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000
FXUS63 KDMX 191129
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
629 AM CDT Fri Apr 19 2024

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

.KEY MESSAGES...

- Breezy conditions today, perhaps windy at times over northern
  Iowa.

- Freezing temperatures possible tonight north and west but low
  potential for frost. High chance for area wide frost Saturday
  night.

- Next chance for precipitation arrives Monday/Monday night.

&&

.DISCUSSION...
Issued at 336 AM CDT Fri Apr 19 2024

Ridge of high pressure is extending from Montana and into southwest
Iowa early this morning and as expected, temperatures have fallen
into the 30s as of 3 am. Expect a few areas to reach the upper 20s
in the next few hours over north central Iowa and into the
Nishnabotna Valley over the west. Despite the presence of the
surface ridge over the southwest, some clouds based around 12 kft
are passing across that area with radar echoes showing up as well
with mid level forcing passing by. Very dry air in the sub cloud
layer though is evaporating any hydrometeors upon descent.

Good mixing will occur today to near 800 mb. Mixed layer winds will
vary with a peak near 20 kts over southern Iowa to 35-40 kts over
northern Iowa. These peak mixed layer winds will not be realized at
the surface with a weaker pressure gradient and the lack of strong
cold advection, but wind gusts over 35 mph are possible over
northern Iowa. An upper level system and surface cold front will be
approaching Iowa from the north today and will reach north central
Iowa by mid to late afternoon. The differential cold advection which
will be not as strong at the surface, will result in deeper mixing
initially and should negate any surface cold advection impacts on
temperatures. It will however keep the gusty wind in place over the
north into the early evening before decoupling occurs. An area of
showers is expected to develop this afternoon behind the boundary in
Minnesota but there is a quick drop off in available moisture into
Iowa so while some puffy cumulus could develop, much of the cumulus
will be quite shallow and at this time, no precipitation is expected.

The Frost and Freeze headlines may still be needed tonight and again
Saturday night. In collaboration with all surrounding offices, the
plan is to allow the current headlines to expire then have any new
headlines be issued on the day shift each day. For tonight, The wind
will remain breezy at times despite the eventual decoupling. This
may limit or prohibit frost formation in addition to the drier air
in place leading to lower relative humidity values. Therefore, any
headlines may be limited to below freezing areas. Lighter winds and
a greater potential for radiational cooling and frost development
occurs Saturday night and that will likely be the coldest night
during this stretch. Saturday itself will be on the cool side with
highs in the upper 40s to low 50s. Sunday and beyond will be warmer
with high temperatures in the 60s more common with overnight lows
staying above freezing.

The next system to impact Iowa arrives on Monday. As it arrives, the
large surface high pressure will be moving into the southeastern
CONUS. The timing of this movement and how strong the ridging
remains west into Texas, will have a big impact on how quickly Gulf
moisture returns north on the backside of the highs to interact with
the system moving across Iowa. Shower and thunderstorms will move
across the state. Greater instability will occur if the Gulf
moisture arrives, especially into southern Iowa but at this time,
the overall instability looks meager with a low severe threat. Of
greater interest is the end of next week and into next weekend as a
strong system moves into the western CONUS leading to good southwest
flow aloft into Iowa. There is still a lot to unpack with that
system including lead short waves ejecting out ahead of the primary
system then the eventual primary system lifting into the Midwest.
These systems tend to be delayed from guidance this far out but this
is a severe weather setup for somewhere in the region.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 625 AM CDT Fri Apr 19 2024

The wind will increase this morning and will become gusty from
late morning and into the afternoon. Gusts over 35 kt are
possible over northern Iowa. The wind will diminish this
evening. Otherwise, VFR conditions will persist. Clouds will
increase over northern Iowa mid to late afternoon with cigs
around 6 kft. Mid-level cloudiness will pass across southern
Iowa today as well.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Freeze Warning until 8 AM CDT this morning for IAZ004>007-
015>017-023>028-033>038-044>046-057-070.
Frost Advisory until 8 AM CDT this morning for IAZ039-047>050-
058>062-071>075-081>084-092>095.

&&

$$

DISCUSSION...Donavon
AVIATION...Ansorge