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March, winds Of Change

March is a transition month with perhaps the greatest variety of weather of any month and some very notable extremes. Arctic air masses can still bring sub-zero cold to the northern states while tropical warmth and humidity begins to show itself for the first time on the southern border states.

Storms feeding off the great contrast in temperatures can bring blizzards, flooding rains and, especially in the south, the first tornado outbreaks of the severe weather season. On average there are approximately a dozen tornado days in March with a total of 56 tornadoes. The season will peak in May and June with nearly 25 tornado days and 180 plus tornadoes on average in each month.

As the days grow in length and the sun rises rapidly in the sky, the surface warms quickly this month. Average daily temperatures rise 10 degrees F during the month in many eastern and central cities with the changes accelerating late in the month. The rate of warming will peak in April in most areas.

Because the sun warms the earth's surface faster than the air above, the air becomes increasingly unstable. This result is an increase in convective (shower) activity and the first thunderstorms of the season. The instability of the air causes deep atmospheric turbulence and mixing which helps bring stronger wind gusts down to the surface from aloft. The combination of deep storms and unstable air makes March for many locations the windiest month of the year. Blustery March earns it reputation for "roaring like a lion".

Storms continue to move inland from the Gulf of Alaska into western Canada. These storms jump the mountains and reform over Alberta to become the fast moving "Alberta Clippers" with bouts of mostly light precipitation.

Other Pacific storms come inland into Oregon and Washington state and then reform east of the Rockies in Colorado or over the Texas or Oklahoma panhandles and head towards the Great Lakes or Ohio Valley. These storms can be very wet and produce heavy flooding rains and snows. Blizzard conditions can prevail to the northwest of the storm track.

The more southerly Pacific storm track into California becomes less frequent. Precipitation in southern California begins to diminish as the 'winter wet season" wanes.

The Gulf of Mexico remains important as either a genesis region for storms or as an energy and moisture source for storms tracking further north. Storms from the Gulf usually track up the Appalachians or out into the western Atlantic. Blocking polar air masses often settle over eastern Canada and slow the northward movement of these storms. This often prolongs the storms influences along the coastal areas and can accentuate the damage due to coastal flooding.

March extremes range from 108 F at Rio Grande City, Texas on March 31, 1954 to -50 F at Snake River, Wyoming on March 17, 1906.

April - Spring Makes Its Long Awaited Entry

April is the first full spring season month. It brings the first real signs of spring to many parts of the nation although very winter like conditions can still occur.

Frozen Hudson's Bay in Canada still refrigerates air masses which dip into the north central and northeastern states especially during the early part of the month. The southern states though are becoming more dependably warm and, as vegetation springs to life, increasingly humid. Feeding on this strong contrast in temperatures, the main storm track is still very active across the central US and now can produce both heavy snows (even some local blizzard conditions) in the cold air to their north and outbreaks of severe weather in their warm sector.

April on average is drier than prior months in both the west and east but wetter in between. This is a reflection of both the emergence of these powerful spring storms and the stabilizing effect of the now colder than air ocean waters. The rainy season comes to an end in most years in California during April.

The proverbial April Shower is not a myth but a fact. The more widespread and continuous rains and snows on the winter season which fall from mostly stratiform (flat, layered) clouds give way in the spring to briefer more localized rains which fall from smaller scale convective (puffy, vertically developed) cloud types. In the early spring, the surface of the earth is being warmed much faster than the air above.

This causes the air to become unstable (bouyant), to rise, cool and when moisture is sufficient, form clouds. Because the surface is not uniform in its ability to warm, this cloud building is somewhat chaotic and localized. When there is a more general lifting mechanism such as a front or a mountain barrier, the activity is better organized. The spring storm squall lines are examples of these organized convective features.

The severe weather season really heats up in April in most years. On average there are 18 tornado days in April with a total of about 107 tornadoes, more than double the number in March. For the nation as a whole, the number of tornadoes will peak in May (160 tornadoes) but actually for most states from the Gulf to Michigan the number of tornadoes peak in April.

Also April outbreaks can be especially deadly. The number of tornado deaths peaks in April (an average of 38). The Tornado 'Super-outbreak' of 1974 is the most infamous outbreak with an incredible 148 twisters in 12 states which caused 309 fatalities and 5300 injuries. Xenia, Ohio was devastated by a powerful tornado during this outbreak.

Like March, April can be a very windy month. Strong pressure gradients can exist around strong spring storms, especially when polar air masses are still involved. Mt. Washington established the world wind speed record on April 12, 1934 when winds reached 231 mph. Also like March, winds tend to be blustery. The instability of the air can cause deep atmospheric turbulence and mixing which helps bring stronger wind gusts down to the surface from aloft.

April temperatures have been as hot as 118F (Volcano Springs, CA on April 25, 1898) and as cold as -36F (Eagle Nest, NM on April 5, 1945).