Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 291124
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
624 AM CDT Fri Mar 29 2024

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

.KEY MESSAGES...

- Low chance (15 to 30%) for a few showers and thunderstorms
  this evening mainly over the southern and eastern portions of
  the area. A few storms could produce marginally severe hail.

- Mild temperatures on Saturday and Sunday

- More prominent system bringing precipitation chances Sunday
  through Monday and into early Tuesday. Primarily rain with a
  chance for some wintry precipitation as the low departs early
  Tuesday.

&&

.DISCUSSION...
Issued at 341 AM CDT Fri Mar 29 2024

After a comfortable spring day, it’s been a fairly quiet night over
Iowa. High clouds have all but taken over the area, with only a few
pockets of broken cloud cover over the south and eastern forecast
area. Cloud cover becomes a bit more patchy through the early
morning hours, initially leading to some filtered sunshine before
more widespread cloud cover develops ahead of an approaching wave
this afternoon.  In the upper levels, this wave shows as only a
minor blip in the overall flow, however it’s coincident surface low
will bring both warmer temperatures today as well as the chance for
a few showers and thunderstorms in the eastern half of the state
this evening.

A warm front in place over southern Iowa will continue to push north
through the day today, boosting temperatures into the upper 50s
north to near 70 south. High temperatures yesterday outperformed
guidance thanks to plenty of sunshine and persistent WAA. Expecting
a similar trend with temperatures today due to southerly surface
flow and warming temperatures aloft. The only limiting factor today
will be more cloud cover in the afternoon keeping solar
contributions somewhat at bay.

In addition to the warmer air, a stream of gulf moisture will be
advected into the state through the day. This, in conjunction with
some elevated instability, will be conducive for the development of
a few showers and thunderstorms into the evening, especially in
southern and eastern Iowa where the nose of better moisture
transport will reside. Further north and west, moisture will be less
abundant, leading to a good deal of low to mid level dry air to
inhibit precipitation chances. Where convection does develop, it
will have access to 500 to 1000 J/kg of MUCAPE with plenty of deep
layer shear to produce a few organized storms. However, due to the
time of day and a warm layer aloft, storms likely wont become
surface based, making hail the primary threat. Similarly, with CAPE
maxing out just over 1000 J/kg, it will be difficult to produce
overly large hail stones, but sufficient for producing severe hail.
Due to this chance for marginally severe hail, the storm prediction
center has put out a day 1 marginal risk that just clips our far
eastern forecast area and then encompasses much of eastern Iowa
where the best chance for convection resides.

A cold front will move through on the backside of the wave tonight,
resulting in a slight drop in temperatures on Saturday, albeit with
highs still in the mid 40s north to near 60 south. A brief period of
dry weather is expected Saturday before an upper level trough
digging in off the west coast begins to bring another shot of theta
e advection and coincident precipitation on Sunday. This will be
driven primarily by WAA along a boundary that looks stall out over
southern Iowa/northern Missouri, so expecting mainly a steady
light to moderate rainfall with little in the way of convection.
As we move into Monday, the main surface low associated with
the upper level trough looks to pass through the area, bringing
additional precipitation Monday. However, guidance has yet to
reach agreement on how the low will evolve, with the GFS showing
a more amplified low pressure right over southern Iowa while
the Euro shows a more modest solution, tracking a weaker low
over southern Missouri. Obviously, these will provide two very
different outcomes for precipitation on Monday, therefore, going
to continue to watch how things evolve through the weekend and
wait for better agreement on amounts and locations. That being
said, it looks like if we get precipitation, it will be within
the deformation zone and any convective precipitation will be
further south and east in the warm sector of the low. Cooler air
on the backside of the low may even lead to a brief period of
light wintry precipitation as it departs early Tuesday morning.
Temperatures then cool off on Tuesday before warming again into
the late week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 618 AM CDT Fri Mar 29 2024

VFR conditions are expected to prevail through the day today at
all sites. Main impacts to aviation will be a short period of
gusty winds moving through the area, resulting in gusts out of
the south southeast at 20 to 25 kts at times. Later this
evening, a few isolated showers and thunderstorms are possible
near KALO and KOTM. Due to low spatial coverage, confidence in
any impacts at terminals is low at this time.

Tonight, a cold front will bring a wind shift to more north
northwesterly winds as well as an increase in wind speeds.
An area of lower clouds looks to also develop behind this
boundary, creating MVFR to potentially IFR conditions early
tomorrow morning.

&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...Dodson


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