Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 211707

Area Forecast Discussion
National Weather Service Des Moines IA
1207 PM CDT Fri Apr 21 2017

.SHORT TERM.../Today through Tonight/
Issued at 322 AM CDT Fri Apr 21 2017

Subsidence and drier air led to a rapid erosion of the status last
evening over central Iowa.  In the wake, some high clouds are
passing above portions of southern Iowa, however much of the state
is seeing clear skies with light winds and cool temperatures.  For
today, will continue to see cool and dry air advected into the state
from the north with Iowa sandwiched between ridging across Minnesota
and low pressure in the central Plains.  High clouds will stream
across portions of the state today with thickening high cirrus in
southern Iowa but thinning towards the north.  Temperatures will be
fairly similar across the state with thicker cirrus in the south
making up for the cooler temperature profile in the north with highs
around 60 in most locations.

Quiet weather is expected to persist tonight with some cirrus
continuing in the south from the storm system in central Plains.
Otherwise, a cool airmass will remain in place with light winds and
clear skies in the north with overnight lows likely dropping into
the mid 30s and some patchy frost possible.

.LONG TERM.../Saturday through Thursday/
Issued at 322 AM CDT Fri Apr 21 2017

Hazards: Lightning, Strong Winds
When: Monday Afternoon/Evening
Where: Far west
Confidence: Medium

Saturday-Monday Morning...
Models in solid enough agreement with propagating a 1025mb or so
high southeastward through the Dakotas, placing it in SW Minnesota
by 12z Sat. Only fcst action here would be tweaking temps a
degree or two from guidance. Overnight temps should stay above
frost/freeze criteria.

Monday Afternoon-Early Tuesday...
All models pointing towards a very progressive shortwave plowing
through the upper Midwest. SFC reflection to come off the Rockies
in South Dakota and will likely be near west-central Minnesota by
00z Tue or so. An attendant cold front will drape off this low and
extend through all of Iowa as the system propagates northeastward
through MN. Timing of this low will be important, as the boundary
will likely serve as a focusing mechanism for strong to possibly
severe storms during peak heating...with capping taking over after
sunset. At this point in time, it appears the remnants of any
strong storms may nose our far western counties between will have to monitor this forecast for any shifts in
the projected track/timing of this low. Very steep lapse rates and
DCAPE values approaching 1000 j/KG suggest large hail and
damaging winds main threats.

Tuesday and beyond...
Zonal flow dominates the middle of this week. Have widely
scattered, low-confidence pops in to account for susceptibility
to shortwaves with this setup in the extended period. Depending on
long-range model of choice, next Thursday through Saturday could
be interesting. In short, models seem to feature a panhandle low
passing from Oklahoma into the Midwest...however, they are all
over the place with timing. Potentially very heavy rainfall is
suggested at this point, along with strong to severe storm
potential. Run-to-run consistency is nearly nil, and model
agreement is nearly nil. Therefore, will be monitoring synoptic
trends closely and not worth getting into mesoscale details at
this point.


.AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/
Issued at 1206 PM CDT Fri Apr 21 2017

Little impacts expected this period. Though mixing of north
northeast winds today and Saturday may push values above 12kts at
times in favored 16-23z time frames...overnight winds tonight
will be 4 to 8kts most areas. VFR high clouds blanket region today
through evening mainly south...with few035 to few060 expected
today/Saturday respectively. Otherwise no weather or significant
vis/cig issues expected. /rev




LONG TERM...Kotenberg
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