Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 210854
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
354 AM CDT SAT MAY 21 2016

.SHORT TERM.../Today/
Issued at 323 AM CDT Sat May 21 2016

Only real concern today will be the degree of temperature rebound.
Water vapor imagery nicely shows a PV anomaly/shear vorticity zone
across North Dakota which has combined with central Plains warm
advection to spread mid and high level cloudiness into the mid
Missouri River Valley. The aforementioned PV anomaly and shear
vorticity is expected to drop into Iowa today and should keep its
attendant forcing just to our south and west and Iowa mostly sunny.
Examination of soundings and projected mixing suggests highs should
be persistence plus several degrees with warmer readings the inverse
of what typically occurs, warmest northeast and a touch cooler
southwest.

.LONG TERM.../Tonight through Friday/
Issued at 323 AM CDT Sat May 21 2016

For tonight through Sunday the weather will remain benign but
subtle changes will be taking place and setting us up for a very
active pattern through the rest of the extended period. high
pressure both at the surface and aloft will be shifting east
across the upper midwest through Sunday. By Sunday night we will
be in Southwest flow across the region which will begin to bring
in warmer air and more moisture. Thunderstorms will develop West
of Iowa and be ongoing Sunday night into Monday but should remain
West of the forecast area. During the day Monday a shortwave will
push across the upper midwest coincident with a cold front
sweeping the state. there will be sufficient instability across
Iowa and while low level shear looks decent...deeper shear is
lacking and as a result throws into question the severe potential.
Another caveat for Monday is the role that ongoing convection will
play. Given the time of year and the strength of the front, large hail
and damaging wind from at least a storm or two appear likely but
the overall threat is not that impressive...at least at this
point. Heavy rain potential for Monday does look pretty good as
well so while we may not have a lot of severe...we will be seeing
some heavy rain which could prime things for later in the week.

On Tuesday another short wave moves across the upper midwest and
this time the instability is much better and the shear while not
what I would call really strong...is better than Monday and a
little deeper as well. Storms on Tuesday...especially South where
the better shear and instability will exist...will have a better
shot at becoming severe.  We lack a good boundary though.

Tuesday night and Wednesday comes yet another shortwave and
another surface low and frontal boundary crossing the state...with
continued strong instability and even better shear. Wednesday
appears to be the best shot at severe storms...especially South
again.

The pattern continues to be active into late week and the weekend
however models diverge on the timing of the shortwave and the
evolution of the West Coast low/trough. The Euro closes the low
off and lifts it into the Northern Plains while the GFS keeps the
low off the west coast and continues to eject shortwaves across
the region. The GFS would be the wetter solution but it has a
habit of looking more like the Euro with time. At any rate...I
kept the chances going for thunderstorms to keep with persistence
and until the models begin to converge on a more consistent
solution. This weekend will be good for getting outdoor things
done because it will be wet through the week and will take some
time to dry out later in the weekend.

&&

.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1138 PM CDT Fri May 20 2016

VFR conditions expected through the forecast. Light and variable
winds.

&&

.DMX Watches/Warnings/Advisories...
None.
&&

$$

SHORT TERM...Small
LONG TERM...FAB
AVIATION...Beerends


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