FXUS63 KDMX 242337

Area Forecast Discussion
National Weather Service Des Moines IA
637 PM CDT Tue May 24 2022

...Updated for the 00z Aviation Discussion...

.SHORT TERM.../Tonight/
Issued at 341 PM CDT Tue May 24 2022

Key Messages:
-- Chilly, gloomy, and rainy tonight

Chilly, gloomy, and rainy will be the topic of discussion today
through the early morning on Thursday. The expansive area of
precipitation covering much of the Midwest has now pushed into our
CWA. The start time for the precipitation lagged a few hours this
morning due to the dry air at the surface. The OMA 12Z observed
sounding and the HRRR and RAP model soundings indicated that the
vertical motion and precipitation would overcome the dry air near
the surface around 11am to 12pm for our southern portions which was
on target for what occurred. The precipitation will continue to
spread across the forecast area throughout the late afternoon as
large scale forcing for ascent increases ahead of an approaching
upper level low. The NAM and GFS 300K isentropic surface continue to
indicate moisture advection is expected to lift through the state
tonight before exiting to the north and east by midday Wednesday.
This allows for widespread precipitation to continue into early
Wednesday. The storm total rainfall across the southeastern area is
expected to amount 0.75" to 1" with areas in western and central
portions of the CWA seeing the highest QPF amounts of 1.30" to
1.75". The GEFS and EC ensemble probabilities continue to suggest
some accumulations in excess of 2" possible south central or
southwest. These areas with higher amounts are in response to the QG
convergence being maximized with strongest omega residing over the
west. Winds are beginning to increase this afternoon as the surface
pressure gradient tightens between the approaching low and Great
Lakes high. Winds will increase into the overnight hours with gusts
of 25 to 35 mph possible. Given that the rain is expected to fall
over a 24-hr period, flash flooding is not anticipated and
convection will be limited. Some areas in far southern Iowa near the
IA/MO border could hear a few rumbles of thunder due to the elevated
instability that will creep into that area overnight. Overnight lows
will remain brisk in the upper 40s for northern portions and in the
low to mid 50s in southern potions.


.LONG TERM.../Wednesday through Tuesday/
Issued at 341 PM CDT Tue May 24 2022

Key Messages:
-- Small chance of strong/perhaps severe storms southeastern Iowa
   Wednesday afternoon
-- Turning drier, warmer Friday into this weekend
-- Storm chances Sunday and Memorial Day

Details: Rain will be common over many parts of the state early
Wednesday morning with the upper level closed low over western
Oklahoma and Kansas with a surface low over eastern Kansas that
will track northeastward toward southeastern Iowa by late in the
day. However, the strongest push of QG convergence and theta-e
advection will be lifting northeastward in the morning hours as
the low approaches. Lingering appreciable QG convergence along
with deformation will remain over northwestern half of the state
promoting spotty showers.

As previous discussion noted and morning guidance remains showing,
it looks like southeastern Iowa including the southeastern portion
of our forecast area will be in the warm sector Wednesday afternoon.
The 12z HREF shows thinning of the cloud deck in the low and mid-
levels towards Ottumwa and this sunshine may give a boost to
instability. Forecast sounding at OTM show a saturated profile and
skinny CAPE profile in the low to mid-levels (below 600mb or so in
the 15z RAP, perhaps a little past 500mb in 18z HRRR) that would be
surface based. The peak of the instability will be a few hour window
starting around mid-afternoon (4pm or so) til early evening (8pm or
so) when the low pressure will move northeast of the area and sweep
the warm sector out of the forecast area. The line of storms in the
12z and 18z guidance doesn`t look to reach our forecast area til
near 5pm. Deep layer in the 0-6km layer is around 30 to 35 knots
suggesting all modes of severe possible. However, weak mid-level
lapse rates and saturated profile should limit the hail and wind
potential. Wind profile and hodographs have not looked overly
impressive with southerly flow that becomes south-southwesterly or
southwesterly as the line of storms arrives. This has limited storm
relative helicity. However, 18z HRRR shows much better backed flow
resulting in appreciable low level helicity. In contrast, the 15z
RAP forecast soundings at Centerville and Ottumwa show minimal low
level helicity as the hodograph is nearly linear. That said, the 0-
3km shear vector looks to be favorably oriented to the line of
storms, though any QLCS tornadoes may be localized as the magnitude
will be near or below 30 knots. The more likely area looks to be
just east of Ottumwa/Bloomfield line and seems supportive of the
eastward push of the SPC day 2 outlook compared to the midnight

The persistence of the rainfall will be waning into Thursday ending
from west to east as QG convergence finally wanes. As the closed
low/trough axis moves east of the forecast area, a ridge axis will
push into the region by Saturday morning. This will allow for
temperatures to be near or a little above normal by Friday and
likely above normal through the Memorial Day weekend. Initial
guidance from the NBM may be too low biased by the recent cool
conditions may need to adjust values a few degrees upward in the
coming days. The caveat to the above normal temperatures will be
as the ridge axis is flattened by a broad longwave trough pushing
southward over the western US, shortwave troughs will be ejected
through and north of the state with this being the higher location
for showers and storms. This may keep conditions closer to normal
if clouds and/or storms limit insolation. The 12z GFS pulls some
storms through Friday night into Saturday morning and again
Saturday night while the ECMWF remains largely north. However, the
setup of Iowa being in the warm sector with a boundary/warm front
to the north or over parts of northern Iowa could offer storm and
severe chances if this sinks farther southward. This idea is
supported by the 00z Colorado State`s machine learning random
forest outlook, which highlights Iowa on Sunday and more so on
Memorial Day. In addition, 00z CIPS Experimental Analog-Based
Severe Probability Guidance shows 15% probability of severe both
of those days as well.


.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 637 PM CDT Tue May 24 2022

Widespread rain showers are expected across Iowa tonight into
Wednesday. Conditions will worsen during the period with ceilings
and visibilities becoming MVFR across much of the state with
localized IFR conditions. Surface winds are expected to be rather
robust from the east overnight and gusty as the pressure gradient
remains tight. Some easing of the winds are expected into
Wednesday afternoon as surface low pressure approaches the state.





SHORT TERM...Ansorge/Viken
LONG TERM...Ansorge

NWS DMX Office Area Forecast Discussion