Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/29/22

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 842 PM CDT Sat May 28 2022

.UPDATE...
Issued at 842 PM CDT Sat May 28 2022

Main updates to the forecast had been with adjustment to our
gridded pops since this afternoon, to focus on a small area of
mainly sprinkles moving east-southeast across far northern IL and
northwest IN. Remainder of forecast is in good shape this evening,
and no other significant changes made.

Isolated high-based convective showers (reaching the ground as a
few sprinkles) were noted from the south suburbs along the Cook-
Will county line, eastward along the south shore of Lake Michigan
as of 825 pm. These were occurring along the southeastern flank of
a small mid-level short wave tracking east across northeast IL,
where an associated pocket of mid-level moisture and convergence
was taking advantage of steep mid-level lapse rates. A recent
AMDAR ascent sounding out of KMDW depicted this moist layer just
below 12 kft, or around 640 mb, with very dry low levels depicted
below supporting evaporation below the cloud base. A pair of
embedded smaller MCV features produced a few more robust elevated
showers (and isolated lightning) earlier this afternoon along the
I-88 corridor, but these have moved well east of the region this
evening. A few isolated showers will linger from south of Chicago
into northwest IN for another 1-2 hours this evening, before the
mid-level wave (nicely evident in GOES water vapor imagery) moves
east of the forecast area. Otherwise, partly cloudy cirrus skies
are expected overnight along the northern edge of another mid-
level wave passing across downstate IL/IN.

Temperatures will be milder overnight than last night, thanks to
modest south winds and increasing boundary layer moisture. Lows
will dip into the upper 50s along the IL Lake Michigan shore where
an onshore wind component has brought chillier marine air, but
most of the area will see lows in the lower 60s. Windy and warmer
weather is expected for Sunday, with another chance of high-based
sprinkles across about the northwest half of the forecast area in
the afternoon.

Ratzer

&&

.SHORT TERM...
Issued at 230 PM CDT Sat May 28 2022

Through Tonight...

The forecast summary for the rest of today into tonight is
fairly pleasant, although sprinkles or isolated light showers are
on the scope in far northern Illinois late today and early this
evening. The potential for thunder with this remains low.

A somewhat stretched out upper level short wave trough stretches
from northeast Wisconsin through eastern Iowa this afternoon. This
has largely outpaced the 700-850 mb warm air advection zone and
reached a drier inherent air mass. Sprinkles to spotty light
showers have made it into far northern Illinois as of 230 PM. The
lightning trend in the eastern Iowa activity has been gradually
downward, with GLM data showing multiple 10-minute windows in the
past hour of no lightning. With most of the sprinkles/light
showers moving at the mid-level flow, would envision these
traversing across far northern Illinois with a diminishing in
their footprint as they do through sundown.

For this evening into tonight, forcing from the short wave trough
will have weakened/passed on, with gradual theta-e advection at
the low-level jet layer. With a lack of a clear focus, the chance
for any showers seems low, even though a few convection allowing
models (CAMs) indicate spotty QPF. The exception would maybe be if
there is some residual effects --small scale MCV or elevated
boundary -- from this afternoon shower activity. But not seeing
that at this time. Southerly winds should level out tonight
without much diminishing and then begin increasing in the pre-
dawn time. Lows will be about 5 to 10 degrees above normal.

MTF

&&

.LONG TERM...
Issued at 326 PM CDT Sat May 28 2022

Sunday through Saturday...

Sunday: An upper ridge building into the Great Lakes region as a
stout EML advects in from the southwest. Temps and winds should
quickly increase through the morning hours under a 23-25C 875hPa
warm nose at the base of the EML. Widespread mid-80s are expected,
with some temps pushing into the upper 80s as higher surface dew
points remain confined well to the west (upstream dew points in
the mid 50s today).

A weak wave embedded in stronger SW flow aloft on the western
flank of the building ridge will brush the northwest half of the
CWA in the afternoon and early evening. Similar to today, forcing
within a layer of higher (but still marginal) moisture from
12-15kft may be sufficient to generate isolated to scattered
elevated showers. Steep 8C/km 400-600 hPa lapse rates will allow
showers to grow deep enough that some sprinkles may survive to the
surface even in the presence of an exceptionally dry sub-cloud
layer.

The strong inversion combined with increasing mid-level
cloudiness in the afternoon will limit mixing to some extent, but
mixing should become sufficient to tap into 35-40kt flow along the
inversion in the afternoon. Expectations are for southerly gusts
to frequently reach 35 mph area-wide by early afternoon, with some
gusts to 40+ mph mid to late afternoon. Lake Michigan
modification will likely result in a slight backing of the winds
along the Illinois shore. With waves building to 3-5ft on a longer
fetch toward Lake (IL) County, opted to issue a Beach Hazard
Statement mid-morning into the evening.

Memorial Day: Sub-850 hPa mixing heights under the existing deep
EML will allow for rapidly warming conditions during the morning
hours. Coming off morning lows in the upper 60s to low 70s in the
Chicago metro combined with 925 hPa temps of 23-25C and mostly
sunny skies will yield afternoon temps around 90F for much of the
area. Temps will have a chance to over-perform into the low 90s if
better low- level moisture advection remains confined to areas
west of the CWA and dew points mix out into the upper 50s.
Climatologically speaking, temps of at least 90F on Memorial Day
occur less than 10% of the time, with the Monday`s record high of
93F in Chicago not totally out of reach.

Tuesday into Thursday: The broad trough currently over the
western CONUS will eject a slow-moving wave NNE through the Great
Plains on Monday before being absorbed into another trough digging
southeast into Manitoba and northern Ontario on Tuesday. An
associated cold front will drift southeast into the forecast area
late Tuesday afternoon into Tuesday night before stalling
somewhere from central Illinois into the Ohio River Valley. A
ribbon of higher low-level moisture advecting in ahead of the
front will push MLCAPE values to around 1500 J/kg amid deep layer
shear on the order of 25-30kts. This should support some organized
deep convection and a localized severe thunderstorm risk
conditional upon eroding what is remaining of the EML. Pwats
rising well over 1.5" with propagation vectors only 30 degrees or
so off the front will pose a localized heavy rain threat.

The ultimate southward reach of the front will hinge on the
amount of convection and strength of any more expansive cold front
Tuesday night. While consensus guidance is favoring the front to
remain south of the CWA mid-week, another broad mid-level trough
shifting across the central CONUS will interact with the front and
existing higher Pwats to the south to produce a locally heavy
rain threat that may extend northward into the forecast area.

Kluber

&&

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

Aviation forecast concerns for this TAF period include:
* Breezy southerly winds beginning Sunday morning and lasting
  through the remainder of the TAF period
* Marginal low-level wind shear threat Sunday evening

The main focus of the going TAFs is the winds, which will be quite
breezy throughout much of the TAF period. Any residual gusts to
about 20 kts or so occurring late this afternoon should cease for
the most part as the sun begins to set, but sustained winds to
around 10 kts out of the south will continue through the overnight
hours. Gustiness will pick up shortly after daybreak on Sunday and
will peak during the afternoon, where gusts in excess of 30 kts
will become commonplace. These gusts may come down a bit and/or
become less frequent as we head into the evening hours on Sunday,
but at least intermittent gusts of 25-30 kts (possibly higher
depending on how much deep mixing can be sustained after sunset)
could still be seen through the end of the current 30-hour TAF
period for ORD and MDW.

There will also be a threat for marginal low-level wind shear
Sunday evening as a 55 kt low-level jet develops at 1500-2500 ft
AGL. Given that winds at the surface will still likely be gusting
to 25 kts or greater at this time and that 925 mb flow will be
roughly parallel to the direction of the winds at the surface, it
appears at this time that the criteria for necessitating a LLWS
mention in the TAFs will not be exceeded, and thus, have forgone a
LLWS mention in the going TAFs.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement...ILZ006...10 AM Sunday to 10 PM Sunday.

IN...None.
LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...10 AM Sunday to 10 PM Monday.

&&

$$

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