699
FXUS63 KDMX 031129
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
629 AM CDT Fri May 3 2024

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

.KEY MESSAGES...

- Early Morning Fog...Patchy to Areas Dense Fog through 8am
- Showers & Storms Tonight and early Saturday || Dry Sunday
- Storms Return Monday Evening With Some Severe Risk
- Sun/Cloud Mix with passing Showers Much of Next Week; Turning
  Cooler by weeks end.

&&

.DISCUSSION...
Issued at 312 AM CDT Fri May 3 2024

.Short Term /Today through Saturday/...

Confidence Short Term:  Medium to High

Active weather pattern for much of the seven day period, though we
may luck out a few days next week with precipitation south/north of
us. Rainfall is still needed in some areas, but not the southeast.
The filling low that brought the moderate to heavy rainfall to the
region yesterday has now migrated to the far Northern Plains. We had
a front at H850 still over the eastern counties of the state at 00z,
but that has now edged east a bit since then. Another weak area of
low pressure is located near Springfield, MO at H850 with a third
area of low pressure in northern New Mexico. The Gulf moisture
stream has temporarily been pushed south of our area. However, a
large plume of +10C to +15C dew points is just south of the region
at this time.  Meanwhile a weak ridge of high pressure will cool the
boundary layer through early morning. Weak winds and ample boundary
layer moisture from yesterdays rainfall continue to promote fog
development. This will likely peak around 5 to 7 am over the area.
Have updated the grids for areas of fog into the morning commute and
will address conditions with either an SPS or maybe an advisory if
it looks more problematic before 4 am. After the fog burns off, we
will be rewarded with a rather pleasant day to round out an active
week. Highs today with patchy fair weather cumulus will reach the
lower to mid 70s as south southeast winds increase to 10 to 15 mph
by mid to late afternoon. Tonight a wave currently showing up on
water vapor imagery over Colorado/Idaho will track east. This will
pull an area of low pressure and front east. At the same time, the
moisture plume to our south will be pulled back northeast overnight.
PWATs again increase to around 1.25 inches and warm cloud depths
increase to over 10kft again from 06z to 18z Saturday. The models
continue to indicate the main forcing at H700/H500 will peak from
06z to 12z across the area. As the wave reaches to near the IA MN
border and the LLJ weakens significantly overnight, the showers and
storms will weaken with time from 06z to 12z. Lesser rainfall is
anticipated in the southeast, with amounts northwest of there from
.75 to 1.5 inches and in the southeast about a quarter inch. Severe
weather chances tonight are not high, but the southwest to the south
central has some risk of an isolated stronger storm with a small
risk of wind/hail. Shear is just strong enough for some rotation.
Lows tonight will fall to the mid 40s northwest to the mid 50s in
the far south. The lingering showers and isolated storms early
tomorrow will generally exit the east by mid afternoon as high
pressure builds south and east from the Northern Plains. We
will be fighting lingering clouds in the afternoon mixed with
some peaks of sunshine. Highs will reach the lower 60s northwest
to the lower 70s southeast.

.Long Term /Saturday Night through Thursday/...

Confidence: Medium

Saturday night will be similar to this morning. Clearing skies may
lead to some patchy fog once again. We will need to address that on
Saturday to see how much dry air is advected southeast into the
state. Otherwise, Sunday will be dominated by high pressure slowly
drifting east by late afternoon. Other than some fair weather
clouds, the day will again be very pleasant. H850 temperatures begin
to warm due to return south flow. This will help push highs into the
upper 60s to lower 70s by afternoon. We continue to see a southern
stream wave in the southeast on Sunday, but there is really no sign
of any moisture return across Iowa at that time, so have removed any
mention of precipitation. Lows Sunday night dip to the 40s to lower
50s. A large scale trough over the western CONUS will begin to move
east on Sunday. This feature has been consistently forecast by the
medium range models to form an elongated trough with a double barrel
low; one migrating to Alberta and the southern one wrapping up
nearer eastern Nebraska. As the entire system deepens and occludes,
the southern stream low will pull a wing of moisture/instability
into the area later Monday afternoon and into the night. An
impressive jet max will increase collocated columnar wind fields
from H850 up to H500 by 06z Tuesday over the area. Winds will
average 50-65kt through the column with some diffluence at H300.
This, along with enough wind shear and instability to promote some
rotation as well as a potential QLCS wind and tornado threat
overnight. Obviously, we have several days and some changes may
occur. Highs Monday will be mild ahead of the system with 70s across
the board. The Euro and GFS are beginning to diverge a bit by
Tuesday; GFS faster and the Euro slower. The Euro shows only a quick
break early Tuesday from the overnight convection, with another
speed max forecast to plow into an area of lingering instability
across Iowa. This would tend to promote another area of strong to
severe storms over mainly eastern Iowa and states east and northeast
of our area. At this time, no solution is favored but the GFS
generally trends too fast by days 4 to 5. Will need to remain aware
of a second potential round of stronger storms later Tuesday near
our area. Tuesdays highs are going to be difficult to nail down for
a few days, due to the various solution differences. The most likely
range would be the 60s northwest to the 70s southeast. There is some
consensus for Wednesday into Thursday with regard to the Northern
Plain system evolution. It appears that the large scale system will
drift back into the Midwest with more clouds, some passing showers
and cooler temperatures by the end of the period. Highs should
generally be in the 60s to around 70 by Thursday with 70s still
likely on Wednesday. There is some indication that more clouds and
cooler conditions will persist late into the week and the following
weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 628 AM CDT Fri May 3 2024

Fog continues early this period with some VV through 13z,
then fog mainly burning off between 13 and 14z over the region.
Otherwise, expect light winds and fair wx cu today. Showers and
storms arrive aft 06-08z west and move east through remainder
of period. Cigs will also lower to MVFR west half by 12z
Saturday.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 8 AM CDT this morning for IAZ006-007-
016-017-024>028-035>039-044>050-057>062-070>075-081>085-092.

&&

$$

DISCUSSION...REV
AVIATION...REV