Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 201735

Area Forecast Discussion
National Weather Service Des Moines IA
1235 PM CDT FRI MAY 20 2016

.SHORT TERM.../Today/
Issued at 310 AM CDT Fri May 20 2016

Primary concern today will be subtle precipitation trends. Long
wave trough continues to drift through the Middle and Lower
Mississippi Valley this morning with most noted short wave/PV
anomaly across the Oklahoma/Missouri border. All of this will
slowly move east with time. Better forcing will stay to our south
and east, but some weak forcing in the form of mid or upper level
diffluence and DPVA will exit Iowa this morning leaving behind
little but lingering moisture. This may still be sufficient for
some sprinkles or light showers, especially south closer to the
system. By afternoon the moisture will mainly be below 3km and
with mixing may generate some cumulus or isolated light showers.
With nil convergence much like yesterday feel areal coverage would
be quite isolated and not even worth a mention so afternoon PoPs
are mainly less than 20 percent.

The nearly barotropic airmass in place has changed little since
yesterday and will do nothing to help precipitation. This will
also keep our high temperatures quite homogeneous with highs
somewhat similar to Thursday in the upper 60s to lower 70s. The
warmest readings will likely be north where more sunshine may

.LONG TERM.../Tonight through Thursday/
Issued at 310 AM CDT Fri May 20 2016

Main forecast concerns include pcpn chances and heavy rain /
severe wx potential next week. Rather significant pattern change
is expected by early next week along with the subsequent potential
for multiple rounds of strong to severe weather as well as heavy

At onset of the long term period...the H5 shortwave that will
pass through the region today will enter the lower Ohio River
valley. CAA and surface high pressure following this shortwave
will bring slightly cooler temperatures to parts of the CWA
tonight...or just below normal values.

Rather vigorous and compact shortwave / PV anomaly is still
progged to move SE through the northwesterly upper-level flow
across the CWA Saturday into Saturday evening. Best moisture and
forcing appear to be out of phase with this feature so no longer
expect any pcpn with it...instead increasing cloud cover at most.

Flow across the CWA then transitions quickly to southwesterly
flow starting on Sunday. Tightening surface pressure gradient
still indicates breezy conditions on Sunday mainly afternoon.
There have been model run-to-run differences in terms of timing
the arrival of the initial shortwave and moisture...with latest
runs delaying their arrival slightly from Sunday night into

Initial shortwave is now progged to traverse the CWA on Monday.
NAEFS percentiles and GEFS M-Climate values have consistently
advertised anomalously high PWAT values on Monday and continuing
into Monday evening. Given these values along with the presence of
ample forcing and the progged Corfidi vector orientations...have
introduced heavy rain wording into the forecast to accompany the
likely POPs. Shear is rather unidirectional so not overly
concerned with severe wx potential but will have to be watched.

Models differ in timing of the various impulses going through the
upper-level SW flow during week but there is some agreement on
the timing of an impulse from Tuesday night into Wednesday...which
is reflected in the elevated POPs during that time. Severe weather
parameters become somewhat more favorable during this time frame
so will again have to monitor for the potential.

Southwestern CONUS trof then ejects as a potent shortwave
Wednesday night into Thursday...and progged to reach the High
Plains Thursday night. Again there are model differences in
placement and timing. Some solutions...such as the ECMWF...are
rather ominous for the CWA next Friday. It progs the upper-level
low and closed surface low located over northern Nebraska into
southern SD. Instability and shear parameters would be conducive
to severe wx across the CWA. GFS is farther south but is also
favorable for severe wx potential. Temperatures next week will be
near or slightly above normal.


.AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/
Issued at 1235 PM CDT Fri May 20 2016

VFR conditions are expected through the period with light east to
southeast winds. Light showers over southeast Iowa should weaken
and shift out of the area this afternoon.


Issued at 310 AM CDT Fri May 20 2016

Given the potential for multiple episodes of heavy rainfall next
week...flash flooding is possible...with subsequent river flooding
possible by the end of next week. Greatest concern would arise if
rainfall from the multiple episodes of active weather affects the
same locations.


.DMX Watches/Warnings/Advisories...


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