Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 130500
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
1100 PM CST Thu Jan 12 2017

.SHORT TERM.../Tonight through Friday/
Issued at 351 PM CST Thu Jan 12 2017

Area of high pressure settling into the region tonight, with
bitterly cold air that has been pushing into the state through the
day today. As the high moves overhead tonight temperatures to drop
below zero across much of the northern CWA. The cold temperatures
combined with east southeast winds of around 5 mph will create
wind chill values around -20 across far northern IA. Therefore a
wind chill advisory has been issued for this area for late this
evening into Friday morning. Clouds to increase late tonight with
waa aloft as return flow sets up in the low levels. This push of
lift with some low level moisture will bring some light snow to
northwest and north central Iowa Friday. Very light accumulations
of around a few tenths of less are expected.

.LONG TERM.../Friday night through Thursday/
Issued at 351 PM CST Thu Jan 12 2017

Majority of the focus in the mid/long range is on the large storm
system set to impact the region late Saturday night into early
next week. Prior to that storm system an initial push of moisture
will skirt the southeastern CWA as another weak impulse of energy
moves through Missouri. This will bring the chance for some very
light freezing rain across the southeastern CWA. Little or no ice
accumulations are expected.

Focus then shifts to the large upper trough digging into the
southern Rockies/Baja area of Mexico, and the energy that
continues to be ejected northeastward from that large trough into
the Central Plains Saturday. This system to spread a large swatch
of precipitation off to our south and west Saturday and start to
push precipitation across southern Iowa late Saturday night as an
overrunning scenario sets up with waa and strong southerly flow
off the gulf. This will send temps warming in the lower layers
aloft over the cold air situated near the surface. A warm front
will lift north across the CWA as the surface low lifts east
northeast through the state into Monday/Monday night. However that
will leave an extended duration of warmer air and moisture moving
over the surface cold layer which will result in a decent chance
of mixed precipitation/freezing rain event across the southern
half to two-thirds of the state.

All models keep surface temps around 30 degrees of cooler through
much of the day Sunday and start to push temps across the south
toward freezing Sunday night. Initially enough cold air that may
get some snow, but as the warm layer moves in aloft any frozen
hydrometeors will be melted suggesting a transition to sleet and
ultimately freezing rain. With surface temperatures remaining
colder and dewpoints cool as well, a significant period of
freezing rain is expected with moderate icing possible from around
hwy 30 southward. Ice accumulations of around a few tenths to a
quarter of an inch are looking increasingly likely with higher
amounts possible toward the Iowa/Missouri border. Even as temps
and dewpoints warm into Monday, road temperatures have been so
cold some icy roads may still be possible even after
precipitation changes over to all rain.

Winds look to stay around 5 to 10 mph which will help with any
icing that occurs to keep power lines from flapping too much, etc.
However the icing amounts are enough that some spotty power
outages and limb damage will be possible. Travel will become
increasingly difficult through the day Sunday and continue that
way into Monday until surface temperatures begin to warm as the
sfc low lifts into Iowa and precipitation changes over to all
rain. As colder air moves in on the backside of the system and the
main upper low pushes through the state late Monday into Tuesday a
transition back to light wintry precipitation is expected. Given
the possibility of liquid precipitation amounts of around a half
an inch to an inch possible through Tuesday, some within bank
rises on local rivers can also be expected. Additionally with the
rainfall and warmer temperatures expected for next week, there is
the potential for ice jams and minor flooding from the
rainfall/ice jams also possible through the middle of next week.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1100 PM CST Thu Jan 12 2017

VFR conditions will remain widespread overnight into Friday as
surface ridging passes from the north to the east. Ceilings will
lower with time but should remain above 3kft for the forecast
period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday morning through Monday morning
for IAZ044>049-057>062.

Winter Storm Watch from late Saturday night through Monday
morning for IAZ070>075-081>086-092>097.

Wind Chill Advisory until 7 AM CST Friday for IAZ004>007-015>017.

&&

$$

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



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