100
FXUS63 KDMX 050441
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1141 PM CDT Fri Oct 4 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Windy and very warm Saturday with elevated to critical fire
  weather conditions

- Dry conditions continue through the forecast with warm
  temperatures again next week

.DISCUSSION...
Issued at 311 PM CDT Fri Oct 4 2024

Our key weather elements of concern into the weekend will be
focused on wind, warm temperatures, and associated fire weather
concerns with essentially a dry forecast right on through next
week. The fast moving PV anomaly entering the Pacific NW at
midday will move quickly across the northern Plains by early
Saturday. Strong forcing and a deepening MB surface low will
accompany this system, with the tail end of the forcing lobe
crossing IA along the associated frontal passage. Although
there is a non-zero chance of spotty weak convection with the
frontal passage, moisture will remain limited, so the forecast
remains dry with our biggest sensible weather concern and
reflection warm temperatures and strong, gusty winds. FV3 core
models, such as the GFS and HRW FV3, remain over-mixed even this
late in the warm season due to dry soil conditions, however
even non-FV3 model cores like the RAP, HRRR, and NAM suggest
1.5-2+km mixing by late afternoon. Bufkit mixing algorithms
suggest a few hour period where 40kt+ wind gusts are possible
21-22Z, aligning with typical peak mixing ahead of a frontal
passage. Several models also show areas of 0.5-1km winds at
40 kts that should be realized as brief surface gusts in a SW-
NE corridor through the heart of the forecast area, including
central IA. No wind headline has been issued as of yet due to
its limited duration (<3 hrs), but it is certainly something to
be noted and monitored. See Fire Weather section for more
information on concerns tomorrow afternoon.

The deep frontal passage should occur during the late afternoon
and early evening hours with clear skies and brisk winds
becoming northwesterly, although not to the magnitude that is
expected to occur Saturday afternoon. This will lead into a more
stagnant, higher amplitude pattern into next week with upper
level ridging building into the Plains. Temperatures will be
near normal to start the week, but building heights and weak but
persistent return flow will boost temperatures above 80F again
for several days for the middle to latter portions of the week.
Some weak short waves will traverse the northwest flow at times,
but moisture will remain limited and any periods of forcing
weak and disorganized so the forecast will remain dry.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1141 PM CDT Fri Oct 4 2024

Cloud cover largely remains over southeast Iowa, though will
gradually clear into Saturday. However, expecting to keep VFR
through the TAF period, with at least some high clouds otherwise
moving through at times. A low potential for patchy fog this
morning remains, mainly over KFOD, but the uncertainty remains
high so left out at this time. Winds will turn quite breezy by
mid to late morning from the south-southwest, with gusts around
30-35 knots and isolated values around 40 knots at times.
Lighter winds look to return into the evening, shifting more
northwesterly as a front pushes across the state.

&&

.FIRE WEATHER...
Issued at 311 PM CDT Fri Oct 4 2024

Warm temperatures, lowering humidities into peak mixing, and
gusty southwest winds will certainly elevate fire weather
conditions Saturday afternoon. Wind criteria for Red Flag
conditions will certainly be met tomorrow, but humidities may be
somewhat of a limiting factor. Minimum relative humidities do
approach or reach criteria far west, so have introduced a small
Fire Weather Watch for west central sections in coordination
with adjacent offices. Dewpoint return tomorrow, into the 50s in
most areas, will limit eastward expansion for the time being,
and even with 70+% Curing west standard GFDI values are no worse
than the low end of the Very High category, with Extreme
typically noted during Red Flag situation.

However, it needs to be strongly emphasized that fire weather
conditions will still be quite elevated tomorrow afternoon due
to the warm temperatures, drying grasses and crops, and
especially strong winds. There is a particular emphasis and
concern for crops with Ag GFDI values (a proxy for worse case
scenario in dried down crops and 90% Curing) in the Very High to
Extreme category. Any fires, including in fields, could spread
very quickly with wind gusts from 35-45 mph possible. Fire
weather headings may be expanded eastward if mixing depth
increases, and dewpoints and associated RH values lower.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Saturday afternoon through Saturday
evening for IAZ033-044.

&&

$$

DISCUSSION...Small
AVIATION...Bury
FIRE WEATHER...Small