Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 162338

National Weather Service Des Moines IA
638 PM CDT Sun Oct 16 2016

.SHORT TERM.../This evening through Monday/
Issued at 318 PM CDT Sun Oct 16 2016

Confidence:  Medium to High

Fog has finally lifted across the area with the slow advance of the
warm front this afternoon. Warm air advection and increasing
moisture transport will move across northern Iowa this evening with
a potential for some showers and isolated thunderstorms through 06z.
Then the focus returns to fog potential. The time of year...along
with unseasonably moist air and light winds will again combine to
produce areas of dense fog overnight.  Tonight as the western trough
moves east...winds will relax over the west enough and moisture
convergence will increase enough that fog and light drizzle will
increase toward 08-10z. Will go ahead and issue an FG.Y for western
areas from 07-14z tomorrow with potential for slow erosion during
the morning hours where winds are lightest in the west. Most of the
remainder of the region will either have winds too strong (10 to
12kts) or thickness too warm to support much fog. This would include
portions of central and southeast areas. Lows will vary from the 50s
northwest to the mid 60s in the southeast...very atypical over the
south for mid October as a more summerlike airmass remains for
another day.

.LONG TERM.../Monday night through Sunday/
Issued at 318 PM CDT Sun Oct 16 2016

Not much has changed in the overall pattern or forecast.  With a
deepening trough out West the Upper Midwest will be in a Southwest
flow pattern and we will see some record or near record temps in the
80s across the Southern two thirds of the forecast area on Monday.
It will also be very windy.  Forecast soundings showing 40kts of
wind atop the mixed layer.  During the afternoon a cold front
approaches from the Northwest as a weak shortwave rides across the
far North.  Coincident with all of this is a pretty good slug of
forcing coming across Southern MN into Northern IA.  For this
reason, slight chance pops for showers and thunderstorms were
expanded a little across Northern Iowa and nearest the MN border
chance pops were added.

A cold front is still expected to slide through the state Monday
night but with a Southwest upper flow, temps, while cooler, will
still be above normal on Tuesday. Mid 60`s to mid 70`s for this time
of year is pretty nice. Soundings are very dry so despite a frontal
passage the combination of weak forcing exiting the area early on...
and mainly North of our area...and lack of moisture will minimize
any chance of precip.

Likewise for mid-week, the deepening trough to the West shifts into
the plains buckling the flow and dropping colder air into the
region.  It will also increase precip chances across the
Southern/Southeast portions of the forecast area where better
forcing and moisture will reside.  Still precip chances are not
great and warrant only slight chances at this point.

For late in the week into the weekend...seasonal to slightly cooler
than normal temps to start with are expected with the passage of the
trough but temps will gradually warm through the weekend. Models
differ on whether a shortwave will drop through the flow mainly
impacting Northern/Northeast Iowa in the Thursday to Friday
timeframe. Current forecast is dry and with lower confidence that
far out, I was inclined to leave it dry until a model consensus
occurs.  Right now the Euro paints a wide swath of precip from
Nebraska into Illinois while the GFS has a sharper trough and precip
confined to Nebraska/Kansas.  Both solutions are viable it just
depends on how much the trough deepens.


.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 638 PM CDT Sun Oct 16 2016

A warm front is still lifting slowly northward across Iowa, while
a trough approaches from the northwest. Early tonight a few light
showers and possibly isolated thunderstorms will affect northern
Iowa as the front advances, but coverage and impacts will be very
low and will advertise only with VCSH at MCW and ALO. After
midnight and toward sunrise Monday, the stalling warm front and
approaching trough will result in the development of a col region
across northwestern Iowa with very light winds. Given the
unseasonably high dewpoints pooling along the warm front the
development of fog and stratus is likely, perhaps affecting FOD
and MCW and have maintained it in those 00z TAFs. On Monday
conditions will improve rapidly by late morning.


Dense Fog Advisory from 2 AM to 9 AM CDT Monday for IAZ004-005-



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