WW 340 TORNADO IL MO 171250Z - 172000Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 340
NWS Storm Prediction Center Norman OK
750 AM CDT Wed Jun 17 2026
The NWS Storm Prediction Center has issued a
* Tornado Watch for portions of
Central and Northern Illinois
Far Northeast Missouri
* Effective this Wednesday morning and afternoon from 750 AM
until 300 PM CDT.
* Primary threats include...
A few tornadoes and a couple intense tornadoes possible
Widespread damaging winds expected with isolated significant
gusts to 85 mph possible
Scattered large hail and isolated very large hail events to 2.5
inches in diameter possible
SUMMARY...An intense line of storms with history of significant wind
gusts across Iowa will continue to quickly progress
east-southeastward into and across central/northern Illinois early
today. This includes a significant potential for wind damage aside
from an increasing risk for tornadoes, as well as bouts of large
hail.
The tornado watch area is approximately along and 70 statute miles
north and south of a line from 20 miles south southwest of
Burlington IA to 35 miles east of Champaign IL. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU0).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Tornado Watch means conditions are favorable for
tornadoes and severe thunderstorms in and close to the watch
area. Persons in these areas should be on the lookout for
threatening weather conditions and listen for later statements
and possible warnings.
&&
OTHER WATCH INFORMATION...CONTINUE...WW 339...
AVIATION...Tornadoes and a few severe thunderstorms with hail
surface and aloft to 2.5 inches. Extreme turbulence and surface wind
gusts to 75 knots. A few cumulonimbi with maximum tops to 600. Mean
storm motion vector 30045.
...Guyer
WW 0340 Status Updates
STATUS REPORT ON WW 340
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 35 E IRK TO
25 SW PIA TO 25 WNW MMO.
..THORNTON..06/17/26
ATTN...WFO...LSX...DVN...ILX...LOT...
STATUS REPORT FOR WT 340
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
ILC001-009-013-017-019-021-023-029-035-039-041-045-053-061-063-
075-083-099-105-107-113-115-117-123-125-129-135-137-139-143-147-
149-155-167-169-171-173-179-183-203-171740-
IL
. ILLINOIS COUNTIES INCLUDED ARE
ADAMS BROWN CALHOUN
CASS CHAMPAIGN CHRISTIAN
CLARK COLES CUMBERLAND
DE WITT DOUGLAS EDGAR
FORD GREENE GRUNDY
IROQUOIS JERSEY LA SALLE
LIVINGSTON LOGAN MCLEAN
MACON MACOUPIN MARSHALL
MASON MENARD MONTGOMERY
MORGAN MOULTRIE PEORIA
PIATT PIKE PUTNAM
SANGAMON SCHUYLER SCOTT
SHELBY TAZEWELL VERMILION
WOODFORD
THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE
REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL
WW 0339 Status Updates
STATUS REPORT ON WW 339
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 40 ESE LWD
TO 30 NNE DBQ.
..THORNTON..06/17/26
ATTN...WFO...DMX...DVN...FSD...ARX...
STATUS REPORT FOR WS 339
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
ILC015-071-073-085-131-161-187-195-171540-
IL
. ILLINOIS COUNTIES INCLUDED ARE
CARROLL HENDERSON HENRY
JO DAVIESS MERCER ROCK ISLAND
WARREN WHITESIDE
IAC031-045-051-057-061-087-097-101-103-105-111-115-139-163-177-
179-183-171540-
IA
. IOWA COUNTIES INCLUDED ARE
CEDAR CLINTON DAVIS
DES MOINES DUBUQUE HENRY
JACKSON JEFFERSON JOHNSON
JONES LEE LOUISA
MUSCATINE SCOTT VAN BUREN
WAPELLO WASHINGTON
THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE
MD 1163 CONCERNING TORNADO WATCH 340... FOR CENTRAL ILLINOIS INTO WESTERN INDIANA
Mesoscale Discussion 1163
NWS Storm Prediction Center Norman OK
1043 AM CDT Wed Jun 17 2026
Areas affected...central Illinois into western Indiana
Concerning...Tornado Watch 340...
Valid 171543Z - 171745Z
The severe weather threat for Tornado Watch 340 continues.
SUMMARY...Damaging wind and tornado potential continues within
WW340.
DISCUSSION...Several broken thunderstorm clusters continue across
south-central Illinois. The leading line of this convection appears
to still be tied to the stronger cold pool/outflow producing gusts
60-65 mph in the last hour. The air mass across southern Illinois
into Indiana is only marginally unstable, however, temperatures are
warming into the mid to upper 70s F under mostly sunny skies with
dew points in the mid to upper 60s F. Additionally, the low level
jet axis (as shown in SPC Mesoanalysis and sampled from VAD profiles
from LSX and ILX) still extends into central/southern Illinois with
ample deep layer shear for organization, which may overcome the more
marginal air mass. Hi-res CAM guidance suggests this cluster will
weaken with time into eastern Illinois. Though guidance suggests
weakening, the continued low-level jet influence and heating ahead
of the line leads to low confidence in exactly when severe potential
will decrease downstream. Trends will be monitored, with potential
for a watch to be issued downstream of WW340.
Within WW340, tornado potential continues along the southern edge of
the current ongoing cluster. Here, more favorable low-level shear
may support a tornado or two within more discrete cells.
..Thornton/Hart.. 06/17/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...IND...LOT...ILX...LSX...
LAT...LON 39649038 40128976 40508902 40528786 40078711 39678708
39268703 38808724 38798920 39219031 39649038
MOST PROBABLE PEAK TORNADO INTENSITY...100-125 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
Public Severe Weather Outlook
PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1137 AM CDT WED JUN 17 2026
...Severe thunderstorms expected over parts of the Midwest this
afternoon and tonight...
* LOCATIONS...
Central Illinois
Central Indiana
* HAZARDS...
Several tornadoes, a couple intense
Scattered damaging winds, some hurricane force
Scattered large hail, some baseball size
* SUMMARY...
Numerous severe thunderstorms are expected this afternoon into
tonight, with the peak threat centered over Illinois and
Indiana. Intense tornadoes, swaths of damaging gusts over 75 mph
and damaging wind-driven large hail will all be possible.
Preparedness actions...
Review your severe weather safety procedures for the possibility
of dangerous weather today. Stay tuned to NOAA Weather Radio,
weather.gov, or other media for watches and warnings. A tornado
watch means that conditions are favorable for tornadoes to form
during the next several hours. If a tornado warning is issued for
your area, move to a place of safety, ideally in a basement or
interior room on the lowest floor of a sturdy building.
&&
..Hart.. 06/17/2026
$$
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0759 AM CDT Wed Jun 17 2026
Valid 171300Z - 181200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS ILLINOIS
AND INDIANA...
...SUMMARY...
An outbreak of severe thunderstorms is expected today into tonight,
with the peak threat centered over Illinois and Indiana. Several
intense tornadoes, swaths of damaging gusts over 75 mph and damaging
wind-driven large hail will all be possible.
...Midwest including Illinois/Indiana/Missouri/Ohio...
A very active/potentially dangerous day is expected today into
tonight, although some sub-regional forecast details remain a bit
uncertain. This is largely attributable to an upscale-growing
intense MCS which has been evolving in the predawn hours across
central/eastern Iowa, moving south of the I-80 corridor as of 730am
CDT. Measured significant wind gusts in excess of 80 mph have been
observed before sunrise, including a measured 94 mph measured wind
gust in Marshall County, Iowa.
This intense and increasingly well-organized MCS will continue to be
influenced by an extremely strong southwesterly jet of 70 kt and
robust warm advection/moisture transport, and likely continue
southeastward from southeast Iowa into north-central/west-central
Illinois. This will likely include an increasing potential for
surface-based storms and an appreciable uptick in damaging
wind/tornado potential early today, especially on the
south-southwest flank of the MCS in closer proximity to the
northeastward-shifting warm front.
Ahead of this early activity, a warm front will push
north-northeastward across Indiana/Ohio. New severe storm
development, perhaps MCV-influenced and transitioning out of the
remnant activity and/or forming near the warm front, is possible
across Indiana into Ohio. Shear profiles will be excessive, with
tornado risk only conditional on minimal instability being present.
The result may be a isolated tornadic supercells. The warm frontal
position will need to be monitored northward toward the
Indiana/Michigan border vicinity. Even if instability is elevated
into Michigan, extreme shear and lift may still yield damaging winds
and even a tornado risk.
To the west, rapid air mass recovery is expected on the
west-southwestern flank of the early day MCS from Missouri into
central/possibly parts of northern Illinois, even where appreciable
early day MCS impacts occur early. This recovery will be fueled by
mid-June insolation/moisture content and robust advection, again
attributable to atypically robust (50-65 kt) low/mid-tropospheric
west-southwesterly flow by mid-June/diurnal standards. In the
presence of 65-70 F surface dewpoints, this will likely result in a
corridor of 2000-3500 J/kg MLCAPE.
This will likely set the stage for the development of a broken line
of intense supercells, potentially favoring prior outflow (or
outflow-augmented warm front) and post-MCS recovery zone of
differential heating across Illinois and perhaps eventually into
western Indiana. Given the clearly supercellular shear profiles and
ample venting aloft, linear storm mode is unlikely for most of the
event. Long-tracked supercells producing tornadoes and damaging
large hail are likely. Some strong to potentially intense tornadoes
are plausible given the magnitude of the low/mid-tropospheric flow,
and again potentially heightened in vicinity of the prior
outflow/warm front. Some damaging wind threat will likely also
increase by evening as storms continue across Indiana into Ohio and
potentially southward toward the Ohio River.
...Upper Texas Coast/Middle Gulf Coast...
The NHC forecast shows Potential Tropical Cyclone One moving into
southwest Louisiana by this evening. Wind fields associated with
this system will strengthen out of the south ahead of it, resulting
in areas of strong low-level shear from the upper Texas coast across
southern portions of Louisiana and eventually into southern
Mississippi. Mid to upper 70 F dewpoints will contribute to modest
CAPE values, supporting embedded stronger cells with tornadic
potential.
..Guyer/Broyles.. 06/17/2026
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1128 AM CDT Wed Jun 17 2026
Valid 171630Z - 181200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
ILLINOIS AND INDIANA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TONIGHT OVER
SOUTHEAST LOUISIANA AND SOUTHERN MISSISSIPPI...
...SUMMARY...
Numerous severe thunderstorms are expected this afternoon into
tonight, with the peak threat centered over Illinois and Indiana.
Intense tornadoes, swaths of damaging gusts over 75 mph and damaging
wind-driven large hail will all be possible.
...MO/IL/IN...
An intense and fast-moving shortwave trough continues to approach
the Midwest today, with an associated 90+ knot mid level jet
streaking across the region. A very strong southerly low-level jet
precedes this trough, and has resulted in widespread thunderstorms
over central IL. The effects of this early convection will be
important to the mesoscale details of where the main risk of severe
storms will develop later today.
The primary outflow boundary from ongoing storms currently extends
from extreme northeast MO into south-central IL, and continues to
sag southward. Strong heating is occurring to the south of the
boundary, and given the intense low-level flow, some northward
return is expected. However, it appears unlikely to substantially
destabilize as far north as earlier forecasts. The zone in vicinity
of the boundary will become very unstable by mid-late afternoon,
with forecast soundings continuing to show impressive shear values
and hodograph structures suggestive of tornadic supercell potential.
Very large hail and damaging winds will also be possible with this
activity as it tracks quickly eastward into central IN. Strong
tornadoes are possible.
By mid-evening, a line of severe storms will likely extend from
central MO into southern IN, with damaging winds becoming the
primary threat.
...Southeast MN...
A small area of heating/destabilization has developed near the
surface low over southern MN. Cold temperatures aloft and strong
deep-layer shear suggests a threat of a few severe storms capable of
hail and gusty/damaging winds this afternoon.
...LA/MS...
Tropical Storm Arthur will track northward and affect LA and
southern MS tonight. A zone of strong southerly low-level winds to
the east of the circulation will result in some concern for
overnight and pre-dawn tornadoes across southeast LA into far
southern MS.
...Southern AZ/NM...
Scattered afternoon and evening thunderstorms are expected across
southeast AZ and southwest NM. Strong heating and ample instability
will pose a risk of damaging wind gusts in the strongest cells.
..Hart/Chalmers.. 06/17/2026
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1223 PM CDT Wed Jun 17 2026
Valid 181200Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
KENTUCKY INTO THE MID-ATLANTIC AND PORTIONS OF NEW ENGLAND...
...SUMMARY...
Isolated to scattered severe thunderstorms will be possible from
Kentucky to the Mid-Atlantic, and across parts of the Northeast.
Damaging wind gusts will be the main hazard with this activity.
...Synopsis...
A potent upper trough and associated mid-level jet streak will move
into the northern Mid-Atlantic/New England Thursday morning. A deep
surface low moving through southern Ontario/Quebec will drive a
surface cold front through the regions. This front will extend
southwestward into the Ohio Valley/southern Appalachians and parts
of the central/southern Plains. The remnants of what is now Tropical
Storm Arthur will continue through parts of the Southeast.
...New England/Mid-Atlantic...
Convection will likely be ongoing ahead of the upper trough during
the morning, particularly from eastern New York into New England.
While this activity is likely to inhibit afternoon destabilization,
strong wind fields will still promote some risk for damaging winds
and perhaps a brief tornado. The strongest activity will develop by
early afternoon along the cold front and progress eastward. Bowing
segments and marginal supercell structures will be possible. The
strong low-level jet will be shifting eastward during the day, but
portions of New England will still have strong 850 mb winds during
the early/mid afternoon. If sufficient heating occurs, this is where
the tornado risk will be marginally greater.
...Kentucky/West Virginia/Virginia...
Stronger instability is expected south of the surface front on
account of richer low-level moisture. Scattered storms are expected
to form along the front by mid afternoon. Though the low-level jet
will weaken much quicker in these areas, deep-layer shear near the
front will remain sufficient for organized cells and linear
segments. These storms will move eastward through the afternoon and
pose a risk of damaging wind gusts.
...Southern Plains into Ozarks...
Elevated convection may be ongoing early in the period near and
north of the cold front in southern Kansas/southwest Missouri. These
storms could produce large hail. With time, the front will sag
southward. Strong heating of a 70+ F dewpoint airmass will
potentially promote afternoon thunderstorms capable of marginally
severe hail and isolated severe gusts. During the evening,
additional thunderstorms may develop as a modest increase in the
low-level jet occurs. Some guidance suggests this activity may
cluster into a small MCS within western Oklahoma/northwest Texas.
Where and if this occurs is not certain. Some risk for severe gusts
could extent into the evening if this occurs.
...Southeast...
The remnants of Tropical Storm Arthur will move through a very moist
(70+ F dewpoints) airmass. Local shear magnitudes will be modestly
enhanced by the remnant circulation. Scattered convection will be
capable of wind damage and perhaps a tornado or two. Portions of
Georgia may see greater surface heating ahead of the circulation. A
few stronger storms are possible here. Even so, poor mid-level lapse
rates and deep-layer shear (especially away from the circulation
center) will limit the overall severe threat.
..Wendt.. 06/17/2026
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1136 AM CDT Wed Jun 17 2026
Valid 171700Z - 181200Z
...Morning Update...
The forecast remains on track. Current satellite imagery portrays
clear skies over the western CONUS and unsettled conditions across
the Upper Midwest. In the CO West Slope and eastern Great Basin,
surface observations depict widespread sub-15% RH values, owing to
poor overnight humidity recoveries. On a broader scale, as sustained
west-northwesterly winds increase to 10-20 mph (up to 25 mph in
terrain-favored areas) this afternoon, localized critical conditions
could emerge, especially where receptive fuels exist. See the
previous discussion for more information.
..Elizalde-Garcia.. 06/17/2026
.PREV DISCUSSION... /ISSUED 0159 AM CDT Wed Jun 17 2026/
...Synopsis...
Between an expansive large-scale trough encompassing the northern
half of the CONUS and an upper ridge centered over the Southwest, a
belt of strong midlevel northwesterly flow will extend from the
Northwest into the Great Plains. To the south/southwest of this
strong midlevel flow, diurnal heating of a dry antecedent air mass
across the Great Basin into the central/southern Rockies and
adjacent High Plains will yield widespread 5-15 percent RH during
the afternoon. Moderate deep-layer flow along the periphery of the
primary belt of midlevel northwesterlies will overspread this
well-mixed boundary layer, resulting in 15-20 mph sustained
west-northwesterly surface winds across the region. Given an
expansive area of increasingly dry/receptive fuels, elevated
fire-weather conditions are expected, with locally critical
conditions possible within terrain-favored areas.
...Please see www.spc.noaa.gov/fire for graphic product...
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