Last Freeze 2015

Last Freeze 2015

Spring Freeze Climatology Update and Forecast

April 28, 2015

Nebraska map showing last spring freeze
Figure 1. Median date of last 28 °F spring freeze for Nebraska (based on 1981-2010 average). (Source: Midwest Regional Climate Center)
Nebraska map showing last spring freeze
Figure 2. Climatological date of the latest last 28 °F spring freeze (based on 1980-81 to 2009-10 average). (Source: Midwest Regional Climate Center Vegetation Impact Program)

Now that we are only days away from the mid-way point of the 2015 spring season, we can focus on when to expect that last freeze. Predicting the last freeze in some locations of Nebraska will never end. For example, at the Agate weather station in Sioux County, there is still a 10% chance of receiving a 32 °F freeze after June 25 and a 10% chance of receiving a 32 °F freeze before August 19 (based on 1900-2014 climate data)

We can compare that to the Hebron weather station in Thayer County, which has a 10% chance of receiving a 32 °F freeze after May 11 and a 10% chance of receiving a 32 °F freeze before September 25 (based on 1893-2014 climate data). 

This makes it difficult to forecast weather events for the entire state. The only thing certain about Nebraska weather is that nothing is certain (note 0% chance is not mentioned). However, using the forecast and climatology, we can assess our risk of a late spring freeze. 

When assessing freeze risk, we can look at the potential for a 28 °F (hard) freeze or a 32 °F freeze. Due to the increased risk of severe crop damage, we will focus on the 28 °F freeze. For Nebraska, the median date of the last 28 °F freeze (Figure 1) and the date of the latest-last 28 °F freeze (Figure 2) from 1981-2010, show that there is still some climatological risk for another 28 °F freeze, especially in the Panhandle. Areas south and east of North Platte have surpassed the median date, and some areas in eastern Nebraska have surpassed the 30-year latest-last freeze date.

Looking at the climate data, our risk of a hard freeze is decreasing rapidly in central and eastern Nebraska, so we can turn to the forecast to get closer to the latest frost date. The forecast for the next seven days has temperatures warming up and staying warm into next week. Nighttime lows are our biggest concern for a potential freeze, and low temperatures look to remain in the upper 30s and lower 40s the rest of this week and be in the 50s by the beginning of next week.

The most recent 6-10 day and 8-14 day outlooks (Figure 3) from the Climate Prediction Center (CPC) can be useful when looking out past seven days. The 6-10 Day outlook (released on April 28) for May 4-8, has increased odds for above normal temperatures for Nebraska and a large portion of the U.S. The 8-14 day outlook for May 6-12 has portions of Nebraska with increased chances for above normal temperatures with the cool temperatures predicted in the southwest U.S. The most recent model run keeps the freezing line up in Canada and the higher elevations in the Rockies through the middle of May. This gives us some confidence that warm temperatures should remain in the area for another two weeks, thus getting most Nebraska sites past their climatological last 28 °F freeze date.

Early May forecast
Figure 3. 6-10 Day (left) and 8-14 Day (right) Temperature Outlook released on April 28. (Source: Climate Prediction Center)

The forecast and climate data tell us that most of Nebraska may be in the clear for another hard freeze, but we all know that the Nebraska weather can surprise us. We can never be sure that we have seen the last hard freeze, however the risk is low in southern and eastern Nebraska for having temperatures below 28 °F again this spring.

Tyler Williams
Extension Educator


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