309 
FXUS63 KDMX 141011
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
411 AM CST Wed Feb 14 2018

.SHORT TERM.../Today through Tonight/
Issued at 338 AM CST Wed Feb 14 2018

Southerly flow continued across Iowa overnight and while a large
area of high pressure remained over the far eastern CONUS.
Overnight temperatures remained in the 20s to low 30s across much
of central Iowa though a few locations across the state completely
dropped off into the teens and had fog develop, including Ames and
Iowa City to the east. Warm advection overnight around 925 mb has
created a significant inversion across the state. The inversion
will create a challenge with temperature forecasts for today as it
will be difficult to mix through much of the inversion with the
existing snow cover. Temperatures warmed better than expected on
Tuesday however, the mixing was also better than it will be today.
Therefore, have kept highs below guidance and mainly in the mid to
upper 30s north to mid to upper 40s south.

The primary challenge overnight will be fog potential. Higher dew
points will continue to advect northward. Dew points in the 30s
over the central and south moving over the current snow cover, combined
with additional moisture from the snow melt that will be trapped 
by the inversion, should help lead to fog development. The fog 
could potentially become dense.

.LONG TERM.../Thursday through Tuesday/
Issued at 338 AM CST Wed Feb 14 2018

The fog may linger into Thursday ahead of a boundary that will
move through the state late in the day and into the evening. High
temperatures will remain mild and in the 30s and 40s. The boundary
will move through and bring a chance of light snow far north in
the evening. Gusty northwest winds will follow with gusts over 30
mph likely. Friday will be much colder with highs in the teens and
20s. Warm advection will return this weekend with highs back into
the 30s for Saturday then the 30s and 40s for Sunday. The next
system to impact the state arrives Sunday night and Monday. Very
mild air may remain across central and southeast Iowa Sunday
night. Have increased Monday morning low temperatures but likely
will need to raise several more degrees if this pattern holds.
This system could bring a wide variety of precipitation to Iowa.
Precipitation could range from showers and a few thunderstorms to
snow northwest. The cooler air will remain into Tuesday with some
precipitation chances lingering east.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1130 PM CST Tue Feb 13 2018

Primary concerns through this TAF period will be fog development
tonight, low clouds arriving tomorrow, and then fog development
again toward the end of this period. Confidence is increasing 
that most of the patchy fog will be confined to northern Iowa with
perhaps some development over western Iowa where dewpoint 
depressions are generally less than 5 degrees. Within these areas,
MVFR visibilities will be possible. 

An area of stratus clouds has been progressing northeastward and
is currently nearing the I-70 corridor in Missouri. This should
reach southern Iowa mid to late morning and may produce a brief
window of MVFR ceilings before lifting. 

Another round of fog is expected to develop Thursday evening. 
While MVFR visibilities are mentioned at this point, further 
reduction in visibility will be possible with future TAFs.

One last note that low level wind shear mention was left out.
While flow is not purely unidirectional, wind speed difference
between the surface and 2000 foot wind remains below 30 knots.


&&

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

$$

SHORT TERM...Donavon
LONG TERM...Donavon
AVIATION...Ansorge