Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 160832
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
332 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...
310 PM CDT

Monday night through Sunday...

A continued progressive, active flow pattern will remain through
the week. The mid-level wave path is forecast over or near the
area. In simpler terms, this means limited duration of warm-ups as
well as precipitation chances.

Cyclonic flow will continue into Monday night with gradual drying.
It is a challenge to say whether or not skies will clear,
especially east, but temperatures will depend highly on that.
Record lows are possible in some places if clearing were to occur
(Rockford record low for Tue a.m. is 24 set in 1983).

The next closed low, while must less amplified, will move into the
Iowa region by Wednesday. Warm advection aloft Tuesday night is
forecast to move over the area. Moisture looks slower to increase,
and as such we have removed Tuesday night chance of precipitation.
If precipitation were to occur by early Wednesday morning in
northern areas, there could be isolated convection and surface
temperatures may be close to freezing...but do think temperatures
will be quickly rising as winds turn south.

Highs on Wednesday are likely to push into if not well into the
50s if the surface warm front can indeed push through the area.
Scattered showers are possible especially north, and then by
Wednesday night the mid-level low passing over will likely
support precipitation depending on the path. Some of this could
fall as light snow.

Beyond, the next low for the weekend is forecast south of the area
at this time, but confidence is low in this. Worry that blended
temperatures may be a little on the warm side for Thu and Fri
given the wind direction and if clouds stick around behind the
midweek system.

MTF

&&

.AVIATION...
For the 06Z TAFs...

Overall, I didn`t make many changes to the TAFs as the previous
forecast looks really good. A band of light to moderate snow
showers is beginning to weaken. RFD should only see flurries for
the remainder of this morning. The eastern terminals will continue
to see MVFR snow showers that ocnly lower vsbys to IFR through
the early morning hours. MVFR cigs will also continue through much
of the day.

Northwest to west winds will gust to around 25 kt. Additional snow
showers will develop this afternoon with the upper level low
overhead and surface instability in place. Guidance is really
struggling to capture the snow showers, so I kept the previous
forecast`s timing of 17-21 UTC. The stronger snow showers may
produce IFR vsby and cigs.

The upper level low finally shifts east this evening/overnight
allowing cigs to become VFR. Gusty northwest winds will
continue tonight.

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
     Tuesday.

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

&&

$$

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