Tuesday, July 22, 2014

How to keep from getting Zapped in a Thunderstorm

 (Note: This is re-posted here from the original article that appeared in Jackson Hole News & Guide Mountain Weather column on July 9, 2014.)

In my last Mountain Weather column (June 25) I gave you a few facts and statistics about lightning related incidents, both nationally and locally. This week I will give you some more practical knowledge about thunderstorms and lightning, and what to do if you find yourself outdoors during a dangerous thunderstorm.

The first thing you need to do is follow the weather forecast, every day, to see what the chances are for thunderstorms. Have some idea if thunderstorms are going to be a threat, and get the latest updated forecast, before you head out the door.

Once out the door, keep an eye on the sky and see how the clouds are developing as the day progresses. If they are growing taller, and the bases of the clouds are getting darker, then thunderstorms and their accompanying lightning may be imminent. Remember: what you observe always trumps what the forecast said!




When to Hide

As soon as you can hear the thunder, lightning is close enough to strike, and it is time to seek shelter. Lightning can be seen from about 15 miles away, and thunder can be heard up to about 10 miles away, on a good day. In a canyon, or out in the wind, it may not be heard until much closer.

You can estimate how far away the lightning is by counting the seconds between when you see the flash of lightning and when you hear the thunder. Count in seconds (one-thousand-one, one-thousand two, etc.). Five seconds equals one mile. If you count to 25, that means the lightning is 5 miles away, which is actually close enough to be able to reach out and kill you.

Don’t wait for it to start raining before you think about seeking shelter, or for the first bolt to hit nearby, as most people tend to do.

Where to Hide

If you can get to a building, or a car, that is the safest place to be. Picnic shelters, a gazebo, a dugout at the ball field, are NOT good shelters from lightning. Your car is, not because the tires insulate, but because the frame and body take all the electrical current and disperses it. Get in the car, don’t touch the doorframe, and wait it out.

If you find yourself stuck outside, far from the car or a building, don’t run underneath the biggest, loneliest looking tree for shelter. A better option is to get into a stand of trees of similar height, and make sure you are not standing on top of any tree roots. If all else fails, get into a low spot in the terrain, that is not a watercourse, and crouch down.

If you are in the mountains, get down off the higher ridgetops, get into a gully or low spot between ridges, but don’t sit in a gully that might become a running watercourse. Also, DO NOT get under an overhanging rock or in a cave. Electricity will often jump the gap that you are sitting or standing in when lightning strikes nearby.

If you are on a lake or river, get out of the water, and off the boat. Water is a great conductor of electricity! Get to shore and find a stand of similar sized trees to wait it out.

How to Hide

The absolute best thing you can do to prevent injuries from lightning striking nearby is: KEEP YOUR FEET TOGETHER.

Keeping your feet together will help prevent dangerous ground currents from running up through one leg and exiting down the other. You may feel a bump under your feet as the ground current passes, if both feet are together, but it is unlikely that you would receive a serious electrical injury. Your other option is to sit on the ground with your legs crossed, Indian-style.

This is why lightning, due to the difference in voltage of the ground current between each leg, frequently kills cows and sheep. They don’t have the ability, or the sense, to put all four of their feet together.

Also, get away from any metal objects, or empty your pack of any metal. You might want to also take off any metal jewelry.

Lastly, don’t huddle together in a group, as cows and sheep also tend to do during thunderstorms. Spread out, at least 25-feet feet apart, 50 feet of separation from your companions is even better.

A lightning strike has about the same kill-casualty radius as a standard Army-issue hand grenade. Either one can kill you and everyone that is within a 25-foot radius of the explosive, and injure you or everyone out to a 50-foot radius.

You should stay in a safe location or position for at least 20 to 30 minutes after the last lightning bolt strikes, to make sure the thunderstorm is a safe distance away. That’s another thing that is hard to get people to do. We usually come back out to play way too soon.

TIMING LIGHTNING to THUNDER

Lightning travels at the speed of light, which is faster than the speed of sound that Thunder travels. Therefore, lightning is seen before the thunder is heard.
You can time how far away the lightning is by counting, in seconds (one-thousand-one, one-thousand-two, etc.), From the time you see the flash, until the time you hear the thunder.
Take the number of seconds and divide by 5 to calculate the distance the lightning is from you in miles.
Seconds Counted / 5 Seconds per mile = Number of Miles Away.
25 seconds = 5 miles away.  5 seconds = one mile away.  1 second = less than a quarter mile away.

 20/20 Lightning Rule
If the time between the lightning flash and the thunder is 20 seconds or less, then the lightning bolt was less than 5 miles from your location.  It is time to seek shelter IMMEDIATELY!
After the last lightning bolt is seen, give it at least 20 minutes until you return to any exposed area. ( A “30/30” Rule is even safer!)

Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Mountains for over 20 years.

Tuesday, July 15, 2014

Thunderstorms and Cool Clouds from July 14, 2014

Monday afternoon and evening provided some great visuals in the sky, with clouds, lightning, and some cool colors around the Jackson Hole area.
Below is a selection of the great photos various weather fans sent in.
As I receive more, I will add them onto this blog post.

Thanks to all those who made a submission, and I will also try and rotate some of these onto the mountainweaher.com Homepage this next week. I was hard to pick just one favorite!

I ordered them by time of day to give you a feeling of the sequence of the day as storms rolled through in several waves between around 2:00 pm and 9:00 pm on July 14, 2014.

Other notes from Monday's Thunderstorms:
Lots of lightning, both in-cloud & ground strikes. "Marble" or "grape" sized hail was reported on the Teton Village Road and in Rafter-J south of town.















Lightning Strike map from Monday Evening's T-storms

Post by meteorologist Jim Woodmencey

Saturday, May 24, 2014

What makes the wind blow?

(Article re-printed from the Mountain Weather Column in the Jackson Hole News and Guide, May 14, 2014)

Spring is the time of year that we can experience an increase in the wind around western Wyoming, even here in the relatively wind-protected Jackson Hole Valley. Usually when the wind picks up around here, I am asked one of two questions, either, “When is it going to stop?” or “Why is it so windy?”

Answering the first question correctly depends on how good a forecast I did that day. Answering the second question usually requires a lengthier and more technical explanation.

In this week’s column, I will give you that more technical explanation, to save us both some time when I see you on the street on the next “windy” day.

The Wind Blows

Bob Dylan says, “You don’t need to be a weatherman to know which way the wind blows”. I say to Bob, “But, it doesn’t hurt!”

Wind is a rather elusive meteorological variable, especially since we can’t really see it, like we can clouds or precipitation. Wind, during a storm, is something we expect. Wind can be an unpleasant nuisance though, especially on a bluebird day, to cyclists, sailors, paragliders, climbers, etc.

The atmosphere is constantly adjusting itself, trying to balance the changes in temperature and humidity from one part of the planet to the other. This leads to different areas of high and low pressure that encircle the globe, and the bigger the difference in temperature, and/or humidity, from one area to another, the bigger the difference in pressure, and the faster the wind blows.

That’s what gets it started in motion, always moving from high pressure towards lower pressure. Friction at the surface, mountains, buildings, etc. can slow the wind down and alter its direction. In the upper levels of the atmosphere, the wind starts moving from high to low, but it gets re-routed, and turned to the right in the northern hemisphere, because the earth is rotating. This is known as the Coriolis Effect.

When we observe stronger winds, it means that there is a big difference in pressure across the region, or sometimes across the entire country. A big low-pressure center over the mid-western U.S. and a big area of high-pressure along the West Coast, for instance, could result in strong winds in-between, over the Rockies.

That difference in pressure from Point-A to Point-B is known as a pressure-gradient. A strong pressure-gradient equals strong winds. You can track that each day by looking at a surface weather map, and look for big highs and big lows, and lots of pressure contour lines in-between, as well.

The other thing that can cause strong winds at the surface is when the jet stream is directly overhead.

The Jet Stream

The jet stream lives up at around 30,000-ft. in the atmosphere, up where jets fly. It is defined as the region of the atmosphere where the fastest winds are occurring. The jet stream is also a dividing line, of sorts, between the coldest air to the north, and warmest air to the south. And once again, wherever there is a big difference in temperature across a region of the world, there will be a big difference in pressure, and thus faster wind speeds.

In the springtime, the jet stream is trying to migrate from a more southern position to a more northern position, following the line between the warmest and coldest air, which is changing rapidly with the tilt of the earth, the angle of the sun, and increased solar radiation over the northern Hemisphere.

Whenever that jet is directly overhead, it has the potential to translate down to the surface and give us a little more wind down here at the surface.

You can track when the winds will be decreasing by following the progression of the jet stream, and when it is moving away from your location.

Find current, and forecasted, surface maps and jet stream maps here:
USA Forecast Maps


Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Mountains for over 20 years.






Weather Map Examples of Northerly Wind over Rockies


Source: MeteoStar
Source: NCAR
Surface Map
Jet Stream Map

Tuesday, March 18, 2014

St. Patty's Day Storm


Meteorologist Jim Woodmencey
The storm that hit Jackson Hole Monday afternoon, on Saint Patrick's Day, dumped 3 to 6 inches of snow around the valley. A total of 10 to 16 inches of new snow in the mountains, was reported at Jackson Hole and Grand Targhee Tuesday morning, from the previous 24-hours. Most of that snow fell between Noon and 6:00 pm on St. Patty's Day.

Winds were strong, as well, with gusts of 49 mph at the Jackson Hole Airport and 75 mph at the top of the Tram.

A pretty good snow & blow for late March. Spring Season begins on Thursday!

Some weather maps below from yesterday afternoon & evening.
And the Snowcover Map for USA.....western Wyoming looking the fattest of anywhere.


Surface Map from Monday Afternoon. Courtesy of MeteoStar.

Jet Stream Monday morning. Courtesy of MeteoStar.

Pocatello Radar Monday @ 2pm MDT
Snowcover Map as of Tuesday March 18, 2014





Post by meteorologist Jim Woodmencey
Maps from MeteoStar LEADS On-Line
& NOAA/NWS

Wednesday, March 5, 2014

A Rare "Thundersnow" Event in Jackson Hole

Meteorologist Jim Woodmencey
There was a "Thundersnow" event that occurred over the Jackson Hole area Tuesday evening, March 4th, 2014.  A small, but very potent upper level disturbance passed through, concentrating a brief but intense period of snowfall right over Teton County Idaho & Teton County Wyoming between 5:00 and 8:00 pm MST.

Thundersnow is a rare occurrence, but basically it is a summer-like thunderstorm with winter-like snow in it, and yes, there was lightning in it. In 2 or 3 hours this storm produce between 3 and 5 inches of snow around Jackson Hole and the Teton Mountains.

To produce a thundersnow-storm,  a very unstable atmosphere is required, we had that as temps in the valleys were up around 40 degrees or warmer Tuesday afternoon, and the much colder air aloft associated with that Trof created the needed instability in the atmosphere. The timing of the clashing of the warmer air down low and the colder air aloft could not have been better. And, there was a nice impulse of moisture to go with it.

In this case, in order to generate lightning in the winter months, the mountains provided the extra lift required to develop that thunderstorm last evening. As the cell dispensed it's precip, temperatures
in the valley dropped to 30-degrees almost instantly.
 
Lightning Map below, with satellite & radar images from around the time of greatest intensity.


Lightning Strike Map from Tuesday evening



Infra-red Satellite Image
Base Relectivity Radar Image

You can see how small this thundersnow cell was, relatively speaking. Because of its size, it is one of those weather events that is difficult to forecast for, at least very far in advance. There was virtually no indication that this storm would blossom like it did, until about an hour ahead of time. Small features like this totally slips through the cracks in the computer models.

There was very little indication on anything I looked at early on Tuesday morning to suggest there would even still be any precipitation by evening Tuesday.


Post by Jim Woodmencey, meteorologist
Lightning Map & Radar graphic from Leads On-line
and Satellite image from NOAA

Tuesday, February 25, 2014

Stationary Front Divides the Warm from the Cold

Meteorologist Jim Woodmencey
It can be a game of inches sometimes on the weather map. A stationary front that lies across central Idaho and Northwest Wyoming is separating cold air to the north of that line from warmer air to the south of that line.

This morning (Tuesday Feb. 25), temperatures in Southwest Montana are between 6 and 12 degrees, north of that in Great Falls, MT it is 9 below zero!

Temperatures in Southeast Idaho and Western Wyoming are between 35 and 40 degrees.

Snowing pretty heartily to the north of that line, from Dillon to Billings. Some rain showers at lower elevations to the south of that line, with some snow falling at higher elevations. Let's root for that line to shift back to the south a few inches today and bring Jackson Hole a little shot of snow!

Surface Weather Map with Fronts & Radar. Tuesday, February 25, 2014 at 3:00 am MST

Further south of that stationary front, it is just warm and dry across California, Nevada, Utah, and western Colorado.

By the way, it was along that same stationary front that we saw copious amounts of snow in Jackson Hole/Tetons over the weekend, when we were on the colder side of that line.


Post by meteorologist Jim Woodmencey
Map from NOAA

Friday, February 7, 2014

The Next Big Winter Storm for the West & Jackson Hole

Meteorologist Jim Woodmencey
Another good storm cycle for a strip of the western United States, from Tahoe to the Tetons. And of course, the best powder will fall in western Wyoming's mountains this weekend, where temps and  elevations are ideal.

Powerful Westerly Jet stream carries lots of Pacific moisture across California and the Sierras, unfortunately for that area the freezing levels will be rather high, and snow levels will rise through the weekend, with rain below about the 7,000-ft. elevation, in general. But heavy snow above that elevation, measured in feet! Like 3 or 4 or more! Be happy for the water down there, I guess, which will exceed 4 inches from this cycle through the weekend.

Over the Intermountain West, Idaho, western and central mountains do well, and the further north you get the lower the snow levels. In western Wyoming, a couple of feet of snow accumulation is possible over the weekend for Teton Mountains and a foot in the Hole itself. Looks like another 1.50 to 2 inches of water will be added to the mountain snowpack.

The maps below show accumulated snowfall totals and water amounts for the period beginning Friday morning Feb. 7th through Monday morning Feb. 10th.

Satellite Photo shows connection of moisture from Hawaii to West Coast, another "Pineapple" connection.

Jet stream map shows position of jet across North America on Saturday morning. Te core of that jet that will be right over Idaho and Wyoming at 35,000-ft. will have wind speeds of 170 to almost 200 mph, according to this models prediction. Strongest jet we've seen this winter.

February is starting to look really good, with a good scenario for producing snow for the coming weekend and through the end of next week.

Satellite Friday morning, white line traces the "pineapple" connection of moisture all the way to Hawaii

Jet stream forecast position at Noon MST on Saturday, red zone is over 150 knots 170 mph).

Forecast Total Snow Accumulations, Friday morning thru Monday morning. In the "pink is approaching 2 feet.

Forecasted Water Amounts for same time period.

Zoomed in to snow accumulations for ID-NV-UT-Western WY

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