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000
FXUS63 KDMX 222339
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
639 PM CDT Mon Apr 22 2024

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

.KEY MESSAGES...

- Few showers tonight; isolated thunder far south. Cooler
  tomorrow; especially northeast
- Larger wave with severe risk ramping Friday/Friday Evening.
  Periods of moderate to locally heavy rainfall possible.
- Second fast moving event late Saturday Night/Sunday with
  another round of severe storms possible. Periods of moderate
  to locally heavy rainfall possible.

&&

.DISCUSSION...
Issued at 229 PM CDT Mon Apr 22 2024

.Short Term /Tonight through Tuesday Night/...

Confidence Short Term:  High

Winds continue this afternoon with both wind criteria being met:
sustained at 30 mph and gusts to around 50 mph across the
region. Clouds across the area today have not hindered daytime
heating much and we should end up in the upper 60s/lower 70s.
Surface weather map this morning showed the approaching system
to the west with increasing gradient and stronger warm air
advection. Moisture continues limited across the region and this
afternoon little in terms of showers are anticipated over the
area. With an H850 low level jet of 50kts slowly weakening as it
crosses the region today, the mixing will remain into the early
evening. Tonight will see pockets of lingering showers to
around 00z, then the focus for more developing showers shifts to
the far south and northern Missouri. There has been a narrow
ribbon of moisture transport northeast toward Iowa last night,
as seen at H850 with dewpoints around 2C at Omaha at 12z. As the
pronounced high over the Southern Plains shift south, moisture
should increase over the south into the evening hours. There
remains very limited instability across the south overnight and
most of the models have cut back any thunder to just our far
south southwest later in the evening. Rainfall will be light and
generally under a tenth of an inch. Lows tonight will begin to
drop off with the passage of the first, pacific front. The
colder air was still locked up behind the southern Canadian low
this morning and will finally make it into northern Iowa by
Tuesday evening. Highs tomorrow now appear a bit warmer, as the
secondary trough/front will only brush the far north during the
evening hours. That also limits any chance for late day showers,
though clouds will be on the increase in the north in the
afternoon. Highs tomorrow will top off at near 70 in the south
to the lower 60s in the north. Decent mixing is likely tomorrow
with wind gusts of 25 to near 35 mph at times during the day
from the northwest.

.Long Term /Wednesday through Monday/...

Confidence: Medium

The extended period will continue to ramp up to very active weather.
Similar to yesterdays discussion, we continue with a Great Lakes
High which will bring a pleasant day Wednesday with lingering cool
air tracking into the region. Highs will remain in the lower 60s
over most of the forecast area. Warm air advection begins to push
east Wednesday evening into Thursday with mainly mid level clouds
crossing through Iowa. Temperatures aloft by Thursday will respond
at H850 to 5 to 8C. Clouds increasing late day may hold highs down a
bit, but upper 60s to lower 70s will easily be attainable. The first
of two major waves will begin to influence our area by Thursday
evening. Todays deterministic models have sped up the arrival
by a few hours into Thursday evening, but overall the evolution
remains the same. A stronger push of thetae advection late
Thursday will bring a round of showers/isolated storms across
our west/south around 06z. The deeper instability will arrive by
12z Thursday and spread from southwest to east northeast
through the day. There are still some minor differences between
the GFS/Euro low strength, with the GFS and EC strengthening
slightly the system, then weakening it as it lifts northeast.
The Euro had generally began to weaken it as it crossed the
area. Todays GFS would suggest that the overnight convection
would give way to a dry slot by mid to late morning with most of
our area in the warm sector on Friday. With the jet shifting
east, similar to our last Tuesday system, most of the stronger
storms are going to build along the dryline/front over the east
in the afternoon and evening. Other development may take place
in northern Iowa along the retreating warm front. In both cases,
all modes of severe will be possible. Moderate to locally heavy
rainfall is also expected with the heavier areas of storms
dropping at least an inch of rainfall east and north; some +2
inch totals also possible along the warm front north. Highs
Friday will vary quite a bit, with upper 60s to mid 70s
expected. Stronger south winds will also develop with winds
gusting to near 35 mph. The medium range signal has been
consistent with a quick departure of the storm by early
Saturday, leaving a warm and dry day over the region. A trailing
cool front will stall from southwest to northeast Iowa and even
with some cloud cover, highs Saturday will be in the 70s to
near 80 south of the front, while the northwest falls back to
the 60s to lower 70s. The stronger of the two storms will begin
to eject from the southwest US and track toward the Central
Plains Saturday. The EC is now faster with the arrival of the
second storm, with showers and storms developing along the
nearly stationary front by mid to late afternoon. Though it
shows sufficient shear in the afternoon for stronger storms,
that weakens over Iowa and shifts southeast as the low tracks
nearly due north. Today the Euro is weaker than the GFS and the
models are struggling with the second system details for now. In
both models, however, the main axis of severe appears to move
off to the Mississippi River Valley by late afternoon and early
evening. Both systems will have an appreciable amount of
moisture to bring rainfall to Iowa. The first has PWATs in the 1
to 1.25 inch range with the second ramps up to 1 to 1.5 by late
Saturday afternoon/evening. The majority of the higher rainfall
will fall along and south of the boundary setting up in eastern
Iowa; closer to the Mississippi River and along the warm front
in northern sections with the first system. Despite our dry
conditions, rises in river levels are expected. More details on
that when confidence in coverage and rainfall amounts becomes
higher. Sunday highs may end up cooler with clouds and better
chances for precipitation. Also, both events appear to be
somewhat messy in terms of severe storm mode and coverage, so
expect more details in the coming days. Both medium range
guidance lifts the storm northeast of the region by Monday,
leaving our forecast area in a weak ridge of high pressure,
breezy west northwest flow and highs back in the 60s to lower
70s. The rainfall over the weekend will likely help build fair
weather cumulus clouds through the mid to late morning hours,
with even some overcast to begin the day in the north and
northeast.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 633 PM CDT Mon Apr 22 2024

VFR conditions expected to prevail across sites. Windy
conditions ease through the evening as front slowly drops
through the area and begin to turn W/NW. With abundantly dry
low-levels, rain has struggled to gain much of a foothold over
northern areas so far this evening. Have kept precip mentions
out of TAFs as a result of that, but may be possible in/around
KALO this evening. Best opportunity for showers will be over
KOTM after 06z as front sags down into that area. During daytime
tomorrow, NW winds increase with another breezy day, albeit a
bit lighter. Expect sustained to around 20 kts and gusts to
around 30 kts at this point in time.

&&

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

&&

$$

DISCUSSION...REV
AVIATION...Curtis