Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 262055
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
255 PM CST Mon Jan 26 2015

.SHORT TERM...(Tonight)
ISSUED AT 255 PM CST MON JAN 26 2015

Today`s short wave diving into the mean eastern North American trof
ended up remaining a little more robust than anticipated, despite
indications yesterday that it would be much more sheared out and
weaker by the time it arrived. The result has been at least a few
hours of light snow across most of the forecast area. While the
threat area will continue to shift east tonight before pushing out
of the area, the channeled vorticity within the mean flow will keep
a risk light snow or flurries across east central and southeast
Illinois for several more hours. However, most areas will only see a
dusting of snow. Away from the snow threat, across the western
portion of the forecast area, clouds should continue to hold tough.

One thing that will be need to be watched closely across the entire
forecast area, at least through this evening, is the threat for
freezing drizzle. Forecast soundings suggest that a fairly thick
low-level moist layer will persist after the upper energy and
associated ice crystals depart. However, the shear within the moist
layer is not very impressive and there is minimal indication of
drizzle upstream. So, plan to leave the mention out for now.


&&

.LONG TERM...(Tuesday through Monday)
ISSUED AT 255 PM CST MON JAN 26 2015

One more cool day (but near normal for late January) is expected
across central and southeast Illinois on Tuesday as northerly low
level flow develops ahead of an approaching ridge of high pressure.
Temperatures will also be held down by considerable cloud cover.

Southerly low-level flow and a quick warm-up is expected for midweek
as the surface ridge departs and low pressure approaches from the
Plains. The approaching storm system is still on track to bring some
rainfall to the area Wednesday night into Thursday as it moves
through. However, the latest indications are that the rain will be
delayed a bit and lighter than previously anticipated. The reasons
for the delay and lighter amounts are two fold. First, whereas this
system was initially expected to be primarily driven by energy and
associated moisture from the cutoff low of Baja California, now a
drier northern stream wave looks like it will be more of a dominant
player. Second, it also looks like low level ridging along the Gulf
coast will be stout enough to preclude much moisture return until
the system pushes east of the forecast area.

After a brief lull, our next system is expected to arrive by the
weekend. However, considerable model spread exists with respect to
the details, and there has also been significant run-to-run
variability. This uncertainty is resulting in an extended period of
low chance PoPs from Saturday into Sunday. The models agree that it
will be cold enough for snow, but little agreement exists with
respect to explicit timing and amounts. Hopefully the snow threat
will become more clear soon.

Forecast guidance has continued to suggest for several days that a
period of below normal temperatures is on the way beyond our normal
7 day forecast. However, once the forecast period draws closer, they
have been backing down. So, it still looks like temperatures should
average at or above normal for the next seven days. We`ll just have
to see if the how long that can last.


&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 1247 PM CST MON JAN 26 2015
Wave moving through Central Illinois and bringing quick drops in
category to IFR and isolated LIFR with some of the heavier snow bands.
Heavier showers not always discernible on radar making the TAF
trends difficult. PIA and SPI soon to the on the back edge of the
heavier snows...with cigs around 2kft...but a few obs with holes
to VFR. TAF forecast to the more degraded conditions as moisture
saturates through the column and drops categories more widespread
through the afternoon and into the overnight hours. Winds becoming
more NWrly. Models keeping low cigs through the overnight with
some MVFR reductions in vis predominant...with possible patchy drops
to IFR.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Bak
LONG TERM...Bak
AVIATION...HJS





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