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fxus63 kdvn 171219 

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
619 am CST Fri Jan 17 2020

..aviation update...

issued at 312 am CST Fri Jan 17 2020

A 1045mb Arctic high was located over the Great Lakes which has cold
air locked in place locally. Temps early this morning ranged from
the single digits in the northwest to the low to mid teens
elsewhere. The atmosphere was also very dry with dewpoints in a
similar range.

Storm Prediction Center mesoanalysis and regional radar is already showing a large
area of wintry precipitation across the Central Plains. This
region is downstream of a large upper trough where divergence
aloft has been increasing and southerly 40-50 kt 850mb winds have
been advecting in higher Theta-E air.


Short term...(today through Saturday morning)
issued at 312 am CST Fri Jan 17 2020

Today through Saturday morning

Main message:

Widespread snow and a mix of precipitation is on track to impact
the forecast area later today into Saturday morning. Forecast
total snow and sleet accumulations will range from 2 to 5 inches
for most areas. Warming temps to near or above freezing, periods
of sleet, and even freezing rain, will make for a heavier or dense
snow. This will lead to a greater impact to travel even with the
amounts not being very high. The snow will move into the west and
southwest near or after 8-9 am, reach central sections like the
Quad Cities around midday to early afternoon, and into the NE by
the mid/late afternoon.

Snow amounts:

The highest snow and sleet amounts are forecast generally north
of I-80 and this is the area that stands the best chance for 3 to
5 inches, although amounts around 5" may be more isolated
depending on how much sleet mixes in across the north half of the
County Warning Area. Forecast snowfall amounts were nudged down slightly south of
Highway 30 because of the expectation for sleet and freezing
rain/drizzle, and since surface temps are forecast to rise above
freezing southeast of a Sterling, Illinois to Cedar Rapids, Iowa line.
But I think it's important not to focus on the exact snowfall
amounts because the impacts from a mainly wet/dense snow, with
sleet and periods of ice, will lead to significant travel hazards
as has been messaged the past few days.

Ice potential:

One of the biggest uncertainties with this forecast is the risk for
freezing rain accumulation over a tenth of an inch. A tenth to a
quarter inch is possible along/south of I-80; however, it's very
difficult to determine which narrow corridor could receive around
a quarter inch or a little more. The good news is surface temps
will be warming above freezing in the areas that receive the
highest ice accumulations, thereby limiting the impacts somewhat
to a shorter period.


In coordination with neighboring offices left my east-central and NE
forecast area in a Winter Weather Advisory, but all-in-all there
will not be a big difference in impacts in this area compared to
counties west of the Mississippi River in the warning. With that
said, winds are forecast to be a bit stronger in the warning area
from Saturday morning through the afternoon, likely leading to
blowing and drifting snow in rural areas where it wasn't crusted
over from freezing rain. Will let the day shift reassess and
consider possible warning extension to the east as precip won't
arrive there until midday at the earliest.

Late tonight and Saturday morning

Once the dry slot overspreads the area late tonight, little
additional snow accumulation is expected Saturday morning due the
absence of a deformation zone associated with the mid-level open
wave crossing through the area. Most places should be under 1
inch. The main story will shift to the increasing northwest winds gusting
up around 40 mph or a bit higher in rural areas.

Long term...(saturday afternoon through thursday)
issued at 312 am CST Fri Jan 17 2020

The extended period features a very cold start, not much in the way
of precipitation, and a warm-up back into the 30s to low 40s midweek
and beyond.

1. Frigid conditions will be found Sunday through Tuesday with wind
chills plummeting into the teens to mid 20s below zero Sunday and
Monday mornings with somewhat less extreme wind chills in the zero
to minus 15 range for Tuesday morning.

2. North and northwest portions of the County Warning Area may meet or exceed Wind
Chill Advisory criteria of minus 20 and colder both Sunday and
Monday mornings.

3. A storm system is currently slated to affect the area Wednesday
night through Friday with another wintry mix of rain and snow.

Saturday night some lingering patchy blowing snow may be found, but
winds are expected to be diminishing as the system pulls away from
the area. The focus then turns to temperatures. The big caveat in
the temperature forecast is snow cover or lack there of. The current
lows for Sunday morning are between 5 above and minus 5. For Monday,
they are slightly colder; roughly between 3 and -7. The temp
forecast and resultant wind chills are all hinging on what happens
with the short term system. Depending on how much of a crusty snow
cover there is remaining after Saturday, these temps could be even
colder. A positive aspect though is that both potential wind chilly
mornings fall when most schools are not in session, Sunday and the
mlk Jr Holiday. Highs Sunday will struggle into the 0 to 15 range,
with Monday seeing mid single digits and teens.

After the wind chill issue Monday morning, attention then shifts to
a prolonged window of possible precipitation chances which comes
through in waves Wednesday through Friday. The best chances of 40-50
pops are Thursday night and Friday. As expected, this far out in the
forecast there are uncertainties-a-plenty with qpf, timing, track,
and phasing differences. As of now, it appears to be a rain/snow mix
scenario driven by diurnal temperature trends. Snow during the
night, changing to rain/snow mix or rain during the day, and back
again. As for temps, Wednesday should see highs in the 30s, with mid
30s to low 40s both Thursday and Friday.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 610 am CST Fri Jan 17 2020

Periods of IFR/LIFR are likely this afternoon into tonight as
widespread steady snow, and eventually mixed precipitation,
overspread eastern Iowa and northwest Illinois. Visibilities
should improve as the snow begins to mix with sleet but ceilings
will remain at IFR or lower. Snow and sleet accumulations of 2 to
5 inches are possible. The highest amounts of 4-5 inches are
favored at kcid and kdbq.

A light glaze of ice is possible tonight at all sites. There is a
chance for higher amounts of a tenth or two of freezing rain
accumulation at kmli/kbrl before the precip changes to all rain as
temps rise above freezing.


Dvn watches/warnings/advisories...
Iowa...Winter Storm Warning from noon today to 6 PM CST Saturday for

Winter Weather Advisory from 9 am this morning to 6 PM CST
Saturday for Des Moines-Henry Iowa-Jefferson-Lee-Van Buren.

Illinois...Winter Storm Warning from noon today to 6 PM CST Saturday for
Mercer-Rock Island.

Winter Weather Advisory from 9 am this morning to 6 PM CST
Saturday for Hancock-Henderson-McDonough-Warren.

Winter Weather Advisory from noon today to 6 PM CST Saturday for
Bureau-Carroll-Henry Illinois-Jo Daviess-Putnam-Stephenson-

MO...Winter Weather Advisory from 9 am this morning to 6 PM CST
Saturday for Clark-Scotland.



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