Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 312057
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
357 PM CDT TUE MAY 31 2016

.SHORT TERM.../Tonight/
Issued at 356 PM CDT Tue May 31 2016

Main forecast concerns include timing of precip out of the CWA this
evening...as well as fog potential later tonight.

Line of showers with scattered TSRA will continue working its way
eastward across the CWA the rest of this afternoon into this
evening...ahead of a surface cold front. Marginal risk of severe
weather will remain at least until early-mid evening...when the
boundary layer will begin stabilizing. Effective shear is negligible
but MLCAPE values are supportive of at least brief updrafts with
hail and strong wind potential. Funnel clouds are possible
especially on the leading edge of the convection...as supported by
SPC non-supercell tornado parameters. TSRA will also be capable of
producing brief heavy rainfall but any flooding impacts are expected
to be isolated and sub-warning criteria at worst.

Guidance times the front and precip out of the CWA by 06-09Z...with
winds becoming rather light and variable. With decreasing cloud
cover...fog will become a possibility especially southeastern half
to third of the CWA. Hi-res models suggest fog formation...with
dense fog possible...after 04Z. Will add mention of fog to the
grids.

.LONG TERM.../Wednesday through Tuesday/
Issued at 356 PM CDT Tue May 31 2016

Primary concern through the period will be precip trends toward the
end of the week. Weak convection from the current system should have
exited southeastern sections at onset giving way to decreasing
clouds in drying subsident northwest flow. This will lead to dry
conditions into Thursday. The next precip window will begin later in
the day as warm advection begins to spill over the h85/h7 ridging,
and some weak surface convergence develops along a very subtle
northwest Iowa warm front. Instability, convergence and forcing are
all fairly weak however, and mainly north, so pops will remain on
the low end.

The potential for more appreciable convection increases somewhat
later Friday however. Both the instability and deep layer shear
increase slightly heading into peak heating with the potential
for surface based development along a cold front which should be
moving through the Siouxland area around 00z. This will be coupled
with decent deep QG forcing and have raised pops into the likely
category, expecting a lower end MCS. Weak warm advection and low
level moisture transport just ahead of the boundary should
maintain the convection into the evening to some extent but what
intensity there is should wane fairly quickly. Much of the
available Cape will be based on surface heating which will wane
through the evening. Have also continued chance pops into
Saturday, but this would mainly be for unfocused weak showers or
isolated storms in broad low level cyclonic flow. The remainder
of the extended forecast looks dry with fairly inactive northwest
flow. Temperatures and humidity levels will remain near normal
with fairly pleasant conditions.

&&

.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1218 PM CDT TUE MAY 31 2016

A surface cold front will slowly progress eastward across IA the
rest of this afternoon into tonight. Scattered SHRA/TSRA will be
prevalent in advance of it. Sfc winds will switch from southerly to
Wly or NWly behind the boundary. Mainly VFR conditions are
expected...with some local MVFR conditions possible due mainly to
vsby in the heavier SHRA/TSRA. Have not included in the TAFs attm.
Hi-res models suggest BR is a possibility later tonight especially
across the southeast half of the state. Have suggested vsby
restrictions in the TAFs.

&&

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

&&

$$

SHORT TERM...Zogg
LONG TERM...Small
AVIATION...Zogg



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