Area Forecast Discussion
Issued by NWS Central Illinois

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218
FXUS63 KILX 221755
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1155 AM CST Wed Nov 22 2017

.UPDATE...
Issued at 1040 AM CST Wed Nov 22 2017

Minor updates made to the forecast late this morning, primarily
to bump highs a tad in northern parts of the forecast area and
adjust wind speeds a bit higher toward evening.

Surface high pressure centered in western MO will drift toward the
Ohio Valley by early this evening. This will keep central and SE
IL along the ridge axis through much of today, resulting in plenty
of sunshine, but with a cool NW flow. High temperatures today will
generally be in the upper 30s, with a few lower 40s south of a
Rushville to Lawrenceville line.

Satellite extrapolation of the mid level/warm advection clouds
from MN to the central Plains keeps the clouds out of the forecast
area through much of the afternoon. However, NW parts of the
region should see the clouds move in before sunset, spreading
toward the I-55 corridor around 00z.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 315 AM CST Wed Nov 22 2017

09Z/3 am surface analysis shows 1032 mb Canadian high pressure
over eastern Nebraska and ridging from west Texas through MN. NW
winds have diminished to 6-12 mph over central and southeast IL
and have ushered in colder and drier air. Temps currently range
from 19F at Galesburg, to 29F along highway 50 in southeast IL at
Flora, Lawrenceville and the Mount Carmel airport. Dewpoints
ranged from 16-23F from nw to se and temps will approach these
levels around sunup. Skies generally clear over CWA with cirrus
clouds spreading se into west central/sw IL. Stratus clouds were
ne of Lafayette, IN and dropping SSE and should stay east of IL
this morning.

00Z forecast models take high pressure ridge eastward from central
Texas ne into central IL by 18Z/noon and then into the Ohio and
mid MS river valley by early evening as it weakens to 1026 mb. A
fair amount of sunshine and lighter winds expected today over CWA
with high clouds increasing over the IL river valley later this
afternoon. Will be cold today with highs only 36-41F, coolest
from I-74 ne.

Temperatures will slip to 24-28F during this evening and then be
nearly steady overnight as SSW winds develop from nw to se as high
pressure ridge shifts into the TN river valley and mid Atlantic
states by dawn Thu. Also will see clouds increase from nw to se
during this evening and into southeast IL by early overnight and
help keep temps from getting as cold as this mornings readings.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 315 AM CST Wed Nov 22 2017

Upper level trof over the central Great Lakes and into the Oh/Tn
river valleys will pull away from IL on Thanksgiving day as a
frontal boundary washes out as it moves south into northern IL.
WSW winds along with partly to mostly sunny skies to modify temps
into the mid to upper 40s, which is close to normal levels for
Thanksgiving Day. Lows mostly in the lower 30s on Thu night with
fair skies and light ssw winds.

992 mb low pressure off the British Columbia coast will track
eastward across southern Canada and deepen to 980 mb as it moves
near James Bay Canada overnight Friday night and pulls a cold
front se across our CWA. Like the system yesterday afternoon,
could see isolate light rain showers ne of I-74 Fri evening, while
most areas appear to be dry as best forcing is further north and
moisture limited over our area. Breezy ssw winds on Friday to warm
temps into the mid to upper 50s, with areas from Springfield sw
near 60F, so similar weather to what we saw this past Monday.
Clouds to increase by later in the day Friday and into Friday
evening.

Cooler temperatures ahead for this weekend behind the cold front
with highs Sat ranging from 45-55F from nw to se and in the low to
mid 40s on Sunday. 1025 mb Canadian high pressure settles into the
mid MS river valley by 18Z/noon on Sunday and returns more
sunshine this weekend. A broad upper level ridge shifts east over
the Great Plains Sunday night and into IL by sunset Monday while
upper level trof digs over the Rockies. Breezy SSW winds develop
during Monday and modify temps into the upper 40s and lower 50s,
with mid 50s from Jacksonville sw. Highs back into the 50s across
area on Tuesday and continued dry weather with increasing clouds.
GFS and ECMWF models eject surface low pressure into the central
plains by 12Z/6 am Tue and eject it ne into the western Great
Lakes Tue night, with GFS model stronger and faster with low
pressure system. Brunt of moisture appears to set up north of IL
Tue night and also into southeast IL overnight Tue night into Wed
morning with passage of cold front. Highs next Wed close to
seasonal levels in the mid to upper 40s and GFS and ECMWF MOS
guidance similar.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1155 AM CST Wed Nov 22 2017

VFR conditions will prevail throughout the TAF period in central
and eastern Illinois.

A ridge of high pressure will move across the forecast area this
afternoon into early this evening, resulting in a clear sky and
light wind. During the evening, increasing mid level warm
advection ahead of weak shortwave trough will result in mid and
upper level clouds approaching from the NW. A lack of low level
moisture is expected to keep cloud bases at or above 8 kFT
overnight.

The shortwave is expected to pass the area by early Thursday
morning, leaving us with only a few clouds and an increasing
southwest wind.

&&

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

$$

UPDATE...Miller
SHORT TERM...07
LONG TERM...07
AVIATION...Miller



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