Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 161125
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
625 AM CDT Mon Apr 16 2018

.SHORT TERM...
332 AM CDT

Through tonight...

Main forecast concern in the near term is with the ongoing snow
across far northeast early this morning with snow covered roads
and slippery conditions likely creating hazardous conditions for
the morning commute across far northeast Illinois, and have issued
a short duration winter weather advisory this morning for these
likely conditions.

Latest radar imagery depicting persistent snow development for
locations in northeast Illinois, mainly along and north of I-90.
This snow is tied to the upper level system slowly moving across
the region. As this system slowly pivots across the area, expect
this snow to persist this morning, likely into the mid morning
time frame. Late last evening, moderate to heavy intensity was
occurring with this snow. Since then, there has been some slight
diminishing trend, although there is still likely some areas of
heavier intense snow. Despite some slight diminishing trend, air
temps in the 20s and surface temps likely well below freezing will
support accumulating snow on all surfaces. Most webcams at this
time support this, with many showing snow covered roads for
locations along and north of I-90. Snow amounts in this location
will be mainly in the 1-2 inch range, but could see some isolated
amounts around 3 inches closer to the IL/WI border. Given the
likelihood of snow covered roads and slippery conditions that will
impact the morning commute, have decided to issue a short
duration winter weather advisory for Boone, McHenry, and Lake IL
counties. South of the advisory, more light to moderate snow will
occur and although some slippery conditions may be observed here,
don`t think it will be as widespread as areas to the north. So
have issued a special weather statement detailing the possible
slippery conditions for those traveling in this location this
morning.

Later this morning, should begin to see this snow depart.
However, as this system continues to pivot across the area, could
see this snow push southward and impact areas more int east
central Illinois and northwest Indiana. Moving into the daytime
hours should help to limit any additional snow accumulation
though. The pattern will then support continued scattered snow
showers this afternoon into the evening.

Rodriguez

&&

.LONG TERM...
402 AM CDT

Tuesday through Sunday...

The period starts off dry, as high pressure spreads across the
region. However, quickly turn attention to anticipated system to
arrive by mid week that could provide another period of a wintry
mix. Approaching closed upper level system and surface low will
arrive late Tuesday night into Wednesday, with precip chances
increasing throughout the day Wednesday. Anticipate strong WAA out
ahead of this system that should help with warming temps,
however, its possible for temps to be around freezing across
portions of northern Illinois early Wednesday morning. If this
were to occur, a brief window of freezing rain could be possible
before all rain is expected. Returning cold air on the back side
of this system will help for a transition over to all snow. At
this time, there is the possibility for a light accumulation, and
will monitor the possibility for slightly higher amounts.

Rodriguez

&&

.AVIATION...
For the 12Z TAFs...

Two regions of snow are shifting across the region. The southern
band of snow should remain south of the terminals. The northern
band will continue to slowly shift east through mid to late
morning. My confidence is low in how long the snow showers will
linger. MVFR cigs will continue, and northwest winds will begin
gusting to arnd 25 kt.

Another round of snow showers is expected to form this afternoon.
Guidance continues to struggle with the snow, so I opted to keep
the previous forecast`s timing. Snow showers could form later than
currently forecast. The stronger snow showers will produce IFR
vsby, and may produce IFR cigs. I have higher confidence in vsby
than lower cigs.

Snow ends early this evening, and cigs improve to VFR. Winds
diminish and become northwest around 10 kt overnight with skies
scattering from west to east.

JEE

&&

.MARINE...
158 AM CDT

Winds diminished below gales, so the gale warning for the northern
end of the lake was allowed to expire. No changes were made to the
small craft advisory.

Low pressure over the Ohio Valley will reach southern Quebec through
Tuesday morning. Meanwhile, high pressure is over the Plains, which
will cause north winds to 30 kt today. Some models indicate we could
see ocnl gale force gusts, but my confidence is low, so I will not
include gales in the GLF. Winds back to northwest overnight and
diminish Tuesday as the high shifts east to the Mississippi Valley.
The next low reaches the lake mid week with another broad surface
high late in the week.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory...ILZ004-ILZ005-ILZ006 until 9 AM Monday.

IN...None.
LM...Small Craft Advisory...nearshore waters
     until 10 AM Tuesday.

&&

$$

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