We’re projecting an average May temperature of 65 to 68 degrees (normal is 66 degrees) with rainfall between 3.5 and 4.5 inches (normal is 3.99 inches). This would be a bit warmer and wetter than last year, which was the coolest May in 15 years.
Like April, the spring pattern over North America should continue to offer considerable variability for the eastern United States. Over the next two weeks, we foresee alternating warmer and cooler and drier and wetter periods.
Check out the latest 15-day model forecasts for temperature and precipitation differences from normal from the American (National Oceanic and Atmospheric Administration), European (European Center for Medium-Range Weather Forecasts) and Canadian (Canadian Meteorological Center) weather agencies:
These sources generally agree on a near- to slightly warmer-than-normal start to May, but little sustained warm or cool weather is anticipated.
The precipitation forecast is more complicated, though, as the models agree on a pronounced fetch of moisture from the Gulf of Mexico into the eastern United States, but notice how the European model positions the boundary west of Washington. Such a pattern has been present over the past week, with the heaviest rain from approaching storm systems tracking to our west and north, as shown below.
Our rain outlook is a hedge in that it is drier than the American and Canadian modeling but wetter than the European. Even if the heaviest precipitation passes to our west, we lean toward showers and storms from nearby cool fronts to keep May’s rainfall rate on track. The coming week should see two to three more chances of rain over our area. May is normally our wettest month of the year, so we will need to pick up some heavier rain at times to keep on pace.
What about the second half of May? The latest batch of long-term modeling from NOAA favors a near- to slightly cooler-than-normal outlook and a near- to wetter-than-normal rain outcome, as seen below.
Taking everything together for May in its entirety, model forecasts favor near-normal temperatures and near- to somewhat above-normal rain even as day-to-day weather is quite variable.