Pacific Northwest Storm System: “A significant severe weather event is likely this week,” forecasters say



CNN

A new robust storm system moving into the Pacific Northwest on Sunday is expected to bring severe storms to the south this week.

The Storm Prediction Center has issued an early warning calling for “a significant severe weather event” in parts of the lower Mississippi River Valley on Tuesday.

“This storm system will have the potential to create severe thunderstorms that can cause tornadoes, damage straight-line winds and also large hail,” Bill Bunting, head of forecasting operations at the Storm Prediction Center, told CNN Weather. “Details on the areas most at risk from tornadoes will become clearer as Tuesday approaches and smaller trends become more apparent.”

The entire region, including Memphis, has been assigned an elevated Level 3 risk of 5 for severe storms. However, Tuesday’s larger severe storm threat could affect more than 25 million people from east Texas to southern Indiana.

The forecast center also noted in its forecast discussion Sunday morning that “categorical upgrade will be possible in later forecasts,” meaning the severe storm threat has the potential to rise to level 4 or 5 out of 5 as Tuesday approaches and the prognosis greater becomes clear.

Notwithstanding, this week’s storms are expected to be strong and potentially damaging. Be sure to keep up to date with the latest forecasts as they develop over the next few days.

You can follow CNN weather updates here.

The system is likely to create tornadoes and damaging winds in the lower Mississippi Valley after dark Tuesday, which can be particularly dangerous.

“Unfortunately, it looks like the severe storm threat will continue into the evening and night hours on Tuesday,” Bunting said.

The time of day that a tornado occurs also makes a big difference in the death rate. Nocturnal tornadoes are more dangerous because many people are asleep, unaware that they need to find a safe place.

While the greater tornado danger for this particular event is during the daytime, there is still a possibility of some rotating storms in the evening hours.

Among the areas most at risk from overnight storms on Tuesday are southern Illinois down to Louisiana.

“Another challenge with nighttime tornadoes, particularly in the fall and winter, is that storms typically move very quickly, sometimes at 50 or 60 miles per hour,” Bunting said. “That means you need to make decisions quickly and take shelter based on the information in the severe thunderstorm or tornado warning, rather than waiting for the storm to come.”

Bunting pointed out that another concern will be the potential for flooding, thanks to heavy rains resulting from repeated rounds of thunderstorms.

Widespread precipitation is expected to fall in the 1 to 2 inch range, but could fall as much as 4 inches in some isolated locations.

While tornadoes can occur any month of the year in the US, they most often occur in the spring, thanks to the clash of cold and hot air with the changing seasons. The same merging of temperatures also occurs in autumn, which is why you’ll often see a secondary “severe season” later in the year.

“While severe storms occur less regularly in the fall and winter than in the spring/summer months, major severe weather outbreaks have occurred during this time of year,” Bunting noted. “Just think back to last December and the record number of tornadoes for the month and the tragic death toll.”

Earlier this month, a Level 3 Severe Storm risk was issued three days in advance, before later being upgraded to a Level 4 risk. Dozens of tornadoes were reported across Texas, Oklahoma, Louisiana and Arkansas, damaging numerous homes and businesses.

If Tuesday’s threat is upgraded to a Level 4 risk, it would be the first time two Level 4 risks have been issued anywhere in the US in the month of November.

“You can see that while the spring months are our busiest time climatologically, there is a secondary increase in tornado activity in November,” said the National Weather Service in New Orleans.

Texas, on average, sees the most tornadoes (7) in the month of November, followed by Alabama (6), Louisiana (5), and Mississippi (5).

“Severe thunderstorms in the fall and winter can be extremely devastating and sometimes catch people off guard, as thunderstorms occur less frequently in the cooler months,” Bunting added. “Now is the time to consider or develop a severe weather contingency plan for you and your family.”

Know where to go when storms hit and make sure flashlights are working and cell phones are fully charged in case you lose power.

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