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000
FXUS63 KDMX 181132
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
632 AM CDT Thu Apr 18 2024

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

.KEY MESSAGES...

- Widespread precipitation this morning before ending from
  northwest to southeast through the afternoon.

- A few chances for below freezing low temperatures over mainly
  northern and west central Iowa tonight and Friday night and
  area wide Saturday night.

- Next chance for precipitation is early next week.

&&

.DISCUSSION...
Issued at 335 AM CDT Thu Apr 18 2024

Two well defined areas of precipitation have developed this morning.
The first area of precipitation extends from southern Minnesota,
though northwest Iowa and all the way back to northeast Colorado.
That band is associated with mid-level frontogenesis and the arrival
of colder air. This precipitation is mostly stratiform though there
are a few areas with lightning associated with it in Nebraska. The
second area of precipitation is associated with low pressure moving
into southeast Kansas with a warm front extending north towards
Topeka and Kansas City. A few strong storms have been occurring
along that boundary. The low level jet extends further north and is
pointing into southern Iowa and this is a region where strong theta-
e advection is ongoing along with a broad area of rain while
thunderstorms have been developing into southeast Nebraska. A few
storms are expected into southern Iowa but any strong storms should
remain to the south of the area.

These two areas of precipitation will continue to move
east/northeast across the area this morning before gradually
weakening/diminishing by late morning. Renewed shower and
thunderstorm development is possible this afternoon over the
southeast. One of the challenges for today is how much the In-
Between (in this case central Iowa) will fill in with precipitation
or will there remain a null void. Central Iowa should fill in with
precipitation as overrunning and isentropic lift continues to lift
northward this morning. There likely will be lower precipitation
values in that region. Overall, precipitation amounts of one to one
and one half inch are possible far south, one half to one inch north
and one quarter to three quarters inch central. By this afternoon,
much drier dew points will move in to northwest Iowa and move
southeast quickly, dropping values into the 20s and 30s. The wind
will become gust as the boundary moves through the state and the
switch to northwest wind occurs. Peak wind gusts will be in the 25
to 30 mph range and will drop off this evening as decoupling occurs.
High temperatures today are currently in the low to mid 50s. This
may be overly optimistic, especially if cloud cover hangs around
much of the day.

Another push of cooler air arrives Thursday night and the wind will
become light from the west. With the growing season ahead of
schedule, the Frost/Freeze headlines are now turned on and available
if needed. Temperatures will fall into the 30s and likely below
freezing in some areas north and west. Frost potential is not
certain pending how low the wind is and the dew point depression
could remain large enough to inhibit frost. Therefore, no headlines
at this time.

A ridge of high pressure will settle and be just south of Iowa on
Friday. Gusty west winds are expected across northern Iowa where
better mixed layer winds exist and the pressure gradient will be a
bit stronger than southern Iowa which will be near the ridge. Wind
criteria could be approached over far northern Iowa on mixing layer
wind potential. The lack of any strong cold advection will prevent
the realization of peak mixed layer winds from reaching the surface
though. High temperatures Friday will be in the 50s. Another cold
front will reach northern Iowa by late Friday and will move through
the remainder of the area Friday night and Saturday morning. The 850
mb temperatures Saturday morning will be in the -5C to -10C range
over the northern half of the state, which is quite cold for mid
April. The boundary layer may remain slightly mixed Friday night and
along with the breezy winds, temperatures may again hold into the
30s over northern Iowa. Saturday will be the coolest day of the
period with highs in the upper 40s to low 50s. Ridge of high
pressure will move across the state Saturday night and this will be
the period with greatest potential of widespread freezing or below
temperatures with overnight lows in the upper 20s to low 30s. Highs
next week will be in the upper 50s and 60s. The next chance for
precipitation arrives Monday and Monday night with a few showers and
thunderstorms possible then another system possible late next
week.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 627 AM CDT Thu Apr 18 2024

Widespread precipitation across the area today. A wide range in
cigs initially with VFR over the eastern half of Iowa and a mix
of MVFR to local IFR elsewhere. Cigs will continue to lower at
all sites. Guidance would suggest widespread IFR cigs but so far
has been overly aggressive and thus have not gone as aggressive
with the forecast. Still expect MVFR cigs to become widespread
with areas of IFR. Vsbys will vary but generally 4sm or greater
in rain. Conditions will begin to improve this afternoon then
VFR area wide tonight. The wind will become northwest today and
will be breezy at times this afternoon before diminishing
tonight.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon