Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 011136
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
636 AM CDT Sat Oct 1 2016

.SHORT TERM.../Today/
Issued at 331 AM CDT Sat Oct 1 2016

A stacked low pressure system will remain nearly stationary over the
lower Great Lakes region today, resulting in little change in
sensible weather across Iowa. Skies will remain cloudy with light
generally north winds as a surface ridge lies draped over Minnesota
and the Missouri River valley just to our west. The clouds will
prevent any significant rebound in temperatures with highs expected
generally in the mid to upper 60s. Regional radar indicates a few
light showers moving around the western quadrants of the large low
pressure system and spreading slowly westward. These showers may
impact our eastern counties this morning and have maintained some
low POPs accordingly, but nothing of any impact is anticipated.
Otherwise just occasional/patchy drizzle such as was observed around
the Des Moines metro overnight with little to no accumulation.
During the afternoon rising cloud heights and drier air just above
the surface should diminish precipitation chances and result in a
day much like Friday.

.LONG TERM.../Tonight through Friday/
Issued at 331 AM CDT Sat Oct 1 2016

Some concerns already early in the period tonight.  Though cloud
cover will be the primary weather element through midnight...the
departure of the upper level low and little surface flow along with
plenty of boundary layer moisture will lead to fog over the area late
tonight into Sunday morning. Some uncertainty exists as to how much
clearing will take place...but any clearing should quickly lead to
fog development due to radiational cooling. Have included patchy
wording for now...and will have day shift evaluate any need for potential
more widespread wording...drizzle and possible headlines. Brief ridging
aloft is expected to take place Sunday night into Monday. Along with
that some stratus may redevelop in the cull between the two systems
as airmass will not change much through Monday. Model and guidance
along with Bufkit soundings show potential for drizzle and some
fog Sunday morning and perhaps a few isolated very light showers
Sunday afternoon over the south. Once the stronger western trough
arrives...surface mixing and warm air advection will allow temperatures
to increase both Monday and Tuesday with Tuesday potentially seeing
lower 80s across the south as mixing allows for warmer afternoon
highs and breezier conditions both days. Confidence lowers slightly
on details Tuesday into Tuesday night/Wednesday... though overall
evolution of upcoming system remains intact. The Euro is preferred
over the GFS as the GFS faster and generally has a fast bias
toward days 4-5. Initially some moisture transport into western
areas Tuesday morning may result in isolated showers or thunderstorms
west. The slower Euro suggests that the chances for any organized
convection remains quite low. While the GFS is nearly 6 hours
faster than the Euro...it too diminishes MUCAPE quickly by 06z and
mostly west of our area. However with the GFS being faster...and
rather high low level helicity along with some overnight cape would
suggest the potential for some severe potential. For now will lean
toward the Euro until better consensus is realized. After a warm
Tuesday...another push of cooler air will arrive in the Midwest
later on Wednesday into Thursday. The models begin to diverge
somewhat by weeks end though trends are similar. Both the GFS and
Euro bring a shot of colder air into the region...with the Euro
farther south into Iowa. This may lead to lows in the lower to mid
30s both by Friday and Saturday morning of next week. Since
confidence is low...a blend of previous guidance has been used for
now. After the midweek system dry weather will return for the end
of next week.

&&

.AVIATION.../For the 12Z TAFS through 12Z Sunday morning/
Issued at 636 AM CDT Sat Oct 1 2016

Low clouds will persist for most of the next 24 hours, along with
occasional drizzle/light rain. Ceiling heights will remain mostly
MVFR this morning, possibly briefly IFR at ALO/DSM/OTM, gradually
lifting toward VFR by the afternoon. There is some question as to
how much scattering out may occur late in the day, especially
toward FOD, and this could lead to some fog development tonight
along with remaining ceilings lowering once again. Have trended
the 12Z TAFs that way but details will need to be refined in
subsequent issuances.

&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...REV
AVIATION...Lee



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