National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KLOT 140830
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
330 AM CDT Sun Apr 14 2024

.KEY MESSAGES...

- Summer-like warmth in store today, with the exception of areas
  near Lake Michigan this afternoon. Not as warm but still well
  above normal Monday, except again notably cooler near the
  lake.

- Waves of showers and scattered thunderstorms late Monday night
  through Tuesday night-early Wednesday. Some thunderstorms may be
  severe, particularly Tuesday afternoon through early Wednesday.

- Windy late Tuesday through Wednesday. Gusts peaking 40+ mph on
  Wednesday.

- Unseasonable warmth continues through Tuesday, except near the
  lake on Monday and along/near the Illinois shore on Tuesday,
  followed by a noteworthy cool-down late in the week.

&&

.DISCUSSION...
Issued at 330 AM CDT Sun Apr 14 2024

Through Monday:

An early summer preview is on the way for most of the area today.
Lakeshore areas will be warm until mid-day when an enhanced lake
breeze front spreads inland with much cooler conditions in its
wake. A weak cold front will shift across the area this morning
through mid day, shifting winds to west and then northwest. As we
tap into the departing stout low-level jet, expect gusts up to
20-30 mph through the mid to late morning. Behind the frontal
passage as winds turn synoptically more northerly, the sharp land-
lake thermal gradient will help quickly turn winds onshore by mid
day/early afternoon. The synoptically enhanced lake breeze will
then make steady progress inland through the afternoon.

Our expectation is for dew points to similarly to Saturday
run lower than most guidance and more in line with the HRRR, RAP,
and ECMWF MOS. The drier boundary layer plus plenty of sun, the
mild start to the day, and very warm temps aloft (850 mb temps of
13-15C and 925 mb temps of 18-21C) will set the stage for very
warm temperatures inland, peaking in the lower to mid 80s. Near
the lake, as alluded to earlier, temps will likely reach the mid
to upper 70s by mid day prior to the lake breeze passage, but then
steadily fall through the 60s and down into the upper 50s by early
evening. Lake cooling behind the lake breeze will be noticeable
about 10-15 miles away from the lake, but progressively less so
the farther inland you go.

High pressure will build over the area tonight, resulting in a
relatively cool night, especially considering the warmth away from
the lake this afternoon. Lows will be in the mid 40s to around
50F, coolest north of I-80 outside of Chicago, and particularly
across far northeast Illinois where localized lower 40s are
probable. Monday will be cooler aloft (low teens C at 850 mb and
low-mid teens C at 925 mb, so highs won`t be quite as warm.
However, paired with plenty of sun and low dew points (mid 30s to
lower 40s) temps will still reach well into the 70s far inland,
warmest and in the upper 70s in the far western and southern CWA.
Onshore flow through the day with lake breeze reinforcement will
keep highs along the lakeshore 15-20F cooler, only in the mid 50s
to around 60F. A more pronounced lake cooling footprint will
extend farther inland than today.

Castro


Monday Night through Tuesday night:

The main focus during the period will revolve around the potent
spring storm system expected to evolve from the upper low
currently centered just offshore of San Francisco, CA. Forecast
and ensemble solutions continue in good generally agreement that
this mid-level wave will induce Lee cyclogenesis across the
Colorado Rockies on Monday before tracking east-northeastward
across the Corn Belt Tuesday into early Wednesday. However, there
has been a notable slowing trend with the system as it begins to
occlude while tracking across southern WI late Tuesday night into
Wednesday. While such a trend in guidance is not atypical of such
systems, it does add some concern that a local severe weather
threat could persist across at least eastern sections of our area
through Wednesday morning.

In spite of the slowing trend noted in the latest guidance, big
picture-wise there has not been any major changes with the
forecast thinking for the Monday night through Wednesday time
period. The systems warm front is expected to make northward
progress across central IL on Tuesday, but several waves of
elevated convection across the area late Monday night into
Tuesday is likely hinder its northward progress into far northern
IL (north of I-80) through at least the daylight hours of
Tuesday. For this reason, breezy onshore east-southeasterly winds
north of the warm front will result in chilly conditions along
and near the lake, as temperatures hold in the 50s through the
day. High temperatures on Tuesday for the IL lakeshore areas may
actually occur Tuesday evening as the warm front finally begins
to make northward progress across far northeastern IL. Conversely,
areas south of the warm front will warm into the 70s on Tuesday,
amidst gusty southerly winds.

The initial waves of showers and storms north of the warm front
late Monday night into Tuesday morning will be elevated and
largely non-severe. However, later in the day, warm sector
convection is likely to fire west and southwest of the area across
parts of IA and MO in closer proximately to the stronger dynamics
associated with the approaching storm system. The presence of
strong deep layer shear will support organized severe convection,
initially across IA and MO Tuesday afternoon. However, the severe
storm risk may then shift eastward into most of northern IL and
northwestern IN Tuesday evening/night as all of this activity
tracks east-northeastward. Confidence in the extent of the severe
threat into our area Tuesday evening/night remains medium at this
time. It certainly does not look to be timed well diurnally for
our area. However, the presence of strong shear and dynamics with
the incoming system could certainly (at least to some degree)
support the maintenance of severe storms as they shift into our
area after dark on Tuesday. We still have to see what kind of
take some of the shorter range, higher resolution forecast
guidance has on all this before we can start to nail down the more
salient, finer scale details of the severe weather threat with
higher confidence.

KJB


Wednesday through Saturday:

The system`s cold front will eventually sweep across the area on
Wednesday as the occluded, weakening surface low pressure tracks
toward central Lake Michigan. Some showers should persist through
mid-day Wednesday and possibly into the afternoon in spots, with a
chance for additional thunderstorms. Given the latest trends in
the guidance with slowing the forecast timing of the cold
frontal passage, the threat for renewed severe weather could
develop as far west as parts of my eastern areas (east of I-57)
on Wednesday. We will have to continue to monitor this
potential. Otherwise, westerly winds could gust up to 40-45 mph
behind the cold front Wednesday afternoon during the period of
strongest pressure rises and steepening low-level lapse rates.
A noteworthy cool-down to solidly below normal temperatures is
then in store for the latter half of the week into the weekend.
In fact, we may be dealing with frost/freeze concerns Friday
night and/or Saturday night in parts of the area, as the growing
season will be off to a fast start with all the warmth (and
additional rain) this week.

KJB/Ogorek/Castro



&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1230 AM CDT Sat Apr 13 2024

Aviation Forecast Concerns:

- LLWS and sporadic south-southwesterly surface gusts
  associated with 50-60 kt low- level jet overnight.

- Surface wind trends through the day.
- A northwesterly wind shift expected area-wide by mid-
      morning.
- Lake breeze induced east-northeasterly wind shift expected
      to follow this afternoon at the Chicago metro sites.

An area of low pressure will race eastward across the Upper
Great Lakes this morning. While no precipitation is expected
locally with this system, it will continue to drive a potent 50
to 60 kt southwesterly low-level jet (only a couple thousand
feet off the surface) across the area overnight. Accordingly,
low-level wind shear will be of concern overnight until the
low-level jet abates with daybreak this morning. Sporadic gusts
up around 25 kt can also be expected overnight, especially at
the main metro area sites (KORD/KMDW).

A cold front, trailing from the Upper Great Lakes low, will
shift southward across the area by mid-morning, resulting in a
northwesterly wind shift. As mixing develops after sunrise, we
may see brief bump in wind gusts (around 25 kts) as we start to
tap into the bottom of the weakening low-level jet, though
wind gusts should gradually ease by midday. Thereafter, an
east-northeasterly wind shift is expected across the Chicago
area terminals as a lake breeze shifts inland through the
afternoon. This lake breeze wind shift should reach KGYY by
early afternoon (18-19z), and KMDW and KORD will see it arrive
sometime in the 19 to 21z timeframe.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 7 AM CDT this morning for the IL
     and IN nearshore waters.

&&

$$

Visit us at weather.gov/chicago