Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 182251
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
551 PM CDT Wed Apr 18 2018

.UPDATE...
Issued at 545 PM CDT Wed Apr 18 2018

Downgraded Winter Storm Warning to Winter Weather Advisory for the
southern tier of counties that were in the warning. Additional
snow accumulations will be light, from a half inch up to 2 inches
for most locations. Additionally, pavement temperatures remain
above freezing. Further south into the I-80 corridor, periods of
freezing drizzle and light snow could lead to slippery travel on
untreated roads after sunset, so kept the advisory going for now.

Otherwise, no changes to the Winter Storm Warning for Buchanan,
Delaware, and Dubuque Counties where an additional 1 to 3 inches
of snow is possible. Steady bands of snow will impact the highway
20 corridor for the next several hours as wrap around low- level
convergence NW of the 850mb low and mid- level warm air advection
both pivot through.

&&

.SYNOPSIS...
Issued at 327 PM CDT Wed Apr 18 2018

An intense upper low was evident on satellite imagery over north
central Iowa at mid afternoon. An associated dry slot east of this
feature encompassed most of northern IL and eastern IA, where the
initial round of mixed precipitation this morning has since
changed to widespread drizzle and freezing drizzle. This feature
was beginning to accelerate eastward with area radars showing an
advancing axis of light to moderate snow spreading into the Vinton
and Independence areas at 3 pm. So far, the heaviest snow with
this system has been north of the highway 20 corridor and points
well north and northwest along and north of the upper low track.
Some light ice and sleet accumulations have been reported over
eastern IA into northwest IL so far today. At the surface, the
associated low was over far southeast IL with a primary inverted
trough reaching north into Lake MI and a weaker, more subtle,
boundary reaching northwest into eastern IA.

&&

.SHORT TERM...(This Evening through Thursday)
ISSUED AT 327 PM CDT Wed Apr 18 2018

Main focus is on the departing storm system. Forecast models
continue to depict the upper low weakening/filling and shifting
east then east/southeast this evening. This along with the low
level cyclonic flow and deformation axis should continue the
eastward spread of at least light snow into eastern IA late this
afternoon into northwest IL this evening. With the lift and fgen
forcing rapidly weakening, additional snowfall will likely be less
than one inch over the area.

Headlines: Will keep the current Winter Storm Warning and Winter
Weather Advisory areas intact for now. Incoming snow and falling
temperatures may allow some light snow accumulations on roadways.
This, in combination with falling temperatures and a potential
freezing of liquid on untreated paved surfaces, may lead to
hazardous travel conditions, especially after sunset this evening.
Based on the expected back edge of the snow, these headlines may
be cut much earlier than the 1 am expiration time west of the
I-380 corridor and possibly even over northwest IL by late
evening.

The rest of tonight will have north winds around 10 to 15 mph and
cold air advection driving temperatures into the mid 20s north to
around 30 south by sunrise. Gradual clearing should take place
Thu morning as high pressure works into the region. With 850 mb
temperatures holding well below zero celsius, surface temperatures
will struggle to reach the mid 40s north to lower 50s south.

.LONG TERM...(Thursday Night through Wednesday)
ISSUED AT 327 PM CDT Wed Apr 18 2018

Dry weather and a gradual warming trend will dominate the
extended forecast. The next strong storm system tracks well to the
south over the weekend, leaving the forecast area dry.
Temperatures return to closer to normal next week with consistent
highs in the 60s. There are low confidence chances for rain from
Tuesday night onward where models have a front moving into the
area with poor agreement or consistency.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1231 PM CDT Wed Apr 18 2018

Conditions range from MVFR to near LIFR with freezing
precipitation and snow as a storm system moves across Iowa. MVFR
to near LIFR conditions will continue through 02z/19 as the storm
system moves into Illinois and then Indiana. After 02z/19
conditions will slow improve to more widespread MVFR conditions as
precipitation slowly ends. After 12z/19 conditions will improve
to VFR.


&&

.HYDROLOGY...
Issued at 327 PM CDT Wed Apr 18 2018

Latest forecasts for the Cedar River at Conesville continue to
have the river reaching minor flood stage, just above 13 feet, by
midday Friday. This is driven by routed flow from snowmelt and
QPF. With QPF from the current system trending lower than
anticipated, confidence of the river reaching this level is low
and thus no warning has been issued. If later forecasts maintain
this crest, a flood watch may be needed.

Other sites along the Iowa and Cedar Rivers are forecast to rise,
but remain below flood stage over the next week.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory until 1 AM CDT Thursday for Benton-Cedar-
     Clinton-Iowa-Jackson-Johnson-Jones-Linn-Muscatine-Scott.

     Winter Storm Warning until 1 AM CDT Thursday for Buchanan-
     Delaware-Dubuque.

IL...Winter Weather Advisory until 1 AM CDT Thursday for Carroll-Jo
     Daviess-Rock Island-Stephenson-Whiteside.

MO...NONE.
&&

$$

UPDATE...Uttech
SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Sheets
AVIATION...08
HYDROLOGY...Sheets



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