Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 102133

Area Forecast Discussion
National Weather Service Lincoln IL
333 PM CST Mon Dec 10 2018

.SHORT TERM...(This evening through Tuesday)
ISSUED AT 330 PM CST Mon Dec 10 2018

Initial concerns center on potential of fog redevelopment
tonight. Think that some fog will develop again overnight in our
eastern counties, where dense fog lingered the longest. There was
limited mixing this afternoon, and residual moisture is likely
still present in the low levels. Have added areas of fog to areas
east of I-55, but will have to watch visibility trends for the
possible need to expand fog farther west.

Otherwise, fog free areas should remain mostly clear overnight.
High pressure will depart to the southeast, setting up a return
flow into Illinois. That will mean increasing southwest winds in
our western counties starting our slow warming trend. As a result,
low temps look to be slightly warmer west of I-55, in the 23-25F
range, while eastern areas drop toward 20F.

After fog clears out Tuesday morning, sunshine will prevail the
rest of the day. Steady southwest winds will continue to bring
warmer air to the region, pushing high temps above normal for the
first time in a while. Highs will reach the low 40s north of I-74,
and upper 40s toward Jacksonville.


.LONG TERM...(Tuesday night through Monday)
ISSUED AT 330 PM CST Mon Dec 10 2018

The next storm system will approach from the west later Tuesday
night, as low pressure tracks across Iowa toward NW Illinois. As
the low approaches, a warm front will lift north through Illinois,
triggering warm air advection precipitation across our far
western counties by sunrise on Wednesday. GFS, NAM 12km, and
Canadian all keep precip north of our counties, closer to the
track of the surface low in N Illinois. The 3km NAM, 4km NAM nest
and the NMM east all show spotty rain or mixed precip late Tues
night W of I-55, and quickly push it east of our counties by Noon.
Low level thermal profiles in those models do look favorable for
a possible mixed precip event, but QPF amounts look very light.
Rain could be the primary precip type south of Fulton county,
with spotty northern areas seeing a mix of freezing rain and snow
late Tuesday night into Wed morning. A steady warming of surface
temperatures Wed morning will help any mixed precipitation
transition to all rain by afternoon, if any precipitation
continues in any of our counties that long.

The next wave of precipitation in our forecast area will be tied
to a southern stream storm system the the last half of the week.
An inverted trough will extend north into Illinois from a surface
low that is expected to track from the southern Oklahoma Wed night
to eastern Tennessee by Friday night. Early Thursday morning,
isentropic lift will help to trigger rain south of I-70, and rain
or freezing rain between I-70 and I-74. The precipitation should
transition to all rain after 9 am, with widespread rains likely
Thursday afternoon and Thursday night. Rain could mix with or
change to snow north of Rushville to Bloomington later Thursday
night into Friday morning. Daytime warming on Friday should
change precip back to all rain, as the main forcing for precip
shifts east of I-55 through Friday night. The slow movement of
the low will allow precipitation to linger into Saturday morning
east of I-57, with another round of rain-snow mix in northern
areas later Friday night and Saturday morning. Precip should end
by Saturday afternoon in our entire forecast area.

Since that precip event will be an inverted trough event, without
a cold frontal passage, temperatures on Sunday will remain
slightly above normal, with highs in the 40s across the board.
Slightly cooler temps are expected on Monday, as readings settle
out around normal for mid-December.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1205 PM CST Mon Dec 10 2018

Dense fog has dissipated around 4 of the 5 the TAF sites, with
CMI still seeing 1/4sm at the ob location. Satellite images show
some slow but steady dissipation starting to develop, so CMI
should see MVFR or VFR conditions develop by 20-21z. Otherwise,
no other major concerns for aviation the remainder of the 18z TAF
period, under mostly clear skies. A high pressure ridge
stretching over the area will gradually shift south this afternoon
and tonight, allowing light and variable winds to become light
southwest later this afternoon and tonight. Wind speeds look to
climb to 8-10kt and remain steady overnight, which will help keep
another round of dense fog at bay.




LONG TERM...Shimon
AVIATION...Shimon is the U.S. government's official web portal to all federal, state and local government web resources and services.