Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 222316

Area Forecast Discussion
National Weather Service Des Moines IA
616 PM CDT Sun Oct 22 2017

.SHORT TERM.../Tonight through Monday/
Issued at 313 PM CDT Sun Oct 22 2017

The primary concerns will be gusty winds tomorrow and subtle precip
chances to a lesser extent. The elongated long wave trough and
associated PV anomaly axis continues to slowly move through Iowa
this afternoon and has resulted in persistent mid/high level
cloudiness from Ottumwa to Waterloo. Clearing should gradually
continue tonight with the surface ridge already into south central
IA at 19z.

Attention will turn to the current MT PV anomaly as it reaches the
Dakotas and MN toward 12z. Although low levels will remain dry, this
will result in a shot of deep, moderate thermodynamic and kinematic
forcing ahead of these feature during the morning with potentially
some light rain or sprinkles.

The passage of this feature will also introduce brisk NW winds, cold
advection and mixing from the afternoon into the early evening
hours. The MSLP gradient will push sustained winds to the brink of
an advisory /26kts/ west as suggested by MOS winds which are often
best in high wind events. Mixing and projected gusts is somewhat
more problematic with lower confidence. The NAM and GFS soundings
seem to be showing their typical moist and dry low level bias
respectively, but a blend of those and suggestions from SREF Mean
soundings show gusts may reach 35kts+ during the afternoon in these
areas, also on the brink of gust advisory criteria /39kts/. Thus
have issued an afternoon wind advisory for far western counties
where the 00z NCAR Ensembles also suggest may be the eastern fringe
of higher MO Valley winds tomorrow. This mixing and steeper low
level lapse rates may also produce a second round of shallow showers
and/or sprinkles north late.

.LONG TERM.../Monday night through Sunday/
Issued at 313 PM CDT Sun Oct 22 2017

The long range forecast continues to look like a temperature roller
coaster with multiple shots of cold air and a brief mid-week warm up
sandwiched in between. The period begins Monday night with gusty
northwest winds, which will back off some over night as CAA wanes
and the boundary layer decouples. Winds will become breezy again by
Tuesday afternoon as boundary layer mixing transports stronger winds
back to the surface. 850mb temps of -2C to -4C will lead to a chilly
day with highs ranging from the mid 40s to low 50s across the
forecast area.

A return to west/southwesterly low level flow will push temperatures
back to near or above normal levels for Wedensday and Thursday, but
this warm up will be short lived. 12z GFS/Euro have come into much
better agreement regarding the timing and evolution of a substantial
cold snap on deck for the end of the week. A significant shortwave
pushes southeast out of Canada and undergoes significant
amplification as the upper low digs into the Upper Midwest. This
will shove a seasonably strong cold front through the forecast area
late Thursday. Strong CAA behind the front will result in blustery
conditions as 850mb temps drop to -5C to -10C . Forecast highs only
top out in the 30s and 40s for Friday and Saturday with below
freezing overnight temperatures, which will likely result in the
first freeze for central and southern Iowa. Afternoon superblend run
still a little warmer than statistical guidance, especially MEX
guidance which has some lows in the upper teens over northern Iowa
Saturday and Sunday morning. With that in mind would not be
surprised to see the forecast to cool little further as confidence
increases through the week, however the difference is not enough to
make any impact to the current prevailing message of cold/freezing
temperatures late in the week. Models still hinting at the potential
for light rain and/or snow Friday into Friday night, but the more
favorable moisture and lift profiles remain off to our north.
Forecast was adjusted to keep most PoP mention in northern zones.


.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 616 PM CDT Sun Oct 22 2017

Main concerns this period will be wind. Two cold fronts will be
passing through the region in the next 36 hours with the first
cutting across the region between 14-18z with a second following
quickly between 18z northwest to 00z Tues southeast. In both cases
a burst of wind aloft accompanied by cold air advection will
result in sufficient mixing to amplify sfc winds/gusts. Each
passage may also show a few light showers...mainly VCSH northeast
with generally VFR cigs...6kft or higher through the period. /rev


Wind Advisory from 1 PM to 7 PM CDT Monday for IAZ004-015-023-



LONG TERM...Martin
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