Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 252326
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
526 PM CST Sun Feb 25 2018

.SHORT TERM...
1102 AM CST

Through Monday...

Gusty winds in place today will continue this afternoon, but
diminish soon after sunset. Although an additional slight increase
in speeds may arrive here by midday with better mixing, don`t
anticipate them to be as strong as the winds late last night into
earlier this morning. WAA returns on Monday, and with sunny skies
and southwest winds in place, still expect highs in the 50s on
Monday.

Rodriguez

&&

.LONG TERM...
115 PM CST

Monday night through Sunday...

Mild conditions will begin the period as low amplitude ridging
aloft traverses the midwest. At the surface, high pressure in
response to the ridging aloft will expand across the eastern third
of the country. Southwest flow behind the high and in response to
a northern stream surface low near the Canadian border will lead
to unseasonably mild conditions, with any moisture sources still
cut off. Highs in the 50s to around 60 will bring another taste of
spring.

High pressure will shift off the Atlantic on Tuesday night into
Wednesday. A cold front associated with the northern stream low
will shift through Wisconsin and south across the lake Tuesday
night into early Wednesday. Meanwhile, weak impulses in the
southern stream flow will tap into gulf moisture but largely
south along the Ohio valley. Much of northern Illinois and
northwest Indiana will remain on the fringes of these two systems
precipitation wise, and therefore some scattered light rain is
possible mainly far north and far south. The cold front will bring
a temperature contrast between far northern Illinois and the
lakefront which will hold in the mid 40s or so, though areas south
of I-80 which will stay on the warm side of the front will make
another run at the upper 50s.

Our next system of interest continues to be an upper low that
really is still taking shape off the Pacific Northwest coast. This
low will dip into southern CA and eventually shift into the Ohio
valley. Additional upper level forcing will come from energy off
the Canadian Pacific coast. It is the phasing of these systems
which looks to impact the strength of the associated combined
system. Given the lack of sampling thus far by the upper air
network, there is significant spread in the extended models on
the track, system phasing, and strength of the low, so specific
impacts are tough to say just yet. What we can say is
precipitation chances will increase Wednesday night and continue
into Thursday morning. The deeper gulf moisture will likely remain
confined south of our region, but models do still prog seasonally
elevated moisture values which could bring decent rainfall to
some areas. Guidance does also indicate a potential significant
batch of precipitation on the back side of the approaching low.
Models up to this point have largely kept the precip as rain until
the tail end where a few tenths of snow may still be possible,
and will continue to favor this solution in the forecast for now
given very few GEFS members supporting much snow south of the
Wisconsin border. The 12z EC depicts some of the concerns as it
now features more of a closed low solution aloft (like the GFS).
There is not a huge surge of arctic air in its solution, but the
associated dynamic cooling from its strong back side precip shield
could support more of a wet snow profile on the tail end of the
event.

High pressure will hold for most of the weekend for dry conditions
and seasonal temps in the low to mid 40s.

KMD

&&

.AVIATION...
For the 00Z TAFs...

A much quieter period is forecast thanks to high pressure. Gusty
WSW winds diminish this evening. VFR conditions continue tomorrow
with southwest winds of 10 kt or less.

JEE

&&

.MARINE...
115 PM CST

Strong low pressure that brought has strong gales and a brief
period of storm force gusts to the north half will shift into
Quebec tonight and allow winds to drop below gale force by early
evening. High pressure will build across the Ohio Valley later
today and continue into Monday which will result in a moderate
west to southwest breeze into early Tuesday as winds approach 30
kt. Low pressure moving east across the Canadian Prairies on
Tuesday will send another cold front down Lake Michigan Tuesday
evening/night. Another potentially significant low will develop
over the Central Plains midweek and lift into the Midwest on
Thursday. Gales are a strong possibility, especially on the
backside of this system Thursday and Thursday night.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...nearshore waters
     until 10 PM Sunday.

&&

$$

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