Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 190551
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1251 AM CDT Sat Jun 19 2021

.SYNOPSIS...
Issued at 315 PM CDT Fri Jun 18 2021

Strong to severe thunderstorms will be possible across central and
southeast Illinois tonight, as a cold front starts to move into
the area. The front is expected to become fairly stationary into
the weekend, resulting in a chance of showers and storms
continuing through the weekend. Hot and humid conditions are
expected to persist, with the heat index around 100 degrees both
Saturday and Sunday afternoons.

&&

.UPDATE...
Issued at 932 PM CDT Fri Jun 18 2021

Made some adjustments to PoPs as storms continue to elude model
depiction. Storms this evening have been few and far between, but
with the arrival of the LLJ into the region shortly, this should
ramp activity across west central Illinois into central and
eastern Illinois tonight. Will have to monitor over the next
couple of hours to see how propagation of storms occurs as to the
overall coverage across the region. A Severe Watch was issued at
the bottom of the hour, and will linger through the overnight,
ending at 09z/4am CDT. The first hour or two is expected to remain
quiet, however once storms begin to develop, expecting this to
flow west to east, drifting east south east with the frontal
boundary.

&&

.SHORT TERM...(This evening through Saturday)
ISSUED AT 315 PM CDT Fri Jun 18 2021

We`re in a waiting game this afternoon for significant convection
to fire. We have temperatures well into the 90s and some residual
boundaries to fire off, but the central and northern CWA remains
capped. Thus, the periodic showers/storms that have been tracking
southeast out of Iowa have not been able to get well established.
South of I-70, there`s no cap and CAPE values are an impressive
5000+ J/kg, but nothing for storms to really fire on, and little
in the way of clouds. Much of the morning model guidance has been
suggesting more of a post-sunset event for us, coming in from the
northwest and tracking southeast through the night. Focus seems to
be more in areas north of I-72, though latest SPC Day1 outlook
maintains an enhanced risk over nearly the entire area, favoring
more of a wind threat across the southeast half and a large hail
threat in the northwest.

There is some concern for training echoes. Area has largely been
dry and could take some rain, but consideration of a flash flood
watch was made. HREF precipitable water values of 1.5-2 inches
persist through midnight in a northwest/southeast axis from near
Macomb to Terre Haute, before pooling near and south of I-70. Rain
amounts were beefed up and the highest amounts near 1.50 inches
are in the areas east of I-57, with around an inch northwest to
Galesburg.

Incoming cold front is expected to become stationary over the
area, which will keep the rain threat going into Saturday.
Marginal risk of severe over most of the forecast area, though
shear values are much weaker and any convection will be of a pulse
type scenario.

For the heat situation, the advisory will remain in place, though
many areas are a tad below advisory criteria. The more extended
period of sun in the central/southern CWA allowed for more mixing
and dew points lowered into the mid to upper 60s in some cases.
Heat index on Saturday will be close to 100 in many areas, though.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 315 PM CDT Fri Jun 18 2021

Upper level pattern will be trending toward cooler conditions
across the northern U.S. early next week, with the morning model
guidance in good agreement with a broad upper trough digging
southward into the Ohio Valley. After one more day of hot and
humid conditions Sunday, we will struggle to get out of the 70s in
many areas Monday and Tuesday. Upper ridging and associated heat
build east again during the second half of the week, though the
longer range models have lesser agreement in how strong this ridge
holds together as it gets this far east.

Entire forecast area is in a marginal (level 1) risk of severe
weather on Sunday. Bulk shear is respectable at 40-50 knots with
CAPE`s potentially above 3000 J/kg, though the best shear is with
the cold front, which will arrive late evening. Some residual
convection remains in the area on Monday until the arrival of the
upper trough.

After a couple days of dry weather, rain chances are hinted at,
but will depend on the overall pattern. The GFS would favor
Thursday and Thursday night with the best chances, with the
arrival of a cold front, while the European model would favor more
of a nocturnal MCS pattern with us getting some of the remnants
late nights. Will not vary with the blended guidance too much, but
with more of the activity later in the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1242 AM CDT Sat Jun 19 2021

Currently seeing a setup of storms arching into the area along and
south of I-74 from GBG to PIA. This will continue tracking ese
through the area, and expecting to build as the LLJ works into the
Midwest. VFR ceilings are expected to persist through the
overnight into the morning, with the chance for reduced visby`s as
storms pass terminals. Included TEMPO group for PIA for a couple
hours as this terminal is being impacted by storms currently, and
is the only 24 hour terminal in the CWA. Winds will vary through
the period, mainly remaining between 5-10kts sustained. Will
include gusts early in the period, upwards of 15-20kts. Gusts drop
through morning, with decreasing winds late in the period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Baker
SYNOPSIS...Geelhart
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Baker


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