Almanack Weather Prognosticator Chad Merrill
May: Spring Chill Doesn't Want To Fade
Saturday, April 30, 2022
April produced one of the most volatile months in weather history for Cumberland with a high temperature of 87 degrees and 4.4 inches of snow within the 30-day period. Now many of you are wondering if Mother Nature’s big sneezes will continue into May and when it will be safe to plant flowers in the garden.
The average date for Cumberland’s final hard frost of the spring season in 1979 was April 18 and since then has trended two days earlier. However, the extremes around the average are even more noteworthy. The earliest observed final hard frost of the spring season since 1979 was March 27, 2010 while the latest date was May 10, which occurred in 1983 and 2020 respectively. That’s a difference of 44 days!
Farther west on the Allegheny Plateau, the average final hard frost in spring has shifted five days earlier (May 10 to May 5) over the last 42 years. Again, the extremes with the dates of the final spring freeze are mind-blowing, with the earliest since 1979 occurring April 4, 2019 and the latest happening on June 11, 1988. That’s a difference of 68 days!
The lower stratospheric polar vortex warming event occurred around April 10, which set the jet stream in a north-south orientation. It helped to dislodge the cold weather and snowstorm the region had on April 18. Since then, high-latitude blocking has fueled a negative North Atlantic and Arctic Oscillation, which is responsible for the below-average temperatures in western Maryland and the Potomac Highlands late this month.
Looking ahead to May, the negative North Atlantic and Arctic Oscillation pattern is the biggest driver in the weather and will likely return to a neutral or positive state between May 8-12. Additionally, the equatorial Pacific water remains cooler than normal and thus La Nina will continue unabated through May.
Therefore, we expect an active storm track across the Mississippi and Ohio valleys to bring above average rainfall to western Maryland and the Potomac Highlands. For Garrett County, this means the likelihood of more than 5.3 inches of rain and for Cumberland this amounts to more than 4.3 inches of rain.
We do expect one final burst of snow in Garrett County in early May with less than 2 inches of accumulation. We don’t see a pattern though that would produce an anomalous snowstorm east of Route 36. In May, Garrett County averages less than 2 inches of snow accumulation while Cumberland averages none.
It’ll be safe to begin work on your garden in Allegany County after May 12 and in Garrett County after May 19. These dates will mark the final spring freeze west of Sideling Hill. Don’t worry… if you enjoy the heat, expect temperatures to hit the 90s in central and eastern Allegany County and 80s along and west of Route 36 on one occasion between May 13-16 (yes, after much of Allegany County’s final spring freeze but before Garrett County’s final hard frost of the season) and again the week before Memorial Day.
Now, a quick preview for the summer months in western Maryland and the Potomac Highlands shows a very strong signal for La Nina to continue. Historically, La Nina summers produce 9 inches of rainfall in Cumberland, which is 1.4 inches below average. In Garrett County, La Nina summers average almost 13 inches, which is just under one inch below average.
We do see upside risk for rainfall in western Maryland and the Potomac Highlands to be near average for the summer season. That being said, there will still be dry periods within the summer when lawns and crops will need watered. There is a strong signal east of the Appalachians for above average rainfall this summer, particularly the Interstate 95 corridor.
Temperatures will likely trend above-average from June through August in both Garrett and Allegany County. La Nina is notorious for producing warm summers in the northern Appalachians. A few days in mid-July and mid-August will see heat advisory criteria with heat indices pushing 100 degrees in mountain Maryland.
Enjoy the transformation from late-winter to early summer temperatures in May and when we talk to you again, we’ll take a more detailed look at June’s expected trends.
Hagerstown Town and Country Almanack Weather Prognosticator/Meteorologist
Chad Merrill is a Cumberland native and meteorologist who serves as the Hagerstown Town and Country Almanack weather prognosticator and senior meteorologist at Earth Networks in Germantown. Merrill previously was a meteorologist with WDVM (formerly known as NBC25) in Hagerstown and WJAC-TV in Johnstown, Pennsylvania. Feel free to contact him at email@example.com or 240-285-8476.