DeKalb, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

147
FXUS63 KLOT 021132
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
632 AM CDT Wed Apr 2 2025

.KEY MESSAGES...

- Waves of showers and storms will parade over the area through
  early evening, some may be severe.

- Primary threats this morning are large hail and gusty winds.
  All hazards are possible this afternoon (contingent on
  morning storms clearing).

- Gusty southeast winds continue this morning with gusts to
  35-40 mph. Strong south winds develop this afternoon,
  especially south of I-80 where gusts in excess of 45 mph are
  possible.

- Periods of rain, possibly heavy, late Friday afternoon into
  Saturday morning, with possible localized flooding south of
  I-80.

&&

.DISCUSSION...
Issued at 330 AM CDT Wed Apr 2 2025

Through Thursday:

The main focus remains the potential for waves of thunderstorms
through early evening, some of which could be severe with all
hazards possible.

Low pressure continues to consolidate early this morning across
central Kansas. Meanwhile a line of mainly pre-frontal strong
to severe thunderstorms currently extends from Kansas City
southwest into north central Oklahoma and is drifting northeast
toward the region. Embedded within this line appears to be one
or two developing embedded MCVs that we will have to keep an eye
on as they approach. Well ahead of the low, warm advective
showers and thunderstorms have begun to increase in coverage
across the area, with more robust clusters of storms currently
in southern IA/northeast MO and central IL. This will continue
to consolidate and lift across the local area between now and
daybreak as a mid-level lapse rate plume moves overhead
allowing storms to tap into better elevated instability. Main
hazards this morning are frequent lightning, large hail up to 1"
in diameter and localized flooding in poor drainage areas. We
will also continue to watch for the potential for a gusty wind
threat if any gravity wave associated convection develops (some
guidance continues hint at this potential and storms over Kansas
City are beginning to take on this appearance) which could
allow for strong downbursts to punch through the stable surface
layer in spite of storms remaining elevated.

Unfortunately confidence in how the rest of the day unfolds
remains quite low so expect frequent updates from us throughout
the day. The surface low is expected to gradually deepen as it
lifts north northeast toward the Upper Mississippi Valley
through the day today. The aforementioned line of pre-frontal
convection is expected to lift across the area through the
morning hours. While there continue to be notable model
differences in handling the various waves/lines of convection,
particularly around midday, if some clearing can occur during
this time, strong low-level flow would support rapid recovery
of the low-level thermal environment, especially south and east
of I-55. Areas further north we continue to have the lowest
confidence. Will also have to keep an eye on the cold front
which could serve as another focus for renewed development in
the late afternoon into early evening with the 6Z NAMNest still
showing this scenario.

Thus we plan to continue messaging the conditional potential
for severe weather across the entire area, though with greater
confidence (albeit still relatively low) in areas mainly south
and east of I-55 this afternoon into early evening. All hazards
remain possible with the afternoon/early evening thunderstorms,
including damaging winds, large hail, and tornadoes. Lastly,
given the expected multiple rounds of convection, localized
flooding will be possible in low-lying, urban, and poor drainage
areas.

Non-Thunderstorm Winds:

There is a window where if storms are able to clear out even
briefly in the afternoon, with a strong low-level jet overhead,
slightly deeper mixing would tap into these stronger winds. Due
to this potential, opted to issue a Wind Advisory for our
southwestern counties (mainly south of a Mendota to Kankakee to
Fowler line where non-thunderstorm wind gusts could exceed 45
mph in the afternoon. Further north, wind gusts to 35-40 mph
will remain possible with perhaps a short 1-2 hour period where
sporadic gusts to 45 may still occur.

Tonight through Thursday:

After storms clear the area, expect winds to ease and
temperatures to drop into the 40s across the area. Heading into
Thursday we warm back into the 50s with our next weather system
beginning to lift toward the area toward the end of the day with
increasing rain chances south of I-80.

Petr


Thursday Night through Tuesday:

There remains uncertainty for a period of showers Thursday
night, generally south of I-80. The NAM was the first to show
this potential as it entered the end of its runs and it still
shows showers across the southern half or so of the cwa Thursday
night. The 03z RAP is now out through part of this time period
and it too is showing showers across much of the southern cwa
Thursday night. Otherwise, not much support for this potential.
Chance pops seem reasonable for now.

If those showers develop, a short break is expected from early
Friday morning through early Friday afternoon and then the
models continue to bring the next system further north with each
run with periods of rain, possibly heavy at times from late
Friday afternoon into early Saturday morning. Precipitable water
values increase to an inch or so across the north to as high as
1.5 inches across the south during this time period. With the
possibility of hours of moderate/heavy rain, there could be a
band of qpf amounts in the 2-3 inch range across the southern
cwa. While confidence is increasing with the northern shift to
this rain/qpf axis, still 3 days away and more changes are
possible. If these trends were to continue, hydro concerns may
develop across the southern cwa. Precipitation looks to
dissipate by mid/late Saturday morning and then one more push of
precip Saturday afternoon/evening as the system finally pulls
away. GFS actually turns some of the precip to snow early Sunday
morning, as the system departs and colder air moves into the
area. No snow mention planned with this forecast.

Now appears there will be a stronger cold front moving south
sometime Monday that will bring colder air into the region with
perhaps a low chance for precip, maybe snow showers, as it
passes the area. cms

&&

.AVIATION /12Z TAFS THROUGH 18Z THURSDAY/...
Issued at 632 AM CDT Wed Apr 2 2025

Primary forecast concerns include...

Scattered thunderstorms this morning.
Chance of thunderstorms this afternoon.
Ifr, possible lifr cigs this morning.
Strong southeast winds shifting southwest this afternoon.
Low level wind shear mid morning into mid afternoon.

Current thunderstorm activity will shift east of the terminals
in the 12z-13z time period with a few hour lull then another
round of thunderstorms is expected in the 15z-18z timeframe and
some timing tweaks may be needed as trends emerge. Once this
activity moves east of the terminals by early this afternoon,
expect a prolonged lull in the activity until the chance of
thunderstorms mid/late afternoon extending into the early
evening. Confidence is low for this time period and if storms do
form, they will likely be a fast moving line and perhaps only
last 1-2 hours at any location. Once this potential activity
ends/moves east of the terminals, the rest of the period is
expected to be dry.

Cigs have quickly dropped to low mvfr/ifr in the past hour.
The trend should be for prevailing ifr cigs by mid morning.
Guidance has been slowly backing away from lifr cigs and for now
have only maintained lifr cigs in the tempo groups. Cigs should
slowly lift into low mvfr by early afternoon and then scatter
out mid/late afternoon.

Southeast winds will gust into the 25-30kt range this morning,
possibly diminishing a bit by late morning. Directions will turn
south/southeast early this afternoon and then turn to the south/
southwest mid/late afternoon when gusts are likely to increase
into the 35-40kt range. These higher gusts will persist through
sunset when directions turn west/southwest with gusts into the
lower/mid 20kt range tonight.

Low level winds will steadily increase this morning and the
higher speeds combined with the directional differences support
low level wind shear through mid afternoon, when surface speeds/
gusts increase. cms

&&

.MARINE...
Issued at 330 PM CDT Wed Apr 2 2025

- Gale Warning in effect through 7 PM CDT this evening.

Southeast gales gusting to 35 kt are expected to continue
through daybreak this morning. It is possible there is a brief
lull in gales toward midday. However, expect wind gusts to
increase out of the southwest during the afternoon to 35 kt as a
deepening surface low lifts across the Upper Mississippi
Valley. Winds then gradually ease toward sunset behind a
departing cold front.

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory from noon today to 7 PM CDT this evening for
     ILZ019-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039.

IN...Wind Advisory from noon CDT /1 PM EDT/ today to 7 PM CDT /8 PM
     EDT/ this evening for INZ010-INZ019.

LM...Gale Warning until 7 PM CDT this evening for the IL and IN
     nearshore waters.

&&

$$

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