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000
FXUS63 KLOT 192003
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
303 PM CDT Fri Apr 19 2024

.KEY MESSAGES...

- Gusty west winds 35-40 mph persist this afternoon.

- Potential for patchy frost/temperatures briefly near freezing
  toward sunrise across our northwest cwa. Freezing
  temperatures more likely Sunday morning for the same area.

&&

.DISCUSSION...
Issued at 303 PM CDT Fri Apr 19 2024

Through Saturday Night:

Deep upper level low pressure was evident in water vapor
imagery across Ontario this afternoon, with a fast westerly 125+
kt upper level jet streak along the southern periphery of the
low across the upper Midwest. At the surface, low pressure was
stacked beneath the upper low to our north, while a ridge of
high pressure extended from Montana to the lower Missouri and
Ohio river valleys. Within the gradient north of the ridge axis,
strong west to west-northwest flow was in place across the
forecast area, with otherwise dry but cool conditions across the
region. The surface ridge is forecast to eventually drift
eastward Saturday and Saturday night, allowing winds to
gradually ease with time.

In the near term, surface dew points in the 25-30F range were
producing relative humidities in the 30-35 percent range in
spots this afternoon, and may go a little lower still through
mid- afternoon. Combined with winds gusting as high as 35-40 mph
at times, this will continue to produce a somewhat elevated
fire danger through sunset. The cool, dry air mass will also
support temperatures lowering into the 30s across the area
tonight, with some potential for dipping near the freezing mark
across our northwest cwa for a brief time toward sunrise.
However, winds are expected to remain up a bit overnight within
the stronger pressure gradient, and those 7-12 mph will likely
prevent widespread freezing temperatures and frost formation for
our cooler northwest areas. At this time, in collaboration with
WFOs DVN and MKX have elected to hold off on any frost/freeze
headlines for tonight but later shifts will monitor for stronger
decoupling of boundary layer winds which could portend a
greater freeze risk. Winds will remain breezy, with 20-25 mph
gusts on Saturday, but will diminish more Saturday night with
the surface ridge edging east. Frost/freeze conditions thus look
to be more of an issue late Saturday night/Sunday morning.

Otherwise, a period of mid-level cloud cover is expected this
evening across our southern cwa, with mainly clear conditions
farther to the north. Forecast soundings suggest more of a
diurnal scattered to broken stratocu deck on Saturday, before
skies clear Saturday night. HRRR/RAP actually depict some light
convective precip during the day Saturday, though forecast
soundings suggest fairly shallow cloud layer and a stout
inversion around 5 kft which argues against carrying any
pops/precip mention in the forecast. Persistent low-level cold
advection will result in cooler temps through Saturday, with
low-mid 30s for lows tonight and highs from the upper 40s to
lower 50s Saturday. As indicated above, more widespread
lower-30s are possible across parts of northern IL away from the
metro late Saturday night.

Ratzer


Sunday through Friday:

To be sent shortly.

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1229 PM CDT Fri Apr 19 2024

The sole forecast concern for this TAF period is the gusty
west-northwest winds this afternoon. Gusts are generally
expected to remain around 30 kts this afternoon, but
occasionally higher gusts between 30 to 35 kts are possible.
While gusts will diminish somewhat this evening, forecast
soundings show that the atmosphere may remain mixed overnight so
expect at least periodic gusts around 20 kts to persist
overnight and through Saturday. Otherwise, expect FEW to SCT
VFR clouds this afternoon to gradually increase to BKN VFR
ceilings Saturday afternoon.

Yack

&&

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

&&

$$

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