Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 281806
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
106 PM CDT Sat Mar 28 2020

.SYNOPSIS...
Issued at 1134 AM CDT Sat Mar 28 2020

Showers and thunderstorms will likely affect central and southeast
IL through this evening. There is a risk of severe storms through
this evening. Locally heavy rains will also be possible with
thunderstorms and could produce over 1 inch of rainfall in some
areas. Expect mild temperatures in the mid to upper 70s today with
breezy southerly winds. Generally dry and seasonably cool weather
will return to the area overnight Saturday night and Sunday along
with very windy conditions.

&&

.UPDATE...
Issued at 1134 AM CDT Sat Mar 28 2020

A disturbance propagating out of northern MO into west central IL
has set off a few clusters of storms late this morning. A
disorganized frontal zone is somewhat stalled roughly just south
of I-74. The strongest storm feeding off a region of over 1000
J/KG MLCAPE have been able to produce hail over 1 inch diameter
just southeast of Springfield. This disturbance should move
steadily eastward reaching the IN state line by 1 p.m. Overturning
associated with this convection could diminish the afternoon
development of stronger instability to some degree, however there
should still be plenty of heating potential this afternoon. Given
strong lift and shear associated with the deepening low moving
into IA and the upper Midwest today, and organized by the trailing
cold front, severe thunderstorm potential continues today, and all
of central/southeast IL remains in a moderate or enhanced risk
according to SPC. Large hail and tornadoes are the primary
threats, while locally damaging downburst winds are also a threat.
Consensus of CAMS models indicate this last line of storms should
form in western IL mid afternoon, 3-5 p.m. or so, and progress
eastward through the evening hours. Updates this morning center
around trends in PoPs/thunder chances, mainly due to the late
morning convective clusters.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 400 AM CDT Sat Mar 28 2020

Early morning surface map shows warm front had lifted north to
just south of Macomb, and just north of Bloomington and Rantoul.
Warm front extends back to 998 mb low pressure over south central
KS. Temps range from upper 40s and lower 50s from Peoria north to
the mid to upper 60s in warm sector from Lincoln south with St
Louis still at 72 degrees. Also have moist dewpoints in the mid
60s in the warm sector. A severe thunderstorm watch expired in our
6 sw counties at 4 am. Scattered showers and thunderstorms were
over heart of central IL north of I-72 and se of the IL river.
More widespread showers and thunderstorms with heavy rains were
over northern IL north of I-80 and into parts of central/eastern
IA, southern WI and lower MI. Low level jet interacting with
frontal boundary aiding this convection. Held off on issuing a
flash flood watch as our convection is more isolated to scattered
and latest CAMs show convection staying less widespread over our
CWA while more widespread convection is north and ne of CWA with
the surface to 850 mb warm front. Unseasonably warm highs in the
mid to upper 70s today, with a few cities se of I-70 and from
Springfield sw reaching near 80 degrees, and will be the warmest
day since early October.

Latest models continue to deepen surface low pressure to 988 mb as
it lifts ne to west central IA by sunset, while warm front lifts
into northern IL. A cold front/dry line to push eastward to near
the MS river by sunset and sweep quickly eastward thru IL during
this evening, exiting east into IN early overnight. SPC day1
outlook continues enhanced to moderate risk of severe storms over
much of central (Shelbyville to north of Paris and northward) and
northern IL with slight risk in southeast IL. There is a 30% risk
of very large hail (2 inch diameter or larger) and 10-15% risk of
EF2 or stronger tornadoes that could be long tracked tornadoes.
Much of IL has 15% risk of damaging wind gusts. Great threat of
severe storms is during mid/late afternoon and again during this
evening as a broken squall line races eastward. Effective bulk
shear values greater than 50 kts this afternoon/evening along
with ML Capes of 1500-2500 j/kg by late afternoon. Storm relative
helicities of 300-500 m2/s2 from strengthening low level jet to
enhance tornado development and some possibly strong and longer
track ones racing ne. SPC said an upgrade to a high risk may be
considered in later day 1 updates for portion of our region.

Convection to shift east of IL overnight with strong sw winds
behind the cold front. Lows overnight in the mid 40s over the IL
river valley, and upper 40s to around 50 in eastern IL, mildest
near the Wabash river.

.LONG TERM...(Sunday through Friday)
ISSUED AT 400 AM CDT Sat Mar 28 2020

Strong low pressure of 992 mb will lift to northern Lake MI and
eastern upper MI by early Sunday afternoon and its wrap around
moisture could skirt far northern/ne CWA with isolated light
showers north of I-74. Main wx story Sunday will be the strong
west winds with gusts of 35 to 45 mph late Sat night into Sunday.
May eventually need a wind advisory on Sunday north of I-70. Highs
Sunday range from mid 50s ne CWA where mostly cloudy skies
prevail, to the lower 60s sw CWA where more sunshine expected
Sunday.

Winds gradually diminish during Sunday night as large low pressure
weakens as it pushes eastward toward the southern Quebec/Ontario
province line by dawn Monday. More sunshine and lighter winds on
Monday to make for a nice day. Highs Monday in the upper 50s and
lower 60s, mildest over sw CWA and southeast IL. Lows Mon night in
the upper 30s and lower 40s as clouds increase.

The 00Z forecast model suite continues to show weak low pressure
moving through the deep south on Tuesday, as upper level trof/low
moves over the mid MS and lower OH river valley. Models have
trended further south with this system, so likely rain chances
have correspondingly shifted southward, with highest pops over our
southern CWA on Tue while isolated thunderstorms should be in far
southern IL into southeast MO and southern KY on Tue afternoon.
Models have trended a few degrees cooler with highs Tue in the
upper 40s to near 50 degrees with cloudy skies.

Weak high pressure ridge to settle over IL and mid MS river valley
late Tue night, returning drier weather Tue night and early Wed.
A northern stream upper level low moves east over the northern
plains late Wed and could bring small chances of light rain
showers into central IL on Wed afternoon/evening. High pressure
over the gulf coast states on Wed will block moisture into IL so
any pcpn amounts should be quite light if they happen. Highs Wed
mostly in the lower 50s. Generally dry and seasonable temperatures
expected Thu thru next Saturday with highs of 50 to 55 degrees
and lows in the mid to upper 30s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 106 PM CDT Sat Mar 28 2020

Scattered showers and thunderstorms are active across the central
IL terminals at 18Z, producing a variety of flight conditions.
Although a lull in significant storm activity could take place for
a few hours this afternoon, additional thunderstorms, likely
strong and severe, should develop by around 20Z in western IL,
becoming more organized and sweeping eastward through the
terminals through this evening. There is a good chance a line of
strong storms should sweep through the terminals by around 00Z,
and have included a tempo group for thunderstorms with this
activity, although more uncertainty exists with potential for a
second line later in the evening. Outside thunderstorms,
predominant conditions should become VFR by around 20-22Z. A
return to MVFR cigs expected around 09Z. Winds generally variable
and disorganized initially due to recent thunderstorm activity
and a warm front roughly just south of I-74, but should become
S15-20g25-30 kts by this afternoon, shifting to WSW 20-25G35 kts
overnight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...37
SYNOPSIS...37
SHORT TERM...07
LONG TERM...07
AVIATION...37


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