Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 222205
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
405 PM CST Wed Feb 22 2017

.SHORT TERM.../Tonight through Thursday/
Issued at 404 PM CST Wed Feb 22 2017

Surface boundary has been passing through Iowa this afternoon
after another day of record warmth. However, the polar surge is
still in the Dakotas into central Minnesota and this will be
arriving later tonight, along with lower clouds. However, forcing
and deeper moisture do not arrive until later Thursday with
surface low deepening in western Kansas. Will begin to see
isentropic lift increase through the day along with increasing
convection instability in the south, albeit elevated. Anticipate
precipitation to begin to develop in the south by afternoon north
of the surface front and may begin to see some thunder as well.
Farther north, frontogenetical forcing near the Minnesota border
should help in increasing lift and precipitation potential in the
NW by later in the afternoon. Temperatures will be slow to recover
on Thursday with best recovery in the south where the cool air
will be most shallow.

.LONG TERM.../Thursday night through Wednesday/
Issued at 404 PM CST Wed Feb 22 2017

Bulk of forcing and action arrive Thursday night into Friday.
initially, convection will be of concern with instability axis
lifting into southern Iowa by early evening. Showers and some
thunderstorms will expand in this area during the evening with the
potential for a few severe storms, primarily from large hail. This
convection will ride northeast on the nose of the dry slot which
will be punching toward the state overnight, entering the
southeast by daybreak. Meanwhile, strong frontogenetical forcing
will exist across northern and western Iowa overnight providing
strong lift with precipitation expanding quickly during the
evening. Transitions to snow will begin in the NW forecast area
during the evening with synoptic cooling with the strong forcing
plus the drawing in of cooler air from the north as winds increase
from the north and northeast. This transition zone will slide
gradually southeast overnight but generally remain north of
highway 3.

Friday will see intense forcing across the northwest half of the
forecast area with strong frontogenetical forcing. In addition, QG
forcing will also be strengthening with the arrival of the upper
low. Near surface cold advection will push the rain/snow line to
southeast through the day as the surface low moves into eastern
Iowa. Moderate to heavy snow in the northwest will spread
gradually east during the day with moderate to heavy
accumulations. The rain in the southeast will transition to snow
by evening with only light accumulation, generally less than an
inch in the southeast 1/3 of the forecast area. Winds will crank
up later Thursday night and continue into Friday with the
increasing cold advection and tightening pressure gradient.
Soundings in north/northwest Iowa were all showing a period of
40-50kts at the top of the mixed layer Friday into the early
evening. This will likely push wind gusts toward 35-40 mph at the
surface and the potential for blizzard conditions exists,
especially in the far northwest where the snow will be a bit
drier. Have upped the headline to a blizzard watch in those
locations. Total amounts of near a foot will be possible near
Estherville with 5-7" on the southeast side of the winter storm
watch. Conditions will slowly improve on Friday night as the
system begins to exit to the east and forcing wanes. Winds will
remain brisk with some lingering blowing and drifting snow.

There will remain the threat of a few other systems during the
extended period with temperatures more seasonal, but still above
normal.

&&

.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1134 AM CST Wed Feb 22 2017

VFR conditions will remain widespread through this afternoon as a
frontal boundary passes through the state. Modest southwest winds
will become west northwest behind the boundary during the
afternoon as it moves southeast through Iowa. Cooler air will
spread into the state tonight with low ceilings spreading from
north to south during the night. MVFR to localized IFR ceilings
can be expected after the clouds move in until the end of the
forecast period. Surface winds will eventually switch from
northwest to northeast as low pressure develops across Colorado.
Precipitation is also expected to begin around the end of the
forecast period but is not reflected in the current TAF issuance.


&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Thursday evening through Friday evening
for IAZ007-016-033.

Winter Storm Watch from Friday morning through Friday evening
for IAZ017-024-025-034-035-044-045.

Blizzard Watch from Thursday evening through Friday evening for
IAZ004>006-015-023.

&&

$$

SHORT TERM...Cogil
LONG TERM...Cogil
AVIATION...Cogil



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