Memorial day storms threatens more than half the U.S.

Showers and thunderstorms threaten to interfere with Memorial Day festivities across more than half of the United States.

That does not mean that half of the picnics, parades and other outdoor events throughout the nation will not be able to go on as scheduled.

Monday will not be a complete washout in most communities being threatened by showers and thunderstorms. There will still be stretches of dry weather.

Residents should monitor their local forecast pages to determine the best time to schedule outdoor plans. On the actual holiday, a close eye will have to be kept on the sky and AccuWeather MinuteCast® to know when to move indoors.

Widespread severe weather is not a concern on Monday, but lightning is.

"While only a small number of storms become strong enough to produce damaging winds, large hail and tornadoes, every thunderstorm produces lightning," stated Brian Lada.

"Lightning is one of nature's deadliest phenomena, claiming roughly 55 to 60 lives every year across the United States and injuring hundreds more," added Lada.

The most active parts of the nation in terms of thunderstorms will lie from Texas and the northern Gulf Coast states to the Midwest and St. Lawrence Valley and across the northern Plains and Intermountain West.

A large corridor of showers and thunderstorms will be found on Monday from the Gulf Coast to the Midwest with steamy air in place and a storm system located over the Upper Midwest.

The morning hours will be more active than the afternoon around Chicago and St. Louis.

On the cool side of the storm, periods of rain will dampen the northern Plains--Fargo, North Dakota, included. Just south of this zone, thunderstorms will return to Nebraska with a few of the thunderstorms becoming strong in the afternoon.

The greatest concern for the thunderstorms to be heavy and trigger flash flooding lies from Texas to the lower Mississippi Valley, home to Shreveport, Louisiana.

In addition to flooding downpours, the threat also exists for some of the thunderstorms in central and eastern Texas to turn severe with damaging winds, hail and an isolated tornado. San Antonio, Dallas and Houston are among the communities at risk.

These violent thunderstorms will eventually bring yet another round of flooding downpours to the lower Mississippi Valley at night.

Meanwhile, the thunderstorms set to develop from the eastern Gulf Coast and Georgia to the eastern Tennessee Valley will mainly be limited to the afternoon and spottier in nature. Most of the Carolinas will stay dry.

Along the leading edge of the surging warm and humid air, a steadier band of rain and thunderstorms threatens to cause more significant disruptions to holiday plans across the upper Great Lakes.

The eastern extent of this wet weather will nose into the St. Lawrence Valley, while the rest of the Northeast and mid-Atlantic remain dry and turn warmer.

Two other storm systems will work to keep a large part from the Rockies to the Cascades and Sierra unsettled with showers and thunderstorms. The afternoon hours will be the most active time of the holiday.

Anyone planning to spend Monday at a national park or forest, including Yellowstone or Rocky Mountain, should have a plan in place of where to seek shelter during a thunderstorm.

As soon as thunder is heard, the risk of being struck by lightning is present.

The Desert Southwest and the immediate West Coast should escape wet weather on Memorial Day. In the Southwest, that means residents will have to remain diligent when participating in some holiday festivities to avoid starting a brush or wildfire.

Away from the contiguous United States, showers will dot Alaska and a few windward communities on Hawaii this Memorial Day. The shower chance will come after Fairbanks, Alaska, experiences a rare feat of recording a high greater than Phoenix on Saturday.