Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 151559

Area Forecast Discussion
National Weather Service Lincoln IL
1059 AM CDT Tue Aug 15 2017

Issued at 1056 AM CDT Tue Aug 15 2017

Weak high pressure ridge over the center of the country and up the
Mississippi River Valley. A stalled boundary is draped over
northern IL, and light southerly winds are helping to push
temperatures up over much of Central IL. Made some minor
adjustments to the grids, but not much in the way of large scale
changes. HRRR maintains the potential for very sct showers/TS this
evening, and keeping the very low pop in for that as well.
Otherwise, forecast is maintaining the general warming trend for
the week.


.SHORT TERM...(Today and tonight)
ISSUED AT 250 AM CDT Tue Aug 15 2017

A weak frontal boundary has been struggling to make any headway
into Illinois during the night, with the 2 am surface map showing
it coming into the Quad Cities area. The high-resolution short
range models do have it settling across the Peoria/Bloomington
areas toward 9-10 am, before stalling out. Moisture profiles are
sparse per forecast soundings and the boundary doesn`t have a lot
of oomph in terms of large scale forcing, so PoP`s were scaled
back a bit and will only go with isolated wording this afternoon.
It is also looking like most of the night will be dry as well, as
the storm system coming in from the west is a bit slower to
arrive. Will only mention PoP`s west of the Illinois River late

With a nice Gulf flow in place, dew points should reach the 70s
later today, helping to nudge heat index values into the 90s
across most areas southwest of I-74.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 250 AM CDT Tue Aug 15 2017

Upper wave currently over Idaho and western Montana will emerge
onto the Plains on Wednesday, reaching the Mississippi Valley on
Thursday. The GFS is the only model featuring any widespread
precipitation ahead of the system during the morning hours of
Wednesday, and will wait until afternoon to introduce chance PoP`s
over the CWA. More widespread showers and thunderstorms will
wait until Wednesday night, as the surface boundary starts to move
into the region. The NAM and Canadian are fastest in bringing dry
conditions back in as early as Thursday afternoon, but the
forecast is trended more toward the ECMWF with lingering some low
chance PoP`s west of I-55 into afternoon. The cooler and drier air
will lag some behind the front, so Thursday still looks to be
quite muggy.

The next strong upper wave is poised to move across the region
Friday night and Saturday, with the GFS the slowest with its
arrival and passage. This trend seems a bit sluggish, and will
favor the faster solutions of the ECMWF and Canadian models. Late
in the weekend, the upper flow starts to shift the storm track
closer to the Canadian border, as a west-east expanse of high
pressure starts to strengthen.

Eclipse outlook (Monday): Both the GFS and ECMWF models track a
weak shortwave along the northern periphery of the upper high,
with the GFS the stronger of the solutions. The ECMWF has been
hanging firm with keeping things dry, while the GFS tries to pop a
few storms here and there. Currently thinking that 700 mb
temperatures near +10C will provide a decent cap to help keep the
rain largely at bay. Morning forecast will go with 30-40% sky
cover during the critical midday and early afternoon hours.
However, remember this is 7 days out and it`s too early to lock
into specifics.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 528 AM CDT Tue Aug 15 2017

Main concern is with fog over the next few hours. Low cloud deck
has been advecting out of southwest Illinois along with areas of
dense fog. So far it hasn`t gotten too far out of hand, though the
RAP and HRRR have been showing this expanding northeast to KSPI-
KCMI in the 11-12Z time frame. GOES-16 11-3.9 fog product shows
some recent advection of the lower clouds northeast to between
KDEC-K1H2, and the latter site had a recent period of 1/4SM
reported. Amended the TAF`s earlier for KSPI-KCMI to bring in a
TEMPO period of dense fog, and will keep this going with the new
TAF set. Dense fog also reported just northwest of KPIA, but they
have had more of a persistent feed of VFR clouds and this may help
keep them up. The fog should lift by 15Z.

Later in the period, as a weak surface boundary settles southward
along a KPIA-KDNV line, a few showers may form early in the




SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Geelhart is the U.S. government's official web portal to all federal, state and local government web resources and services.