Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 161758

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1258 PM CDT Fri Mar 16 2018


Issued at 310 AM CDT Fri Mar 16 2018

Northeast surface winds have established themselves over the CWA
early today, with thin high clouds over most locations. That is
allowing for a slow drop in temperatures overnight, as we keep the
boundary layer mixed. The winds are increasing as the high pressure
in the Great Lakes remains in place, while low pressure develops in
western KS. This gradient will remain tight through the day as the
low moves east, and will keep dry air feeding in at low levels.


.SHORT TERM...(Today and Tonight)
ISSUED AT 310 AM CDT Fri Mar 16 2018

Today and tonight is a bit of a battle of positive and negative
factors that could come together to bring freezing rain to much of
the northern 1/2 of the area tonight. The dry air feeding in at low
levels, which is already occurring with both allow for the
expected evaporative cooling (below freezing at night) and will
also likely delay precipitiation`s movement northeast today and
this evening. In fact, it may keep our far northeast dry for
nearly the entire event. Much higher confidence in saturation is
found in the southwest 1/2 and categorical pops will be maintained
there this afternoon and evening. The delayed precipitation and
morning filtered sunshine, will certainly allow for pavement
temperatures in the northeast 2/3rds of the area to climb
diurnally, well above freezing. That should allow for several
hours lag in time in all areas for temperatures dropping near to
below freezing, minimizing any ice accumulation on roads and
sidewalks. The low pressure will be weakening this afternoon and
tonight as is moves east across Missouri. So, despite a near
direct hit from the warm advection rains and dynamics tonight, the
forcing will be weakening with time, while still advecting in
very dry low level air. That all suggest the QPF may be rather low
on this event, and our impacts from any moderate intensity
rainfall will be short duration tonight. That is important, as the
narrower the window of moderate rainfall tonight, the less impact
sustained evaporative cooling and ice accumulation will have.
This all said, I am on the fence on whether an advisory is high
enough of a probability to be issued this a far out. I could see
waiting to later today and having a great knowledge on pavement
temperatures at that time helping identify the exact areal outline
of the travel threat. On the other hand, the minimal impacts of
wind shield ice, trees ice, decking ice could be used to have a
very low end advisory as well tonight. In any case, we`re talking
about a 9 PM to 9 AM time frame. For now, in coordination with
surrounding offices, will issue a lower end freezing rain impacts
advisory for counties between Highway 20 and Highway 30 in Iowa,
from Jones county eastward and into our Illinois counties of
Carrol and Whiteside.


.LONG TERM...(Saturday through Thursday)
ISSUED AT 310 AM CDT Fri Mar 16 2018


Wintry mix of freezing rain and wet snow may continue into the mid
morning - mainly over central sections of the forecast area as the
precipitation slowly sinks southward. Precipitation intensity will
decrease through the mid morning as the 500mb vorticity max
is sheared out and low-level deformation wanes. As colder air
wraps in on the northwest side of the surface low, could even have
some wet snow south of I-80 before the precipitation ends. The
potential impacts from this system were discussed in the short
term section (above).

If there are slippery conditions early in the morning, all pavement
should just be wet by the mid morning hours due to effects of the
mid March sun angle. The remainder of the day will be quiet with
highs in the 40s.

Sunday through Thursday

Main storm track is expected to set up over the Southern U.S. and
East Coast, which will keep us dry through this period. On
average, temperatures are forecast to be slightly above normal
into the 40s and 50s. The exception is Tuesday and Wednesday when
a mid-level trough digs into the eastern third of the U.S. The
model blend has highs in the upper 30s to mid 40s for Tuesday, and
a few degrees warmer on Wednesday. Uttech


.AVIATION...(For the 18Z TAFS through 18Z Saturday Afternoon)
ISSUED AT 1255 PM CDT Fri Mar 16 2018

VFR conditions with brisk easterly LLVL winds until the precip
shield saturates and spreads up from the southwest...leading edge
is remaining aloft with such dry east flow to overcome. But the
precip will eventually win out by late afternoon and especially
this evening north of I80. Initially rain and lowering CIGs into
the low VFR to MVFR realm with the top-down saturation. Then
thermal profiles supportive of sleet mixing in with the rain at
almost all sites. The rain-sleet combo will turn to freezing
rain/sleet and snow mix at CID and DBQ after 10 PM CDT. MLI may
even have bouts of wintry mix/icing after midnight into early Sat
morning. BRL may have sleet mix n with the rain at times this
evening, but then should transition to all rain and drizzle for
the overnight. CID may switch over to all wet snow after 09z
tonight and into Sat morning. Lowering CIGs into the low MVFR or
even IFR levels late tonight into Sat morning especially south of
I80, with some fog and drizzle also possible, Then expect most
precip to slide southeast out of the area after 10 AM CDT Sat
morning. Sfc winds should decrease some tonight out of the east to
northeast as the low presssure system approaches out of the
central plains.  ..12..


IA...Winter Weather Advisory from 10 PM this evening to 10 AM CDT
     Saturday for Clinton-Jackson-Jones.

IL...Winter Weather Advisory from 10 PM this evening to 10 AM CDT
     Saturday for Carroll-Whiteside.



LONG TERM...Uttech
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