607
FXUS63 KLOT 281944
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
244 PM CDT Tue May 28 2024

.KEY MESSAGES...

- Scattered thunderstorms will continue into early this evening,
  the strongest storms could produce gusty winds and small hail.

- Dry conditions with seasonable temps Wed-Fri, followed by at
  least periodic chances of showers/storms over the weekend into
  early next.

&&

.DISCUSSION...
Issued at 244 PM CDT Tue May 28 2024

Through Wednesday Night:
Scattered thunderstorms have developed ahead of the wave moving down
from Wisconsin. As they moved down, 1000 J/kg of CAPE is assisting
in convective development and sporadic lightning. This actively is
expected to continue through the rest of the afternoon and evening
with chances dimminishing after sunset. Better mid level lapse rates
look to be farther to the south and west, and wind shear values are
fairly minimal keeping the severe risk marginal (level 1 out of 5
from the Storm Prediction Center). The main threats are expected to
be the potential for small, up to penny size, hail as well as
localized wind gusts capable of downing some tree branches. As
stronger storms develop, there is also the risk for heavier
downpours than may result in ponding on roadways and localized
flooding, especially for urban areas. Lastly, while the chances may
be low, with the cold air aloft that is moving in and potentially
interacting with the lake breeze boundary that arrived earlier
today, it would not be surprising if there were a few funnel clouds
that get reported.

The wave will gradually move east through the night, and shower
chances will gradually diminish. The HRRR/RAP/RRFS have a little
moisture wrapping around the back side of the wave, so added a
slight chance for a few sprinkles overnight, though confidence is
low and impacts should be minimal.

Winds behind the wave will turn to the north and strengthen. Cooler
air will be advected in for temperatures in the low 50s and isolated
ares in the upper 40s. Stronger winds over the lake will increase
wave heights creating high swim risk for beaches from Cook County
and down the Indiana shores of Lake Michigan on Wednesday.
Otherwise, an upper level ridge grows over the region allowing for
height rises and drier conditions with temperatures in the 70s
inland and 60s along the lakeshore on Wednesday.

DK

Thursday through Tuesday:

Break in the active pattern should continue through the rest of
the work week with dry conditions expected. Seasonable
temperatures are expected Thursday, though lake breeze will keep
temperatures cooler near the lake. Friday will be a bit warmer as
narrow upper ridging moves across the area. Lake cooling Friday
looks more likely to be confined to the IL shore.

EPS and GEFS both suggest there will be a transition to a more
zonal flow pattern across the country this weekend into early next
week. There will undoubtedly be low amplitude waves rippling
through the zonal flow this weekend into early next week.
Unfortunately, these type of waves can easily become convectively
enhanced and are notoriously have low predictability in the medium
range. NBM PoPs are in the chance range over the weekend into
early next week and this is certainly reasonable. Also worth
noting that there will be many day hours over the weekend into
early next week, so important not to be deceived by precip
chances every period of the forecast, the weekend shouldn`t be a
washout. Temperatures this weekend into early next week will be
above average, outside of any convective interruptions.

- Izzi

&&

.AVIATION /18Z TAFS THROUGH 00Z THURSDAY/...
Issued at 1259 PM CDT Tue May 28 2024

Forecast concerns for the terminals...

- Lake breeze may impact the Chicago terminals early this
  afternoon

- Scattered showers and thunderstorms this afternoon and evening

- Period of low-end VFR to MVFR ceilings late tonight into
  Wednesday morning

Scattered to broken VFR clouds will continue to develop this
afternoon with otherwise light northwest winds around 6 to 8
kts. However, a lake breeze is trying to surge inland across
northern IL and northwest IN this afternoon which may result in
an easterly wind shift at ORD and MDW. Given that winds with the
lake breeze are equal to the prevailing winds, confidence is
low as to whether or not the boundary will actually surge
through ORD and MDW or stall just east of the airports.
Therefore, have decided to forgo a formal mention of an easterly
wind shift at ORD, but since the lake breeze is almost to MDW
did add a wind shift at 1830z. Regardless, winds at the Chicago
terminals should turn back northwest as showers arrive later
this afternoon.

Scattered showers and thunderstorms are expected to develop
across northeast IL and northwest IN this afternoon as an upper-
level disturbance pivots through the area. While instability
continues to look modest, shower and storm coverage is forecast
to be more robust than yesterday thus confidence on storms is
higher today especially in the 22z to 00z timeframe.
Additionally, there is the potential that the strongest storms
may produce locally gusty winds and small hail but widespread
severe weather is not expected.

Showers and storms will come to an end this evening (likely by
02z at the latest) with dry conditions expected for the rest of
the period. However, guidance continues to hint that some 2000
to 3000 ft ceilings may try to develop overnight and linger into
Wednesday morning. While most guidance is in good agreement on
the ceilings, ensemble probabilities are only around 30% for
MVFR conditions tonight so have decided to maintain the SCT020
mention for now. Any MVFR ceilings that develop tonight will
erode by midday with otherwise northwest winds becoming
northeasterly Wednesday afternoon.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement from late tonight through Wednesday
     evening for ILZ103-ILZ104.

IN...Beach Hazards Statement from late tonight through Wednesday
     evening for INZ001-INZ002.

LM...Small Craft Advisory from 4 AM to 10 PM CDT Wednesday for
     Wilmette Harbor IL to Michigan City IN.

&&

$$

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