Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 241836

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

135 PM CDT

Through Tuesday...

High pressure will move overhead tonight for light winds and some
patchy fog. Before cloud cover arrives, we could have some patchy
frost in outlying areas as well. Low pressure will approach later
Tuesday. Expect clouds to gradually lower through the day with
increasing lift ahead of the system. At this point the low levels
(below 10k ft) are dry on forecast soundings and supports the
pattern of a drier ese wind. Given the strong warm frontogenesis
and associated lift there could be a few sprinkles late, but
expect better precipiation chances arrive Tuesday night and more
so Wednesday. Expect similar highs to today on Tuesday.



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 18Z TAFs...

- Wind speed/direction
- Precip chances later Tuesday

Winds have been somewhate variable between 330 and 040 this
afternoon as high pressure moves in from the west. As the high
continues east...coupled with a lake breeze...will generally shift
the winds to an ENE direction through the afternoon with speeds of
7-10 kt. The high will move overhead tonight for light winds and
some patchy fog. Low pressure will approach later Tuesday. Expect
clouds to lower through the day with increasing lift ahead of the
system. At this point the low levels (below 10k ft) are dry on
forecast soundings and supports the pattern of a drier ese wind,
therefore have kept the ORD 30 hr TAF dry for the Tuesday
afternoon period. Given the strong lift there could be a few
sprinkles though this will be of low impact. Better chances arrive
after the current TAF cycle.



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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