Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 250028

National Weather Service Des Moines IA
628 PM CST Tue Jan 24 2017

.SHORT TERM.../Tonight through Wednesday/
Issued at 321 PM CST Tue Jan 24 2017

Heavy snow band will continue to press northward and expand
across northern to northwest portions of the forecast area through
the rest of the afternoon and into this evening. Models are in
very good agreement with timing of the precipitation and the
location of the low track through tomorrow and utilized a blend of
the hires models and GFS/ECMWF.

Significant pressure falls (near 6 mb in past 3 hours ending at 20z)
over northern Missouri with the low centered over Cameron to
Chillicothe. Heavy snow band advecting northward oriented from Storm
Lake eastward through Waterloo area. Expecting this heavy band to
slowly transition north and pivot itself oriented more southwest to
northeast from around Sac City to Mason City area this evening. This
matches up well with the strong frontogenetical forcing between 600-
650mb through around 03z tonight. Huge omega (-20 ubar/s) bullseye
within the dendritic layer this afternoon into this evening over
northern Iowa with some negative EPV present leading to some upright
convection and possibly a brief stint of thundersnow. This will
enhance snowfall rates to near 2-3 inches per hours this evening
within the warning location. A slight shift northward with the
southern fringe of the heavy band and have a very sharp snow
gradient between the Warning and Advisory locations. Some counties
along Highway 30 may see several inches in the north while the
southern parts likely just a dusting. The sharp gradient extends
northeast toward Waterloo/Marshalltown area with the dry slot
punching into the southeast this evening.

Overnight tonight, the deformation zone develops on the backside of
the surface low over northwest to north-central Iowa. The forcing is
weaker within the dendritic layer but strong QG forcing should keep
the light to moderate snowfall going through at least 15z Wednesday.
The ECMWF/GFS continue light snow throughout the day tomorrow with
winds atop the mixed layer near 35 to 40 knots. Hence, with the
falling snow throughout the day tomorrow but questionable if the
winds will be strong enough to cause blizzard conditions. Something
to continue to monitor for northern Iowa tomorrow. Regardless,
travel conditions will be very hazardous due to the blowing snow and
snow covered roads. One caveat is the NAM and even the GFS suggest
some of the soundings in the location of southern edge of the snow
band over northern Iowa lose ice introduction for a short while
tomorrow morning. This would lead to the potential for freezing
drizzle and thus cutting down snow amounts slightly. However, it`s a
short period and mainly just the NAM suggesting this trend, so left
out mention attm.

.LONG TERM.../Wednesday night through Tuesday/
Issued at 321 PM CST Tue Jan 24 2017

The winter storm will be pulling away from the region as low
pressure moves over the Great Lakes with the deformation zone
hanging back over Iowa at the start of the long term period. Brisk
breezes from the northwest will accompany the lingering snow causing
areas of blowing snow overnight Wednesday. Blowing snow is expected
to be rather limited during the daylight hours as most of the snow
should be over by that time. Winds will lessen through the day
Thursday as well.

From Thursday into early next week, a prolonged period of north or
northwest flow will prevail. During this time, several short-wave
troughs and PV anomalies will pass over the area with chances for
flurries or light snow. The strongest PV anomaly will move through
later Saturday into Sunday so that will be the best potential for
some snow, but nothing like the ongoing mid-week winter storm.
Considered lowering lows Friday morning due to new snow pack and
cold pool moving overhead, but with cloud cover may not see the good
cooling that sometimes occur after a winter event. Otherwise, high
temperatures will be around long-term climatological norms with lows
a bit above.

The next PV anomaly is set to move into the region by late Monday
into Tuesday with low pressure dropping out of Canada into the Great
Lakes. At this time, precipitation looks to be more focused north of
the area, though parts of northern Iowa could be brushed as the
system passes.


.AVIATION.../For the 00Z TAFS through 00Z Wednesday evening/
Issued at 620 PM CST Tue Jan 24 2017

Heavy snow with LIFR visibilities of <=1/4SM were occurring along
the MN border and this should persist through the evening.
Farther south widespread IFR conditions were in place with more
spotty snow and MVFR toward the MO border. Stratus, snow and
blowing snow restrictions should keep conditions <=IFR through
much of Wed as well with low pressure tracking from northeast KS
at 00z to near the IL/WI border by 18z Wed. NW winds will increase
and become somewhat gusty by this time as well with some blowing
snow restrictions.


Winter Weather Advisory until 6 PM CST Wednesday for IAZ038-039-

Winter Storm Warning until 6 PM CST Wednesday for IAZ004>007-



SHORT TERM...Podrazik
LONG TERM...Ansorge
AVIATION...Small is the U.S. government's official web portal to all federal, state and local government web resources and services.