Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/03/21
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
633 PM CDT Mon Aug 2 2021
156 PM CDT
Through Tuesday night...
Spotty light sprinkles/showers will continue this afternoon within
an expansive region of diurnally-enhanced cumulus north and west
of I-55/57 and east of I-39. Latest VAPOR AMDAR soundings out of
MDW/ORD suggest that, when accounting for dewpoints in the upper
50s, MLCAPE values around 250-300 J/kg are being realized. Stout
warming just under 600 mb will continue to limit vertical growth
of any convective cores today, even with the arrival of an
upstream shortwave. We`ll continue to indicate some low shower and
sprinkle chances through around sunset today.
With skies expected to clear this evening and overnight, the dry
airmass in place, combined with light winds will allow
temperatures to drop back into the low to mid 50s away from
Chicago once again, with a smattering of near 50 degree readings
not out of the question in our typical cool/outlying locales.
Suppose some spotty, very shallow fog is possible where
temperatures settle to the dewpoint overnight.
Broad cyclonic flow continues aloft tomorrow with an altogether
similar look to things compared to today, with a secondary vort
lobe slated to drop into southern Wisconsin through the afternoon.
Forecast soundings look a bit less supportive of precipitation
tomorrow, however, with slight boundary layer drying, combined
with the warm layer/subsidence inversion descending to around 700
mb or so. As a result, will continue with a precipitation-free
forecast tomorrow under another healthy late-morning and afternoon
Cu field. High temperatures should be a degree a few degrees
warmer than today.
229 PM CDT
Wednesday through Monday...
An upper trough extending from the Great Lakes to northern Florida
will weaken and drift eastward Wednesday while weak high pressure
will be in place at the surface. This will yield another pleasant
day with highs similar to or a couple degrees warmer than Tuesday.
A southeasterly lake breeze will develop keeping IL lakeshore
areas several degrees cooler. Dry weather persists for Thursday
but an upper shortwave will approach Thursday night and cross the
area Friday morning. There will not be a great opportunity for
much moisture return but there will be enough support for low
chances for showers/thunderstorms late Thursday night through
Friday morning. A stronger trough pushing into the Pacific
Northwest will force upper ridging eastward across the plains and
Mississippi River Valley into Saturday while also breaking it
down. Stronger southwesterly low level flow sets up bringing a
warmer and more humid airmass into the area. Expect highs to warm
into the upper 80s to around 90 Saturday over the weekend and into
Monday. Low to mid 70s dewpoints will bring heat index values to
around 100 Sunday and Monday. Shower/thunderstorm chances are more
ambiguous at this point and should be focused to the north
overall, but the warm and unstable airmass would be supportive of
development with any ripple in the newly established zonal flow.
For the 00Z TAFs...
Aviation Forecast Concerns:
* Easterly lake breeze winds diminishing and veering southeast
this evening. Becoming light with westerly land breeze component
overnight, then easterly lake breeze again Tuesday afternoon.
Weak surface pressure gradient was in place across the region late
this afternoon/early evening in the vicinity of high pressure
ridge across the Midwest. Combination of light/variable winds,
lake breeze and some isolated shower outflow/differential heating
has made for a messy...but light...wind field. Overall trend
should be fore easterly lake breeze winds across the Chicago
terminals to weaken and veer southeast this evening, potentially
becoming light/variable for a time before taking on a light
westerly land breeze component overnight. VFR ceilings in the
6-10 kft range should also scatter out during the night with the
loss of diurnal heating and the passage of a mid-level wave this
Similar weather expected Tuesday, with diurnal increase in VFR cumulus
and an easterly lake breeze wind shift for the Chicago metro
terminals in the early afternoon hours.
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