Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 252141
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
341 PM CST Sat Feb 25 2017

.SHORT TERM.../Tonight through Sunday/
Issued at 338 PM CST Sat Feb 25 2017

Confidence: High.

Little impactful weather through tomorrow. Water vapor imagery
shows two weak short waves moving east through the flow. An area
of mid level clouds over Nebraska and western Iowa will move east
tonight keeping skies generally cloudy during most of the
overnight hours. This will help hold temperatures in the teens and
20s over the area tonight. Along with cloud cover a small push of
warm air advection at H850 with an associated surface warm front
will help to keep mins from dropping too far. Once daybreak hits
the milder air will remain through the afternoon with southwest
surface flow over most of southern Iowa. Over the north a switch
to west winds will occur by afternoon Aloft the main area of
thetae advection will be northeast of the region with most of the
mid level clouds east of the state. This will allow for more
sunshine and milder temperatures...especially over the south where
lesser snowcover exits. With highs expected to reach the mid 40s
from I80 south...with upper 40s in the southeast it is likely that
a fair amount of Fridays snowfall will quickly melt away leaving
only a bit left for Monday into Tuesdays warmup.


.LONG TERM.../Sunday night through Saturday/
Issued at 338 PM CST Sat Feb 25 2017

Light Precip/Wintry Precip Potential... Tue-Wed
Confidence: Low-Med
Impacts: Very Minimal

WAA in place Monday as 850mb temps go from -5C or so on 12z Sun to
+0 to +3C by 00z Tue. With snowpack (though obviously much less
pristine than today) lowered temperatures a few degrees across the
north. This warming is in advance of somewhat of an overall nebulous
system(s) expected to impact the Midwest Tuesday through Wednesday.
The basis of Tuesday morning`s precip seems to be generally
thermodynamically-driven as a band of theta-e advection, primarily
noticeable near 850mb, is advected across Iowa. Overall ascent
processes are very marginal, and vertical cross-sections depict a
layer of dry air from 850mb to 700mb. So total QPF is very little.
P-type will be an issue Tuesday morning as temperatures near the
low 30s across our north. With a nod to the cooler 12z ECMWF plus
snowpack, left temps on the cooler side and kept light fz rain
mention across much of the north. Again, QPF will only be a few
hundredths, so confidence high that any ice accum will be well
under 0.05 inches.

Base of the longwave trough makes its push across the upper Midwest
on Wednesday morning. Models somewhat flip-flopping run to run
between having more of a closed sfc low, or an open-wave propagate
through central MN/northern IA. The ECMWF has been much more
steadfast with this feature, so slight lean towards it and its
northerly track with the low...suggesting more rain than snow/wintry
mix of precip across the DMX CWA Wednesday. By Wednesday afternoon,
low looks to be east of Iowa...commencing a period of cold/dry air
entrainment, large-scale subsidence, and strong winds.


Rest of the week...
Confidence... Low-medium

The region looks to stay in NW flow through Friday. Long-range
models slow to work in a 1035mb or so high by Late Thu/Early Fri.
The low from Tuesday-Wednesday is proggd to "bomb out" over the east
coast, which will help keep the pressure gradient up through Friday.
850mb temps by Fri am look to reach the -10C to -15C range...so lows
in the teens seem very reasonable. By next weekend, hints of a
thermal ridge building over the intermountain west and crashing over
Iowa...possibly bringing another shot of +10C to +15C 850mb temps to
Iowa...meaning highs back into the 60s and 70s. GFS fcst soundings
actually suggest legit fire wx concerns over Midwest next
weekend...but confidence is low at this time, however.


&&

.AVIATION.../For the 18Z TAFS through 18Z Sunday afternoon/
Issued at 1130 AM CST Sat Feb 25 2017

Main concern will be mixing winds today and again on Sunday.
Northwest flow still showing occasional momentum transfer this
afternoon to about 20 to 22z. Otherwise mid level warm air
advection expected to produce cloud deck overnight with light
southwest winds. Aft 15z Sunday winds again increase across the
region from SW at 12 to 18kts through end of period. /rev


&&

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

$$

SHORT TERM...REV
LONG TERM...Kotenberg
AVIATION...REV



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