Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 170337

Area Forecast Discussion
National Weather Service Quad Cities IA IL
937 PM CST Mon Jan 16 2017

Issued at 928 PM CST Mon Jan 16 2017

Late evening update to expand Dense Fog Advisory northward across
all but the extreme northwest counties. HRRR visibility probs
have a good handle on current fog coverage and indicate dense fog
expect for periods of showers. For the sake of simplicity, will
expire the entire advisory at 10 am. However, western counties may
improve before then and later shifts can trim as the situation
warrants. Far northwest Illinois counties may have to be added to
the advisory eventually. Showers and isolated thunder expected to
end east of the Mississippi River after midnight. Some areas have
received more than an inch of rain, and will continue to monitor
some rising tributaries overnight.

UPDATE Issued at 443 PM CST Mon Jan 16 2017

Following collaboration with neighboring offices, have issued a
Dense Fog Advisory for areas along and south of Interstate 80
through midnight. There is some potential for the dense fog to
spread north of I-80 and persist past midnight, so later
adjustments to the headlines may be needed.


Issued at 334 PM CST Mon Jan 16 2017

Area radars showed an arching band of mainly rain out ahead of a
nearly stacked surface and sharp upper level low near Kansas City. A
pronounced dry slot was evident behind this band on satellite water
vapor imagery over central MO into south central IA with a trailing
line of showers and scattered thunderstorms from near Quincy south
across MO and AR. Under this dry slot and along and ahead of surface
warm front, dense fog with visibilities below a quarter mile was
reported across northern MO into central IL. Temperatures over the
local area have risen above freezing across the entire forecast area
today, ranging from 33 along the highway 20 corridor to near 40 in
far northeast MO. The surface and upper level low are expected to
continue northeast and gradually weaken tonight, bringing a high
likelihood of dense fog and continued light precipitation overnight
across the forecast area.


.SHORT TERM...(This Evening through Tuesday)
ISSUED AT 334 PM CST Mon Jan 16 2017

Main challenges center around rain chances and the potential for
dense fog overnight as the surface low tracks across southern IA
into southern Lake MI overnight. Have included widespread fog in the
forecast for now as winds go calm in the deep, saturated airmass
over the cold surface. Anticipate there will likely need to be dense
fog advisories over much of the area this evening, then primarily
east of the MS river early Tuesday morning before drier air starts
to wrap in behind the system. Enhanced lift ahead of the upper low,
correlated with lightning observed over northeast MO will spread
into the south and southeast, mainly our west central IL counties
and will keep a mention of thunderstorms this evening. Temperatures
through the night are progged to stay close to the freezing mark in
the far northwest, where readings have not budged much so far today.
Additional precipitation should be light in this area, and with near
saturated air advecting in the potential for any ice accumulation
looks very low. Elsewhere, the heaviest QPF for this system is
currently occurring with the band of rain and additional amounts
overnight are likely to be less than a quarter of an inch. Higher
rainfall rates with thunderstorms early on in the south could lead
to minor ponding issues due to the frozen soils.

Tuesday, the system exits into lower MI with an increasing pressure
gradient and influx of drier and only slightly cool air in the lower
levels to sweep out the early morning fog. However, clouds will
likely hang on in the cyclonic flow, limiting highs to the mid and
upper 30s.

.LONG TERM...(Tuesday Night through Monday)
ISSUED AT 334 PM CST Mon Jan 16 2017

Tuesday night and Wednesday...Spring-like pattern still being
advertised for the coming week and weekend by the latest medium range
model solutions.  A passing bout of sfc ridging, under northeastern
flank of broader upper ridge off western CONUS Rex Block, will make
for clearing and cooler conditions later Tue night into Wed morning.
Fcst lows in the mid to upper 20s may have to be adjusted cooler in
some locations. The upper low portion of the western CONUS rex block
will edge eastward acrs the southwestern plains through Wed night
and open along the way. Lee side southerly return flow to begin some
moisture transport up off the western Gulf and toward the MO
Bootheel by Thu morning. Before then, southerly sfc flow and at
least partial sunshine to make for a seasonably mild day Wed, with
mixing depth and large building inversion aloft limiting the warm up
potential. For now will go with low to mid 40s north of I80, to the
mid and upper 40s south. But could see some sites in the south
approach 50.

Thursday and Friday...Both the 12z GFS and ECMWF agree that a
portion of the upper low in upstream block to roll northeastward and
interact with some me of the moisture return to produce mainly
showers or areas of rain into portions of the area late Thu and into
Fri morning. In areas of convergent light east to southeasterly
flow, could also have some fog issues Fri morning. Fri highs still
well up in the 40s despite clouds and boundary layer saturation. If
the more organized areas of rain hold off or stay to the east and
west, fog, drizzle and low clouds may be the story fro Fri night.

Saturday through next Monday...The latest run medium range solutions
suggest the next main upper wave in the southern stream of the
western into central CONUS blocking complex, will roll out toward
the western OH RVR and TN Valleys through Sunday night. Besides a
lull period for a portion of Sat allowing for another unseasonably
mild day with highs in the upper 40s to lower 50s in much of the
local fcst area, this upper level feature with a trowal like wrap-
around moisture source may make for a rather wet second half of the
weekend and into Mon if the current low center advertised by the 12z
runs verifies. The 12z GFS would have seasonably heavy rainfall of a
half inch to around an inch hitting the southern half to third of
the CWA, while the ECMWF if further south with it`s heavier rainfall
wrap-around hitting MO and southern IL on northern flank of the
vortex.  With cold air bottled up acrs Canada, the weekend system
look to be mainly rain, but will have to watch for some northerly
draw on the northwest flank of the large passing cut-off low late
Mon into Monday night that may eventually produce some precip type
issues especially in the western and northern portions of the CWA.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
ISSUED AT 539 PM CST Mon Jan 16 2017

Widespread LIFR to VLIFR conditions will be common at all TAF
sites overnight with dense fog, drizzle and low stratus. There
will likely be a 2 to 3 hour window of showers and perhaps a
rumble of thunder prior to midnight, most favored at KMLI/KBRL.
Visibilities will improve somewhat during the rain. Drier W/NW
winds behind the exiting surface low will provide some improvement
between 08z-13z.


IA...Dense Fog Advisory until 10 AM CST Tuesday for Benton-Buchanan-
     Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry IA-Iowa-
     Muscatine-Scott-Van Buren-Washington.

IL...Dense Fog Advisory until 10 AM CST Tuesday for Bureau-Hancock-
     Henderson-Henry IL-McDonough-Mercer-Putnam-Rock Island-

MO...Dense Fog Advisory until midnight CST tonight for Clark-Scotland.



UPDATE...RP Kinney
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