Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 171750
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1150 AM CST Sat Feb 17 2018

.UPDATE...
Issued at 1150 AM CST Sat Feb 17 2018

Strong forcing with the upper level shortwave was producing a
wide, fast moving wide north to south band of moderate to heavy
snow moving into eastern IA and northeast MO late this morning.
Roads were quickly becoming slick with visibilities as low as 1/4
mile at observing sites. This suggests a quick inch of
accumulation likely and forecasts have been updated this direction
and further tweaks will be needed as this forcing spreads through
the remainder of the forecast area this afternoon.

Have issued a special weather statement and graphical nowcast to
advise on the rapidly changing conditions and slick roads, which
have already resulted in accidents and blockages reported on the
IA DOT website in the Cedar Rapids and Des Moines interstate
corridors late this morning.

&&

.SYNOPSIS...
Issued at 247 AM CST Sat Feb 17 2018

06Z surface data has high pressure over the Ohio Valley with a
developing low in southeast Colorado. Dew points were in the 20s and
higher from the Ohio Valley south to the Gulf Coast and into the
southern Plains. Dew points in the single digits and teens ran from
the Great Lakes into the central and northern Plains.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 247 AM CST Sat Feb 17 2018

Through sunrise, quiet and cold conditions will be seen with
increasing clouds.

Saturday, moisture will stream into the area as forcing aloft
increases during the morning. As the atmosphere saturates it will
cool and allow the precipitation to initially begin as all snow.
South of I-80, the snow will change over to a rain/snow mix and then
eventually over to all rain. The rain/snow mix should make it as far
north as the highway 30 corridor during the afternoon.

Saturday afternoon the precipitation will end from west to east. The
best chances for precipitation are east of the Mississippi where the
forcing maximizes as warmer air flows in from the south. By sunset
most if not all of the area will be dry.

As for snowfall amounts, areas along and south of the highway 30
corridor will see a dusting of accumulation at best. Some areas
south of I-80 may see the new snow melt by sunset. North of the
highway 30 corridor accumulations will range from a dusting to less
than an inch.

Tonight, quiet and dry conditions will be seen across the area as
the next high pressure moves through the Midwest.

.LONG TERM...(Sunday through Friday)
ISSUED AT 247 AM CST Sat Feb 17 2018

Above normal with rain and embedded thunder Monday and Monday night
the main issues with locally 1+ inch amounts possible.

Long term forecast confidence assessment...fair or average.  The
main issue is precipitation amounts with cool front Monday into
early Tuesday.  Phasing issues are main challenge and suggest some
moderate to locally low end heavy rain totals that will better known
next 24 hours.

Sunday and Monday...minor changes made. Above normal temperatures
with highs in the 40s to 50s, with 60s south sections on Monday.
Areas of rain and isolated to scattered embedded thunder. WPC is
concerned with a slight risk of excessive rain so will be mentioning
locally heavy rain risk in HWO product. Best estimate of 1+ inch
amounts. Lows mainly in the 30s with some upper 20s NW in NW
quadrant Tuesday AM  behind cold front.

Tuesday...current forecast has cold air coming in with default
freezing rain risk on NW winds is more likely to be light snow if
occurs at all for later shifts. Expect falling temperatures during
the day to below freezing everywhere by evening on blustery NW
winds. Precipitation should be light with no significant winter
weather issues.  Tuesday night night to bring clearing skies and
lows mostly in the teens by morning.

Wednesday through Saturday...mostly dry with highs 20s and 30s
rising Friday and Saturday into the 40s. Lows teens and 20s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
ISSUED AT 1150 AM CST Sat Feb 17 2018

A fast moving upper level shortwave will bring a 1 to 3 hour round
of moderate to heavy snow early this afternoon. This will result
in IFR conditions and possible LIFR, which is mentioned in the
terminals. An improvement to VFR is likely by evening, but the
confidence in the timing of this transitions from IFR to MVFR to
VFR is below average. VFR conditions then follow overnight into
Sunday morning.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

UPDATE...Sheets
SYNOPSIS...08
SHORT TERM...08
LONG TERM...16
AVIATION...Sheets



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