included in the next
update or two.

&&

.HYDROLOGY...
Issued at 243 PM CDT Sat Jun 28 2025

Soil moisture remains high though across much of the CWA owing
to last week`s heavy rainfall. NASA SPoRT soil moisture
percentiles for the top 40 cm of the soil (usually considered
for river forecasting purposes) remain above normal north of US
30, while generally more normal south.

Additional rainfall is forecast Sunday into Sunday night, however.
At this point, the best chances for heaviest rainfall appears
to be with most likely location of more organized storms in the
central and south - generally away from the aforementioned area
of above normal soil moistures (in the north). Latest tools
suggest this additional rainfall will have a minimal impact on
existing river trends especially at those locations where levels
are or will be running high. The rainfall may add minor amounts
to the crests or slow falls. Although not a great chance given
that southern Iowa is less flash flood prone, localized flash
flooding would be a possibility over urban areas or if storms
are able to move parallel to the boundary.

&&

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

&&

$$

DISCUSSION...Hahn
AVIATION...Hahn
HYDROLOGY...Hahn