069
FXUS63 KDMX 181146
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
546 AM CST Tue Nov 18 2025

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

.KEY MESSAGES...

- Rain showers remain possible this morning and perhaps some
  patchy drizzle lingering a bit longer.

- Widespread stratus/clouds through Wednesday leading to cool
  conditions.

&&

.UPDATE...
Issued at 412 AM CST Tue Nov 18 2025

An upper level closed low has moved into western Iowa early this
morning. This closed low is being dominated by two distinct
vorticity maximum. The first vort max is on the leading edge of the
upper low and aided in the strong kinematic and thermodynamic
forcing that resulted in widespread showers and thunderstorms over
much of Iowa overnight. As of 330 am, this precipitation has lifted
into northern and eastern Iowa as the mid-level dry slot has arrived
into central Iowa. Expect that area of precipitation to continue to
lift more north/northeast out of the area. In last night`s AFD,
discussed the potential failure points with a transition to snow
over northern Iowa. At least one of the failure points has occurred
with surface dew points still in the 35-37 degree range that is
creating an near surface melting layer. The second failure point is
the mid-level dry slot lifting north and the loss of ice
introduction is also occurring. Bottom line here is not expecting
snow at this point and even if there was a brief transition, no
impacts would occur.

Some wrap around showers are possible into central Iowa yet this
morning. The second vort max referenced above is trending farther
south and any forcing associated with that feature is now focused
into Missouri. For Iowa, the broad stratus deck will persist through
the day with the steering flow turning more northernly. Low cloud
ceilings are already developing over northern Iowa. This cloud cover
will settle southward throughout the day and fill in any current
breaks in the cloud cover. Far southwest Iowa may see a period of
morning sun before the clouds arrive. With low level saturated
profiles, there will be little room for warming today with little
warming impact from low sun angle solar penetrating the cloud cover.
Patches to areas of light drizzle may develop as these saturation
depths reach to near 5 kft with modest vertical ascent occurring at
times in this layer to induce collision coalescence. The turbulence
and shear in this saturated layer drops off quickly after 12z this
morning so that should also limit drizzle production.

The stratus will linger through much of Wednesday before return flow
arrives later in the day and should push the cloud cover back north.
A quick note for the end of the week. A trend to more dry conditions
for later this week with a large Canadian high pressure descending
into the Northern Plains will push precipitation chances south and
perhaps all the way south of the IA/MO border.

&&

.DISCUSSION...
Issued at 228 PM CST Mon Nov 17 2025

Early afternoon satellite imagery shows a cyclonic spin over
the Nebraska panhandle, which is associated with a compact PV
anomaly. Ahead of it, low level thermal lift is increasing over
the state and this will result in cloud cover increasing through
the remainder of the afternoon. There is some MUCAPE associated
with this wave this afternoon and simulated reflectivity shows
attempts at showery activity. However, forecast soundings reveal
low level dry air being funneling into the state on
southeasterly flow so expecting this first wave this afternoon
to mainly be saturating the mid-levels and increasing cloud
cover with perhaps a shower or two here or there that can break
through the dry air. As we head into the nighttime hours,
another wave of low-level thermal advection will push over the
state as the PV anomaly reaches Iowa. This will help to
generate more widespread shower activity. Further, MUCAPE values
ranging from 500 to 1000 J/kg will pass through the state
allowing for embedded thunderstorms to occur, particularly in
the evening hours to a few hours after midnight. The deep layer
shear is unimpressive, but the instability would be sufficient
for small hail growth or graupel production with the stronger
instability. While SPC did introduce a marginal risk of severe
weather over Missouri, the lack of stronger kinematics will
likely preclude any severe hailstones or a marginal risk this
far north. The showers will push into far northern Iowa and
northeastern Iowa by sunrise Tuesday. Near the Minnesota border,
a few snowflakes may work in as the column cools overnight, but
at the same time drier air will be working to deplete the ice
introduction. So, the time window for any snowflakes mixing in
is narrow. With the warm ground temperatures, any snow that
does survive will melt on roadways. As the drier air does arrive
in the column and ice introduction is lost, we may be left with
just a period of drizzle. The depth of this saturation thins
with time such that drizzle production will end and will be left
with low stratus clouds through much of the day. Thus, have
lowered temperatures a few to several degrees away from the
initial National Blend of Models (NBM), which was closer to the
75th percentile of available guidance and too high.

While clouds will linger Tuesday night into Wednesday morning,
the recent moisture and light winds may allow fog to form in
some areas. MOS and NBM text guidance shows this potential,
though will have to see if this occurs given the lingering
stratus clouds. Soundings do not show the typical low level/near
surface inversion and would favor the stratus.

The next window for rain will be late this week as a amplified
trough over the Western CONUS pivots east and northeastward.
Meanwhile, a trough will pass over the Canadian prairies and
over the Great Lakes. This latter feature will force a cold
front through the state with high pressure following it. With
this high over the northern states helping to push dry air into
at least northern Iowa, the moisture from the southern stream
amplified trough will be focused more southward in the state if
not south of the state. This is also shown in the NBM data over
the last day or so and will see if this trend continues to
hold in the coming days.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 541 AM CST Tue Nov 18 2025

IFR conditions already developing over northern Iowa this
morning. Expect cigs will continue to lower from north to
south today as the MVFR and IFR stratus settles south. That
stratus will then persist through the forecast period. A few
areas of rain or even drizzle possible this morning at all
sites. Did not mention everywhere due to limited vsby impact.
It is possible vsbys diminish in BR overnight under the low
stratus but enough uncertainty remains to not mention in the
forecast at this point. The wind will be from the
east/northeast.

&&

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

&&

$$

UPDATE...Donavon
DISCUSSION...Ansorge
AVIATION...Donavon