Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 281150

Area Forecast Discussion
650 AM CDT Thu Aug 28 2014

.SHORT TERM...(Today and tonight)

The location of the cold front appears to be just south of our
forecast area. It is forecast to return north as a warm front,
moving from SW to NE tonight. The unstable air mass extends well
north of the front all across our counties, as evidenced by the
isolated showers popping up early this morning across the northern
half of central IL. Added sprinkles to the northern counties for the
pre-dawn hours, and may need to extend the sprinkles after 12z east
toward CMI/DNV if the channel of precip continues. Otherwise,
overall thoughts on showers/storms are for a progression of chance
PoPs from west to east as the warm front begins to approach W-SW IL
in response to low pressure lifting from Nebraska into Minnesota.
The high res HRRR, ARW, and NMM along with the Canadian GEM all are
very scarce with coverage of storms over the next 12-24 hours, and
mainly in our far W-SW counties this afternoon. The 00z NAM, GFS,
and ECMWF all are a bit more aggressive, bringing precip as far east
as I-57 and LWV/Robinson. We kept the previous trends in the grids
of diurnally driven coverage, with higher chance PoPs in the SW half
of our forecast area this afternoon into early evening, then
trimming them back west later this evening/overnight. Confidence is
still low on precip coverage and timing based on very weak triggers
expected in our area northeast of the frontal boundary.

Sunshine will be filtered by mid-high clouds today, with highs in
the lower 80s north and some upper 80s S of Jacksonville to LWV.
Lows tonight will remain mainly in the lower 70s as the approaching
warm front keeps some cloud cover and higher dew points in our


.LONG TERM...(Friday through Wednesday)

Upper wave across the Rockies to make slow progress eastward
while dampening out Friday night over the Mississippi Valley.
Showers and storms Friday afternoon should be more scattered, with
a larger area of rain and storms coming in Friday night ahead of
the cold front. Have increased PoP`s to around 60% from I-55 west
by late Friday night and area-wide on Saturday.

The frontal boundary starts to become more diffuse Saturday night as
the upper wave flattens, and is difficult to discern by Sunday
morning. Have lingered the likely PoP`s across the southeast CWA
Saturday night as moisture continues to surge into the Ohio Valley,
and will keep high chance PoP`s going there into Sunday as well.
Further northwest, mainly dry conditions are on tap on Sunday.

Digging wave across the Rockies on Saturday night will be tracking
through the Mississippi Valley by Monday. Latest ECMWF draws some
cooler weather further south than the GFS, although not quite this
far south, as the west-east ridge across the lower tier of states
starts to strengthen again. Reasonable model agreement exists with
the associated cold front passing through on Monday, then hanging up
just south of I-70 as it becomes parallel to the upper flow. Showers
and storms to start moving back in Sunday night with the highest
chances on Monday. With the front hanging up, have lingered the
PoP`s across the southern CWA into Tuesday night, but did dry out
areas north as a small surface high drifts into the Great Lakes.

Rather muggy conditions to continue into early next week, with drier
air settling southward beginning Monday night behind the second


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)

Instability appears favorable for isolated showers to continue
this morning, as a moisture axis continues to feed into IL in the
mid and upper levels. Time-height cross sections show plenty of
VFR cloud cover is expected over the next 24 hours, but lower
chances of MVFR ceilings outside of any brief thunderstorms that
happen to pass over a terminal site. Some low clouds near
PIA/SPI/DEC could briefly produce a BKN MVFR deck through 14z.
Diurnal increase in instability will help increase the chances of
thunderstorms this afternoon. However, there is too much
uncertainty in the timing of any storm complexes to include much
more than VCTS from 19z to 01z.

Winds will remain easterly this morning with more of a southeast
component this afternoon and overnight. Speeds will continue less
than 10kt.




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