Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 230815

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
315 AM CDT Mon May 23 2022

Issued at 315 AM CDT Mon May 23 2022

Through Tuesday...

There are no noteworthy short term forecast concerns. The strong
surface high pressure resulting in the unseasonably chilly start to
the day will remain in control, bringing another dry and cooler than
average day today, albeit a few degrees warmer than Sunday for
inland areas, which will see highs in the mid to upper 60s.
Locations near the lake and a few miles inland will only top out in
the mid to upper 50s thanks to steady northeast winds through the
day, with lake cooling footprint extending several miles inland for
highs around 60/low 60s. Expect increasing mid and high level cloud
cover this afternoon, particularly across northern Illinois. Despite
only a little over a week out from the start of meteorological
summer, afternoon dew points today will be positively fall-like in
the mid to upper 30s.

The currently 1030 mb high pressure will remain anchored over the
northern Great Lakes through Tuesday while weakening slightly.
Disturbed west-southwest flow aloft will keep fairly extensive mid
and high cloud cover in place, while dry east/east-northeast low
level flow will provide a feed of dry air extending well inland.
Expect dry conditions area wide through tonight with cool but a bit
milder overnight lows than early this morning.

Thereafter, increasing large scale ascent from the trough
deepening to the southwest and gradually increasing column
moisture may allow isolated to widely scattered sprinkles into the
western or northwestern 1/3 or so of the CWA on Tuesday
afternoon. While a few of the CAM solutions show some light
simulated reflectivity in that area, the HREF mean QPF has but a
sliver of measurable in the extreme NW and most ensemble
probabilities of measurable are below 15%. The forecast message
for most, therefore, is a dry day. As heights rise in response to
the deepening trough to the southwest, temperatures will warm a
bit more near and south of I-80 where cloud cover should be less
opaque than farther north. Highs north of I-80 will be fairly
similar to today, while lakeside locales are limited to the upper
50s to lower 60s by breezy east-northeast winds gusting up to
20-25 mph.



Issued at 315 AM CDT Mon May 23 2022

Tuesday night through Sunday...

The main points of interest during the long term portion of the
forecast include:

* Continued trend towards a slower/drier and solution and delayed
  precipitation chances Tuesday night

* Conditional threat for low-topped strong-severe convection
  Wednesday morning and afternoon

* Strong and gusty non-thunderstorm wind gusts Wednesday, mainly
  south of I-80

* Warmup into the upcoming Memorial Day weekend. Some storms
  possible, but not a guarantee.

Our main weather feature of interest Tuesday evening--a notable
shortwave and associated deep/high amplitude attendant upper
trough--will be scooting east of the Continental Divide. Broad,
yet altogether modest isentropic upglide will develop eastward
across Illinois through the evening and overnight hours. That
said, the trend in guidance over the last several nights has been
one of an overall slower solution with a slightly deeper 500 mb
wave and associated increases in downstream ridging over the local
area. Strengthening and persistent east and northeasterly low-
level flow additionally looks to maintain a fairly parched airmass
across northern Illinois and northwest Indiana during this time
frame. All of that taken together suggests that much of Tuesday
evening and even most of the overnight hours could remain mostly
dry as an initial sharpening frontogenetic circulation develops
more into central Wisconsin and northeast Iowa. Have continued the
trend of slicing PoPs through Tuesday night, confining the
greatest chances to our I-39 corridor locales and west.

By early Wednesday morning it does look like we`ll get close
enough to the developing/deepening surface reflection to result in
waves of showers (perhaps with some embedded thunder) with better
coverage. It`s still somewhat unclear how the rest of Wednesday
morning and afternoon pan out, but a steadily increasing low-level
mass response will result in strengthening 925-850 mb flow during
this period, and guidance is suggesting we may manage to tap into
some of this enhanced southerly momentum through the day. Have
nudged wind gusts up a bit south of I-80 towards 35 mph or so to
account for this.

The other uncertainty continues to be on the somewhat conditional
threat of strong-severe showers/storms from roughly late-morning
and into the afternoon. With the slower/deeper solutions now
featuring a ~1004 mb surface low developing northward across
eastern Iowa (and some like the NAM even suggest it may be
deepening with time), this conceptually suggests a severe threat,
contingent on the degree of destabilization and boundary-layer
moisture return. Current guidance seems to be in better alignment
suggesting mid and even upper 60s dewpoints arriving with the
northward-advancing warm front through midday Wednesday. While
this reservoir of deeper moisture will have been relegated to the
deep south through Tuesday, the aforementioned impressive mass
response looks to effectively drive this swiftly northward on
Wednesday, with surface-850 mean mixing ratios increasing to near
or in excess of 12 g/kg across the guidance suite. Essentially
moist adiabatic mid-level lapse rates and a general dearth of
instability suggests low-topped convection would be favored if
some degree of destabilization can be realized, although in these
environments, considerable insolation is not necessary to fully
erode MLCIN.

From a parameter-space perspective, the 00z NAM is the most
concerning, although in all likelihood is overdone with what look
to be convectively-induced and probably spurious low-level wind
increases. Regardless, a general blend of the guidance suite
suggests near-surface storm-relative winds nearing 25-30 kts and
associated corridors of enhanced hodograph curvature with at least
modestly-supportive deep layer shear values around 35-40 kts
suggestive of at least some threat for more organized convective
elements and brief tornadic/wind-producing mini supercells
perhaps south of I-80 and east of I-55. Certainly far from a high
confidence forecast at this range, but something we`ll be keeping
close tabs on over the next few days.

Extended guidance now suggests precip chances with this system
could linger through the end of the week as the upper trough
attempts to close off and brief cut-off from the large scale
flow. Thereafter, indications point to a potential brief period of
shortwave ridging developing towards Friday night-Saturday, but
cyclonic flow won`t be too far away, with all guidance to some
degree suggesting periodic chances for showers and thunderstorms
through the Memorial Day Weekend. Certainly doesn`t look like any
washout periods at this point, but convective threats exist into
and through Monday at this point. We should see a bit of a jump in
temperatures during this period as well as 850 mb temperatures
push back into the upper teens/near 20 C.



For the 06Z TAFs...
Issued at 1240 AM CDT Mon May 23 2022

There are no concerns for the next 24-30 hours with VFR conditions
prevailing. Light east-northeast to variable winds prior to daybreak
will pick up to around 10 kt out of the east and northeast by mid
morning. Speeds will ease later this evening into the overnight.





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