Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 112315

Area Forecast Discussion
National Weather Service Des Moines IA
615 PM CDT Sun Mar 11 2018

.SHORT TERM.../Tonight through Monday/
Issued at 317 PM CDT Sun Mar 11 2018

Day Cloud Phase Distinction RGB from GOES-East shows plenty of
clouds over the western part of the state with breaks in the clouds
over south central Iowa with even more sunshine over southeast Iowa
at 230pm. However, to the north and west GOES imagery shows plenty
of clouds with a back edge from International Falls, MN to near
Aberdeen, SD to near O`Neill, NE. Therefore, any peeks of sunshine
or clear sky this afternoon or early this evening will give way to
clouds as low stratus moves over the state. Beneath the stratus,
question is whether there is enough moisture depth and lift for
freezing drizzle or squeeze anything out. Cross sections and
soundings from the NAM and RAP and less so with the GFS show low
level saturation around 1km with dry air above this moisture.
However, lift is quite weak with a microbar/second or so at best.
Therefore, will keep the forecast dry overnight at this time.

The clearing edge of the clouds will reach the northwest part of the
forecast area after midnight and move southeastward through the
remainder of the night into Monday morning. Much of central Iowa
will have ample sunshine by late morning at the latest. While an
upper level trough will begin to develop over the eastern US on
Monday, this will keep Iowa within a northwest flow regime as a
surface high pressure approaches from the Dakotas. Winds may perk up
a bit late in the morning into the afternoon being sustained at 10
to 20 mph. Sunshine will help to warm temperatures tomorrow as 850mb
temperatures maybe rise 1 or 2C. Highs will range from the the low
30s near the Minnesota border to the 40s over central and southern

.LONG TERM.../Monday night through Sunday/
Issued at 317 PM CDT Sun Mar 11 2018

Upper ridging will commence to the west while over the Great Lakes a
deep trough will set up.  A shortwave dropping down the Great Lakes
low will buckle the flow over the Upper Midwest and while we will be
dry...we will be slowly moderating in temperature through Tuesday
and perhaps Wednesday as well.  All models move the upper ridge east
but only so far as the Rockies which still keeps our area in a deep
northwest flow.  By late week the upper ridge moves over the Upper
Midwest but now the Euro brings a system further into the west
coast/Rockies that breaks down the ridge somewhat.  While we will be
warmer for the end of the week...there is about a 10 degree
difference in the MOS output for highs between the Euro and the GFS
as a result of this change in the Euro.  The Canadian model is still
similar to the GFS.  The result of this was that I knocked highs
down several degrees, especially on Friday to account for some
modification to the ridge.

The next chance for precip is still in the Friday timeframe as all
models bring a shortwave across the Plains...the intensity of which
varies greatly.  In addition to the upper level feature, a surface
low will develop over the Plains with a frontal boundary extending
somewhere across Missouri or Iowa which will move across the region
through Friday.  There is some weak instability with this Friday
system as well and I tried to indicate this with the use of more
convective wording with respect to precip.  Showers were indicated
where during times of better instability.

On Sunday a stronger low moves in from the west coast and into the
Plains by Sunday evening.  A decent surface low develops with this
system though at this timeframe the models are all over the place
with where these features set up.  We`ll likely see widespread
precip develop with this Sunday night through Monday morning.  At
this point, temps look warm enough for rain during the day and
likely a mix across at least northern locations at night.  We will
need better clarity from the models before defining specific details
on ptype.  Temps will at least be spring-like with highs in the
upper 40s north to around 60 south and lows in the 30s and 40s.


.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 615 PM CDT Sun Mar 11 2018

Main challenge will be continued stratus overnight and increasing
winds Monday aft 14z. Upper level system pulling out but area of
low level moisture remains trapped w/i the boundary layer. A few
breaks in the MVFR deck showing up near KDSM at 23z but solid
shield of MVFR/at time IFR remains over much of the region. This
will slide southeast through 12-14z Monday...keeping most of the
area within MVFR/IFR overnight. Will likely see improvement 10-12z
at KFOD/KMCW then southeast thereafter. Winds will increase from
the northwest aft 12-14z with mixing gusts to 18-24kts through
near end of period as VFR conditions return. /rev




SHORT TERM...Ansorge
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