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Area forecast discussion 
National Weather Service Des Moines Iowa
1142 PM CST Tuesday Jan 27 2015

Short term /tonight/...
issued at 338 PM CST Tuesday Jan 27 2015

Central Iowa will be in between the departing surface high and a
surface low developing over the plains. The main forecast problem
will be that of clouds and temperatures tonight. Low clouds were
persistent across the north and east today indicating a fair amount
of low level moisture. As the low moves in warm advection will
increase tonight and the winds will increase which means there will
be better mixing than what occurred today however soundings are
showing a Big Warm nose aloft creating a very big inversion which
will be tough to break. As such the low level moisture should
remain trapped and thus cloud cover should remain for tonight. The
question is will there be enough mixing to perhaps thin the
overcast. Furthermore...if the low clouds persist temperatures will be
warmer but if we clear or thin out then temperatures should cool a bit.
The southeasterly flow should prevent temperatures from being too cold. At
this point given the persistent cloud cover already and the expected
inversion I kept cloud cover in across the north central and
northeast and kept the southwest mainly clear. With the warm
advection expected overnight I kept temperatures on the warmer side of
guidance and nudged them up a bit across the north Central/Northeast
due to cloud cover. Fog should not be an issue tonight due to
increasing wind.

Long term /Wednesday through Tuesday/...
issued at 338 PM CST Tuesday Jan 27 2015

Amplified pattern currently in place with large eastern trough and
western ridge. Upper low is sliding up the backside of the ridge
across California and will provide the next threat of
precipitation on Wednesday night. Prior to the arrival of that
system...thermal ridge will build into the state on Wednesday with
another very warm day. Only issue will be cloudiness in the far
north and east from low status in moist layer beneath the
inversion. This will limit overall highs there but in the
southwest...highs approaching 60 seem likely. Forcing will be
ongoing throughout the day...although with very limited moisture
little saturation is expected. However...with the arrival of the
wave on Wednesday night and the enhanced lift across the
north...anticipate some patchy drizzle into the early morning
hours before strong cold advection takes over and a transition to
some freezing drizzle seems likely before ending by daybreak on
Thursday morning. Little if any precipitation is expected in
central or southern areas during this time. Strong northwest winds
are forecast into Thursday and may need a Wind Advisory with wind
gusting to 45 miles per hour or so seeming likely.

Focus then will shift to another system passing through the
southwest United States. This upper low will pull ample moisture
northward toward the Midwest. Meanwhile...a wave moving south from
Canada will begin to interact with the southern stream system
enhancing lift across the state. While the 12z GFS has backed off
on precipitation over Iowa...the Euro continues to indicate a
generous snowfall across much of central Iowa from Saturday
afternoon into Sunday morning. There is some concern about
precipitation type on Saturday across southern Iowa where near
surface temperatures may be warm enough for some rain...but
synoptic cooling and eventually near surface cold advection will
transition all precipitation to snow by Saturday evening in the
south. Given model quantitative precipitation forecast from the Euro of close to three-quarters of
an inch...moderate to possibly heavy snow amounts seem reasonable
by midday Sunday. The GFS does give some reason for pause but will
at least highlight the potential of moderate snow accumulations in
the severe weather potential statement at this point. Thereafter...a surge of cold air will push
into the state with temperatures returning below normal after a
two week hiatus.


issued at 1140 PM CST Tuesday Jan 27 2015

IFR to MVFR stratus expected to impact all sites tonight in
addition to some visibility restrictions due to fog. Currently stratus
is just east of kfod and kdsm but should shift slightly west.
Some breaks over the south on Wednesday but stratus likely will
linger north. A frontal boundary will begin to arrive late
Wednesday and will bring another area of IFR or lower ceilings to
northern Iowa by 06z. Breezy southeast winds becoming northwest with frontal passage


Dmx watches/warnings/advisories...


Short term...fab
long term...cogil

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