Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 141809
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1209 PM CST Wed Feb 14 2018

.UPDATE...
Issued at 1111 AM CST Wed Feb 14 2018

The boundary layer air mass is becoming more saturated with time
this morning, as a stationary frontal boundary begins to advance
across central Illinois. As a result, low clouds, fog, and
drizzle look to dominate the rest of today and at least this
evening. Areas of dense fog have developed around Bloomington to
Champaign and Rantoul. High res guidance shows a general trend of
the fog shifting north of I-74 by late afternoon, then gradually
building back south and east tonight.

The showers in our southeastern counties should continue to
diminish and exit to the east-southeast by early afternoon.

Southerly winds will help high temps today will climb above
yesterday. However, we still trimmed a couple degrees off the high
temps due to nearly no sunshine.

Other updates this morning were to add fog and drizzle to the
northern and eastern areas the rest of today and much of tonight.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 338 AM CST Wed Feb 14 2018

Southwesterly upper-level flow has developed across the
Plains/Midwest...which will lead to a period of warm and wet
weather over the next couple of days. A weak short-wave trough
embedded within the flow is currently tracking through the Ozarks
and is triggering scattered showers across southern Illinois.
09z/3am radar imagery shows the showers approaching the far
southern KILX CWA...with trends suggesting precip spreading as far
north as I-70 over the next 2-3 hours. NAM forecast soundings show
MUCAPE values peaking at 200-300J/kg at KLWV between 15z and 18z,
so have added isolated thunder to the far southern counties this
morning as well. NAM/HRRR suggest a few showers could potentially
spread as far north as a Danville to Shelbyville line...with dry
weather expected further north and west. The showers will quickly
shift further eastward into the Ohio River Valley by early
afternoon, with dry weather returning across the board at that
time. Elsewhere around central Illinois, increasing cloud cover
will be noted with afternoon high temperatures ranging from the
lower 40s far north around Galesburg and Lacon...to the middle 50s
south of I-70. With warm/moist air flowing over the significant
snow cover across the north, fog will likely develop later today
into tonight...particularly along/north of a Rushville to
Bloomington line.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 338 AM CST Wed Feb 14 2018

Low pressure will track from the Plains across north-central
Illinois on Thursday...bringing widespread showers to the area.
MUCAPE values continue to be negligible, so have not mentioned
thunder in the forecast at this time. With the low tracking across
the area, there will be a significant north-south temperature
gradient...with highs ranging from the middle to upper 40s far
north...to the middle 60s south of I-70. Once the low tracks into
Ohio, it will drag a cold front southward through Illinois
Thursday night. Showers will come to an end from north to south
accordingly, with a brief period of snow possible on the northern
periphery of the precip Thursday night into Friday
morning...mainly along/south of a Danville to Shelbyville line. No
accumulation is expected.

After a brief cool-down on Friday with highs dropping back into
the 30s, another warming trend will get underway over the weekend
into early next week. 00z Feb 14 GFS has now sped up the next
approaching wave by 12-24 hours...bringing it across the Midwest
on Saturday rather than Sunday as it had done with its prior runs.
As a result, have introduced precip chances on Saturday...with
snow or a rain/snow mix in the morning changing to all rain by
afternoon as highs climb into the upper 30s and lower 40s. After a
mild and dry Sunday, a warmer/wetter pattern will set up early
next week. Rain chances return to the picture for both Monday and
Tuesday...with highs climbing back into the 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1205 PM CST Wed Feb 14 2018

Locally dense fog will linger near BMI and CMI this afternoon, as
the boundary layer remains near saturation. A stationary boundary
extending from the west into west-central Illinois seems to be
becoming a focus for our fog and low clouds. Weak lift in a broad
area seems to be just enough to expand our low clouds and fog
formation, along with some areas of drizzle. HRRR and RAP updates
show visibility at or below 1/4sm mainly across our northern
counties, and drifting north later this afternoon. However, they
also indicate the dense fog potential and VLIFR conditions should
expand back southward tonight, including areas east of I-55 down
to I-70. Have not included widespread VLIFR conditions with the
18z TAFs, but may need to add that as more data analysis is
conducted.

Most of the terminal sites should remain IFR or LIFR due to
clouds, with brief MVFR possibly around SPI as a narrow corridor
of dry air advances into our SW counties later this afternoon and
evening.

Showers will expand in coverage tomorrow morning as low pressure
progresses from west to east across north-central IL. Have
included prevailing rain in the last 3 hours of this TAF period as
a result.

&&

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

$$

UPDATE...Shimon
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Shimon


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