Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 250505

Area Forecast Discussion
National Weather Service Des Moines IA
1205 AM CDT Sat Mar 25 2017

.SHORT TERM.../Tonight through Saturday/
Issued at 352 PM CDT Fri Mar 24 2017

20z Fri water vapor imagery clearly showing upper low
spinning/propagating eastward across the TX/OK panhandle. Sfc
reflection nearly vertically stacked with this low, with warm front
extending and oriented SW-NE all the way through Iowa. All models
have done a terrible job of handling the progression of the front,
which has demonstrated upwards of a 20 degree temperature
gradient over only a 50 mile span. Models have generally been too
slow and too far north and west with the boundary. Subsequently,
the models have been too far north and west with precip as the
best forcing/saturation phasing has been confined along and SE of
the boundary. With stratus covering the CWA and lack of
WAA/moisture advection to help generate instability, have
generally removed thunder from the rest of the forecast...except
for far southern and SE CWA. With the cloud cover, not much of a
diurnal swing expected overnight-Saturday.

For Saturday, 500mb charts showing this low becoming "cut-off". This
helps track the low NNE through Missouri and into northern Illinois.
This projected track seems plausibly, as the low almost begins to
show signs of wanting to retrograde Sunday morning. With cloud
cover expected to continue Saturday and the source region for air
on Saturday being nearly overhead, have knocked Saturday`s highs
down close to persistence from today.

.LONG TERM.../Saturday night through Friday/
Issued at 352 PM CDT Fri Mar 24 2017

20z water vapor imagery also picking up on a longwave trough coming
onshore along the western coast of the CONUS. This trough will slide
across the Rockies by late Sunday, serving to push the low impacting
us in the short term off to the east and preventing it from
retrograding. Medium range models are starting to dial in with a
southerly track across the ozarks for the sfc reflection. The ECMWF
has been the most consistent with the track over the past few days,
so have favored it as a guidance solution. Resultingly, have lowered
POPs for Monday...and cannot rule out precip chances being removed
for most of Iowa in future updates if southerly solution holds.

The next upper low looks to impact the Midwest Thursday. In between
Monday and Thursday, not a lot happening as our region will be more
or less locked in zonal flow.  With this overall large-scale setup,
have begun to nudge temperatures towards a persistence forecast.
As typical, long-range models showing variation with Thursday low.
The ECMWF is much further north, meaning a precip-filled middle
to end of the week if it verifies...whereas the GFS is further
south...meaning clouds for Iowa. Regardless of model, at this
time, best instability looks to be south and SE of Iowa, meaning
thunder chances are initially marginal at best. Will not sweat
details now, as much time for variation between now and Thursday.


.AVIATION.../For the 06Z TAFS through 06Z Saturday night/
Issued at 1205 AM CDT Sat Mar 25 2017

Little change from previous forecast. Cigs remain IFR/MVFR
with either -ra or -dz for the period. Across the north cigs will
lower but precipitation chances will lessen with time through the
period. Winds remain strong from the north northeast at 15kts with
gusts to 20 to 25 kts through at least 20z. Little improvement
from IFR/MVFR is expected through the period. /rev




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