Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 181146
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
546 AM CST Thu Dec 18 2014

.SHORT TERM...(Today)
ISSUED AT 331 AM CST THU DEC 18 2014

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)
ISSUED AT 331 AM CST THU DEC 18 2014

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 12Z TAFS through 12Z Friday morning)
ISSUED AT 546 AM CST THU DEC 18 2014

A weather system approaching from the west will bring increasing
cloud cover and areas -sn today, while MVFR ceilings linger from
around KCMI-K1H2 eastward through the morning. Expect areas MVFR
cigs returning late morning through portions of the evening,
earliest KSPI westward. Areas -sn with sct MVFR vsby likely
southwest of KGBG-KLWV from 14Z-20Z. VFR conditions expected to
return overnight, with MVFR cigs remaining latest KSPI-KDEC
southward. Winds N-NW less than 5 kts through the period.

&&

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

$$

SHORT TERM...Onton
LONG TERM...Geelhart
AVIATION...Onton





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