Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 202025

Area Forecast Discussion
National Weather Service Des Moines IA
325 PM CDT Tue Mar 20 2018

.SHORT TERM.../Tonight through Wednesday/
Issued at 322 PM CDT Tue Mar 20 2018

Ongoing light snow/rain and even a little drizzle will continue this
afternoon into the mid evening.  Extended slight chance through 04z
Wednesday across the western CWA per the latest hires models keeping
light precipitation going through this time frame. Sounding remains
fairly saturated and look to be deep enough to keep just snow and/or
rain. Towards the later part of the evening, ice introduction is
lost and there might be a brief period of fzdz over the west. Low
confidence in mentioning attm as the forcing looks to move east by
the time ice introduction is lost.  Other concern is fog development
past 06z tonight. Light winds and plenty of low level
moisture/saturation leads to high confidence in the fog overnight
into Wednesday morning. However, lower confidence in the widespread
1/4 mile visibility fog as the majority of the hires models are very
sparse in the lower visibility.  If there is an advisory needed,
it`s likely going to be west central to far northwest portions of
the CWA.

.LONG TERM.../Wednesday night through Tuesday/
Issued at 322 PM CDT Tue Mar 20 2018

Progressive flow will continue into the weekend. Upper ridging will
amplify across the lee side of the Rockies Wednesday night into
Thursday as a deep upper low drops south towards the Pacific
Northwest. A short wave will drop south through the northwest flow
and into Iowa by late Wednesday night into Thursday. This system
will be moisture challenged but will have better moisture as it
moves to the southeast, therefore best light rain chances are across
the southeast and could potential mix with snow early though no
snow accumulations are expected.

The most significant system will impact Iowa Friday into
Saturday. A strong short wave will undercut the upper ridge as it
moves east into the central CONUS. Surface low pressure is
expected to develop in response to the upper level feature over
eastern Colorado and western Kansas on Friday then move east into
central Missouri Friday night. This system will have a vast amount
of moisture advecting toward the system. Both the southern
Pacific stream which will provide moisture in the mid to upper
levels and the Gulf moisture lifting north supplying the low level
moisture. This system could pose a couple issues. Thermal
profiles over northeast Iowa into southern Minnesota would suggest
that the northern edge of the precipitation could be moderate to
heavy snow. Placement of vertical profiles will be critical as to
how much winter weather will impact portions of the forecast area.
The other potential issue with this system could be widespread
one inch or greater rainfall south of the snow band. This would
lead to significant rises on area streams and likely some
flooding. This is a highly dynamic system and certainly convective
weather could extend well north.

Another dynamic system is forecast to impact the region especially
Monday into Tuesday. The forecast area may be in the warm sector
with this system and may bring thunderstorms to the area.


.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1243 PM CDT Tue Mar 20 2018

MVFR ceilings are possible late this afternoon and tonight, mainly
impacting FOD and MCW. Lower confidence in mentioning at DSM and
other TAF sites as the duration and any onset remains
questionable. Certainly cannot rule out a few brief periods of
MVFR ceilings at DSM later this evening as a few of the hires
models suggest lower ceilings but DSM is on the eastern fringe of
this stratus.




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