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000
FXUS63 KDVN 231735
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1135 AM CST Wed Jan 23 2019

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 250 AM CST Wed Jan 23 2019

As of 230 AM, a 1008mb low was centered NW of St. Louis and was
tracking toward SE Lake Michigan. GOES mid-level WV imagery
showed a comma head feature over south- central Iowa into SE
Nebraska and a moist conveyor streaming from the western Gulf of
Mexico into the Midwest, then curling westward into Illinois and
Iowa.

Cold air advection north of the surface low has already dropped
temps into the upper teens in the NW forecast area (19 F in Cedar
Rapids). However, the far east-central and southeast were still in
the lower 30s with rain or a rain/snow mix.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 250 AM CST Wed Jan 23 2019

For headlines, the Winter Storm Warnings and Advisories will expire
at 9 AM with the exception of Jo Daviess, Carroll, and Stephenson
Counties which are 12 PM.

Early This Morning

Model-time height sections have the strongest ascent over eastern
Iowa and northwest Illinois from now (230 AM) through 5 or 6 AM,
which will be our heaviest period of snow - hourly snowfall rates
will likely reach 1" on a localized basis. From now through 6 AM,
generally 1-3 inches is forecast across the CWA.

The heaviest bands of snow have been supported by strong upper
dynamics and corridors of low to mid-level frontogenesis. At times
these bands have had a convective look on radar as they tap into
elevated instability. This is corroborated by the SPC mesoanalysis
which has max 2-6 km lapse rates of 7-8 C/km.

Later this Morning through Tonight

The winter storm will be winding down through the morning hours
as the surface and 700mb lows shift to the NE into southwest Lower
Michigan. Additional forecast snowfall between 6 AM and 12 PM is
between 1-3" NE of a line from Independence to Iowa City to
Princeton. The higher end of the range will be in the NE CWA
toward the Freeport area. SE of this line, amounts should be under
1 inch. Still anticipate storm totals of 4-7 inches (isolated
higher) in the warning counties.

NW winds gusting 20-25 mph through midday will lead to some blowing
and drifting of the fresh snow, especially in rural, open locations.
The pressure gradient weakens a bit during the afternoon, which
should decrease wind gusts to 15-20 mph. Even as the storm winds
down, hazardous travel is expected to last through the day due to
snow covered roads and cold temps in the teens and lower 20s.
Tonight will be cold with lows in the single digits. Uttech

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 250 AM CST Wed Jan 23 2019

No change to overall pattern with active Polar NW flow to bring
periodic arctic fronts/clippers with bouts of wind, snow, and
dangerous cold through next week.

First arctic front will sweep across the area Thursday morning.
Very strong cold advection will follow and lead to crashing
temperatures, very cold wind chills, and strong NW winds.
Strongest winds likely in a several hour period immediately
after frontal passage with juxtaposition of pressure rises and
intense cold advection. Forecast soundings continue to show
around 30-35 kts of wind atop the mixed layer to near 900 mb,
which is supportive of wind gusts of 35 to 40 mph at surface.
These winds combined with fresh snow cover of 1-5+ inches will
lead to concerns with considerable blowing/drifting snow impacting
travel, especially in rural/open areas. Can`t rule out some
brief periods of whiteout conditions. Feel blizzard potential
low, as deepening surface low below 985-990 mb, near 20 mb
pressure gradient across Iowa, winds of 45 kts at 850 mb with
heights below 1300m shown and rapidly deepening negative tilt
trough... all shown to be typical ingredients in pattern
recognition (per study from DMX)...are absent at this time.
Nonetheless, anticipate impacts to travel on Thursday which will
likely warrant headlines.

Dangerous cold will overspread the area Thursday afternoon, with
the strong winds and temps crashing to into the single digits
above and below zero by evening. Wind chills by Thursday evening
will be in the range of 15 below to 25 below. Winds will lose
their gustiness Thursday night, allowing temps to plummet to
around 10 below to 20 below zero. These readings could be within
several degrees of records. Add winds and dangerous chills will
intensify into range of 20 below to 35 below zero, and persist
through Friday morning, which will also require headlines.

Still seeing consistent signal for another clipper/arctic front
on Friday accompanied by snow, and then followed again by more
dangerous cold and gusty winds Friday night into Saturday morning.
Still some uncertainties on track and timing, but generally
this snowfall continues to look like a typical clipper system of
1-4 inches. Currently looks like SW 1/3-2/3rds of CWA most favored
for the light accumulating snow, but again track is far from certain.

Starting to see more agreement in models of a much stronger clipper
system for Sunday into Monday. Stronger dynamics/forcing and
cold snow ratios point to the potential for accumulations of 4+
inches along it`s track, which is uncertain at this point. What is
more certain however, is that this system will likely dislodge
another chunk of arctic air that will persist through the middle of
next week. Anomalies suggest this airmass could be even colder than
the one for the end of this current week. Should the magnitude of
this cold remain unchanged and with a deepening snowpack between now
and then, this would bring the likelihood of record cold to the region.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1131 AM CST Wed Jan 23 2019

MVFR conditions will improve to VFR through 00z/24 as high
pressure moves in from the Plains. After 06z/24 MVFR conditions
will start moving back into Iowa and eventually Illinois as a
strong arctic front moves into the Midwest. After 12z/24 MVFR
conditions are expected across the area with blowing snow as
sustained winds increase to 20 to 25 knots. Wind gusts to 35 knots
will be likely which will cause low level mechanical turbulence.

&&

.HYDROLOGY...
Issued at 250 AM CST Wed Jan 23 2019

Many rivers still have open water and rather high flows, so with the
cold weather forecast this week, conditions have become favorable
for the rapid development of ice, which could cause freeze-up ice
jams. These types of ice jams form when water temperatures are
approaching freezing, there is no previous ice cover in place, flows
are above normal, and then sub-freezing air settles in over the
area. A few of the area rivers favored for development of ice jams
are the Rock River, the La Moine River, Mill Creek, Pope Creek, and
the Wapsipinicon. If ice jams do form, there is a threat for
flooding in areas upstream of the jam as water backs up behind it.

A jam has already been observed just upstream of the local area on
the Rock River.

While conditions are favorable for the development of freeze-up
jams, they are still very unpredictable, in both occurrence and
severity. Also of note, river level rises due to ice jams may not be
tied to a river gage.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...Winter Storm Warning until noon CST today for Carroll-Jo Daviess-
     Stephenson-Whiteside.

     Winter Weather Advisory until noon CST today for Bureau-Putnam.

MO...NONE.
&&

$$

SYNOPSIS...Uttech
SHORT TERM...Uttech
LONG TERM...McClure
AVIATION...08
HYDROLOGY...Brooks