Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 271719
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1119 AM CST Sun Nov 27 2016

.UPDATE...
Issued at 925 AM CST Sun Nov 27 2016

Forecast was updated to issue a Dense Fog Advisory for the
remainder of the morning, except south of I-70 and in the far
southwest CWA around Rushville and Jacksonville. Large area of
dense fog continues to advect northeast and has covered a large
part of the area. Based on upstream obs, the worst of the fog
lasts for about 3 hours or so, and improvements are starting to
take place in the Galesburg-Taylorville corridor. Most of the CWA
should be back up to a few miles by midday, although the fog may
linger a bit longer over the far northeast corner.

Given that clouds have already overspread the area, high
temperatures were also lowered about 2-3 degrees.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 334 AM CST Sun Nov 27 2016

A storm system, that is progged to become quite strong, is beginning
to develop over the Plains. This system will begin to impact central
and southeast Illinois later today, with its impacts being felt for
the next couple of days.

Southerly low-level winds have developed across the region behind a
departing ridge of high pressure, and ahead of the developing
system. Low-level moisture return ahead of the system has developed
an area of stratus/fog from Arkansas into extreme southwest
Illinois. Forecast guidance is all over the place with respect to
how this stratus will evolve today. Some of the higher resolution
guidance has the stratus quickly covering the entire forecast area
with clouds this morning, while much of the other guidance has
clouds only increasing gradually today as the main storm system
approaches and clouds thicken from the top down. Given the strong
low-inversion that is currently in place, and will only be
strengthened by strong WAA aloft, have leaned sky forecast toward
the more pessimistic high-res guidance. However, have slowed the
onset of the clouds based on satellite loops/trends. Have nudged the
forecast highs a little cooler today, mainly a few degrees either
side of 50, with the earlier expected arrival of the thicker cloud
cover.

Most of the day should end up dry across the forecast area, but it
will quickly trend rainy by tonight. A vigorous short wave over the
southwest U.S. will eject northeast into the Midwest by tonight. A
period of enhanced isentropic ascent will spread from west to east
across the forecast area tonight with the passage of this wave. This
forcing will result in widespread showers across the region. A mild
night is on tap given the strengthening southerly winds with the
approaching storm system. Expect overnight lows in the 40s to only
be around 5 degrees below the daytime highs.

.LONG TERM...(Monday through Saturday)
ISSUED AT 334 AM CST Sun Nov 27 2016

A vigorous upper level trof over the Pacific States, will move east
into the Great Plains Monday with a cutoff low over the eastern
Dakotas border by sunset Monday. Surface low pressure ejects ne from
CO into this area too, and IL to have strong warm air advection and
moisture advection ahead of this storm system through Monday. Still
appears to be a lull in the rain showers over nw CWA Monday morning
while showers likely continue over southeast IL. Along with the low
clouds and scattered showers, may see some fog and drizzle by Monday
morning over areas from I-74 northeast. But will also see fairly
strong southerly winds on Monday with gusts of 25-35 mph.
Will see showers expand during Monday afternoon/evening from
southeast IL back up into central and east central IL with
thunderstorms possible Monday afternoon and Monday evening. Showers
will quickly end from west to east behind a prefrontal trof
overnight Monday night. Rainfall amounts by overnight Monday night
will range from 0.75 inches by Galesburg, to about 1 inch along I-55
and 1.50 inches over southeast IL from I-70 southeast. These heavier
rainfall amounts aided by 45-60 kt 850 mb ssw jet and precipitable
water values of 0.75-1.25 inches especially east of the IL river.
Highs Monday in the low to mid 50s. Lows Monday night in the low to
mid 40s, mildest in eastern IL. SPC keeps marginal risk of severe
storms Monday afternoon/evening south of IL over far southern MO
into AR with a slight risk of severe storms over the southern MS
river valley, with an enhanced risk of severe storms over nw half
of LA.

Tuesday looks like the mildest day of the week with highs in the
upper 50s/lower 60s with return of mostly sunny skies and breezy ssw
winds. Large low pressure system moves into west central MN by
sunset Tue while a weakening cold front moves east over IL Tue night
and appears to pass through dry.

Latest forecast model ensembles continue to show a large upper level
low slowly weakening from central MN Wed and into the northern
Great Lakes Wed night. Meanwhile another surface wave develops
and lifts northeast along a frontal boundary southeast of the Ohio
river near mid TN on Wed. Most of the forecast models continue to
keep qpf southeast of our CWA on Wed with just the ECMWF model
showing light qpf in far southeast IL at 12Z/Wed. Will continue a
dry forecast Wed as low clouds increase especially Wed afternoon,
along with cooler high temperatures Wed in the mid to upper 40s
over central IL and lower 50s in southeast IL.

Large low pressure system moves into the eastern Canadian/St
Lawrence valley late this week while another cutoff upper level low
emerges over the desert sw by Friday. IL is in between these two
features and in a dry confluent upper level flow. Some light snow
showers will impact the great lakes and latest forecast models
keeps these north of CWA, though have increased cloud cover during
2nd half of week especially north of I-70. Temps cool closer to
normal for early December with highs of 39-45F from Thu thru
Sunday and lows in the upper 20s/lower 30s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1117 AM CST Sun Nov 27 2016

IFR/LIFR conditions remain widespread at midday, although the
dense fog continues to lift. Ceilings should increase through the
afternoon and a short period of VFR conditions is likely by late
afternoon. Focus then shifts toward the storm system approaching
from the west, which will bring lower ceilings/visibilities again
in periods of rain. Increasing gradient will result in southerly
wind gusts of 25-30 knots developing this evening, and persisting
through the rest of the TAF period. IFR conditions will prevail
again by late in the period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST today for ILZ028>031-037-038-
042>046-053-055.

&&

$$

UPDATE...Geelhart
SHORT TERM...Bak
LONG TERM...07
AVIATION...Geelhart



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