Scientific Forecaster Discussion
fxus63 klot 120446
Area forecast discussion
National Weather Service Chicago/Romeoville, Illinois
1046 PM CST Mon Nov 11 2019
Update...910 PM CST
Winter weather advisories have been allowed to expire. There is
still some lingering snow across lake adjacent counties of
Northwest Indiana, though we have been a decreasing trend across
lake and Porter. Expect there will still be some showers and
occasional winds to 35 mph across the snowbelt with better chances
for accumulation and higher impacts from La Porte County
northeast. Lakeshore flood warnings remain in effect for northwest in,
while we have downgraded the Illinois side to an advisory given the
Wilmette buoy is still fluctuating from 7-8 ft and winds are northwest
and mostly offshore.
Clearing skies and continued cold advection could bring lows this
evening to near record for the day. See the climate section below
for more details on this upcoming climatologically significant
cold outbreak for early-mid November.
305 PM CST
Through Tuesday night...
Light snow continues across much of northeastern Illinois early this
afternoon. However, the main axis of moderate snow has been over
my southern counties in east central Illinois and northwestern in. It is
in this area that snow accumulations are expected to continue for
the next couple hours, before the snow begins to wind down across
most areas. Little additional accumulation is expected over the
Lake effect/enhancement will continue to result in snow shower
impacting portions of northwestern in into this evening. This
may result in some additional light accumulations into lake and
Porter counties in Indiana. Otherwise, it appears the threat for
heavier lake effect snows may remain east of Porter County in
The main story now turns to the record breaking cold expected
tonight through Tuesday night. Temperatures this afternoon have
hovered in the low 20s over far northern IL, and with sunset
expect these values to fall through the teens this evening.
Overnight lows are expected to fall into the single digits over
north central IL, and into the low to mid teens over northeastern
Illinois and northwest in. Wind speeds will remain in the 10 to 15 mph
range with these cold temperatures, thus wind chill values will
fall into the single digits below zero later tonight into early
Tuesday morning. Temperatures then look to struggle to reach 20
degrees across much of northern Illinois. This looks to result in new
record coldest high temperatures for the 12th at both Chicago and
Low temperatures Tuesday night look to be a bit tricky. Winds will
become light by Tuesday evening, and with a snow cover this could
result in temperatures dropping like a rock early Tuesday evening.
However, it does appear that as a surface high shifts to our
southeast later in the evening, the lower level winds will shift
southerly allowing for some modest warm air advection. High level
cloudiness only looks to increasing during the evening. For this
reason it appears unlikely that temperatures will drop much colder
than tonight's temperatures. We may even end up with low
temperatures occurring early in the evening, then rising
overnight. Eighter way, it will still be near record breaking low
temperatures for this date.
315 PM CST
Wednesday through Sunday...
South winds will increase Wednesday morning on the backside of
departing high pressure while a weak clipper system approaches
from the northwest. This looks to set the stage for some decent
isentropic upglide over the area late Wednesday into Wednesday
night, which should support some light snow over northern Illinois
during this period. Overall, this does not appear to be a major
accumulating snow for the area, but the potential is there for
some minor accumulations under 2" over northern IL, generally
north of I-80.
High pressure will move across the central U.S. Thursday/Thursday
night. A stronger high will then move across the northern Great
Lakes on Friday sending a cold front toward the area into Friday
evening. While this front will not push much cold air over the
area, it will act to keep temperatures on the cold side of normal
into the weekend.
Next potential system would be on Sunday as the GFS/Gem have a
weak system spreading across the area during the daytime. Temps
would likely be warm enough for mainly rain but chance pops also
in the nighttime periods over the weekend include some rain/snow
mix. The ECMWF weakens this system as well and stays mainly dry
over the weekend thus low confidence during this time period.
Record minimum temperature for November 11th
-chicago: 15 in 1950
-rockford: 10 in 1926
Record low maximum temperature for November 11th
-chicago: 28 in 1894
-rockford: 26 in 1986
Record minimum temperature for November 12th
-chicago: 8 in 1986
-rockford: 7 in 1986
Record low maximum temperature for November 12th
-chicago: 28 in 1995
-rockford: 27 in 1940
Record minimum temperature for November 13th
-chicago: 6 in 1986
-rockford: 3 in 1986
for the 06z tafs...
VFR conditions will dominate through the taf cycle, though there
will be lake effect clouds/snow showers to the east of kgyy. Very
cold air mass moving into the area will keep low levels well
mixed. This will support fairly frequent northwesterly (310-330
deg) gusts into the high teens to as high as mid 20s kt through
Tuesday morning (likely highest at gyy) at the Chicago area
terminals. Forecast soundings suggest that gusts will end by about
mid day Tuesday and then light southwest winds are expected
Tuesday evening as high pressure crosses the area. Higher clouds
will spread in from the west Tuesday night as winds back southerly
and increase toward daybreak Wednesday.
Illinois...Lakeshore flood advisory...ilz014 until 9 am Tuesday.
In...Lakeshore Flood Warning...inz001-inz002 until 4 PM Tuesday.
Lm...Small Craft Advisory...Illinois nearshore waters until 3 PM Tuesday.
Gale Warning...in nearshore waters until 9 am Tuesday.
Small Craft Advisory...lmz743-lmz744-lmz745...9 am Tuesday to 10
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