Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 080252
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
852 PM CST Wed Dec 7 2016

.UPDATE...
Issued at 845 PM CST Wed Dec 7 2016

Quite a bit of mid and high level cloud cover over the state this
evening, with upstream observations indicating some lower clouds
starting to push into our far northern counties. Every now and
then have seen reports of flurries in this particular band of
clouds so will insert some scattered flurries in our far northern
counties for the next 4-6 hours. After that, the short term
models suggest this band of cloud cover will shift off to our east
with a larger area of stratocumulus clouds across Wisconsin and
southeast Minnesota. That band of clouds will push southeast into
our area on Thursday with NAM forecast soundings showing an increase
in low level moisture which will get trapped underneath a strengthening
subsidence inversion, keeping the clouds around into at least the
first half of Friday.

Cold temperatures and a gusty northwest wind late tonight through
Thursday morning will drive wind chills down to between zero north
to around 10 above far southeast, with not much improvement during
the day on Thursday. With a weak surface trof forecast to shift
across the area during the late morning into the afternoon hours
coupled with low level cold advection, we may see a scattering of
flurries reappear over the north, roughly along and north of the
Interstate 74 corridor. However, it appears the main thrust of
any lift associated with the trof will be well north of our area,
so will maintain the current forecast with no mention of flurries
for now. We should have the updated zones out by 9 pm.

&&

.SHORT TERM...(This evening through Thursday)
ISSUED AT 252 PM CST Wed Dec 7 2016

Sprawling ridge of high pressure extending from western Canada to
the Ohio River Valley will dominate the weather across central
Illinois for the next 24 hours.  Mid/high clouds currently
blanketing the area will gradually dissipate and shift further
southeast tonight, resulting in clearing skies overnight.  W/NW
winds around the periphery of the high will continue to bring colder
air into the region, allowing lows to drop into the teens and lower
20s.  Wind-chill values by dawn Thursday will range from around zero
northwest of the Illinois River...to the teens along/south of I-70.
Chilly weather will continue through Thursday, with afternoon highs
remaining in the 20s and wind chills hovering in the single digits
and teens.  Meanwhile...an upper trough currently over the Upper
Midwest will pivot southeastward into central Illinois by Thursday
afternoon.  Model RH progs suggest overcast conditions will spill as
far south as the I-74 corridor, with partly to mostly sunny skies
persisting further south.  May even see a few flurries across the
far N/NE CWA Thursday afternoon, but have left them out of the
forecast for the time being...as best lift/moisture should remain
across northern Illinois.

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 252 PM CST Wed Dec 7 2016

Quiet and cold weather is expected to start the period, with
widespread single digit Wind Chill values expected into midday
Friday. A quick moving storm system will track toward the area on
Saturday. Strong WAA/isentropic lift ahead of the system should have
light snow starting to break out by late Saturday afternoon into
Saturday night. The initial arrival of the system is pretty well
agreed upon by the model guidance. However, significant disagreement
and run-to-run inconsistency exists Sunday into Monday. The GFS has
remained progressive with the system, suggesting dry weather for the
end of the weekend. However, the operational ECMWF has been
insistent that a wave will develop along the front, spilling
precipitation back into the area Sunday into early Monday. In fact,
the 12Z ECMWF significantly strengthened this secondary wave and
could bring significant precipitation to the area if it verifies.
The strength of the ECMWF system would actually be warm enough for
rain to the east of the storm track. The latest Canadian model has
trended toward what the previous run of the ECMWF had (a secondary
but much weaker wave to end the weekend). This significant
variability between operational models, and within their respective
ensembles, suggests a low confidence forecast for the weekend. Have
not made considerable changes to prior forecast, with the bulk of
the precipitation (light snowfall) occurring Saturday night.

One other system is progged to impact the area during the forecast
period. It is a fairly weak upper-level weak wave that is expected
to arrive sometime between Tuesday and Wednesday. However, there is
at least a 24 hour spread between the slowest and fastest solutions
with this wave. The unfortunately result of this disagreement is an
extended period of low PoPs (for snow), when the eventual period of
expected snowfall will be rather short.

Temperatures will be well blow normal to start the period. Then,
they will trend warmer, with only slightly below normal readings for
the weekend and early next week. Another blast of cold air, colder
than the one currently pushing in, is likely to arrive by the middle
of next week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 510 PM CST Wed Dec 7 2016

High pressure to our northwest will slowly drift towards the
Midwest over the next 24 hours. Meanwhile, a surface trof
is expected to rotate southeast into the lower Great Lakes on
Thursday which should result in an increase in MVFR clouds and a
rather gusty west to northwest wind. Surface observations to our
north over the past couple of hours have indicated some scattered
stratocumulus with bases in the 2500-3500 foot level with a larger
band of low VFR and some MVFR cigs over northeast Iowa and southern
Wisconsin. This band of clouds is expected to edge southeast
tonight into Thursday with most of its lower (MVFR cigs) cloud
cover holding off arriving into our area at or shortly after 18z.

Westerly winds around 10 kts tonight with a west to northwest wind
expected on Thursday at 12 to 17 kts, with a few gusts around 20
kts at times.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Smith
SHORT TERM...Barnes
LONG TERM...Bak
AVIATION...Smith



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