Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
228 am CST Mon Dec 9 2013
issued 225 am CST Mon Dec 9 2013
Much of the earlier light snow and freezing drizzle has exited the
forecast area, with some patches of flurries continuing. Clearing
line just starting to edge into the far northwest County Warning Area as of 2 am.
The low clouds have helped keep temperatures up in the 20s, but
teens will start moving into the northwest shortly as skies start
Main concerns with the forecast involve timing of periodic, fast-
moving systems and associated precipitation chances.
Short term...today through wednesday:
An upper wave, currently entering the Texas/Oklahoma panhandles,
will zip northeast as a second, but stronger, trough swings
eastward from the Dakotas across the upper Mississippi Valley.
Main energy in our area will be with the southern wave, with a
narrow axis of light snow associated with enhanced lift in this
system. Have increased pop's after midnight to around 40% south
of I-70, where a couple tenths of snow are possible, but the
precipitation should be out of the area by sunrise.
Next in the parade of shortwaves expected to race through the
Great Lakes on Wednesday. Most forcing and moisture will remain
just to our north, but have added some 30% pop's for Wednesday
morning across the north.
Wind chills across the northwest late tonight should be getting
rather close to advisory criteria, with values of around 10 below
Long term...Thursday through sunday:
Upper pattern still looking to shift enough later this week to
keep the coldest air further to our north, with more of a split
jet stream setting up Thursday night. An initial weak cutoff low
in the southern stream will weaken to a trough as it ejects
eastward late Thursday night, reaching the mid-Mississippi Valley
late Friday night or early Saturday. May see some light
precipitation edging into the far southwest County Warning Area late Friday
afternoon, but bulk of the precip will be Friday night into the
first part of Saturday. Concern will be amount of warmer air
available with this system. Latest GFS soundings showing a
freezing rain and sleet mixture Friday night over most of the County Warning Area
before trending more toward snow, but the cooler European model (ecmwf) keeps the
precip mostly as snow. At this point, will not get too cute and
will just mention the snow, except for rain or snow across the
southeast on Saturday. Too many question with the pattern setup,
especially given that the European model (ecmwf) sends another slug of Arctic air
into the Midwest late in the weekend while the GFS keeps it much
issued 1154 PM CST sun Dec 8 2013
A threat of -fzdz and -sn will continue for the first 3-4 hours of
this taf period for all terminal sites. Despite the radar returns
diminishing significantly in the last couple of hours, we are
seeing evidence of additional lift sufficient to produce light
fzdz or snow as a trailing trough across northwest Illinois into southeast Iowa slides
east. That will make northern terminals have the better chances of
additional light precip. Additional ice or snow accums will be
minimal. However, travel surfaces will remain slippery through
IFR ceilings should begin to lift as dry air mixes into the
boundary layer from aloft. We could see MVFR clouds linger into
the first half of the day tomorrow, but eventually some clearing
is projected across all of central Illinois. The clearing may be brief
as mid clouds quickly return by Monday evening. Some light snow
for a fast moving disturbance will affect our southern counties,
but should not drop snow on any terminal site. Dec will be close,
but no snow was included in the taf with this issuance.
Winds will be gusty from the SW at times the rest of the night.
Directions should veer to the west in the morning, and become
gusty to 20-22kt. Gusts will diminish with sunset tomorrow.