000
FXUS63 KDMX 140440
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1140 PM CDT Sat Apr 13 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Warm temperatures continue into Tuesday

- Storms return mainly Monday evening & Tuesday with potential for
  stronger winds Tues as well.

- Cooler by midweek to end of next week

&&

.DISCUSSION...
Issued at 225 PM CDT Sat Apr 13 2024

.Short Term /Tonight through Sunday Night/...

Confidence Short Term:  Medium to High

While the transition to a period of stormy weather is just
beginning, we will continue to be the benefactor of warmer
temperatures and more moisture return over the next 24 to 36 hours
prior to storms late Monday.

Early today at 12z, high pressure is already east of the region with
a warm front cutting across western sections this morning. Low
pressure over the Northern Plains will help to increase winds today
with gusty winds into early evening. Any fire weather concerns will
end by that time. Aloft at H850, stronger warm air advection has
been building over the Western Plains with an area of +20C now
covering most of western Kansas, Nebraska, South Dakota and Wyoming.
That will be continue moving into Iowa today and remain in part,
across the region tomorrow. Moisture return so far has been rather
limited with dry conditions over Iowa. To the southwest, dewpoints
in the 40s and 50s are coming into view over Kansas south to Texas.
At H850, deeper moisture remains confined to southwest Texas and
Mexico but will be drawn quickly north by Monday.

After highs today into the upper 70s northeast to the mid 80s south
and west, tonight will continue mild. The weak cool front to our
west will slide east southeast by 12z Sunday and turn surface winds
around to the northwest tomorrow. Lows tonight will remain elevated
for mid April, with lower to mid 50s expected. Temperatures at H850
will peak around 06z in the mid to upper teens and then recede back
to the lower teens for Sunday afternoon. Today continues to look
slightly warmer than Sunday with the shift in wind, slightly cooler
air aloft and less mixing expected. The difference that might help
us reach similar afternoon highs is the much warmer start; about 13
degrees milder to begin the day. For now will lean toward the lower
side of the spread in highs for Sunday which keeps us in the 70s to
lower 80s. Tomorrow night an area of low pressure over eastern
Colorado will begin to deepen in response to the large H500 wave off
the California coast finally moving east toward the Rockies. This
process will continue for Monday into Tuesday with the system
becoming the main weather feature for Iowa and the Central Plains.
With another weak bubble of high pressure over our area Sunday
night, temperatures will fall to the mid 40s north and the lower 50s
south.

.Long Term /Monday through Saturday/...

Confidence: Medium to High

Details on the upcoming storm are coming into view, but still
somewhat uncertain in terms of magnitude of the overall event for
our area. The main takeaway for now is the projected timing of the
approaching low will bring it near southwest/western Iowa by 00z
Wednesday after it has already occluded during the day on Tuesday.
The deterministic models and ensemble guidance supports this general
scenario, though both the EPS/GEFs are slightly farther north/west
with the surface low by 00z Wednesday and generally still hugging
the Iowa/Nebraska border. With the rapid moisture return during the
day on Monday, we will see surface dewpoints climb into the 50s over
the south while the north will remain with dewpoints in the 40s. The
more widespread moisture will arrive later Monday evening with the
first real push of warm air advection and precipitation. As an
embedded wave arrives around 04 to 06z Tuesday, we will see the
first wave of showers and thunderstorms progress over the region
during the night. The main and more expansive forcing in the form of
a well developed jet max will arrive between 17z Tuesday and
00z Wednesday as it rapidly tracks through the region. Upper
level wind fields remain favorable for some severe storm
development and maintenance, but there is still a rather
conditional picture for Tuesdays storm coverage after the
initial surge of mainly elevated storms Monday night. Any
lingering activity through the morning near the warm front will
likely slow redevelopment during the day Tuesday. An approaching
dry line and favorable shear environment for a portion of the
early to mid afternoon hours over southern to southeast Iowa may
be enough of a window to see a few more well developed storms
form and then quickly progress east as the upper level jet
flares more east than northeast. This will likely create a
limited window of severe potential over our forecast area, while
the window may be longer from southeast Iowa south toward the
mid Mississippi River Valley. There may be some additional low
topped storms closer to the occluding low over west central to
northwest Iowa as well between 18 and 00z. The uncertainty as to
the track of the low into Tuesday afternoon still yields a
larger possible catch area for severe storm potential. Tuesday
continues to look rather windy; especially in the afternoon.
Wind fields are quite strong from H925 to H850 and with some
downward momentum transfer along and behind the occlusion, there
may be a period of advisory wind/gusts in the south as the
dryline punches east. At the moment it remains conditional upon
the system track as per the other elements at this time. Will
need to continue to evaluate. As the upper level system fills,
the chances for any stronger storms will lessen into the late
evening hours as cooler air begins to replace the warm
conditions earlier in the day. The filling low will continue to
bring stronger northwest flow into Wednesday with lingering
showers or light precipitation on Wednesday, as well as cooler
temperatures for the balance of the week. A quick moving
southern stream system may clip southern Iowa with a few showers
early Thursday. We eventually see H850 temperatures fall back
to 5 to 8C below zero by weeks end as a larger H500 trough
carves out an area over the eastern Canadian provinces. This
will keep us in and out of clouds, some patchy showers and
rather chilly temperatures in the 40s to lower 50s by Friday.
Some moderation is expected again by late Saturday and next
Sunday.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1140 PM CDT Sat Apr 13 2024

Confidence remains high in VFR conditions through the period at
the terminals. There is low level wind shear ongoing at OTM,
DSM, and ALO, but as a cold front drops through the state
tonight this will cease.

&&

.FIRE WEATHER...
Issued at 340 AM CDT Sat Apr 13 2024

Increasing winds out of the south and well above normal
temperatures will combine with the dry conditions and fuels to
create very high to extreme fire weather conditions across
especially northern Iowa today where a Red Flag Warning was
issued from midday to early evening. Minimum relative humidity
values fall towards 25-30% through much of the area but the
highest sustained winds and gusts will be in the north where
sustained winds of 20-25 mph with gusts up to 30-35 mph are
expected. Fuels in northern Iowa also remain mostly cured with
more green-up further south. Fire weather conditions will
certainly be elevated for those not in the Red Flag Warning so
outdoor burning is not recommended today as any fires that start
could spread quickly in these conditions. Warm conditions
remain on Sunday with similar minimum relative humidity values
but winds are expected to be lighter and out of the north to
northeast.

&&

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

&&

$$

DISCUSSION...REV
AVIATION...Ansorge
FIRE WEATHER...KCM