Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 181055

Area Forecast Discussion
National Weather Service Lincoln IL
555 AM CDT Sun Mar 18 2018

.SHORT TERM...(Today and tonight)
ISSUED AT 304 AM CDT Sun Mar 18 2018

Skies have been slowly clearing from north to south across the
area early this morning...with 07z/2am IR satellite imagery
showing cloudy skies persisting along/southwest of a Lawrenceville line. Further north
where skies have cleared, light winds and residual boundary layer
moisture have led to fog development. The fog was first noted on
satellite imagery in the Illinois River Valley from Peoria to
Lacon, but has developed/spread further west and east over the
past couple of hours. Latest obs show a cluster of sites with
visbys at 1/4 mile from Galesburg and Macomb eastward to Lacon and
Peoria. Further east, little or no visby restriction is seen
across the NE KILX CWA where light N/NE winds are advecting a
slightly drier airmass into the area. Despite NAMNest suggesting
widespread dense fog across the northern two-thirds of the CWA,
think the lowest visbys will mainly be confined to areas
along/west of the I-55 corridor where winds are calm and
temp/dewpoint spreads are 0-1F. Rapid Refresh has been
consistently highlighting this area for most widespread fog
development...and this seems to be coming to fruition quite
nicely. As a result, have issued a Dense Fog Advisory along and
west of a Bloomington to Lincoln line through 15z/10am. Will
monitor obs over the next hour or two to see if the advisory may
potentially need to be expanded further south and east. Once the
morning fog burns off, mostly sunny and mild conditions will
prevail today with afternoon highs in the lower 50s.

A short-wave trough noted on latest water vapor imagery over
southern Nevada will track eastward over the next 24 hours,
pulling moisture back northward toward central Illinois tonight.
00z Mar 18 models have backed off on the timing of precip onset
due to prevailing dry E/NE boundary layer flow. As a result, will
only carry slight chance PoPs for light rain across the far south
around Flora and Olney toward dawn Monday. Elsewhere, skies will
become overcast but conditions will remain dry through the entire

.LONG TERM...(Monday through Saturday)
ISSUED AT 304 AM CDT Sun Mar 18 2018

All models track the Nevada short-wave through the Ozarks into the
Ohio River Valley on Monday...confining the heaviest precipitation
to southern Illinois/Kentucky. With high pressure anchored over
Manitoba/Quebec continuing to provide a dry E/NE flow, think there
will be a sharp cut-off to the northern edge of the precip area.
Have therefore sharpened the PoP gradient across central Illinois
on Monday...with categorical PoPs south of I-70 tapering down to
just low chance along a Danville line.
Further north, think dry condtions will prevail as the system
skirts by to the south. Rainfall amounts will be heaviest south of
I-70 where one half to three quarters of an inch will be likely.

Once the initial wave tracks into the Appalachians, two additional
northern-stream waves will drop through the area Tuesday into the prevailing upper trough over the
eastern CONUS. These features will be weak and moisture-starved,
so am not anticipating any precip. Main story will be the chilly
weather, with highs both days remaining below normal in the lower
to middle 40s.

After that, condtions slowly warm by the end of the week:
however, rain chances also come back into the picture. While the
primary synoptic features of both the GFS and ECMWF are in good
agreement through the extended, one small difference is making the
precip forecast somewhat tricky. Both models feature upper ridging
building across the Midwest/Ohio River Valley, with a trough
digging across the western CONUS. The GFS is now showing a lead
short-wave ejecting eastward from the main trough, which brings
clouds and precip back into Illinois as early as Thursday night
into Friday. Meanwhile, the ECMWF is weaker and about 12-24 hours
slower with the wave, thus focusing its precip during the Friday
night/Saturday time frame. Current forecast features PoPs Thursday
night through Saturday: however, as models come into better
agreement with their timing, some of these PoPs will be removed
with later forecasts. Bottom line will be warmer and more
unsettled conditions by the end of the week.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 555 AM CDT Sun Mar 18 2018

Dense fog continues to slowly spread southeastward early this
morning, with latest obs showing visbys at 1/4 mile or less at
both KPIA and KSPI. Based on IR satellite imagery, it appears the
fog may reach KBMI/KDEC over the next hour or so before the sun
comes up and starts eroding the shallow dense fog bank. Further
east, enough dry air is filtering southward to prevent fog
formation at KCMI. Visbys will improve to P6SM across the board
after 15z, followed by mostly clear skies and light winds through
the afternoon. Clouds will once again begin increasing from the
south tonight, as a storm system approaches. Forecast soundings
show low VFR ceilings developing at KSPI by around 04z...but
remaining south of the I-74 terminals through 12z.


Dense Fog Advisory until 10 AM CDT this morning for ILZ027>031-



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