Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 131034

Area Forecast Discussion
National Weather Service Lincoln IL
534 AM CDT Thu May 13 2021

Issued at 216 AM CDT Thu May 13 2021

The stretch of quiet weather will extend through the remainder of
the work week as temperatures gradually approach seasonal norms.
Today will warm into the upper 60s beneath abundant sunshine.
Clouds and precipitation will increase in coverage later this
weekend into early next week.


.SHORT TERM...(Today and tonight)
ISSUED AT 216 AM CDT Thu May 13 2021

Surface high pressure will remain anchored over the region today
as the upper-level ridge makes little eastward progression. The
net effect will be another dry day with afternoon highs warming
into upper 60s. Forecast soundings suggest deep boundary layer
mixing up to 7-8 kft this afternoon as air parcels hit their
convective temperature. This should result in a scattered cumulus
field as we mix into some moisture.

Skies will clear this evening allowing overnight temperatures to
bottom out into the lower 40s.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 216 AM CDT Thu May 13 2021

The pattern begins to change Friday into Saturday as the upper-
level ridge and its associated surface high pressure shift
eastward in response to a digging shortwave trough along the
Pacific Coast. Low-level flow will begin to veer to the south,
allowing for a plume of Gulf moisture to surge northward into the
Corn Belt Friday evening ahead of mid-level shortwave energy and
an upper-level jet core. This will primarily result in increased
cloud coverage, and not rain, as the lower troposphere struggles
to saturate. The better chance for scattered light showers
arrives Saturday afternoon as warm advection/moist isentropic
ascent overruns a stationary boundary to our south. With virtually
no instability north of this boundary, convective activity should
stay well south of the region on Saturday afternoon and evening.
Temperatures should warm between the upper 60s and lower 70s each
day Friday and Saturday with overnight lows near 50 degrees.

The frontal boundary begins to lift northward along the I-70
corridor Sunday afternoon as the upper-level shortwave trough
along the Pacific Coast digs further inland across Death Valley.
It is not clear yet whether showers and thunderstorms will develop
Sunday afternoon as the boundary layer begins to destabilize
ahead of some weak shortwave impulses embedded in the mid-level
flow, OR if convection will be delayed until later Sunday evening
when the nocturnal LLJ impinges on the frontal boundary ahead of a
better- looking mid-level shortwave. Nevertheless, it is
important to note that the 00z ensembles (GEFS/ENS) have come into
better agreement on the placement of the frontal boundary, which
largely keeps it along I-70 through the weekend. The highest QPF
will likely be along and just north of the front, with a very
sharp cut-off in amounts north of I-74. This isn`t the final word,
but the trend has definitely been toward the south. QPF amounts
could still be between 1-2 inches, especially with a particularly
moist air mass in place (PWATs progged above the 95th percentile
of the climatological norm for this time of year). Temperatures on
Sunday should warm near 70 degrees, especially south of the front
across southern Illinois.

There may be some ongoing convection Monday morning, but the
expectation is for a drier air mass to settle-in across the upper
Midwest and Great Lakes region early next week. This would
effectively shunt the frontal boundary and any Gulf moisture well
south of the region. Temperatures will respond by warming well
into the 70s by mid-week.

A warm and wet pattern then looks increasingly likely by the
middle-to-late stages of next week as a slow-moving upper-level
low opens up and pivots across the Southern Plains.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 526 AM CDT Thu May 13 2021

VFR conditions will persist through this TAF period as an upper-
level ridge and surface high pressure remain anchored over the
region. SCT/FEW cumulus with bases 7-8 kft will develop beyond
18z, then dissipate after sunset. Surface winds will largely
remain light and variable through the TAF period with the
influence of high pressure directly over head.




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