Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 122000

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

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.



ISSUED 1257 PM CDT Sat Jul 12 2014

Major issue for this forecast is the timing of the FROPA and the
associated TSRA. Going to begin the progression a little sooner
than prev issuance with a 03-06z approach and VCTS, with tempo
TSRA shortly after for a couple hours. Dropping to IFR vis with
storms. Otherwise, BKN mid/high deck and south southwesterly winds
until the passage of the boundary when winds become more westerly.
Ending the precip before dawn in the NW may bring risk of reduced
vis 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



FLASH FLOOD WATCH from 10 PM CDT this evening through Sunday
afternoon FOR ILZ038-043>046-053>057.


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