676
FXUS63 KDMX 221143
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
643 AM CDT Tue Apr 22 2025

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

.KEY MESSAGES...

- Shower and storm chances increasing this afternoon and
  evening, with a few stronger storms being capable of producing
  gusty winds and hail.

- Intermittent shower and thunderstorm chances persist through
  the remainder of the work week. Some strong storms remain
  possible through the week, but the overall severe threat is
  low.

- Brief break from precipitation moves in late Friday into
  Saturday but shower and storm chances then return Sunday into
  Monday.

&&

.DISCUSSION...
Issued at 408 AM CDT Tue Apr 22 2025

Broad lift and marginal instability has allowed elevated
showers and thunderstorms to persist over roughly the northern
half of the state through the early morning hours. Fortunately,
many of these storms have remained sub-severe over our forecast
area, producing gusty winds to around 40 to 50 mph and
potentially some small hail at their strongest. Expecting these
storms to remain steady state as they continue east through the
remainder of the morning, riding along the instability gradient
and along the nose of the low level jet. After these storms
depart this morning, well see a brief lull in precipitation
later this morning before additional showers and storms develop
along a weak boundary in southern Iowa through the afternoon and
early evening hours. Moderate mixed layer instability of 1000
to 1500 J/kg will be conducive for a few stronger updrafts this
afternoon, especially further south in the state. That said, the
better deep layer shear will be further north in the state,
along and north of the boundary where instability values
approach zero, meaning storms will need to find the Goldilocks
zone to take advantage of both the shear and instability. This
will likely be right along the boundary, as indicated by recent
CAM guidance showing relatively weak but consistent updraft
helicity tracks passing along and south of I-80 this afternoon
and evening. If one of these stronger storms materializes, the
main concerns will be hail, wind and potentially some heavier
rainfall, especially with the mean wind being generally oriented
with the boundary, favoring training storms. While models
suggest a period of surface based convection with low level
shear around 25 to 30 kts developing in the afternoon, the
tornado threat doesnt appear overly pronounced with surface
winds out of the south southwest and only moderate turning in
the low levels.

The boundary pushes north Tuesday night and weak theta-e
advection continues to surge into the area. With the weakly
forced environment and a steady stream of warm air and gulf
moisture, models are struggling to agree on a solution for the
overnight convection, with some only showing sporadic showers
and others developing numerous storms along the boundary as it
progresses north into northern Iowa. Therefore, confidence is
fairly low in the location and coverage of precipitation
tomorrow night, but expecting to see at least some scattered
showers and storms redeveloping further north overnight. The
forecast reflects this, with roughly a 30 to 40% chance for
precipitation continuing into Wednesday morning. Again, the
severe threat wont be overly high, but elevated storms may
produce hail and occasionally gusty winds overnight as well.

The steady stream of moisture/theta-e advection, as well as
weak lift aloft, will allow precipitation chances to persist
through Wednesday as well, with slightly better moisture and
forcing allowing for more widespread rainfall Wednesday
afternoon. As has been mentioned in previous discussions, this
environment looks a bit more like a heavy rainfall environment
rather than a severe weather environment. This is primarily due
to the lack of deep layer shear and fairly saturated profiles on
Wednesday, although instability will still be fairly
respectable around 1500 to 2000 J/kg. Therefore, while a few
stronger storms may be possible, the severe weather threat
appears fairly low on Wednesday. PWAT values wont be what you
would expect from a heavy rain event in the middle of summer,
but will be quite respectable for this time of year with values
around 1 to 1.5 draped from southwest to northeast along and
south of the boundary. This also happens to be the direction
storms will be moving, which will allow for another period of
training storms. Therefore, while not expecting torrential
downpours, could see some healthy rainfall amounts from showers
and storms on Wednesday.

Our persistent moisture stream persists through Thursday and
part of Friday, with intermittent rain chances continuing on
both days before being shut off by high pressure diving south
into the weekend. This should give us a brief break from
rainfall into Saturday, but we will be looking at yet another
chance for showers and storms Sunday into Monday as our wet
pattern looks to continue into next week as well.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 636 AM CDT Tue Apr 22 2025

Showers and storms from the overnight hours have all but
departed the forecast area, with just another hour or so of rain
expected at KOTM. A stratus deck around 3k to 4k ft is in place
over portions of northern Iowa, and will impact KMCW and KALO
through the morning. MVFR ceilings in this deck have been
sparse, and seem to be confined to the tail end of it. This may
lead to brief MVFR ceilings at KMCW this morning. Low clouds
will dissipate through the morning, but mid to upper level
clouds will stream through the state throughout the day.

Later this afternoon, expecting additional shower and
thunderstorm development in southern Iowa. Confidence is low on
exact timing of impacts to sites, but expecting KOTM and
potentially KDSM to be impacted at some time this afternoon.
Most likely windows for precipitation are included in TAFs.

Finally, additional shower and storm development is possible
farther north overnight, potentially impacting KFOD, KMCW, and
KALO. However, confidence is too low to include in TAFs at this
time.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Dodson