Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 241139

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
639 AM CDT Mon Oct 24 2016

306 AM CDT

Through tonight...

Not much to talk about in the short term. Bank of stratus over WI
has been steadily moving SSE toward N IL early this morning, but
the area is eroding on all flanks and would anticipate this trend
continuing with just a period of some SCT-BKN cloudiness this
morning, especially eastern CWA. Otherwise, look for diminishing
north winds this morning with a lake breeze probable this
afternoon but with no significant cooling as area-wide temps
should be in the 50s today. Clear skies initially and calm winds
should allow for a quick drop in temps this evening before
leveling off a bit overnight as mid-high cloudiness increases



306 AM CDT

Tuesday through Sunday...

In the longer term, first forecast concern is with shortwave
trough forecast to traverse the region mid-week. The 00Z GFS and
ECMWF are in pretty good agreement in tracking sfc low across our
CWA, largely following the I-80 corridor. There is still spread in
the models, with NAM farther north (though with little ensemble
support), and GEM a bit farther north. If GFS/ECMWF verify then
stiff east winds, low cloudiness, and steady rain would likely
result in temps holding in the 40s roughly from I-88 northward
(though probably a bit warmer near the lake). A fairly large temp
gradient is expected near the track of the low, with GFS/ECMWF
favoring 60s in our far southern counties. Should the farther
north solutions pan out, then highs would be warmer farther north
with rain more spotty. Didn`t make any changes to the model blend
that we initialize the gridded database with, however, if the
GFS/ECMWF remain steady with their track then later forecasts
would need to sharped up the temp gradient across the CWA cooling
highs north and warming them a bit far south.

No significant push of cold air in the wake of this system with
dry conditions and temps near seasonal norms Thursday. Late in the
week we continue to see substantial run-to-run volatility in the
medium range models. Earlier runs, particularly of the ECMWF, took
shortwave energy5 off the west coast and phased it some with
northern stream. Latest run hang the west coast shortwave back and
now feature a dominant northern stream shortwave, with resultant
sfc much farther north. Assuming this latest trend in the models
were to verify, then Friday would likely be a breezy/windy and
unseasonably warm day with just a small chance of scattered
showers/T-storms along the cold front Friday night.

Given the volatility of the models in this time range, opted to
just leave the blended model cocktail alone in the grids. Latest
guidance would support highs similar to what we saw Sunday (mostly
low 70s), followed by a quick chance of sctd convection along a
front, then dry conditions the remainder of the weekend with more
seasonal temps. Once guidance locks onto a solution, some
respectable changes to the forecast we`re putting out this morning
are quite possible.



For the 12Z TAFs...

Expect VFR conditions for much of the forecast period as high
pressure builds across the region. There is a small window when
MVFR ceilings could occur this morning, but this should remain
brief. Winds will likely continue to vary around due north this
morning, starting just slightly west of north. Speeds may approach
the 10-12 KT range closer to mid morning but this will likely be a
short duration window of a couple of hours. Also expect the winds
to become more north northeast by mid to late morning.



259 AM CDT

Stronger northerly winds still in place early this morning as
deep low pressure is situated over southeast Canada and as high
pressure builds east from the Northern Plains. This will likely
keep winds elevated slightly longer today and have adjusted the
forecast to reflect the likelihood of 30 KT persisting for a time
today. This will impact the nearshore waters as well, with longer
duration of elevated waves today. Did adjust the small craft
advisory with these changes, with hazardous conditions for small
craft continuing longer today. High pressure will then move across
the lake later today into tonight, with speeds diminishing. Next
forecast concern still remains with expected low pressure to move
across the region by midweek. This still looks to provide a period
of gales across the lake during this time. Will need to continue
to monitor this period for the potential for these higher winds,
and especially as there is some variability with the exact track
of the low that could impact highest winds.



LM...Small Craft Advisory...INDIANA NEARSHORE WATERS UNTIL 7 PM Monday.

     Small Craft Advisory...ILLINOIS NEARSHORE WATERS UNTIL 4 PM Monday.




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