298
FXUS63 KDMX 062345
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
545 PM CST Thu Mar 6 2025

 ...Updated for the 00z Aviation Discussion...

.KEY MESSAGES...

- Band of moderate snowfall moves in this evening through Friday
  with totals averaging between 3 to 6 inches around roughly the
  Highway 20 to 30 corridor. A narrow strip of even higher
  snowfall remains possible, as does an overall shift in track.
  Winter Weather Advisory in effect for north central Iowa.

- Weekend through Tuesday is dry with warmer conditions as high
  temperatures of 15 to 20 degrees above normal are forecast.
  Will need to monitor for break-up ice jams.

&&

.DISCUSSION...
Issued at 348 PM CST Thu Mar 6 2025

Surface ridge that has kept our weather quiet much of today
continues to push off to the east this afternoon as a surface low
treks through Kansas tonight and into and through Missouri on
Friday. Theta-e advection and QG forcing both increase tonight
leading to the return of precipitation to the area. As noted in the
previous discussion, Gulf moisture wraps into the eastern side of
the low, but mainly only influences the warmer side of the
system/southern Iowa where rain is largely expected to prevail. In
the north, a fgen band with moisture accompanying it will lead
to a banded snow event with accumulating snow setting up tonight
into Friday. A number of nuances, and as such uncertainty,
remain surrounding the exact location and details of this snow
band.

Some hi-res guidance this morning shifted this main snow band
further northward, though notably some midday data has actually come
back slightly further south around where the band was previously
forecasted prior to this morning runs. The fgen band itself in
various models actually differs as far north as far northern Iowa,
to as far south as near to south of the I-80 corridor. However,
looking at temperature profiles and the location of the low/forcing
still suggest overall that our previous forecast is on track with no
changes to the current Winter Weather Advisory nor really to snow
amounts which still vary from around 2" to 7" within the advisory
area surrounding roughly the highway 30 and 20 corridors. The
thermal profiles and a 1-2 degree temperature difference will
have a large impact on the forecast in addition to the ultimate
location the fgen band sets up. Hi-res models, as noted in the
previous discussion, have been running on the warm side and have
kept focus on more deterministic GFS/Euro solutions which do a
better job of dynamically cooling the column to support snow in
the band itself. Some of this cooling will be rate driven with
the higher snow rates helping to lead to greater cooling and
thus snow versus a lower rate actually could support a rain/snow
mix temporarily where thermal profiles are right on the edge
before changing back to snow if rates increase. Although most
areas will support rain initially, areas in north central Iowa
quickly change to a wet snow while closer to the I-80 corridor a
rain/snow mix is supported and further south, as noted
previously, mostly rain, except potentially around daybreak
Friday when some snow could mix in as well. Forecast soundings
are mostly all isothermal further driving home the point that a
couple degree change in temperature could mean the difference
between rain and snow prevailing but also will drive snow
character to be a wet, heavy snow as the thermal profiles reside
in the lesser-known DGZ, but snow amounts/rates will be further
enhanced by the saturating profiles as they reach into the more
traditional DGZ. Snow rates largely seem similar to previous
forecast with rates exceeding 0.5" per hour at times Friday
morning, which could certainly lead to additional impacts for
the morning commute, especially in areas with lingering impacts
from earlier in the week. Prior experience with banded snow
events suggest that the narrow band of heaviest snow amounts
will have a tighter gradient than currently forecasted, and with
the location of this band likely to shift slightly north or
south heading into event onset. As a result, we`ll have to keep
monitoring as precipitation moves into the area tonight for any
adjustments in track as well as temperatures thus keeping
forecast confidence in snow amounts and exact location lower (as
is always the case in banded snow events). On the northern edge
of the snow band, a sharp gradient in snow could mean the
difference in snow to no snow/precipitation at all as drier air
is wrapped into the system. Thus it should be noted in far
northern Iowa, locations may stay completely dry. Lastly, the
Winter Weather Advisory covers the bulk of the area most likely
to see the highest snow totals at this point, but as noted in
describing all the nuances, these higher snow amounts could be
less than a county wide making for large discrepancies in snow
amounts north to south within a county, or could occur just
across a county border not included in the headline. In good
news, the wind will be much lighter with this event leading to
few to no concerns about blowing snow than earlier in the week
given the wetter character of the snow as well.

The snow/rain ends into late tomorrow afternoon to evening west to
east as the low shifts east of the state. Quiet and dry weather then
returns for the weekend and into early next week with any nearby
precipitation chances all outside of the area. Although
Saturday will be warmer, temperatures really start to increase
again Sunday and even more so Monday as highs reach the 50s and
60s again with temperatures remaining in these ranges through
much of the rest of the week. Active weather then returns late
next week into next weekend with additional details to come.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 544 PM CST Thu Mar 6 2025

Clouds thicken and lower this evening with rain and snow
developing across central Iowa. Initial VFR conditions will give
way to widespread MVFR to IFR conditions overnight as the
precipitation slides across the state. The precipitation remains
across central and northern portions of the state into Friday
before departing during the afternoon. The poor aviation
conditions persist into Friday morning with the precipitation
but improve by the end of the period as the rain and snow depart
and ceilings and visibilities quickly improve. Winds become
northeast overnight and increase into Friday becoming more
northerly by the end of the period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 PM this evening to 6 PM CST
Friday for IAZ023>026-033>038-044>050-057-058.

&&

$$

DISCUSSION...KCM
AVIATION...Cogil