Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180932

Area Forecast Discussion
332 AM CST Thu Dec 18 2014

.SHORT TERM...(Today)

An elongated high pressure ridge remains over IL this morning while
a shortwave is approaching from the west, moving into MO at this
time. The shortwave will weaken considerably today as it moves into
the ridge over Illinois. The result will be a good chance of
precipitation west of Springfield and I-55, but lower chances to the
northeast of Springfield. Only a slight chance as far northeast as
Galesburg to Decatur to Lawrenceville. Precipitation will be in the
form of snow given the depth of moisture extending well above the
-10 Celsius level, although some drizzle could develop during
periods where showers are less active. Snowfall amounts should be
quite light with this weakening system, reaching only up to around
one half inch near Jacksonville. Temperatures should only reach to
around the freezing mark today throughout central IL, with light and
variable to light northwest winds.


.LONG TERM...(Tonight through Wednesday)

Shortwave currently swinging through northern Baja California on
track to reach southern Texas by Friday afternoon, where the
associated surface storm system will be developing. The models have
been continuing their trend of pushing this system further south of
our area, with only the GFS producing some flurries as far north as
I-70. Have thus removed the remaining snow mention over the
southeast CWA Friday night and Saturday morning.

Primary focus is thus with the active pattern setting up ahead of
the Christmas travel rush next week. A broad upper trough will be
digging across the Plains Sunday and Monday. Strong jet stream of
120-160 knots will be coming down from the Pacific Northwest toward
the southern Plains early next week, helping to develop a closed low
over the northern Plains and a strong surface cyclone under it. Bulk
of the precipitation into Tuesday morning looks to be all rain, with
some snow mixed in at times in the far north. Complicated part comes
behind the cold front passage on Tuesday. Given the strength of the
system, the surface and upper low will be slow to move out,
lingering over northern Wisconsin or the Upper Peninsula through
most of Christmas Eve. The core of the heavier precipitation will be
east of our area by evening, but precipitation will wrap around the
low through this period. The GFS is faster in bringing in the colder
air, with 850 mb temperatures down to -10C by Wednesday morning,
while the ECMWF is a couple degrees warmer. Rain will transition to
snow most areas Tuesday night, although a mix may persist south of
I-70 late into the night. Have kept snow in most areas on Wednesday,
although a rain/snow mix again possible across the south, although
obviously some adjustments may later be needed with the system that
far out.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)

Clouds are still slowly exiting the area to the east. BMI, DEC,
and CMI still have broken to overcast clouds at MVFR levels. These
will eventually head east but broken cirrus has overspread all TAF
sites. As the next system advances closer to the area, clouds will
lower into the mid range to around 8kft at all sites sometime
during the morning, with SPI lower first. Models continue to show
very light snow getting to SPI only. So this is the only site
where I have cigs dropping to MVFR and having light snow/flurries
in the TAFs. All other sites will see slightly lower clouds to
around 5kft. Could be some MVFR cigs that slide over the other
sites, so will have TEMPO groups of 3-4 hrs for the others to
account for possible cigs around 3kft. During the late afternoon all
sites should see lower clouds scatter/dissipate with cirrus left
the rest of the evening. Winds will remain light and variable due
to the high pressure ridge sitting right over the area.




LONG TERM...Geelhart
AVIATION...Auten is the U.S. government's official web portal to all federal, state and local government web resources and services.