Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 161116
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
516 AM CST Sat Dec 16 2017

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 346 AM CST Sat Dec 16 2017

A strengthening warm front stretched from a developing low over the
eastern Dakotas southeast across southern MN into southern WI early
this morning. Flurries, patchy fog and temperatures in the teens
to lower 20s were found northeast of this boundary, while further
south, breezy and relatively mild conditions were in the system`s
warm sector over the local forecast area. Temperatures at 3 am
were mostly in the lower to mid 30s over eastern IA and northwest
IL with southwest winds of 10 to near 15 mph and high clouds in
the upper level northwest flow affecting mainly areas north of
I-80.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 346 AM CST Sat Dec 16 2017

The primary challenge is the well above normal temperatures today as
sunshine and low level warm advection will be in place to start out
the day. Forecast soundings suggest relatively shallow mixing today
in the warm sector ahead of the weakening surface low and front that
will advance south during the day, reaching roughly the I-80
corridor by 00z. Mixing to around 925 mb under initially mostly
clear skies, temperatures should at least reach the mid 50s over
far northeast MO, west central IL and far southeast IA. Further
north, the earlier arrival of the wind shift and greater potential
for high level clouds will limit highs to a range from the lower
40s along highway 20 to lower 50s along highway 34.

Tonight, the approaching shortwave in the southern branch of the
split flow aloft will result in increasing high cloud cover through
the night. At the surface, the front is expected to be stalled
roughly along the I-80 corridor with weak low level moisture
convergence to its north leading to low clouds and possible patchy
fog, which has been kept over mainly far northwest Illinois
toward morning. Low temperatures were kept in the mid and upper
20s north of the boundary, while lower to mid 30s are likely to
the south.

.LONG TERM...(Sunday through Friday)
ISSUED AT 346 AM CST Sat Dec 16 2017

Sunday

Fog Potential:

Fog is possible through the mid to late morning as a weak convergent
flow sets up across the northern half of the CWA. Although
confidence is low on the extent and severity, the favored location
is across the NE CWA where snow cover would have melted today
(Saturday).

Precipitation:

A sfc low is forecast to move from NE Kansas across E Iowa/NW
Illinois during the day, spreading light rain across parts of the
region. The best chances for measurable precip are in the counties
south of I-80. However, the northern edge of the light precip shield
may reach to around the highway 30 corridor.

Sunday Night into Monday morning.

Very low overcast will continue into Monday morning. Model forecast
soundings are indicating the possibility for periods of light precip
and patchy fog Sunday night. Saturation is focused below 850mb and
at temps warmer than -3 C. Therefore, no chance for in-cloud ice
crystals - if any precip occurs it would be drizzle.

We`ll have to watch the potential for areas of freezing drizzle too,
as temps fall to near or below freezing. For now, added patchy fog
to the forecast and will let later shifts re-evaluate drizzle chance.

Monday Afternoon through Wednesday

Zonal mid-level flow brings mild and dry weather with highs
averaging near 40 F far north to the upper 40s far south.

Thursday and Friday

Models are in good agreement developing a low in the Midwest along
an 850mb baroclinic zone on Thursday. The model trends over the past
24 hours have been to shift the sfc low track further south.

Most recent runs of the GFS/ECMWF ensemble means and the ECMWF/CMC
deterministic all track the sfc low from Missouri to northern
Indiana, which would be favorable for accumulating snow across parts
of our CWA Thursday and Thursday night. The deterministic GFS is a
little further north with the track, while the CMC is the strongest
with the sfc/850mb low.

Because this system is 5-6 days away, it`s still too far way to get
much more into the details. Behind the low, expect below normal
temps into next weekend. Uttech

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
ISSUED AT 516 AM CST Sat Dec 16 2017

VFR conditions will prevail with south to southwest winds and mild
temperatures today. A weak front dropping south into the area may
result in light fog and possible low clouds after midnight at DBQ
and CID. For now, have introduced only MVFR conditions in this
timeframe for these two sites.

&&

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

$$

SYNOPSIS...Sheets
SHORT TERM...Sheets
LONG TERM...Uttech
AVIATION...Sheets



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