Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 210438
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1138 PM CDT FRI MAY 20 2016

.SHORT TERM.../Tonight/
Issued at 338 PM CDT Fri May 20 2016

H300 trough currently over the mid-Mississippi River valley in water
vapor imagery will slide eastward into the southern Great Lakes
region by 12Z Saturday. At the same time, a Great Lakes high
pressure system will backbuild westward across the state tonight.
Increasing subsidence coincident with the departing trough should
help keep skies on the clearer side once the diurnal CU dissipate.
Given how temperatures bottomed out in the low 40s north to mid 50s
south last night, have nudged down lows for tonight a few degrees
into the upper 40s to around 50.

.LONG TERM.../Saturday through Friday/
Issued at 338 PM CDT Fri May 20 2016

First few periods of the long term pose little to no concern with
pleasant conditions, though flow will transition southwesterly
Sunday. The concerns exist Monday onward through the remainder of
the long term as multiple short waves will move through the upper
level southwest flow and provide multiple opportunities for
precipitation and even severe weather.

Backing to the beginning of the period, Saturday will see the region
remain in northwest flow as the upper level ridge axis will remain
over central Nebraska. A vorticity max will move down through the
state Saturday, but with a lack of moisture, cloud cover will be all
that results. The pattern will begin to break down Saturday night
into Sunday as the ridge axis passes over the state and southwest
flow aloft and southerly flow at the surface sets and dew points
make a modest return to the 50s by Sunday.

The first round of showers and storms will work through Monday as a
cold front approaches the region, but stalls to the west, and a
short wave moves through the upper level flow. At this point CAPE
around 1000-1500 J/kg looks likely and shear appears rather
lackluster, limiting severe potential. That thinking appears
reflected in the SPC Day 4 outlook as well, with best potential
further west where greater CAPE and shear will exist, though a
severe storm or two cannot be ruled out. Bigger concern may be heavy
rainfall with likely slow moving storm clusters/MCS.

Tuesday continues to appear better for severe weather, especially
across southern portions of the state. Another shortwave will eject
from the SW US and work through the region, helping usher through a
cold front by the afternoon. The shortwave itself will have moved
through ahead of peak heating, but with 3000 J/kg CAPE and more
supportive 0-6 km shear around 35 kts, storms should have little
issue initiating along/ahead of the front in the afternoon with a
few severe seeming likely.

Through much of the remainder of the week, models differ on the
timing and strength of shortwaves moving through the flow. As a
result, POPs continue through every remaining period of the long
term. The best window for potentially dry conditions appears to be
Wednesday night to Thursday morning, especially when favoring the
Euro, and have thusly lowered POPs a bit in that window, though not
enough to go fully dry. By the end of the period, the Euro ejects
the SW trough into the plains, while the GFS continues to eject
short waves through southwest flow.

&&

.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.

&&

.HYDROLOGY...
Issued at 338 PM CDT Fri May 20 2016

Potential for flooding, both flash flooding and river flooding,
remain a concern for next week. While details in precipitation
potential is large through the latter parts of next week, it
appears more than likely that multiple rounds of showers and
storms will come to fruition next week. As a result, areas that
see multiple rounds of moderate to heavy precipitation may see
significant river level rises and flash flooding concerns.

&&

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

&&

$$

SHORT TERM...Skow
LONG TERM...Curtis
AVIATION...Beerends
HYDROLOGY...Curtis



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