Our current estimate is for slightly warmer than normal temperatures and slightly above normal precipitation.
For reference, here are the 30-year climatology benchmarks for Reagan National Airport for April, along with our projections for the coming month:
Average temperature: 56.8 degrees; Forecast: 57-58 degrees
Average precipitation: 3.06 inches; Forecast: 3.15 inches or more
Average snowfall: Trace; Forecast: 0 to trace
Let’s discuss the primary factors utilized for the April outlook.
Warmer front half: Even though April 1 is cooler-than-normal, we expect the next two weeks to see more warmer than cooler days overall. There may be some much warmer than normal days in the mix — like what we’re expecting on Thursday and Friday this week. In fact, the current estimate for the first half of April is something in the ballpark of 2 to 4 degrees warmer than average! However, we still expect to see some transient cooler periods and the pattern variability should give us sufficient chances for precipitation.
Cooler second half? Longer-range weather models favor the large scale pattern to shift back to the cooler direction by the final half or third of April, as yet another round of high pressure ridging rebuilds over the far Northeast Pacific and Alaska. This has been a frequent theme over the past year and a half, and is mostly responsible for our wintry March. Cooler than average weather at month’s end will not feel like winter, but it could offer up some brisk overnights and early mornings at times.
Between the warm first half and the cool second half, I believe April will end just slightly above normal in terms of temperature.
Here is the most recent guidance from the National Weather Service CFS model output for April. Notice temperatures are near to just slightly above average, and precipitation is about a 0.25 inches above average:
Similarities to 2014: Last year is a really good proxy for this year in a lot of ways. After a cooler and snowier March last year, April turned out to be quite variable and we ended up slightly warmer than normal and very wet compared to climatology. I’m not sure we’ll get quite as wet on the whole, but we seem to be tracking toward another wetter than average month, at least.
Ocean and atmosphere: We’re still tracking a positive Pacific Decadal Oscillation (PDO) in the North Pacific as well as a weak El Niño situation in the Tropical Pacific. The connection between these features and our April weather in Washington is weaker than the connection in the winter months. But, in general, these prevailing pattern features should prevent big warmth, thanks to enough Pacific variability and more regular weather systems. The positive PDO pattern will try to position warm and dry high pressure ridging over the poor folks on the water-starved West Coast again later this month, which then brings back cooler chances for us.
National Weather Service
Here are the latest forecasts from the National Weather Service issued on March 31. They have the Washington area wedged in between elevated chances for warmer than average temperatures in the Southeast, and cooler than average temperatures toward the Northeast. I agree that there are going to be some tricky boundary issues at times this month, but warm should win out. The National Weather Service has higher confidence on the precipitation side and this seems reasonable given the ongoing weak El Niño conditions. You can read the Weather Service’s discussion here.
March Outlook Verification
March looked more like an extension of winter rather than the first month of spring. You can read all about how March ended here in D.C. in our monthly summary post. But in terms of our outlook blog from a month ago, we can give it an “A” thanks to getting all three category directions correct. I’m far more uncertain about this variable April, so our score may not work out as well a month from now!