Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 250007
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
707 PM CDT Sat Oct 24 2020

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 206 PM CDT Sat Oct 24 2020

Strong zonal flow is setup across the northern US with a potent
shortwave trough moving into western Montana. Surface high
pressure extends from the Canadian prairie provinces southeast to
the mid-Mississippi River Valley, while a surface low organizes in
CO-WY. Persistent stratus has kept temps chilly in most areas,
though those locations seeing some sunshine have been able to
poke up into the 40s.

&&

.SHORT TERM...(This Evening through Sunday)
ISSUED AT 206 PM CDT Sat Oct 24 2020

Main concern in this timeframe is the development of the system to
the west and the onset time of light snow/rain associated with it.
CAM ensembles suggest dry weather to persist through Sunday
morning with precip chances increasing in the northwest and
northern parts of the CWA beginning around midday Sunday. A few
spots north of Cedar Rapids could see up to 1/2 inch of snow on
grassy area, though it maybe mixed with rain and times and melting
will limit accumulations during the day. Locations south of I-80
will likely remain dry through the day.

A mid-high level cloud deck on top of the stratus will help limit
how cold we get tonight, but also likewise limit any serious
warmup on Sunday. Lows tonight will be mainly in the 30s with
highs in the 30s and 40s tomorrow.

.LONG TERM...(Sunday Night through Saturday)
ISSUED AT 206 PM CDT Sat Oct 24 2020

Initial focus is on the light snow that will likely be on-going
across the the north Sunday evening. This axis of light, wet snow
will translate south across the forecast area overnight through
at least Monday morning, producing trace to light accumulations.
The rest of the week will see continued below normal temperatures
with another chance for precipitation with a system that passes
south of the region midweek.

A band of snow is expected to set up in the highway 20 and highway
30 corridors under a band of frontogenetical forcing. This will
be in response to an modest upper level jet couplet, between one
jet max departing into the Great Lakes and another advancing from
the central plains in the southwest flow aloft ahead of the
developing longwave positive tilt trough out west. This, and the
related low level f-gen band of lift will be initially strongest
over the north Sunday evening, then gradually weakening and settle
southward through the forecast area overnight into Wednesday
morning. Thermal profiles suggest primarily snow overnight, with a
rain/snow mix possible along the southern and eastern fringes of
the lift.

As for amounts, the limited moisture and mostly weak forcing is
likely to limit QPF totals to less than .10 in most areas, leading
to overnight snowfall up to an additional 1 inch NW of a Cedar
Rapids to Dubuque line, with generally .5 to local 1 inch amounts
elsewhere before snow ends Monday. Overnight temperatures in the mid
20s to around 30 may allow some light accumulation on paved surfaces
and may lead to some slick spots for Monday morning commuters.
Temperatures Monday will struggle to climb under the cloud cover and
northerly flow at the surface, holding highs to the 30s. Snow will
end in the north by mid morning, but continue in the south through
the afternoon, where the light accumulations will be possible,
mainly on grass and vegetation. While the forecast has a mention of
rain or a rain/snow mix before precipitation ends, there is a
likelihood that many areas will see all light snow based on forecast
thermal profiles before the system exits Monday evening.

Tuesday through Sunday will see mainly dry weather with continued
below normal temperatures. The longwave trough out west is shown
spinning off a closed low that pushes eastward, passing south
of the forecast area Wed night through Thursday, leading to a
period of chance pops for rain or snow. This will be better
clarified in later forecasts. Current forecast highs in the upper
40s to lower 50s would not be supportive of any daytime
accumulating snow.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
ISSUED AT 705 PM CDT Sat Oct 24 2020

Low VFR cigs will turn to MVFR tomorrow across the area. Winds
should remain below 10 knots across the area. There is a low
chance for light sn at DBQ and CID near 00z Monday. Will leave out
of forecast at this time due to low confidence in timing.

&&

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

$$

SYNOPSIS...Wolf
SHORT TERM...Wolf
LONG TERM...Sheets
AVIATION...Gibbs


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