Area Forecast Discussion
Issued by NWS Des Moines, IA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
000
FXUS63 KDMX 222024
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
324 PM CDT Fri Mar 22 2024

.KEY MESSAGES...

- Light snow (20-25%) moving into the northern half of the area
  Saturday afternoon with a few flurries/sprinkles possible
  further south.

- Prominent synoptic system bringing precipitation chances
  (>90%) on Sunday and Monday. Precipitation starting initially
  as snow Sunday before switching to rain Sunday afternoon into
  Monday. Greatest snow accumulations north.

- Potential for a few thunderstorms Sunday night into Monday,
  and a few stronger storms possible on Monday. Gusty winds also
  expected both Sunday and Monday.

&&

.DISCUSSION...
Issued at 321 PM CDT Fri Mar 22 2024

After a messy morning of mixed precipitation types, things have
quieted down across much of central Iowa. The precipitation that
passed through Iowa this morning produced a decent band of snow
amounts from 3 to 5 inches with a few locations in east central Iowa
seeing amounts near 7 inches. Surrounding areas experienced lower
snowfall amounts due to a mix of rain, snow and wintry mix through
the area. Tonight and tomorrow morning will remain dry with some
brief clearing overnight tonight into Saturday morning. However,
this moment of tranquility doesn’t last long as another, more
prominent wave makes it’s way across the U.S. this weekend and
precipitation returns to the area starting tomorrow afternoon.

The first of this precipitation will track over northern Iowa
tomorrow afternoon and evening, resulting in light amounts of
snowfall. Lift with this first finger of precipitation won’t be too
strong, and therefore not expecting overly impressive snow rates as
it passes through. Likewise, much of the moisture that will
accompany this first wave will originate from the Pacific and lacks
lower level moisture contributions from the Gulf. Therefore,
snowfall will be reliant on saturation through a “top down” process
rather than low-level moisture transport. This will hinder rain
chances further south where FGEN/forcing is weaker and lower-level
dry air is more difficult to overcome. That being said, some models
are still hinting at a few pockets of light precipitation in the
southern half of Iowa, so have included some low end precipitation
chances through much of central Iowa should some of these areas of
better forcing saturate through to the surface. Regardless, impacts
from this initial wave will be minimal Saturday night and would be
focused close to the Iowa/Minnesota border.

Right on the heels of this lighter precipitation will be strong warm
air/theta e advection ahead of a synoptic scale system bringing much
needed precipitation to the area. This system checks a lot of the
boxes, with good kinematic and thermodynamic support throughout the
layer. Moisture also won’t be an issue, as the pacific moisture
stream mentioned earlier will phase with a developing lower level
moisture stream from the Gulf of Mexico. As the broad scale lift
helps to induce widespread precipitation, there will also be
localized FGEN support on the leading edge of the warm air advection
stream.

So what’s this all mean for sensible weather? Well, as the theta e
advection pushes into the state on Sunday morning, cooler
temperatures will initially cause moderate to heavy snowfall in
roughly the northern half of the state with rain further south.
However, as the warmer air and higher dewpoints stream north, this
snowfall will quickly flip over to rain for much of central Iowa by
mid-day Sunday. As this transition occurs, it’s possible some will
see a brief wintry mix before rain takes over completely Sunday
afternoon, although no impacts are expected due to an icy
precipitation. The warmer temperatures will arrive in northern Iowa
the latest, and therefore the highest snow totals are  expected near
the Iowa/Minnesota border and north. For those further south, snow
may initially accumulate on cooler surfaces, but rain falling on top
of snow, as well as higher temperatures and dewpoints should quickly
melt any snow on the ground. This snowfall distribution is pretty
unanimous across the current deterministic and ensemble output, as
the trend in guidance leans towards a deeper, more amplified system
pulling more warm air into Iowa sooner on Sunday, and therefore a
northern trend in the higher snowfall totals.

The fun doesn’t end after Sunday, as the surface low pivots over
eastern Kansas and Nebraska late Sunday night, then tracking through
western Iowa on Monday morning. As mentioned previously, the trend
in guidance has been towards a deepening and more amplified system,
which has slowed the low and pushed it further west, placing the
warm sector over much of central Iowa. This trend not only leads to
continued precipitation into Monday, but also poses the risk for
some stronger thunderstorms mid-day. While it is still too far out
to get too bogged down in the details, this setup looks to be your
typical early season low CAPE, high shear scenario. Models are
starting to hint at a pocket of 500 to 700+ J/kg of surface based
CAPE within the warm sector as well as more than enough shear to
produce an organized storm or two. Again, not going to dive too far
into the possibilities at this time, especially as the threat looks
somewhat conditional on how much instability is present. However,
keep the potential for severe weather in the back of your mind as we
get closer to Monday.

Finally, not to be overshadowed by the rain, snow and thunderstorm
chances this weekend, this system will also be quite wound up,
meaning tight pressure gradients and gusty winds. EPS ensemble wind
gust statistics are quite impressive, with a mean wind gust
magnitude of 35+ mph on Sunday and up to 45 mph on Monday. This is
corroborated by GFS and NAM soundings mixing up to 800 mb with 50
kts at the top of the mixed layer on Monday. NBM seems to be
handling this well for now, putting gusts over 30 kts both days and
over 40 kts on Monday. Should this trend continue through future
forecast cycles, wind headlines will likely be needed for one or
both of these days, but will hold off on that for now.&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1239 PM CDT Fri Mar 22 2024

Widespread IFR to MVFR ceilings remain early this afternoon with
the rain/snow/wintry mix having moved out of the area but some lingering
drizzle or fog has kept some MVFR visibility reductions around
at some sites. Overall trend through the afternoon and evening
will be gradually increasing ceilings with a return to VFR at
all sites by mid to late evening. Winds out of the north will
be breezy this afternoon before decreasing tonight and then
shifting to be out of the northeast to east by Saturday
morning into midday.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...KCM


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.