Freeze Risk Forecasts
Of the dozen or so devastating freezes that have impacted the citrus industry and other agriculture concerns over the last century or in the Southeast, nearly all of them occurred during times of Neutral conditions in the Pacific Ocean, when there is neither El Niño or La Niña present. The table below lists the impact freezes and the corresponding Phase of the Pacific Ocean.
| Freeze Event | Climate Phase |
|---|---|
| December 1894 | Neutral |
| February 1899 | Neutral |
| December 1934 | Neutral |
| January 1940 | Neutral |
| December 1962 | Neutral |
| January 1977 | El Niño |
| January 1981 | Neutral |
| January 1982 | Neutral |
| December 1983 | Neutral |
| January 1985 | Neutral |
| December 1989 | Neutral |
| January 1997 | Neutral |
Risk of damaging freezes lower during 2010-2011
During La Niña winters the preferred or average setup of the jet steam is that of high pressure or "ridging" over the Pacific near the U.S. west coast and low pressure or "troughing" over the mid-section of the country. This configuration tends to steer winter storms up the Mississippi Valley and Midwest. This jet stream configuration also causes severe or damaging freezes to be less likely during La Niña than in neutral years. However, the risk of early or late season freezes (like in April of 2007) does not seem to be affected by the Pacific Ocean. To view a map of probabilities of reaching critical temperatures at least once during this winter visit our freeze risk tool at: www.agroclimate.org/tools/freez/
Early Season Freezes
We have found no connection between the Pacific Ocean and first frost/freeze dates. Presented here are the expected dates of first freezes at the 10%, 50%, and 90% probability levels. 50% probability maps show the average dates when the first 32°F freeze occurs in your county. In practical terms it means that half of the freezes occurred before that date and half after that date. 10% probability maps show how soon the first freeze can occur. In practical terms it means that in 1 out of 10 years, the first freeze will occur that soon. 90% probability maps show the other side of the probability distribution. In practical terms it means that in 9 out 10 years, the first freeze occurs before that date, or only in 1 out 10 years the first freeze will occur by or after that date.
First Freeze Dates
Late Season Freezes
We have found no connection between the Pacific Ocean and last freeze dates. Presented here are the expected dates of last freezes at the 10%, 50%, and 90% probability levels. 50% probability maps show the average dates when the last 32°F freeze occurs in your county. In practical terms it means that half of the freezes occurred before that date and half after that date. 10% probability maps show how late the last freeze can occur. In practical terms it means that in 1 out of 10 years, the last freeze will occur by that date or later. 90% probability maps show the other side of the probability distribution. In practical terms it means that in 9 out 10 years, the last freeze occurs by that date or later, or only in 1 out 10 years the last freeze will occur that soon.
Last Freeze Dates