The Hagerstown Almanack Monthly Weather Column

  

The warmest temperatures of the year will push into the region as we finish April. As a matter of fact, the new HeatRisk product by the weather service puts the region in a code orange for Monday. This new code-based heat product takes into account forecast temperature, departure from average temperature, antecedent conditions (first heat spell of the season, coming out of a cool spell or within a hot spell) and data from the CDC relating to heat deaths from previous years. An orange or moderate risk for heat-related illness means those sensitive to heat or who don’t hydrate effectively could dehydrate and experience dizziness and require medical attention.

 

Leaping ahead into May, the major pattern drivers include a positive West Pacific Oscillation, which supports warmer than average temperatures. The Pacific-North American pattern for most of May supports a western trough with rain and mountain snow. For the East, this brings a high-pressure ridge and preview to summer. The temperature gradient along the boundary will foster an uptick in severe weather in the Plains. Meanwhile, the North Atlantic Oscillation will stay in a negative phase, which triggers a transient cool spell or two.

Another factor which will mitigate the risk for a major cold snap in May is the final warming of the winds at 10-hectopascals. This is related to the Stratospheric Polar Vortex. A dramatic final warming typically yields a cold snap that pushes across the Northern Hemisphere and eventually western Maryland and the Potomac Highlands. A far less dramatic warming, which will occur in early May, will likely have no major implications on our weather. Therefore, no big cold snap that would bring a late-season snow is expected.

Air conditioners will get their first test of the season in May with above average temperatures. However, there will be a handful of days with cooler than average temperatures, best chance in the middle of the month.

May will not overproduce on rainfall like April did, but instead amounts will be a hair above the 30-year average of 4.22 inches in Cumberland and 5.34 inches for Garrett County. There is strong evidence to suggest the severe weather season will continue to remain very active in the Plains and Mississippi Valley going forward into May. Tulsa, Okla., Oklahoma City, Kansas City, Mo., Des Moines, Iowa and Minneapolis will exceed average rainfall with upside risk for an active month of severe weather. The moderate to severe drought encompassing the Plains and Upper Mississippi Valley will be chipped away in May.

El Nino is rapidly fading and La Nina will develop along the Equatorial Pacific during mid-summer. Historically, La Nina summers bring well-above average temperatures to the region. A likely negative Pacific-North American Pattern is expected, which brings a soggy summer. Based on our analysis, an occasional cold front will provide heat relief in June, but sustainable warmer than average temperatures are likely late in June and then again from mid-July to mid-August. Rainfall will likely trend near average, so drought development appears unlikely in western Maryland and the Potomac Highlands.

In 2016, 2018, 2019, 2020, 2021, we saw the first tropical system of the season form in May. In 2017, we actually had the first named storm form in April. Given the historical trends and a warmer than average Main Development Region of the Atlantic, we will likely see our first named storm prior to June 1. These systems are most known for developing on the tail end of a stalled front along the Gulf of Mexico or Atlantic coast and bring enhanced rain to a small area with little to no wind and storm surge impact. 

Stay tuned at the end of May to see if western Maryland and the Potomac Highlands will be turning the air conditioners on full-throttle for an extended time in June!