000
FXUS63 KDMX 191805
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
105 PM CDT Sat Sep 19 2020

...Aviation Update...

.DISCUSSION.../Today through Friday/
Issued at 200 AM CDT Sat Sep 19 2020

Little has changed since the previous update as we continue to
look at an extended period of relatively quiet weather over the
region. There is nearly unanimous agreement amongst deterministic
and ensemble model data sets for dry conditions through the next
7 days. The primary forecast challenge revolves around gusty winds
and the potential for elevated fire weather conditions over the
next few days. A trough digging into the Pacific northwest will
induce upper level shortwave ridging over the central conus.
Increasing southerly flow beneath the ridge will promote gusty
winds during the daylight hours as boundary layer mixing
transports higher momentum air to the surface. The strongest gusts
of 25-30 kts are expected over northwest Iowa today, potentially
increasing up to 30-35 kts on Sunday. The breezy conditions
combined with minimum RH values between 30-40 percent range may
lead to elevated fire weather conditions west of I-35. The threat
of Red Flag conditions appears low at this time as forecast
dewpoint values would have to drop another 5 to 10 degrees to
approach critical RH thresholds. Hazy skies persist as thick smoke
from western wildfires rides the upper ridge into the region. The
veil of some remains well aloft around 20 kft, but may still have
a subtle impact on highs over the weekend.

The Pac NW trough takes on a negative tilt as it swings northeast
Sunday into Sunday night, but the track takes the bulk of the
kinematic forcing into south central Canada. There may be just
enough lift to squeeze out a few showers in far northern Iowa as
northward moisture transport picks up in concert with a
strengthening LLJ late Sunday, but any rainfall will be light.
The zone of phased low-level baroclinic/upper level forcing and
associated precip shield remains well off to our north.

The first half of next week looks rather redundant as daily
conditions are nearly stuck on repeat. Flow aloft becomes pseudo-
zonal with some embedded low-amplitude perturbations, but scant
moisture availability all but squashes any precip chances.
Persistent southerly low level flow will keep highs above normal
in the low to mid 80s. A stronger upper wave dives southeast out
of Canada over the latter half of the week and shoves a frontal
boundary through the state. Models take the bulk of the upper
forcing and deeper moisture across the Great Lakes region, so we
may be left with just some low chances for a few showers.

&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1231 PM CDT Sat Sep 19 2020

VFR conditions will prevail across the area, though not completely
trouble free. The main concern both today and tomorrow will be
the strong southerly winds, especially over western/northwest
Iowa. Sustained winds today will reside in the 15 to 20 kt range
with gusts pushing 25 kts. Sunday, sustained winds will push 20 to
25+ kts with gusts 30 to 35+ kts.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

DISCUSSION...Martin
AVIATION...Curtis

NWS DMX Office Area Forecast Discussion