Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 232153
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
353 PM CST Fri Feb 23 2018

.SYNOPSIS...
Issued at 350 PM CST Fri Feb 23 2018

Weak high pressure nosing in from the Dakotas had helped to scour
out some of the clouds, but high clouds remained. The result has
been partly to mostly cloudy skies. Mid afternoon temperatures
were in the 30s to lower 40s.

&&

.SHORT TERM...(This Evening through Saturday)
ISSUED AT 350 PM CST Fri Feb 23 2018

Forecast focus on wintry mix late tonight into Saturday morning.
Then a chance of thunderstorms later Saturday afternoon into
Saturday evening.

Headlines: A winter weather advisory has been issued for the
counties south of Interstate 80 for late tonight and Saturday
morning. This is for mainly freezing rain, but mixed with sleet
and snow. The advisory may need to be expanded northward if
temperatures do not warm as quickly as expected.

Tonight and Saturday: Potent negative-tilted trough will swing
out of the southern Rockies and head into the southern Plains by
morning. Increasing low level moisture will be transported
northward on a strengthening LLJ. Operational models, including
the HIRES, brings freezing rain into our far southern counties
late tonight, mixed with light snow and sleet. Unfortunately,
temperatures will be near or just below freezing making for slick
and hazardous roads and sidewalks. Later in the morning,
temperatures should warm well above freezing (from south to north)
that just plain rain should occur.

Later in the afternoon into the evening on Saturday an
intensifying cyclone will track out of the southern Plains and
into far northeast MO towards evening. This will be accompanied by
strong dynamics associated with the negative-tilt trough. We will
need to keep an eye on the triple point which may get close to
our far southern and southeast counties as the low tracks into
eastern IA. Deep layer shear and helicity are impressive but
models show little in the way of SBCAPE, but this will need to be
monitored for any sign of increased instability if temperatures
can warm more than expected. For now I have added isolated
thunderstorms to the grids but there is the potential for a couple
of strong storms to keep an eye on.

Lows tonight will be in the 20s to lower 30s with highs on
Saturday ranging from the upper 30s nw to around 50 se.

.LONG TERM...(Saturday Night through Friday)
ISSUED AT 350 PM CST Fri Feb 23 2018

Forecast focus on much warmer temperatures early next week then
another storm system arriving about the middle of next week.

Saturday night: Tricky snow forecast as to how fast the rain can
change to snow before ending especially in our nw cwa. There is
the potential for a couple of inches of accumulation if the
moisture is still available, as the colder/drier air arrives
behind the departing deepening cyclone. This low should track to
Upper Michigan by 12z Sunday. Low confidence for now for later
shifts to monitor. West winds will be gusting to 35 mph with the
tight pressure gradient around the intense cyclone. Minimum
temperatures will bottom out in the 20s, with wind chills mainly
in the teens.

Sunday through Tuesday: Operational models indicate a quiet
period but much warmer, as a zonal to sw flow continues. Highs
will be in the 40s on Sunday but in the 50s over much of the cwa
early to mid next week. On Tuesday, lower 60s are possible in our
southern counties.

Wednesday through Friday: The GFS has another strong storm system
pushing from the southern Rockies into the Midwest. The ECMWF is
much weaker with this system as of now. This looks to bring more
rain and snow but too far out for specific impacts.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1206 PM CST Fri Feb 23 2018

Areas of MVFR cigs becoming mainly VFR as the afternoon
progresses, with VFR this evening. A storm system should spread
light freezing rain and snow at KBRL late tonight into Saturday
morning. As temperatures rise above freezing this precipitation
should change to light rain later in the morning, as it gradually
spreads northward. Conds will become MVFR late tonight at KBRL and
then gradually IFR Saturday morning. Northwest winds this
afternoon veering northeast tonight then east on Saturday. Wind
speeds should be around 10 knots through this taf cycle.

&&

.HYDROLOGY...
Issued at 350 PM CST Fri Feb 23 2018

Flooding due to runoff from recent heavy rainfall continues mainly on
portions of the Rock and Pecatonica Rivers.

On the Wapsipinicon River near DeWitt, river levels have fallen to
near flood stage and it should drop below flood stage by late
this afternoon or early this evening.

On the Pecatonica River, moderate flooding is occurring and the
river is forecast to crest with major flooding this weekend.
Yellow Creek dropped back within its banks last night, thus the
areal flood warning was allowed to expire. However, with the
Pecatonica on the rise eventually toward major flooding there may be
some renewed rises on Yellow Creek, so persons with interests along
the creek will need to remain alert.

On the Rock River, Major flooding continues at Moline and near
Joslin. Joslin is cresting now, while Moline continues to rise.
Recent surveys of the river reveal a couple of ice jams between
Erie and Prophetstown, contributing to high water and impacts along
the river. Until this ice moves further downstream, rapid changes in
river levels will be possible. Further upstream, minor flooding is
occurring at Como with the river levels slowly receding.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory from 6 AM to noon CST Saturday for Des
     Moines-Henry IA-Jefferson-Keokuk-Lee-Louisa-Van Buren-
     Washington.

IL...Winter Weather Advisory from 6 AM to noon CST Saturday for
     Henderson-Mercer.

     Winter Weather Advisory from 3 AM to noon CST Saturday for
     Hancock-McDonough-Warren.

MO...Winter Weather Advisory from 3 AM to noon CST Saturday for Clark-
     Scotland.

&&

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Haase
AVIATION...Haase
HYDROLOGY...McClure


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