Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Lincoln Illinois
552 am CST Fri Dec 13 2013
issued 300 am CST Fri Dec 13 2013
Early morning calm before the winter storm features some patches
of high clouds moving through the area. Temperatures staying up in
the 20s across the southwest County Warning Area where there is no snow on the
ground, but mainly mid to upper teens elsewhere. Water vapor
imagery showing closed upper low near Phoenix beginning to open up
a bit, while the northern branch of the jet stream continues to
stream southeast through the Great Lakes.
Short term...today through saturday:
Temperature trends will be critical in the precipitation type at
the onset of precip this afternoon and early evening, before a
more uniform change to snow in most areas. Latest NAM and rap
soundings are showing enough warm air for a fair amount of rain
with some sleet mixed in at times, especially in the southwest, but
the GFS is more solidly snow. Given that the European model (ecmwf) MOS guidance
has highs near 40, and upper 30s did occur over the southwest
yesterday when such an occurrence seemed unlikely, am somewhat
hesitant to completely ignore these solutions. Thus, will keep the
Winter Weather Advisory going, and not upgrade to a warning at
this time, although some areas may end up approaching warning
criteria. Across the northeast, have backed off on precip until
very late afternoon. Bulk of the snow will be falling tonight,
although up to an inch may fall across the east Saturday morning
as the system pulls away. Have gone with around 5 inches in most
areas, with some locally higher totals. The far southeast may see
the mixture lasting longer into the evening, so totals down there
are a bit lower.
Long term...Sunday through thursday:
Quick shot of Arctic air behind this system expected for Sunday,
before some moderating temperatures for a few days. The Arctic air
will be locked up in Canada for the first half of the work week.
However, both the European model (ecmwf) and GFS show another significant surge
southward late in the week, with the former model much faster in
this regard. Have pretty much kept the extended dry. Some light
precipitation may be moving in later Thursday, with some
indication of this by both models, so will go with slight chances
issued 552 am CST Fri Dec 13 2013
Winter weather is still forecast to move into the area later this
afternoon and continue during the night and overnight hours. Mid
and high clouds will move into the area this morning and
overspread the tafs by this afternoon. However, by late afternoon,
clouds will thicken and cigs will drop very quickly as pcpn
begins. Spi could have a mix of snow and rain early so have a
tempo group to cover that for couple hours. Remainder of the sites
will start as snow. All sites will see light to moderate snow
during the evening hours. Then overnight all snow will be light.
Cig heights during the snow will drop to below 1kft. Vis will drop
to 3/4 mile, with a tempo group for 4hrs of 1/2 mile with moderate
snow. During the overnight hours, after 06-08z, vis will improve
to IFR category of 1sm. Think conditions might improve during last
6hrs of taf period, but unsure if they will given the light snow
that will likely continue into early morning hours at each site.
Winds will generally be light through the period. Wind direction
will be southerly, but then become easterly late tonight.
Winter Weather Advisory from 3 PM this afternoon to noon CST
Saturday for ilz045-046-055>057-062-063-066>068-071>073.
Winter Weather Advisory from 3 PM this afternoon to 6 am CST
Saturday for ilz027>031-036>038-040>044-047>054-061.