Area Forecast Discussion
Issued by NWS Central Illinois

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124
FXUS63 KILX 210503
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1103 PM CST Mon Feb 20 2017

.UPDATE...
Issued at 840 PM CST Mon Feb 20 2017

Weak cold front over central Iowa was making slow progress east
this evening with a band of showers and isolated thunderstorms
along and to the east of the boundary. The leading edge of the
showers was pushing across far west central Illinois with a
track more to the north than east. Based on the current track
and speed, the showers should approach the I-55 corridor around
between 1 and 3 am. Models continue to suggest the slow moving
boundary to our west will weaken as it tracks across our area
Tuesday morning with the scattered showers moving out in the
early afternoon across the east. Another very mild night over
central Illinois thanks to the cloud cover and southerly breeze
with most areas remaining in the low to mid 50s, threatening
many record warm lows (see climate section below) across the
central, east central and southeast Illinois. The current
forecast has a good handle on the late evening and overnight
trends with respect to the precipitation timing from west to east,
as a result, no ZFP update will be needed at this time.

&&

.SHORT TERM...(This evening through Tuesday)
ISSUED AT 233 PM CST Mon Feb 20 2017

Earlier clouds/fog did not keep a damper on the unseasonably warm
weather, as partly sunny skies have pushed temperatures into the
upper 60s to mid 70s across the forecast area this afternoon. Gusty
southerly winds of 25-30 mph is helping out as well.

The large area of precipitation that was west of us continues to
lift north-northeast this afternoon, as the frontal boundary edges
eastward. A few echoes are scraping the Illinois/Iowa border, but
surface observations indicate these are largely not reaching the
ground. Water vapor imagery shows a nice moisture plume tracking
ahead of the deep trough in the Plains, and our rain chances will
mainly await this surge to moisten up the lower levels of the
atmosphere, currently suggested in forecast soundings to take place
mid-late evening. Latest high-res model guidance suggesting the rain
may only make it as far east as I-55 by midnight, but have included
some low chances east to I-57 late this evening, with the highest
PoP`s there after midnight. Thunder threat appears to still be
isolated and mainly west of I-55, although the RAP model has
MUCAPE`s up to around 100 J/kg as far east as Champaign and
Effingham after midnight. Temperatures will remain very balmy
overnight, only falling into the mid 50s, which could set some
record warm lows for the month.

While the upper trough starts to move into the western parts of the
state Tuesday morning, it will start to weaken as an upper low cuts
off over eastern Texas. The front will fall apart as a result, and
temperatures on Tuesday should still reach the upper 60s to lower
70s. The NAM/GFS suggest most of the lingering rain over the eastern
CWA would be early in the day, but some showers may linger into
afternoon as the trough passes.

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 233 PM CST Mon Feb 20 2017

With the Mon night-Tue weather system east of the area, high
pressure ridge will slide across the CWA Tue night into Wed. This
will keep the area dry with continued southwest flow. This southwest
flow will keep the near record to record temps in the area through
the day Wed. Models look very similar with a weather system moving
through the flow across the northern US and into the Great Lakes
region Wed night. However, the trailing cold front associated with
this system will be dry as it moves through the region. It will be
the weather system developing in eastern CO and pushing out into the
plains that will ultimately bring the showers and thunderstorms to
the area for Thur through Fri.

This next system will develop a warm front that will extend into
central IL by Thursday afternoon. Showers are expected to begin
developing along this boundary over central IL Thur afternoon.
Amount of moisture return ahead of this system is in question right
now, so will just have a chance of showers along the boundary.
Potential for showers will increase during for the evening hours as
the system strengthens some and moves northeast...causing the warm
front to slowly lift northward. Models differ on amount and
location of qpf during the evening and then overnight, but all agree
that an increase in precip will occur during the night. Highest pops
will shift to the north as well. Fri should bring an increase in
moisture and continued warm temps ahead of the associated cold
front. Models differ with timing of the cold front, with the ECMWF
pushing the front quickly through the area, while the NAM and
Canadian still have the front west of the area at 18z and then
through the center of the CWA by 00z. The low pressure area
associated with the system is also slower on the GFS and Canadian
than the ECMWF. Despite the differences in speed of the front, all
three models generate precip in the eastern half of the CWA Fri
afternoon. So, higher pops warranted along the front Fri afternoon.
In addition, with increased moisture, instability should be
maximized ahead of the front during the afternoon, which should lead
to thunderstorms being more likely. So, have increased pops for
thunder as well...to likely. The low pressure area will lift
northeast across the state Fri night with some lingering showers in
the east during the evening and then colder air coming in on the
back side. This colder air will come around in the wrap around
section of precip, so precip should go from rain to a mix of rain
and snow, to all snow Fri night. The chance of snow will continue
into Sat, but with temps warming into the upper 30s to the middle
40s across most of the area, the snow will change back to rain
during the day.

After a dry and cooler period Sat night more precip is possible
Sunday afternoon and Sunday night. New runs of the extended models
are differing with location and amount...if any...qpf in the area
during this time frame, so will just keep the consensus forecast
going for now. Then pops will increase as the next significant
weather system moves into the area for Monday. All models agree on
this, but differ on timing. So, consensus pops have likelies in the
area during the day Monday.

Temps the rest of the week will stay above normal with record highs
still possible Wed through Friday. Sat temps will drop back down to
around or just below normal during the day, with Sat night lows
below freezing across the area. Temps will begin to warm back up to
above normal beginning Sun and then continue into Monday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1100 PM CST Mon Feb 20 2017

Clouds will continue to lower after midnight as an area of
showers just out to our west moves slowly east across the TAF
sites. VFR cigs will lower to MVFR as a frontal system moves
across central Illinois Tuesday morning with a low probability for
a brief period of IFR cigs in the 09z-14z time frame. Models
continue to indicate the rain will shift east of the TAF sites by
early afternoon with a return to VFR conditions by late morning
across PIA and SPI and by 20z at CMI. Winds will be south to
southwest ahead of the weak cold front tonight at 5 to 10 kts, and
then become light and variable on Tuesday as the weakening front
edges slowly away from the forecast area. The light winds and
added low level moisture from the rain tonight may lead to some
patchy fog later Tuesday night...primarily after 06z.

&&

.CLIMATE...
Issued at 312 PM CST Sun Feb 19 2017

Record Highs / Record Warm Lows - Monday Feb 20th...
Peoria........ 68 / 46
Lincoln....... 70 / 46
Springfield... 74 / 46
Champaign..... 71 / 45
Bloomington... 67 / 45
Decatur....... 70 / 47
Danville...... 70 / 48
Galesburg..... 64 / 41
Charleston.... 73 / 48
Effingham..... 68 / 54

Record Highs / Record Warm Lows - Tuesday Feb 21st...
Peoria........ 69 / 46
Lincoln....... 69 / 45
Springfield... 69 / 48
Champaign..... 67 / 47
Bloomington... 69 / 46
Decatur....... 68 / 48
Danville...... 67 / 50
Galesburg..... 68 / 40
Charleston.... 71 / 52
Effingham..... 73 / 52

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

&&

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

$$

UPDATE...Smith
SHORT TERM...Geelhart
LONG TERM...Auten
AVIATION...Smith
CLIMATE...WFO ILX



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