Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 210509
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1209 AM CDT Fri Apr 21 2017

.SHORT TERM.../Tonight through Friday/
Issued at 330 PM CDT Thu Apr 20 2017

The upper low approaching the Great Lakes will continue to lift off
to the Northeast through this evening.  As a result the stratus
shield over Iowa will gradually lift with it.  Satellite imagery
already showing Southern Iowa becoming more cellular and breaking up
and this trend should gradually continue Northward.  Flow will
remain North tonight then switch to the Northeast on Friday.  With
the Northerly flow and a clearing trend, lows tonight will be chilly
once again with mid 30`s North and lower 40`s South.  Highs on
Friday still generally in the 50`s.  Soundings and time/height cross
sections depict a brief period of increased low level moisture near
the surface as the last of the stratus lifts which may be
responsible for some patchy fog across the North.  Any fog that
develops would have minimal impact to visibility.

High pressure both at the surface and aloft will be in place Friday
and this will push a low that is developing over the Plains to the
South of the region.  Friday will be dry and cool with some high
cloud cover from the low shifting to the South but overall we should
see plenty of sun.

.LONG TERM.../Friday night through Thursday/
Issued at 330 PM CDT Thu Apr 20 2017

High pressure remains in control of the weather across Iowa thorugh
Sunday with a gradual moderation in temperatures through the period.
On Sunday a shortwave over the NW U.S. starts to push into the
Rockies and a surface low develops over Wyoming/Montana area with
a frontal boundary developing and pushing into the Upper Midwest.
During the day the low and frontal boundary pushes closer to Iowa
and switches the wind from the Northwest to the South.
Sunday/Monday should be the warmest days of the next 5 with highs
back in the 60`s and 70`s.

The shortwave and associated surface low push East across the
Northern Plains and Northern portions of the Upper Midwest bringing
a chance of showers mainly to Northern Iowa late Monday and Monday
night.

On the heels of this first shortwave comes another wave further
South.  This one will track across the Central Plains with a surface
low and frontal boundary developing near Missouri/Iowa and has the
potential to produce some showers and thunderstorms Tuesday/Tuesday
evening across all of the forecast area.

For the remainder of the forecast period the models are not at all
in any kind of consensus in handling a deep trough coming into the
Rockies and what to do with more subtle shortwaves ejecting out of
the base of the trough.  For now just kept the slight chance/low
chance pops across the region but I could see Wednesday and
Wednesday evening being dry before the trough pushes far enough to
the lee side of the Rockies to give us a better chance for
precipitation.  This trough will be responsible for a prolonged
period of showers and thunderstorms from Thursday into Saturday but
time will provide more clarity as to how this system will evolve.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1208 AM CDT Fri Apr 21 2017

Only very small patches of MVFR stratus remain at 05z with the
vast majority of ceilings VFR due to scattered 4kft clouds and
higher clouds streaming across the MO River into IA. Low level
relative humidities are still fairly high so there could be some
brief radiation fog, but have omitted for now without better
overall clearing. High confidence in VFR later Fri with nothing
beyond scattered mid/high clouds.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...FAB
LONG TERM...FAB
AVIATION...Small


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