939
FXUS63 KILX 260923
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
423 AM CDT Thu Sep 26 2024

.KEY MESSAGES...

- Clouds will increase over areas southeast of the IL river during
  today as it remains dry across central IL into this evening.
  There is a 20-40% chance of light rain showers in southeast IL
  late this afternoon and evening. More widespread moderate rain
  showers will spread into southeast IL during overnight and
  Friday while a chance of lighter rain showers will get as far
  northwest as I-55 by Friday afternoon. A good chance of rain
  showers will occur over central IL this weekend, with likely
  chances of rain over southeast IL Friday night and Saturday
  where rainfall amounts of 1 to 2 inches are likely, with a
  50-60% chance of greater than 2 inch rains from highway 50
  south. The IL river valley to the northwest may only see a tenth
  inch or less of rainfall.

- Strong northeast winds are expected to develop on Friday and
  continue Friday night as the remnants of Hurricane Helene move
  into the lower Ohio river valley. There is a 40-60% chance of
  wind gusts of 45 mph or higher from Friday afternoon into early
  Friday evening from I-55 east, with a 60-80% chance of wind
  gusts over 45 mph in southeast IL.

&&

.DISCUSSION...
Issued at 400 AM CDT Thu Sep 26 2024

The early morning surface map shows weak 1014 mb high pressure
over WI/IA and northern IL while a frontal boundary extended from
the eastern Great Lakes southward through central Ohio, eastern
parts of KY/TN and near the AL/GA border. Quiet weather prevailed
over central/se IL with some cloud bands in east central/se IL and
nearly clear skies from Gibson City to Decatur and Litchfield nw.
Seasonably cool temps were in the mid to upper 50s, except lower
50s over the IL river valley. Fog is very limited so far this
morning mainly patchy shallow fog near river valleys like the MS
and IL. Aloft a 566 dm 500 mb low was near Paducah KY over mid MS
river valley.

Weak high pressure ridge to remain over the Great Lakes region
today and ridging back over Iowa, and will keep central IL dry
through at least this evening. More sunshine is expected over the
IL river valley with mostly sunny skies overall today, while
clouds increase over central IL this afternoon and becoming mostly
cloudy to cloudy in southeast IL. Isolated light showers possible
se of I-70 late this afternoon and early evening with chance of
light rain showers in southeast IL during mid/late evening. Highs
were in the upper 70s to near 80F yesterday and feel similar temps
expected today over much of the CWA, with areas nw of the IL river
being the warmest where more sunshine expected through the day. NE
winds increase a bit today with gusts up to around 20 mph.

At 4 am cdt, Hurricane Helene was nw of Cuba with 90 mph winds and
moving NNE at 12 mph. The NHC has Helene becoming a major
hurricane in about 12 hours with 115 mph winds by 18Z/1 pm today
and possible further strengthening before landfall over FL Big
Bend by mid evening. Helene rapidly lifts northward across western
GA tonight, reaching near Chattanooga by dawn Fri and then
turning nw and tracking over central KY on Friday afternoon.
Models have shifted track back further north/nw to rainfall
amounts have trended higher over se CWA and NE winds have also
come up further on Friday and Friday night. Surge of moisture to
push nw over se half of CWA overnight into Friday while NE winds
increase tonight with gusts to 30 mph or higher late tonight over
southeast IL. NE winds increase further on Friday afternoon/early
Fri evening with gusts could reach 35-45 mph east of the IL river,
and potentially above 45 mph east of I-55 Fri afternoon and early
Fri evening. Later shifts will need to monitor possible wind
advisory if trends continue. Have likely to categorical pops in
southeast IL Fri into Fri night while still dry from IL river nw
on Friday with 20-40% pops over IL river valley by overnight Fri
night.

The remnants of Hurricane Helene gets absorbed by cutoff low
moving into southern TN river valley Friday morning and into the
lower Ohio river valley during Friday night as Helene gets
absorbed into the cutoff low. The cutoff low and Helene remnants
slowly lifts ne from the lower Ohio river valley Sat and into the
mid Atlantic States by Monday. Chances of showers will linger this
weekend, with likely pops yet in southeast IL on Saturday.
Rainfall amounts by Saturday evening range from 1-2 inches in
southeast IL with over 2 inches possible from highway 50 south,
while nw of the IL river may only see less than a tenth inch. Of
course track of Helene remnants will determine extent of
rainfall, though currently looks like a sharp nw to se gradient of
rainfall amounts, with beneficial rains expected over se CWA. WPC
has marginal to slight risk of excessive rainfall over southeast
IL Fri and Fri night, with marginal risk in southeast IL by Wabash
river valley on Saturday.

A strong 590 dm 500 mb high over the 4 Corners of SW US to ride
into the upper MS river valley during this weekend and gradually
work closer to IL early next work week. Deterministic models
differ on how fast this occurs and stayed close to model ensemble
solution and blended forecast. This has slight chance of showers
in eastern IL Monday then dry Monday night into middle of next
week. A cold front passes through IL during overnight Monday night
into Tue and has limited moisture while lift/forcing is north of
IL, so front appears to pass through dry. Cooler temperatures
behind the front for middle of next week as highs in the upper 70s
to near 80F on Monday drop into the lower 70s central IL Tue and
mid 70s in southeast IL. Highs in the upper 60s and lower 70s Wed
lows in the mid 40s to near 50F Tue and Wed nights.

07

&&

.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1100 PM CDT Wed Sep 25 2024

High pressure and associated clear skies will become increasingly
predominant as an upper level low over southern IL continues to
drift southward tonight into Thursday. Mid level cloud cover will
increase from the southeast late in the period as moisture
associated with remnants of tropical system Helene approach.
Winds light and variable overnight, becoming NE 7-10 kts after
15Z.

37

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$