Hot Temperatures and Strong Winds Fuel Western Wildfires

Summer is wildfire season in the American West and this year it is off to an explosive start.

As of Wednesday, according to the National Interagency Fire Center, thirty large wildfires – defined as greater than 100 acres – are burning in ten western states.  These include Alaska, Arizona, California, Idaho, New Mexico, Nevada, Oregon, Texas, Utah, and Washington.

The largest is the Brian Head Fire in southern Utah. It has burned approximately 50,000 acres and forced the evacuation of nearly 1500 people. Ignited on June 17, the massive blaze is only 10% contained.

Another hard hit state is Arizona, where six large fires are currently burning. The governor, Doug Ducey, has declared a state of emergency in Yavapai County in response to the Goodwin Fire, which has burned more than 20,000 acres near the Prescott National Forest. Local officials have ordered the full evacuation of the town of Mayer, AZ.

These huge fires are being fueled by extremely hot and dry conditions that have left the region’s vegetation susceptible to any type of spark. Just a few days ago, excessive heat advisories were in effect for a large swath of the area as temperatures soared into the triple digits. Now, high winds are fanning the flames and helping the fires to spread.

Year to date, 2.7 million acres in the US have been charred. The country’s worst wildfire season on record was 2015 when more than ten million acres burned.

Brian Head Fire, UT. Credit: Desert News

Weather Lingo: Rain Shadow

The world of weather has some interesting words and phrases. One of these is “Rain Shadow”.

While it sounds rather poetic, a rain shadow refers to the land area on the leeside of a mountain that is exceptionally dry. Mountains act as barriers for weather systems traveling in a region’s prevailing winds, forcing them to drop most of their moisture on the windward side before they can pass.

As an air mass rises up and over a mountain, it enters an area of lower atmospheric pressure where it expands and cools. As a result, the moisture it contains condenses, clouds form, and precipitation falls. After the air mass moves over the mountain, it starts to descend the other side. The air is warmed by compression and the clouds dissipate. This means little to no rain falls on the leeward side.

Rain shadows are found all over the world, from the Tibetan Plateau in Asia to the Atacama Desert in South America. Here in the US, Death Valley is a famous example as it lies in the rain shadow of four different mountain ranges.

The Rain Shadow Effect. Credit: Kagee Commons

If You Don’t Like the Weather in Iceland, Just Wait Five Minutes

In Iceland, people are fond of saying, “If you don’t like the weather, just wait five minutes.” This popular expression is written on everything from t-shirts to coasters, and during the course of my recent visit I also found it to be true.

The notoriously changeable weather of this island nation is largely the result of its location. Situated just south of the Arctic Circle, Iceland sits at the border between the Arctic Ocean with cold air masses to the north and the Atlantic Ocean with milder air masses to the south. A branch of the warm Gulf Stream Current known as the Irminger Current also flows along the country’s southern and western shores moderating the climate. As this mild air interacts with cold arctic air, it produces frequent changes in the weather. A relatively mild, sunny day can quickly turn cold and rainy. Strong winds are also very common.

So, when in Iceland, heed the advice of the locals and be prepared for all four seasons on any given day.

Coaster for sale with the popular saying, " Welcome to Iceland. If you don't like the weather, just wait five minutes." Credit/Source: Gullfoss.is

Coaster for sale with the popular saying, “Welcome to Iceland. If you don’t like the weather, just wait five minutes.” Credit/Source: Gullfoss.is

A March-like Chill in May for NYC

The calendar says mid-May, but it felt more like March in New York City this weekend.

After a warm spring day on Saturday with readings in the 70s, a cold front swept through the region ushering in significantly cooler conditions. The high on Sunday only reached 57°F, which is 13°F below average. This dramatic cool down was also accompanied by strong winds with gusts in excess of 40-mph.

Moving from Sunday into Monday, the over-night low in Central Park fell to a chilly 43°F. That is the coolest May temperature the city has seen in three years. It was also just one degree shy of tying the record low of 42°F set in 1878. Our normal low temperature for this time of year is 54°F.

With Memorial Day – the un-official start of summer – just two weeks away, many New Yorkers will be happy to hear that temperatures are expected to rebound to more seasonable levels later this week.

High Winds Whip through NYC

March, a month where the seasons transition from winter to spring, can produce some fickle weather. But, it is probably most famous for strong winds, and they were on full display in New York City yesterday.

According to the NWS, sustained winds of 25mph were measured in Central Park and gusts reached as high as 45mph. A wind advisory was issued in the afternoon and remains in effect until later this evening.

Below is a short video of strong winds whipping a tree in a NYC backyard.  Even though it is largely protected by buildings, it still moves quite a bit.

Video Credit: The Weather Gamut.

Microburst Winds Damage Town in Massachusetts

A strong microburst toppled trees and power-lines in the town of Easthampton, Massachusetts early Wednesday morning. With winds in excess of 100mph, the damage to the area was equivalent to an EF-1 tornado.

According to the National Weather Service in Boston, the powerful storm cut a path of destruction one mile long and a quarter mile wide. No serious injuries have been reported.

A microburst is a powerful, but short-lived, downward moving column of air generated by a thunderstorm. It produces intense straight-line winds – as opposed to the rotating winds of a tornado – that generally impact localized areas less than 2.5 miles wide.

microburst

How a mircoburst works.   Credit: NOAA

Damage from microburst in Easthampton, MA.  Credit: MassLive

Damage from microburst in Easthampton, MA.   Credit: MassLive

Opposing Winds Help Shape Great Sand Dunes National Park

When you think of the Rocky Mountains, sand dunes are probably not the first thing that come to mind. While driving across southern Colorado earlier this month, however, giant white sand dunes glimmered in the distance. No, it was not a mirage; it was Great Sand Dunes National Park and Preserve.

Sprawling across the arid San Luis Valley between the San Jose Mountains to the west and the Sangre de Cristos to the east, the dunes cover 30 square miles and rise as high as 750 feet. They are the tallest dunes in North America and were formed, and continually maintained, by a complex interaction of geology and weather.

Over the millennia, according to the National Park Service, rocks from the surrounding mountains eroded and their sandy sediments were transported by stream to the valley floodplain. Prevailing southwesterly winds then carried the sand grains toward a low curve in the Sangre de Cristo Mountains, where they accumulated in a natural pocket.  On occasion, when the wind direction reverses during storms, the sand is pushed back toward the west. This process causes the dunes to grow vertically.

Two mountain streams, the Medano and Sand Creeks, also border the dunes. They capture sand grains from the eastern side of the dunes and carry them back to the valley floor.  This effectively recycles the sand and re-exposes it to the winds.

While the forces of wind and water are continually reshaping the massive dunes, they essentially remain in the same position.

Sand dunes nestled against the foothills of the Sangre de Cristo Mountains, Great Sand Dunes National Park, CO.  Image Credit The Weather Gamut.

Massive sand dunes nestled against the foothills of the Sangre de Cristo Mountains, Great Sand Dunes National Park, CO.  Image Credit: The Weather Gamut.

North American Monsoon

The summer phase of the North American Monsoon is in full swing. But what, you may wonder, is a monsoon?

While most people associate a monsoon with rain, that is only half the story. It is actually a wind system. More specifically, according to NOAA, a monsoon is “a thermally driven wind arising from differential heating between a land mass and the adjacent ocean that reverses its direction seasonally.” In fact, the word monsoon is derived from the Arabic “mausim”, meaning seasons or wind shift.

In general, a monsoon is like a large-scale sea breeze.  During the summer months, the sun heats both the land and sea, but the surface temperature of the land rises more quickly. As a result, an area of low pressure develops over the land and an area of relatively higher pressure sits over the ocean. This causes moisture-laden sea air to flow inland. As it rises and cools, it releases precipitation. In winter, the dry season, this situation reverses.

Monsoon wind systems exist in many different parts of the world. In the U.S., we have the North American Monsoon that impacts states across the southwest. Summer temperatures in this region – mostly desert – can be extremely hot. Readings in the triple digits are not uncommon. This intense heat generates a thermal low near the surface and draws in moist air from the nearby Gulf of California. In addition, an area of high pressure aloft, known as the subtropical ridge, typically moves north over the south-central U.S. in summer. Its clockwise circulation shifts the winds from a southwesterly to a southeasterly direction and ushers in moisture from the Gulf of Mexico. This combination of heat and moisture rich air produces thunderstorms and heavy rainfall across the region between July and September. In fact, summer monsoon rains are reported to supply nearly 50% of the area’s annual precipitation.

Replenishing reservoirs and nourishing agriculture, these seasonal rains are a vital source of water in the typically arid southwest. Conversely, they can also cause a number of hazards such as flash flooding, damaging winds and hail, as well as frequent lightning.

The summer monsoon officially begins, according to the National Weather Service, when there have been three consecutive days with a dew point above 54°F.

North American Monsoon: Summer Weather Pattern. The thermal low sets up  over the desert southwest, while the subtropical high  moves into the southern plains. The winds draws moisture (green arrows) from the Gulf of California and the Gulf of Mexico.  Source: NOAA/NWS

North American Monsoon: Summer Weather Pattern. The thermal low sets up over the southwest, while the subtropical high moves into the southern plains. Their circulating winds draw moisture (green arrows) from the Gulf of California and the Gulf of Mexico.   Credit: NOAA/NWS

High Winds and the Macy’s Thanksgiving Day Parade

The Macy’s Thanksgiving Day Parade is a long-standing holiday tradition in New York City.  This year, high winds could ground the event’s famous giant character balloons.

According to city guidelines, the multi-story balloons cannot fly if there are sustained winds in excess of 23 mph or gusts above 34 mph.  The current forecast for Thanksgiving Day expects winds close to this threshold.  Parade organizers say they will monitor the weather conditions and consult with the city on Thursday morning to decide if the balloons can fly and at what height.

While the parade marches in rain or shine, high winds are a serious threat to the massive balloons and the crowds of spectators that line the route.  In 1997, gusty winds sent the “Cat in the Hat” balloon careening into a light post, which caused debris to fall on parade goers, seriously injuring one person. Following this incident, a mayoral commission established the wind regulations currently in place.

With or without balloons, the 87th Annual Macy’s Thanksgiving Day Parade is scheduled to begin at 9 AM on Thursday morning.  Happy Thanksgiving!

“Hello Kitty” Balloon floats down Broadway as part of the Macy’s Thanksgiving Day Parade.                         Image Credit: 1000cutethings.com

A Week of Wild Weather Across the U.S.

Extreme weather battered much of the United States this past week.  From heavy snow and tornadoes in the plains to a tropical storm in the Gulf and blustery Santa Ana winds in California, this country saw it all in just six days.

Starting on Tuesday, a pre-season winter storm dumped massive amounts of snow across Wyoming and South Dakota. Some places, like Deadwood, SD received as much as 48 inches.

On Wednesday, the NWS named Tropical Storm Karen. Moving north across the Gulf of Mexico, it threatened coastal communities from Louisiana to Florida with heavy rain and storm surge flooding.  Luckily, however, the storm was downgraded to a rainstorm by the time it came ashore.

By Friday, the cold air that produced the blizzard in the northern plains collided with warm moist air to the east and unleashed severe thunderstorms across the region.  They, in turn, spawned numerous tornadoes.  One of the hardest hit areas was Wayne, NE where an EF-4 twister with winds measured up to 170-mph tore through the town.  While widespread property damage and numerous injuries were reported, there were no fatalities.

Over the weekend, powerful Santa Ana winds blasted southern California with gusts reaching 90-mph in some areas.  These warm, dry winds helped fuel a large wildfire in San Diego County.

While extreme weather events are not unusual in this country, having such a large number and wide variety happen more-or-less at once is very rare.