Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260521

Area Forecast Discussion
1121 PM CST Sun Jan 25 2015


Have tweaked temps/winds/sky for tonight and flurries for
tomorrow.  For most part current package is on track.

Precip coming to an end as surface system over central KY
continues to pull away from Illinois. Still could be a snow or
rain shower over the next several hours east of I-57, but for the
most part any significant precip has ended. Weak ridge is building
into Illinois from the northeast scattering out the cloudcover
over western Illinois this evening. This partial clearing will
likely spread only slowly south and east and then be overtaken by
clouds associated with next quick system for Monday. Moisture
remains quite limited with this second cliper and for now will
keep only flurry wording. Forecast soundings from 18z NAM and GFS
suggest that there also could be some freezing drizzle/sprinkles as the
atmospheric column is expected to be quite dry above -8C and it
may be difficult to form ice crystals. Will have to look closer at
this potential once the full 00z model suite has been analyzed.


.SHORT TERM...(Tonight)

Area of low pressure which has brought our precipitation was
centered near Carbondale early this afternoon. Rain/snow transition
line has been struggling to move any further south, and in fact
areas from Macomb to Bloomington which had switched over were
starting to mix with rain again. Temperatures have been above
freezing over most of the snow area and accumulations have been
minor and slushy, but some more substantial 1-2 inch totals have
occurred north of Galesburg where temperatures are now below
freezing. The deformation band of snow has been weakening some the
last few hours, and there is a substantial hole in the precip over
the central 2/3 of the forecast area.

The RAP model shows a further weakening of the the deformation band
over the next few hours, and actually has the entire CWA dry by 6
pm. Have some concerns that may be too quick across the southeast,
as the upper wave continues to dig across southeast Missouri, and
have lingered some likely PoP`s down there slightly beyond that time
frame, but reduced PoP`s to below 20% by 9 pm.

Overnight, models are trying to show some substantial clearing over
most of the forecast area beginning late evening. While there is
some breakup of the clouds upstream across Wisconsin, it is not
completely clear up there and the north/northeast flow is not
especially conducive to rapid clearing. Have gone with partly cloudy
skies overnight across the northwest half of the forecast area, but
clouds will already been increasing ahead of the next clipper which
will be dropping southeast into northern Minnesota overnight.


.LONG TERM...(Monday through Sunday)

A couple of cooler days are on tap across central and southeast
Illinois in the wake of today`s clipper. There is still a chance we
may see a few snow flakes or sprinkles on Monday as a shearing
upper-level wave, currently diving across the Canadian Prairies,
passes through the Great Lakes region and parts of the Midwest.
However, looking at forecast soundings, there will be a very small
window of opportunity where ice crystals will be present, suggesting
the chance of measurable precipitation is quite low. So, for now,
will only carry a chance of flurries Monday across the northern
portion of the forecast area as the very sheared wave passes to our
north. It is definitely possible that we will see nothing at all, or
perhaps some light drizzle or freezing drizzle (depending on surface
temperatures) due to the paucity of ice crystals.

Temperatures will warm heading into midweek as the persistent
amplified upper-level flow briefly turns more zonal, and a system
approaches from the Pacific coast. This system will mainly pose a
rain threat as it moves through Wednesday night into Thursday. A
brief period of snow is not out of the question later Thursday as
cold air filters in behind the system, but forecast soundings
currently suggest the moisture depth will be too shallow to support
precipitation (no ice crystals) by the time the thermal profile
would support snow.

Another cool down is expected in the wake of the midweek system, but
temperatures should still be near normal for late January. The
eastern North American mean trof that has been in place will try to
reestablish itself by the weekend. A clipper type wave in the
returning northwest upper-level flow may bring a chance of snow to
the area over the weekend. However, the current storm track keeps
the best snow chances to our north, and have only included a slight
chance of snow at this time.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)

Clearing area associated with weak ridge building into Illinois
has slowed its southeast progress near I-55. High clouds from
next cliper system already beginning to cross Mississippi River
and will likely overspread sites experiencing clearing over next
few hours.

NAM from 00z suggests that partial clearing will resume its
progress slowly southeast after 06z, but that will be followed by
MVFR deck from next system during the day Monday. Model suite from
00z a bit further south with low measurable pops and impacts all
TAF sites at one time or another. Forecast soundings suggest that
there may still be some potential for FZDZ given the dry air in
crystal formation layer. Will include about a 4-hr tempo group for
I-74 terminals for -SN at this time but later shifts will need to
monitor closely.

Winds are diminishing quickly as the gradient weakens as the
surface ridge moves in. Winds should shift around to the south
Monday and then back to the northwest after the cold front passage
associated with the cliper which will likely be just beyond the
valid time of this set of terminals.




SHORT TERM...Geelhart
AVIATION...Barker is the U.S. government's official web portal to all federal, state and local government web resources and services.