Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 022349

Area Forecast Discussion
549 PM CST Mon Mar 2 2015

.SHORT TERM...(Tonight)

A large area of high pressure will pull away from the area this
evening as the upper-level flow turns southwesterly ahead of a large
& somewhat phased northern/southern stream trof. Strong mid-level
WAA/isentropic ascent will spread across the region by late evening
and persist through the overnight hours in this southwest flow

The WAA/isentropic lift will provide top-down moistening of an
initially very dry airmass, which will result in rain developing
locally after midnight tonight within a strong elevated warm layer.
The rainfall is not necessarily expected to spread into the area
from the southwest, it will mostly develop overhead as the local
airmass saturates. However, WAA at the surface will take some time
to bring bring surface temperatures above freezing, so once the rain
develops, freezing rain should prevail for the balance of the night.
Rain falling through the initially dry airmass may provide enough
evaporational cooling for the precipitation to mix with or change to
sleet for the first few hours of the event.

A Winter Weather Advisory will be posted for the entire forecast
area starting at midnight tonight due to the sleet and freezing rain
potential. However, expect the bulk of the precipitation to be
freezing rain. Ice accumulation through the overnight hours is
expected to remain below a tenth of an inch, but this will be more
than sufficient to produce very slick conditions for the morning
commute on untreated surfaces.


.LONG TERM...(Tuesday through Monday)

Freezing rain should be ongoing across most of the forecast area to
start the day. However, increasing southerly winds are expected to
push surface temperatures above freezing by late morning, changing
the precipitation to rain. That being said, the frozen ground may
still cause slick spots for a few more hours even when the air
temperatures climb above freezing.

The cold front with the approaching system will sink through the
forecast area from northwest to southeast during the Tuesday
afternoon and evening hours. The passage of the front will result in
diminishing precipitation chances from the northwest, which will
finish as a snow or rain/snow mix on the back edge, especially as
you head into Tuesday night.

Confidence is growing the dry weather will not return to the entire
forecast area until at least late Wednesday night. The cold front
coming through Tuesday is progged to become parallel to the
upper-level flow and stall out south of the Ohio River. One more
wave is expected to ride northeast along the front and spill snow
back into the southeast portion of the forecast area Wednesday,
despite our location well north of the surface boundary. Current
indications suggest a few inches of accumulation are possible south
of I-70 Wednesday.

The front finally sinks further away from the area Wednesday night,
allowing a chilly surface high to build into the area through
Thursday night. Wednesday night & Thursday night lows should be in
the single digits, with highs Thursday mainly in the teens.

The chilly high will pull away by Friday. The rising upper-level
heights and low-level return flow on its back side will transport
milder conditions into the area for the end of the week and weekend.
While temperatures should still be a little below normal, we will be
much warmer than we have been lately. As far as precipitation is
concerned, the balance of the forecast period looks pretty quiet
beyond Wednesday.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)

VFR conditions will prevail at start of TAFs with a mid level deck
around 9-10kft this evening. Then around midnight, lower clouds
around 4kft will advect into the area and effect all TAF sites.
This will be in advance of the pcpn, expected to arrive after
midnight. Expecting the FZRAPL to begin at SPI first, around 08z,
and then spread east and north, reaching DEC/PIA/BMI around 09z
and CMI around 10z. Vis will be around 4sm, but cigs will be below
1kft, so IFR conditions expected at all sites once pcpn begins.
Once temps rise to above freezing, around 15-16z, think pcpn will
change over to all rain. Vis and Cigs will be about the same.
Winds will be southeast this evening but then gradually rotate to
southerly during the late morning hours and then south-southwest
in the afternoon. Could be a little gusty as well with around
22kts possible during the late morning to afternoon.


WINTER WEATHER ADVISORY from Midnight tonight to 10 AM CST
Tuesday FOR ILZ027>031-036>038-040>057-061>063-066>068-071>073.



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