Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 221006
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
406 AM CST Wed Feb 22 2017

.SHORT TERM.../Today through Tonight/
Issued at 258 AM CST Wed Feb 22 2017

Confidence: High. Main theme today will be warmth once again.
Near to record highs expected across the area today. Though some
mid to high level clouds likely over the north through the
morning/early afternoon hours... getting such a warm start today
that even the north should near 60 by the afternoon which will
eclipse records there. Over the central and south...pre-frontal
warming aloft to 14- 15C over the southeast will likely push highs
into the mid 70s there with lower 70s across the I80 corridor.
This will be the last day of our extraordinarily warm weather for
February and will mark the 7th day in a row that Des Moines has
been in the 60s/70s. Models remain in good agreement today that a
cool front will drop southeast of the region by 00z this evening
with lower clouds increasing from the northwest overnight as
colder air settles across the region. Though the term is
relative...tonights lows will still be quite pleasant for this
time of the year with upper 20s far northwest to the mid 40s in
the far southeast. Winds today will increase to 15 to 20 mph from
the south/west with the frontal passage and over the
northwest...about 15 to 25 mph by the afternoon hours. Tonight
northwest winds will drop to 8 to 15 mph over the area. No
precipitation is expected though with increasing isentropic lift
to our west and southwest overnight tonight...shower chances will
be increasing over the south by 12z and into the morning hours.

.LONG TERM.../Thursday through Tuesday/
Issued at 258 AM CST Wed Feb 22 2017

Showers will develop throughout Thursday and become widespread
across Iowa as isentropic lift proceeds a trough of low pressure
over the Rockies. This trough will help in the development of a
surface low over western Kansas. Low pressure tracks have been
varying among the models over the past several days as they
typically do. In this instance, this could be a result of
southern stream energy that the models may be having difficulty
resolving how exactly it will interact with the main
trough/northern stream energy. Overall, this model cycle found
the low tracks farther south and perhaps a bit slower compared to
the 12z models.

As the low approaches Iowa Thursday night, some elevated
instability will exist over the southern half to southern 2/3rds
of Iowa. MUCAPE values are marginal so while there may be some
thunder, not much confidence in anything more than that. Farther
to the northwest, cold air will begin to wrap around the low and
the transition from rain to snow will begin over northwest Iowa
Thursday night. Soundings continue to indicate that the cold air
will come in fast enough that sleet/freezing rain will be very
limited if non-existent and have kept mention of these
precipitation types out of the forecast.

As the low moves through the state on Friday, the dry slot will
reach southern Iowa bringing a brief dry period. However, as the
low moves east towards the Great Lakes, the precipitation
transition will work its way to the southeast. Winds will increase
on Friday with sustained winds averaging 15 to 25 mph. Over
northern Iowa, confidence is growing in wind gusts over 40 mph.
With the gusty winds and falling snow there, blowing and drifting
snow will likely have a significant impact on travel over at
least the far northern part of the state late Friday into Friday
night. With the snow gradually tapering off after midnight Friday,
have extended the Winter Storm Watch until that time. Snowfall
was shifted a bit south with models tracks farther south and
therefore added a few counties to the south and east of the
existing counties of the watch.

In the remainder of the long term period, travel impacts may
linger into the first part of Saturday before gusty winds abate as
high pressure begins to move in allowing the pressure gradient to
relax later in the day. Saturday will be rather cold, especially
with all the recent very warm weather. Otherwise, primarily zonal
flow will set up over the state into early next week. Confidence
is low beyond Saturday as several weak, fast-moving short waves
pass through the region bringing chances of precipitation of which
the type will be dependent on the exact track.

&&

.AVIATION.../For the 06Z TAFS through 06Z Wednesday night/
Issued at 1141 PM CST Tue Feb 21 2017

Potential for LLWS early with strong inversion in place around
1500 ft agl. Otherwise generally VFR through the period though
localized fog may occur far north near KMCW and southeast in
vicinity of KOTM. Breezy southwest to west winds on Wednesday will
diminish shortly after sunset.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Thursday evening through Friday
afternoon for IAZ004-005-015-023.

&&

$$

SHORT TERM...REV
LONG TERM...Ansorge
AVIATION...Donavon


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