Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 181137

Area Forecast Discussion
National Weather Service Quad Cities IA IL
537 AM CST Sun Feb 18 2018


Issued at 304 AM CST Sun Feb 18 2018

06Z surface data has high pressure from the western Great Lakes into
the lower Mississippi Valley. A frontal boundary ran from eastern
Lake Superior into northern Nebraska. Dew points were in the 20s and
higher from the Great Lakes to the Gulf Coast. The exception was
eastern Iowa and northern Illinois were dew points were in the teens
across a new snow field. north of the frontal boundary, dew points
were in the single digits and teens.


.SHORT TERM...(Today and Tonight)
ISSUED AT 304 AM CST Sun Feb 18 2018

The relatively warm air over the new snow field has resulted in
patchy dense fog to develop. This patchy dense fog will continue
through sunrise and a dense fog advisory has been issued for parts
of the area.

After sunrise, the fog will burn off due to daytime heating and
increasing winds. Once the fog burns off dry and warmer conditions
will be seen through sunset.

Tonight, moisture will move into the area allowing the atmosphere to
saturate. Based on atmospheric profiles, dry conditions should be
seen across the area through midnight.

After midnight, saturation of the atmosphere is achieved as strong
forcing moves into the area. Rain will develop and overspread the
area with the best chances along and south of I-80. As forcing
increases further, some embedded thunderstorms may be possible in
the pre-dawn hours south of a Peru, IL to Ottumwa, IA line.

.LONG TERM...(Monday through Saturday)
ISSUED AT 304 AM CST Sun Feb 18 2018

Seasonably quite mild into Tuesday with increased likelihood of
significant and much needed rains and some embedded thunder Monday
and Monday night the main issues with widespread 1+ inch amounts.

Long term forecast confidence assessment...fair or average.  The
main issue continues to be precipitation amounts with a slow moving
cool front Monday into Tuesday.  Phasing issues with forcing remain
the main challenge.  Best forcing tools suggest some moderate to
locally low end heavy rain totals expected with most locations to
receive .5 to 1.5 inches.

Monday and Monday night...very minor changes made. Above normal
temperatures with highs in the lower 40s NW to 50s central, with
low/mid 60s southeast sections. Periods of rain and isolated to
scattered embedded thunder. Reasonable estimate of .5 to over 1 inch
amounts NW to SE over 24 hours. Lows mainly in the 30s with some
upper 20s NW in far NW quadrant Tuesday AM behind cold front mostly
40s and lower 50s southeast of front in SE 2/3 quadrant of area.

Tuesday...poor confidence on how forcing and cold air interplay.
Best trends indicate cold air coming in slightly behind best forcing
limiting freezing and frozen precipitation.  This may take another
24 hours to better quantify. The default freezing rain risk on NW
winds is more likely if occurs to be changing to a mix of sleet and
light snow due to strong CAA.  Expect falling temperatures during
the day to below freezing everywhere by evening on blustery NW
winds. Any significant precipitation should move southeast or area by
late PM. Tuesday night night to bring clearing skies and lows mostly
in the teens by morning NW to lower 20s far SE.

Wednesday and Thursday...mostly dry with some light snow possible as
a weak disturbance passes.  Highs 20s and 30s with lows teens and

Friday and Saturday...near seasonable with highs 30s and 40s and
lows teens and 20s. Chance of light rain and snow as weak
disturbances passes with any suggested amounts light.


.AVIATION...(For the 12Z TAFS through 12Z Monday Morning)
ISSUED AT 531 AM CST Sun Feb 18 2018

Conditions range from VFR to VLIFR across eastern Iowa and
northern Illinois due to fog. GOES-16 fog product shows holes have
opened around KDBQ/KMLI than may fill back in. Conditions will
improve to VFR by 18z/18 as winds increase across the area.
Starting around 00z/19 there may or may not be a risk of LLWS but
was not included in the 12z TAFs as this was a new trend. After
06z/19 conditions will slowly deteriorate to MVFR/IFR as low
clouds and rain move into the area with a storm system.


Issued at 304 AM CST Sun Feb 18 2018

Suggested .5 inch to 1.5 inches of rainfall Monday and Tuesday may
result in moderate in bank rises of some area rivers with a few
forecast points on Rock River possibly approaching action stage by
middle of the week.


IA...Dense Fog Advisory until 10 AM CST this morning for Benton-

IL...Dense Fog Advisory until 10 AM CST this morning for Bureau-
     Carroll-Henry IL-Jo Daviess-Mercer-Putnam-Rock Island-



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