Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 160510

Area Forecast Discussion
National Weather Service Des Moines IA
1110 PM CST Thu Feb 15 2018

...Updated for 06z Aviation Discussion...

.SHORT TERM.../Tonight through Friday/
Issued at 331 PM CST Thu Feb 15 2018

Colder air surges in tonight on brisk winds. Taking a look at
soundings show winds atop the mixed layer around 30kts which would
be below advisory criteria. Of bigger concern is the combination
of the very cold temps coming in along with the brisk wind
dropping wind chills to between 10 and 15 below...especially north
of highway 20. There is some weak forcing coming across northern
Iowa tonight as a weak wave and some associated vorticity comes
across that area. We have deep enough moisture in place for some
light snow or flurries but the event is not going to put a damper
on any activities.

Friday will be cold despite mostly sunny skies. At least winds
will not be very strong so wind chills are not expected to be a
factor at this point.

.LONG TERM.../Friday night through Thursday/
Issued at 331 PM CST Thu Feb 15 2018

Friday night and Saturday...a stronger shortwave pushes across the
region with respectable forcing and theta-e advection coincident
with the wave. Things get a little better organized over eastern
Iowa and I have placed the highest PoPs in this region. QPF is
fairly light and with warming temps on Saturday, snow ratios are a
little lower than previously thought however, we should still see
an inch or less over areas across northeast to east central Iowa.

Sunday into Monday looking very interesting as a deep trough digs
into the southwest U.S. while at the surface a low develops along
with an associated frontal boundary over western Iowa. Temps will
vary wildly Sunday into Monday...especially Monday. Sunday we are
looking at highs in the 40`s NW to near 60 SE and Monday we`ll
have mid 20`s NW to the lower 60`s SE. Low confidence in ptype at
this point but rain looks certain across the southeast. We become
quite unstable Monday and I would not be surprised to see an
isolated thunderstorm however uncertainty is high enough to keep
this out of the forecast at this point. Somewhere between far NW
Iowa where snow is probable and far SE Iowa where we will see
rain, we will see an area of freezing rain. Soundings show warm
air aloft with pretty cold air undercutting the warm air aloft.
Pretty good setup for freezing rain...if the forecast soundings
pan out. The most likely area for this to occur would be
along/north of the highway 20 corridor. Low confidence at this
point in where this boundary will set up and it is still in the
day 5 period so without decent agreement I left the wintery mix
ptype in the forecast. In the coming days we will have better
clarity on the boundary position and introduce an area of freezing

The boundary sinks south Monday night/Tuesday with light snow
expected for this period and much colder temps again. Strong
winds will accompany this frontal passage.

Beyond Tuesday we are looking mainly dry with moderating temps mid
to late week. The exception is Wednesday night when models hint at
a weak wave riding up and grazing southwest Iowa with slight
chance Pops.


.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1109 PM CST Thu Feb 15 2018

MVFR ceilings have lifted and scattered into VFR category over
the northern terminals late this evening. This trend will
continue at the rest of the terminals through the night. Gusty
winds from the northwest will also persist through the night. VFR
conditions are expected at all the terminals by daybreak and
continue through the end of the period as high pressure moves
across the state.




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