Special Weather Statement, NWS Lincoln, IL

Area Forecast Discussion
National Weather Service Lincoln IL
553 AM CDT Thu Jul 29 2021

.SYNOPSIS...
Issued at 156 AM CDT Thu Jul 29 2021

Oppressive heat is expected today as heat index values surge into
the triple digits. Showers and thunderstorms will likely develop
later this afternoon and extend into early evening along and ahead
of a cold front. A few of these storms may become severe with
damaging winds, large hail, localized flash flooding, and even a
tornado possible. Cooler temperatures arrive Friday and will
extend into early next week.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 156 AM CDT Thu Jul 29 2021

Impactful weather is expected today across the region as a dual
threat bears down on the Midwest. Dangerous heat has triggered a
Heat Advisory for this afternoon, while a severe weather episode
looms by evening.

Dangerous Heat:
The periphery of a 594mb heat ridge continues to build eastward
into portions of the Mississippi and Ohio River Valleys.
Temperatures are expected to warm into the lower 90s this
afternoon juxtaposed to surface dewpoints climbing into the upper
70s. This combination of heat and humidity will produce heat index
values between 105F - 110F, and has prompted a Heat Advisory for
our entire outlook area until 8 PM CDT.

Severe Weather Potential:
All eyes remain on the MCC pushing across WI/IA/IL early this
morning. While convection may linger into the daylight hours
across northern IL, the expectation is for this complex of storms
to weaken as the LLJ begins to recede and the main mid- level
shortwave departs toward the eastern Great Lakes region. A quick
glance at LOT/DVN Radar imagery reveals a pair of outflow
boundaries that are sagging southward across northern Illinois
ahead of a weakly forced cold front. This convective debris will
prove critical for storm re- initiation later this afternoon.

The boundary layer will become very unstable today ahead of the
cold front, and will be aided by an elevated mixed-layer that
advects in from the northwest. Upper 70s surface dewpoints and
steep mid- level lapse rates will yield highly buoyant parcels
(4000-5000 J/kg SBCAPE) ahead of the front as a capping inversion
erodes by 18z. At this time, it is not clear whether convective
initiation will occur along a pre-existing outflow boundary, or
the front, as both features figure to lie in fairly close
proximity to each other early this afternoon.

As with any severe weather setup, there are a few limiting
factors. Today, the main one is insufficient deep layer shear.
With the upper- level jet core displaced northward across the
Great Lakes region, central Illinois will only have 20-25 kts of
deep layer shear to work with. This figures to limit the amount of
updrafts that can become organized/severe this afternoon. Other
limiting factors include weak surface convergence and the lack of
a definable mid- level shortwave trough to help enhance forcing.
Nevertheless, we do anticipate isolated instances of severe
weather to develop later this afternoon given the supreme
instability in place. Storm- relative hodographs favor mostly
multi-cell clusters, but a few discrete cells cannot be ruled out,
especially east of I-57 where shear will be highest. Thus, all
severe weather hazards remain possible going into early evening.
Localized flash flooding is also a concern given the very humid
air mass. The HREF is signaling some 1"+/hr rates across the
area.

The front will push south of our outlook area by 03z, and skies
will begin to clear from north to south in its wake. Overnight
lows will cool into the mid-to-upper 60s.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 156 AM CDT Thu Jul 29 2021

Cooler and drier conditions will return by Friday as surface high
pressure begins to build in from the north. The NBM knocks
temperatures down into the mid-to-lower 80s heading into this
weekend as the 594mb heat ridge gets squeezed westward by a
strong upper- level low developing over the Hudson Bay.

Showers and thunderstorms will remain a possibility late Friday
evening into Saturday, mainly south of a Galesburg to
Lawrenceville line, as an MCS skirts the Mid-Mississippi Valley.
A stretch of drier but continued cool weather then looks likely by
Sunday as another cold front pushes across the region. These
cooler conditions will remain in place through the middle of next
week with daily highs in the low 80s and overnight lows near 60.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 538 AM CDT Thu Jul 29 2021

Convective debris from overnight thunderstorms across WI/IA/IL has
laid out a cirrus shield and multiple outflow boundaries. Despite
these features, VFR conditions are expected to persist throughout
much of the TAF period. A slow moving cold front will move from
north to south this afternoon, bringing isolated-to-scattered
thunderstorms with cloud bases between 4-5 kft across the
regional terminals. Skies will scatter out and gradually clear
from north to south beyond 03z.

Surface winds will be from the west sustained around 10-15 kts
with occasional gusts to 25 kts this afternoon, then becoming
west-northwest and diminishing to 4-9 kts this evening in the wake
of frontal passage.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 10 AM this morning to 8 PM CDT this evening
for ILZ045-046-055>057-062-063-066>068-071>073.

Heat Advisory until 8 PM CDT this evening for ILZ027>031-036>038-
040>044-047>054-061.

&&

SYNOPSIS...MJA
SHORT TERM...MJA
LONG TERM...MJA
AVIATION...MJA

Hazardous Weather Outlook
National Weather Service Lincoln IL
638 AM CDT Thu Jul 29 2021

ILZ045-046-055-301145-
Champaign-Douglas-Vermilion-
638 AM CDT Thu Jul 29 2021

...HEAT ADVISORY IN EFFECT FROM 10 AM THIS MORNING TO 8 PM CDT
THIS EVENING...

This Hazardous Weather Outlook is for portions of east central
Illinois.

.DAY ONE...TODAY AND TONIGHT...

Scattered thunderstorms will develop this afternoon and evening.
Some of the storms could become severe, with damaging winds and
large hail. Locally heavy rainfall is also possible.

Heat index values will reach 102 to 108 degrees this afternoon.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY...

Isolated to scattered thunderstorms will be possible at times
Friday night through Saturday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed between 4 pm and 9 pm.

ILZ027>031-036>038-041>044-053-054-301145-
De Witt-Fulton-Knox-Logan-Macon-Marshall-Mason-McLean-Moultrie-
Peoria-Piatt-Stark-Tazewell-Woodford-
638 AM CDT Thu Jul 29 2021

...HEAT ADVISORY IN EFFECT UNTIL 8 PM CDT THIS EVENING...

This Hazardous Weather Outlook is for portions of central
Illinois, east central Illinois and west central Illinois.

.DAY ONE...TODAY AND TONIGHT...

Heat index values will reach 102 to 110 degrees this afternoon.

Scattered thunderstorms will develop this afternoon and evening.
Some of the storms could become severe, with damaging winds and
large hail. Locally heavy rainfall is also possible.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY...

Isolated to scattered thunderstorms will be possible at times
Friday night through Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed between 4 pm and 9 pm.

ILZ040-047>052-061-301145-
Cass-Christian-Menard-Morgan-Sangamon-Schuyler-Scott-Shelby-
638 AM CDT Thu Jul 29 2021

...HEAT ADVISORY IN EFFECT UNTIL 8 PM CDT THIS EVENING...

This Hazardous Weather Outlook is for portions of central
Illinois and west central Illinois.

.DAY ONE...TODAY AND TONIGHT...

Heat index values will reach 102 to 110 degrees this afternoon.

Scattered thunderstorms will develop this afternoon and evening.
Some of the storms could become severe, with damaging winds and
large hail. Locally heavy rainfall is also possible.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY...

Isolated to scattered thunderstorms will be possible at times
Friday night through Saturday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed between 4 pm and 9 pm.

ILZ056-057-062-063-066>068-071>073-301145-
Clark-Clay-Coles-Crawford-Cumberland-Edgar-Effingham-Jasper-
Lawrence-Richland-
638 AM CDT Thu Jul 29 2021

...HEAT ADVISORY IN EFFECT FROM 10 AM THIS MORNING TO 8 PM CDT
THIS EVENING...

This Hazardous Weather Outlook is for portions of east central
Illinois and southeast Illinois.

.DAY ONE...TODAY AND TONIGHT...

Heat index values will reach 105 to 110 degrees this afternoon.

Scattered thunderstorms will develop this afternoon and evening.
Some of the storms could become severe, with damaging winds and
large hail. An isolated tornado is possible as well.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY...

Isolated to scattered thunderstorms will be possible at times
Saturday and Saturday night.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed between 4 pm and 9 pm.

Shimon

Special Weather Statement
National Weather Service Lincoln IL
743 AM CDT Thu Jul 29 2021

ILZ028>031-037-291345-
Tazewell-Marshall-Peoria-Woodford-Stark-
743 AM CDT Thu Jul 29 2021

...SIGNIFICANT WEATHER ADVISORY FOR MARSHALL...WOODFORD...SOUTHERN
STARK...NORTHEASTERN TAZEWELL AND NORTHEASTERN PEORIA COUNTIES UNTIL
845 AM CDT...

At 743 AM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Camp Grove to near West Jersey. Movement
was southeast at 35 mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
these storms.

Locations impacted include...
Peoria, Eureka, Lacon, East Peoria, Morton, Washington, Chillicothe,
Metamora, Germantown Hills, Henry, Minonk, Roanoke, Princeville,
Rome, Wyoming, Dunlap, Toulon, Washburn, Bradford and Spring Bay.

This includes the following highways...
 Interstate 155 between mile markers 30 and 31.
 Interstate 39 between mile markers 20 and 29.
 Interstate 474 near mile marker 14.
 Interstate 74 near mile marker 93, and between mile markers 98 and
105.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 4115 8964 4115 8939 4112 8934 4110 8935
      4110 8932 4094 8905 4093 8904 4093 8903
      4086 8893 4058 8949 4107 8992 4120 8964
TIME...MOT...LOC 1243Z 328DEG 29KT 4112 8955 4101 8984

Shimon