207
FXUS63 KDMX 081143
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
543 AM CST Sat Nov 8 2025

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

.KEY MESSAGES...

- Winter Weather Advisory issued for portions of western and
  northwest Iowa this morning. Snowfall rates up to 3 inches
  possible with locally higher amounts. Main impacts will be
  visibility reductions from snowfall rates.

- Brief snow showers possible Saturday night into early Sunday.

- Blustery and cold on Sunday.

- Turning milder next week with a mainly dry forecast.

&&

.UPDATE...
Issued at 358 AM CST Sat Nov 8 2025

Main change from the previous package was the issuance of a Winter
Weather Advisory for western and northwestern portions of the area
for this morning, but an expansion eastward was not done overnight
due to lingering uncertainty in the temperature forecast. A pocket
of clearing and light northeast flow cooled northern Iowa down to
around freezing, again the transition zone residing in the familiar
corridor between Highway 30 and Interstate 80. The dew points there
also dropped into the low 30s, lower than what most of guidance had
predicted. The wet bulb temperature hovers just above freezing at
sites like this, and values in the cold sector of the approaching
system won`t deviate much during the day. The main slug of WAA still
appears to be along and south of Interstate 80, it`s role of
moisture advection will bring Tds in eastern Iowa into the mid 30s
by midday. The warm layer described at the surface will be shallow,
residing in the lowest 1.5kft, or so. The profile aloft,
particularly in the Winter Weather Advisory, continues to exhibit
signs that snowfall rates will be able to overcome the warm layer
and warmer ground temperatures to some degree (pun intended).
Snowfall rates probabilities are highest here, with a 30% chance for
1"/hr snowfall rates in the SREF.

Within the headline, this is where the left exit region and
diffluent flow from the approaching upper jet reside, as well as Q
vector convergence associated with the small but potent wave
(analyzed to have -10 dam height falls by the RAP). Cooling
temperatures aloft steepen lapse rates to over 7 C/km in the DGZ and
above, paired with supersaturation with respect to ice. Lift on the
order of -20 microbars maximizes in the DGZ. As mentioned in the
discussion below, snow depth forecasts will better account for the
melting that still will occur. Much of the 00z and 06z guidance
yielding a narrow band of 1-2 inches of snow within the advisory.
What transpires as we approach the noon hour will be worth closely
monitoring. Frontogenesis circulations will begin to extend
into the DGZ (located at roughly 600mb). Convective processes
will increase with negative EPV and theta-e lapse rates also in
the DGZ, plus continued supersaturation with respect to ice. Hi-
resolution guidance churns what appears to be high snowfall
rates with this, increasing omega to -30 microbars and beyond,
but the probability for 1"/hr snowfall rates remains peculiarly
low (10%). This is partially due to how they are resolving the
lowest 5kft as the day progresses, this layer hugging the 0C
isotherm until late morning, and perhaps assimilating too much
melting in a warm layer of only around 1.5kft. It remains
difficult to tell how warm the thermal profile will be over Des
Moines around noon, but it remains a possibility that rate-
driven impacts will be a factor in a very short window of 1-2
hours, amounting mostly to visibility reductions. The HREF keys
in on this threat well with 70-90% probabilities of visibilities
under a half mile. The chance of this wanes as the system
interacts with a warmer profile further east. Expansion may be
necessary if impacts start being realized later this morning.

CAA behind the wave steepens low-level lapse rates and hangs onto
saturation. Snow showers with reduced visibilities will be possible
through much of this evening. Temperatures plummet into the teens
tonight which will bring road temperatures low enough that slick
spots could form for Sunday morning.

&&

.DISCUSSION...
Issued at 314 PM CST Fri Nov 7 2025

Early afternoon satellite imagery shows an area of clouds
sagging southward this afternoon, which has reached northern
Iowa and is associated with the leading edge of a cold front.
Behind this front, 850mb and 925mb analysis shows low level cold
air advection with surface observations showing northwest winds
and cooler and drier air filling in. There may be a few showers
in far northeast Iowa with sprinkles perhaps as far southwest
as Waterloo, but overall this is passing through dry.

Upstream of Iowa over the northern Rockies along the US/Canada
border, GOES-East upper level water vapor imagery shows a compact
shortwave trough/PV anomaly. This shortwave will quickly drop into
Iowa through the day Saturday and bring our first chance of
accumulating snowfall. Clouds will increase and thicken overnight
with precipitation chances starting to tick upward along the Highway
71 corridor into our forecast area as early as 3 or 4 am. This is
when strong low level QG convergence and theta-e advection coupled
with the left exit region of a jet streak will arrive over
central Iowa. This forcing will help to spread the precipitation
chances quickly east-southeastward and be in our eastern forecast
area reaching the Highway 63 corridor by around 8 am or so.
With snowflakes expected to fly in less than 24 hours, there
still remains a great deal of uncertainty with regards to
precipitation type due to low level temperatures and dewpoints
and surface/ground temperatures as well as if rates will be
sufficient to overcome those factors for what accumulation may
occur and in what location. As has been the theme this week,
temperatures were lowered from the initial National Blend of
Models (NBM) given the clouds and falling precipitation, which
will limit how much the air warms tomorrow. In addition during
the day, dewpoints that start in the 30-34 degree range look to
rise slightly by a few degrees, which may result in wet bulb
temperatures above what would allow for snow and/or snow
accumulation. While wet bulbing may not occur, dynamically
cooling the column may be in play as cross sections show a
period of several hours of at least moderate lift, which
coincides within the dendritic growth zone (DGZ), as it passes
over the state. Latest HREF snowband probability tracker does
show several models with possible banding coming across Iowa
somewhere between Highway 20 and I-80. What`s interesting about
this potential is the lack of support in ensemble data for the
probability of 1 inch per hour snowfall rates, with no higher
than 10% in the 0z/12z HREF and up to only 30% in the 9z SREF.

So given that uncertainty, here is how we think this will play out.
Precipitation will spread in as mostly snow roughly north of
Highway 30 in the pre-dawn hours and a rain/snow mix between
Highway 30 and Highway 92. For our northwestern forecast area
from say roughly Crawford up to Pocahontas counties in the
morning hours, this may be the window of peak snowfall as the
moderate lift is in the DGZ. This may foster rates that are high
enough to be able to accumulate vs melt on the ground with 4
inch soil temperatures in the middle and upper 40s. BUFKIT
soundings at CRL show higher rates of an inch per hour or a bit
more for several hours, though these may not be showing the full
extent of melting. For those that like to look at raw snowfall
output online, looking at the snow depth output can be useful in
these borderline temperature events to show to some degree the
extent of melting. As precipitation chances slide eastward to
I-35 and more so Highway 63, the rain/snow mix may move
northward. This will be a result of moving into the part of the
day that will be `warmer` along with solar radiation still
penetrating through the clouds and helping to warm surfaces,
especially paved surfaces. With the bulk of precipitation
ending in most areas across central Iowa by late afternoon, the
potential for a flash freeze would seem to be lower given no
falling precipitation as temperatures lower into the evening.
Total snowfall still looks to be highest over northwest Iowa
into our northwestern forecast and north central Iowa. Where
there is dynamic cooling, this could lead to pockets or a narrow
corridor of snowfall higher than currently shown in the
forecast. While no winter weather advisory was issued on this
shift, it is still possible that this may occur if not tonight,
Saturday morning as upstream observation trends and webcams are
monitored. While not often desired, this may offer little lead
time other than the messaging that has been provided much of
this week.

There will be a break in the precipitation as mentioned above late in
the afternoon and early evening as the shortwave trough departs. A
second push of shortwave energy arrives Saturday night along with
the delivery of colder air. This colder air will help to steepen low
level lapse rates. Forecast soundings show some low level
instability and thus may be able to generate convective snow showers
Saturday night into a little after sunrise Sunday. These could bring
brief, passing snow bursts with visibility reductions Saturday night
into the morning hours of Sunday with this activity ending from
north to south. Otherwise, Sunday is shaping up to be a raw
November day with highs in the low and middle 30s and blustery
winds accentuating the chill of the day. These conditions will
combine to make wind chills in the upper teens to low 20s at
their highest. Needless to say, if you have outdoor plans one
will need to bundle up with their favorite winter gear.
Fortunately, temperatures will begin to rebound into next week
with 50s expected in most areas on Tuesday through week`s end
with a mainly dry forecast as the jet stream stays northwest of
the area.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 536 AM CST Sat Nov 8 2025

Adjusted the arrival time of precipitation and lower ceilings,
as well as changed some of the precipitation mentions from RASN
to SN for northern sites. IFR/LIFR cigs expected as well as vsby
restrictions to around a half mile, perhaps less at times. KDSM
sits right on the transition zone between rain and snow, so
added in a PROB30 mentioning LIFR vsbys and cigs from snow. KALO
and KOTM will see the least amount of snow, remaining primarily
rain for the event.

Snow showers are possible behind this departing system for most
all sites through at least 05z (namely KOTM). Localized vsby
restrictions from a burst of snow possible with these showers,
but coverage is sparse enough to keep PROB30s only.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon CST today for IAZ015-023-
033-034-044-045.

&&

$$

UPDATE...Jimenez
DISCUSSION...Ansorge
AVIATION...Jimenez