317
FXUS63 KDMX 040443
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1143 PM CDT Mon Jun 3 2024

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

.KEY MESSAGES...

- Minimal shower and storm chances into Tue morning, but more
  widespread storms expected Tue mid-afternoon into the evening.
  Some of those storms may be strong to severe with large hail,
  damaging wind, and locally heavy rain.

- Mainly dry with seasonal temperatures and lower humidities
  Wed-Mon

&&

.DISCUSSION...
Issued at 250 PM CDT Mon Jun 3 2024

Outside of a bit slower progression on the frontal passage
later tomorrow, expectations haven`t change a whole lot over
the past few days with storm chances peaking late Tuesday and
followed by an extended period of more tranquil and pleasant
weather into early next week. The upper trough passage driving
our convection potential tomorrow should usher in an extended
period of higher amplitude flow, slowed by a meandering eastern
CONUS closed upper low, and keeping Iowa in prolonged mainly
inactive northwest flow aloft.

There wasn`t much going on by mid-afternoon with most of the
precip from earlier in the day now re-firing off to the east.
The airmass south and east remains conducive for some
development however with uncapped 1000-2000 J/kg MLCAPEs. GOES
Cloud Phase Distinction products note some enhanced development
in the Waterloo vicinity, and also southeast, so there is some
potential for peak heating convection into the early evening for
those locations. With effective shear <=25 kts any strong to
severe potential appears to be minimal. Albeit low, there is
some potential for additional development south and east later
into the night however. Satellite imagery continues to note a
lingering MCV over eastern KS, which is expected to drift north
and east overnight with its subtle vertical motion field into
weak low level moisture transport, which may trigger some
additional weak nocturnal warm advection response.

After a brief late morning lull, vertical motion ahead of the
current deep Pacific NW PV anomaly should reach the Siouxland
area or beyond by early afternoon, possibly triggering some
isolated convection ahead of the front. The frontal progression
is a bit slower than previously anticipated, but this synoptic
lift should couple with the frontal low level convergence NW-SE
starting no earlier than mid-afternoon, and then gradually
spread south and east into the evening. There is some severe
weather potential with MLCAPE ~2,500 J/kg, but organization and
maintenance will be a question with effective shear often <=20
kts. Updraft strength will be marginal too with projected mean
wind storm motion only 15-25 kts until the trough approaches
and corresponding associated low level storm relative inflow at
those values or weaker. With these lower storm relative winds,
and soundings relatively dry post afternoon mixing,
experimental Entrainment Cape values are ~40% less than
traditional MLCAPE reflections which also suggest tempered
updrafts. This slow movement may lead to some locally heavy
rains however with climatologically anomalously high moisture
parameter space, including precipitable water values 1.75"+.
12z HREF localized probability matched-mean (LPMM) 24hr QPF
suggests isolated 1-3 amounts are possible.

Any precipitation should move off to the east approaching
daybreak Wednesday starting what looks to be an extended period
of little precipitation, seasonal temperatures, and atypically
lower dewpoints. This will be driven by fairly uniform northwest
flow surface to above keeping us with little in the way of
forcing or moisture with surface high pressure progressing no
further than Iowa until the weekend. The only precipitation
window of note looks to be late Fri into early Saturday across
central and southwest Iowa as weak waves top the Rockies ridge
and induce warm/theta-e advection aloft through the MO Valley.
There are a few other brief precipitation opportunities in
various deterministic solutions, but right now the NBM does not
reflect a sufficient signal for any mention beyond later this
week. One higher confidence reflection of sensible weather will
be lower humidities in prolonged northwest low level flow
pushing dewpoints into the 40s at times later this week,
atypically low for early June.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1139 PM CDT Mon Jun 3 2024

VFR conditions currently prevail over the area. Primary aviation
forecast challenge revolves around thunderstorm timing and
extent of impacts later today. Model guidance suggests a
disorganized area of iso to sct shra/tsra and pockets of low VFR
to MVFR stratus may move over portions of southern Iowa late
this morning into the early afternoon hours. No mention was
included at KOTM through that period due to low probabilities
and confidence. Much more widespread tsra is expected along a
frontal boundary moving across the area from late afternoon into
the evening hours. Tempo categorical restrictions and gusty
winds are possible as this activity moves east, however is only
covered with prevailing VFR conditions for now until confidence
increases in tsra timing and potential impacts at respective
terminals.


&&

.HYDROLOGY...
Issued at 250 PM CDT Mon Jun 3 2024

A Flood Warning remains in effect for Estherville, with all of
this morning`s river forecasts based on 24 hours worth of QPF
(through 12Z Tue). While heavy rains are possible Tue afternoon
and evening beyond that period per the Discussion section,
additional flooding concerns beyond the current Estherville
Flood Warning are not expected at this time based on recent HEFS
output and RFC contingency forecasts. Neither GEFS based HEFS
median to 30th percentile QPF exceedance probabilities or the
120 hour deterministic QPF suggest additional flooding beyond
what is already occurring, hinting at mainly within bank rises
unless rainfall greatly exceeds expectations.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Martin
HYDROLOGY...Small