Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 072025
Area Forecast Discussion
National Weather Service Lincoln IL
225 PM CST Sat Dec 7 2013
ISSUED 225 PM CST Sat Dec 7 2013
Main concern this package has to do with the possible wintery mix
of freezing drizzle and snow tomorrow and tomorrow evening over
the area. Short term models seem to have a good handle on the
upper level pattern and the sfc features and their expected
trends. Differences, however, are seen with the actual
temperature profiles across the area. These differences will make
a big difference in precip type tomorrow through tomorrow evening.
Extended models seem in good agreement as well.
SHORT TERM...Tonight through Tuesday
Models have slowed the onset of pcpn with the next system moving
into the area tomorrow. Appears that cwa will be caught in the
middle of the best dynamics with the upcoming system. The sfc low
will move out of northwest MO and into southern WI, northwest of
the area, while another frontal system will be kept to the south.
Looks like enough dynamics over our area for some pcpn, though
main concern is precip type. Looks like once atmosphere becomes
saturated in the lower levels, the pcpn should start as snow.
However, just after that, we will lose our moisture at the level
where the ice crystals would be forming. So since where pcpn will
develop will be little warmer than needed for snow, the precip
will form as liquid and continue to fall through the cloud that
way. This means that the pcpn should reach the ground as liquid
water and with the sfc temperatures below freezing, then pcpn type
will be freezing; and given the slightly weaker dynamics than to
the northwest and south, the pcpn will be drizzle. So, expecting
freezing drizzle tomorrow afternoon through tomorrow night. Some
light snow could be mixed with this tomorrow afternoon, but
expecting all light freezing drizzle tomorrow evening. The pcpn
should end before midnight as the system pushes northeast and the
atmosphere dries out. Beyond this system, another arctic high
pressure area will build in for Mon and Tue.
Temps will warm a tad ahead of the system tomorrow evening, but
cold temps are expected again early Tue morning. Overall temps
will remain below freezing through the period, which is 10+
degrees below normal.
LONG TERM...Tuesday night through Saturday
High pressure will continue to dominate the weather across the
area through most of the week. There is a minor system that is
forecast to move across the northern part of the state Wed, but
expecting only clouds out of this system at the moment. Another
system approaches the area at the end of the week, but only a
slight chc of pcpn is expected at this time; which will only show
up in the grids and not in the worded forecast.
Temps will remain cold through the period with coldest temps being
Wed and Wed night. As the high pressure area shifts to the
southeast at end of the week, temps will warm to above freezing by
Friday. However, this will still be below normal for middle of
ISSUED 1147 AM CST Sat Dec 7 2013
High pressure dominates area terminals through early this evening
with gradual shift from north wind to light east as high center
passes to our north. A weak wave rotating through western U.S.
trough will produce some isentropic lift over the area late
tonight and Sunday. Falling ceilings should develop after 06z with
precip possible at KSPI and KDEC prior to the end of valid time of
this TAF issuance. Big question is as to the type of precip.
Forecasts soundings showing little in way of ice crystal formation
and suggest that precip may include freezing drizzle or light
freezing rain in addition to light snow. For now will include a
tempo group with a mix after 15z at KSPI and 16z at KDEC. Expect
more refinement in later TAFs as more certainty as to precip type