Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 272057

Area Forecast Discussion
257 PM CST Fri Feb 27 2015

.SHORT TERM...(Tonight)

Strong 1040 mb arctic high pressure near the IA/MO/IL border
projected by latest forecast models to strengthen to 1045 mb as it
moves east to northern PA by 12Z/6 am Sat and mid Atlantic states by
18Z/noon Sat. High pressure ridge still ridging back west into
central/northern IL through midday Saturday. This will continue dry
weather across central and southeast IL through at least 21Z/3 pm
Sat afternoon. Mid and high clouds to increase from the wsw during
tonight with low clouds spreading in late Sat morning and afternoon.
Less cloud cover over northern counties tonight especially this
evening will give colder temps there with snow pack and light winds.
Temps currently in low to mid teens central IL and upper teens to
near 20F in southeast IL. Dewpoints only range from 4 below to 4
above zero. Favored the colder MAV lows tonight especialy over the
northern counties with lows Zero to 7 below nw of Lincoln. Lows of
4-9F in southeast IL.


.LONG TERM...(Saturday through Friday)

Complex and active weather pattern is expected to impact central and
southeast Illinois from later Saturday into the middle of next week.
Model guidance is in reasonable agreement with the big picture, but
there has still been some important run-to-run variability. This has
especially been true with the heaviest snow axis for Saturday night
into Sunday and with the thermal profiles for the next system Monday
night into Wednesday.

A vigorous upper wave is currently diving down the west coast of the
United States, and this will eventually help to cause downstream
southwesterly flow across much of the lower 48 from later Saturday
into the middle of next week. This development will result in
numerous disturbances ejecting through the vicinity of the forecast

For our initial system, impacting the area Saturday night through
Sunday, the forcing will be provided more by a northern stream
disturbance that will dive across the Midwest. However, the
developing southwesterly flow from the Pacific wave will help
transport more copious moisture into the region than would normally
be expected ahead of a northern stream wave approaching from the
northwest. The upshot is that an 18-24 hour period of snow will
spread across the area beginning Saturday night and continuing
through Sunday. A swath of 4-6 inch snows appears likely across
parts of central Illinois, fairly close to the I-72 corridor, with
significantly lower amounts to the north and south of this axis.
Thermal profiles suggest a rain/snow mix is possible south of I-70
Sunday afternoon.

Do not plan to issue any winter weather headlines with the initial
system at this time, and will continue to highlight in a Special
Weather Statement. Current indications suggest snowfall totals will
be too low and/or fall over too long a duration to reach
watch/warning criteria. Expect a Winter Weather Advisory to be
needed, but will wait until the system is a little closer and target
area can be selected a little better.

High pressure will build across the area Sunday night into Monday,
although it will not be as cold as our recent Canadian highs have
been. Then, a large & fairly well phased northern/southern stream
trof will produce another round of precipitation across the area
Monday night into Wednesday. Ahead of the trof, significant warming
is anticipated locally and will result in much of the associated
precipitation falling in liquid form. However, the near surface
temperatures will not respond so quickly given the cold weather of
late as well as more considerable snow cover that should be in
place. This is likely to result in some sleet and/or freezing rain,
especially Monday night and early Tuesday. While it is too early to
pinpoint the significance of the ice threat, it will need to be
watched closely.

Cooler/quieter weather will return for the second half of next week
in the wake of the major trof. Temperatures will not be as cold as
the past few days, but should still average well below normal.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)

VFR conditions to continue across the central IL airports next 24
hours through 18Z/noon Sat. Few stratocumulus clouds this
afternoon especially in eastern IL per RUC/NAM curule. Cirrus
clouds to spread ene across central IL this afternoon with broken
ceilings developing. Ceilings will gradually lower during tonight
with mid level clouds and then to 5-10k ft during Sat morning.
Strong 1041 mb arctic high pressure over northern MO/southn IA and
west central IL to drift east into ohio river valley tonight and
continue the fair wx over the region through Sat morning. Light
winds into tonight will become ESE 4-8 kts by Sat morning. No fog
is expected tonight due to very dry arctic airmass.




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