Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 241717

Area Forecast Discussion
National Weather Service Des Moines IA
1217 PM CDT Tue Apr 24 2018

.SHORT TERM.../Today through Tonight/
Issued at 339 AM CDT Tue Apr 24 2018

Bottom Line up Front...
Light precip possible later today into tonight across
southwestern Iowa, otherwise, another day of temperatures in the
60s and 70s likely across much of Iowa.

08z Water vapor imagery picking up on a well-advertised upper low
crossing into western South Dakota from Montana/Wyoming. High
confidence now in forecast track as model consensus is high.
Effectively, the ECMWF/non-GFS track of this system won out. Trend
has still been to inch movement of this system along ever so
slowly. By 12z Wed, this upper low should be crossing into
northern Kansas, and by 00z Thu, the low will be crossing into
Oklahoma- taking its impacts well south of Iowa. Ultimately,
could be a high POP/low QPF setup over SW Iowa. DMX CWA literally
on the fringes where the gradient from where High POP to no POP
would be in place. So, will have to make "touch-up" adjustments by
late morning.

For temperatures, air mass in place for today effectively the same
as yesterday. Difference is increasing cloud cover- starting from
west to east. So persistence a great starting point for
temperatures, more or less knocking highs down a degree or two more
than yesterday. Snow mostly melted in NW Iowa, but cloud cover
should keep persistence a good forecast in NW Iowa as well.

.LONG TERM.../Wednesday through Monday/
Issued at 339 AM CDT Tue Apr 24 2018

Bottom Line up Front...
Trend locking into above normal temperatures across Iowa for the
next 7 days. Thursday into Friday is most active time period as
frontal boundary passes through Iowa from NW to SE... possibly
bringing a few thunderstorms to the area.

Drawing nearer to fropa time, so increasing look into details...
Run-to-run consistency starting to improve as spaghetti plots
tighten. At this point, think model consensus is prudent path to
take. Timing of fropa will remain key in temperatures... at this
time, central to SW IA looks to stay in the "warm sector" through
daytime heading, but if fropa is sped up just a few hours, temps
may need to be dropped into the mid 50s. Overall trend has been a
slight uptick in low- level moisture with this system.
Frontogenetical forcing and other ascent processes well- phased
with moisture profile in this fropa yielding increased confidence
in not only precip with this fropa, but a few rumbles of thunder
may also be possible. Strong winds likely the biggest impact, as
we could see brief wind gusts nearing 30 to 35 mph with this
boundary passage.

Into this upcoming weekend, large thermal ridge begins to build over
the intermountain west as a large 1025mb low propagates into
northern Oklahoma by Friday night, with a complementary sfc high
dropping through the Great Lakes region. By Sunday, these highs
should be over the Ohio Valley region, setting Iowa up for strong SW
flow/WAA. By 12z Sun, 850mb temps look to make it to +7C east to
+10C west. By 12z Mon, the thermal ridge may begin to crash over
Iowa, indicated by 850mb temps of +12C to +14C. Subsequently, have
begun to beef up temps vs guidance Sunday and Monday. At this time,
max temps in the 80s cannot be ruled out for Monday as far east as
Des Moines. Strong winds expected with this WAA will keep min temps
up overnight in the mid 50s... at least. Record high minimum
temperature in Des Moines for next Monday and Tuesday is 67 degrees
for both days. Worth keeping an eye on...


.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1217 PM CDT Tue Apr 24 2018

Few real concerns for impactful conditions...though mid level
clouds may accompany the approaching/weakening shortwave from KFOD
south to KDSM and west and south of those a few light showers may
occur aft 00z through 16z Wed. Winds expected to become northwest
through 00z as a weak boundary slides southeast today. Most of the
clouds will exit the region by 18z Wed with the exception of some
higher overcast at KDSM/KOTM. /rev




SHORT TERM...Kotenberg
LONG TERM...Kotenberg
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