Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 261750
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1150 AM CST Sat Nov 26 2016

.SHORT TERM.../Today through Tonight/
Issued at 351 AM CST Sat Nov 26 2016

A pleasant Saturday is shaping up for the state of Iowa with
southwesterly return flow and strong H850 WAA helping to push
temperatures into the upper 40s north to the upper 50s south. Made
minimal changes to the going max temp forecast given the possibility
of increasing cirrus cloud cover and the going forecast already on
the upper end of the guidance envelope. Increased sky cover over the
northern 2/3rds of the CWA for today and into this evening given the
influx of cirrus cresting the H500 ridge over the western High
Plains on IR imagery. NAM/RAP/GFS vertical RH cross-sections all
hold the cirrus into the early afternoon hours, though there are
some timing differences in the clearing of the clouds with the RAP
in particular holding the clouds well after sunset in the NE.
Tonight will be quiet weather-wise with increasing high clouds
streaming in from the SW towards sunrise ahead of our Sunday rain
event.

.LONG TERM.../Sunday through Friday/
Issued at 351 AM CST Sat Nov 26 2016

Vigorous short wave energy will cross over the Rockies early
Sunday with strong lee side cyclogenesis occurring from eastern
Colorado and into Nebraska. The deepening sfc low will lead to
strong moisture advection streaming north from the Gulf of Mexico
and into Iowa. Profiles will start the day quite dry but will
saturate quickly. As profiles saturate the mid level lapse rates
will steepen and weak MUCAPEs will develop. Thus expect elevated
thunderstorms to develop during the day. Showers and a few
thunderstorms may linger into early Sunday evening then subsidence
in the wake of the passing PV anomaly will arrive along with a
return of drier mid level air. The near surface moisture will
remain along with some turbulence and vertical ascent and this may
result in drizzle development.

The upper level energy will evolve into a deepening upper low
pressure that will slow and linger over the Dakotas on Monday then
move slowly east into Minnesota on Tuesday before eventually
reaching the mid Great Lakes on Thursday. How long clouds linger
on Monday is the main challenge for the temperature forecast. If
the clouds scatter, mixing will push high temperatures back into
the mid to upper 50s for central and southern Iowa. The primary
push of cold advection arrives late Monday afternoon and into the
overnight then 850 mb temperatures will continue to cool as the
upper low progresses east. The 850 mb temperatures will be near
-8C by Thursday. Mixing during this time will keep highs in the
30s to 40s with overnight lows generally in the 20s. Light rain or
snow will be possible over northern Iowa Tuesday into Wednesday
with little to no accumulations expected. The remainder of the
extended forecast will be mainly dry.

&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1150 AM CST Sat Nov 26 2016

Main concern this afternoon is increased wind through 23z then
diminishing. High clouds will remain over region with approaching
trough/storm Sunday. Otherwise near the end of the period from
16-18z Sunday expecting cigs to lower to MVFR at KFOD and quickly
drop around 18z at KDSM. Will see continue trend of poorer
conditions from 11/27 18z to 11/28 00z as main forcing arrives
with showers and IFR conditions developing during that time. /rev

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Skow
LONG TERM...Donavon
AVIATION...REV



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