Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 131114
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
614 AM CDT Wed Mar 13 2024

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Showers/storms likely tonight into Thursday. Few may be strong
  to severe in southern Iowa tonight with a threat of hail and
  strong winds. Severe threat diminishing for Thursday.

- Fire weather concerns may develop Saturday.

- Cool and blustery Sunday into Monday.

&&

.DISCUSSION...
Issued at 234 AM CDT Wed Mar 13 2024

Primary forecast challenge over the next 24 to 48 hours is pinning
down precip timing, coverage, and severe threat as multiple
shortwaves emerge from a deepening western conus trough. Lee side
cyclogenesis ramps up today with a deepening sfc low over KS and
attendant warm front eastward across northern MO. Phased
kinematic/thermodynamic forcing contributions overspread the
region in concert with an approaching lead shortwave and
activate convection along the warm front by this evening.
Storms propagate north of the warm front into a less unstable
environment over southern Iowa after 6pm, although shear
profiles and steep lapse rates could still support loosely
organized strong updrafts and a marginal hail threat. The
threat of strong/severe convection further wanes as the
shower/storm activity spreads further north. Most hi-res
guidance eventually amalgamates the surface based convection in
northern MO into a line segment that quickly tracks east along
the main instability axis. Depending on the location of the warm
front, this organized linear convection could bleed into far
southern Iowa and pose a threat for strong wind gusts after
midnight through the early morning hours.

Showers and storms continue into Thursday as another shortwave
disturbance emerges from the western upper low. One axis of
showers will be across northern Iowa associated with a gradually
decaying mid-level deformation zone. Dry air from the north
impinging on the precip shield could undercut rainfall amounts
below model consensus, but confidence is still high (>75%) that
much of northern Iowa will see 0.25-0.50+" of rain. Further
south, the main focus is on convective trends and possible
severe weather. Models over the last 24 hours have trended
faster and further south with the track of a surface low on
Thursday, now taking the low across MO and possibly clipping
southeast Iowa. This has pushed the warm sector and surface
based instability further south/east. HRRR is very stubborn to
pull the warm front northward as it fights cold outflow from
earlier day convection. The warm front will serve as the focus
for afternoon redevelopment. These storms could still cross the
warm front and maintain a hail threat as they feed into weaker
elevated instability but highly sheared environment over
southern Iowa. These mesoscale details will need to be further
resolved over the next 24 hours, however trends certainly
suggest a diminishing severe weather threat compared to this
time yesterday. PoPs have been pulled back to account for the
latest trends as well.

Conditions dry out by Thursday night and through the end of the week
as a dry Canadian airmass surges south behind the departing low.
Downslope adiabatic warming of this airmass off the high Plains
will keep temperatures above normal for mid-March with highs in
the 50s to low 60s. Elevated fire weather conditions may
develop Saturday as a frontal boundary passes. Deep boundary
layer mixing behind the front counters CAA and keep temps warm,
however this will also tap into 25-35 kts of flow near the top
of the mixed layer and further depress surface RH. NBM has
consistently overdone surface dewpoints the last several days
and confidence is high that this will be the case again
Saturday, which would bring min RHs closer to critical
thresholds. Much cooler air spills south by Sunday as an upper
low carves out a home over the Great Lakes region. Sunday and
Monday are blustery and chilly with highs in the 30s and 40s.
Monday morning wind chills may fall as low as the single digits.
The cold air is quickly eroded by warm air advection beneath
building upper heights Tuesday into the middle of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 614 AM CDT Wed Mar 13 2024

VFR conditions privily over the area through at least 00z this
evening. Beyond that point, showers and storms are expected to
steadily increase in coverage, especially over southern Iowa
including KDSM and KOTM. Periodic restrictions to MVFR or lower are
expected with any TSRA activity. TAF only reflects MVFR reductions
at this time, but TEMPO groups with further reductions and more
precise timing may be necessitated in future TAF issuances.

&&

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

&&

$$

DISCUSSION...Martin
AVIATION...Martin


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