850
FXUS63 KDMX 071714
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1214 PM CDT Sat Jun 7 2025

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- A 20% chance of a few showers, a storm this afternoon over
  northern Iowa ending this evening.

- 50% to 70% chance of showers and thunderstorms Saturday over
  southern into central Iowa. Another round of showers and
  storms Sunday, but highest chances over 40% are over northeast
  Iowa. Any appreciable severe weather is unlikely.

- Gusty winds of 20 to 30 mph after a front passes Sunday and again
  during the day Monday.

- Seasonal to a bit below normal temperatures through Tuesday, then
  warmer.

&&

.UPDATE...
Issued at 222 AM CDT Sat Jun 7 2025

Small, isolated showers continue to bubble up early this morning
and have carried slight chance (20%) POPs accordingly, mainly
over the northern half or so of the area. As a trough crosses
the region today expect coverage of showers to increase, with
widely scattered thunderstorms developing by the afternoon and
then ending later this evening, concurrent with the diurnal
heating cycle. Instability and shear/flow fields are very
limited so no severe weather is anticipated. Maintained
relatively cool temperatures today due to cloud cover, light
low-level flow, and showers.

Tonight light southerly flow will return and clouds will linger,
resulting in limited overnight cooling with lows Sunday morning
only in the upper 50s. Meanwhile, a large low pressure system
will move southeastward over far southern Canada Saturday night
and approach the Minnesota border on Sunday. Like spokes on a
wheel, multiple surface troughs will spin out of this low and
across the Upper Midwest, with the first reaching northern Iowa
after midnight tonight and exiting our southeastern counties
late in the day Sunday. The slow passage of this trough, along
with subtle shortwave impulses rounding increasingly cyclonic
flow aloft, will result in prolonged POPs from late tonight in
the north through the day Sunday across the area. More
thunderstorms are expected but overall the severe weather threat
will remain low due to limited instability - the exception being
in our southeast corner, down around
Ottumwa/Centerville/Bloomfield, where there may be a narrow
opportunity for stronger storms on Sunday afternoon. This will
be dependent on the timing of the advancing surface trough and
destabilization ahead of it, which may allow for the emergence
of a threat of large hail/strong winds. However, any window for
severe will be brief and small within our service area, likely
limited to a few counties and a few hours Sunday afternoon. If
the expected progression of the surface trough speeds up such
that it will exit our area before sufficient destabilization can
occur to support stronger updrafts, then even this limited
threat of severe weather may diminish before Sunday afternoon
arrives. We will be monitoring this threat over the weekend.

&&

.DISCUSSION...
Issued at 208 PM CDT Fri Jun 6 2025

Low amplitude and largely zonal flow is over the central part of the
United States with a jet streak passing to the north and one over
the southern Rockies. While jet streak dynamics are favorable for
lift over Iowa, low level thermodynamics and focused convergence are
rather weak and nebulous. This has resulted in clouds with a bit of
sunshine with a few attempts at sprinkles. A few showers or a
storm is possible this afternoon, likely over northern Iowa,
with an expectation that this activity will diminish overnight.
A stronger shortwave trough that is currently over Wyoming will
move into Iowa by Saturday morning. This along with a weak
surface low just south of Iowa will increase QG convergence with
a higher chance of showers and isolated thunderstorms through
the day. The highest chances over 50% will be over southern into
central Iowa due to the proximity of the shortwave and low
tracks with all chances lowering in the evening as the shortwave
moves east of the state. Severe weather is not forecast with
weak lapse rates and instability.

Right on the heels of this shortwave will be a larger trough that
will be moving out of Canada Sunday into the western Great Lakes. At
the surface, low pressure will be over Canada ahead of the trough,
but a cold front will extend southwestward and move through Iowa
Sunday morning. While low level theta-e advection looks to be at
least modest ahead of the front, the best phasing of this forcing
with mid-level thermodynamics will be over northeastern Iowa into
Wisconsin and northern Illinois. Thus, the highest chances for
showers and storms will be over these areas with lower chances,
generally less than 30%, over central into southern Iowa. While at
first glance deep layer kinematics look impressive, there is a lack
of effective shear, lapse rates are weak, and instability is at most
around 250 J/kg meaning that severe weather continues to look
unlikely. After the front passes, winds from the northwest will
increase. The pressure couplet is weak and while there is a surge in
advection right behind the boundary, sustained winds of 10 to 20 mph
with gusts between 20 and 30 mph will be common. These winds will
draw drier air into the state with dewpoints falling from the middle
50s to low 60s Sunday morning to the middle 40s to low 50s by Monday
morning.

The fitful and gusty winds look to return on Monday as the
trough moves east over the Great Lakes and the southeastern
Ontario province. Another lobe of vorticity will spin
cyclonically around the trough and drop over northeastern Iowa.
This will bring another shot of showers from north central into
northeastern Iowa on Monday. As this trough`s influence departs
the region, mid-level ridging and increasing heights look to
replace it. This will bring rising temperatures with conditions
above normal from mid-week to the end of the week. It will also
result in a mainly dry forecast from Tuesday until at least late
Thursday.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1214 PM CDT Sat Jun 7 2025

Scattered showers and storms were over central Iowa early this
afternoon and these are causing visibilities to drop into MVFR
or briefly IFR while ceilings may briefly drop out of VFR.
With the exception of OTM where a broad area of rainfall will
move across this afternoon, timing much of the rest of this
activity is difficult. This has resulted in some long PROB30
groups. Overall, this activity will be moving east and
diminishing late this afternoon and early this evening with VFR
conditions returning. Then, attention will be on a cold front
that will bring lowered, but still mainly VFR ceilings and a
shift in the wind from the south to from the northwest by late
in the period. Have maintained PROB30 group at ALO for possible
showers along this front, but have removed thunder mention due
to low confidence. Additional PROB30 or prevailing groups may
be needed in future updates at other terminals.

&&

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

&&

$$

UPDATE...Lee
DISCUSSION...Ansorge
AVIATION...Ansorge