Scientific Forecaster Discussion
fxus63 klot 140916
Area forecast discussion
National Weather Service Chicago/Romeoville, Illinois
416 am CDT Mon Oct 14 2019
301 am CDT
Through Wednesday night...
Sunny with seasonably cool temps today. By late tonight and
particularly Tuesday, the area will be affected by a vigorous
clipper-like system amplifying as it drops southeast into the
Great Lakes region.
Biggest impact from this clipper which will track well north of
our area will be from moderately gusty southerly winds Tuesday,
followed by even stronger west then northwest winds on the back
side of the system Tuesday night into Wednesday. Precip chances
with this system are a bit of a conundrum, with some guidance
suggesting a dry frontal passage with precip breaking out to our
east while some guidance brings the return moisture north into the
area just in time for showers and perhaps a T-storm to develop
Tuesday. While there is uncertainty regarding how quickly moisture
returns, guidance is in good agreement in depicting a plume of
steep mid-level lapse rates wrapping into the cyclone and into the
region Tuesday. Will likely see some altocumulus castellanus and virga/sprinkles
even if the moisture return isn't in time for more robust
Cold front with this system will clear our eastern County Warning Area early
Tuesday evening but expecting a fairly extensive Post frontal
stratus deck to rotate into the area in the cold air advection
regime on the back side of this cyclone. The cloud cover should
limit the diurnal swing in temps Tuesday night through perhaps
Wednesday night. Have nudged temps up some at night and down a
bit for wed's high given the expected cloudiness. Low level flow
begins turning anticyclonic Wednesday night, so should eventually
begin to see clearing at some point in time Wednesday night.
301 am CDT
Thursday through Sunday...
Tuesday/wednesday's trough will lift out of the region with rising
heights and warm air advection resulting in a warming trend late
in the week and continuing into the weekend. Medium range models
do have a weak/low amplitude wave rippling across the region
Saturday with an accompanying shower threat. The more significant
rain chances look to be beyond next weekend with models continue
to advertise a powerful long wave trough traversing the country
with ample time for Gulf moisture to return in advance of this
system. In the meantime, look for moderating temps and no
significant precip chances Thursday through the upcoming weekend.
for the 12z tafs...
416 am CDT
No concerns today-tonight
concerns on Tuesday morning:
* chance for scattered rain showers and maybe a ts
* gusty southerly winds developing
* MVFR cigs possible toward mid day
VFR with no aviation concerns through tonight. Westerly winds
generally less than 10 kt will become briefly southwest toward
sunset this evening and then southeast this evening. A cold front
will approach on Tuesday morning, possibly accompanied by
scattered rain showers activity and maybe a couple thunderstorms and rain. With uncertainty
on whether enough moisture will arrive in time for rain showers to
develop, for now indicated a prob30 in the Ord/mdw 30 hour tafs
mid Tuesday morning and Onward and for the last couple hours of
the rfd 24 hour taf.
Winds will turn from south-southeast to south-southwest ahead of
the cold front during Tuesday morning and likely gust into 20-25
kt range by the mid to late morning. Cigs may lower to higher end
MVFR ahead of the front, possibly tied to any rain showers. A better
chance for a period of prevailing MVFR cigs may come behind the
cold frontal passage Tuesday afternoon.
227 am CDT
Northwesterly gales are possible on Southern Lake Michigan on
Tuesday night into Wednesday. A strong cold front will sweep
across the lake Tuesday afternoon. The parent low pressure system
will strengthen as it tracks eastward from the northern lakes to
the eastern lakes Tuesday night into Wednesday morning, tightening
the pressure gradient. In addition, a seasonably cold air mass
moving over the relatively mild lake waters will result in unstable
conditions and effective mixing. At this time, confidence is highest
in gales for the Indiana nearshore, but they are certainly possible
for the Illinois nearshore as well. The northwesterly wind direction
means that waves will be largest along the Indiana nearshore. Should
trends hold with this system, a gale watch will likely be needed
later today or tonight.
ilz023-ilz032-ilz033-ilz039 until 8 am Monday.
In...frost advisory...inz001-inz002-inz010-inz011-inz019 until 8 am
Lm...Small Craft Advisory...Gary to Michigan City in until 9 am Monday.
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