Area Forecast Discussion Issued by NWS Chicago, IL
000
FXUS63 KLOT 180525
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1225 AM CDT Mon Mar 18 2024
.KEY MESSAGES...
- Intermittent flurries possible through this afternoon
- Breezy and dry conditions on Tuesday
- Period of accumulating snow possible Thursday night into
Friday morning (mainly along/north of I-88)
&&
.UPDATE...
Issued at 909 PM CDT Sun Mar 17 2024
Forecast remains on track this evening with no notable changes
made.
A positively tilted upper-level trough continues to pivot
overhead this evening which has allowed mid-level stratus to
fill in across northeast IL and northwest IN. While light radar
echoes have persisted beneath the stratus, flurries have thus
far struggled to reach the surface due to a large amount of dry
air within the sub-cloud layer. However, recent vapor soundings
out of MDW are showing this low-level dry air eroding which may
allow flurries to become more prevalent over the next couple of
hours. Despite the current near freezing temperatures and mid
to upper 20s forecast overnight, no accumulation is expected
with the flurries as pavement and ground temperatures are likely
to remain above freezing.
Scattered lake effect snow showers are also expected to develop
after midnight across portions of northwest Indiana, mainly
Porter County. Forecast soundings continue to show decent lake
effect parameters developing overnight, but the west-northwest
winds aloft are expected to keep the bulk of the showers into
northern Indiana and Lower Michigan. Nevertheless, the
advertised 20% POPs for portions of Porter County remain
reasonable. Similar to the flurries, accumulations are generally
expected to be nonexistent (at least on paved surfaces) but some
light accums up to a tenth or two on grassy surfaces cannot be
completely ruled out, especially with more robust lake effect
bands.
The lake effect showers should gradually push east of Porter
County shortly after daybreak but a secondary wave pivoting
through the aforementioned trough does look to support
additional chances for flurries areawide through Monday
afternoon. Though no accumulations are expected. Otherwise,
expect another blustery afternoon with highs in the upper 30s
and northwest gusts of 20 to 25 mph.
Yack
&&
.DISCUSSION...
Issued at 239 PM CDT Sun Mar 17 2024
An upper level trough will continue to dig southward overnight
and shift eastward on Monday morning. Lingering flurries are
possible over northeastern IL, but no accumulations are
expected. The focus becomes over northwestern Indiana, primarily
in Porter County, where good northwest fetch, decent lake
induced instability, and equilibrium levels up to 8000 feet can
produce a few additional lake effect snow showers. Temperatures
have been in the upper 30s (a few isolated low 40s) this
afternoon, so most areas are not expected to receive
accumulations. But with temperatures expected into mid 20s
overnight, there is a chance for a tenth or so of snow
accumulations in Northwest Indiana but it will be dependent upon
how quickly surface temperatures can cool overnight. Current
thinking for any banded features that can created higher totals
look to be farther east in Indiana or in Michigan, but will be
monitored through the night.
Another short wave will drop south as the parent long wave
phases and moves east on Monday. Moisture profiles on most
models remain too dry; however, the HRRR and the RAP are the
more aggressive reintroducing snow showers. While they have been
aggressive, even today, they have trended better with handling
moisture profiles. Rather than biting too hard for snow
showers, the slight chance for flurries was introduced for late
tomorrow morning/afternoon with no accumulations expected, but
can always be increased if later model runs come into better
agreement.
Clouds start to move out of the region for better chances for
clearer skies on Tuesday. However, another robust low level jet
is expected to develop Monday night into Tuesday morning over
the region. With deeper mixing this can make for another windy
day with the potential for gusts to be in excess of 30 mph.
Additionally, drier conditions are expected to develop with RH
values into the 40s and upper 30 percent. The combination of
lower relative humidity levels and stronger wind gusts could
set the stage for the potential for an elevated fire risk
threat.
By mid week, northwest flow sets up over the area with cooler
temperatures to the northeast and warmer temperatures to our
southwest. However, models have trended that baroclinic zone
farther south with has translated in cooler yet seasonal normal
high temperatures through the week. By Thursday, a short wave
clipper will drop down out of Canada providing the next chance
for precipitation. There is still uncertainty with the exact
path, but it looks like it could be the next chance for
precipitation. Colder temperatures north of I-88 Thursday night
into Friday provides better chances for snow, while the chance
for slightly warmer temperatures south of I-88 could lead to a
rain snow mix.
Temperatures are slated to warm over the weekend. However, with
the potential for another wave move over the Plains over the
weekend, it looks like the region might be in store for a more
unsettled pattern.
DK
&&
.AVIATION /06Z TAFS THROUGH 12Z TUESDAY/...
Issued at 1225 AM CDT Mon Mar 18 2024
Non-impactful intermittent flurries remain possible overnight and
through this afternoon. Opted to hang onto PROB30 groups for -SHSN
late morning into early afternoon when a slightly better signal
exists for more persistent flurries (30% chance).
Winds will be sporadically gusty early this morning with more
persistent gusts to around 20kt expected during the daytime hours.
Gusts then ease after sunset but quickly ramp back up early Tuesday
morning with gusts already in the mid 20kt range by daybreak
Tuesday. Marginal LLWS may occur early Tuesday morning as the low-
level jet moves overhead. However, that window appears to be
very brief as surface gusts readily increase.
Petr
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory until 10 PM CDT this evening for Gary to
Burns Harbor IN-Burns Harbor to Michigan City IN.
&&
$$
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