Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271752

Area Forecast Discussion
1152 AM CST Fri Feb 27 2015


Wind chill advisory over portions of central IL expired at 10 am and
updated the forecast for this expiration. Coldest wind chills late
this morning are 5 above to 14 below zero over central IL. Strong
1041 mb arctic high pressure over northern MO, southern IA into
west central IL will drift east across central IL this afternoon
and into the Ohio river valley tonight. This will provide dry wx
through tonight along with cold temperatures and lighter winds.
Highs in the mid teens central IL and upper teens south of I-70.
Sunny to mostly sunny skies as few stratocumulus clouds appear and
thin cirrus clouds increase this afternoon especially southern counties.


.SHORT TERM...(Today)

A very cold but dry day is on tap across central Illinois today as
high pressure builds into the region.  Early morning wind-chills
will range from 10 to 20 below zero across the northern half of the
KILX CWA, where a Wind-Chill Advisory will remain in effect until
10am.  Abundant sunshine will prevail: however, temperatures will
struggle to climb into the teens.


.LONG TERM...(Tonight through Thursday)

Plenty of challenges in the extended as an active southwesterly flow
pattern brings several rounds of precip from Saturday night through

As a vigorous short-wave trough currently evident on water vapor
imagery off the coast of Washington digs southward, weak ridging
will develop downstream across the central and eastern CONUS and a
baroclinic zone will lift northward accordingly.  This boundary will
become quasi-stationary across central Illinois and will serve as
the focusing mechanism for the first round of precip Saturday night
into Sunday.  A piece of energy will eject northeastward from the
amplifying upper low over the Southwest US on Saturday, tracking
along the front Saturday night into Sunday.  Forecast soundings
indicate a very dry airmass initially, but once sufficient
moistening occurs, thermal profiles support snow across central and
southeast Illinois Saturday night into Sunday.  As surface flow
becomes more southerly, temperatures will warm into the lower 30s
across much of the area on Sunday and into the middle to upper 30s
across the SE CWA.  Precip should remain in the form of wet snow
throughout the day, with a transition to rain along/south of I-70.
As the first wave exits the region, precip will gradually come to an
end from west to east Sunday evening.  Models are in fairly good
agreement with the track and timing of this feature, although a
slight southward shift in the highest QPF axis has been noted.  GEM
continues to be the furthest south, focusing the heaviest precip
across southern Illinois into the Ohio River Valley.  Meanwhile,
both the GFS and ECMWF are further north across the heart of central
Illinois.  Will have to watch future model runs to see if further
southward shifts occur, but for right now, it appears the entire
KILX CWA will see a substantial snowfall.  Exact amounts are still
in question, but accumulations in excess of 4 inches are likely
north of the I-70 corridor.

A lull in the precip will occur late Sunday night through Monday as
high pressure temporarily takes control of the weather.  As the high
moves off to the east, a stronger wave will eject northeastward from
the prevailing Southwest CONUS trough early next week.  Timing
discrepancies still exist, with the ECMWF lagging about 12 hours
behind the GFS.  This could have major implications on precip type,
as the cold low-level airmass will likely be difficult to initially
dislodge, especially given the presence of a fresh snow-cover.  For
now will follow the more consistent GFS, which spreads precip into
the area Monday night.  Forecast soundings show a pronounced warm
layer developing aloft, with max temps in the layer reaching 5-10C
by 12z Tue.  With surface temps hovering in the upper 20s, freezing
rain and sleet will be a concern as the precip spreads from
southwest to northeast across the area Monday night.  As deepening
surface low pressure approaches from the southwest, strong low-level
WAA will boost temps above freezing Tuesday morning, bringing en end
to the threat for icy precip.  Rain will fall through the remainder
of the day Tuesday before coming to an end as a period of light snow
Tuesday night as colder air arrives behind the departing system.  If
the slower ECMWF pans out, rain may continue through Tuesday night
and Wednesday as well.


.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.





LONG TERM...Barnes
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