Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 171752

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1252 PM CDT Sat Mar 17 2018


Issued at 745 AM CDT Sat Mar 17 2018

Radar trends, surface observations, and IA DOT web cams indicate
that a changeover from rain and sleet to all snow has taken place
over the last 1-2 hours northwest of a line from Sigourney, IA to
Clinton, IA line. A web cam near Williamsburg, IA showed snow
accumulation covering the ground, including I-80 of 1 inch or
slightly more. Updated the forecast to account for the changeover.
Additional accumulations over the next few hours should range
from a half inch to around 1 inch in the steadier bands, but
could approach 2 inches just south of I-80 in Iowa and Johnson
Counties (well southwest of Iowa City). Low-level deformation on
the NW side of a mid-level vorticity max has led to a slow moving,
pivoting corridor of frontogenetic forcing in this area -
supporting moderate to heavy snow. Expect travel conditions to
improve after 9 AM as surface temperatures rise above freezing and
snowfall intensity decreases.


Issued at 315 AM CDT Sat Mar 17 2018

The weakening low pressure over Missouri continues to produce a few
bands of light freezing rain and sleet over the area early this
morning.  We remain somewhat convectively unstable over central Iowa
into southeast Iowa, where the upper low continues to bring very
small thunderstorm/convective showers. This feature will continue
eastward and southeastward this morning, while the precipitation in
the northeast continues to gradually weaken in place. Temperatures
cooled to the lower 30s during the late evening precipitation. That
is allowing for some elevated ice glaze, but so far, no reports of
road icing have been taken.  The sleet seems to have been the main
impact thus far, with partially covered roads in the north currently
reported by the DOT of IA and IL.


.SHORT TERM...(Today and Tonight)
ISSUED AT 315 AM CDT Sat Mar 17 2018

Though the impacts are rather minimal for most of the advisory as of
2 AM, the narrow bands of ongoing freezing rain/sleet will have me
keeping the headlines going for the meantime. Temperatures should
not cool much more than already seen over the CWA at 2 AM, and that
will allow for a rapid improvement of *ANY * impacts of by 10 AM.

Additional QPF should be under a tenth of an inch, except for
localized convective bursts found near to south of I-80 through 9
AM. In the mean time, we`ll handle this with SPS products for the
localized heavier totals.

After 10 AM today, the system will pull away, with some clearing in
the afternoon from the north to south, and that trend continues
through this evening. This will result in milder temperatures north
than south today, with upper 40s north to lower 40s south. Any
remaining accumulation of snow or sleet in the CWA will have melted
off by late today.

Tonight, under light winds and clear/clearing skies, temperatures
will drop to the mid 20 to lower 30s. Though there shouldn`t be any
impact associated with it, a rather heavy frost appears likely

.LONG TERM...(Sunday through Friday)
ISSUED AT 315 AM CDT Sat Mar 17 2018


High pressure over the Ohio Valley and Western Great Lakes will lead
to a nice end to the weekend with dry conditions and highs in the
lower 50s on average.


Model consensus has a cut-off upper low tracking from the
Southern Plains through southern Missouri and then into Kentucky.
The GFS/ECMWF have all of the precipitation staying south of the
forecast area. The NAM/CMC are further north and impact the
southern tier or two of counties. Due to low confidence on the
northern extent of the precipitation shield, 30-50% chances for
measurable precipitation is the best approach at this time.

The current forecast has thermal profiles warm enough for rain.
However, the NAM indicates strong dynamic cooling and a changeover
to snow. Since this is several days away and model spread is high,
there is no confidence in the NAM solution right now. Stay tuned to
forecast trends through the weekend.

Tuesday and Wednesday

A longwave trough will deepen over the eastern third of the U.S.
leading to colder weather (30s and 40s) for the Upper Mississippi
Valley. On the western periphery of the longwave trough, weak
vorticity maxima embedded in northwest flow may result in brief
periods of light rain and snow showers. Confidence is low on
timing and areal coverage of any precipitation, so did not mention
in the forecast with this update.

Thursday On

After a quiet Thursday with near normal temperatures, models have
an active pattern returning for the end of the week into next

A lee-side low is forecast to form in eastern Colorado on
Friday, and then track through the Midwest on Saturday along an
impressive baroclinic zone that features spring warmth (60s and
70s) to the south and winter cold (20s and 30s) to the north.
Widespread precipitation is possible over portions of the Midwest,
but confidence on types, amounts, and timing are low. Keep up
with the forecast through the week ahead as changes can be
expected. Uttech


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 1247 PM CDT Sat Mar 17 2018

Skies will become mostly clear to clear this afternoon with VFR conditions
as a storm system moves southeast. Winds will be light northeast until
this evening and light and variable under clear to mostly clear skies
as high pressure moves in.





LONG TERM...Uttech
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