Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 222321

National Weather Service Des Moines IA
621 PM CDT Sat Oct 22 2016

.SHORT TERM.../This evening through Sunday/
Issued at 316 PM CDT Sat Oct 22 2016

Weak surface ridging exists over the state this afternoon with
very pleasant fall conditions. Will see ridge slide east this
evening with weak southerly flow developing ahead of approaching
shortwave and associated front. The bulk of forcing will remain
well north of Iowa with this system tonight and even the weak
forcing that will exist across the state overnight will work on a
very dry airmass. Therefore, little in the way of precipitation or
even cloudiness for that matter is expected tonight as the system
approaches. Temperatures are a bit tricky as there will be warm
advection ongoing but clear skies and relatively light winds
promoting radiational cooling. Readings should be at least a few
degrees warmer than last night just with the warm advection alone
and have trended the lows in that direction.

.LONG TERM.../Sunday night through Saturday/
Issued at 316 PM CDT Sat Oct 22 2016

The main forecast concern continues to be the system in the
Tuesday/Wednesday time frame then a weak system for next Saturday.

Beginning late Monday night both the Euro and the GFS show a subtle
shortwave over the front range of the Rockies with a corresponding
surface low over the area.  The Euro has the low a little further
East than the GFS thus the attendant warm front nosing into Iowa
about 6 hours earlier.  While the best forcing is still West of
Iowa...some does move into the northwest with an area of theta-e
advection moving west to east across the state overnight.  For now I
kept the slight chances going across the northwest but could
certainly see a little more widespread precip across the west.

Then during the day Tuesday through Tuesday night the shortwave
intensifies as it moves across the state even through Wednesday
morning.  At the same time the surface low lifts across Iowa lifting
the warm front across the state and into southern MN by Wednesday.
Theta-e advection increases across the north and east Tuesday
afternoon and we should see thunderstorms breaking out by the
afternoon through Tuesday night.  Instability and shear aren`t
overly impressive and the time of day should limit the severe
potential however both models have over an inch of qpf across
northern Iowa.  Heavy rainfall is already mentioned in the HWO and
will remain in that product.

During the day Wednesday the surface low shifts into eastern Iowa
along with the upper trough.  There will still be a chance for
lingering showers central and east but overall precip trends will
be diminishing through the day.

The upper ridge then rebuilds into the central Plains late in the
week for warming temps Friday but another shortwave moves into the
region Friday night.  The Euro is much more pronounced with this
feature than the GFS and as such the GFS confines precip to the
South while the Euro spreads it across the state...albeit very
light.  At this point confidence is too low in any one solution and
the model blends are still keeping the weekend mainly dry.  I
suspect pops will increase in area in later runs but at this point
it is a long way out and models have too much variance.


.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 620 PM CDT Sat Oct 22 2016

Light winds tonight will switch and become northwesterly and breezy
late Sunday morning and into the afternoon. Mostly clear skies are
expected throughout.




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