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346
FXUS63 KDMX 021941
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
241 PM CDT Sun Jun 2 2024

.KEY MESSAGES...

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- Thunderstorm chances through Tuesday. Confidence in details
  and severe potential is low however, especially tonight
  through Monday night.

-  Little or no precipitation Wed-Sun with seasonal temperatures
   and lower humidities
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&&

.DISCUSSION...
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Issued at 241 PM CDT Sun Jun 2 2024

Our pattern will undergo a fairly significant change through
the period transitioning from one that remains active with lower
amplitude flow, to one less progressive with much higher
amplitude as a large eastern CONUS closed low and corresponding
western ridge keep a drier regime in place for at least several
days. The current scenario at mid afternoon is largely
inactive, but recent satellite imagery continues to suggest some
large scale ascent is still present from lingering synoptic
short waves and remnant MCVs, one of which is vaguely noted over
the DSM metro. Several CAMs and thus the 12z HREF are fairly
emphatic that peak heating development will occur soon across
the NW Iowa and the Siouxland area, although there doesn`t
appear to be much of a focus for initiation beyond the
aforementioned mid level triggers from overnight convection.
There is little noted with regard to surface features, and
recent HRRR runs have been more tranquil in those areas, so
confidence in that occurrence is diminishing, as is confidence
overall. Several missing RAOBs upstream across central and
southern Plains were missing model ingest with 12z launches
omitted (LBF/TOP/DDC/AMA/DNR). Recent RAP/HRRR runs have placed
less emphasis on the NE/KS wind potential, and its remnants
into IA overnight, and more emphasis into a MN MCS, which may
fit trends as RAP 0-2km moisture convergence trends shifts from
the Siouxland area northward. Convective trends still remain
uncertain though with lingering larger scale vertical motion
still drifting through the MO Valley in a low CINH ~1000 J/kg
MLCAPE regime across IA, and effective shear +/- 30kts. Thus the
HREF members increasing convection central/NW later this
afternoon and evening cant be discounted, with broad-brush
chance PoPs until increasing overnight when upstream convection
may still reach the state, or drop southward from MN.

Moving into tomorrow, behind whatever occurs overnight, there
isn`t much in the way of low level focus or baroclinicity with
Iowa in the generalized warm sector. Some chances will still
linger Monday and Monday night with weak waves continuing to
traverse the developing southwest flow aloft ahead of the
maturing northern Plains upper level trough. This changes by
Tuesday however with much higher confidence in evolution, as the
model signal has been fairly consistent over the past few days
with phased large scale support and low level convergence along
the associated surface front later in the day. Although recent
GFS and EC deterministic runs have depicted weak 0-6km shear
ahead of the boundary, seasonal instability of 1000-2000 J/kg
MLCAPEs should be in place still suggesting at least some severe
potential with a disorganized wind/microburst environment the
most likely concern. Recent GEFS/EC ensemble specific humidity
and precipitable water values are anomalously high for early
June too suggesting some heavy rain potential. Corresponding
recent deterministic runs also continue to reflect healthy 1-2"
amounts in or near Iowa with the system passage.

A pattern change can then be anticipated for the remainder of
the week and through next weekend. Persistent northwest flow
aloft will result in little if any precipitation chances with
minimal moisture or forcing. A few weak waves traversing the
flow could result in brief and infrequent light precip through
the Upper MS Valley at times, and the baroclinic zone through
the Plains may be active at times, but generally removed from IA
with little anticipated in between. Although temperatures
should remain at seasonal levels, northwest flow both aloft and
at low levels should keep dewpoints seasonally low with readings
no better than the 50s as the stagnant pattern keeps surface
high pressure no further east than the MO Valley.
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&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1249 PM CDT Sun Jun 2 2024

VFR conditions were in place across the forecast area at midday
with varied cloud coverage and heights, and weak showers
approaching KDSM. Confidence in how things progress later in
the period is low however. There is certainly some potential for
additional storms, especially tonight, but timing and location
details are non- descript at this time due to variable guidance.
The most likely scenario will be a period of storms west and
central, with less confidence east, which has been reflected in
a period of -TSRA or VCSH for the time being. MVFR or less
conditions are possible with any stronger storms, but as
mentioned confidence is too low for inclusion.

&&

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

&&

$$

DISCUSSION...Small
AVIATION...Small