Area Forecast Discussion
Issued by NWS Central Illinois

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910
FXUS63 KILX 151701
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1101 AM CST Sun Jan 15 2017

.UPDATE...
Issued at 1059 AM CST Sun Jan 15 2017

Update the forecast to remove the remainder of the counties along
and south of I-70 from the freezing rain advisory. The rest of the
central IL counties remain in the freezing rain advisory another
hour until noon. Continued the winter weather advisory for
northern CWA tonight into Monday morning starting at 6 pm today.
Radar mosaic and surface observations show the brunt of the light
rain and light freezing rain has been south of I-72 this morning,
with the light rain along and south of I-70 by late morning as
temperatures there have slowly risen into the mid 30s. Temps were
mostly 29-32F over central IL north of I-70 at late morning where
light freezing rain or patchy freezing drizzle possible next hour
or so. The latest HRRR model run shows the light precipitation
band spreading ne across areas from I-72 north during the
afternoon and reaching ne of I-74 toward early evening. Temps to
reach just above freezing this afternoon across much of central IL
with precipitation changing to light rain. Temps then slip back
to near or just below freezing this evening along and north of
I-72 where light freezing rain will be possible again. The winter
weather advisory northern CWA looks good tonight.


&&

.SHORT TERM...(Today and tonight)
ISSUED AT 325 AM CST Sun Jan 15 2017

08z/2am surface analysis shows 1034mb high centered over
Minnesota/Wisconsin...while frontal boundary remains draped from the
southern Appalachians to Texas.  A weak short-wave trough tracking
north of the front is currently triggering an area of freezing rain
across central/eastern Missouri.  This precipitation is tracking
E/NE and will eventually spread across the southern KILX CWA this
morning.  Based on radar trends and latest HRRR forecast...it
appears most of the precipitation will remain south of the I-72
corridor today...with only patchy drizzle further north.  Have
therefore focused high chance to likely PoPs across the southern
half of the CWA...while areas along/north of a Galesburg to Lacon
line remain dry through the entire day.  Precip type will
initially be a mix of freezing rain and sleet: however, as surface
temps slowly warm, it will gradually mix with rain.  Models seem
to be too warm today, with both the MET and MAV guidance
suggesting highs reaching the middle to upper 30s.  This seems
unreasonable based on extensive cloud cover and continued light
E/NE boundary layer flow.  Have therefore gone several degrees
below guidance, with afternoon highs ranging from the lower 30s
north to the upper 30s far south.  End result will be precip
transitioning to all rain along/south of a Paris to Taylorville
line this afternoon.  Given light QPF and marginal temps, ice
accumulations will remain under one tenth of an inch this morning.
The Freezing Rain Advisory will therefore continue through noon
to account for potential slick spots on mainly secondary and
untreated roads.

The initial push of light precip this morning will diminish as it
lifts further northward toward the prevailing high over the southern
Great Lakes this evening.  Meanwhile, the strongest forcing will
shift further south and west in association with the main upper
system lifting out of northwest Mexico.  As a result, have lowered
PoPs to slight or low chance tonight.  With temperatures hovering
around freezing, additional freezing drizzle or sleet will be
possible.  The current Winter Weather Advisory for the northern CWA
will remain in effect tonight through Monday morning and may need to
be expanded southward toward the I-72 corridor depending on how
surface temps respond this afternoon and if very light precip
lingers into the evening.  Any ice accumulations will remain very
light tonight, amounting to less than one tenth of an inch.

.LONG TERM...(Monday through Saturday)
ISSUED AT 325 AM CST Sun Jan 15 2017

Temperatures will slowly begin to rise late tonight as boundary
layer winds veer to the southeast in advance of the approaching
system.  May see some lingering freezing rain along/north of I-74
into early Monday morning, but this will rapidly change to rain as
temps climb into the middle 30s.  As stronger forcing arrives from
the southwest, rain will become widespread across the area by Monday
afternoon.  With low pressure tracking from Oklahoma Monday morning
to southern Lake Michigan by Tuesday morning, central Illinois will
punch into the warm sector of the system Monday night.  NAM/GFS
forecast soundings show MUCAPE values of 200-400J/kg, suggesting the
possibility of isolated thunderstorms.  Once the low moves into the
Great Lakes, any lingering showers will come to an end Tuesday
morning followed by mild/dry weather through Wednesday.

After that, model consistency is quite poor and resulting forecast
confidence remains low.  One thing is for certain though...a big
warm-up is in store for the end of the week as southwesterly upper
flow establishes itself across the region.  Temperatures will climb
into the 50s Thursday through Saturday, with readings perhaps
reaching the lower 60s across the southeast CWA next weekend.  Main
questions will revolve around track and timing of waves embedded
within the flow.  Models have been flip-flopping on a potential wave
Thursday night into Friday.  The 00z Jan 15 GFS has backed off on
the wave, while the ECMWF has now latched onto it.  At this point,
have decided to go with a dry forecast through Saturday until better
model consistency is achieved.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 554 AM CST Sun Jan 15 2017

Dry and cold high pressure to the north of Illinois has kept VFR
cloud heights for PIA, BMI, and CMI at TAF start time. However,
some light MVFR to IFR fog has developed in the boundary layer at
all terminal sites except for PIA. HRRR and RAP updates indicate
ceilings should continue to lower this morning to IFR, with IFR
vis in fog possibly expanding in coverage for a few hours this
morning as well. IFR or low MVFR ceilings look to prevail for a
majority of this TAF period, as light freezing rain develops south
of I-72. SPI, DEC and CMI will have the better chances of seeing
light icing from freezing rain this morning, before air
temperatures warm above freezing this afternoon.

Forecast soundings point toward stratus clouds lowering to LIFR
after 00z/6pm this evening, with IFR fog becoming widespread as
well.

Precipitation looks to shift northward overnight, with PIA and BMI
getting the focus of an east to west band of light freezing rain
overnight.

Surface winds will be light northeast early this morning, then
shift to the east-southeast by afternoon, with speeds in the 5 to
10 kt range.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Freezing Rain Advisory until noon CST today for ILZ040>057-061.

Winter Weather Advisory from 6 PM this evening to noon CST
Monday for ILZ027>031-036>038.

&&

$$

UPDATE...07
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Shimon



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