2021 Spring Outlook for southeast North Carolina and northeast South Carolina

The latest outlook from the NWS Climate Prediction Center calls for an increased potential of above normal temperatures across the Carolinas this spring.  Rainfall has 'equal chances' of running below, near, or above normal over the same timeframe. 

Meteorological spring consists of the months of March, April, and May, and is the season when temperatures rise quickly due to higher sun angles and longer days.

Climate Patterns

La Nina developed in August 2020 and continues at the present time.  La Nina is a naturally occurring climate oscillation where water temperatures across the tropical east Pacific Ocean become cooler than normal, creating impacts on wind, temperature, and precipitation patterns across the world. 

While La Nina typically brings a warm, dry winter to eastern North and South Carolina, above average rainfall actually occurred locally during the La Nina winter of 2020-2021.  The global jet stream pattern resembled El Nino more than it did La Nina -- the first time such an unusual reversal has occurred since accurate upper level wind data became available in the 1940s.  NWS climatologists believe short-term chaotic variability in the weather may have overwhelmed La Nina's impact, creating the unusual conditions we experienced last winter. 

La Nina is expected to fade away later this spring, with ocean temperatures across the tropical east Pacific warming to near normal during May. 

Average Spring Temperatures

A review of observed temperatures over the past five springs that featured fading La Ninas (1989, 1999, 2000, 2008, and 2011) shows only slight departures from normal.

Climatologists with the NWS Climate Prediction Center based their spring outlook for above normal temperatures mainly on observed trends in spring temperatures due to climate change.

The spring months see the steepest rise in temperatures of any season due to large increases in day length and sun angles, both of which increase the amount of solar energy warming the northern hemisphere.  Here in the eastern Carolinas average daily high temperatures reach the 70s by late March.  Highs in the 80s become common during May but the oppressive humidity of summer is typically absent.  The first hot days of the year usually appear sometime in May as shown in the following table.

Last Spring Freeze Date

The growing season begins after the last freeze occurs in the spring.  For most locations across southeast North Carolina and northeast South Carolina, this happens during mid to late March.  However there is significant year-to-year variability in the date the last freeze occurs. 

On May 2, 1963 freezing temperatures were recorded in Dillon, Marion, Whiteville, and Elizabethtown.  On May 10, 1980 freezing temperatures occurred in Lumberton - the latest freeze on record for any station in this portion of the Carolinas!

During the past five springs where La Nina was fading, there was a tendency toward the last spring freeze occurring earlier than normal across the eastern Carolinas. However there were exceptions in 1989 and 2011, making this a somewhat unreliable predictor.

It is worth noting the the Carolinas are experiencing trends toward an earlier start and later end to the growing season due to climate change.  Data from eight local weather stations with long periods of climate history show the last spring freeze is occurring an average of 1.6 days earlier per decade, and the length of the growing season is expanding at a rate of 3.3 days per decade.

Spring Rainfall and Severe Weather Risk

Mirroring the official NWS Climate Prediction Center outlook, a review of the past five times when La Nina was fading during the spring shows no clear trend toward below, near, or above normal rainfall amounts across the eastern Carolinas.

Spring is typically one of our driest periods of the year across the Carolinas.  This is because the number of low pressure systems and fronts that frequently bring rain during the winter decreases, but the air is typically not yet humid enough to support plentiful pop-up thunderstorms like during the summer.  With rapidly rising evapo-transpiration rates during the spring due to warmer temperatures and increased water usage by plants, drought conditions can rapidly develop if several weeks of dry weather occur.  Fortunately the National Drought Monitor currently shows no drought conditions currently exist across the Carolinas and soil moisture remains adequate.

Warming temperatures during spring creates larger atmospheric instability -- one of the necessary ingredients for severe thunderstorms.  Local research shows a peak in severe weather reports in April, May, and June. 

A 2016 paper published in Environmental Research Letters suggests La Nina can enhance the frequency of springtime tornado outbreaks across parts of the eastern United States.  However the most significant impacts on tornado frequency appear to be limited to locations west of the Appalachians.  A 2017 article published on climate.gov mentioned how several springtime tornado outbreaks across the eastern U.S. occurred during La Ninas including 2011, 2008, and 1974.  It's worth noting the major tornado outbreak of April 16, 2011 occurred during a similar climate setup to what we anticipate for this spring.

The Atlantic Hurricane Season doesn't officially begin until June 1, however North and South Carolina have dealt with multiple pre-season tropical storms over the past decade.  These include Tropical Storms Bertha and Arthur in 2020, Bonnie in 2016, Ana in 2015, and Beryl in 2012. 

In response to more frequent tropical storm activity observed in May, the National Hurricane Center will begin regularly issuing Tropical Weather Outlooks on May 15 this year, two weeks earlier than before.

Coastal Flooding and Water Temperatures

Tidal ranges naturally vary throughout the month as a result of the moon's changing phase and gravitational influence on the oceans.  High tides are typically higher during new and full moons.  During full moons in late April and May there is a risk coastal flooding could develop if storminess or strong onshore winds occur.  Predicted astronomical tides are within 1 foot of minor coastal flood levels April 25-30, and again May 24-29.

Beach water temperatures increase rapidly during the spring due to higher sun angles, longer days, and warming air temperatures.  Water temperatures in the chilly 50s in March typically warm into the mid 70s by late May, warm enough for comfortable swimming for beach-goers and vacationers alike.

Water Temperature Climatology for Myrtle Beach, SC

Local water temperature data is available for Wrightsville Beach, Oak Island, Myrtle Beach.

Links

NWS Climate Prediction Center Latest Temperature and Precipitation Outlook

Current ENSO (La Nina/El Nino) Discussion

NC State Climate Office: Winter Recap 2020-2021

Climatological Spring and Fall Freeze Dates for southeast North Carolina and northeast South Carolina

Current and Climatological Beach Water Temperatures

Page Research and Author: Tim Armstrong
Last Updated: March 16, 2021