FXUS63 KDMX 201732
Area Forecast Discussion
National Weather Service Des Moines IA
1132 AM CST Tue Nov 20 2018
.DISCUSSION.../Today through Monday/
Issued at 341 AM CST Tue Nov 20 2018
Stratus across much of central and eastern Iowa is gradually
shifting southeast and eroding. A few flurries remain possible for
the next few hours as the stratus layer is near the dendritic zone.
Warm advection is beginning to approach from the west and will
overspread the state this morning and this warm advection will be
accompanied by another band of stratus, especially over northern
Iowa. High temperatures today will range from around 30 over the
northeast to near 40 west. An upper level system will pass to the
north and east of the area tonight and will drag a cold front into
northern Iowa and this will keep temperatures in the low 30s on
Wednesday in that area while low 40s are forecast south.
Stronger warm advection will arrive Wednesday night and into
Thursday as an area of high pressure settles over the Great Lakes
and low pressure organizes to the west. Expect that stratus will
again develop as saturation occurs below 2.5 kft. Several A
couple impacts possible Thursday. The first is stratus may linger
all day and keep temperatures well below guidance values. This
stratus developing in a warm advection regime could produce
drizzle, which is currently not in the forecast. Finally, it is
possible fog may develop. All of these potential factors do make
the confidence level in Thursday low to medium.
A short wave will arrive late Thursday night and Friday morning and
will bring another round of precipitation to Iowa. Confidence is
increasing that the precipitation type with this system will be
mainly rain as wetbulb values below 850 mb are generally in the 2C-
3C range which will result in rain. Saturday will be a transition
day as the short wave trough departs to the east and a stronger
system drops southeast into eastern Colorado and western Kansas.
Good agreement with the 00z guidance on this system evolving into a
closed upper low Saturday and Saturday night with strong lee side
cyclogenesis occurring during this time. That said, still the
typical spatial and temporal differences occurring at that range.
The sub-tropical high building north into the Gulf of Mexico could
certainly keep this system from shifting further south than
currently progged. In this case, the potential is there for a
significant winter storm to impact a portion of the Midwest with
snow and wind on a potential busy holiday weekend travel day.
Another cold snap is on track to follow this system early next
.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1131 AM CST Tue Nov 20 2018
Stratus on the leading edge of warmer air move in will produce a 3
to 4 hour window of MVFR cigs across TAF locations mainly from KMCW
to KDSM eastward. KFOD should only have these cigs through 19Z. VFR
cigs expected though northern TAF locations may see MVFR cigs return
after 08Z as a cold front drops across the state through 21/18Z.
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