Storms Head Across the U.S. This Week
We just lived through one of the warmest winters in recent memory. The warmth and relative lack of storminess was odd compared to a normal year, but the weather was downright quiet compared to what we've seen over the last couple of years. Unfortunately, our luck is running out as the Sun creeps into the Northern Hemisphere and the atmosphere slowly warms up. The clash of the seasons will cause a steady train of storms to glide across the country through the end of March, bringing along with them noticeably rapid changes in weather from day to day, including the risk for severe thunderstorms and some beneficial heavy rainfall.
The forecast position of the jet stream from the GFS weather model on the evening of Monday, March 27, 2017, showing three troughs (southward dips) in the jet stream as they cross the United States. Image Credit: Tropical Tidbits
Current weather models suggest that a series of upper-level troughs—elongated areas of lower air pressure—will come ashore on the West Coast every couple of days for the next two weeks, each wave taking about three days to traverse the length of the United States before retreating over the Atlantic Ocean. Each trough will be sandwiched between ridges of high pressure, which are associated with warmer air and calmer skies. This trough-ridge combination will allow warm, unstable air to flow north from the Gulf of Mexico before the trough arrives to take advantage of the favorable atmosphere ahead of it. The end result will be heavy rain and thunderstorms, some of which could turn severe.
The greatest risk for severe thunderstorms with each wave will lie across the southern Plains and interior sections of the Gulf Coast states, exactly where you'd expect dangerous weather to develop at the end of March. The extent of the severe weather depends on how much instability, moisture, and wind shear are present when the storms bubble up. If the right mix of ingredients doesn't come together at the right time, the weather won't be much more than an inconvenience. If storms are able to take advantage of the right conditions, though, all types of severe weather—damaging winds, large hail, and tornadoes—will be possible with each outbreak of severe thunderstorms.
It shouldn't come as too much of a surprise that severe weather is ramping up as we get closer to April. We're rapidly approaching prime season for severe thunderstorms and tornadoes. The average number of tornadoes that touch down each day climbs rapidly between the end of March and the beginning of summer, with each day of spring becoming historically more favorable for nasty severe weather outbreaks.
The Weather Prediction Center's precipitation forecast (in inches) between March 24 and March 31, 2017. Image Credit: NOAA/WPC
The silver lining to the cycles between calm and stormy is that it will bring much-needed rain to just about everyone east of the Rockies who are currently experiencing drought conditions. The same weather pattern that allowed California to climb out of its drought in just a couple of months also dried the eastern half of the country to the point of drought. Moderate to severe drought conditions covered nearly 16 percent of the contiguous United States on the U.S. Drought Monitor's analysis for March 21, with the worst drought covering the central Plains and much of the East Coast.
Rain from the upcoming train of storm systems will drop several inches of rain over a widespread area, helping to put a small dent in the drought. It won't be enough to cure the parched earth in many places, but as Californians will tell you, any amount of rain can help.