261
FXUS63 KDMX 042021
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
321 PM CDT Tue Jun 4 2024

.KEY MESSAGES...

- A few strong storms possible through early this evening.
  Damaging wind gusts is the primary threat.

- A strong storm or two possible over northern Iowa late
  Wednesday afternoon.

&&

.DISCUSSION...
Issued at 313 PM CDT Tue Jun 4 2024

An upper short wave is moving across southeast Iowa this afternoon
and it can be seen as the swirling on satellite over that area.
Getting a few funnel cloud reports in that area as well. The upper
short wave combined with good 0-3km CAPE and good stretching
potential which aligns well with landspout funnel potential. Also
monitoring northwest and north central Iowa where the non-supercell
tornado parameter is highlighting again due to the stretching
potential and low level instability. The landspout funnel potential
over the northwest should be maximized over the next few hours
before the primary boundary arrive and gives the line more momentum
to the east, which will help disrupt some of the landspout processes.

Deep layer shear will remain quite weak today which will keep most
storms short lived with a lack of any storm organization. There have
been hints that some deep layered shear could briefly reach 25-30
kts that could help maintain a few storms a bit longer. The 0-3 km
theta-e differences area in the -10k to -20k range with is near the
range for sustained cold pool development but of course, it could be
difficult to maintain cold pools if the storms themselves don`t
maintain. More likely is the potenitial wind gusts/damaging winds as
storms collapse with the lack of shear. Small hail is also possible
at least through this afternoon when the greatest instability is
available. Dew points in the low 60s are lingering a bit behind the
initial boundary passage and could have some shower/isolated
thunderstorm redevelopment within this ribbon before the much drier
air arrives.

Much of the precipitation will be east of the area by midnight or
shortly after. The early portion of the daytime Wednesday will be
quiet. The wind will be increasing by mid to late morning. Another
short wave and boundary will arrive over northern Iowa by mid to
late afternoon. A few showers and storms will be possible over the
northeast as this system moves through. Sounding profiles show
higher LCLs values and thus cloud bases at 6-8kft. Unidirectional
wind flow with some potential for mixed layer winds to approach 40
kts or more. Any storms could have a marginal severe wind potential
with 60 mph winds gusts. This scenario will be contingent on
available moisture for the storm development.

Once that system passes, the upper flow over Iowa will be a modified
northwesterly as a dual upper low over much of southern Canada in
addition to upper ridging over the western CONUS. The result will be
cooler temperatures and a mostly dry period. That main upper low
over Manitoba will dive south around Sunday/Monday timeframe and
will be followed by some precipitation chances early next

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1243 PM CDT Tue Jun 4 2024

A few showers and local MVFR cigs are across central Iowa early
this afternoon. A few thunderstorms may develop over the next
few hours but the areal coverage will be low. A line of
thunderstorms will enter western IA by mid to late afternoon
and move east across the area and should impact most sites in
front of a boundary, which will also bring a wind shift to more
west/northwest. Gusty winds will be possible with the storms.
VFR conditions will follow. Expect breezy to gusty southwest
wind by late Wed morning.

&&

.HYDROLOGY...
Issued at 345 AM CDT Tue Jun 4 2024

The potential for widespread rainfall above 2 inches remains
low with the current event. Outside of the current flood warning
at Estherville, all other sites are expected to mainly have
within bank rises as the exceedance probabilities and 120 hr QPF
continue to support those forecasts. There still is the
potential for significant ponding in low lying areas over the
next few hours while storms remain slow moving but that
potential will also diminish as storms become more progressive
late this afternoon and evening as the boundary arrives and
accelerates the activity to the east.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon
HYDROLOGY...KCM