April 2017: Mild and wet, with above-normal snowfall
April brought us welcome rains, which helped cut deeper into the two-year drought around the region.
Enough rain fell to allow for the National Drought Mitigation Center to cut the lower Merrimack Valley’s drought status back to “abnormally dry.”
April exhibited many of the weather patterns we would expect to see, including large temperature gyrations; periods of damp, cool weather; brief spikes of warm temperatures; and even some snow to begin the month.
April was a milder than normal month, but several spikes of warm and cold temperatures were noted. During the spring, it’s quite normal for warm and cold temperatures to play tag, leading to large temperature gyrations.
Not only can we see cold air from Canada quickly replace warm intrusions from the South, we have an ocean that’s still very cold immediately to our east. Temperatures can tumble 20 or 30 degrees in an hour or two with just a wind switch from west to east at this time of year, especially at the coast. One day can be summerlike, while the next brings out the winter coat.
Nashua’s average temperature as recorded at Pennichuck Water Works was 49.4 degrees, above normal by 3.5 degrees and the seventh-warmest out of 124 years of April temperature readings. One record high was recorded on April 12 when the high of 86 replaced the 83 set in 1945.
The first two months of spring have averaged 0.6 degrees below normal thanks to the very cold March. 2017 to date is averaging 2.5 degrees above normal thanks to the warm winter.
Generous rains fell across New England during April, putting a dent into but not an end to the hydrological drought. Short-term dryness and surface soil moisture isn’t a concern at this time, but the groundwater is still lacking and further rains are needed to allow for recharge of the area’s aquifers.
Hydrologic droughts normally take many months to erase. The way to do this is to have several months in a row with above-normal rainfall. So far, April is the only above-normal rainfall month of the last six. Fortunately, it appears that the weather pattern will continue to produce beneficial rains well into May, and hopefully longer.
April erased 1.5 inches of the nearly 24-inch deficit built during the last two years. We don’t need to recover the entire deficit, but several more inches of above-normal rains during the next few months would be needed to bring the aquifers back to normal.
Nashua’s rain total of 5.84 inches during April was 1.51 inches above normal. April ranked as the 14th-wettest April out of 134 years of records. For 2017, the total of 14.94 inches is still 0.66 inches below normal. The spring to date (March and April) precipitation total of 8.96 inches is 0.28 inches above normal.
Snow was falling when April began, and the 3.5 inches that was recorded fell from 7 a.m. March 31 into the daytime of April 1. Official records are kept on a 7 a.m.-7 a.m. time scale, and that is why some of the snow that fell during the calendar month of March gets recorded in April. The same is the case for rain and temperature.
April was the 28th-snowiest out of the last 108 April with snow recordings. Snow covered the ground for the first few days of April before warming temperatures brought the demise of the last patches of snow.
The final statistics for the 2016-17 snow season show that we had another snowier than normal winter with 69.6 inches. The 14.7-inch surplus made this last winter the 44th-snowiest out of 107 seasons of snow records for Nashua.
During the last 25 snow seasons, we have seen a notable increase in average snowfall for the Nashua area. Beginning with the 1992-93 season, the average snowfall has been 61.7 inches for Nashua. This is 6.8 inches above the long-term normal.
Fourteen of the last 25 winters have featured above-normal snowfall. The current period matches the period from 1955-78 when snow was copious across the region. The previous snowy period was followed by many lackluster snow years from 1979 to the 1991-92 season. One would think our current snowy stretch should be running its course soon based on history.
Currently, the forecast charts are showing potential for an Omega block developing from the North Atlantic to the U.S. during the early and mid-May period. This is a stalled pattern that may leave New England with a lengthy period, possibly as long as a couple of weeks, of cool, unsettled weather.
These slow-moving and sometimes stalled patterns were common during the 1980s, when many of the springs were cool and damp across the Northeast. The good news is that we should see more rain, which will help slice deeper into the hydrologic drought. The downside is that the cool, damp weather won’t be good for outdoor activities.
Sluggish spring weather patterns aren’t uncommon as the jet stream weakens and lifts slowly northward. Sometimes when spring blocking patterns finally break down, summer takes hold.
The weather during May can still wear many hats. It’s all about wind direction this time of year. With a west wind, we can see temperatures soar to summer levels, but the east wind brings chilly temperatures, clouds and sometimes drizzle or light rain.
For the gardener, hardy plantings are good anytime, but other vegetables that can be damaged by frost shouldn’t be planted until Memorial Day. Frosts aren’t unusual through mid-May and can occur infrequently until late month.
The average date for the last 32-degree reading locally is May 10. Keep in mind that this date is an average, with last frost dates over the years varying from as early as mid-April to as late as early June.
Weather & Climate is written by Doug Webster, of Hudson, a consulting meteorologist.
APRIL FACTS AND FEATS DATING TO 1884
April 2017 Average Temperature: 49.4 degrees, 3.5 degrees above normal.
Warmest April: 1941, 51.4.
Coldest April: 1926, 40.0.
All-time April High: 93, April 20, 1941, and April 18, 2002.
April 2017 high: 86, April 12.
All-time April low: 8, April 1, 1969.
April 2017 low: 28, April 3, 4.
April 2017 precipitation: 5.84 inches, 1.51 inches above normal.
2017 annual precipitation to date: 14.94 inches, 0.66 inches below normal.
Wettest April: 2007, 10.72 inches.
Driest April: 1941, 0.48 inches.
April 2017 snowfall: 3.5 inches, 2.7 inches above normal.
Snowiest April: 1982, 16.8 inches.
2016-17 season snowfall: 69.6 inches, 14.7 inches above normal.