Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/01/22

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 811 PM CDT Tue May 31 2022

.UPDATE...
Issued at 807 PM CDT Tue May 31 2022

Continuing to monitor a gradual uptick in showers and some storms
into the evening, with a limited/isolated severe potential.

Since 5 P.M., there has been a slow but steady increase in
showers and some storms in the confluence zone along and about 100
miles ahead of the cold front. This zone is within a plume of
high moisture in the 0-3 km layer, as sampled by the 00Z DVN
sounding, and shown by surface dew points around or just above 70.
The vertical profile on that DVN sounding was uncapped, with
1,500 J/kg of mlCAPE, but lapse rates in mid-levels are fairly
poor (6.5C/km through most of the depth). With the moisture,
including PWATs of 1.5-1.7 inches, would think there will
continue to be a gradual uptick in at least shower coverage and
probably in intensity of a few cells through 10-11 P.M. There is
35-45 kt of deep layer shear analyzed in the northwest quarter of
Illinois, so some organization has been seen with storms, even
despite meager lapse rates, and with some isolated cells, that
probably will continue. Forward motion on the cells is largely
parallel to the boundary/confluence axes, so even though shear
orientation to these boundaries favors discrete/semi-discrete
cells, it hasn`t taken long for cells to merge into small clusters
if they can sustain themselves...and thus far few have done that.

Aircraft soundings from over the Chicago metro indicate still some
capping in place, so while there have been some cumuliform clouds
along some boundaries seen on radar reflectivity, they have not
materialized into any convective cells. This also means the
activity to our west may struggle as it gets toward and especially
east of I-55. But prior to then, through 11 PM or so, there
remains a chance for a couple stronger to possibly one or two
severe storms. That includes with a couple of the clusters from
western Illinois into northeast Missouri, which on GOES-16 water
vapor imagery looks like may have a mid-level sheared wave
supporting them too. If some of those clusters track over the
same area, it would not take much for an isolated 1-2 inch
rainfall occurrence given the moist profiles.

Overall, this is more in-line with an SPC level 1 of 5 (Marginal)
Risk, and accordingly, that`s the level now with their 01Z
updated outlook.

MTF

&&

.SHORT TERM...
Issued at 315 PM CDT Tue May 31 2022

Through Wednesday...

Main focus/concern:

* Threat for any strong to severe thunderstorms through mid to
  late evening, with threat window about 6 PM to 11 PM

The local radar picture is currently devoid of any convection,
likely owing to suppression on the backside of the core of the
MCV lifting into Wisconsin. In addition, as noted earlier,
extensive mid and high cloud cover has limited stronger
destabilization despite temperatures in the lower to mid 80s
northwest of I-55 and mid to upper 80s near and southeast of I-55
amidst dew points in the 60s. It appears likely that there`s at
least some lingering mid-level capping. Most recent HRRR run
initialized well and now focuses main convective threat toward and
beyond sunset.

Another important item of note to the late day and evening severe
weather threat is the lack of surface convergence with the cold
front draped west of the Mississippi River. The cold front
currently serves more as a moisture discontinuity with generally
southwest winds on either side of it. It thus appears that the
anticipated thunderstorm uptick in the early evening will be tied
to forcing related to upstream convection across Missouri, which
may be tied to a 700 mb wave. If any modestly robust MCV can
emerge from this area, that would certainly assist in scattered to
numerous showers and storms developing. A northwesterly wind
shift is now not expected until after midnight behind the front,
hence the above thinking on more mesoscale influences resulting in
convection blossoming and then gradually building east and
southeast.

The lack of stronger large scale forcing and low-level convergence
does cast uncertainty on convective coverage this evening, though
as noted, continued message of scattered to numerous t-storms
with likely PoPs. Turning to the severe threat, the thinking
hasn`t changed from midnight shift of an overall decreased threat.
It appears that debris cloudiness will remain extensive enough to
continue limit strong with inc r destabilization through the
daylight hours, and the strongest effective shear will remain near
or northwest of the northwest CWA. With signs pointing toward
more of an evening timing, we`ll then have to contend with diurnal
decrease of SB/MLCAPE after sunset. While SPC maintained a level
2 (slight) severe risk in their 20z update, suspect trends point
to more of an isolated level 1 (marginal) severe threat for hail
and damaging winds. If convective coverage becomes widespread
enough this evening, can`t rule out an isolated/localized flooding
threat, though confidence is also low in this regard.

Assuming anticipated convective coverage this evening comes to
fruition, it should gradually wane after midnight as cold front
finally makes southeastward progress. The cold front will clear
the entire CWA to the south tomorrow morning and then slow its
progress to the south of I-70 on Wednesday. Lingering weak
elevated instability north of the surface front could enable a
few rogue thunderstorms for southeast CWA sections primarily
during the morning, but otherwise looking at a cooler but pleasant
and primarily dry day for most under partly to mostly cloudy skies.
Have some slight to chance PoPs for the southeast 1/3 to account
for isolated to widely scattered showers pushing in at times.
Highs will be in the 70s inland but only in the 60s near the lake
as onshore flow persists through the day with high pressure over
the Great Lakes. Dew points will be quite comfortable and in the
50s for most locations.

Castro

&&

.LONG TERM...
Issued at 328 PM CDT Tue May 31 2022

Wednesday night through Tuesday...

Wednesday night, a broad center of low pressure is forecast to trek
across the Ohio River basin with a swath of showers and
thunderstorms along its northern periphery. Several of these
showers will fall over the CWA Wednesday night and early Thursday
morning. The greater rain chances will exist in the southern and
southeastern portions of the CWA with far less confidence in rain
occurring along and north of I-88. This also corresponds to the
greatest potential for seeing a couple of thunderstorms with most,
if not all, of the storm activity expected to be confined to
areas south of I-80. Any storms that manage to pop up should be
just your run of the mill thunderstorms with very little
instability present inhibiting the chance for any strong storms.
The ideal timeframe for rain out of this system is roughly 2AM-
7AM meaning a few showers could accompany your Thursday morning
commute, especially if that commute is southeast of I-55.
Following this early morning rain chance, the rest of Thursday
will be dry with clearing skies as some drier air works its way in
aloft with the trough digging in.

Meanwhile, cool northerly low-level flow and height falls aloft
through the morning will keep temperatures in the lower and middle
70`s on Thursday with areas closer to the lake getting stuck in
the 60`s. With the trough axis slated to pass through the CWA
Thursday afternoon, some WAA aloft in the mid and upper levels
will help temperatures climb into the middle and upper 70`s on
Friday. A large center of high pressure descending from the
windward side of the aforementioned through will keep conditions
dry through Friday and most of Saturday. Temperatures will climb
an additional couple of degrees on Saturday, although onshore flow
will keep communities closer to the IL lakeshore down in the 60`s
again.

Saturday evening and night, a weak, developing warm frontal boundary
will propagate into Upper Midwest and park itself over southern
Wisconsin becoming quasi-stationary through Sunday. Isolated showers
are forecast to pop up along this boundary and fall on the CWA as
early as Saturday evening with coverage expected to expand to more
scattered showers for much of Sunday. The rain chances will continue
into Monday with the broad low pressure center expected to pass over
on Monday. A second, more organized center of low pressure will pass
through central IL on Tuesday keeping shower chances rolling
through Tuesday as well. Thunderstorm chances through the weekend
appear minimal with little instability found near and south of the
frontal boundary. A fair amount of instability building in ahead
of the low pressure center makes Monday afternoon and evening our
best chance for seeing thunderstorms early next week. However, a
nearly zonal shear profile and mediocre thermodynamic profile
should keep storms light and brief. Temperatures on Sunday and
Monday will reach the middle 70`s to lower 80`s before dropping a
few degrees following the Low passage on Tuesday.

Doom

&&

.AVIATION...
For the 00Z TAFs...

The primary aviation weather concerns through the 00Z TAF period are
as follows:

- The potential for showers and thunderstorms this evening

- Winds shifting to near-northerly overnight tonight, then onto
easterly early Wednesday afternoon

Following a dry Tuesday thus far, a line of convective showers is
building across eastern IA and far northwestern IL. These showers
will be moving through the area mid to late evening with some
additional showers potentially popping up ahead of this existing
line and reaching the terminals as early as around 01Z. It appears
that there will be some thunderstorms embedded in these showers as
well, however thunderstorm coverage and intensity are still not
entirely certain. While strong to severe thunderstorms are certainly
still possible, best guess is that these will be just some routine
gusty storms with one or two isolated stronger storms. A few rounds
of showers and storms appear possible, primarily between 02Z and 06Z
over Chicagoland. Isolated light showers could then continue into
the predawn hours of Wednesday morning. VFR conditions should
prevail through this event, although some guidance suggests that we
could see cigs drop into high-end MVFR territory for brief periods
underneath some of these showers.

Meanwhile, gusts near 20-25 kts will hang on through around sundown
before winds drop below 10 kts for the overnight. Winds will then
shift from SW to NNW overnight and hang there through the morning.
By early-mid afternoon, winds will turn east of north over ORD and
MDW and continue from an easterly direction at near or under 10 kts
through the remainder of the TAF period. Following tonight`s rain
event, VFR conditions can be expected for the entirety of
Wednesday.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...nearshore waters until 9 PM Tuesday.

&&

$$

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