Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 171203
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
603 AM CST Sun Feb 17 2019

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 343 AM CST Sun Feb 17 2019

Snow continues across much of the area early this morning. More
focused area of moderate to locally heavy snow with snowfall
rates near 1 inch/hr migrating along the Mississippi River into
northwest IL along/n of I-80 attendant to strong low level warm
advection, and additional lift/deep saturation through dendritic
growth zone aided by left exit region of jet ahead of approaching
shortwave. Not many snowfall reports received thus far, but obs/plow
cams suggest at least 1-2 inches in portions of the western CWA.
And, quick measurement here at the office of near an inch a little
while ago.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 343 AM CST Sun Feb 17 2019

Winter weather advisories remain in effect for the region. Mid
level dry slot has moved up near the I-80 corridor, and
approaching portions of the Hwy 30 corridor in eastern Iowa.
This will likely lead to lower snow amounts south of I-80 where
some freezing drizzle will occur at times with loss of in-cloud
ice. Thus, while amounts lower south of I-80 the snow covered
roads and potential for light glaze of ice warrants the
continuation of the headlines, which may need to be extended
beyond noon for the far southern counties pending trends.
Portions of Hwy 30 in northeast Iowa offer challenge on snow
totals with dry slot impinging into this area. This could result
in amounts on lower side of ranges, but not overly confident and
totals could be just fine as some of hi-res guidance wants to
infuse some uptick in intensity of the snow a bit later this
morning with the passage of the shortwave. Strongest low level
925 mb warm advection usually a good indicator for location of
heaviest snow, and trends have shifted this to between Hwy 30/Hwy
20 corridors... so thinking the higher amounts will fall somewhere
in this region. Insentropic lift will drive the snow this
afternoon with mostly light snow, with the potential for a few
bands of moderate snow for a time with sagging 850-700 mb
convergence axis down through areas north of I-80. This evening
waning isentropic lift and convergence will lead to a diminishing
of any organized snow to just flurries overnight. Overall, some
refinement to amounts. Lowest accums far south around 1 inch with
generally 2-6 inches across the rest of CWA with again the highest
amounts appearing to focus on portions of the Hwy 20/30
corridors.

.LONG TERM...(Monday through Saturday)
ISSUED AT 343 AM CST Sun Feb 17 2019

After a break from the snow Monday into Tuesday, attention turns to
the next weather system to affect eastern Iowa and northwest
Illinois from Tuesday night into Wednesday. We`ll start the week off
slightly below normal with highs in the 20s, then moderate into the
30s by Wednesday.

Tuesday night through Wednesday

Main message: Confidence is high on another round of wintry
precipitation for eastern Iowa and northwest Illinois as models
remain very consistent from run to run. A band of moderate to heavy
snow is possible but it is too early to known where it will set up.
The highest amounts in our CWA are favored in the northwest to
northern third.

A broad, sheared out upper-level low will eject out of the
Intermountain West or Four Corners region on Tuesday, spreading a
quick shot of deep layer Q-vector convergence across Iowa and
Illinois. A large meridional component to the mid-level flow will be
manifest as increasing integrated WV transport with PWATs rising to
~0.50 inches; although this will be a quick moving system, there
will be ample available moisture for widespread precipitation.

Thermal profiles aloft support mostly snow. Freezing drizzle is
possible for locations that are engulfed by the system`s mid-level
dry slot as the snow shield shifts north. A little early to pin down
snowfall amounts but several inches appear likely. There are still
model differences on the exact track of the strongest forcing or
path of the 500mb vorticity max. The ECMWF/CMC are further NW which
would translate to lower snow amounts locally. The GFS/NAM are
further SE and higher for snow.

Thursday On

Dry weather expected for the end of the week with near normal
temperatures. Model consensus has another low tracking through the
Midwest along a tight 850mb baroclinic zone this upcoming weekend.
Too early to get into the details on this one and confidence remains
low. But at least worth a mention that this could be a strong system
with cyclogenesis ensuing over the Upper Midwest or Western Great
Lakes. Stay tuned! Uttech

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday Morning)
ISSUED AT 555 AM CST Sun Feb 17 2019

MVFR/IFR will prevail through this TAF period. The first round of
steady snow has moved north of the terminals and ceilings have
improved to MVFR south of KDBQ. A secondary round of snow will
quickly redevelop in the dry slot this morning, which will
eventually drop ceilings back to IFR. The heaviest bands of snow
could temporarily result in LIFR. For the afternoon and evening,
periods of lighter snow are expected. Total additional
accumulations from 6 AM this morning into tonight of 1 to 4 inches
are likely -- highest (2-3"+) toward KCID and KDBQ.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Winter Weather Advisory until midnight CST tonight for Benton-
     Buchanan-Cedar-Clinton-Delaware-Des Moines-Dubuque-Henry IA-
     Iowa-Jackson-Jefferson-Johnson-Jones-Keokuk-Linn-Louisa-
     Muscatine-Scott-Van Buren-Washington.

     Winter Weather Advisory until noon CST today for Lee.

IL...Winter Weather Advisory until midnight CST tonight for Bureau-
     Carroll-Henderson-Henry IL-Jo Daviess-Mercer-Putnam-Rock
     Island-Stephenson-Warren-Whiteside.

     Winter Weather Advisory until noon CST today for Hancock-
     McDonough.

MO...Winter Weather Advisory until noon CST today for Clark-Scotland.

&&

$$

SYNOPSIS...McClure
SHORT TERM...McClure
LONG TERM...Uttech
AVIATION...Uttech


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