Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 081744

National Weather Service Des Moines IA
1144 AM CST Thu Dec 8 2016

.SHORT TERM.../Today through Tonight/
Issued at 330 AM CST Thu Dec 8 2016

The large low pressure gyre over eastern Canada is extending its
cyclonic influence across the Great Lakes and upper Midwest, but
will begin to move off to the east today. In its wake a surface high
pressure area will steadily build into Iowa from the west by
tonight, reinforcing the cold airmass in place across our forecast
area. This morning scattered clouds are producing light flurries at
times, mainly in our northern counties, and this should continue
through midday before tapering off in the afternoon.

.LONG TERM.../Friday through Wednesday/
Issued at 330 AM CST Thu Dec 8 2016

Large area of sfc high pressure stretching across the central US to
dominate the region Friday with an upper level wave moving into the
western US. Weak little wave to move through Friday evening in the
fast westerly flow across the area which could result in a few
flurries across northern IA. Otherwise temps moderate a bit with
return flow setting up into Friday night/Saturday in advance of the
wave deepening as it shoves east from the northern Rockies. This set
the stage for a series of waves to quickly push east through the
period this weekend. The first to move through Saturday into
Saturday night with a developing area of low pressure along the
front range of the Rockies. This places IA into the waa region ahead
of the low with strong southerly flow off the gulf and lots of
moisture streaming northward. Strong lift and moisture associated as
the wave moves through...and therefore still expect a decent snow
event across the CWA for Saturday into Saturday night. Cross-
sections also indicating some potential for enhanced snow
rates/banded snow across northern IA into Saturday
afternoon/evening. Could see snow rations approach 15 to 18 to 1 at
times in northern IA, which should lead to some moderate
accumulations. Currently have around 3-5 inches for the northern
third of the CWA with snow moving in Saturday morning and exiting
late Saturday evening into the overnight hours.

Next wave comes on the heels of the first wave moving through Sunday
into Sunday night. This wave not quite as strong, thus only minor
additional snow amount expected into Sunday. Some uncertainty as the
path of the more decent swath of snow with this second system, with
the GFS taking it further south across southern IA and the EC
keeping it a bit further north. Either way could end up with about
an additional inch to maybe 2 inches of snow through the day Sunday.
This system to quickly push out Sunday night, with a brief reprieve
from precip Monday. Monday night into Tuesday next arctic blast to
come barreling southward through the state, with the parent broad
upper low spinning across central Canada. This will likely bring
another bout of light snow to much of the state. Will have to
monitor with the GFS being more aggressive with this system as the
snow will likely be very dry and fluffy so could get some
accumulation even with low qpf amounts. Other concern is the strong
northwesterly winds possible on the backside of the system moving
through with the surge of arctic air. Therefore will have to monitor
as EC has less wind speed, but GFS is showing 30-40 kt winds
possible which could lead to considerable blowing snow and
reductions in vsbys Tuesday into Wednesday. With H85 temps dropping
into the mid 20s below zero Celsius, very cold temperatures also
expected and have nudged guidance grids down as well. Expect highs
around 5 to 15 above, and lows near zero to 5 above.


.AVIATION.../For the 18Z TAFS through 18Z Friday afternoon/
Issued at 1142 AM CST Thu Dec 8 2016

Cloud bases near 2000ft present over eastern Iowa, SKC over
western Iowa. Confidence lowest at KDSM... which is right on the
western edge of the clouds. Left KDSM in VFR for now as any
periods of MVFR should be brief enough not to warrant a new FM
group. Update from pvs TAF package to keep MVFR in TAFs overnight
at eastern sites. This will need to be monitored as well...KMCW
and KALO could briefly touch IFR.




LONG TERM...Beerends
AVIATION...Kotenberg is the U.S. government's official web portal to all federal, state and local government web resources and services.