Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 191501

Area Forecast Discussion
National Weather Service Lincoln IL
1001 AM CDT Fri May 19 2017

Issued at 1000 AM CDT Fri May 19 2017

Complicated forecast scenario this morning. Initial line of
strong/severe storms was now in western Indiana. A mesoscale
vortex was pushing across areas between Macomb and Peoria with an
increase in rain there, while additional showers were increasing
over eastern Illinois ahead of a low tracking through south
central Illinois. The rain threat will continue to increase for a
couple hours, then fade off for a bit as the low pushes into
Indiana and we await the next surge out of Missouri this evening.

Temperatures are a significant issue as well. 9 am readings were
only in the mid 40s in a large area from Havana-Bloomington but
had reached the mid-upper 70s over the extreme southeast CWA. The
frontal boundary will not make a lot of progress as the low rides
along it, and the stiff northeast winds will not bring in much
warmer air behind it. Have made some adjustments to the highs
today across mainly the northern CWA, with a more widespread area
of low-mid 50s, and mid-upper 60s along I-72. South of I-70, kept
highs generally in the lower 80s.


.SHORT TERM...(Today and tonight)
ISSUED AT 345 AM CDT Fri May 19 2017

Active weather expected through Sat night across central and
southeast IL with 1.5 to 2 inches of rain likely by Sunday
morning. Strong 557 dm 500 mb low low over western CO to eject ne
to MN Sat night and bring the unsettled wx to IL.

An expanding area of showers and thunderstorms that started near
a frontal boundary just south of I-72 late Thu evening, has
expanded almost as far north as Peoria and Bloomington and as far
south as Shelbyville to Terre Haute. Thunderstorms mainly
producing heavy rains and frequent lightning though had a few hail
reports earlier in the night including 1 inch hail in Ivesdale in
Champaign county at 1045 pm. Currently the frontal boundary has
sagged south of a Taylorville to Mattoon to Terre Haute line with
the convection along and north of this boundary. Increasing ENE
winds north of this boundary have been gusting to around 30 mph
over northern CWA. Temps range from lower 50s from Lacon and
Bloomington ne to the upper 60s and lower 70s in southeast IL.

A larger area of convection was over IA/MO and will lift ne across
central IL during this morning. Frontal boundary will slip into
southeast IL during today, getting a better push south during the
afternoon and reaching near Lawrenceville by sunset. Looks like a
lull in convection for a time late this morning into mid
afternoon. Then isolated to scattered convection to develop late
this afternoon or more likely this evening as another wave lifts
ne. SPC has central and southern CWA in a slight risk while
marginal risk from Rushville to Rantoul north, and just general
risk of thunder over Knox, Stark and Marshall counties. Highs
today to range from near 60F north of Peoria, to the lower 80s in
southeast IL south of I-70. Lows tonight range from mid to upper
50s northern CWA to the mid to upper 60s southern CWA.

.LONG TERM...(Saturday through Thursday)
ISSUED AT 345 AM CDT Fri May 19 2017

Surface low pressure ejecting ne from central plains into western
IA late Saturday to pull the front north as a warm front across
central IL during Sat morning and be accompanied by another round
of showers and thunderstorms. Should be a lull again during midday
Saturday before more convection develops in unstable airmass and
approaching cold front later Sat afternoon and evening. Cold front
to track east over IL later Sat evening and overnight Sat night.
SPC has slight risk of severe storms east of I-55 on Sat
afternoon/evening while marginal risk along and west of I-55.
Warmer highs Sat of 80-85F expect upper 70s nw of the IL river.

Deepening surface low pressure moves into nw WI by 12Z/7 am Sunday
and north of Lake Superior by sunset Sunday. 00Z models continue
faster trend of returning drier weather on Sunday from the west,
with just slight chance of showers along and east of a Danville to
Effingham line Sunday morning, then dry with partly to mostly
sunny skies and breezy westerly winds. Cooler highs Sunday in mid
60s nw of the IL river and lower 70s in southeast IL. Cool night
Sunday night as winds become light and fair skies with weak high
pressure of 1020 mb settling into mid MS river valley. Lows
Sunday night in the upper 40s and lower 50s.

Dry condtions still expected Monday with some increasing clouds
from the west Monday afternoon. Highs Monday in low to mid 70s.
Models continue to dig a strong upper level trof into the Midwest
on Tue with cold front moves se through IL by Tue afternoon.
Showers and isolated thunderstorms to spread east over area during
Monday night and continue through Wed as upper level low/trof
shifts east into the ohio river valley. Highs Tue range from mid
60s over IL river valley to lower 70s in southeast IL, similar to
Sundays highs. Then cooler highs in the lower 60s on Wed across
area. Have 20-30% chance of showers in eastern IL Wed evening,
then dry across area by overnight Wed night. But this is short
live as another chance of showers and isolated thunderstorms
returns to CWA by Thu afternoon/evening as clipper low pressure
dives se into ne IL and southern Lake MI. Highs Thu in the upper
60s to near 70F and in the lower 70s on Friday.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 600 AM CDT Fri May 19 2017

A frontal boundary near I-70 will stay south of central IL
airports through tonight. ENE winds of 10-20 kts and gusts of
20-25 kts expected at times this morning and will veer more NE
this afternoon and evening and weaken to around 10 kts, then turn
more easterly later tonight. Widespread showers and scattered
thunderstorms over central IL this morning and will bring MVFR
conditions to possibly IFR conditions with heavier rains this
morning. The convection should diminish from sw to ne between
15-17Z though MVFR ceilings are expected. Isolated to scattered
thunderstorms to develop and spread ne during the evening and
become more widespread during overnight. IFR to MVFR ceilings
expected tonight ranging from 500-1200 ft.




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