Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 130339
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1039 PM CDT Sat Jul 12 2014

.DISCUSSION...
ISSUED 1038 PM CDT Sat Jul 12 2014

A cold front approaching from the northwest will bring increasing
thunderstorm activity to northern portions of the ILX forecast
area over the next few hours. Rotation has been observed in storms
approaching this region, and a tornado watch has been issued from
around Fulton to McLean county northward. In addition to an
isolated tornado possible in this area, a severe wind gust and
large hail risk exists in this area as well. Showers have now
reached Peooria...although strong-severe storms still just moving
into knox/Fulton county.

Increasing shear and precipitable water will move into the central
IL forecast area overnight, along with significant, although
decreasing instability (CAPE). Overnight...heavy rain on the
already saturated area from McLean to Moultrie to Edgar and
Vermilion Counties is more of a concern and a flash flood watch
remains in effect for these areas.

Onton
&&

.AVIATION...
ISSUED 618 PM CDT Sat Jul 12 2014

VFR conditions across central/southeast IL will deteriorate this
24 hour TAF period as a cold front sweeps across the region
bringing a line of TSRA containing heavy rain, and isolated severe
wind gusts. 00Z TAFs include VCTS and TEMPO TSRA with IFR
visibility and gusty winds beginning at 02-03Z for KPIA ranging
to 06Z for KDEC. Otherwise, BKN mid/high deck and south
southwesterly winds until the passage of the front when winds
become more westerly. Ending the precip before dawn in the NW may
bring risk of reduced vis due to fog in the wake of the system,
but the clearing potential is sketchy in models as well as on vis
sat imagery. Will keep a subtle drop for the early morning hours
in PIA and BMI but should the mid deck maintain solid coverage,
the vis drop will be minimized. For Sunday...mention of VCTS/TSRA
is gradually removed from TAFS after 11Z-21Z as probability
becomes too low once the front moves east.

Onton
&&

.PREV DISCUSSION...
ISSUED 300 PM CDT Sat Jul 12 2014

Eastern Illinois finally drying out after the copious rains that
occurred during the morning hours. Radar showed a large area of 3 to
5 inches between US-51 and I-57, with a sizable area of 6 to 8
inches from Champaign northwest along I-74 into far southeast
McLean County. Areas further west pretty much missed out on the
rain, and some sunshine has formed out near Springfield. Tongue of
75+ degree dew points has spread into the western half of the CWA,
causing heat index values to rise into the 95-100 degree range.

Immediate forecast concern involves flooding potential tonight
and Sunday, followed with the well-advertised, unseasonably cool
weather occurring a bit later in the week.

SHORT TERM...Tonight through Monday:

Cold front still back across the northwest third of Iowa this
afternoon, and this will be settling across the northern part of
the forecast area overnight, finally clearing the the southeast
corner by mid afternoon Sunday. MCS expected to develop across
Iowa and northern Illinois this evening, sinking southward into
our area beginning mid-late evening. Low-level flow will increase
a bit, with a concern that this will slow the southward
progression. Precipitable water values up around 2.3" will mean
additional heavy rains are likely with this MCS, primarily in the
northern half of the CWA. Areas west of Bloomington and Decatur
should be able to absorb some of this heavier rain, at least
initially, but east of there, it will take very little to cause
additional water concerns due to the morning flooding. Thus, will
be issuing a Flash Flood Watch basically from Bloomington to
Decatur eastward for late this evening through midday Sunday.

Initial thunderstorm activity should be exiting the southeast CWA
Sunday evening. However, scattered showers/storms expected to
develop again Monday as a surge of energy accompanies the incoming
cool air mass.

LONG TERM...Tuesday through Saturday:

850 mb temperatures fall to around 6-7C by Tuesday morning as the
deep trough digs across the Midwest. Have lowered Tuesday morning
temperatures a bit as a result, with lows 50-55 except upper 50s
south of I-70, and we may struggle to reach 70 north of I-74 on
Tuesday. Have added some small rain chances across the far north,
due to potential for instability showers with the core of the
trough overhead.

Temperatures should rise a couple degrees each day for the
remainder of the week, as the air mass modifies. Have kept the
forecast dry the remainder of the period, as high pressure takes
its time pushing eastward. Latest ECMWF does show some potential
for rain across the south by Saturday, but the longer range models
have some discrepancy on the strength of an incoming trough at
that point, so have left it out for now.

Geelhart

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH through Sunday afternoon FOR ILZ038-043>046-
053>057.

&&

$$








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