Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/08/21
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
856 PM CDT Sat Aug 7 2021
.UPDATE...
855 PM CDT
Quick update to continue to trend PoPs (and thunder chances) down
through the rest of the evening and early-overnight hours. Initial
compact MCS we were monitoring over southern Wisconsin continues
to track safely off towards the east. Regional radars are sampling
some spotty returns near Chicago and out across the lake, but
these should be of little consequence. Evening RAOB out of the
Quad Cities sampled some significant mid-level dry air in the
850-600 mb layer which has likely helped to greatly limit
southward development of additional convection so far this
evening.
Have recently seem some slight increase in mid-level echoes
pushing across eastern Iowa, but thus far much of these seems to
be evaporating before hitting the ground. While we`ll continue to
pare PoPs back through the overnight, we`ll still be keeping an
eye on this activity and its associated low-amplitude sheared vort
max as it`ll be pushing through a region of conditionally very
unstable air with lapse rates in the 800-600 mb layer near and in
excess of 8 C/km. As it stands now, forecast soundings look just
too dry to support elevated thunderstorm development out of this
activity later, but we`ll keep an eye on things.
The next question becomes the degree of upscale growth/storm
amalgamation tonight across southern Minnesota into west-central
Wisconsin at the nose of a strengthening low-level jet. Current
thinking is that the combination of the aforementioned dry mid-
level pocket analyzed drifting east of the Mississippi River and
the location of developing echoes north of the warm front (well
north of our area) will help curtail additional precipitation
chances through the overnight hours but have noted some better
southward push to the cores in central Wisconsin.
Carlaw
&&
.SHORT TERM...
320 PM CDT
Through Sunday Night...
There remains considerable uncertainty regarding the evolution of
shower and thunderstorm activity for the remainder of the day and
tonight, but the general idea is that areas along the WI line will
be most favored late this afternoon and evening, with scattered
activity possible over a more widespread area this evening and
overnight. Overall the coverage is not expected to be extensive
through tonight and Sunday morning, except perhaps near the state
line. By Sunday afternoon into Sunday evening, shower and
thunderstorm chances increase further for most of the area.
Interestingly enough, several of the available CAMs have a similar
depiction of the situation over the next 24-26 hours, with expected
differences in specific details. Many actually keep the entire CWA
dry through midnight or so, with only light activity overnight. This
would likely be related to the weak riding in place that has been
hindering the southward development of activity to our north. Even
so, 3000-4000 J/kg of MUCAPE late this afternoon will provide
considerable instability if outflow from the north manages to nudge
a parcel to the LFC. The latest ACARS soundings suggest there is a
weak inversion near the 825 mb layer that shouldn`t be overly
difficult to push through given sufficient forcing.
Sunday morning appears to be a period of relativity little activity
given the diurnally unfavorable timing as well as lingering
influences of ridging aloft. By later on Sunday and especially
Sunday night a more significant upper wave approaches. With the
warm and moist boundary layer airmass in place, along with
additional convergence provided by a developing low level jet, most
areas appear likely to see one or more lines of thunderstorms push
through starting mid-late afternoon and continuing into the
overnight hours. This would include the potential for heavy rain
and localized flooding, especially toward western portions of the
area likely to have the best moisture transport under the LLJ.
Lenning
&&
.LONG TERM...
320 PM CDT
Monday through Saturday...
Unsettled, warm and muggy conditions will persist through much of
the extended period. While there will be many dry periods,
multiple waves will bring off and on chances for precipitation.
Upper ridging builds in behind the departing wave bringing even
warmer conditions through midweek, however, there are some signs
of relief in the heat and humidity toward the end of next week.
Precipitation will likely be ongoing Monday morning from
overnight convection from Sunday associated with an upper wave
lifting north and east across the lower Great Lakes. The greater
coverage and clouds and precipitation should help hold down high
temperatures into the 80s and in turn heat indices below 100
degrees, but still expecting warm and muggy conditions.
The upper ridge axis shifts overhead behind the departing wave on
Tuesday setting the stage for heat indices potentially exceeding
100 degrees across the area. Given the very unstable airmass in
place isolated thunderstorms will be possible during the day. A
more subtle wave will be approaching the area from the west where
convection may drift into the area Tuesday night.
Lingering scattered showers and thunderstorms and clouds on
Wednesday may hold temps in the 80s, similar to Monday which will
help with the heat indices while another subtle disturbance tries
to dip southeast across the lower Great Lakes. Guidance has
trended slower and further north with the upper wave which will
allow for warmer temps to build back in on Thursday where we could
see another day with temperatures warming back into the lower
90s, however dew points may be a bit lower than Tuesday, keeping
heat indices in the 90s.
A surface cold front is expected to move through the area late
week which should bring us some relief in the heat and humidity
Friday into next weekend.
Petr
&&
.AVIATION...
For the 00Z TAFs...
645 PM CDT
The main concerns for the Chicago area terminals include:
* Low confidence convective threat this evening-tonight
* Gusty south-southwest winds Sunday, with 25-30 kt gusts possible
* Scattered TSRA possible mid Sunday afternoon through evening
The main focus for convection approaching 00z is over southern
Wisconsin. Current location and motion of the small bowing cluster
of TSRA near MSN would entail at most WI/IL state line area
getting clipped. Will have to watch for any outflow effects from
this cluster for wind impacts into Chicago. While some farther
southeast propagation can`t be ruled out and/or development over
far northern Illinois, confidence was too low for any TS mention
in the Chicago metro terminal TAFs. Had introduced a VCTS for RFD
for early this evening and while confidence is also low there,
opted to maintain it for threat of development nearby to the south
of the aforementioned cluster near MSN.
For the remainder of the overnight, there are some mainly light
radar echoes on the regional mosaic over eastern and northeast
Iowa. Satellite, observed sounding, and forecast sounding trends
suggest strengthening capping with southward extent over the
TRACON area. However, given the large elevated instability
reservoir and some forcing, can`t rule out farther south
development than shown by recent high resolution forecast radar
reflectivity.
On Sunday, day should start dry and capped, with increasing
south-southwesterly winds (190-210 deg direction). Forecast
soundings indicate frequent gusts in 20-25 kt range, with
potential for occasional 25-30 kt gusts. Attention turns to a much
stronger disturbance currently over the ND/SD border that will
move east-southeast through Sunday evening into a strongly
unstable air mass. Considering uncertainty in the timing of
convective development and overall coverage, especially with
eastward extent, opted for PROB30 TS mention in the TAFs for now,
starting earliest at RFD.
Castro
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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