589
FXUS63 KDMX 300656
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
156 AM CDT Mon Sep 30 2024

.KEY MESSAGES...

- Sunny and warm again today, with some fire weather concern
  over far northwestern Iowa late in the day.

- A cold front will surge through tonight, bringing notably
  cooler weather through Tuesday night.

- Sunny, dry, and pleasant weather returns from Wednesday
  through Saturday with daily highs generally in the 70s. There
  may be an elevated fire weather danger in northern Iowa on
  Wednesday with gusty winds and dry conditions.

&&

.DISCUSSION...
Issued at 156 AM CDT Mon Sep 30 2024

It is another clear and quiet night across the region. A large
surface high pressure area remains anchored over the Great
Lakes and extending southwestward over Iowa. This is resulting
in light winds and clear skies once again, allowing temperatures
to radiate nicely although not as low as was seen a couple
nights ago, given the higher dewpoints in place. Some high-
resolution guidance is indicating an area of fog may develop
over southeastern Iowa toward sunrise this morning, and winds
are lightest in that area near the ridge axis, but even if this
fog does develop it should only affect the fringes of our
forecast area and only for a couple of hours, so no headlines
are anticipated.

Today will once again be unseasonably mild. The ridge will begin
to slide off to the southeast and low-level winds will veer
around to south by midday, promoting modest warm air advection
with continued sunshine. Temperatures aloft are slightly less
warm and mixing will not be as robust as it was on Saturday, but
should reach the levels seen on Sunday with highs around the mid
80s in most areas. Late in the day a sharp cold front will
approach from the northwest, reaching the Estherville area
around 5 PM or so and sweeping across the state this evening and
overnight. Strong northwest winds will follow the front, with
gusts approaching 30 MPH for a period this evening. The mild
and dry conditions in place, combined with these stronger winds
will raise fire weather concerns somewhat in our northwestern
areas. However, relative humidity will be lowest in the
afternoon and the winds will be strongest this evening, leaving
only a brief period of perhaps a couple hours where these spaces
overlap. With the window being so brief and surface fuels only
partially cured, do not plan any fire weather headlines for the
northwest but will monitor this scenario throughout the day.

Once the front pushes through tonight it will be followed by
notably cooler temperatures, reaching highs of only the upper
60s on Tuesday and then falling into the lower 40s in most areas
late Tuesday night. However, this will be a brief period as by
Wednesday morning we will already see a return of southerly
low-level flow and relatively mild weather for the latter half
of the week, though not as warm as the temperatures of the past
few days. On Wednesday afternoon a more concerning fire weather
risk may develop across northern Iowa, as a strong pressure
gradient and deep mixing layer promote wind gusts approaching 35
MPH for multiple hours. Concurrent with these strong winds, the
warming temperatures without a corresponding increase in
dewpoints will promote relative humidity falling below 25
percent, and possibly below 20 percent at times, leading to an
elevated fire weather danger. The primary uncertainty in this
scenario will be the state of surface fuels, as crops may be
largely cured but other vegetation may remain mostly green.
Aside from the fire weather concerns, the period from Wednesday
through Saturday will be dry and quite pleasant, with plenty of
sunshine and daily high temperatures in the 70s. From Saturday
night into early the next week the forecast becomes more
uncertain, as some long-range model solutions indicate another
cold front passage while others less so.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1107 PM CDT Sun Sep 29 2024

Main aviation concern continues to be restrictions at OTM due
to fog development around and after 12z. Some model guidance has
trended lower with visibility restrictions so have added IFR
TEMPO group for this possibility, but this may end up being
south of the terminal. Otherwise, light winds overnight from the
east or southeast will become breezy from the south and later
southwest as a cold front approaches central Iowa during the
daylight hours Monday. This front will move through the evening
hours with winds becoming from the northwest and turning gusty.

&&

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

&&

$$

DISCUSSION...Lee
AVIATION...Ansorge