Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 170855

Area Forecast Discussion
National Weather Service Des Moines IA
355 AM CDT Fri Mar 17 2017

.SHORT TERM.../Today through Tonight/
Issued at 325 AM CDT Fri Mar 17 2017

Any lingering low clouds or patchy fog early this morning over
the eastern part of the CWA will give way to ample sunshine as
winds become from the northwest and quicken bringing in drier air.
These quickening winds will develop by mid to late morning behind
low pressure moving across the state today. Have increased winds
above initial guidance and with excellent deep boundary layer
mixing, wind gust will exceed 30 mph over northern Iowa. As for
high temperatures, 850mb temperatures will be falling, but still
around 6 to 8C over southern Iowa by midday. With the good mixing,
this should easily yield low to middle 60s over these areas.
Farther north, residual snowpack and lowering 850mb temperatures
should limit high temperatures to the middle 40s to middle 50s.

By late today and tonight, winds will begin to subside as the low
pressure moves farther east and high pressure begins to slide out of
the Dakotas toward Iowa. Low stratus clouds currently over the
northern half of North Dakota as viewed in GOES data early this
morning are expected to drop into the northern half of Iowa by late
today and overnight.

.LONG TERM.../Saturday through Thursday/
Issued at 325 AM CDT Fri Mar 17 2017

Saturday through Monday. Confidence High. The initial portion of
the extended has come into better focus concerning the timing of
features and expected range of temperatures. The residual effects
of the colder air arriving this evening will linger into
Saturday...though a return to warmer air aloft and some mixing
will occur over the west half in the afternoon. This should aid in
some recovery in temperatures as a warm front develops to the
west. Highs on Saturday will range from the 40s in the north to
the 50s in the south. As a low pressure trough moves into the
northern Plains increasing clouds and moisture will spread into
the region Sunday. By Sunday a thermal ridge will be building into
Iowa just ahead of the trough with H850 temperatures reaching 11
to 15C over Central Iowa. This will boost highs into the mid 50s
northeast to the lower 70s in the south. A short wave moving
across the southern Plains will help develop a weak surface low
near the Colorado/Kansas border by 00z. This low is expected to
track to between Lamoni and Burlington by 06-12z with some small
differences between the Euro/GFS. Though instability will be
sufficient in either model to aid in thunderstorms during the mid
to late evening Sunday...there are some differences in the
location of the maximum low level jet overnight and where storm
initiation will occur. Soundings suggest elevated convection with
some potential for hail. The storm prediction center has outlooked
the southeast for a marginal risk of some large hail with any
storms that develop here. If the initiation is west enough to
fully develop storms over southern Iowa by 06z...there will be a
better chance of seeing storms with hail. Otherwise a later start
will favor storms more southeast of the forecast area over
northeast Missouri and Illinois. None the less it will need to be
watched for possible stronger elevated convection Sunday night
into very early Monday. After the very warm day Sunday...slightly
cooler air will push south on Monday but warm air aloft will
linger in the south. This will once again allow highs to reach the
lower 60s south and in the lower 50s north.

Tuesday through Thursday.  Confidence Medium.  Initially the
beginning of this portion of the extended looks quiet.  Cooler air
will arrive as high pressure builds south into Iowa and states east.
Some uncertainty exists regarding how quickly moisture will return
to the western half of the forecast area west of I35 Tuesday
afternoon or evening.  For now have removed any mention since there
is yet a strong signal in either the GFS or Euro. By Wednesday the
high will most likely slide just enough east to allow for a warm
front and thetae advection to increase chances for either light rain
or snow. Meanwhile a significant large scale trough will be entering
the west coast with a strong signal for an active end to next week.
The lead wave should be crossing the Rockies Thursday with a renewed
push of warm air advection and potential elevated thunder over the
area on Thursday. Initially rain and or light snow may precede the
threat for Thursdays showers and thunderstorms Wednesday night but
the expectation for a quick warming and quick transition back to
liquid may limit any chance for accumulations.  Still a long way out
and there is sufficient uncertainty. Much of this is the result of
differences between the GFS and Euro. The Euro continues to hold
onto a stronger open wave while the GFS is forecasting a less well
developed and slower wave.  Plenty of time to resolve the
differences. Temperatures should warm up Thursday in either case
given the fetch of southerly surface flow heading our way.


.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1135 PM CDT Thu Mar 16 2017

VFR conditions will give way to MVFR conditions as a surface low
pushes East across Iowa. Winds will diminish some as the surface
trough moves in though looking downstream they still remain around
10kts. Cigs should drop to between 2.5Kft and 3.5Kft. This is
higher than previously thought but again downstream the lowest cigs
are around 2.5Kft. Still expecting fog mainly North once the 40
dewpoints advect over the snow cover. Further South closer to the
low some patchy drizzle will be possible...mainly over KALO and
KOTM. All of this is expected between 09Z and 13Z. Winds become
Northerly behind the low and increase to 18g28kts aft 15Z.




SHORT TERM...Ansorge
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