Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 151754
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1254 PM CDT Tue Aug 15 2017

.UPDATE...
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
tonight.

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 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1251 PM CDT Tue Aug 15 2017

Weak cold front across the northern tier of the state, providing
focus for some mainly diurnally driven showers this afternoon.
Although ascent is weak, still could result in some iso TS...but
not enough confidence to warrant a mention just yet. CU this
afternoon will flatten into BKN stratocu deck this evening,
similar to yesterday. Clear spots could end up seeing some patchy
fog development as well, particularly anywhere that sees a shower
this afternoon. Dropped vis to IFR in several terminals as a place
holder, but will likely see some fine tuning this evening.

&&

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

$$

UPDATE...HJS
SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...HJS


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