Area Forecast Discussion
Issued by NWS Des Moines, IA

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426
FXUS63 KDMX 242356
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
655 PM CDT Thu May 24 2018

.DISCUSSION.../Tonight through Thursday/
Issued at 320 PM CDT Thu May 24 2018

An unseasonably warm and humid airmass continues to lift north
into Iowa today and that will remain the trend through the
Memorial Day weekend. Currently a large area of high pressure
resides over the lower Great Lakes and towards the east coast
while an area of low pressure is over Colorado and while a trough
extends north to Saskatchewan. The airmass across Iowa is unstable
with MLCAPE around 1500 J/kg and very little CIN however currently
lacking a forcing mechanism. The main focus for thunderstorm
development this afternoon into the evening should be over the
Dakotas and Nebraska along the aforementioned trough. Another
region of precipitation this afternoon is located near Sioux
Falls. Some of this activity may clip into the northwest forecast
area yet this afternoon into this evening. As of now, do not
expect any widespread areas of precipitation though the overnight.
An MCV over southern Kansas is expected to lift northeast
overnight into north central Missouri then into southeast Iowa.
This system could bring increased thunderstorm activity to
portions of southern Iowa.

The remainder of Friday should be warm and humid once again. The
trough to the west will enter the state by the afternoon along
with a short wave moving across southern Minnesota. At this time,
the SPC slight risk area appears to be generous on the west side
with any severe threat most likely east of Interstate 35. A few
storms may develop during the afternoon ahead of the trough axis
as strong instability develops ahead of the boundary. Large hail
and damaging winds would be the primary threats. CAMs and a few
other solutions are suggesting an MCS developing over southeast
Minnesota and diving south along the instability axis. These
solutions may have some merit and considering the 0-3 km theta-e
differences of 30-40k, cold pool development may occur and
propagate south and lead to a damaging wind threat. If this would
occur, mainly the far east forecast area would be at risk. Locally
heavy rainfall may also occur considering PWAT values 175% of
normal, good warm cloud depths and slow storm motions initially.

Hot and humid Saturday through Monday and mostly dry with the
potential for record highs across the state each day with highs in
the low to mid 90s. Will continue to message heat impacts
considering it is the holiday weekend and outdoor activities will
be prevalent. Additional sporadic storm chances arrive Monday
night through Thursday. Temperatures should be cooler in the 80s
during this period though 500 mb heights and 850 mb temperatures
will be on the rise towards the end of the period as ridging
builds in.

&&

.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 655 PM CDT Thu May 24 2018

VFR conditions expected through the period.  However storms
developing out west may briefly create MVFR cigs/vsbys over KFOD and
possibly KMCW late tonight.  Overall storm threat will diminish
through the evening and is too uncertain for much more than a VCTS
mention. A storm complex moving over MO may spread TSRA into far
southern IA impacting KDSM and possibly KOTM Friday morning with
better thunderstorm chances re-developing late Friday aftn/eve over
the eastern TAF locations.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

DISCUSSION...Donavon
AVIATION...FAB



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