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Area forecast discussion 
National Weather Service Lincoln Illinois
906 PM CST Friday Nov 27 2015

issued at 900 PM CST Friday Nov 27 2015

Cold front finally cleared entire forecast area earlier this
evening. The Post frontal precipitation has also been on the wane
with the departure of the front and much of the associated
forcing. Based on latest radar trends and mesoscale model runs,
expect that most of the measurable precipitation has ended, except
for areas along/south of the I-70 corridor. Still, a deep moist
layer is still conducive for the patchy Post frontal drizzle that
is being reported. Far northern portions of the forecast area are
approaching 32 degrees, and although these temperatures shouldn't
fall much further overnight, there is some threat of slick roads
due to the currently wet pavement and possibly some patchy
freezing drizzle. Aside from updates to pop trends, only a few
minor tweaks are needed to the nighttime forecast.


Short term...(tonight)
issued at 250 PM CST Friday Nov 27 2015

The cold front draped across the eastern half of the country has
almost made it all the way through ilxs area this afternoon, and is
currently in the vicinity of I-70. Plenty of precipitation in the
region moving up from the SW. Precip is expected to continue,
particularly in the south and east through the overnight. The big
issues are the northern extent of the measurable precip, and the
timing of the cold air moving in behind it. Hrrr and NAM both
trying to pull the precip further south after 06z, which should
remove the threat for freezing rain later tonight. The forward progression
of the cooler air is also working against the rainfall as it is much
drier than the airmass over central Illinois. The dry air is slowly
eroding the llvl relative humidity and some of the weaker echos in the northwest are only
seeing low clouds, and not reporting precip. Even in the northwest where
the rain chances may recede after midnight, the low clouds and
potential for a misty night remain.

Long term...(saturday through friday)
issued at 250 PM CST Friday Nov 27 2015

Our area should be in between shortwaves on Saturday with a definite
trend south with the axis of heavier quantitative precipitation forecast from previous forecasts.
With our area in between shortwave trofs on Saturday, it appears the
better chances for rain will be across southeast Illinois, closer to
the frontal boundary and any associated weak surface wave that will
track northeast along it. Forecast soundings not very supporting of
any precip further north during the day so we will see a gradual
shift south with the higher pops as the boundary gets a nudge to the
south by afternoon. Forecast soundings showing some drier air (900-
800 mb)advecting south into the region during the day as well but
expect quite a bit of cloudiness to hang around during the day with
the lingering pops mainly across the southern third of the forecast
area by afternoon.

Low pops will remain Saturday night into Sunday with the GFS showing
a weak lead shortwave coming out of the large upper low over the
southwest U.S. Sunday afternoon and evening with the main push from
the low to our southwest not getting into central Illinois until
Monday. That is when we will see likely pops return across the
entire area with forecast soundings continuing to support rain
during the day, and then as we see cold advection settle in around
the backside of the upper low Monday night, we will see a mix or
changeover to light snow before the main forcing/lift ejects off to
the northeast on Tuesday. The main 500 mb trof axis will not shift
off to our east until Wednesday, so we will continue with at
least some low chance pops Tuesday and Tuesday night associated
with the cold pool aloft. Finally, by Wednesday, the system should
be far enough to our northeast to have a dry forecast for the
entire area along with seasonably cool temperatures.

As the large upper low continues to drift away from the Midwest late
Wednesday into the end of the work week, upper level heights will
start to increase across the region, with more of a semi-zonal flow
pattern depicted on medium range models. This should result in a
rather quiet weather scene over the region with near normal
temperatures and little if any rain or snow.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 552 PM CST Friday Nov 27 2015

Cold front cleared the central Illinois terminals earlier today,
but Post frontal light showers/drizzle persist. The rain/drizzle
should come to an end by morning, but still expect IFR or low end
MVFR conditions to persist at least into mid-morning Saturday.
Then, as the rain and drizzle threat ends Saturday, and drier air
filters in on the northerly winds, vsbys should be unrestricted
and cigs will climb toward VFR by the end of the day.


Ilx watches/warnings/advisories...


short term...hjs
long term...Smith

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