Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 141752

Area Forecast Discussion
National Weather Service Des Moines IA
1252 PM CDT Sat Apr 14 2018

...Updated for 18z Aviation Discussion...

.SHORT TERM.../Today through Sunday/
Issued at 434 AM CDT Sat Apr 14 2018

Strong upper low to move from the Plains today into the Upper
Midwest tonight and finally lifting into Illinois then the Great
Lakes Monday and Monday night.  The surface low with this system is
currently drifting along the Iowa/Missouri border with the warm front
making it no further north than the far southern tier or two of
counties in Iowa.  There is still some instability across central
into eastern Iowa so the potential for thunderstorms still exists
mainly south of highway 30.

We will be in a forcing lull through early morning but between 12Z
and 15Z a pretty strong push of forcing will move across Iowa with a
decent theta-e advection shifting across northwest into northeast
Iowa through the morning.  This will cause precip to re-develop
across Iowa in the form of showers and an isolated thunderstorm.  As
the low shifts to the east, colder air will push into Iowa.  Precip
will be changing over to snow across the northwest and gradually
change over across the rest of the forecast area by late this
afternoon and tonight.  The NAM is not handling ptype well as it
keeps wanting to lose ice introduction for a time this morning
creating some widespread freezing rain.  This scenario is unlikely
and not supported much by soundings so I have adjusted ice
introduction grids, though there is some brief potential from
northeast into central Iowa. Ground temperatures are warm enough
that ice is not going to be much of a problem...especially since it
will be very short lived if it occurs at all.

Strong winds are in place and will continue to be in place across
the state today and with heavy snowfall expected across the north
and northwest in that push of strong forcing and theta-e advection,
blizzard conditions are still expected.  Not much change to the
blizzard and winter storm headlines were needed.  I did expand the
blizzard warning one county east where snow and wind were expected.
A wind advisory was needed across east central sections as strong
gradient winds were occurring with sustained winds speeds of 25 mph
and gusts near 40 mph.  These should diminish some in the afternoon.
For now, the advisory was issued to the I-80 corridor but may need
to be expanded southeast. For now the stronger winds southeast
are not expected to last more than an hour or two.

Tonight, the cold air will be in place across the forecast area and
precip falling will be in the form of snow. However, much of the
forcing will be over eastern Iowa by late evening and overnight so
the snowfall will not be great, but we will still see an inch or two
across the north with lesser amounts central.  On Sunday the system
will be departing with only lingering snow over the east.  It will
be cold however with highs only in the 30s.

.LONG TERM.../Sunday Night through Friday/
Issued at 434 AM CDT Sat Apr 14 2018

/Sunday Night through Monday Night/...Confidence Medium to High

Storm system will finally be exiting the region Sunday night with
lingering light snow/flurries and continued gusty winds into the
evening hours. H850 temperatures will be nearly -11C across the east
bringing lows in the upper teens/lower 20s over most of the forecast
area. This will likely result in near record lows again over
portions of the forecast area...especially over the north. The only
thing that might prevent record mins will be mixing overnight and
cloud cover. High pressure will return to the region Monday with
overall lesser winds and some sunshine...though highs will remain
cold for this time of the year and only reach the 30s north to the
40s over the south.

/Tuesday through Friday/...Confidence Medium

Another period of active weather returns for the middle to end of
next week.  By Tuesday a strong shortwave will be moving across the
Rockies with a rapidly deepening surface low as it crosses Kansas
then weakening somewhat by Wednesday into Thursday. Once again
across the north on Wednesday temperatures may be cold enough for
either a rain/snow mix or a period of all snow. The GFS and Euro
differ on details with the Euro model showing a more pronounced snow
signal over northern Iowa. At this time it is too early for details.
Though temperatures next week look chilly overall...Wednesday and
Thursday appear to be the cooler days with highs in the upper
30s/lower 40s north to the lower to mid 50s south.  By week`s end
yet another very strong upper level weather system will track into
the Central Plains. This will likely bring milder air ahead of it
and also more moisture than the mid-week system.  Though it occludes
prior to reaching Iowa...the Euro at least...suggests a favorable
environment for rain and some thunderstorms from Iowa south to the
Gulf Coast.  Temperatures ahead of the system should warm into the
50s to lower 60s south Friday or Saturday if the Euro is more
correct.  Currently the GFS is a bit cooler and weaker in strength.
In either case of the Euro/GFS...both models suggest an active week
next week with two storms and more chances for wet weather.


.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1252 PM CDT Sat Apr 14 2018

Blizzard to near blizzard conditions with LIFR or IFR conditions over
northwest and north central Iowa terminals will persist into at
least this evening as winds from the northeast gust towards 40
knots. Farther south, there may be a brief lull in the
precipitation this afternoon with IFR ceilings remaining. While
snow will likely linger through the end of the TAF period, there
should be slight improvement into MVFR category at most terminals
by 18z Sunday.


Issued at 434 AM CDT Sat Apr 14 2018

Little change from previous package: Wet period expected over the
next couple days with seasonally moderate to heavy QPF expected
across the northern CWA. In response, the 2-day QPF hydrograph
ensembles show significant within-bank rises at many forecast
points within the Cedar, Iowa and Des Moines River basins mainly
along and north of US Hwy 20, with the exception being the Des
Moines River at Des Moines SE 6th St where the river may come
within a couple feet of flood stage. Some response to the
overnight precipitation is also taking place early today along
the Winnebago River at Mason City.

The 2-day QPF hydrograph ensembles suggest flooding is possible at a
few locations in the Cedar and Des Moines River basins along and
north of US Hwy 20. A Flood Warning continues for the West Fork
Des Moines River at Estherville. In addition, a Flood Watch
continues for the Cedar River at Cedar Falls.


Wind Advisory until 4 PM CDT this afternoon for IAZ027-028-

Winter Weather Advisory until 1 AM CDT Sunday for IAZ025-035-036-

Blizzard Warning until 1 AM CDT Sunday for IAZ004>007-015>017-

Winter Weather Advisory from 1 AM to 1 PM CDT Sunday for IAZ007-

Winter Weather Advisory until 1 PM CDT Sunday for IAZ026.

Winter Weather Advisory from 4 PM this afternoon to 1 PM CDT
Sunday for IAZ027-028-037>039.



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