Changes to Cold Weather Related Headlines

A number of changes are being made to our cold weather related watches, warnings and advisories, beginning this winter.

Terminology:

New Product Name	Old Product Name	Issuance Criteria
Extreme Cold Watch	Wind Chill Watch	Greater than 50% confidence that apparent temperatures will reach warning criteria
Extreme Cold Warning	Wind Chill Warning	Greater than 80% confidence that apparent temperatures will reach warning criteria
Cold Weather Advisory	Wind Chill Advisory	Greater than 80% confidence that apparent temperatures will reach advisory criteria

Reasoning:

Apparent temperatures are not only driven by wind speeds.
It is not unusual for actual temperatures to be cold enough by themselves to reach the old "wind chill warning/advisory" criteria. However, if the wind is calm, there is no wind chill, so it would not really be accurate to issue a "wind chill" related product.
No changes have been made to the confidence levels needed to issue these products.
No changes are being made to the actual calculation of wind chill.

Criteria:

Issuance criteria is a bit different than past years.

Previously, the criteria would typically be established based on NWS office boundaries, rather than by geography. This did not necessarily make sense, as you could have areas further south have a lower criteria than further north. The issuance criteria has been adjusted to use geography, with the guidance also factoring in public health expertise.

Extreme Cold Watch and Warning criteria:

Extreme Cold Warning criteria

Old Criteria	New Criteria
-25°F or colder across all of central and southeast Illinois	-25°F or colder: Along and north of I-72/Danville. This includes areas around Galesburg, Peoria, Bloomington, Springfield, Decatur, and Champaign. -20°F or colder: Along and south of a Taylorville to Paris line. This includes areas around Shelbyville, Tuscola, Mattoon, Effingham, and Olney.

Old Criteria

New Criteria

-25°F or colder across all of central and southeast Illinois

-25°F or colder: Along and north of I-72/Danville. This includes areas around Galesburg, Peoria, Bloomington, Springfield, Decatur, and Champaign.

-20°F or colder: Along and south of a Taylorville to Paris line. This includes areas around Shelbyville, Tuscola, Mattoon, Effingham, and Olney.

Cold Weather Advisory criteria:

Cold Weather Advisory criteria

Old Criteria	New Criteria
-15°F to -24°F across all of central and southeast Illinois	-15°F to -24°F: Along and north of I-72/Danville. This includes areas around Galesburg, Peoria, Bloomington, Springfield, Decatur, and Champaign. -10°F to -20°F: Along and south of a Taylorville to Paris line. This includes areas around Shelbyville, Tuscola, Mattoon, Effingham, and Olney.

Old Criteria

New Criteria

-15°F to -24°F across all of central and southeast Illinois

-15°F to -24°F: Along and north of I-72/Danville. This includes areas around Galesburg, Peoria, Bloomington, Springfield, Decatur, and Champaign.

-10°F to -20°F: Along and south of a Taylorville to Paris line. This includes areas around Shelbyville, Tuscola, Mattoon, Effingham, and Olney.