Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 201203
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
603 AM CST Tue Feb 20 2018

.SHORT TERM...(Today and tonight)
ISSUED AT 345 AM CST Tue Feb 20 2018

Will issue a Flood Watch from now through tonight along and north
of Sangamon, Macon, Moultrie, Douglas and Edgar counties
(excluding Knox and Stark counties). This area received between
1-2 inches of rain during the past 24 hours, and expect another
1.5 to 2.5 inches of rain through tonight.

09Z/3 am surface map shows a strong frontal boundary over far nw
IL near Galesburg and Quincy, and extending to 1008 mb low
pressure over central MO. Front then extends sw across northern OK
to 999 mb low over central NM. Numerous showers and some
thunderstorms were ahead of this front over portions of central
IL early this morning, mainly nw of a Taylorville to Rantoul line
and lifting ne at 40-45 mph. Unseasonably mild temps were holding
in mostly in the lower 60s over CWA, except colder 40F at
Galesburg while Flora at 65F and nearby Salem at 67F. Very moist
dewpoints in the upper 50s and lower 60s. ILX 00Z sounding had
precipitable water value of 1.33 inches and at record levels for
February.

00Z forecast models have trended a bit quicker with cold front
pushing east over the IL river valley during this afternoon as
surface low over central MO lifts ne of area. Cold front then
pushes thru rest of central IL during this evening, and thru
southeast IL early overnight, reaching the Ohio river by 12Z/6 am
Wed. A couple waves of energy eject ne along this front and
interacting with very moist air mass to continue periods of
showers and thunderstorms over the flood watch area today and
evening and shifting into southeast IL by late evening and
overnight as strong cold front moves thru. An additional 1.5-2.5
inches of rain expected along and se of the IL river through
tonight, with 1-1.5 inches nw of the IL river.

In addition, the rain will change to freezing rain and sleet nw
of IL river during late evening and getting as far east as a
Rantoul to Taylorville line by 6 am Wed. Up to a tenth inch of ice
still expected west of this area overnight and may eventually
need a winter weather advisory. The mixed pcpn to change to light
snow over the IL river valley during overnight before ending late,
and just a dusting of snow possible. Highs today range from the
lower 50s by Galesburg to 70-75F across southeast IL and this will
likely challenge record highs in southeast IL today. Lows tonight
range from lower 20s by Galesburg to 35-40F southeast of I-70.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 345 AM CST Tue Feb 20 2018

Rain will likely continue in southeast IL on Wed with cold front
pushing se over KY/TN while areas from I-72 north to be dry, with
northern CWA seeing partly sunny skies. Northern fringe of
precipitation south of I-72 and north of I-70 could be a light mix
of precipitation on Wed morning. Highs Wed range from mid 30s
northern CWA to lower 40s over the Wabash river valley. Surface
low pressure lifting ne along frontal boundary over TN river
valley Wed night and Thu to lift precipitation chances back north
into central IL by overnight Wed night into Thu morning, though
pops will be higher (likely) in southeast IL Wed night with slight
pops northern CWA. Mainly light snow chances over northern CWA,
rain along and southeast of I-70 and mixed precipitation central
part of CWA including light glaze possible overnight Wed night
between I-72 and I-70. Highs Thu range from lower 40s northern CWA
to around 50F in southeast IL. High pressure over the Canadian
Rockies strengthens to 1044 mb as it moves east across the Great
Lakes on Wed night and Thu and this to keep are area cool, but
still a bit above normals temps for late Feb.

An active weather pattern returns to our area from Thu night thru
Sat night as a couple more waves lift ne along a frontal boundary
to our se, in response to a deepening upper level trof over the
Rockies. Could see mixed pcpn over far northern CWA overnight Thu
night into Fri night, otherwise mainly should be warm enough to
support rain over our CWA. A stronger surface low ejecting ne
toward our area on Saturday could bring chances of thunderstorms
to southeast CWA. Rainfall amounts of 1-3 inches look possible
from Lincoln southeast from Thu night thru Sat night with the
higher amounts in southeast IL. More river flooding is likely to
develop during that time frame especially in southeast IL and
possibly further northward if models keep trending further north
with low pressure system on Saturday. Highs Fri range from mid 40s
by Galesburg to mid 50s in southeast IL. Highs Sat range from
upper 40s by Galesburg to upper 50s and lower 60s in southeast IL
and possibly warmer if low pressure tracks further north.

Generally dry weather expected Sunday through Tuesday of next
week as high pressure settles into the mid/lower MS river valley
by sunset Sunday and off the mid Atlantic coast by sunset on
Monday. Highs Sunday in the mid 40s to lower 50s, then upper 40s
to mid 50s Monday and back into the 40s next Tuesday. A weak
surface low pressure passing north of IL on Monday could bring
slight chances of showers over IL river valley late Monday
afternoon into Monday evening. This brings a weak cold front thru
area late Monday, hence the cooler temps next Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 600 AM CST Tue Feb 20 2018

Several periods of showers and a few thunderstorms will occur
today across central IL, with widespread rain this evening. The
rain will change to freezing rain or mixed pcpn overnight from nw
to se, starting at PIA around 06Z and CMI late tonight. Much
colder air arriving as cold front over far nw IL pushes se to PIA
from 20-21Z, I-55 by 23Z, DEC from 00-01Z and to CMI by 02Z. Aside
from the convection today, another impact will be the strong
gusty SSW winds with gusts of 25-32 kts east of the IL river. LLWS
will occur outside of thunderstorms til mid morning with 2k ft SW
winds (210 direction) of 50-55 kts. VFR ceilings early this
morning will lower to IFR to MVFR during mid/late morning and
remain low through tonight. The exception will be PIA which will
see the pcpn end after 09Z and ceilings elevate to MVFR to VFR.
Visibilities that have lowered to IFR to MVFR at times with
convection early this morning will tend to stay in the 2-4 mile
range later this morning and into tonight. Winds will shift to the
WNW to NW with the frontal passage from mid afternoon into early
evening with wind gusts of 20-25 kts lingering tonight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through late tonight for ILZ029>031-036>038-040>051-
053>055-057.

&&

$$

SHORT TERM...07
LONG TERM...07
AVIATION...07


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