296 
FXUS63 KILX 150304
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
904 PM CST Fri Feb 14 2014

.DISCUSSION...
ISSUED 900 PM CST Fri Feb 14 2014

Snowfall has ended in all of our counties, and clearing skies on
steady NW winds has already dropped temps to 6F at Galesburg and
Champaign. The very cold air will continue to flow into central
and southeast IL overnight, as winds become light after midnight
from NW to SE. With the new snowfall and lighter winds,
radiational cooling will be very efficient. Temps will likely drop
below guidance by several degrees in these conditions. We trimmed
a few more degrees from lows across the northern half of the area.
Sub-zero lows are looking likely in more locations north of
Lincoln. 

Even with light winds, wind chills later tonight will drop to -10F
at times. 

The next wave of snow is still on track for Saturday mid-afternoon
through the evening. The southern extent of 1" snowfall will be
roughly along the I-74 corridor, with a dusting to a half inch
south of there. Northern IL is projected to get around 2-3".

Updates for tonight were mainly temps and dewpoints. Otherwise,
the remainder of the forecast is on track.

Shimon
&&

.AVIATION...
ISSUED 600 PM CST Fri Feb 14 2014

Snowfall will push southeast of CMI and DEC by 01z or so, with
little to no additional snow accumulation at the TAF sites. DEC
ceilings at 1k FT should clear out quickly following the end of
snow. The back edge of the low clouds has already reached PIA and
should continue its progression this evening across the other TAF
sites. VFR conditions should continue until Saturday afternoon
when the next clipper brings more snow to the northern half of
Illinois. PIA and BMI will have the best chances of MVFR ceilings
and vis during light snow. CMI will be close to the MVFR
conditions, while SPI and DEC remain VFR as the clipper passes
over northern IL.

Northwest winds will be gusty into early evening, then should
diminish for the remainder of the night. Wind direction should
change to southwest Sat morning as the clipper approaches, then
become south toward mid-afternoon as the snow begins to fall.

Shimon
&&

.PREV DISCUSSION...
ISSUED 310 PM CST Fri Feb 14 2014

Models in fairly good agreement overall on the sfc and in the
upper levels through Sun night, but then differ on Mon with upper
level temps and temp profile. Main concerns this package include
the ending of snow late this afternoon and early this evening,
followed by another clipper system moving across northern IL
tomorrow afternoon through tomorrow evening, and then another
system coming up into the area late Sun night and Monday. Models
look good with the ending of the current system and with the next
clipper, but with temp profile being different with Sun night/Mon
system, confidence decreases with p-type...though confidence is
high that pcpn will occur. So, with first two systems, blend of
the models looks ok. However, with the last system will increase
pops, but just keep p-type with what was already in forecast. More
on this later.

SHORT TERM...Tonight through Monday

Vigorous clipper system moving through the area is pushing east
and winding down. Light snow is still occurring along and just
west of I-55 while the slightly heavier snow is falling to the
east of I-55 but north of I-70. A dry slot has also moved into
most of southern IL and parts of central IL, so pcpn has become
mixed with FZRA/FZDZ. However, this will switch back to snow as
the deformation area moves over that part of the cwa late this
afternoon. Tonight, then should be dry. 

The next clipper system will move over the area tomorrow afternoon
and tomorrow evening. The low pressure area with this system will
move right over central IL which will put the heaviest snowfall
north of the cwa over northern IL. However, snow is still possible
over central IL, just with highest chances in the north, north of
I-74. Have raised pops in the north to account for that, with most
snow occurring tomorrow afternoon and tomorrow evening. 

Then there will be a dry period Sunday before the next system.
This next system will be different as the upper level pattern will
be southwest flow and bring some warmer air into the region for
all of next week. Concern with this system is with how much warm
air will get into the lower layers of the atmosphere, how far it
will get west, and how much moisture will get advected into the
area ahead of the system. The NAM is colder on the sfc, has more
moisture, and is cooler in the lower layers of the atmosphere,
while the GFS is warmer on the sfc and the lower layers...but
with less moisture to work with. It's agreed that the lower layers
will start out relatively dry, but should moisten up after a
couple of hours of pcpn. Issue is that with the NAM, pcpn could be
all snow in areas northwest of I-55 and then fzra/ip changing to
all rain east of I-55. The GFS shows p-type as maybe fzra/ip
changing to all rain over all the area, but column doesn't really
become saturated enough for much pcpn. Because the models differ
this much on temp profile, though agree that some pcpn will occur,
have decided to keep p-type forecast for late Sun night through
Monday the same as what it has been since yesterday. 

Temps overall will remain below normal across the area, but then
are supposed to warm on Monday. If NAM is right, temps will remain
cold on Mon. GFS is forecasting warmer. Went with warmer for Mon.

LONG TERM...Monday night through Friday

The upper level pattern will remain out of the southwest through
next week, which should help to keep warmer air in the area. Dry
weather is forecast to remain dry through Wed, before the next
system moves into the area. This next system will come from the
southwest and should be a relatively strong system with quite a
bit of rain. This system could have some thunder with it, but it
is still 6 days away and models still have not come to any
agreement on what this system will look like. 

Temps will be warmer, above normal over the whole area through
next week. Though temps will be warm enough to melt a lot of the
snow, temps Mon night and Tue night will still be below freezing. 

Auten

&&

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

$$