Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 280149
AFDILX

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

.UPDATE...
Issued at 835 PM CDT Thu Apr 27 2017

As the lower cloud deck from earlier today moves out of the area
this evening, some mid and high level clouds move in as the next
weather system shifts into the Central Plains. Weak high pressure
across southeast Illinois this evening will move away from our
area overnight as low pressure, currently over the Texas
Panhandle, shifts towards the Midwest on Friday. This should bring
scattered showers to the area starting across our west by dawn
Friday, and the spreading east during the day as a cool front
slips southeast across the area during the afternoon and settles
to the Ohio River Valley Friday night. It is along the stalled
frontal boundary over southern Illinois and Indiana where the
most concentrated area of showers and thunderstorms will develop
later Friday night and slowly spread north on Saturday bringing
the threat for heavy rainfall to parts of central through southeast
Illinois.

Rather chilly temperatures are expected tonight, but thankfully
with a bit more cloud cover across the area, we should stay out of
the 30s across our north with most locations dropping into the
mid to upper 40s, with a few low 40s possible far north by Friday
morning. Current forecast has the evening and overnight trends
well in hand, as a result, no ZFP update will be needed at this
time.

&&

.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 00Z TAFS through 00Z Friday evening)
Issued at 626 PM CDT Thu Apr 27 2017

The backedge of the low VFR and MVFR cigs were starting to
approach the western TAF locations early this evening and we
expect this trend to continue into tonight. However, despite
the decrease in lower clouds, satellite data and upstream
surface observations suggest some mid and high level clouds
will push across the area later tonight and into Friday as the
next weather system approaches the area. Some showers will
approach SPI and PIA towards dawn and have included a VCSH early,
with scattered showers around during the morning and early
afternoon hours which will bring about a deterioration in cigs
once again across all of the TAF sites by afternoon. Most areas by
21z should be MVFR. Surface winds will back more into a southerly
flow tonight with speeds of less than 10 kts. Winds will be
southeasterly on Friday at 12 to 17 kts.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from Friday evening through Monday morning for
ILZ038-042>046-048-051>057-061>063-066>068-071>073.

&&

$$

UPDATE...Smith
SHORT TERM...07
LONG TERM...07
AVIATION...Smith


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