Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 272000

Area Forecast Discussion
National Weather Service Lincoln IL
300 PM CDT Thu Apr 27 2017

.SHORT TERM...(This evening through Friday)
ISSUED AT 300 PM CDT Thu Apr 27 2017

The mid afternoon surface map shows strong 991 mb low pressure over
ne Lake Superior with cold front extending through western Ohio into
central KY/TN. Aloft a 538 dm 500 mb low was over ne MN into western
Lake Superior with a strong upper level trof over the Midwest. Much
of IL remained blanketed by a low cloud deck with patchy drizzle and
isolated light rain showers over parts of central and northern IL.
Breezy WSW winds of 10-20 mph and gusts in the 20s was keeping cool
temps in the mid to upper 40s over central IL and low to mid 50s
over southeast IL.

12Z models lift surface low pressure from ne Lake Superior up to
James Bay Canada by dawn Friday while 993 mb low pressure in
southeast CO ejects into sw Nebraska. Models are slower bringing
light rain showers ne into central IL later tonight into Fri morning
and have trended the forecast in that direction. Lows tonight in the
mid to upper 40s. Highs Friday to range from upper 50s and lower 60s
over the IL river valley and lower 70s se of I-70. Have shower
chances increasing from sw to ne during Friday with isolated
thunderstorms possible in southeast IL Friday afternoon.


.LONG TERM...(Friday night through Thursday)
ISSUED AT 300 PM CDT Thu Apr 27 2017

Will issue a flash flood watch from from Friday night through Sunday
night from McLean, Logan, Menard and Sangamon counties southeast for
4 to 5 inches of rainfall expected, with the heaviest amounts of 1.5-
3 inches falling Sat night. The heaviest rainfall amounts are
expected between I-55 and I-57. 12Z models like the GFS and ECMWF
have trended further nw with heavier qpf and there is a possibility
that later shifts may need to expand the flash flood watch further
nw toward the IL river.

A cutoff upper level low digs over the southern Rockies and ejects
surface low pressure ne over IA/WI Sunday night. A frontal boundary
south of IL will lift northward into southern IL Friday afternoon
and be over southeast IL Fri night and Sat. This will expand shower
chances and amounts further north into central IL during Friday
night into Saturday with thunderstorms chances expanding further
north as well. SPC has slight to enhanced risk of severe storms over
southeast IL Friday night closer to the frontal boundary. The
heaviest rain is expected Sat night with pw values of 1.5-2 inches
and 50-55 kt southerly low level/850 mb jet. High Sat contrast again
from lower to mid 50s over the IL river valley, to the mid to upper
70s se of I-70. The front should lift north of central IL by Sunday
but then a cold front push east over the state by Sunday evening,
keeping high chances of showers and thunderstorms going into Sunday
night. Highs Sunday range from mid to upper 60s nw of the IL river
to the mid to upper 70s in eastern IL.

Much cooler temperatures behind the front on Monday with lingering
chances of showers. highs in the 50s over much of area. Highs in the
low to mid 60s from Tue-Thu of next week. Next chances of rain
showers appears to be Wed/Thu time frame.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1240 PM CDT Thu Apr 27 2017

MVFR ceilings of 1.5-3k ft over central IL early this afternoon
will gradually lift to low end VFR during mid or late afternoon
and then scatter out from sw to ne between 23Z-02Z. Patchy drizzle
early this afternoon so carried VCSH for a few more hours
especially ne of SPI. Strong 991 mb surface low pressure over
eastern upper MI and eastern Lake Superior with its cold front
moves east into far western Ohio and central KY/TN at midday. Low
pressure to deepen to 990 mb as it lifts ne to James Bay Canada
by 12Z/7 am Fri while 998 mb surface low pressure moves east into
sw OK. Some overrunning of frontal boundary/low pressure sw of IL
to bring chances of light rain showers sw IL by SPI later tonight
and over rest of central IL during Fri morning along with return
of MVFR ceilings of 2-3k ft. Breezy West winds 10-15 kts and gusts
of 18-24 kts early and mid afternoon, to diminish to around 5 kts
after sunset and become light and variable much of tonight. Winds
to become SE late tonight and increase to 10-16 kts during Fri


Flash Flood Watch from Friday evening through Monday morning for



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