Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 122055
AFDILX

AREA FORECAST DISCUSSION
National Weather Service Lincoln IL
255 PM CST FRI FEB 12 2016

.SHORT TERM...(Tonight)
ISSUED AT 255 PM CST FRI FEB 12 2016

A weak clipper system will exit southeast of central IL late this
afternooon, 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 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 1155 AM CST FRI FEB 12 2016

A weak clipper system was bringing a band of light snow and
flurries that was progessing se of the IL river and approaching
I-72 at midday. The light snow was bringing vsbys down to 1-3
miles for 1-2 hours at PIA and will affect BMI and CMI next few
hours and possibly briefly bring MVFR vsbys to DEC early this
afternoon. MVFR ceilings are expected to scattered out from nw to
se late this afternoon and early evening. Brisk NW winds of 13-18
kts and gusts of 18-25 kts into this evening will diminish to
around 10 kts by overnight and down to 5-9 kts late tonight into
Saturday morning. 1046 mb arctic high pressure west of Lake
Winnipeg Canada will settle into eastern IA by 18Z/noon Sat as it
weakens a bit to 1041 mb. This will provide the fair weather
tonight into Sat with winds diminishing as high pressure settles
in.


&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...07
LONG TERM...BAK
AVIATION...07


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