Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 191159
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
659 AM CDT Fri May 19 2017

.SHORT TERM.../Today through Tonight/
Issued at 415 AM CDT Fri May 19 2017

Area of precipitation and some thunderstorms have been moving
northward through the state all night with push of upper level
energy moving through the state ahead of the main upper low
currently spinning over Colorado. Majority of the precip expected to
lift through the remainder of the area through sunrise, with some
lingering showers still possible across far northern IA toward mid
morning. Lift to wane through the morning/early afternoon hours
across the CWA, but could still see some spotty activity so kept
some pops around much of the day. However the best chance of
additional precipitation expected more toward late afternoon into
tonight as the next lobe of energy to approach the state as the
upper low begins to lift into the central Plains. Associated surface
low to move into eastern KS with WAA/theta-e advection in place
across Iowa. Most sites have seen between a half inch of rain to an
inch of rain or more with this first wave of precipitation so far.
An additional half inch to an inch is again possible with the second
wave of precipitation spreading northward across the area tonight.
Instability will be limited, went with mainly isolated to scattered
wording.

Given precip chances much of the day and clouds to remain in place,
highs not expected to move much from current temps with maybe a 5
degree rise or so. Additionally with the waa/clouds/precip expected
tonight, lows again Friday night not expected to fall much either.

.LONG TERM.../Saturday through Thursday/
Issued at 415 AM CDT Fri May 19 2017

Saturday...
Deep upper low discussed in the short-term remains on track to
propagate northeastward through the upper Midwest. By 12z Sat, the
parent upper low should be centered over Nebraska, with the sfc
reflection crossing into SW Iowa. Slightly disconcerting with
some disagreement remaining this far out... the 00z NAM continues
to be a fast outlier with the sfc low. New to this 00z run the
ECMWF takes a somewhat strange northerly course. The GFS has kept
the most run-to- run consistency, so have leaned thinking towards
it. The GFS scenario would produce the greatest likelihood of
strong to severe storms in our east/southeastern counties during
Saturday afternoon.

Overall, Saturday PM environment setting up for low-topped supercell
potential... Somewhat low instability with MUCAPE values reaching
around 1000 j/kg or so, strong shear values, and BUFKIT soundings at
KOTM showing ELs near 450mb. Helicity values are marginal, so
tornado threat not as high as hail and damaging wind threat. As it
pertains to our CWA, challenge will be timing. During peak heating,
the best forcing in the warm sector, ahead of the weak cold
front, may be over the DVN CWA, meaning maybe the far eastern tier
or two (at best) of counties along and south of I-35 may be the
only ones under this severe potential. If this trends towards the
faster solutions, the DMX CWA may miss out entirely.

Sunday...
Models showing good run-to-run consistency with wrap-around
stratus overspreading Iowa all day. Thus, have continued with
downward temperature trend. In fact, highs may be around 5 degrees
too warm as 850 temps drop to near zero across our north. If the
00z Sat runs look like they do now, will definitely be lowering
temps several degrees.

Monday into Tuesday...
Long-range models still feature a fast-moving shortwave
propagating south-southeast through Manitoba and phasing with the
backside of the parent upper low discussed above. Long- range
models seem to be in better agreement with this system than the
Saturday one which is obviously counter-intuitive. Attendant cold
front to push through Iowa from west to east as sfc low centered
over the IA/MN border at 00z Tue. With a broad sfc high located
over the Ozarks during this time, Gulf of Mexico moisture access
shut off, which will largely inhibit svr development. Westerly to
northwesterly flow generally looks to dominate beyond Tuesday.

&&

.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 659 AM CDT Fri May 19 2017

Low clouds to be in place much of the day into tonight with
showers moving through northern and eastern Iowa this morning.
CIGS to be around MVFR to IFR through the period. Showers and
possibly some thunderstorms to move back in tonight into early
Saturday. Gusty northeasterly winds expected through the period.

&&

.HYDROLOGY...
Issued at 415 AM CDT Fri May 19 2017

Widespread 1-2 rains with 2-3" possible central and south still on
course by the weekend with some sites already having seen around an
inch of rain overnight. Locally higher amounts will still be
possible especially in areas that do see thunder. However with the
limited amount of instability expected this should preclude much
convection and heavier amounts in just a few hours. Therefore do not
anticipate a flash flood watch being needed at this time, but more
of a focus on rises for local streams/creeks and rivers across the
area due to the prolonged period of rainfall and widespread nature
of the rainfall across the area. Flood Watches for individual river
forecast points may likely be needed today or tonight as rain begins
to accumulate and the RFC 24hr QPF window floats into Saturday. RFC
contingency forecasts suggest multiple locations will reach at least
minor flood stage with isolated moderate flooding possible depending
on which basins are affected by the heavier amounts.

&&

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

&&

$$

SHORT TERM...Beerends
LONG TERM...Kotenberg
AVIATION...Beerends
HYDROLOGY...Beerends


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