Scientific Forecaster Discussion
fxus63 kilx 211800
Area forecast discussion
National Weather Service Lincoln Illinois
100 PM CDT Sat Oct 21 2017
issued at 1045 am CDT Sat Oct 21 2017
Updated the forecast today to extend slight chances of showers
until mid afternoon mainly east of I-55. Also added slight chance
of thunderstorms next few hours from I-72 south to I-70. Weak
short waves east of the Illinois River will lift NE of County Warning Area by 21z/4 PM
and appears to be just enough moisture to produce isolated
convection for a few more hours. Echos are weakening as they move
NE into drier air by I-74 and may just be spotty light rain
showers or sprinkles there. A fair amount of mid/high clouds east
of the Illinois River late this morning while more sunshine west of Illinois
River. Expect skies to become partly sunny during the afternoon
over central and eastern Illinois as more breaks develop in cloud cover.
Temps currently in the low to mid 60s and should warm mostly into
the upper 70s during this afternoon as more sunshine appears. This
should be the 3rd consecutive day with highs in the 75-80f range
aided by breezy southerly winds of 10-20 mph and gusts 20-30 mph.
Tight pressure gradient over Illinois due to 1029 mb high pressure over
the mid Atlantic states, and 990 mb low pressure over central
Manitoba with a cold front extending southward through the far
eastern Dakotas into eastern Nebraska and central Kansas.
Short term...(today and tonight)
issued at 338 am CDT Sat Oct 21 2017
A tightening pressure gradient between a high anchored along the
East Coast and a cold front in the plains will produce strong
S/SW winds across central Illinois today. Numeric guidance and
forecast soundings suggest gusts of 25-30mph, particularly from
late morning through the afternoon. Plenty of mid/high clouds will
stream across the region this morning, as a short-wave trough
tracks just west/northwest of Illinois through Iowa into Wisconsin. While
regional 00z upper air soundings showed very dry air below 500mb,
current radar mosaic indicates 30-40dbz echoes embedded within
the southwesterly flow on the periphery of the wave. No surface
obs have reported precip yet, but have decided to include a chance
for sprinkles everywhere west of the I-57 corridor this morning in
case some very light precip manages to reach the ground beneath
the stronger echoes. Aside from that, the remainder of the day
will be partly to mostly cloudy...breezy...and very warm with
highs once again climbing well into the 70s.
The plains cold front will slowly push eastward tonight,
triggering showers and thunderstorms overnight. 00z Oct 21 models
have continued the recent trend of slowing the eastward progress
of the front, with most high-res solutions keeping showers west of
the kilx County Warning Area until after midnight. Have scaled back evening pops
accordingly, with only slight chances west of I-55. Rain chances
will gradually spread eastward across the remainder of the area
overnight, but may not reach the Indiana border until after 12z.
Storm Prediction Center continues to highlight locations west of the Mississippi River
for potential severe later today: however, by the time any
convection reaches west-central Illinois, instability will be
waning and severe threat appears to be low tonight.
Long term...(sunday through friday)
issued at 338 am CDT Sat Oct 21 2017
Front will slowly push eastward across central Illinois on Sunday,
bringing showers and perhaps a few isolated thunderstorms.
Boundary will slip mainly east of the area by monday: however,
models are continuing to struggle with a rather complex upper air
pattern early next week. The main challenge is how an upper trough
digging across the northern plains will interact with an upper low
tracking through the Mississippi/Tennessee River valleys.
Considerable model spread still exists, resulting in below average
forecast confidence beyond Sunday. At this point, will continue to
forecast showers across mainly the east/southeast County Warning Area on Monday as the upper
low slows. Meanwhile, as the northern plains wave digs further
south and merges with the low, clouds and light showers are a good
bet everywhere on Tuesday. The main weather story for the middle
of the week will be the considerably cooler conditions...as
temperatures drop from the 60s/70s on Sunday into the 50s by
Tuesday/Wednesday. After that...warming conditions are expected by
the end of the week.
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1259 PM CDT Sat Oct 21 2017
Isolated rain showers possible at Dec and cmi til 20-21z though
vsbys and ceilings will remain VFR. A weak short wave east of I-55
will exit NE of cmi by 21z/4 PM and isolated showers to shift
ENE of there after 21z. Scattered clouds of 5-10k ft and broken
cirrus clouds of 20-25k ft to occur this afternoon and evening
though initially be less cloud cover at pia into mid afternoon.
Breezy south winds 12-18 kts with gusts in the 20s to occur next
24 hours and be strongest during the afternoon and early evening
and again during Sunday morning especially east of Illinois River/pia.
A cold front along the Dakotas/Minnesota border into eastern NE and
central Kansas will approaching the Illinois River/pia toward 18z/1 PM
Sunday. Brunt of showers and isolated thunderstorms to occur
later tonight into Sunday morning, though likely not reaching cmi
until after 12z/Sunday. MVFR conditions to develop with showers
later tonight into Sunday morning.