Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 281735
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1235 PM CDT Thu Aug 28 2014

.UPDATE...
ISSUED AT 1045 AM CDT THU AUG 28 2014

Morning surface analysis shows a warm front extending from
northern Missouri into the Ohio River Valley. A vigorous
upper-level low evident on water vapor imagery over western
Kansas/Nebraska has triggered a large complex of showers/thunder
north of the front across Iowa. This precip area is lifting
northeastward and will remain W/NW of the KILX CWA. Further
southeast along the front, only isolated showers are currently
observed across central Illinois. Showers/thunder will become more
numerous as the day progresses, but due to lack of strong upper
support, areal coverage will remain scattered in nature. Due to
clouds and precip, temperatures will be a bit cooler than in
previous days. Afternoon highs will range from around 80 far
northwest to the upper 80s south of I-70. Current forecast is
right on track, so no update is needed at this time.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 303 AM CDT THU AUG 28 2014

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
area.

&&

.LONG TERM...(Friday through Wednesday)
ISSUED AT 303 AM CDT THU AUG 28 2014

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
front.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 1235 PM CDT THU AUG 28 2014

Warm front currently across southern Illinois will be the main
weather-maker over the next 24 hours. 17z radar imagery continues
to show dry conditions across the KILX CWA, although scattered
showers/thunder are beginning to develop further south across
western Kentucky/far southern Illinois. This is shown quite nicely
by the 3-hr HRRR forecast, which also shows widely scattered
thunder developing further north into west-central Illinois after
20/21z. Will continue to feature a period of VCTS this afternoon
into the early evening before any diurnal convection dissipates.
Even after the afternoon showers fade away, forecast soundings are
showing mid-level cloud deck remaining in place tonight. This
should mitigate any potential fog development, with the Rapid
Refresh showing visbys at or above 6sm through 10z. Winds will be
from the E/SE at less than 10kt this afternoon and tonight, then
will become S/SE by Friday morning as the warm front lifts
northward.

&&

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

$$

UPDATE...BARNES
SHORT TERM...SHIMON
LONG TERM...GEELHART
AVIATION...BARNES





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