Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 122317
AREA FORECAST DISCUSSION
National Weather Service Lincoln IL
517 PM CST FRI FEB 12 2016
ISSUED AT 255 PM CST FRI FEB 12 2016
A weak clipper system will exit southeast of central IL late this
afternoon, with its diminishing area of very light snow/flurries
se of the IL river ending soon, with best light snow chances east
of IL over central IN. MVFR clouds already scattering nw of the IL
river like at PIA and HRRR model handling this clearing well.
These clouds to decrease se of the IL river during late
afternoon/early evening, and over southeast IL by mid evening.
Brisk NW winds of 15-25 mph and gusts to 30 mph will gradually
diminish during the night, reaching 5-15 mph later tonight. Strong
1046 mb polar high pressure west of Lake Winnipeg Canada to settle
se into MN/IA by sunrise Sat and bring a frigid night to the
region. Lows by early Saturday morning range from around zero
north of I-72 to 4-8F in southeast IL from I-70 southeast. Wind
chills by dawn will range from 5-15 below zero with a few spots
from I-74 north dipping to 15-17 below zero like at Bloomington,
Galesburg and Champaign. Will hold off on a wind chill advisory
overnight into mid Sat morning, but will issue SPS to address
these bitter cold wind chills especially in our northern CWA.
.LONG TERM...(Saturday through Friday)
ISSUED AT 255 PM CST FRI FEB 12 2016
Very cold conditions expected to start the day Saturday across
central and southeast Illinois as Arctic high pressure builds across
the area. The relatively slight pressure gradient that will
accompany the surface high should keep Wind Chill values warmer than
advisory criteria for the most part, but high temperatures should
only top out in the teens.
Beyond the initially cold conditions, our attention turns to an
approaching clipper system, which is likely to be the most
significant weather system to impact the area over the next week.
This clipper has trended faster in recent model runs, with snow now
expected to start breaking locally after midnight Saturday
night/Sunday morning. The system will be pushing into a very dry
airmass which should limit the snow accumulation to some degree.
However, fairly strong isentropic ascent and mixing ratios of 2-3
G/KG over at least a 12 hour period should be able to produce 2"=4"
snow totals. In fact, would not be surprised if we need to boost
accumulations further once the exact track of the system is more
clear (it has trended s bit south in the latest runs). One other
thing that will need to be monitored is that the moisture depth is
progged to be rather shallow during the period of potential snow.
This fact is also a reason to limit snow accumulations for now, and
we also need to monitor the threat for freezing drizzle due to a
potential lack of ice crystals.
The faster trend of the clipper system should now have Monday ending
up dry. Another weak clipper system may impact the area Tuesday into
Tuesday night, but it does not appear significant at this time.
After that, the next chance for precipitation should not occur
before the end of the week. However, model agreement in the details
of the late week system is weak at best. Temperatures should
gradually be trending warmer next week, with well above normal
temperatures likely by the end of the week (near 50 degrees for
highs). If these trends hold, the late week system, if/when it
impacts the area, should be a rain producer.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 518 PM CST FRI FEB 12 2016
VFR conditions will continue at all TAF sites next 24hrs. Clouds
are clearing from the area so all sites will be SKC to start and
then continue that way remainder of the night and into tomorrow
morning. Models bring in some high cirrus tomorrow in advance of
the next weather system, so have added SCT250 at all sites from
morning and through the day. Main issue is the wind speeds...with
gusty winds continuing this evening and into the overnight hours.
Then winds taper and sites will loose the gusts. Tomorrow winds
should be around 12kts of less. Wind direction will continue to be
northwest through the next 24hrs.