Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 290503

Area Forecast Discussion
National Weather Service Des Moines IA
1203 AM CDT Sat Apr 29 2017

...Updated Aviation Discussion...

.SHORT TERM.../Tonight through Saturday/
Issued at 349 PM CDT Fri Apr 28 2017

Precip is winding down now and will continue to diminish in
coverage and move out of the area around 00Z as the last of the
forcing exits the area. For the remainder of the evening the
challenge will be cloud cover and temps. Temps today were
considerably cooler today and over the West central part of the
state temps remained in the mid to upper 30`s much of the day
allowing for periods of snow to fall. Downstream low clouds are
pushing up into the area so I am expecting low clouds to remain
and temps to level off with little diurnal change.

Around 12Z the next push of theta-e advection work into Southern
then Southeast Iowa through Saturday morning. Soundings in that
area don`t show deep saturation until the morning then rapidly
saturate so rain is expected to move back into the South then
spread North through the day. Precip amounts will be generally
light across the North with moderate amounts of a third to a half
an inch. Look for temps to be similar to today...and perhaps a
degree or two higher.

.LONG TERM.../Saturday night through Friday/
Issued at 349 PM CDT Fri Apr 28 2017

Strong early spring upper level low pressure will be over the
Texas/Oklahoma panhandles by Saturday evening and will begin to
turn northeast on Sunday. Surface cyclone will deepen in response
to the upper low and will lift north into Iowa on Sunday. An
initial wave of theta-e advection will be lifting north into Iowa
Saturday night and will keep widespread light to moderate
precipitation ongoing especially over central and northwest Iowa.
A second stronger surge arrives over southern Iowa by Sunday
morning ahead of the increasing dynamics associated with the
approaching low pressure. This will bring increasing elevated
instability and modest MUCAPEs around 500 J/KG into the eastern
half to 2/3rds of the state and the potential for thunderstorms.
Lapse rates and instability may be enough for a few marginally
severe hail storms.

A strong inversion will develop with cool easterly flow remaining
at the surface ahead of the low. This will keep temperatures on
the cold side ahead of system. The arrival of the low pressure
will bring a dry slot into the state in addition to a warm front
that will move across the southeast. Cold advection will wrap
around the low along with deformation precipitation Sunday night
into Monday. There is the potential for this precipitation to
change over to snow across portions of Iowa and most favored
across northwest Iowa. Can not rule out minor accumulations on
grassy surfaces.

The low pressure will depart Monday night with warm advection
returning along with highs back into the 50s and 60s for Tuesday.
Another upper level short wave will dive southeast and keep the
Midwest in mainly northerly flow aloft while an upper ridge
develops across the western CONUS. This will keep temperatures on
the seasonably cool side. Temperatures should be a bit warmer on
Friday as the upper ridge slides east.


.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1200 AM CDT Sat Apr 29 2017

Little change to ongoing forecast except delayed the precipitation
onset, especially for the northern TAF sites. Once the rain sets
in, have MVFR ceilings and visibility through the rest of the TAF


Issued at 308 PM CDT Fri Apr 28 2017

Minor to significant within-bank rises--and possibly minor flooding--
are expected on area rivers over the next several days owing to the
forthcoming multi-day rain event. The greatest rises are expected
across central and south portions where the higher QPF exists.

Presently the best chances of seeing minor flooding are along
portions of the North Raccoon River, Raccoon River and the Des
Moines River from its confluence with the Raccoon River downstream
to Red Rock Reservoir. Even in these areas, however, confidence is
presently not high enough to issue a river Flood Warning or even a
river Flood Watch. Will continue monitoring QPF trends for possible
changes however.





LONG TERM...Donavon
HYDROLOGY...Zogg is the U.S. government's official web portal to all federal, state and local government web resources and services.