Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 221527
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
927 AM CST Wed Feb 22 2017

.UPDATE...
Issued at 925 AM CST Wed Feb 22 2017

Have extended the dense fog advisory until noon for areas from
about I-72 northward, where the HRRR/RAP indicates a more substantial
breakup beginning between 10-11 am. Further south, the cloud cover
is thinner and has shown quite a few breaks over east central and
southeast Illinois, with surface obs and webcams showing the
visibility more variable, and steady improvement will continue in
this area.

Temperatures continue to be a bit uncertain for this afternoon,
and are highly dependent on the breakup of the cloud cover. Have
lowered them a couple degrees and will watch the trends closely
over the next couple hours.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 320 AM CST Wed Feb 22 2017

Widespread dense fog has once again developed across much of central
Illinois early this morning, prompting the issuance of a Dense Fog
Advisory along/west of a Bloomington to Taylorville line.  08z/2am
obs show visibilities remaining in the 1-3 mile range across the
E/NE KILX CWA: however, HRRR has been consistently showing the fog
becoming dense across this area as well between 10-12z.  Will
continue to monitor trends for the next couple of hours, but think
the advisory will eventually need to be expanded to cover the entire
CWA.  The fog will be slow to dissipate after sunrise, with the HRRR
suggesting a few patches of fog lingering until late morning.  Once
the fog lifts, low clouds will persist before increasing
southwesterly winds and turbulent mixing scours them out.  NAM
forecast soundings indicate skies becoming mostly sunny along/west
of I-55 by early to mid-afternoon...with clouds lingering further
east through the balance of the afternoon.  Cloud cover will play
a significant role in temperature forecast today, as locations
that clear earliest will be warmest.  Based on expected timing of
clearing, think afternoon highs will range from the upper 60s east
of I-57...to the middle 70s along/west of I-55.  A frontal
boundary will drop southward into the region and stall across
central Illinois tonight: however, it will have very little
moisture to work with and will therefore produce no precipitation.
Low temperatures will range from the middle 40s far north...to the
middle 50s far south.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 320 AM CST Wed Feb 22 2017

With front stalling across south-central Illinois on Thursday, a
distinct north-south temperature gradient will develop, with highs
ranging from the upper 50s far north around Galesburg and Lacon...to
the lower 70s south of I-70.  Much of the day should be dry:
however, as synoptic lift increases along the boundary in advance of
a potent short-wave ejecting out of the Rockies, scattered showers
will develop during the afternoon.

Low pressure is still expected to develop in the lee of the Rockies
Thursday evening, then track into the southern Great Lakes by Friday
evening.  Minor model discrepancies are still present: however,
consensus shows a strong cold front bisecting central Illinois by
18z Fri.  Given unseasonably warm/moist southerly flow ahead of the
front, the atmosphere will become moderately unstable across east-
central and southeast Illinois...with GFS indicating MUCAPE values
of around 1000J/kg.  In addition...0-6km bulk shear values will
increase to 55-65kt as a powerful mid-level jet approaches from the
west.  Think strong to potentially severe thunderstorms will develop
along/ahead of the front Friday afternoon, mainly east of I-55 where
likely PoPs are warranted.  Latest SPC Day 3 Convective Outlook
highlights this area...with attendant risk for damaging thunderstorm
wind gusts and isolated tornadoes.  Any storms that fire will
quickly shift into Indiana by early evening, followed by breezy and
sharply colder conditions.  Models continue to suggest wrap-around
moisture will brush the N/NW CWA late Friday night into Saturday
morning.  With temperatures falling into the upper 20s and lower
30s, a period of light snow will be likely.  Given unseasonably warm
ground temperatures and very light nature of the precip...little to
no snow accumulation is expected.

Cool/more typical mid-February weather will prevail over the
weekend...with highs in the 30s on Saturday rising into the 40s by
Sunday.  The return to normal will be short-lived however, as zonal
flow will allow temps to warm significantly by early next week.
Unfortunately the warming trend will also be accompanied by
precipitation.  At this time it appears a brief period of light snow
will be possible Monday morning before temps warm sufficiently for
all rain Monday afternoon into Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 925 AM CST Wed Feb 22 2017

Widespread VLIFR conditions continuing west of a KBMI-KSPI line
this morning and will slowly erode the rest of the morning. More
substantial breaks in the clouds further east is resulting in a
more variable trend between VLIFR and MVFR near KCMI/KDNV. Have
updated all TAF sites to incorporate this, with a general VFR
condition expected to prevail by 18Z.

&&

.CLIMATE...
Issued at 925 AM CST Wed Feb 22 2017

Record Highs / Record Warm Lows - Wednesday Feb 22nd...
Peoria........ 71 / 51
Lincoln....... 71 / 52
Springfield... 71 / 53
Champaign..... 69 / 49
Bloomington... 70 / 53
Decatur....... 72 / 51
Danville...... 71 / 54
Galesburg..... 61 / 45
Charleston.... 71 / 52
Effingham..... 74 / 55

Record Highs / Record Warm Lows - Thursday Feb 23rd...
Peoria........ 64 / 49
Lincoln....... 68 / 50
Springfield... 70 / 50
Champaign..... 65 / 50
Bloomington... 66 / 52
Decatur....... 73 / 53
Danville...... 67 / 51
Galesburg..... 65 / 44
Charleston.... 69 / 52
Effingham..... 75 / 54

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST today for ILZ027>031-036>038-
040>051-053.

&&

$$

UPDATE...Geelhart
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Geelhart
CLIMATE...Geelhart



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