Scientific Forecaster Discussion
fxus63 klot 140157
Area forecast discussion
National Weather Service Chicago/Romeoville, Illinois
857 PM CDT sun Oct 13 2019
857 PM CDT
No changes have been made to the frost advisory this evening. Clouds
in the 800-850 hpa layer have been rather persistent across
primarily the north half of the County Warning Area this evening. However, some
drier air entraining into the cloud deck is evident across northwest
Iowa and should begin to slowly erode the clouds from the northwest
late this evening. Current trends and ongoing weak frontogenesis that
is likely helping to maintain the clouds suggest they may end up
contracting into a more narrow band that persists over some portion
of the County Warning Area well into the night. With uncertainty on where this would
occur, if at all, and the fact that temps should drop quickly once
clouds clear at any given location, felt it prudent to keep the min
temp forecast as is. With that said, did delay some of the more
pronounced cooling until after midnight.
205 PM CDT
Surface low pressure continues to weaken across Lake Superior
early this afternoon, and it will slowly fill and lift to the
northeast. Gusty west-southwest winds will abate some this
afternoon as a shield of low to mid clouds will continue to
spread into the northern Illinois, but expect a quick drop in
winds in the evening as higher pressure moves in from the
southwest and the low to our north fills and pulls away.
The surface high will shift into central Illinois tonight into Monday.
Expect lighter winds and limited impact on Monday as the surface
high pressure ridge will nose in from the south. The trend is
for the lower clouds to erode this evening in spite of some
continued, though weakening cyclonic flow from the upper level low
to the north should support at least some clouds may linger a bit
longer than guidance indicates. While not a classic frost/freeze
setup, it appears winds should slacken enough to promote widespread
low to mid 30s away from the urban core. Some areas northwest
could dip below freezing but confidence on for how long is low
with winds up a little it does not look a hard freeze for most
locations. Will handle this with a frost advisory area wide
(varying times in the npw). Note the gradient in temperatures in
the outer portions of Cook, Lake, Porter from interior to
Lakeshore areas where mid to upper 30s are favored, along with the
mention of sub freezing temperature potential in the zone breakout
across north central Illinois.
There are limited concerns on Monday with the ridge axis progged
to move through, therefore expect slightly below normal temperatures
with highs lower 50s north to near 60 south coupled with largely
237 PM CDT
Monday night through Sunday...
Vigorous trough forecast to dig southeast into the western Great
Lakes Tuesday. Biggest difference in solutions among the various
models is speed of moisture return and when/if precip breaks out.
Morning guidance still showing widely varying solutions, with a
drier trend noted with today's guidance. Blended model guidance
still seems reasonable at this time, with low chance pops early
Tuesday through Tuesday afternoon.
Shot of seasonably cooler air filters in behind the associated
front mid-week, with another period of windy conditions appearing
possible late Tuesday night into Wednesday. Medium range guidance
is in pretty good agreement in depicting an amplification of the
jet stream late in the week into next weekend. Initially, upper
ridging building over the eastern U.S. Will support moderating
temperatures, followed by long wave trough moving east and
bringing rain and perhaps thunder chances to the area next weekend
or early next week.
for the 00z tafs...
Cigs around 5k feet will persist with some breaks at the terminals through
around 05-7z tonight before eroding from the south. This as the
powerful upper level low north of Lake Superior slowly drifts away
and fills. Surface high pressure will then ridge into the area
overnight and dominate weather conditions Monday. Hence expect
mostly clear skies and light winds throughout the day. Winds will
turn light out of the south Monday evening as the high moves off
to the east and low pressure advances east from the plains.
ilz012-ilz019-ilz020-ilz021 until 8 am Monday.
Frost advisory...ilz006-ilz013-ilz014-ilz022...1 am Monday to 8
Frost advisory...ilz023-ilz032-ilz033-ilz039...4 am Monday to 8
In...frost advisory...inz001-inz002-inz010-inz011-inz019...4 am
Monday to 8 am Monday.
Lm...Small Craft Advisory...Gary to Michigan City in until 3 am Monday.
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