382
FXUS63 KDMX 121116
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
616 AM CDT Wed Mar 12 2025

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

.KEY MESSAGES...

- Warmer temperatures Today and Thursday, breezy west on
  Thursday.

- Prominent system arrives on Friday bringing gusty winds and
  potential for severe storms. Damaging winds and hail will be
  the main concerns with any severe storms.

- Additional precipitation and gusty winds possible early Friday
  into Saturday, with light snow possible north and west.

&&

.DISCUSSION...
Issued at 352 AM CDT Wed Mar 12 2025

Another round of quiet and mild weather conditions are
expected, as highs climb slightly higher today than yesterday.
The surface pattern through Iowa is fairly nebulous, with broad
weak low pressure to the west and weak high pressure over the
great lakes region. This lack of any prominent features will
keep winds light today, with only a few clouds streaming across
the south. Further up in the atmosphere, the 500 mb pattern
reflects these surface features as we see zonal flow dominating
through the day today and a shortwave passing to our south. This
wave will keep the area dry and cut off from gulf moisture
through Thursday.

The upper level pattern begins to shift through the day
Thursday as the well advertised end of week system begins to
build off of the western CONUS. As the trough tracks east, low
pressure builds on the the lee side of the Rocky Mountains,
adding a more southerly component to our surface flow on
Thursday. This will allow temperatures to warm into the 70s for
much of the area, as well as bring some stronger gradient winds
to the northern and western portions of the forecast area. Lee
side cyclogenesis continues to build off the Rockies through
Thursday night and into Friday, with the upper low closing off
by Friday morning and pivoting northeastward toward Iowa. This
system will be multifaceted, bringing the potential for gusty
winds, strong to severe thunderstorms, and even potentially some
snowfall. Lets dig into it.

The first and most widely observed impact will be the gusty
winds associated with the system as it passes through the area
on both Friday and Saturday. The surface low will be rapidly
deepening and occluding as it passes into Iowa, which will bring
strong gradient winds into the state. The first instance of
these winds will be observed ahead of the occlusion in the warm
sector. These will be driven to the surface through boundary
layer mixing. As a result, the strength of the surface
winds/wind gusts will be dependent on the depth of the surface
mixing. This makes the forecast a tad tricky, as a warm nose
aloft may inhibit how much the boundary layer can tap into the
stronger winds aloft. That said, if efficient mixing does occur
and that cap is eroded, models are analyzing a 45 to 55 kt jet
around 850 mb just ahead of the occlusion. Those winds at the
top of the mixed layer would translate to gusts of 40 to 45+ mph
at the surface, again assuming we mix out to that height. A
secondary push of gusty winds may also come in behind the
occlusion, as another push of 50+ kt winds comes with the dry
slot on the southern edge of the system. This push of winds is a
little less certain in our area, as recent guidance has been
trending the jet max slightly further south and east, but
something to keep an eye on, especially for those in the
southwest portions of the area. Finally, the low continues
through Iowa Friday night into Saturday, with a 3rd push of
gusty winds on Saturday. This would be coincident with the cold,
descending air on the backside of the low, and primarily impact
the western half of the state.

The next hazard associated with this system will be the
thunderstorms and potential severe weather. When the low arrives
in the state and occludes, storms will begin to fire in the
warm sector ahead of the pseudo dry line/cold front. With
initiation expected in the mid to late afternoon hours, warm
surface temperatures and steep lapse rates aloft should provide
plenty of instability for any displaced parcels. Likewise, as
eluded to above, there will be strong kinematics associated with
the deepening low, leaving no shortage of wind shear to help
updrafts organize. Therefore, still expecting strong to severe
storms in Iowa on Friday afternoon, especially as you go further
east in the state. The well mixed boundary layer and 1000+
meter LCLs will be a deterrent for tornadogenesis on Friday, but
model soundings show a textbook inverted-v at the surface.
Dry low levels combined with the strong wind fields aloft,
suggest damaging winds will be the primary threat with these
storms. Large hail may also be a concern, especially with any
discrete storms that develop a rotating updraft to help sustain
hailstones. The system and associated storms will be moving
quickly as the occlusion pivots northeast and the dry slot
punches in on the southern edge of the low, meaning the window
may be fairly narrow for storms Friday afternoon. However, the
parameter space is certainly there for damaging storms. The
storm prediction center has maintained a slight risk (level 2 of
5) for severe weather over the central and eastern portions of
the forecast area, with an enhanced risk (level 3 of 5) to our
south and east where storms will be progressing into the
evening.

Finally, precipitation chances develop again on the back side of
this low as it rotates through the area late Friday into
Saturday. This will be accompanied by a push of colder northerly
air, bringing the potential for some light snow across the far
northern and western portions of the forecast area. Guidance has
struggled a bit with this precipitation, presumably due to the
dry near- surface air behind the occlusion, but soundings have
shown a bit better saturation tonight especially in the north.
Therefore, well want to keep an eye on snow potential on
Saturday as well, especially given the falling snow could be
accompanied by gusty winds. After precipitation departs on
Saturday night, cool temperatures persist into Sunday before
warming again into next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 614 AM CDT Wed Mar 12 2025

VFR conditions prevail through the period with light and
variable winds generally out of the east to southeast. High
clouds filter through at times during the day.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Dodson