Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 240759

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

141 PM CDT

Through Monday...

We are currently enjoying what will be our warmest day of the week
as a thermal ridge ahead of a cold front and modest southwest
winds have pushed readings into the upper 60s to lower 70s area
wide...even some mid 70s in Central Illinois. These numbers are
some 10 degrees or so above normal for late October.

Changes in the temperature department are seen on the horizon with
a peek at visible satellite this afternoon. There is an area of
status clouds marching southeastward in the colder air mass behind
the cold front. Some of these clouds will move through our region
tonight, but with the low tracking across Lake Michigan toward
Detroit the bulk of the precipitation of the front will miss to
our north. North winds behind the front will likely result in some
lake effect clouds though no precipitation other than maybe a
sprinkle across NW Indy as a stout inversion at 850 mb holds.

High pressure rebuilds quickly Monday bringing mostly sunny skies
but a return to more seasonal conditions under north-northeast
winds, with highs expected to peak in the 50s.




Monday night through Sunday...

222 pm...High pressure will be centered over the western Great
Lakes Monday evening and slowly shift east Monday night into
Tuesday. Light winds and clear skies to start will allow temps to
quickly drop with lows currently expected in the mid/upper 30s.
Clouds will be increasing overnight which may allow temps to
become steady or even slowly rise toward sunrise Tuesday morning.
Potential for some patchy frost but confidence from this distance
is fairly low.

Low pressure will develop over the central plains Tuesday and move
east to the southern tip of Lake Michigan Wednesday evening.
Models initially show what may end up as a narrow band of showers
developing from southeast MN through far northeast IL Tuesday
afternoon. Should be quite a bit of dry air to overcome at first
and maintained low chance pops during this time. Possible that
these showers become heavy/widespread enough for some light qpf
but confidence too low to bump up pops just yet. the
low approaches...these showers will become more widespread and
heavier Tuesday evening into Tuesday night and the trend has been
for these to drift further into northern IL...generally along/
north of pops have been increased and spread further
south accordingly.

As the low approaches on Wednesday...precip will continue to
expand across the area and there may not be much of a lull across
the northern cwa with periodic showers. How long/widespread precip
becomes will impact temperatures especially across the north.
Opted not to make any significant changes with lower 50s north...
near 60 south. Southeasterly winds will also steadily increase
Tuesday night into Wednesday as the gradient tightens with wind
gusts perhaps into the 30-35 mph range. Instability appears
sufficient for some thunderstorms especially across the southern
portions of the area and depending on the track of the low...a few
stronger storms are possible...but likely south of the cwa. Precip
begins to taper off Wednesday evening. As for storm total rainfall
amounts...around an inch still looks likely over the northern
cwa...tapering to a half inch or less for southern areas.

A ridge of high pressure will move across the region Thursday with
dry weather expected. Flow turns southerly Thursday night into
Friday ahead of a cold front that will move across the area Friday
afternoon or Friday night. Temps likely to warm back into the 60s
Friday but then significant differences result in low confidence
from Friday night onward. Gfs is progressive with this front with
a punch of colder air spreading across the Great Lakes region
while the ecmwf develops a surface low over the plains which then
moves across the southern lakes region Sunday maintaining an
unsettled pattern through the weekend. cms


For the 06Z TAFs...

Main forecast concerns are with MVFR ceilings this morning, and
then with a northerly wind for much of the period. Northerly winds
this morning will likely vary around due north, but with more
prevailing north northeast winds expected later this morning into
the afternoon. Upstream cloud cover has shifted overhead with MVFR
ceilings scattered around the terminals. Do think MVFR ceilings
will be possible early this morning across all the TAF sites, and
then with VFR ceilings possibly lingering toward around 12z. Quiet
and VFR conditions then expected through the period.



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 1 PM Monday.

     Small Craft Advisory...ILLINOIS NEARSHORE WATERS UNTIL 10 AM Monday.




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