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fxus63 kilx 211154 

Area forecast discussion
National Weather Service Lincoln Illinois
654 am CDT Sat Sep 21 2019

issued at 314 am CDT Sat Sep 21 2019

A slow-moving cold front will bring significant rainfall to
central Illinois this weekend. The heaviest rain of 3 to 4 inches
will be focused west of the Illinois River...with amounts
decreasing to 1 inch or less further southeast along and south of
the I-70 corridor.


Short term...(today and tonight)
issued at 314 am CDT Sat Sep 21 2019

07z/2am surface analysis shows high pressure anchored along the
East Coast...while a cold front extends across the Western
Plains. In between these two features, increasing southwesterly
flow continues to bring an unseasonably warm and moist airmass
into the region. The 00z Sep 21 kilx upper air sounding indicated
precipitable water of 1.61, while an upstream value of 1.81 was
noted at ksgf. Models continue to suggest these values will
increase to greater than 2 inches later today through Sunday,
which would be at or above record levels for this time of year.
With copious amounts of deep-layer moisture available, the only
missing element needed for rainfall is a forcing mechanism. A
short-wave trough noted on latest water vapor imagery over the
Southern Plains will track northeastward and provide the necessary
forcing to trigger showers and thunderstorms across the western
half of the kilx County Warning Area today. Latest radar imagery is showing
scattered showers beginning to develop across central/eastern
Missouri in advance of this wave, and these will increase in areal
coverage over the next few hours as they spread into the Illinois
River valley. Based on model consensus, have gone with likely
pops along/west of a Bloomington to Jacksonville line. Rain
chances will steadily decrease further east, with dry conditions
expected east of the I-57 corridor. High temperatures will range
from the upper 70s in the Illinois River the upper 80s
south of I-70. The initial short-wave will lift into the Great
Lakes this evening: however, the main upper low currently churning
over the Great Basin/northern rockies will begin to shift
eastward tonight. As it does, increasing synoptic lift along/ahead
of its associated cold front will produce widespread showers and
thunderstorms in the Illinois River valley. Have increased pops to
100 percent across this area accordingly, but have maintained dry
conditions across the east/southeast through the entire night.

Long term...(sunday through friday)
issued at 314 am CDT Sat Sep 21 2019

A rainy day will be on tap for much of central Illinois on Sunday
as the wave and cold front slowly approach from the west. The
exception will be south of I-70 where showers will hold off until
late afternoon. The wave will accelerate Sunday evening, with all
models showing it exiting Illinois overnight. As a result, have
carried likely to categorical pops across the board during the
evening, then have ended pops across the western half of the area
after midnight. By the time the rain comes to an end everywhere by
Monday morning, storm total rainfall totals will range from 1
inch or less along/south of as much as 3 to 4 inches
northwest of the Illinois River. Given expected rainfall, have
continued the Flash Flood Watch for all counties along and west of
the Illinois River through Sunday night.

High pressure building into the region behind the departing front
will bring cooler/drier weather for Monday and Tuesday as the
upper flow becomes zonal. A short-wave trough is progged to dig
southeastward out of the northern plains by the middle of the
week, pushing another weak frontal boundary into central Illinois
by late Wednesday. Models still exhibit some timing discrepancies
with this feature: however, it appears the primary time frame for
scattered showers/thunder will be Wednesday afternoon and night.
After that, the front will stall...then will lift back northward
as a warm front by Friday as an impressive upper ridge builds over
the Midwest. Both the GFS and European model (ecmwf) suggest high temperatures will
return to summerlike readings in the middle to upper 80s by
the end of the week.


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 654 am CDT Sat Sep 21 2019

Showers and thunderstorms will increase from west to east through
the upcoming 24 hours as a cold front slowly approaches from the
west. Several disturbances ahead of the front will bring
occasional showers and thunderstorms, although timing and track of
each generally remains somewhat uncertain. Have included tempo
MVFR conditions with thunderstorms and rain at kpia from 15z-19z for the first
significant disturbance expected. Following this, have included
predominant rain showers with thunderstorms in the vicinity after 00z for kpia, kbmi, and kspi,
with just vcsh mentioned to the east at kdec and kcmi. Winds S
around 10 kts this morning, increasing to around 15 kts with gusts
20-23 kts after 15z. Gusts decreasing after 00z, but S winds
12-15 kts continuing.


Ilx watches/warnings/advisories...
Flash Flood Watch from this evening through late Sunday night
for ilz027>031-036-037-040-041-047>050.



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