Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 241750

Area Forecast Discussion
National Weather Service Des Moines IA
1250 PM CDT Mon Apr 24 2017

.SHORT TERM.../Today through Tonight/
Issued at 407 AM CDT Mon Apr 24 2017

State will remain in warm sector today with surface low remaining
west of the state.  Pressure gradient will remain tight during the
day with strong south winds, especially in favored open areas of
northern Iowa.  Highs for today remain somewhat problematic as
mixing should help readings climb nicely.  However, 850mb temps are
not appreciably warmer than yesterday and there will be an increase
in moisture and cloud cover.  Have actually shaved a few degrees
from Sundays highs, especially toward the northwest where clouds
will be thicker and there is a better threat for a shower or two.
The precipitation threat into the afternoon is the other concern as
moisture axis begins to enter the state.  Short term models have
generally shown little threat for precipitation with bulk of deeper
saturation remaining north of Iowa.  Have still included an isolated
shower threat in the far north, but wouldn`t be surprised to see a
few stray showers farther south as the theta-e advection passes east
through central Iowa.

Boundary enters northwest forecast area overnight and stalls as the
next wave pulls into western Kansas by Tuesday morning.  This will
keep much of the forecast area in the warm sector and overnight low
will mostly stay near 50 or so overnight.  Precipitation threat will
remain rather low for much of the night as subsidence behind the
first shortwave suppresses any showers.  However, will begin to see
increased forcing approach by end of the period and began to
increase pops in the vicinity of the boundary toward daybreak on

.LONG TERM.../Tuesday through Sunday/
Issued at 407 AM CDT Mon Apr 24 2017

Confidence: Medium-High

08z Mon water vapor imagery picking up on an upper low spinning just
off the Washington coastline. Models continue to show good
clustering around a solution for track/timing of this system, so
have favored the general consensus blend. At 12z Tue, models clearly
have core of 850mb low over north-central Kansas, with boundary
extending along the northeast side through western Iowa, into south-
central Minnesota. Effectively oriented perpendicular to this
boundary, a leading band of 850mb theta-e advection and adiabatic
isentropic lift...especially evident on the 305K sfc will enter
SW Iowa and propagate northeastward through the Iowa. This
isentropic lift to be reinforced throughout Tuesday, supporting
prolonged, widespread precip. PWATs look to be around 1 to 1.10
inches. Solid frontogenetical forcing from 950-600mb across
northern Iowa will support higher QPF in this portion of the
state. Northern nose of accompanying LLJ from Ames to Charles City
during Tuesday. In all, will monitor as QPF may need to be
significantly increased Tuesday from current 0.25-0.5 inch range
to 0.5-0.75 inch range across northern Iowa.

Wednesday through Thursday night...
Confidence: Medium-High

Meanwhile, the aforementioned boundary across western Iowa will push
through the state overnight, aligned near to I-35 at 12z Wed. Strong
NW flow, dry air, and CAA will push in behind the boundary. This
should dwindle down precip chances for Wednesday across much of
Iowa. Starting to catch up to notable cooling trend for
temperatures...may only need to knock 1-3 more degrees of max temps
for Wed, which would put much of the state west of I-35 into the

Thursday looks to be a transition day before the next shortwave
impacts the Midwest. 850mb temps continue to look to be in the 0C to
-5C range for Thursday morning. There certainly exists a potential
for frost/freeze Thursday morning...especially across northern Iowa.

Friday and beyond...
Confidence: Low-Medium

At this point, run-to-run consistency of deep trough/upper low &
strong sfc reflection cyclone impacting the heart of the CONUS... So
must buy-in to the occurrence of this feature. Differences still
exist in magnitude/timing of this system...though there appears to
be surprisingly good agreement with the track of the low. In
short, the 00z Mon GFS is stronger and, subsequently, slower with
the progression of this system...In fact, the 00z Mon GFS is
about 24 hours slower with the sfc low through eastern Iowa. The
00z Mon ECMWF deepens the sfc low to 995mb over Iowa, whereas the
00z Mon GFS has the low at 984mb. Gulf continues to be wide open,
with ample moisture transport through the warm sector thanks to
associated LLJ progged to 55 kts. 00z Mon solution places the deep
gulf moisture through the Ozarks, Illinois, and to
Indiana...clipping southeastern Iowa. PWATs continue to look to be
over 1.5 inches, which would be off the charts for this time of
year. Will need to watch closely. ATTM, much of the DMX CWA may be
spared from excessive rainfall, but a slight western and northern
nudge to the track would certainly put us in the mix for heavy
rainfall potential.


.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1250 PM CDT Mon Apr 24 2017

Main concern this period will be wind through 02z this
evening...then development of showers by 12z through remainder of
period. Strong gradient winds with sufficient mixing will persist
into the early evening...gradually diminishing by 02z. Along with
that a few areas may see LLWS overnight. Frontal boundary with
potential for -shra arrives into Tuesday...through remainder of
period. Better coverage along the boundary will exist at KFOD and
KMCW with lesser chances at KDSM/KALO. Have kept VCSH at southern
locations. CIGS to lower toward MVFR by 18z north sites KMCW/KFOD
as well. /rev




LONG TERM...Kotenberg
AVIATION...REV is the U.S. government's official web portal to all federal, state and local government web resources and services.