Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 212023
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
323 PM CDT Mon Oct 21 2019

.DISCUSSION.../Tonight through Monday/
Issued at 321 PM CDT Mon Oct 21 2019

Surface low pressure over northwest Wisconsin and east central
Minnesota continues to deepen this afternoon and is currently near
987 mb. This system is currently to the northeast of the upper low
which is lifting northeast through northwest Iowa. A stronger
shortwave will wrap around the backside of the upper low later this
afternoon and evening and will cause the surface low to pull back
west then southeast in a bit of a Fujiwhara effect. The pressure
gradient will increase dramatically over northwest Iowa and later
into portions of central Iowa as this occurs with the pressure
gradient approaching 75 ubars/km. Cold advection will increase
during this time as well mixing deepening to near 850 mb. Peak winds
within the mixed layer will be near 55 kts at times.  The cold
advection is not strong enough to support max mixing efficiency of
these winds to the surface, the combination of the mixing and
pressure gradient will support wind gusts of 60 to 65 mph over
portion of northern Iowa mainly between 00z and 09z. Will be
monitoring for a potential southward expansion of the warning to
near Interstate 80 and the Des Moines metro. The wind will diminish
a bit on Tuesday but will remain in the Wind Advisory range much of
the day.

A few showers and thunderstorms have developed under the upper low
this afternoon over the northwest half of the state while a more
broad area of stratiform precipitation is further upstream. All of
this activity will continue to rotate east/southeast overnight.
Therefore it will be a rather unpleasant overnight with the
combination of precipitation and wind while temperatures fall into
the upper 30s to mid 40s.

A weak ridge of high pressure will arrive Tuesday night. The next
system will be quickly on its heels with precipitation chances
increasing across northern Iowa. While some light snow is possible
far north, by the time soundings saturate enough for precipitation
to occur, the boundary layer should have recovered enough for mainly
light rain. Another wave of cold advection will arrive Wednesday
night. Thursday and Friday will bring quiet and cool weather. Warm
advection will develop for Saturday in what looks like the warmest
day in the period with breezy southwest winds helping push highs
into the 60s. Some uncertainty beyond that period as the ECMWF/GEM
continue to insist on a closed upper low developing over Texas while
The GFS/Ensembles keep the system an open wave.  This will have
impacts on the area for the end of the period but generally keeping
the forecast for that period dry and cool.

&&

.AVIATION.../For the 18Z TAFS through 18Z Tuesday afternoon/
Issued at 1233 PM CDT Mon Oct 21 2019

Increasing winds today from the west to northwest especially
overnight with wind gusts near 50 kts possible over northern IA
and near 45 kts south. The wind will diminish a bit by late
Tuesday morning but gusts near 40 kts will remain possible. MVFR
cigs are expected much of the period with increasing showers this
afternoon and evening.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 4 PM CDT Tuesday for IAZ007-027-028-038-039-
044>050-057>062-070>075-081>086-092>097.

High Wind Warning until 10 AM CDT Tuesday for IAZ004>006-015>017-
023>026-033>037.

Wind Advisory from 10 AM to 4 PM CDT Tuesday for IAZ004>006-
015>017-023>026-033>037.

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon


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