By Matthew Sittel
After a cold March, April started out warm in Kansas. The average statewide temperature for the first four days of April was over 6 degrees above normal. The warmest day of the year across much of eastern Kansas was April 4, with afternoon highs in the 80s in most areas. The next morning, temperatures had tumbled into the 20s and 30s. Those waiting for warmer weather endure uncertainty every year. When will it be safe to plant? How much risk should one take to get an earlier start on planting? In this report, we explore the chances of a freeze after April 1 across Kansas.
The National Centers for Environmental Information (NCEI) have calculated average daily high and low temperatures for thousands of locations across the US. These averages, based on the period 1991-2020, can be used to calculate the probabilities of a freeze for any location on any given day. Here in Kansas, there are 167 available sites with daily normals. This report examines 27 of these sites, three in each of Kansas’ nine climate divisions (Table 1).
To help interpret Table 1, take a look at the row for Manhattan. In the column headed by “Apr 10,” we see 93%. This percentage is the chance of a freeze on or after the given date. For this example, there is a 93% chance of a freeze occurring on or after April 10 in Manhattan. Two columns to the right, we see there is a lower chance, 62%, of a freeze on or after April 20. By the end of April, the chance of a freeze is only 24%, and on or after May 10, it drops to 6%.
After the first of April, a freeze is still likely to occur statewide. We saw a freeze this week, on the morning of April 5, when the entire state, except for southeast and far east central Kansas, fell below freezing. By late April, there is a wide range of probabilities. There is still an 80% chance of a freeze on or after April 30 in Goodland, but just an 8% chance in both Olathe and Fort Scott. On or after May 15, the risk of a freeze is under 10% except in parts of northwest and west central Kansas.
The impact of low temperatures on newly emerged crops will vary depending on how low the temperature drops, the duration of the low temperatures, and other factors. Using historical weather data, we can get a better idea of the risk of frost (36° or colder), a freeze (32° or colder), and a hard freeze (28° or colder). Table 2 contains probabilities of these three events for the same nine dates in Table 1, but rather than individual locations, the table contains average dates across all the locations within each climate division.
There is a greater than 90% chance of a frost on or after April 15 across the entire state. A freeze is likely in all divisions, but the chances of a hard freeze are less than 50% in eastern Kansas, but 90% in northwest Kansas. There is an 80% or better chance of a frost in western Kansas on or after April 30, and in northwest Kansas, there is still a 42% chance of a frost on or after May 15.
Table 1. Probabilities of a freeze (a minimum temperature of 32°F or less) occurring at selected Kansas locations on or after the given dates, based on 1991-2020 NCEI daily climate normals.
Region | Location | Apr 5 | Apr 10 | Apr 15 | Apr 20 | Apr 25 | Apr 30 | May 5 | May 10 | May 15 |
Northwest | Goodland | >99% | >99% | >99% | 99% | 94% | 80% | 57% | 33% | 15% |
Hill City | >99% | >99% | 98% | 91% | 76% | 54% | 32% | 16% | 7% |
Oberlin | >99% | >99% | >99% | 98% | 91% | 76% | 54% | 32% | 16% |
North Central | Beloit | 99% | 95% | 84% | 66% | 45% | 27% | 14% | 6% | 2% |
Phillipsburg | >99% | >99% | 98% | 90% | 73% | 48% | 26% | 12% | 4% |
Washington | >99% | 99% | 95% | 84% | 64% | 41% | 23% | 11% | 5% |
Northeast | Holton | >99% | 98% | 93% | 80% | 62% | 42% | 26% | 14% | 6% |
Manhattan | 98% | 93% | 81% | 62% | 41% | 24% | 13% | 6% | 2% |
Troy | 99% | 95% | 84% | 67% | 46% | 29% | 16% | 8% | 3% |
West Central | Scott City | >99% | >99% | >99% | 97% | 89% | 70% | 45% | 24% | 10% |
WaKeeney | >99% | 99% | 96% | 87% | 68% | 44% | 23% | 10% | 4% |
Wallace | >99% | >99% | >99% | 99% | 93% | 79% | 55% | 30% | 13% |
Central | Ellsworth | >99% | 99% | 96% | 86% | 67% | 43% | 23% | 10% | 4% |
Hays | 99% | 97% | 91% | 78% | 57% | 35% | 17% | 6% | 2% |
Marion | 88% | 74% | 55% | 35% | 19% | 9% | 4% | 1% | <1% |
East Central | Emporia | 93% | 81% | 63% | 42% | 24% | 12% | 5% | 2% | 1% |
Olathe | 87% | 72% | 52% | 32% | 17% | 8% | 3% | 1% | <1% |
Topeka | 93% | 82% | 64% | 44% | 27% | 14% | 7% | 3% | 1% |
Southwest | Dodge City | 99% | 97% | 89% | 74% | 53% | 31% | 16% | 7% | 2% |
Garden City | >99% | 99% | 97% | 89% | 72% | 47% | 26% | 12% | 4% |
Hugoton | 99% | 96% | 87% | 69% | 45% | 22% | 9% | 3% | 1% |
South Central | Larned | 99% | 95% | 85% | 67% | 44% | 23% | 10% | 4% | 1% |
Medicine Lodge | 92% | 82% | 67% | 48% | 30% | 16% | 8% | 3% | 1% |
Wichita | 87% | 74% | 57% | 39% | 23% | 11% | 4% | 1% | <1% |
Southeast | Coffeyville | 81% | 65% | 46% | 29% | 16% | 7% | 3% | 1% | <1% |
Eureka | 98% | 93% | 81% | 62% | 40% | 22% | 10% | 4% | 1% |
Fort Scott | 87% | 71% | 51% | 31% | 16% | 8% | 4% | 2% | 1% |
Region | Location | Apr 5 | Apr 10 | Apr 15 | Apr 20 | Apr 25 | Apr 30 | May 5 | May 10 | May 15 |
Table 2. Probabilities of minimum temperatures at or below 36°, 32°, and 28°F across each of the nine Kansas climate divisions on or after the given dates, based on 1991-2020 NCEI daily climate normals.
Region | Threshold | Apr 5 | Apr 10 | Apr 15 | Apr 20 | Apr 25 | Apr 30 | May 5 | May 10 | May 15 |
Northwest | 36° | >99% | >99% | >99% | >99% | >99% | 97% | 88% | 67% | 42% |
32° | >99% | >99% | >99% | 98% | 90% | 73% | 49% | 28% | 13% |
28° | 99% | 97% | 90% | 76% | 54% | 33% | 17% | 7% | 3% |
North Central | 36° | >99% | >99% | >99% | 99% | 94% | 80% | 58% | 34% | 16% |
32° | >99% | 99% | 95% | 85% | 65% | 42% | 23% | 10% | 4% |
28° | 96% | 87% | 70% | 49% | 29% | 14% | 6% | 2% | 1% |
Northeast | 36° | >99% | >99% | 98% | 92% | 78% | 58% | 37% | 20% | 9% |
32° | 98% | 94% | 82% | 63% | 42% | 24% | 12% | 5% | 2% |
28° | 85% | 69% | 48% | 29% | 15% | 7% | 3% | 1% | <1% |
West Central | 36° | >99% | >99% | >99% | >99% | 99% | 96% | 83% | 59% | 33% |
32° | >99% | >99% | 99% | 97% | 87% | 67% | 42% | 21% | 9% |
28° | 99% | 96% | 87% | 71% | 48% | 27% | 13% | 5% | 2% |
Central | 36° | >99% | >99% | >99% | 97% | 89% | 72% | 49% | 28% | 13% |
32° | 99% | 97% | 91% | 77% | 57% | 35% | 18% | 8% | 3% |
28° | 91% | 79% | 61% | 42% | 24% | 12% | 5% | 2% | 1% |
East Central | 36° | >99% | 99% | 95% | 85% | 67% | 45% | 26% | 13% | 5% |
32° | 96% | 88% | 72% | 51% | 31% | 16% | 7% | 3% | 1% |
28° | 76% | 57% | 37% | 20% | 10% | 4% | 2% | 1% | <1% |
Southwest | 36° | >99% | >99% | >99% | 99% | 94% | 80% | 55% | 31% | 14% |
32° | >99% | 99% | 95% | 83% | 62% | 38% | 19% | 8% | 3% |
28° | 93% | 83% | 65% | 44% | 24% | 11% | 4% | 1% | <1% |
South Central | 36° | >99% | >99% | 97% | 90% | 74% | 52% | 30% | 15% | 6% |
32° | 97% | 91% | 78% | 59% | 37% | 20% | 9% | 3% | 1% |
28° | 79% | 62% | 42% | 25% | 13% | 5% | 2% | 1% | <1% |
Southeast | 36° | >99% | 97% | 91% | 76% | 56% | 35% | 19% | 9% | 3% |
32° | 92% | 79% | 61% | 41% | 23% | 11% | 5% | 2% | 1% |
28° | 65% | 46% | 28% | 15% | 7% | 3% | 1% | <1% | <1% |
Region | Threshold | Apr 5 | Apr 10 | Apr 15 | Apr 20 | Apr 25 | Apr 30 | May 5 | May 10 | May 15 |
Table 2. Probabilities of minimum temperatures at or below 36°, 32°, and 28° across each of the nine Kansas climate divisions on or after the given dates, based on 1991-2020 NCEI daily climate normals.
It is important to remember that these dates are based on 30-year averages. Conditions vary from year to year. Short-range and medium-range forecasts provide useful information on the likelihood of damaging cold conditions in any given spring. Conditions can change quickly, as we saw earlier this week, so keep an eye on the forecast in the coming weeks for any signs of colder weather.
Source : ksu.edu