Spring 2021 Frost/Freeze Info (still looks like we're "in the clear" from frost/freeze concerns the rest of the spring!)

** PLEASE NOTE: NWS Hastings WILL ISSUE Frost Advisories/Freeze Warnings (as needed) for the rest of this spring **

** Barring an improbable chance of frost/freeze concerns unexpectedly popping up sometime in late May, there now appears to be a high likelihood that our entire coverage area is DONE WITH FROST/FREEZE CONCERNS for the remainder of the spring! As a result, this story is scheduled to "drop off" our website on May 20 and will not return until spring 2022. **

General Overview of Local Spring Frost/Freeze Information:
The mid-April through early-May time frame typically features the final occurrence of freezing temperatures and/or frost of the spring season within our 30-county coverage area of south central Nebraska and north central Kansas. Based on 30-year averages, the date of the AVERAGE last spring freeze (32°-or-colder) ranges from around April 17 in far southeastern local communities (such as Beloit KS), to around April 23-30 in the Tri Cities (Grand Island/Hastings/Kearney), to around May 5th in far northern and western communities such as Greeley, Gothenburg and Cambridge. HOWEVER, after viewing the maps and tables contained in this story, it should be readily apparent that the phrase "average last freeze date" is quite relative, as most sites exhibit a 6-9 week range between the earliest and latest last dates on record!

Please refer to the wealth of information within the tabs below (including tables and maps of average last frost/freeze/hard freeze dates) to "stay on top of" the frost/freeze situation across the local area this spring.

Looking Ahead: ** Frost/Freeze Issues are ALMOST CERTAINLY OVER WITH FOR SPRING 2021! **
(updated May 19)

- Barring a HIGHLY improbable chance of frost/freeze concerns unexpectedly popping up sometime in late May, there is a VERY HIGH likelihood that our entire coverage area is DONE WITH FROST/FREEZE CONCERNS for the remainder of the spring! As a result, this story is scheduled to "drop off" our website on May 20 and will not return until spring 2022. **

Recapping Last Spring's (2020) Final Frost/Freeze:
- Spring 2020: For the majority of the NWS Hastings coverage area, the last official freeze (32º-or-colder) of spring 2020 occurred on May 10...anywhere from 1-3 WEEKS LATER than the 30-year average depending on exact location. However, for most (not all) places this May 10th freeze was not actually a true hard/killing freeze (28º-or-colder). In fact, most sites had already gotten past their last hard freeze a few weeks before this (between April 15-18)...actually pretty close to the heart of the 30-year average.

Frost/Freeze Definitions
Maps & Table of Average Frost/Freeze Dates
Daily Frost/Freeze Maps
Spring First Leaf/Bloom Index Maps

Before continuing, here are a few definitions...

Frost

Frost occurs when there is a solid deposition of water vapor from the air. Frost will form when solid surfaces are cooled below the dew point. An air temperature range of 33°- 36° (or colder), along with light winds, is usually needed to initiate frost formation. At least minor damage is possible to plants. One must keep in mind that frost is not guaranteed at these temperatures if the air is very dry and/or winds are roughly 8+ MPH.

The range of average dates for the LAST frost of the spring across across most of
south central Nebraska and north central Kansas is between May 1 - May 15.

Freeze

Freeze occurs when the air temperature drops to 32°-or-lower. A freeze will result in significant damage to many unprotected plants, especially if the temperature remains at-or-below freezing for several hours.

The range of average dates for the LAST spring freeze across most of
south central Nebraska and north central Kansas is between April 17 - May 6.

Hard Freeze

Hard freeze (per our local NWS definition) occurs when the temperature reaches 28°-or-lower for at least a few hours. It usually means that many types of plants and most seasonal vegetation will be destroyed.

The range of average dates for the LAST hard freeze of the spring across across most of
south central Nebraska and north central Kansas is between April 7 - April 28.

South Central Nebraska and North Central Kansas
30-Year Average Last Frost/Freeze Dates (1991-2020)
(click image to enlarge)


Average Last 36° Date (Last Spring Frost) 1991-2020	Average Last 32° Date (Last Spring Freeze) 1991-2020	Average Last 28° Date (Last Spring Hard Freeze) 1991-2020

Median Dates of Last Spring Freeze & Hard Freeze (1981-2010)
(Midwestern Regional Climate Center)


Median Date of Last Spring 32° Freeze	Median Date of Last Spring 28° Hard Freeze

Below is a table focused on the average dates for reaching particular frost/freeze temperature thresholds. Keep in mind, there is often tremendous variation from year-to-year and between any given location across the area!

Explanation of the following table:

The first column lists 10 locations in south central Nebraska and 3 in north central Kansas with long histories of being NWS Cooperative Observer sites (except for Grand Island and Hastings airports, which are automated systems). This is just a small sampling of dozens of official weather stations within the NWS Hastings coverage area, and these sites are generally organized down the column from north-to south.
The second column shows the average date of the LATEST observance of 28°, 32° and 36° temperatures during the most recent 30-year period from 1991-2020.
The third and fourth columns reveal the earliest last freeze date and latest last freeze date (32° or colder) during the past 30 years. It is readily apparent that the phrase "average last freeze date" is quite relative, as most sites have a 6-9 week difference between the earliest and latest dates. For some of these locations, the incredibly-early last freeze of spring 2012 (between March 9-11) was among the earliest on record. On the opposite spectrum, for several places, the latest freeze of the past 30 years occurred in mid-May 2014.
The final column is a recap of LAST SPRING (2020), showing the actual last dates that 28°, 32° and 36° were observed. A blue-shaded date indicates that the last spring frost/freeze/hard freeze of 2020 occurred at least 10 days LATER than the 30-year average, while red-shaded dates indicate a last spring frost/freeze/hard freeze that was at least 10 days EARLIER than the 30-year average.

Spring Frost/Freeze Data For South Central Nebraska and North Central Kansas
(based on 30-year averages from 1991-2020)

	Avg Last Spring Date Of: 28° Or Colder 32° Or Colder 36° Or Colder	1991-2020 Earliest Last Date: 32° Or Colder	1991-2020 Latest Last Date: 32° Or Colder	Last Spring 2020 Date: 28° Or Colder 32° Or Colder 36° Or Colder
Greeley	April 28 May 6 May 15	April 16, 2007	May 19, 2000	May 10 (27º) May 10 (27º) May 12 (36º)
Osceola	April 12 April 26 May 4	March 31, 1991	May 15, 2014	April 18 (16º) May 10 (32º) May 11 (33º)
Gothenburg	April 21 May 4 May 15	April 11, 2012	May 28, 1992	April 18 (28º) May 10 (29º) May 10 (29º)
Kearney Airport (NWS Observer)	April 19 April 30 May 9	April 10, 2003	May 28, 1992	April 18 (22º) May 10 (30º) May 12 (35º)
Grand Island (airport)	April 13 April 26 May 6	April 9, 2003	May 17, 2014	April 17 (23º) May 10 (31º) May 10 (31º)
Holdrege	April 15 May 2 May 8	April 10, 2003	May 29, 1992	May 10 (28º) May 10 (28º) May 12 (36º)
Hastings (airport)	April 11 April 22 May 2	March 9, 2012	May 17, 2014	April 17 (21º) May 10 (31º) May 10 (31º)
Geneva	April 7 April 20 May 1	March 9, 2012	May 17, 2014	April 18 (24º) May 10 (32º) May 10 (32º)
Cambridge	April 20 May 4 May 13	April 8, 2003	May 29, 1992	April 19 (27º) May 10 (31º) May 12 (36º)
Hebron	April 12 April 25 May 5	March 11, 2012	May 16, 2014	April 18 (25º) May 11 (31º) May 11 (31º)
Smith Center, KS	April 9 April 20 May 2	March 10, 2012	May 11, 2020	April 18 (28º) May 11 (32º) May 12 (36º)
Plainville, KS	April 9 April 21 May 5	March 10, 2012	May 12, 2008	April 18 (26º) April 18 (26º) May 12 (34º)
Beloit, KS	April 7 April 17 May 1	March 11, 2012	May 4, 2004	April 15 (25º) April 18 (32º) May 10 (33º)

The Midwestern Regional Climate Center (MRCC) produces maps that update DAILY, depicting the most recent date that sites across the region that have fallen to at least 32° or 28° this spring. In addition, GRAY shaded areas = places that have NOT YET accumulated at least 150 Growing Degree Days (GDD/base 50º F) since Feb. 1. In general, this means that gray-shaded areas have not yet become favorable for widespread plant/crop growth.

Check out the statewide maps of Kansas and Nebraska by clicking on the images below. These maps originate from the Midwestern Regional Climate Center website.


*KS: Most Recent 32° or Below* This Spring**	*NE: Most Recent 32° or Below* This Spring**

*KS: Most Recent 28° or Below* This Spring**	*NE: Most Recent 28° or Below* This Spring**

The USA-National Phenology Network (NPN) produces several maps that update DAILY, depicting the progression of particular types of spring vegetation across the nation, and how it compares to long-term averages. See their web page for much more detail and information, but the two maps highlighted below depict First Leaf Index Anomaly and First Bloom Index Anomaly. In short, this means they show the current status of some types of spring vegetation (first leaf-out or first-flowering) compared to long-term averages, giving an idea of whether spring is "ahead" of or "behind" schedule.


Spring Leaf Index Anomaly	Spring Bloom Index Anomaly

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