Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 200927

Area Forecast Discussion
National Weather Service Quad Cities IA IL
327 AM CST Sat Jan 20 2018

Issued at 327 AM CST Sat Jan 20 2018

A mild January airmass was over the area early this morning with
light southwest winds and high cloud cover holding temperatures in
the 30s. Aloft, the flow was relatively zonal ahead of a digging
longwave trough moving into the southwest U.S. As this trough
continues eastward, an increasing low level south to southwest
flow will feed low level gulf moisture, evident by temperatures in
the 50s and dewpoints in the 40s as far north as OK early this
morning, northward into the local area tonight into Sunday. This
will lead to fog, low clouds and drizzle tonight, then rain on
Sunday ahead of a developing winter storm system progged to track
through the Midwest Sunday night through Monday.


.SHORT TERM...(Today and Tonight)
ISSUED AT 327 AM CST Sat Jan 20 2018

Temperatures and developing drizzle and fog are the primary forecast
challenges. Satellite fog channel and surface observations showed an
area of stratus along a developing warm front advancing rapidly
northeast across SE KS into SW MO early this morning. At the current
rate, this would reach into our far south by mid morning. The
associated thermal and moisture advection should result in
temperatures returning to the 40s today, even with the accompanying
overcast conditions likely by afternoon. As saturation continues and
low level convergence develops along the stalling warm front,
drizzle and fog will develop from south to north in the evening and
become widespread after midnight. The advection of dewpoints in the
30s to near 40 over the cold, moist surface conditions in place may
lead to dense fog overnight.

Forecast models continue to suffer from poor snow cover
initialization, resulting in artificial surface temperature
gradients and an overall cool bias. Modeled snow depths of .5 to 2
inches shown by short term high res and the WRF across the north and
northeast half of the forecast area, continue to depress forecast
temperatures in the short term into the 20s, which has not
occurred tonight, and is not likely to occur as depicted for
Saturday night. This is especially true considering the advection
of surface wet bulb temperatures well into the 30s by tonight,
when most of any remaining snow cover should be gone. The GFS and
ECMWF appear to have a more realistic, much further northward
edge to the snowfield, resulting in warmer surface temperatures.
Have thus biased surface temperatures more heavily toward these
models, suggesting temperatures will stay near or above freezing
in the far north overnight, limiting the potential for freezing
drizzle. The forecast area along and south of interstate 80 should
hold in the mid 30s to around 40 through the night.

.LONG TERM...(Sunday through Friday)
ISSUED AT 327 AM CST Sat Jan 20 2018

The first surge of warm, moist air builds north across the area
during the day Sunday with drizzle and fog. During the first part of
the morning, there may or may not be some freezing drizzle in the
highway 20 corridor west of Dubuque and into the northern
parts of Benton and Linn counties.

Sunday night the main forcing from the storm system moves through
the area. A saturated lower atmosphere will develop widespread rain
along with some fog. The southeast half of the area may have the
better fog chances where the models suggest a potential boundary.

During the strong forcing Sunday night, some isolated embedded
thunderstorms may be possible south of a Sigourney, IA to Sterling,
IL line.

Monday drier air aloft moves into the area which may or may not end
the rain for a while or take it down to drizzle.

As the cold front sweeps through the area Monday afternoon, rain
will pick up again across the area with a rain/snow mix developing
around sunset west of a Manchester to Williamsburg, IA line.

Monday night the deeper cold air will move across the area changing
the rain over to all snow during the evening. During the transition
period one cannot fully rule out a period of freezing rain or
possibly sleet. After midnight the snow will slowly end from west to

There is still some uncertainty in the overall track of the storm
which will influence overall snowfall amounts. However, early
indications suggest a dusting to less than an inch south of highway
30. North of highway 30 accumulations up to and just over an inch
appear possible.

Tuesday on...

On Tuesday, windy and much colder conditions will be seen across the
area. Some lingering light snow or flurries will be possible during
the early morning in the far east before ending.

Tuesday night through Friday the model consensus has quiet and dry
conditions for the area as high pressure moves through the Midwest
toward the east coast. Temperatures will moderate on Wednesday with
above normal temperatures expected Thursday and Friday. Attention
then turns to the weekend.

Friday night into Saturday the models show another storm system
affecting the Midwest. There are differences in timing and overall
track of the storm system which will affect precipitation type.
Right now the model consensus has chance to likely pops Friday night
and chance to categorical pops on Saturday. Precipitation type
ranges from all rain in the southeast half of the area to a
rain/snow mix or all snow across the northwest half of the area.


.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1115 PM CST Fri Jan 19 2018

A shallow inversion just aloft will bring a quick onset of low
level wind shear to all area TAFs through mid morning Saturday.
Winds near 12 kts at the surface will increase and veer to
southwest (240 deg) and increase to about 45 kts by 2000 ft AGL.
Otherwise, will continue to go VFR as stratus should hold off
formation until Saturday evening around 00-03Z. Stratus will
initially move in around MVFR levels near 2500 ft, then lower with
time to IFR and LIFR overnight. Drizzle and fog can be expected
with cloud bases below 1000 ft.





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