Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 170448
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1148 PM CDT Mon May 16 2022

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

.SHORT TERM.../Tonight through Tuesday/
Issued at 303 PM CDT Mon May 16 2022

Key Messages:

-Thunderstorms return early Tuesday morning with severe chances
 later on in the evening.
-another round of strong to severe thunderstorms possible late
 Thursday into Thursday night.
-Much cooler this weekend.

Discussion:

An area of surface high pressure will continue to preserve fair
weather into this evening over much of Iowa. A deep mixed layer
allowed for wind gusts over 20 mph to mix down. Higher gusts over
35 mph persisted over northeast Iowa where a tighter pressure
gradient existed. Winds will begin to slow down near sunset.

A surface low pressure system will intensify over the central
Plains overnight and gradually make its way towards the Midwest.
Showers and some rumbles of thunder are possible in the morning
in the north due to the LLJ and boundary interaction. Instability
will develop especially in southern Iowa during the day, setting
up for the main convective event in the evening. The severe
threat will be highest in southwest portions of the state before
sunset. SBCAPE and shear are marginal and support hail and
damaging winds primarily. The LLJ will return after dark and
support elevated storms overnight in south-central Iowa. PWATS
remain near 1.5 inches in this area, signaling a chance for high
rainfall totals, especially if storms have an east-west
orientation as some CAMs suggest. Highest rainfall totals are
expected across southern Iowa into Missouri.

&&

.LONG TERM.../Tuesday night through Monday/
Issued at 303 PM CDT Mon May 16 2022

Tuesday Night into Wednesday...Forecast Confidence: Medium to
High

Modest forcing from upper shortwave combined with the
reintensifying low level jet will keep scattered to numerous
showers and thunderstorms ongoing into Tuesday night, especially
along and north of the sfc warm front. As the night wears on,
midlevel lapse rates become increasingly moist adiabatic. While
there is a resevoir of MUCAPE > 1000 J/g and modest effective
shear, feel the threat will quickly evolve from strong storms to
locally heavy rainfall. As noted, higher freezing levels, PWATs
around 1.5 in, and skinnier CAPE profiles could lead to pockets of
heavy rainfall. The greatest threat for heavier rain appears to
be across southern Iowa or northern Missouri but will be dependent
upon the location of the low level frontal zone. The 12Z HREF
local probability matched mean /LPMM/ and recent runs of the HRRR
are also showing areas with greater than 2", which agree well with
the Marginal Risk of excessive rain from WPC.

Frontal zone should push east of the area on Wednesday with weak
high pressure moving into the region. After a few lingering
showers on Wednesday morning, expect partial clearing by
afternoon. Highs on Wednesday should be close to seasonal averages
in the 70s.


Thursday thru Monday...Forecast Confidence: Medium

A much stronger upper trough will develop over the northern
Rockies on Thursday and then slide eastward and deepen over the
central CONUS by late week and into the weekend.

Expect a breezy and warmer day on Thursday as southerly flow
develops head of a strong sfc low over the High Plains. Expect
temperatures to rise into the low to mid 80s with dewpoints
creeping back into the 60s. There is better model agreement on the
cold front front sweeping southeastward across the state on
Thursday evening through Thursday night. Ahead of the front, the
deterministic models and ensembles are indicating about 1500-2500
J/kg of MLCAPE and moderate deep layer shear of 30-40kts. Plenty
of details yet to be ironed out but will need to watch this period
closely. The SPC Day 4 Slight Risk appears on track attm.

Windy and much cooler air is expected behind the cold front on
Friday, with the deep upper trough lingering over the upper
Midwest into the upcoming weekend. Expect much cooler than normal
average temperatures to return with highs on Saturday and Sunday
only reaching 50s and 60s, along with a few chances for showers.
If we clear out on Saturday night, we could even be talking about
areas of frost, with low temps forecast in the mid to upper 30s in
the north...brrr.

&&

.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1147 PM CDT Mon May 16 2022

Scattered SHRA/TSRA may affect MCW/ALO at times overnight, between
about 09Z and 15Z Tue, with conditions remaining VFR for the most
part. Later Tuesday, mostly after 00Z Wed, TSRA and associated
MVFR or lower conditions will become somewhat more prevalent
through the end of the 06Z TAF period, however low confidence in
details precludes more than a VCTS group and MVFR ceilings for
now. Expect details to be refined in subsequent TAF issuances.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Jimenez/Fowle
LONG TERM...Fowle
AVIATION...Lee


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