Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 120448

Area Forecast Discussion
National Weather Service Des Moines IA
1148 PM CDT Tue Aug 11 2020

.DISCUSSION.../Tonight through Tuesday/
Issued at 252 PM CDT Tue Aug 11 2020

The main forecast concern was focused on the continued somewhat
active weather pattern throughout the week and into the weekend.
Not great agreement with the models wrt to convection this week
and seems the ECMWF is the outlier and wettest model run through
Friday. Leaned closer to the hires models through Wednesday which
was a trend downward with storm chances other than over northern
Iowa. Then closer to the GFS late in the week.

Surface high pressure remains over the Great Lakes and keeps any
shortwave off to the west of the forecast area tonight into
Wednesday. Lowered pops considerably across the forecast area but
left low end pops over the west to north per latest NAM as well as
the 11.18z HRRR and RUC suggesting convection trickling into
northwest part of Iowa by Wednesday morning. Overall, low
confidence with much development due the decent dry air
entrainment from the surface high pressure to the east, weak lift,
and the instability axis remaining in western Iowa. Couldn`t
completely rule out and isolated elevated strong storm later
Wednesday, but the overall widespread potential is low.

Thursday...The ECMWF has another shortwave cutting across the
state Thursday and it has been fairly consistent with this trend.
That being said, the GFS has also been fairly consistent with the
northern trend and thus keeping the state dry on Thursday. The
timing of the ECMWF would suggest some severe weather potential as
it passes through the state during the afternoon hours.
Instability is 2000-3000 J/kg but shear remains weak throughout
the day Thursday per GFS. Plus, the better moisture convergence
is suggested to be in Minnesota and possible over far northern

Friday through Sunday...large upper ridge remains in place over
the southwest CONUS and there is a hint of a weak cold front to
pass through the region Saturday. Obviously timing remains
questionable, but the lack of significant frontogenetical forcing
and moisture with this system, low confidence with the storm
chances and thus the severe threat. Much cooler temperatures by
the early part of next week.


.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1147 PM CDT Tue Aug 11 2020

General trends remain the same. Storms developing in north central
NE will lift east northeast entering NW IA aft 08z and arriving
near KFOD aft 15z through 18z. Farther east activity weakens a
bit. With uncertainty have left VC for both KFOD and KMCW.
Additional sct storms may redevelop aft 23z north. More detail in
next package. /rev




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