Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 192042

Area Forecast Discussion
National Weather Service Lincoln IL
342 PM CDT Sat May 19 2018

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT Sat May 19 2018
Weak upper wave moving off to the northeast this afternoon while
another wave over the Central Plains is triggering a convective
complex for the afternoon. Some showers and thunderstorms from an
old outflow boundary to the southwest will move across southern
IL later this evening, bringing some scattered thunderstorms. Main
concern for widespread thunderstorms will be in the overnight
hours as energy from that wave ripples downstream. Models are
inconsistent with how much of the wave moves vs weaker DPVA into
the region. Seeing CAMs vary from little to no
closer to a weakening QLCS by morning. With the uncertainty, the
forecast remains vague, carrying the threat for overnight severe
threat at marginal in the Day One from SPC. Atmosphere decoupled
in the overnight, MUCAPEs remain in the low to moderate category
and the bulk shear is generally less than 20-30kts in the NAMNest.
Given the elevated convection in the overnight hours, after 12Z,
the region is clearing in most model solutions. HRRR is slowing
slightly in the progression of the precip and may end up delaying
the clearing as well in subsequent runs. Surface low/boundary
slips through Central IL tomorrow, with veering winds through the
day. More northerly winds persist north of the boundary after
sunrise, resulting in temps north of I-74 tapping into far cooler
air and highs struggling to reach into the low to mid 70s. Whereas
the southern half of the state in the mid to upper 80s. Along with
plenty of llvl moisture, south of I-70 will see heat indices in
the low 90s tomorrow afternoon. Another round of thunderstorms
will also threaten the region, with the severity of the storms in
the afternoon very dependent on the evolution of the overnight
storms and projected recovery of the atmosphere south of the
front. Lacking deep layer shear, and mediocre lapse rates, any
areas of strong CAPE will still add an element to the afternoon
thunder increasing threat of damaging wind gusts/large hail.


.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT Sat May 19 2018
Models having a really hard time evolving one MCS disparate from
another beyond Sunday. GFS has another complex of storms Sunday
night, whereas the ECMWF is still moving the afternoon storms off
to the east. Either way, it`s safe to say that the active pattern
will likely continue until a weak upper low clears the region, not
anticipated until Mon night/Tuesday. This parallels when the
blended forecast dries out for a while, at least until the latter
portion of the week. The region remains close to the axis of the
upper ridge, with weak NW flow...slowly transitioning to more
southwesterly flow. Either way, the midlevels maintain access to
the warmer temps of the swrn CONUS through the end of the
forecast, keeping temps about 10F above seasonal norms.


.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 133 PM CDT Sat May 19 2018

VFR in the short term, potential for thunder and cigs at 3kft in
the overnight hours. CAMs still coming through with convection
after 06z, but weakening considerably as it passes. Keeping to the
more optimistic VCTS for now, but the NAMNest remains stronger
with the passage of the convection, particularly to the south.
Winds at the surface showing some variability in the short term,
but showing signs of a weak boundary draped across the state, with
more northwesterly in PIA and BMI, more west/southwesterly to the




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