Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 010204
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
904 PM CDT TUE MAY 31 2016

.UPDATE...
Issued at 900 PM CDT Tue May 31 2016

A break in the showers and storms is expected for the rest of the
evening, before a cold front pushes across Illinois later tonight
into Wednesday morning. Some brief clearing in the clouds south of
I-72 should fill back in again as the pre-frontal airmass begins
to lift. A line of showers/storms are expected to progress from
west to east across the area starting after midnight west of the
Illinois river. By sunrise, the HRRR is indicating that precip
should be mainly confined to areas east of I-55. However, the RAP
is forecasting a few post-frontal showers lingering as far west as
the Illinois river through mid-morning. The GFS20, NAM20 and ECMWF
also linger precip east of the IL river through the day tomorrow
as well. Have reduced evening PoPs and kept the increasing PoPs
west of I-55 after midnight.

Clouds will minimize the diurnal temp swing overnight, but some
pockets of clearing could allow for lows to dip at times. Have
kept most low temps in the mid 60s, with upper 60s south of I-70.

Winds will remain relatively light outside of any showers/storms,
with directions generally southeast until frontal passage, then
shifting westerly.

Main updates this evening were to the short term Precip/PoPs, with
minor changes to temps/dewpoints/clouds. Updated forecast info is
already available.

&&

.SHORT TERM...(Tonight)
ISSUED AT 259 PM CDT Tue May 31 2016

Numerous showers and thunderstorms over the western half of the CWA
this morning became more scattered in the afternoon, as the earlier
MCV continues to weaken as it lifts across central Illinois. Earlier
outflow boundary made it all the way over to I-57 before it started
to wash out, and is helping to trigger some storms north of Rantoul
and Danville. The rain significantly dropped temperatures, but have
recovered back into the 80s around Springfield and Danville.
Temperatures over the far southeast CWA have reached close to 90
degrees, where skies have been at least partly sunny through the
day.

Scattered, disorganized showers and storms will continue to be
possible across mainly the western half from the CWA early this
evening, before some diminishing trends with loss of daytime
heating. However, the main cold front is currently tracking across
central Iowa, with convection lined up nicely along the boundary.
HRRR model brings the front across the Illinois border very late
this evening and near Peoria by about 3-4 am, so PoP`s ramp up
again late evening and overnight from the west. The eastern CWA
will see better chances of rain very late in the night, but more
likely Wednesday morning as the front gets closer. Temperatures
overnight should be relatively uniform over the CWA, mainly in the
mid 60s.

.LONG TERM...(Wednesday through Tuesday)
ISSUED AT 259 PM CDT Tue May 31 2016

Models continue to be in good agreement with respect to the main
features expected to impact the forecast area over the next several
days. The main trends noted since yesterday are a slightly faster
cold frontal passage tomorrow, and a bit more phasing with/influence
from a southern stream wave as a northern stream wave digs across
the area this weekend.

The most widespread chances of shower/storms this week will occur
tomorrow as a cold front swings through the area. This front will be
driven by a strong wave, currently centered over the northern
Plains/southern Canadian Prairies, as it shears east along the
U.S./Canada border. While some spotty severe storms can not be ruled
out with the frontal passage and pre-frontal 1000-2000 CAPE values,
shear profiles are forecast to remain weak and should preclude
significant storm organization/severity.

Mostly dry and slightly cooler conditions are expected behind the
front later Wednesday night into Friday, courtesy of neutral upper-
level flow and surface high pressure. Then, a northern stream wave
dives southeast from Canada into the Great Lakes region over the
weekend. This approach/passage of this wave will be accompanied by a
risk of shower/storms. While earlier model runs suggests the
northern portion of the forecast area would be more favored for
rainfall due to its closer proximity to the wave, current runs phase
this system more with a southern stream wave that will slowly be
making its way across the southern plains. The at least partial
phasing of these systems will bring moisture up from the south as
well, resulting in most of the forecast area seeing a decent chance
of showers/storms at some point over the weekend. Drier weather
returns to start the next work week as these waves push east of the
area.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 700 PM CDT Tue May 31 2016

An outflow boundary moving north after later afternoon convection
has pushed through all TAF sites, just reaching PIA in the last 30
minutes. The result will be a few hours of variable winds due to
the boundary passage, then winds should return to a south-
southeasterly direction by mid-evening at all terminal sites.

Showers and isolated storms will affect mainly the northern TAFs
along I-74, where pockets of convection continue to fester into
the evening. SPI and DEC should generally be done with precip for
the evening. Thunder appears limited, with PIA the only airport
near any updrafts with 50+ dbz, so VCTS was only included there at
TAF start time. A break in the precip appears likely for mid to
late evening. Then the HRRR is advertising the approach of a
frontal boundary late tonight, triggering additional showers and
storms after 09z or so. That area of convection may be limited to
the western terminals, based on HRRR output diminishing precip
coverage after the front passes the Illinois river.

As the front pushes east through the forecast area, showers and
storms will be possible, so VCTS was included at all terminals
through at least early afternoon, with the eastern TAFS of DEC and
CMI carrying thunder through 00z/7pm Wed.


&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...Shimon
SHORT TERM...Geelhart
LONG TERM...Bak
AVIATION...Shimon



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