Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 241730

Area Forecast Discussion
National Weather Service Des Moines IA
1230 PM CDT Sat Jun 24 2017

.SHORT TERM.../Today through Tonight/
Issued at 350 AM CDT Sat Jun 24 2017

The primary sensible weather concerns today will be anomalously low
temperatures and dewpoints, along with the potential for scattered
peak heating convection. The current situation has a long wave
trough settling into the MS Valley with a jet segment and PV anomaly
through IA in the base of the trough. Any lift associated with PV
anomaly and weaker waves entering WI should exit shortly.  The upper
low over ND this morning will advance into the Upper MS Valley by
00z bring anomalously cold mid level temperatures. 00Z Bismarck
sounding 700-300mb temps were in the 2.6 or less percentiles and 12z
NAEFS percentiles suggest continued near all time extreme 500mb temp
values as the cold core drifts nearby. This will result in steep
lapse rates sufficient to remove any inhibition and develop
scattered unorganized showers and isolated thunderstorms during peak
heating northeast with several hundred MUCAPEs. Funnel clouds will
be possible with 0-3km CAPEs reaching 50-100 j/kg but relatively
brisk NW winds and the lack of any boundary/surface vorticity would
limit that and really decrease chances of anything reaching the
ground. Dewpoints will be well below normal, into the 40s. A quick
look at climatology would suggest 30s would be needed to approach
all time lows however.

Any weak convection should dissipate quickly into the early evening
hours with loss of heating giving way to mostly clear skies
overnight in subsidence behind the upper low. Mins should dip into
the upper 40s and low 50s, typically 5-10F away from records.

.LONG TERM.../Sunday through Friday/
Issued at 350 AM CDT Sat Jun 24 2017

Central Iowa will remain in northwest flow through Monday. This
will keep the thermal trough across the state through this period.
Breezy and cool conditions can be expected once again Sunday with
highs in the upper 60s to mid 70s. Another short wave/PV anomaly
will arrive ll bring another short wave through the region will
arrive Sunday night and will bring a chance for showers and
possibly an isolated thunderstorm.

Warm advection will develop Monday night into Tuesday as the long
wave trough exits to the east and the upper flow becomes more
zonal through Thursday while another closed low spins over south
central Alberta and Saskatchewan. High temperatures will return to
the 80s as the warmer air arrives. Thunderstorm chances will
arrive Tuesday night and Wednesday as a boundary enters the state.
Some uncertainty Thursday and beyond regarding the
evolution/timing of Canadian upper low as it drops into the
Northern Plains. Regardless, the pattern will be more conducive
for additional precipitation chances through the rest of the week
and into early next weekend.


.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1230 PM CDT Sat Jun 24 2017

Main concerns this period will be thunder potential prior to 00z
north along with breezy winds. Toward the end of the period
possible stratus and MVFR cigs near KMCW. Cool front and upper
level trough combining for scattered convection over the north and
northeast this afternoon through 00z. Coverage remains scattered
enough to warrant VCSH/VCTS at this time. Winds mixing again today
and Sunday with gusts to near 22kts at times. Otherwise cold pool
aloft in Minnesota driving south by 12z Sunday helping to promote
MVFR stratus into far northern Iowa. For now have lowered KMCW to
BKN035 but may see brief period of MVFR aft 12z Sunday. /rev




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