Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 170533

Area Forecast Discussion
National Weather Service Des Moines IA
1133 PM CST Fri Feb 16 2018

...Updated Aviation Discussion...

.SHORT TERM.../Tonight through Saturday/
Issued at 332 PM CST Fri Feb 16 2018

A short wave will move across the region tonight with decent
forcing and pretty strong theta-e advection moving in across the
west late tonight then to the east by Saturday late morning/early
afternoon. This should bring some light snow to areas mainly north
of Highway 20 with snowfall totals of an inch or less. Further
south the forcing is nil and soundings are pretty dry so I removed
PoPs south of Highway 20. Also of note...strong winds just off the
surface will create low level wind shear. Surface winds will be
around 10kts with 40kts above the surface. The upper level wave
and forcing quickly leaves the region by early afternoon Saturday
giving us clearing skies and with southwest to west wind...
moderating temps. We are looking at highs in the mid 30s north to
the upper 40s south.

.LONG TERM.../Saturday night through Friday/
Issued at 332 PM CST Fri Feb 16 2018

Saturday night and Sunday will be dry with a southwest flow aloft
and a surface low setting up from southwest MN back into the
Plains. Most of Iowa will remain in a west southwest flow
saturday night and a southerly flow Sunday. As a result, temps
will be quite mild...especially Sunday. Look for lows in the mid
teens to mid 20s Saturday night with highs mid 40s to mid 50s

Beyond Sunday the weather picture gets interesting. Late Sunday
through Monday morning the aforementioned surface low matures and
drags a front from north central Iowa through southwest Iowa. Very
warm air and some decent instability moves into parts of southern
and southeast Iowa where rain and isolated thunderstorms are
possible...especially Monday morning through early afternoon.
Along and north of the front...very cold air undercuts some pretty
mild air aloft the result will be a fairly substantial area
across northern to west central Iowa of freezing rain. At this
point ice amount are between one and two tenths of an inch but
wind will become a factor by Monday as well with sustained winds
at 15 to 25 mph with higher gusts. This is starting to look like a
decent ice event across northern Iowa...with thunderstorms
possible across the southeast. The front will slowly move across
the area through Monday night and may spread freezing rain further
southeast across the forecast area but confidence in this is low
at this point. It will all depend on whether the cold air will
become deep enough to change precip over to snow in time.

For Tuesday model differences are too large to put much confidence
in any one solution. Both deepen a large trough off the southwest
U.S. but the Euro is deepest. The Euro hangs on to precip much
longer than the GFS in which case we would see some snow on the
backside of this system. If the GFS is right then far
east/northeast Iowa would get brushed by some snow with other
locations just seeing some cold air pushing in.

Beyond Tuesday high pressure settles in with colder temps
Wednesday into Thursday then warming up for Friday, ahead of the
next system to impact Iowa.


.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1130 PM CST Fri Feb 16 2018

Weak and quick moving shortwave will bring light snow to northern
Iowa Saturday morning and looks to mainly impact MCW and possibly
ALO with MVFR visibility and ceilings. Some decent southerly flow
will lead to gusting winds throughout the day Saturday.





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