Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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913
FXUS63 KDVN 162147
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
347 PM CST Thu Nov 16 2017

.SYNOPSIS...
Issued at 330 PM CST Thu Nov 16 2017

Low stratus that was over much of the cwa this morning into early
this afternoon eroded quickly, only to be followed by a layer of
cirrus clouds. The result has been a cold day with mid afternoon
temperatures only in the 30s to lower 40s. At least the winds have
been light.

&&

.SHORT TERM...(This Evening through Friday Night)
ISSUED AT 330 PM CST Thu Nov 16 2017

Forecast focus on storm system to impact the region.

Tonight: Warm air advection will allow for a continued increase
and thickening of mid/high level clouds. Late tonight low level
moisture will be also increasing leading to the formation of low
stratus once again. Temperatures will be warmer than last night
due to the cloud cover and southeast winds, with lows in the
lower to mid 30s.

Friday: Forecast soundings indicate a classic drizzle sounding
in the morning with low level moisture, dry air in the mid
levels, and enough convergence for areas of drizzle. However, by
afternoon saturation occurs throughout the column as moisture
continues to increase on a 40 knot southwest low level jet. This
will increase areas of light rain during the afternoon hours as
cyclogenesis takes place in western KS. Southeast winds should be
brisk with gusts to 25 to 30 mph. Maximum temperatures will range
from the lower to mid 40s north, to the mid 50s far south.
Temperatures may need to be adjusted based on the actual track of
the surface low, which varies among the models.

Friday night: This is when forcing strengthens as the main upper
level trough approaches from the Plains. Right now I will take the
"middle of the road" track of the low using the ECMWF, that is
from Kansas City to south of Chicago. The GFS is a bit farther
north with this track, while the NAM is a bit farther south.
Regardless, there should be widespread rain along with a few
elevated non-severe thunderstorms. SPC has general thunder in our
southern and eastern counties as instability will be quite limited.
A more southern route of the surface low (NAM) would practically
eliminate any threat of thunder. A sharp cold front will be pushing
eastward across the cwa overnight, with northwest winds increasing
to 15 to 25 mph with gusts to at least 30 mph. Minimum temperatures
will range from the mid 30s at Independence to mid 40s at Macomb.

Rainfall amounts (QPF) for Friday through Friday night is expected
to range from 1/4 to 1/2 inch over much of the dvn cwa, with a few
spots possibly to 3/4 inch.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 330 PM CST Thu Nov 16 2017

Saturday

Widespread precip is likely Saturday morning, possibly lasting into
part of the afternoon across the eastern CWA. Early morning thermal
parameters support rain as the precip type. But as low-level cold
air advection and the effects of dynamic cooling both increase,
there is potential for a changeover to a rain/snow mix or all snow.
The best chance is along and north of a line from Fairfield, IA
to Freeport, IL. It`s lower to the SE, but still possible.

Time-height sections have a frontogenetic band developing beneath
a coupled jet structure which produces deep layer ascent across
the CWA. The jet feature and Fgen are actually forecast to be
over southern/central Nebraska Friday night, then reach E Iowa/NW
Illinois by Saturday morning. A meteorological setup like this one
is conducive for a period of light to moderate precip, so the
hardest part about the forecast is definitely the precip type.

If snow occurs, antecedent wet ground conditions and marginal sfc
wet-bulb temps above 32 F, will make it difficult to get more than
slushy accumulation on elevated surfaces or the grass. It is still
too early to have any confidence on where, and if, a localized
narrow band of moderate snow would occur. It`s something we`ll
continue to monitor for in subsequent model runs, because it would
increase the potential for brief snow accumulations, and for
visibility restrictions to those traveling.

Model Trends:

The ECMWF is the warmest model and would be mainly rain. Other
models, NAM/GFS/CMC, are colder and indicate a higher probability
for a period of snow. The 3km NAM nest is the most aggressive model
with dynamic cooling resulting in a quick changeover to snow, which
eventually reaches all the way to the eastern CWA toward late
Saturday morning. Went colder than the model blend sfc temps, but
not as cold/aggressive with the changeover as the 3km NAM. Model
consensus QPF is on the order of 0.10 to 0.30 inches for Saturday,
but could locally be higher within narrow bands. There is still
time to trend toward a more significant/prolonged period of all
snow if models, like the NAM, are consistent over the next few
runs.

Winds:

In addition to the precip, expect breezy NW winds, 20-25 mph
sustained with gusts of 30-35 mph and isolated up to 40 mph.

Sunday through Thursday

Quiet weather is expected leading up to Thanksgiving. And
specifically for Wednesday, the big travel day before Thanksgiving,
high pressure looks to bring dry conditions and light winds to the
Midwest.

Temps will fluctuate ahead of and behind a Monday night/Tuesday
morning cold front. The model blend is slightly below normal for
Sunday and for Tuesday through Thursday next week. The exception
is a brief warm up into the 40s and 50s on Monday. Uttech

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
ISSUED AT 1056 AM CST Thu Nov 16 2017

At KCID/KDBQ/KMLI IFR conds will gradually improve to VFR later
this afternoon, with VFR conds continuing tonight. At KBRL VFR
conds will prevail through this taf cycle. Mainly southeast winds
around 10 knots or less.

&&

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

$$

SYNOPSIS...Haase
SHORT TERM...Haase
LONG TERM...Uttech
AVIATION...Haase



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