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Area forecast discussion 
National Weather Service Lincoln Illinois
1119 PM CST Wednesday Nov 25 2015

issued at 857 PM CST Wednesday Nov 25 2015

Scattered showers are falling across central and southeast
Illinois this evening, and see no reason why this should not
continue through the night. At first glance, the 00z kilx and
forecast soundings do not look especially conducive for more than
drizzle. A nearly saturated layer exists between about 925 mb and
700 mb however, there is a strong inversion at 600 mb that will
keep the showers from getting much vertical extent or allowing the
cloud to become cold enough for ice. Still, 40-50 knots winds through
saturated layer is obviously sufficient to produce significant
collision/coalescence and eventually rainfall. As the moist layer
and accompanying wind field are expected to remain pretty steady
state overnight, plan to adjust pops to better fit what is
occurring at the moment. Otherwise, only minor tweaks are needed
to the hourly grids.


Short term...(tonight)
issued at 300 PM CST Wednesday Nov 25 2015

High pressure is sliding off to the East Coast this afternoon,
and another system is developing over the plains. This storm system
will slowly make its approach to the Midwest for later Thanksgiving
night. In the meantime, scattered showers, low clouds, and drizzle
are expected later this evening and overnight, spreading as dawn
approaches. Continued southerly winds overnight will work together
with the expansive cloud cover to keep the overnight lows mild for
the end of November. Not much of a change in the overall forecast,
heading into a rainy Holiday weekend.

Long term...(thursday through wednesday)
issued at 300 PM CST Wednesday Nov 25 2015

An active weather pattern will be in store for central and southeast
Illinois through the Thanksgiving weekend and into early next week.
Overall the shorter range models are generally in agreement with a
northern stream upper level trough shifting and associated cold
front shift through the Midwest Friday and upper level low/Rex block
situation developing the western states. The differences come into
play later in the weekend and into early next week with the amount
of shortwave energy that is ejected toward the middle MS valley and
when the upper low in the west begins to move out.

The approaching cold front and increasing southerly flow and deeper
moisture will produce the likelihood of light rain in the Illinois River
valley Thanksgiving day, with scattered showers in the rest of
central Illinois. East central Illinois may see some light warm
advection rain in the morning, but then only a few spotty showers
during the afternoon, with mainly cloudy conditions in the
southeast. Despite the potential for rain and the clouds,
temperatures on Thanksgiving will be unseasonably mild with highs
around 60 across the whole forecast area.

The highest potential for moderate to heavy rain will move into
central Illinois Thursday evening, and into eastern/southeast Illinois late
Thursday night as the cold front moves through and area of low
pressure moving along it enhance the rainfall potential. The rain
should linger in most of the forecast area through Friday as the
front slowly sags to the southeast. Temperatures on Friday should be
warmest in the morning, with readings slowly falling during the day
as the cooler air filters in. Forecast soundings indicate that the
western edge of the precipitation shield could see a change to light
freezing rain or snow north of a Rushville-Bloomington line Friday
night. Very little or no accumulation is anticipated from this brief
change over.

Rainfall totals of 1.00 to 1.50 inches are anticipated by Saturday
morning, with the highest amounts staying in southern Illinois or west of
the MS river. Much of the snow cover has melted in the northern part
of the forecast area, so the impact of up to 1.50" of rain should
not be as great on area streams/creeks.

The first piece of shortwave energy coming out of the western U.S.
Upper low is expected to interact with the nearly stationary front
south of the Ohio River valley, and may in fact push it a bit
farther north later Saturday into Sunday. This will keep the chance
of rain in southeast Illinois through the weekend, and move it back into
parts of central Illinois by Sunday morning.

There is a lot of uncertainty with the movement of the western U.S.
Upper low late in the weekend and into early next week. The European
model is quite complex and quicker with the low, while the GFS is
slower. Prefer the slower GFS solution, especially since this upper
level pattern is fairly complex. The result would be a continuation
of unsettled weather and a trend toward cooler temperatures Monday
into early Tuesday. Could see a change from rain to light snow or a
mix of rain/snow in central Illinois Monday night as temperatures
dip below freezing and colder temperatures aloft approach the region.


Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1117 PM CST Wednesday Nov 25 2015

Low clouds will prevail across the central Illinois terminals
through the 06z taf valid time. While they are predominantly low-
end VFR for now, they should trend down into the MVFR category
with time. Spotty showers will be around during the period as
well, but they should stay too light and/or isolated to go above a
vcsh mention. The winds should be gusty out of the south through
the period, but significantly stronger winds just off the deck
will still produce low level wind shear. Expect the low level wind shear to persist even during
the daytime hours Thursday, as the guidance forecasts 50 kt winds
as low as 925 mb through the period.


Ilx watches/warnings/advisories...


short term...hjs
long term...Miller

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