Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 310459
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1159 PM CDT Sat Aug 30 2014

.UPDATE...
ISSUED AT 903 PM CDT SAT AUG 30 2014

Two nearly parallel lines of isolated showers and thunderstorms,
one between I-55 & I-57 and the other near the Illinois River
(along outflow boundaries), have been weakening with the loss of
diurnal heating. This trend should continue over the next few
hours. The bulk of any overnight precipitation is expected to be
south/east of the forecast area along with the stronger deep layer
flow and moisture.

Going forecast is in pretty good shape. Only plan on a few tweaks
for the latest trends, most notably to PoPs.

&&

.SHORT TERM...(This evening through Sunday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

1847z radar imagery shows a broken line of showers beginning to
develop along the I-55 corridor. 12z NAM has a great handle on the
location of the convection, but is about 3-4 hours too slow.
Meanwhile, the HRRR seems to be doing good on both the location and
timing.  Both models develop scattered storms over the next couple
of hours along the I-55 corridor and basically keep them in that
general area through early evening before dissipating them toward
midnight.  Based on latest radar trends, will focus likely PoPs
along I-55 through the afternoon, then will gradually shift them
eastward toward I-57 by evening.  Further east and south, will only
carry chance PoPs this afternoon through tonight as storms should
tend to weaken as they slowly track eastward later this evening.
Partial clearing will take place across mainly the western half of
the KILX CWA tonight.  With plenty of low-level moisture in place
and winds diminishing to 5 mph or less, think patchy fog will
develop overnight. Sunday still appears to be a largely dry day,
with perhaps a few showers/thunderstorms lingering across the far
E/SE.  High temperatures will top out in the middle 80s.

&&

.LONG TERM...(Sunday night through Saturday)
ISSUED AT 310 PM CDT SAT AUG 30 2014

Main issue in the mid range of the forecast is the general slowing
of the next system for Sunday night/early Monday morning.  For now,
Sunday remains dry and the pops start to sneak into the forecast
after midnight Sunday night and spreading into Monday and Monday
night. Mondays fropa will be accompanied with a threat for potential
severe weather.  SPC has Illinois north of I-70 and down into MO and
eastern Kansas in a Day 3 Slight Risk.  Increasing instability with
plenty of moisture in a very warm airmass for Monday before the
frontal passage in combination with deep shear will lend itself to
the potential for severe weather. Timing shifts in the models so far
will likely keep the forecast somewhat conservative.  Monday night
keeping the precip through the overnight and so far, the models
lingering some precip in the morning on Tuesday, though the 12z runs
are speeding that up as well.  Future forecasts likely to see
Tuesday afternoon dry out as well. GFS still sending an MCS for
Wednesday, and being somewhat aggressive with the precip, whereas
the ECMWF is drier for now.  The AllBlend keeping slight and chance
pops through day 7.  Another boundary headed into the Midwest for
late in the week as a wave crosses over the US/Can border...but
heading into quasi zonal flow aloft not really supporting any major
progression of the sfc boundary. Slow boundary pointing to yet another
pd of being just on the edge of the unsettled weather with a signif
lack of 500mb height gradient over the southern half of the CONUS.
Thermal ridging in the south keeps above normal temps over the
region.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1150 PM CDT SAT AUG 30 2014

Tricky aviation forecast for the first several hours of the 06Z
TAF valid time. Despite the loss of diurnal heating, convection
continues to fire along an outflow boundary from previous storms.
At this point, no terminal is immediately threatened by these
storms, though the band, and some associated outflow, is making a
gradual shift to the east. this would threaten at least KBMI
within the next few hours if they persist. Also, further east,
within a deeper moist layer, MVFR cigs have started to break out,
including at KDEC & KCMI. Have a hard time seeing how this will
improve before daybreak as slightly drier air filters in from the
west. Expect condtions to improve to or remain VFR areawide on
Saturday as the more active weather shifts off to the east.

&&

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

$$

UPDATE...BAK
SHORT TERM...BARNES
LONG TERM...HJS
AVIATION...BAK






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