Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/09/21
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
916 PM CST Fri Jan 8 2021
.UPDATE...
915 PM CST
No major changes to the inherited forecast this evening. Stratus
remains expansive across the region, although we`re noting a good
deal of clearing taking place upstream across north-central
Wisconsin and also western/lower Michigan. With the 950-900 mb
steering flow expected to back more northerly with time, would
anticipate most our area remaining pretty socked in with cloud
cover, although it`s possible some brief clearing takes place into
portions of NW Indiana. Temperatures are plummeting where skies
have cleared. This clearing to our east should invigorate a decent
land breeze push overnight which should in turn continue to
locally enhance any near-surface convergence across northeast
Illinois and NW Indiana.
Inversion heights have trended down perhaps just a smidge from
this time yesterday based on evening RAOB and ACARS data,
resulting in a continued very marginal lake effect parameter
space. Still, was a bit surprised to see how `intense` some of the
snow showers were earlier this morning although an impinging low-
level vort max may have assisted things somewhat. Thinking
scattered flurry wording seems reasonable overnight, with a
mention of isolated snow showers towards and after daybreak into
northeast Illinois appears reasonable. IR satellite shows cloud
top temperatures holding near -7 to -9 C which is right on the
verge of losing cloud ice, but observations continue to indicate
light snow/ at this time. Updated products have been sent.
Carlaw
&&
.SHORT TERM...
230 PM CST
Through tonight...
A 1031 mb high pressure is centered over Minnesota with it`s ridge
axis stretching southwest over the Great Plains down to Texas, while
a low pressure is centered off the Carolina coast. Little movement
is expected from the high pressure while the low pressure pushes out
into the Atlantic, allowing the gradient to weaken slightly over our
area. Widespread clouds cover most of the eastern half of the US,
with overcast cloud ceilings averaging 2000 ft throughout our
forecast area. Temperatures are hovering around freezing, while
our winds remain out of the north.
Lake effect snow flurries continues from Milwaukee to Chicago,
with cloud ceilings occasionally falling below 1000 ft and
visibilities as low as 1/2 mile with the heavier snow flurries.
Parameters are not outstanding for lake effect snow, but enough
convergence/lift exists along the land/lake boundary, with
boundary layer convergence and low- level omega fields aligning
with present snowfall. Winds will vary between northwest to
northeast throughout the day, slowly shifting the area of
convergence and lake effect snow further south and eventually east
along the Illinois lakeshore onto the Indiana lakeshore
throughout the remainder of today and overnight Friday.
Saturday and Saturday night...
The upper level and surface patterns will change very little on
Saturday. High pressure will remain centered over the upper Midwest,
continued northerly winds across the area, and nothing to really
scour out the lower clouds.
Saturday will feature another day with a marginal setup for flurries
and isolated to widely scattered lake effect snow showers, very
similar to Friday, though likely even to a lesser degree.
Thermodynamically the lower atmosphere is very similar with a
equilibrium levels generally under 5,000 ft AGL (below 850 mb),
and marginal temperatures for snow production at the top of the
turbulent low level mixed layer. RAP/HRRR and a few other higher
resolution models do still depict another modest uptick in low
level omega/convergence Saturday morning into early afternoon
before winds begin to shift more westerly Saturday night. Limited
temperature changes will occur given the continued cloud cover,
highs in the 30s, lows in the 20s.
KMD
&&
.LONG TERM...
230 PM CST
Sunday through Friday...
Generally quiet, and cloudy, conditions will continue well into
next week ahead of a pattern change to a west coast ridge and
northeast U.S. trough.
Chances of any prolonged clearing appear low through at least
Tuesday as even the GFS maintain a strong inversion under 3kft.
Temps will remain seasonable into the first part of next week with
potentially small diurnal changes if low clouds are prevalent. A
brief warmup is possible mid-week as a portion of a developing
west coast ridge shifts eastward across the Great Plains. While
some guidance had been advertising the arrival of much colder air
by next weekend, there has been a notable consensus shift in
timing toward the early part of the following week. That is not to
say that colder conditions will not arrive by late next week, but
the coldest air (i.e. 850 hPa temps below -15C) should remain
bottled up north of the Great Lakes through next weekend.
High impact winter weather appears minimal through at least mid-
week. A train of weak mid-level disturbances within west to
northwest flow aloft will traverse the region late Sunday through
Wednesday, but a deep reservoir of dry air above the low-level
inversion during this time will likely prevent any precip from
reaching the ground. With that said, thermo/wind profiles do
somewhat mimic those observed this past weekend, so any ice
nucleation, either natural or anthropogenic, in the stratus deck
could produce localized patches of light precip.
Higher precip chances arrive Thursday into Friday as deep
troughing develops over the Great Lakes region.
Kluber
&&
.AVIATION...
For the 00Z TAFs...
North to northeast winds and overcast skies based between 1500 and
2000 feet will prevail through the TAF period at all terminals.
At ORD/MDW/DPA, flurries will be possible through the entire TAF
period. Overnight, land breezes will reinforce a narrow zone of
low-level confluence over the middle of Lake Michigan. With
overnight temperatures in Michigan expected to be much colder than
in Wisconsin and Illinois, the land breeze from the east will be
much stronger and "push" the zone of low-level confluence
toward the western Lake Michigan shoreline by daybreak Saturday.
All the while, the low- level thermodynamic profile will remain
largely unchanged from today and indeed favorable for snowflake
needle growth. As such, we would not be surprised to see a repeat
"performance" of snow showers shifting down Lake Michigan as the
daylight hours progress on Saturday. Pinpointing exact timing of
snow showers, should they even occur, is tough at this determine
at this time. However similar timing to the snow showers today
(e.g. 18-22Z) may be a good starting point in later TAF packages
should confidence increases.
Borchardt
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...nearshore waters
until 9 AM Saturday.
&&
$$
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