Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 010915
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
315 AM CST Sun Mar 1 2015

.SHORT TERM...(Today)
ISSUED AT 313 AM CST SUN MAR 1 2015

Snow continues to fall over all but far northwest sections of the
forecast area early this morning. However, latest radar trends
indicates a bit of push to the north with the snow with precip
starting back up into Macomb this past hour. Short term models
indicate another band of snow to shift further north into the
advisory area by mid-morning. Was on the fence with the area from
Peoria and northwest whether to cancel the advisory early this
morning but with models suggesting this second wave moving into the
area, will hold off canceling the northwest section of the advisory
for now. If trends suggest the snow will shift further south of the
Peoria area, similar to this first wave, will go ahead and cancel
along the Illinois River valley later this morning.

Further south, where we thought we would see a few 6 inch amounts,
we have had reports of 5-6 inches already roughly from along the I70
corridor north towards Taylorville to just south of Paris. For
consistency sake with our neighboring forecast offices, went ahead
and upgraded to a winter storm warning for a storm total of 5 to 7
inches with locally higher amounts from just east of Springfield to
the Indiana state border. Not your classic winter storm, as the snow
has been falling with very light winds, and we really don`t see the
winds coming up much today at all, so its basically an upgrade due
to more widespread 6 inch snow amounts.

Forecast soundings along and south of I-70 suggest a mix with sleet
and freezing rain for a time this morning before we see surface temps
warm into the low to mid 30s, melting any ice accumulation that may
occur in that area this morning.


&&

.LONG TERM...(Tonight through Saturday)
ISSUED AT 313 AM CST SUN MAR 1 2015

Forecast focus quickly shifts to the next late-winter storm system.
The key will be with significant WAA in the mid levels, with 850 mb
temperatures quickly rising into the +4 to +6C range between
midnight and sunrise Tuesday. Any snow/sleet mixture will quickly
transition to liquid precip, with forecast soundings showing the
above-freezing layer as much as 7000-8000 feet thick. Currently
thinking that up to a tenth inch of freezing rain is likely through
early Tuesday morning before the precip transitions to regular rain
everywhere. The big question is how fast the surface temps respond
with a significant snow pack. Hourly temperature projections showing
areas west of Springfield climbing above freezing shortly before
sunrise, with the ECMWF MOS as high as 37-38F by 6 am, the GFS MOS
in the mid 30s and the NAM MOS just shy of freezing. Trended the
hourly grids in more of a GFS/NAM blend initially, with the overall
highs Tuesday close to the GFS MOS.

In terms of precip timing, a lot of dry air below 700 mb will need
to be overcome first, which will take much of the evening. Have thus
kept most of the CWA dry during the evening, with slight chance
PoP`s in the far southwest. The NAM is the quickest in pulling out
the precipitation Tuesday afternoon ahead of the main cold front,
but went a little slower on the timing and lingered some likely
PoP`s in the far southeast into early evening. However, any
lingering precip will quickly exit as strong CAA takes place with an
incoming high. The trailing end of the cold front will briefly get
hung up in the parallel upper flow south of the Ohio Valley Tuesday
night, and have lingered some low chance PoP`s into early Wednesday
mainly south of I-70.

Another slug of cold air will swing across the northern tier of
states midweek, with 850 mb temperatures as low as -15 to -18C over
our area Wednesday night. Another period of temperatures 20-25
degrees below normal will result. However, the split upper flow will
finally start to merge together over the Midwest late week, helping
to bottle up the colder air north of the Canadian border. This will
allow temperatures to get much closer to normal for the end of the
week.


&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1140 PM CST SAT FEB 28 2015

MVFR conditions will continue at BMI and PIA, but some IFR
conditions will be possible, so will have a TEMPO group for those
two sites. Then MVFR conditions will continue through the morning
hours. IFR and LIFR conditions will continue at SPI/DEC/CMI
overnight and into the morning hours. Models continue to indicate
another round of moderate snow overnight, so will keep TEMPO group
for these three sites for next 2 to 3 hrs. Could be another round
of moderate snow toward morning, but timing and location will
remain uncertain given the short range model differences; but will
keep IFR conditions through the morning hours. Then most of the
snow should be east of the area and believe conditions will become
MVFR. Based on model trends, believe snow will end during the
afternoon hours, though MVFR cigs will still be around. Toward
midnight, lower clouds should scatter out and leave a high cirrus
deck. Winds will be light southeast to south overnight, then
become light and variable as the system moves toward the east.
Then by afternoon and into the evening, winds will become westerly
with speeds less than 10kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 6 PM CST this evening FOR ILZ029-
031-036>038-040>051-053-071>073.

WINTER STORM WARNING until 6 PM CST this evening FOR ILZ052-
054>057-061>063-066>068.

&&

$$

SHORT TERM...Smith
LONG TERM...Geelhart
AVIATION...Auten






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