Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
258 PM CST sun Dec 8 2013
issued 258 PM CST sun Dec 8 2013
Main concerns this forecast package include the winter weather
system moving through the area now, another weak system tomorrow,
another possible weather producer Tue night and Wed, and then a
stronger/warmer system Friday night and Sat.
Overall, the models look in fairly good agreement on the surface through
90 hrs, but then show considerable differences beyond that toward
the end of the forecast period. In the upper levels, the models
look good through most of the period, but differ with the speed of
a weak trough at the end of the week, which would have an effect
on precip chances for Fri night and Sat.
So a blend of the models looks good through most of the forecast,
then will lean toward the GFS slightly with the end of week
Short term...tonight through Wednesday
Light snow will continue over the area this evening, however,
light freezing drizzle is beginning to move into the area from the
southwest and south, affecting parts of southwest Illinois and
southeast Illinois. Satellite loop indicates some clouds a little
higher than areas to the south and southeast, possibly giving
those areas more ice crystals; which would result in more snow
than freezing drizzle. However, freezing drizzle will remain
possible, if not mixed with the snow, late this afternoon and
evening. Since most of the area did not receive any snowfall
during the last event, some roadways may not have any ice on them,
so any untreated roadways, bridges and overpasses could become
slick this evening. So we will be issuing a Winter Weather
Advisory for freezing drizzle, for counties along I-55 and to the
east and southeast for late this afternoon through this evening,
ending at midnight; when the pcpn should be out of the area.
Then cold high pressure will build into the plains, affecting our
cwa as well. However, an narrow area of forcing is forecast to
affect extreme southeast Illinois Mon afternoon. With the
continued cold temperatures, light snow will be possible down
there. However, there is no real surface or upper level features
supporting this so will just have slight chance in the forecast.
Otherwise, cold high pressure will dominate the weather for Mon
and Tue and most of the area through Wed. The models do forecast a
weak clipper system that drops into the western grt lks region. It
drags a weak cold front across the northern parts of the cwa Tue
night and Wed. This system will also lack moisture, so a slight
chance of pcpn is a good forecast. This will not show up in the
worded forecast, but will be seen in the grids.
Temps will remain below normal through the period, with a slight
warming trend for Wed. Mon night/Tue morning will see the coldest
temps through the period.
Long term...Wednesday night through Sunday
High pressure will continue to dominate the weather over the area
for most of the week. However, the high pressure area will shift
east and southeast through the week and allow a little stronger
weather system to move toward the area for the latter part of the
week and first part of the weekend. Though the extended models
differ on what the sfc pattern will look like, an inverted trough
will move across the area with an upper level trough right behind
it. So a chance of precipitation is a good forecast at this point.
Temperatures should remain cold enough that all the pcpn should
be in the form of snow. However, this could change as it is still
5 days away. Beyond this, the rest of the weekend should be dry.
As this high pressure moves east, southerly winds will allow
temperatures to warm. Though temps will still be below normal,
afternoon highs should reach above freezing for Friday. Temps will
then cool back into the 20s by Sunday.
issued 1159 am CST sun Dec 8 2013
MVFR ceilings will gradually lower to IFR this afternoon as the
atmosphere continues to slowly moisten from the top-down. Forecast
soundings suggest low ceilings and patchy freezing drizzle will
develop at the I-72 terminals by around 22z. Several hours of IFR
ceilings are anticipated, before westerly winds develop later this
evening and ceilings/visbys begin to improve from west to east after
the 03 to 05z time frame. Further northwest, light snow will
continue at kpia for the balance of the afternoon before tapering
off and coming to an end by early evening. IFR ceilings should
remain east of the Illinois River, so will maintain MVFR
conditions at kpia. MVFR ceilings return across the board after
midnight, as westerly winds bring drier air into the region.
Winter Weather Advisory until midnight CST tonight for ilz038-