Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 211740

Area Forecast Discussion
National Weather Service Lincoln IL
1240 PM CDT Wed Mar 21 2018

Issued at 1030 AM CDT Wed Mar 21 2018

Made some minor updates to temperatures for this afternoon to
tweak highs up a bit south of I-72, and down a bit along the
Indiana border and from Peoria-Danville.

A northerly flow will keep conditions unseasonably cool once again
across central and southeast Il, with highs in the 43-48 range
this afternoon. Most of the clouds have cleared the area, except
for some lingering high cirrus. May see some diurnal CU pop up in
parts of central IL this afternoon, but this should not have much
influence on the temperatures.

With the strong low pressure system off the mid-Atlantic coast,
the pressure gradient in far eastern IL is still strong enough to
produce wind gusts of 20-25 mph. This will continue into early
afternoon and then slack off later this afternoon.


.SHORT TERM...(Today and tonight)
ISSUED AT 321 AM CDT Wed Mar 21 2018

1000mb low centered over West Virginia continues to produce snow
across the Ohio River Valley early this morning: however, regional
radar mosaic and 08z/3am obs indicate the light snow has ended
across the far SE KILX CWA. As the low tracks further away, skies
will gradually clear from north to south across the area this
morning. Latest satellite imagery already shows considerable
thinning of the overcast from Wisconsin into northern Illinois.
Based on HRRR forecast, it appears locations along/west of I-55
will clear soonest...with areas further east hanging on to partial
diurnal cloud cover into the afternoon. Despite increasing amounts
of sunshine, northerly winds of 10-15mph will keep high
temperatures in the middle 40s. As the pressure gradient weakens
further, winds will become light/variable tonight as low
temperatures dip into the middle to upper 20s.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 321 AM CDT Wed Mar 21 2018

High pressure will begin to shift east of the region on Thursday,
allowing a weak impulse to approach from the northwest. Models
have been consistently showing this feature for days: however,
they have not been able to resolve its exact track. 00z Mar 22
models are in much better agreement, showing the subtle short-wave
tracking north of a developing warm front and producing a band of
light precip across mainly the S/SW KILX CWA. GFS/NAM are nearly
identical with their QPF fields, with the ECMWF being slightly
further southwest. Based on model consensus, have included chance
PoPs for light rain along/southwest of a
Lawrenceville line Thursday/Thursday evening.

Once this system passes, a stronger short-wave crossing the
Rockies will lead to surface cyclogenesis over eastern Colorado on
Friday. The low will deepen as it tracks eastward, with models
taking it across southern Illinois into the Ohio River Valley on
Saturday. Strong synoptic lift and increasing deep-layer moisture
ahead of the low will create widespread precipitation primarily
Friday night into Saturday. While high temperatures on Friday will
be in the lower 50s, cool/dry easterly flow preceding the system
will allow for enough cooling to potentially cause some precip
type issues across the northern CWA Friday night/Saturday morning.
Forecast soundings suggest a rain/snow mix or perhaps a change to
all snow north of a Hoopeston line.
Further north, a swath of significant snowfall will be possible
from eastern Iowa across north-central Illinois. Will need to keep
a close eye on the exact track of the low, as it will play an
important role in the positioning of the heavy snow axis as well
as potential snow accumulations across the northern CWA. At this
point, will mention a rain/snow mix across the far N/NE Friday
night into Saturday morning...with a minor snow accumulation
possible. As the low tracks into the Ohio River Valley and colder
air is pulled southward, the rain may mix with or change to snow
further south into central Illinois Saturday afternoon/evening
before the precip exits into Indiana.

Quiet weather will return early next week, with all models showing
a break in the active pattern for Sunday and Monday. With upper
heights rising, temperatures will respond accordingly...climbing
well into the 50s by Monday. In fact, numeric guidance suggests
temps may be considerably warmer with readings reaching the 60s.
The next storm system looks to come into the picture by Tuesday
when high chance to likely PoPs for rain are warranted.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1240 PM CDT Wed Mar 21 2018

VFR conditions can be expected during the entire 24 hour TAF
period. The only concern will be low level winds in eastern IL
this afternoon. The gradient between low pressure off of the mid-
Atlantic coast and high pressure in the southern Plains will
produce brisk N-NNW winds, particularly east of I-57. There may be
a gust up to 20-22kts at times, but not often enough to include
in the KCMI TAF.

The high pressure ridge axis will move into central IL by daybreak
Thursday. This will result in a rapid diminishing of the wind
early this evening, which is expected to continue through Thursday




LONG TERM...Barnes
AVIATION...Miller is the U.S. government's official web portal to all federal, state and local government web resources and services.