Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 181124
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
624 AM CDT Fri May 18 2018

.DISCUSSION.../Today through Thursday/
Issued at 332 AM CDT Fri May 18 2018

Iowa will be between two systems today. An upper low over the mid
Mississippi valley will lift north/northeast today. This system will
stall the eastward progression of the potent upper level short wave
this is over the intermountain west. It is possible a few showers
could clip into far southeast Iowa by this afternoon but expect the
forecast area to remain dry today. High temperatures should remain
warm in the low to mid 80s. Some fog is possible, especially
across southeast Iowa tonight.

Thunderstorms should develop tonight west of Iowa tonight from the
Dakotas southward into Kansas and Colorado. These storms should
remain west of the forecast area yet tonight as the system to the
east continues to lift slowly northeast and block the flow. This
system will finally lift out by late Saturday and this will allow
better forcing and instability to reach Iowa. The low level jet will
increase Saturday evening and will bring increasing theta-e
advection and MUCAPES of 2000 J/kg or more to portions of southern
Iowa. Surface based storms should develop over Nebraska and
northeast Kansas by the afternoon and then will move into Iowa late
in the day. A few of these storms could be severe, however, current
projections would keep the surface warm front just south of Iowa and
timing pointing to the evening all suggesting storms will be a bit
elevated but could still carry an attendant damaging wind and hail
threat initially. SPC has issued an Enhanced threat for severe
weather extending into which has a northern extent clipping into
Taylor county. This is for severe weather potential in the vicinity
of the warm front, which as mentioned above, may be farther south
than this.

Sounding profiles do become quite saturated Saturday night and this
would lessen any hail threat with mid level updrafts velocities
weakening. However, there could be some localized heavy rainfall
with PWAT values increasing to 1.5 to 1.75 inches which is nearly
175 percent of seasonal values. Thunderstorms will remain possible
on Sunday though some uncertainty on the areal extent due to
potential impacts from Saturday nights storms and the location of
the surface low Sunday.

The system will depart by Monday. Another upper low will have
settled into the far southwest CONUS by this time and will keep the
warm temperatures across Iowa though the extended. The upper flow
will gradually transition from southwesterly to weak ridging by
Wednesday. High temperatures will be in the 70s and 80s throughout
the extended and likely will have some warmer days included.
Sporadic thunderstorms chances are also possible.

&&

.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 624 AM CDT Fri May 18 2018

VFR conditions are again expected to prevail through much of the
period. Some fog potential tonight especially vicinity of KOTM
could drop vsbys to less than 3SM. The wind will become breezy
from the southeast today then will diminish overnight.

&&

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

$$

DISCUSSION...Donavon
AVIATION...Donavon



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