Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 122006
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
306 PM CDT Tue Mar 12 2024

.KEY MESSAGES...

-Isolated showers and storms southeast late tonight (30-50%), a few
strong storms possible

-More widespread chances for rain (70-80%) with strong to possibly
severe storms late Wednesday into Thursday

-Drier into Friday and Saturday, much cooler Sunday

&&

.DISCUSSION...
Issued at 305 PM CDT Tue Mar 12 2024

Fairly quiet weather has prevailed throughout much of today, with
high level clouds streaming from southwest to northeast across Iowa
this afternoon. However, with warm air advection pushing into much
of the state today, temperatures continue to warm nicely with values
through the 60s to low 70s. Analyzing the surface closer, a weak
boundary can be seen, which is responsible for the slightly warmer
temperatures across the south/southeast as winds have been a bit
more breezy out of the southwest with higher relative humidities in
the upper 30s to low 40s, while portions of northern and western
Iowa have been experiencing lighter north/northwest winds, along
with drier RH values in the teens to 20s. Despite the clouds,
expecting temperatures to continue climbing with highs this
afternoon topping out in the upper 60s to low 70s. Looking upstream,
a weak surface low associated with a passing shortwave currently
over Kansas is expected to translate eastward later tonight. As
theta-e advection with increasing moisture as dewpoints rise into
the upper 40s to low 50s across southeastern Iowa pushes into the
region, with temperatures remaining relatively warm with the frontal
passage, showers and storms are expected to develop, with timing
generally after 8-9pm tonight. Guidance remains generally consistent
that the bulk of the forcing and instability remaining further south
into MO, though CAPE values around 500-700J/kg and steeper lapse
rates look favorable to at least allow for a small hail threat over
southeastern Iowa with any storms, which look to be elevated in
nature.

While the rest of the state remains dry into Wednesday, models
continue to show a large trough circulating in place across the
western CONUS, with a shortwave in the larger scale flow passing
through the Intermountain West and resulting in lee cyclogenesis as
a defined surface low develops over the western portion of the
Central Plains. This system is expected to push E-NE, becoming
centered over Kansas by Wednesday evening into Thursday. With this,
a warm front is expected to drape across MO, lifting northward into
Iowa into Wednesday evening, paired with increasing dewpoints in the
50s, along with moderate instability as theta-e advection becomes
quite strong, along with and shear values in the 30-40 knot range
with an increasing low level jet. As frontogenesis occurs,
widespread showers and storms are expected to form over northern MO
into southern Iowa and move across the region through much of
Thursday morning into the afternoon. Overall, conditions are
favorable for larger hail and damaging winds, along with a
conditional threat for a tornado or two. While there are some slight
differences on the overall track of the system, can expect
accumulations up to a half inch across much of the state, with
highest values over northern Iowa approaching 0.75-1 inch. Not a
drought-buster by any means, but some much needed rainfall to say
the least.

As the low pressure system pulls away from the region into Friday,
changes are on the way as the flow pattern shift
north/northwesterly, bringing in much cooler air than has been
experienced lately, but closer to seasonal norms as highs are
expected in the 50s. High pressure passes through briefly Friday,
though remaining dry. A defined trough dropping down into the Upper
Midwest region into Sunday continues to signal even cooler
temperatures returning across the region as low level northwesterly
flow increasing. Cannot rule out a few snow showers northeast
Sunday, though guidance has backed off a bit over the latest runs as
dry air remains the main limiting factor. High temperatures by
Sunday with the arrival of cooler air will be about 20 degrees
cooler with highs in the upper 30s to 40s, compared to Saturday`s
forecast highs in the 60s.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1239 PM CDT Tue Mar 12 2024

VFR conditions continue for the start of this TAF period across
all terminals. Winds will gradually decrease tonight at all
sites and switch direction across northerly terminals from
north northwesterly to easterly by Wednesday morning. May see
some showers and thunderstorms near the KOTM vicinity and
southern Iowa after 02z. Confidence on any direct impacts for
this terminal is low at this time, thus have opted for VCTS
mentions. Reductions in visibility are possible with any
showers and storms. Ceilings will lower to MVFR across KOTM and
areas southeast by Wednesday morning.

&&

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

&&

$$

DISCUSSION...Bury
AVIATION...Castillo


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