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Area forecast discussion 
National Weather Service Des Moines Iowa
1147 PM CST Sat Nov 28 2015

issued at 1137 PM CST Sat Nov 28 2015

Updated aviation for 06z tafs below.


Short term /tonight/...
issued at 335 PM CST Sat Nov 28 2015

Surface ridge gliding across northern Iowa this afternoon will
remain in place overnight as a weak wave lifts northward into the
region. Weak forcing associated with the wave will help bring light
precipitation into southwest third of the forecast area tonight.
Precipitation type across the south appears to be in the form of
freezing rain overnight with elevated warm layer although this layer
diminishes farther north into central portions of the state and a
mix of light freezing rain and ice pellets may be more common. Any
precipitation will be fighting dry low level air moving southward
from the center of the high and this will limit overall
precipitation amounts with highest amounts near Missouri border.
Some minor ice accumulations will be possible in the far southwest
where precipitation amounts will be greatest and have gone with Winter
Weather Advisory for these accumulations. Otherwise...will likely
see temperatures fall quickly this evening across the north half of the
forecast area where clear skies and light winds will lead to fast
cooling. However, as clouds move back in overnight...readings will
level off and may even rise a few degrees.

Long term /Sunday through Saturday/...
issued at 335 PM CST Sat Nov 28 2015

Main concern for extended will be at beginning of period with
large low pressure system expected to push across Iowa Monday
bringing chances for a wintry mix of precipitation to the area.
Models are in fairly good agreement with system...though have
trended slightly slower and further east with precipitation
chances. Have therefore trended forecast accordingly...with best
precipitation chances Monday...generally towards European model (ecmwf) solution.
Forcing with system is sufficient...though not robust...and best
forcing remains confined to lower levels. Therefore...still a lot
of uncertainty with system in timing and placement of heaviest
precipitation...precipitation amounts as well as precipitation
type. Given uncertainties...have kept snow amounts near lower end
of guidance...though latest guidance has come in under going
amounts...with more of mixing precipitation type....which becomes
main concern with system.

With onset of precipitation expect temperatures aloft to be warm
enough to limit ice introduction and with surface temperatures
near freezing Sunday night may see period of freezing rain across
much of the area...persisting into Monday especially in the south.
Models also keep ice introduction limited through Monday...though
surface temperatures will warm across the south and expect a
change over back to rain. However...may see a wider zone of
freezing rain...or wintry mix with elevated warm layer warm enough to
partially melt ice which may be introduced...further to the north.
With track of low still uncertain have kept precipitation type
more mixed...though have increased ice accumulations slightly in
the south. Will need to monitor system for icing potential...with
potential for ice introduction to remain limited throughout much
of Monday. Expect precipitation to finally change over to all snow
by Monday night before system pulls out Tuesday. Have issued
Winter Storm Watch for area in which highest snowfall totals are
expected and a bit further to the south and east to account for
potential shifts in track. However...could pull watch further to
the south with icing potential...especially into southwestern County Warning Area.
However...given ongoing Winter Weather Advisory in this area
overnight tonight will leave out of watch at this time.

For middle week system pulls out with dry conditions expected beyond
Wednesday. Temperatures beyond period will be generally
persistent...with slightly warming temperatures into next
weekend. Expect temperatures to be above normal for early


issued at 1137 PM CST Sat Nov 28 2015

Expecting VFR conditions to continue at all terminals the
remainder of the night and through most of the day on Sunday.
Middle-level clouds continue to increase over the region although
ceilings should remain VFR. Radar mosaic continuing to indicate areas
of -fzra/pl over southern Iowa. While kdsm/kotm could see a brief
period of wintry precipitation...impacts should be minimal. After 00z on
Monday...a stronger storm system will approach the area. Expect
ceilings to fall into the MVFR category...possibly IFR towards o6z.
Precipitation coverage should also increase...and decided to include a
period of -fzra at kdsm and kotm. However...some fine tuning of
this forecast will likely be needed.


Dmx watches/warnings/advisories...
Winter Storm Watch from Monday morning through late Monday night
for Adair-Audubon-Boone-Calhoun-Carroll-Cass-Cerro Gordo-
Hardin-Humboldt-Kossuth-Palo Alto-Pocahontas-SAC-story-Webster-

Winter Weather Advisory until 6 am CST Sunday for Adams-Decatur-



short term...cogil
long term...awb

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