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000
FXUS63 KDMX 242046
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
346 PM CDT Wed Apr 24 2024

.KEY MESSAGES...

- Shower and thunderstorms late Thursday night into Friday.
  Severe weather is possible during the day Friday.

- Additional thunderstorm chances expected on Saturday, with
  severe weather possible. Some uncertainty remains on location
  and timing.

- Final wave of thunderstorms possible through Sunday. High
  uncertainty at this time, but severe weather may again be
  possible.

&&

.DISCUSSION...
Issued at 335 PM CDT Wed Apr 24 2024

>> Breezy with Increasing Cloud Cover Thursday

After a comfortable and quiet day today, expect a flip to a more
active weather pattern starting late tomorrow and lasting
through most of the weekend. Surface low pressure will begin to
build in to our west as the surface high overhead drifts east.
This will result in a tightening pressure gradient ahead of the
low pressure, increasing southeasterly winds through the night
tonight and into Thursday, with the strongest winds on Thursday
being to the west. As the low pressure system to our west
deepens and slowly make it’s way east, we will also see
increasing cloud cover through the day with the potential for a
few sporadic showers in the south. However, with low level dry
air still in place, any showers that form during the day
Thursday will be fairly light with minimal accumulations.

>> Showers and Thunderstorms Thursday night into Friday

Starting Thursday night, we will see a succession of intermittent
shower and thunderstorm chances through the weekend. Due to the
timing of these systems being so close to each other, there is a
good deal of uncertainty on how things will play out through the
weekend. The evolution of the first system will greatly dictate how
the rest of the weekend plays out and where the greatest impacts
will take place.

This progression will start with a surface low tracking
northeast out of the lower plains region through western Iowa
and into southern Minnesota on Friday, which will put much of
our CWA in the warm sector. Friday’s parameter space looks a bit
messy and many similarities can be drawn between this and the
storm system we saw last week. There will be a good amount of
broad scale lift with the theta-e advection ahead of the low,
which will favor widespread precipitation through the morning.
This will likely keep the low- levels fairly saturated and
somewhat inhibit the ability to destabilize the boundary layer.
Therefore, initially on Friday morning, storms will likely be
elevated and fed by the 40 to 50+ kt LLJ aloft. Through the day,
warmer air and higher dewpoints will continue to advect north
and the environment will attempt to destabilize near the
surface. As of right now, this looks most likely over
southern Iowa, while areas further north will be fighting a bit
more convective inhibition. That being said, should any storms
become surface based on Friday, the high amount of low level
shear and SRH would suggest that a few tornadoes are possible.
Hail and wind would be secondary threats, but marginal
instability (~1000 to 1500 J/kg) and mostly saturated low levels
would inhibit these two hazards.

>> Second Round of Thunderstorms Possible on Saturday

As the Friday system departs north overnight into Saturday, a front
will remain draped behind it and down to the second wave approaching
from the southwest. This front will be the source for showers and
thunderstorm chances again on Saturday but the location of this
front is more uncertain and will partially depend on what the Friday
system does. Currently, guidance has the front from roughly
southwest to northeast Iowa, crossing through north central Iowa and
putting the southeast two thirds of the CWA in the unstable air.
Regardless of where the front sets up, the environment on the warm
side of the boundary looks conducive for strong storms, and seems to
follow a more “traditional” severe environment when compared to
Friday. A warm nose aloft will erode through the day, with
convection becoming completely surface based in the afternoon.
Surface based CAPE will be high (~2000 to 3000 J/kg) with mostly
unidirectional speed shear resulting in straight hodographs. This
environment would favor rotating storms but with large hail and
winds being the main threat. The lack of higher low level shear on
Saturday would inhibit tornado chances some, but certainly cant rule
it out. Another important factor with Saturday would be the
potential for heavy rainfall along the boundary as the LLJ orients
parallel to it in the evening hours and overnight. Conditions are
still fairly dry, so main impacts from heavy rainfall would be
confined to urban areas with poorer drainage. But again, will want
to see some higher resolution guidance before getting too committed
to any specific timing, locations or impacts.

>> Final Wave Lifting Through The Area Sunday

Finally, on Saturday night into Sunday, another surface low pressure
system will lift up into the state, roughly following where the
surface boundary was in place on Saturday. This will put portions of
our area in the warm sector and bring more shower and thunderstorm
chances Sunday. This system has the highest amount of uncertainty
with it, but the parameter space would again be favorable for a few
severe storms. Beyond that, not going to speculate too much on how
Sunday will play out at this time. The important takeaway will be
that multiple rounds of showers and thunderstorms are expected
through this weekend, with the potential for severe weather on all
three days at least somewhere in the state. If you have plans
outdoors, make sure you keep up to date on the forecast for your
area, especially as details become clearer in the coming days.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1209 PM CDT Wed Apr 24 2024

VFR conditions with light and variable winds will prevail
through the day today. Winds will generally be shifting from
northeast to easterly to southeast through the afternoon and
evening hours. Increasing winds and VFR clouds are expected
overnight into tomorrow.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Dodson