827
FXUS63 KLOT 111723
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1223 PM CDT Sun Aug 11 2024

.KEY MESSAGES...

- Seasonably cool conditions will persist through Monday, with a
  low (20-40%) chance of light rain toward central Illinois on
  Monday.

- Period or two of showers and t-storms appearing increasingly
  likely Wednesday night through Thursday night time frame

&&

.DISCUSSION...
Issued at 231 AM CDT Sun Aug 11 2024

Through Monday:

Another day with seasonably cool conditions and mostly sunny
skies is expected today with high pressure building in from the
west. Temps this afternoon will rise into the mid to upper 70s
while WNW winds settle around 10-15 mph. With light west winds
tonight and periods of passing upper-level clouds, expect low
temps tonight in the mid 50s inland and low 60s near the lake.

A seasonably strong upper-level jet stretching across much of
the CONUS today will consolidate into a pair of 100-110 knot jet
streaks across the northern Great Plains and Ohio Valley by
Monday. Meanwhile, a weak mid-level wave within modest WNW flow
aloft will track across most of Illinois and into Missouri on
Monday. Guidance remains highly split on how the mid and upper-
level dynamics interact with Pacific-based moisture aloft and
Gulf moisture slowly advecting northeastward across Missouri,
with global deterministic guidance favoring more of an open wave
and precip expanding well into the CWA, CAM guidance favoring
loosely organized convection well southwest of the area, and
ensemble guidance split between both solutions. Overall,
expectations are that a round of two of convection should shift
southeast across Missouri along a more pronounced theta-e
gradient while lighter mid-level precip spreads into at least
central Illinois and possibly northern Illinois and northwest
Indiana. With little low-level moisture advection into the
antecedent air mass over our area, precip chances (20-40%) seem
limited to a couple periods of light rain or sprinkles eroding
from west to east through the day on Monday. It is entirely
possible that the entire forecast area remains dry on Monday,
especially for areas north of the Illinois/Kankakee River
valleys.

Kluber

Monday Night through Saturday:

Our stint of below average temperatures will come to an end
Tuesday and Wednesday as transient short wave ridging moves
across the region allowing high temps to rebound back into the
80s. Humidity levels will remain quite comfortable by August
standards with dry conditions expected.

Next trough is still slated to move across the region Wednesday
night through early Friday time frame, likely resulting in a
bout or two of showers and thunderstorms. After days of
southerly flow from the Gulf transporting moisture northward,
this system looks to pose a greater risk of a meaningful
rainfall and thunderstorms. There remains a lot of variability
in the details among the medium range models and their
respective ensemble members, but there is enough of consensus
to support the high chance/low end likely pops in the NBM.

Low confidence in the forecast next weekend as there is
considerable spread in location and depth of a trough that is
expected to be over the Great Lakes or New England. A more
progressive solution, weaker trough would likely allow for a
mostly dry weekend with seasonable temps. Conversely, if the
slower, more amplified solutions pan out, then there could be
some scattered showers and storms around at times, particularly
during the afternoon/early evening.

- Izzi

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1222 PM CDT Sun Aug 11 2024

There are no major aviation weather concerns for the 18Z TAF
period.

NW winds will continue to gust to near 20 kt into the late
afternoon before subsiding to around 10 kt for the evening and
closer to 5 kt during the overnight. Westerlies are expected
tomorrow mostly under 10 kt. A lake breeze will attempt to
approach the Chicago terminals in the afternoon, although it
remains unclear if it`ll actually make it across the airfields.
Best guess as of now is no and winds will remain westerly,
although there is plenty of support on both sides. If it does,
winds on either side of the boundary should be moving at around,
most likely under, 10 kt. MDW has a seemingly better shot at an
afternoon wind shift than ORD. Most guidance that brings the
lake breeze through does so at around 20-21Z at both ORD and
MDW. VFR can be expected throughout the period.

Doom

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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