828
FXUS63 KLOT 141730
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1230 PM CDT Fri Jun 14 2024

.KEY MESSAGES...

- Hot and humid conditions next week along with periodic
  chances for showers and thunderstorms.

&&

.DISCUSSION...
Issued at 214 AM CDT Fri Jun 14 2024

Through Saturday:

No notable weather is expected in the area through Saturday as
surface high pressure will rule over the Great Lakes going into this
weekend. Expect seasonably warm temperatures today, along with
abundant sunshine and comfortable humidity levels once the residual
moisture from last night`s storms is mixed out and shunted southward
this morning. A lake breeze will also march inland today and cause
high temperatures near the lakeshore to end up being about 10-15
degrees cooler (in the low to mid 70s) than at locations farther
inland (low to mid 80s).

Saturday looks similarly quiet as we remain on the southwest
periphery of the Great Lakes surface high pressure bubble and an
upper-level ridge axis begins to slide over the area. High
temperatures should be nearly a carbon copy of what they`ll be
today, though southeasterly return flow will keep lake cooling
efforts focused into Illinois and allow for locales near the
northwest Indiana lakeshore to see similar temperature readings to
locations that are farther inland. There should be more high-level
cloud cover on Saturday compared to today as a result of a subtle
shortwave trough cresting the upper-level ridge. Actually wouldn`t
entirely be surprised if this cloud deck thickened up enough to
support some virga over our northwestern CWA late in the day, but
dry air in the low and middle levels of the troposphere should
preclude any hydrometeors from actually reaching the ground.

Ogorek


Saturday Night through Thursday:

For Sunday, have held onto some slight chances for showers and
storms mainly through midday and north of I-80. Several mid-level
disturbances and even a larger-scale shortwave are slated to be in
our vicinity, and in the presence of appreciably steep mid-level
lapse rates, this could support some shower/storm chances.

The main story in the extended remains on the likelihood of
building heat and humidity as an anomalously deep upper ridge
builds off to our east. There seems to be decent agreement in the
general placement of the core of the high at this point, centering
across the Mid Atlantic and eventually the Northeast towards the
middle and end of next week. This puts us on the western fringes
of the primary zone of large scale subsidence and certainly opens
the door up for perturbations embedded within the southwesterly
flow aloft to be carried across the forecast area. As a result,
isolated to scattered storms can`t be ruled out, and these would
obviously have an impact on temperatures and dewpoints, at least
to some degree.

Sunday and Monday may end up being the most uncomfortable days of
the stretch as the core of the building high makes its closest
approach to the area. There are some significant differences in
how guidance is handling afternoon mixing trends within the
deepening PBL, however, which is resulting in quite a bit of
spread in the high temperature and dewpoint departments. The GFS
looks much more like the extended NAM on Sunday with a less mixed
boundary layer and much higher dewpoints and lower air temperatures
compared to the more deeply-mixing ECMWF, UKMET, and CMC. The
differences aren`t necessarily trivial either, with dewpoint and
air temperature differences near 10 degrees at times. From a heat
index perspective though, this may not result in much of a
material difference as heat indices would still even out in the
mid to upper 90s on Sunday, and then a few degrees higher than
that on Monday with a smattering of 100 degree readings in play.
For now, elected to maintain warmer air temperatures and lower
dewpoints, in line with the blended offering and the ECMWF,
UKMET, and CMC output. This results in uncomfortable conditions,
but heat indices largely staying under advisory criteria (105
degrees) on Monday.

Muggy and warm conditions will continue through the middle of the
week, although likely not quite to Monday`s levels as the the core
of the high builds further east into the Northeast US. As
mentioned previously, diurnally-driven, isolated pulse convection
will be possible given the heat/humidity Monday and Tuesday
afternoons. By Wednesday/Thursday a synoptic front will approach
from the northwest, which may help to focus a bit more in the
way of shower and storm coverage.

Carlaw

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1230 PM CDT Fri Jun 14 2024

A lake breeze has flipped winds to the northeast at KORD, KMDW,
and KGYY and will get to KDPA between 19Z to 20Z. There remains
a chance for northeast winds at KRFD this afternoon, but
confidence is lower with the uncertainty if the boundary can
hold itself together that far inland. Gusts have already been
observed 15 to 20 knots, but they are fairly sporadic so while
they may continue occasionally, it was kept out of the TAF.

Other than some light cumulus development both this and
tomorrow afternoon, VFR skies are expected through the TAF
period. Winds will turn to the southeast Saturday morning. Once
again it will not be ruled out for occasional gusts up to 20
knots in the late afternoon Saturday, but confidence in
persistence was too low to add to the TAF.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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