Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 262352

Area Forecast Discussion
552 PM CST Mon Jan 26 2015

.SHORT TERM...(Tonight)

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)

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 00Z TAFS through 00Z Tuesday evening)

Patchy drizzle is occurring at BMI and CMI this evening, so will
be including this in those TAFs. Other sites might have it around,
but have not received any reports as of yet. Radar seems to
indicate some light pcpn, but will not include in TAFs yet. Temps
with the drizzle are right at freezing and below. However, warmer
air is moving into the area from the west and will change it over
to just plain drizzle. So FZDZ will continue at BMI and CMI for
several hours, ending last at CMI. Cloudy skies will continue at
all sites with conditions varying from LIFR at PIA and BMI to MVFR
at SPI only...DEC is IFR. Satellite shows clearing to the west,
but clouds advecting south. So, do not see a change in cloud cover
overnight and into the morning, even with wind shift to the
northwest when the warmer temps arrive later tonight. Based on
model data, clouds/conditions could improve around noon tomorrow.
Winds will be south and then become southwest just ahead of the
warmer airmass. Then northwest winds with some gusts to near 15kts
possible behind the warm front...then becoming north-northeast
overnight. Winds will decrease tomorrow afternoon.




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