Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 181549

Area Forecast Discussion
National Weather Service Lincoln IL
949 AM CST Sun Feb 18 2018

Issued at 949 AM CST Sun Feb 18 2018

Cirrus has been thickening across the area over the last few
hours, but the overall bands are lifting northeast, and some
thinner spots will develop again toward midday. Far northern CWA
got off to a colder start due to the residual deeper snow cover,
so some 20s still linger north of I-74 on the 9 am observations.
However, even these areas should still reach well into the 40s.
Some minor updates were sent for the sky and temperature trends,
and also to remove the fog mention from earlier this morning.
However, the overall forecast is on track.


.SHORT TERM...(Today and tonight)
ISSUED AT 355 AM CST Sun Feb 18 2018

Updated the forecast a few hours ago to increase coverage of
freezing fog (locally dense) through mid morning especially north
of Peoria and also south of I-72. Also cooled low temperatures
over snow covered northern CWA early this morning with far
northern CWA near 10F again. The 3 am temps ranged from 12F at
Galesburg to 29F at Lawrenceville and the Mount Carmel airport.
1028 mb high pressure over the lower Ohio river valley in
southeast IL, southern IN and western KY was ridging northward
into central IL and providing fair skies and light to calm winds.
Patchy freezing fog noted north of Peoria and south of I-72 with
pockets of dense freezing fog observed at times at Galesburg,
Olney and Taylorville.

Latest HRRR model has been trending more widespread with freezing
fog and locally dense into a larger part of central IL, and less
coverage over east central IL. Will continue to monitor for
possible dense fog advisory. Models diminish the fog during
mid/late morning as south winds pick up to breezy levels as high
pressure over lower Ohio river valley quickly moves over WV at
1030 mb high by 18Z/noon today and 1032 mb high off the mid
Atlantic coast by sunset. Ample sunshine through increasing thin
cirrus clouds and breezy south winds with gusts 20-30 mph by
afternoon. Milder highs in the upper 40s and lower 50s today,
coolest over northern/ne CWA. Clouds increase during this evening
with isolated rain showers western CWA late evening, then
widespread showers and isolated thunderstorms moving in during
overnight as 1000 mb low pressure emerges over central KS by dawn
Mon with a frontal boundary just nw of IL. South breezes to keep
temps from falling too much tonight, with lows in the upper 30s
to mid 40s, coolest from I-74 ne.

.LONG TERM...(Monday through Saturday)
ISSUED AT 355 AM CST Sun Feb 18 2018

Will update the ESF product to continue to highlight the heavy
rain and increasing flooding threat Mon thru Wed morning. A flash
flood or flood watch may eventually be needed for a good chunk of
our area. Widespread 1.5-3 inches of rain expected over CWA
during this time frame with locally 3-4 inches east of the IL
river with heaviest rain expected Tue afternoon into Tue night.
Potential exists for another round of moderate to heavy rainfall
Friday thru Saturday, especially se of i-55.

Low pressure to eject ne from central KS into northern IL by
sunset Monday, and bring more rain showers and isolated
thunderstorms, though becoming more scattered in coverage Mon
afternoon. Rainfall amounts from overnight Sunday night through
sunset Monday average a half to three quarter inches north of i-70
and lighter amounts from I-70 south. Unseasonably warm highs
Monday in the 60s with areas from Springfield and Lawrenceville sw
near 70F with stronger south winds gusting 25-35 mph.

A deepening upper level trof over the Rockies early this week
while a 500 mb high of 595 dm strengthens off the southeast
Atlantic coast. This to eject another surface low pressure into
central/southern KS by sunrise Tue and eject ne into nw/northern
IL by early Tue evening. A subtropical jet and plume of moisture
coming from baja into the ohio river valley has precipitable water
values going up to 1.3-1.6 inches which is near the climatological
max for late winter. Showers with some thunderstorms and moderate
to heavy rains sets up over area Tue with heaviest rains over IL
river valley Tue and shifting into southeast IL during Tue night
as cold front pushes se across CWA and toward the ohio river by
dawn Wed. Highs Tue range from upper 50s/lower 60s nw of the IL
river to mid/upper 60s over heart of CWA and lower 70s over
southeast IL.

As much colder air arrives behind the strong cold front during Tue
night, rain will change to freezing rain and sleet nw of IL river
late Tue evening and east to along I-55 during overnight Tue night
while IL river valley has mixed pcpn eventually change to snow
before ending. Could be some ice accumulations up to a tenth inch
from I-55 west overnight Tue night and will need to watch this
possible winter wx advisory. Continued chances of rain showers
from I-72 south on Wed with likely pops se of I-70 Wed morning as
cold front pushes into the TN river valley. Highs Wed range from
low to mid 30s over the IL river valley, to the low to mid 40s in
southeast IL.

Models differ with how far north qpf gets Wed night with ECMWF
further north with qpf/mixed pcpn into central IL while GFS is
drier and GEM is in between. Stayed close to consensus with
chance pops over CWA, highest in southeast IL. A period of dry wx
expected Thu and Thu night as a strong high pressure over 1040 mb
pushes east over the GReat lakes region. Models then show another
wx system ejecting ne across the frontal boundary to our southeast
late this week, spreading qpf ne over area, though some timing
issues (ECMWF is faster than GFS model). Went with consensus for
pops Friday through Sat and threat is there again for moderate to
heavy rains se of I-55.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 559 AM CST Sun Feb 18 2018

Patchy freezing fog will occur into mid morning across central IL
and will have MVFR visibilities, but may drop to IFR at times
thru 14Z.

1029 mb high pressure over the Ohio river valley, will quickly
move east off the mid Atlantic coast by sunset. Meanwhile 994 mb
low pressure over central WY will weaken to 1003 mb as it ejects
eastward to southern MN by sunset, then lift ne of the great lakes
overnight as another surface low emerges out of the central
Rockies into eastern KS, with a cold front approaching far nw IL
by Mon morning. Once fog dissipates during mid morning, expect
fair conditions through mid evening with some cirrus clouds. SE
winds 4-8 kts early this morning, will become SSE and increase to
12-18 kts by late morning with gusts of 20-25 kts into mid
evening. Continued LLWS in TAFS tonight, starting between 00-01Z
with 2k ft SSW winds 45-55 kts and turning SW by overnight. MVFR
ceilings to spread in late evening and early overnight along as
rain showers become more widespread overnight. This will reduce
vsbys down to 2-4 miles between 08-10Z overnight and ceilings by
late tonight to drop to 1-2k ft.




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