All posts by Jim Woodmencey

Jackson Hole’s Winter 2014-15 Reviewed

Mountain Weather Blog
Meteorologist Jim Woodmencey

This winter began pretty much the same way it ended, with people thinking about mowing their lawns. Those thoughts were squashed at both ends with abrupt changes from warm and sunny to cold and snowy.

In this week’s column I will review the winter season and see how it stacked up against the historic records. In brief, I am sure everyone would agree it was warm and relatively dry. But here are all the details to put it in perspective, from beginning to bitter end.

Late Fall

Think back to the first week of November, when temperatures were in the lower 60’s in Jackson, and in the 50’s for the start of the second week of November. The grass was green, the birds were chirping, and no one was thinking of heading south.  Heck, it was 54-degrees on Sunday afternoon November 9th. Then it snowed the next day. Five inches in town, over a foot in the mountains, followed by record cold temperatures for early November. Overnight lows in Jackson got down to 22-below zero on November 16.
So much for mowing the lawn, everyone figured it was “game-on” at that point. Some headed south, others waxed skis.
November snowfall finished strong; with almost triple the normal monthly snowfall in town, 28 inches compared to an average of 10 inches. November was also more than three degrees colder than normal. And it would end up that November was the snowiest month of the season, and the only one with below normal temperatures.
December-January
December was about as close to normal as you can get for snowfall in town, with 19 inches in December 2014, compared to an average of 18 inches. In the mountains, at the bottom of Rendezvous Bowl at JHMR, there was 76 inches of snowfall, normal December snowfall is 79 inches.
December started the trend of warmer temperatures, ending up four degrees warmer than normal. January temps were only one degree above normal, when you compare monthly mean temperatures, that is, the average of the monthly average high and low temps.
February-March
February was the fourth warmest on record in Jackson, with the mean temperature for the month a full eight degrees above normal. Total snowfall in town was only four inches, well below the norm of 12 inches for the month.
February snowfall in the mountains was well below normal also, with 48 inches compared to the average of 67 inches in February.
March was cold for the first few days, then whimpered heavily as we hit a spell of warm and dry weather that lasted from March 6th through March 23rd. That spell peaked when we hit 60-degrees for the first time this year on March 16th. Hardly any snow fell in town, and the grand total for the month was just four inches, less than half the average of nine inches.
The mountains didn’t fair much better, with a total of just 23 inches at Rendezvous Bowl in March. Average March snowfall is 65 inches at that location. Not the grimmest March ever in the mountains, that distinction belongs to March of 1994 with just 16 inches. March of 2007 was another bleak one, with only 18 inches of total snowfall up there in March.
Winter Snow Totals
For the four-month period, December through March, the Town of Jackson had 40 inches of snow or 68-percent of normal, the average is 59 inches. However, if you were to include the snowfall we got in November, that would push the total snowfall to 68 inches. Normal snowfall for the five months is 69 inches. So, that would mean we had a pretty normal “snowfall season”, with 99-percent of our average snowfall for November through March. How about that for a stat!
Same thing was true with the water in that snow, December through March was 74-percent of normal for the four month period. Toss November’s water in there and we were 96-percent of normal precipitation for the five month period.
The mountains received 202 inches for December through March or 68-percent of normal, the average is 295 inches. If you pile November’s snow on top of that, it brings the entire season’s snowfall total up to about 81-percent of normal at JHMR. Once again, November carried us through an otherwise dry winter season.
  
Winter Temps
Temperature-wise this winter we ended up about 4-degrees warmer than normal in Jackson, when you look at the average mean temperature for the four-month period, December through March. The historic average mean winter temperature would be about 21-degrees, this winter we had an average mean temperature of 25-degrees.
That would make the Winter of 2014-15 the sixth warmest winter on record in town. The Winters of 2004-05, 2002-03, 1999-00, 1994-95, and 1952-53 were all warmer than this one, for the four-month period. That is still quite a feat to string together four winter months in a row with above normal mean monthly temperatures.
We should count ourselves lucky, compared to many other areas around the Western United States this winter. Our snowfall was way ahead of everyone else, west of the Mississippi, and temperatures at elevation stayed cold enough to preserve the snow until the end. The Eastern United States was the complete opposite of the West this winter, much colder, and much, much snowier than normal.
Looks like I’ve run out of space, so I will have to save any discussion of “why” this winter was like it was for a future column. For now, get out and enjoy your last licks of the ski season.
(*Note: This blog post originally appeared in the JH News & Guide April 1 2015).
 
Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Mountains for more than 20 years.

Big Snow & Blow in the Tetons

Mountain Weather Blog
Meteorologist Jim Woodmencey

Lots of SNOW & wind for Jackson Hole, ski areas and weather instruments around the mountains reporting 20 to 26 inches of new snow from Friday night through Monday morning in the Teton Mountains. 

But, this is not technically a big “storm system”. It is a STORM, and we are getting very stormy weather…..but it is not being generated from a typical low pressure system, or what we would call a storm system.

This is a strong Northwest Flow aloft that is carrying moisture over the top of a Ridge of High pressure that is parked over the Western U.S.


Yes, this is sometimes referred to as a “Dirty Ridge”, when moisture rides over the northern periphery of the Ridge axis and causes some weather, rather than the clear skies we normally experience when directly underneath the Ridge itself (like California is right now).

There is no Trof of Low pressure in the upper atmosphere anywhere nearby. Just a weak surface Low pressure over Montana. 

But this is one of the best ways to produce snow in the Tetons, with a very moist and strong NW flow.

— 700mb map and Satellite photo shows flow and moisture (RH) in that flow.
— Surface Map shows the overall weather pattern with High pressure to south & west of Wyoming, and a stationary front east of the Continental Divide, with warm air to the west of that line and colder air to the east of that line.

— Snowfall forecast map is for Monday morning thru Tuesday morning.
Good snow producer across the northern Rockies. Nothing going on to the south of Idaho or Wyoming with this current flow.

Infra-Red Satellite 0800 MST 05JAN15

700mb or @ 10,000-ft. 0500 MST 05JAN15
Surface Map 0500 MST 05JAN15

Snowfall forecast map 05 to 06 JAN 2015


Posted by meteorologist Jim Woodmencey
05JAN15

Understanding Winter Weather Warnings

Mountain Weather Blog

Meteorologist Jim Woodmencey
This past year, I became what is known as a “Weather Ready Nation (WRN) Ambassador” The WRN program started in 2011 and it partners private meteorologists, like myself, with NOAA and National Weather Service forecasters, to help spread the word and educate people about how to be prepared for hazardous weather conditions.
In this day and age of the Internet, Facebooking, Tweeting, NIXLE alerts, etc. there is virtually no reason we should not all be getting the message when extreme or hazardous weather is on the way.
For instance, on my website mountainweather.com on the Jackson Hole Forecast page, whenever the NWS in Riverton issues any kind of weather alert, advisory, watch or warning for Teton County Wyoming, a red box appears above the forecast.
This box works great for the big stuff, but it becomes a bit annoying when there is an “Alert!” issued for things like: colder temperatures, valley fog, or slick driving conditions. These are things that would be extreme weather events in L.A., but this is Wyoming, and I think we can handle that sort of stuff on a daily basis.
What is more important than an “Alert”, is an “Advisory” or most importantly, a “Watch” or “Warning”, of more severe weather. Weather that might cause a true Wyomingite to take heed.
Here are some links to the “Ready Weather Nation” websites:
Advisories
The National Weather Service will issue Winter Weather “Advisories” to alert the public to weather situations that may present a hazard. “Advisories” are for weather that may cause significant inconvenience or difficulty to travelers.  Although, these weather situations should not be life threatening.
The most common Advisories issued during the winter are:
1) Winter Weather Advisory:  Issued for snow events or when a combination of precipitation is expected, such as: snow, sleet, freezing rain, or blowing snow.
2) Snow Advisory: Issued when snowfall is expected to be between 3 and 6 inches in 24 hours in valley locations. For mountain locations the criteria is for 6 to 12 inches of accumulation within 24 hours.
3) Blowing Snow Advisory:  Issued when wind-driven snow intermittently reduces visibility to ¼ mile or less.
Watches and Warnings
“Watches” and “Warnings” are more serious business than advisories.
Winter Storm Watch means: Be Prepared! The NWS issues these when conditions are favorable for dangerous winter weather to occur. It does not mean it will occur, but you should start making preparations in case it does.
Watches are intended to provide enough lead-time so that people can adjust their schedules. They may be issued up to 48 hours in advance of the event and often will precede a “Warning”. 
Winter Storm Warning means: Take Action!  A warning is issued when a winter storm is imminent or occurring. If you hear a warning, immediately go home or seek shelter until it is safe to travel again. Blizzards, extreme cold and windchill can quickly become deadly outside.
Winter Storm Warnings are usually issued when heavy snow and/or strong wind are possible. Heavy snow means that snowfall is expected to exceed 6 inches per event in the valley. For mountain locations it is 12 inches or more per event.
Blizzard Warnings imply strong winds of 35 mph or greater, cold temperatures, and considerable falling and/or blowing snow that frequently drops visibility to ¼ mile or less. These conditions are expected to last for 3 hours or longer.
While a “Winter Storm Warning” may not necessarily translate into a “big dump” for skiers, it should at least prepare you to be cognizant of bad visibility, and some “western” driving conditions.
Unfortunately, there are times when I feel like we are being “over-warned”, and we run the risk of suffering from the “cry wolf syndrome”. That is, we stop paying attention to the warnings, because they come too often, in the form of alerts or advisories, that may seem like just everyday winter weather here in Jackson Hole. Hopefully this article helps to sort out the most important stuff, and explains some of the lesser weather events we may get alerted to during the winter.
 (This article was re-printed in part from the Mountain Weather Column in the Jackson Hole News & Guide)
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.

Winter Outlook 2014-15

Mountain Weather Blog
Meteorologist Jim Woodmencey
(Note: This blog post was re-printed from the Mountain Weather column in the JH News & Guide, Nov. 12, 2014).

Even with the recent snowfall in mid-November, it is a rare day this time of year when someone doesn’t ask me, “What kind of winter are we going to have?”  I know what they are really thinking, they want to know how much powder will we get this winter? Will it be the epic winter to end all winters, or will it just be mediocre, or will it be a total bust?
In an attempt to answer these questions, and save me from having to repeat myself over and over for the next month or so, in this week’s column I will take a look at some of the long-range outlooks and predictions for this coming winter’s weather.
Farmer’s Almanac
One of the most oft-quoted sources of long-range weather prediction is the Farmer’s Almanac. I usually defer to the Old Farmer’s Almanac, the original, familiar, yellow-cover Robert B. Thomas Farmer’s Almanac that was founded in 1792.
Other Almanacs may claim to have been around longer, but this one is the one I have accumulating on my bookshelf from the past 20 years or so. I will tell you what info I plucked out of this year’s edition for this part of western Wyoming, but I will warn you, you may want to cover your eyes or skip this next paragraph, especially if you are prone to weather paranoia.
The Old Farmer’s Almanac 2015 has most of the western U.S. painted into the “mild & dry” category. Western Wyoming and Idaho are expected to have above normal temperatures and below normal snowfall, but above normal precipitation.
I take that to mean, we may see more rain down low, but it should translate to snow up at higher elevations.
Only the Desert Southwest, Arizona and New Mexico fell into the “cold & snowy” categorization. Well, the Midwestern U.S. and the Atlantic Coast, from New Jersey to Rhode Island, also fell into the “cold & snowy” regime, but who cares, there’s no good powder skiing there anyhow.
Now, before you get your Gore-Tex pants in a bunch, let’s look at what the Old Farmer’s Almanac said about last year. They said it would be “cold and snowy”, technically it wasn’t all that cold, and only February and March were snowy. But I’ll give it to them and say that was an accurate forecast of last winter.
But wait, how did they do forecasting the weather this past summer? Oops, they called for “hot & normal precipitation”. That couldn’t be further from correct, as we had a cooler and wetter than normal summer. Therefore, the Almanac’s accuracy rate just dropped to 50-percent.
Climate Prediction Center
Now let’s take a look at what the CPC (Climate Prediction Center) has to say about this coming winter. The CPC is the branch of the National Weather Service that is responsible for doing the long-range weather predicting for the United States.
The CPC has a team of meteorologists and climatologists who sit around all week trying to figure out what the weather is going to do months ahead of time. What they do after a 40-hour workweek of analysis is they assign a probability to whether temperatures or precipitation are going to be above or below normal, for a month or three-month time period. 
When their confidence is high, the probability percentage goes up. When they can’t make up their minds for a certain portion of the country, for instance, then they just say there will be “Equal Chances” (EC) of it being above normal, below normal, or near normal.
For this winter, the CPC is pretty confident that we will have above normal temperatures all winter long. However, after a 40-hour workweek, they apparently still have no opinion on how much precipitation we should expect, as we are in the EC category from December to April.  (See table).
Last year the CPC had us under above normal temperatures and above normal precipitation for November-December-January. Which was not the case. They then gave us “Equal Chances” for the second half of the winter, January-February-March. Seems like the safe bet, in this case they can be correct, no matter what happens.
Are you getting the feeling that maybe putting your faith in long-range forecasts is a waste of time? As I have always maintained, it is difficult enough trying to figure out what tomorrow’s weather will be, let alone the weather two or three months from now.
But here is my prediction for this winter anyway: We will have “Equal Chances” of the powder skiing being better than it has ever been, worse than last year, or just as good as it always is in Jackson Hole.
Climate Prediction Center
Winter Outlook 2014-15
3-Month Outlooks
Temperatures
Precipitation
Dec-Jan-Feb
Above (33%)
EC
Jan-Feb-Mar
Above (40%)
EC
Feb-Mar-Apr
Above (40%)
EC
Probability of above or below is given in a percent, higher percentage relates to high confidence. “EC” means that the CPC believes there are “Equal Chances” of being above, below, or normal.
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.

Wet August in Jackson and Snow in Tetons

Mountain Weather Blog
Meteorologist Jim Woodmencey

It was a much wetter than normal August here in Jackson, as well as in most of Idaho and Wyoming. The Southwestern US from Arizona to Utah was exceptionally wet also.
Early in August it was all about the monsoon, then it was about some cold Low pressure systems the last two weekends, that left behind some decent snowfall in the higher Tetons.

Read all about his past August’s weather in the Mountain Weather column of this week’s Jackson Hole News & Guide.

Some pics of the snow up high in the Tetons from these last two storms below:

These first three are from the first cold storm August 22 to 24, 2014

Black Rock Chimney between Lower & Upper Saddles-Grand Teton.
Photo courtesy of Mike Ruth (August 23)

Looking up Valhalla Canyon at west side of Grand Teton, from Cascade Canyon (August 24)
Photo Jim Woodmencey

Nearing the summit of the South Teton (August 25)
Photo Scott Pedersen

These last three photos are from the second cold storm August 30-31, 2014

On the fixed ropes below the Lower Saddle of the Grand on morning of August 31.
Thse photos all courtesy of David Bowers.

Lower Saddle Exum Hut August 31

Looking North towards the Upper Saddle from Lower Saddle Hut

Post by meteorologist Jim Woodmencey

July Not as Hot as it used to be….

Mountain Weather Blog
Meteorologist Jim Woodmencey

(Reposted from the Mountain Weather column in Aug. 6 Jackson Hole News & Guide).

I heard some complaining in late July that it was “too hot”, which sparked some memories of Julys not so long ago, which truly were “hot”. This July was not.

That also prompted me to dig back through the records to see which Julys were the hottest here in Jackson.  What I found may surprise you, or at least it should cause you to apologize for any whining you may have done about the heat this July.

 To no one’s surprise, July is normally the hottest month of the year here in Jackson. Our average high temperature in July is 82 degrees (actually 81.8) over the last 80-some years of climatological record.

July of 2014 had an average high temperature of 80-degrees, two degrees below normal. There was one day this July (the 23rd) that some thermometers in town hit 90-degrees. However, the highest temperature recorded “officially” at the Town of Jackson Climate Station was 87-degrees. Close, but no 90-degree readings this July.

As a matter of fact, upon further investigation I discovered that we have not seen a temperature reading of 90-degrees at the Jackson Climate Station since August 1, 2008. Prior to that, there were quite a few.

Official Hottest

Probably the best way to gauge a “hot” July is to look at the average high temperature for the month. Another way is to count how many days we hit 90-degrees or above, which usually coincides with those average high temperatures.

Prior to the early 2000’s, July of 1988 was the hottest July on record. That was the famous summer of the Yellowstone Fires, and the average high in Jackson was 88-degrees (actually 87.6). We had eight days with high temperatures of 90-degrees or warmer that July. I should also mention there were four days that weather readings were not recorded in July 1988, which might have pushed that average even higher.

Then along came July 2003, which set the new record with an average high of 90-degrees (actually 90.2). There was a whopping 17 days that July with high temperatures of 90-degrees or warmer, more than twice as many as in July 1988. There were no missing days of weather readings that month. 

Other Julys of note were: July 2007, with an average high of 88-degrees and 13 days that went into the 90’s. And also July 2000, which had an average high of 87-degrees and 11 days in the 90’s.

From Jackson, WY Climate Station records. Note, there were no records for 2012.

Unofficial Hottest

In order to be included in the monthly average temperature record, there cannot be too many missing weather readings. Months that have five or more missing days are not considered when calculating our averages.

There is a July in our official climate record that was likely even hotter than 2003. Unfortunately, there were too many missing days in the record, but I thought it interesting enough to give it an honorable mention. That was way back in July of 1934.

The climate station at that time was located somewhere in the valley to the south and west of town. The observer was Albert Butler, and I would love to know if anyone related is still living in Jackson.

Perhaps Mr. Butler was too busy haying his fields that July and he missed his daily weather readings 11 out of 31 days. Yet, of the remaining 20 days, he did record 14 days with high temperatures of 90-degrees or hotter. His average high temperature in July 1934 was 92-degrees (92.5 actually).

But here is the real kicker, he recorded two days that month, on July 17 and 20, with a high temperature of 101-degrees. And that is the highest temperature we have, for any month, in the official weather records for Jackson.

Cooling Trend

I did not have time to go back through and look at the entire temperature history for July in Jackson to see all the ups and downs between 1934 and 2014. However, there is an obvious trend that you may have noticed if you have lived here for at least the last 15 years.

Looking at the average high temperatures in July from 2000 to 2014, we were on the uphill climb with some very warm Julys from 2000 to 2007. Since then, we have seen a cooling trend, from 2008 through 2014. (See graph).

If you complained in the early 2000’s about the July heat, it was warranted. If you have complained about the heat in recent July’s, it has been unjustified, because July in Jackson is not as hot as it used to be.

Summary of July High Temperatures in Jackson WY
(*From Jackson Hole Climate Station historical data).
  • The historic average high temperature in Jackson in July is 82-degrees.
  • Average high temperature for July 2014 was 80-degrees.
  • No days in July 2014 that were “officially” 90-degrees or warmer.
  • Hottest July ever was in 2003, with an average high of 90-degrees.
  • July 2003 had 17 days of 90-degrees or warmer.
  • The last time we hit 90-degrees in Jackson (officially at the Climate Station) was back on August 1, 2008.

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.

Posted by meteorologist Jim Woodmencey
jim@mountainweather.com

The Monsoon Explained

Mountain Weather Blog
Meteorologist Jim Woodmencey

A couple of summers ago I posted an explanation of the “Monsoon” on this blog, seemed appropriate to re-visit that this week.

We were getting some good surges of moisture from the Desert Southwest Monsoon this week, with rain and thunderstorms plaguing us, and some heavy downpors with late day thunderstorms the last two days (August 5 & 6, 2014).
 

If you happen to read my forecast discussions on the JH Forecast page of www.mountainweather.com or perhaps you listen to my forecast rap in the mornings on the radio (iMix 92.3 FM) you will frequently hear me mention “monsoon moisture”, during the summer months.

The term “monsoon” comes from the Arabic word mausim, which means “a season”. It refers to the large-scale wind flow that lasts for a whole season near the Indian Ocean and the Arabian Sea.
A “monsoon”, therefore, is simply a seasonal wind flow pattern. The Desert Southwest Monsoon that occurs in the United States is similar to the Asian Monsoon that affects India and the Himalayas during this same time of year, from July to early September.
The North American version of the monsoon kind of originates over the interior of Mexico, where very moist (i.e. humid), tropical air is converging over the land from the Pacific Ocean to the west and from the Gulf of Mexico to the east. That moisture is then drawn northward by southerly winds over the hot, dry deserts of the Southwest. This causes frequent strong thunderstorms over New Mexico and Arizona.
Often in July and August the monsoon will surge up into Utah and Colorado, causing thunderstorms over the deserts of southern Utah and western Colorado. Some of these thunderstorms create flash flooding situations in the canyon country of the Southwest.
A few times a summer that monsoon moisture will reach as far north as Northwest Wyoming and Southwest Montana, causing thunderstorms here, which are often some of the strongest of the summer season.
The typical weather pattern that sets up in July and August that will transport the monsoon moisture this far north is when a thermal Low pressure (dry low pressure caused by heating) develops over southeast California and western Arizona, at the same time High pressure develops over eastern Texas. Then when a Low pressure system or upper level Trof of Low pressure moves into the Northwest U.S., that helps draw that monsoon moisture northward. (See today’s weather map, which kind of shows that pattern, but not as well defined as some years).
Surface weather map Wed. August 6, 2014
Monsoon Surge early August 2014

This round of monsoon moisture has been particularly WET, with flooding, landsldides, mudslides, etc. from California to Nevada, and Utah. 

The downpours we had this afternoon (Wednesday August 6, 2014 ) in Jackson were aided by an upper level Trof of Low pressure that is moving over the Great Basin and making things even more unstable. Thunderstorms produced 0.40 inches of rain at my rain gauge in less than an hour! That’s more than we got the previous 24-hours.

Here are some weather maps from today…….Wednesday August 6, 2014.

Satellite showing extent of monsoon moisture from California to Wyoming

Pocatello Radar @ 5pm Wednesday

Snow King Lightning Detector screen shot @ 5pm Wed.

Post by meteorologist Jim Woodmencey

What does Probability of Precipitation Mean?

Mountain Weather Blog
Meteorologist Jim Woodmencey

(Re-posted from original article that appeared in the Jackson Hole News & Guide’s Mountain Weather column, July 23, 2014).

From where I sit, thunderstorm forecasting during the summer season is quite challenging, and on par with snowfall forecasting in the winter. Nailing down where, when and how strong the thunderstorms might be is as difficult a task as deciding where, when and how much snow will fall in the winter season, throughout the Jackson Hole area.

By definition, if there is thunder, there is lightning. And with any thunderstorm, it is implied that there could also be heavy downpours, and/or gusty winds, and/or hail involved. Or, all of the above!

In this week’s column, I will give you some insight into how those forecasts are made, and what they really mean. Maybe that will help you when planning your next outdoor activity.

PoP

Most weather forecasts will provide you with a “probability of precipitation”, or PoP, which might say something like: “30-percent chance of showers today”. That is often interpreted to mean, “it is going to rain for 30-percent of the day”, or “30-percent of the area will get precipitation”. Actually, neither of those is totally accurate.

The correct meteorological translation of “Probability of Precipitation” is: “The likelihood of occurrence of a measurable amount of precipitation (at least 0.01 inches) at any given point within the forecast area.”  The same could be said for the probability of thunderstorms occurring.

From the National Weather Service, PoP is defined mathematically as follows:
PoP = C x A where “C” = the Confidence that precipitation will occur somewhere in the forecast area, and where “A” = the Percent of the Area that will receive measureable precipitation, if it occurs at all.

A  “30-percent PoP” could be calculated one of two ways, as per these examples:

1) There is 100-percent confidence that precipitation will occur, but only 30-percent of the area will get it. (PoP= 1 x .30 = .30 or 30-percent chance).

2) There is only 30-percent confidence that precipitation will occur, but if it does occur, it will produce precipitation over 100-percent of the area. (PoP = .30 x 1 = .30 or 30-percent).

Either way, you should interpret a 30-percent chance to mean: there is a 30-percent chance precipitation (or thunderstorms) will occur at any given point within the forecast area.

You could also interpret that to mean that there is a 70-percent chance there won’t be any precipitation (or thunderstorms) where you are.

Using the Forecast

Nowadays, computer models generate the POP’s and chances for thunderstorms. In some cases, the local forecaster’s experience will get factored into the equation, as well.

What you should look for in the forecast before heading out the door for the day is how certain or uncertain the forecast sounds to you. In other words, if the POP or thunderstorm probability is quite high, 70-percent or greater, that means the computer model, and/or the forecaster is highly certain about what will happen during the forecast time period, and the odds are good that the forecasted weather will materialize.

“Slight chance”, “Chance”, “Possible”, or “Likely” are all uncertain descriptive terms that can be used interchangeably for the percent probability in the text of the forecast. (See the table).

If no uncertain terms or probability numbers are used, then certainty is high, such as, “Thunderstorms today”, or “Showers this afternoon”. Take that to mean the probability of occurrence is greater than 80 percent.

Final Check

Arm yourself with the latest weather forecast before you launch on your next outdoor adventure this summer, then keep an eye on the sky to see how well those probabilities are panning out, I guarantee it will be different everyday. Precipitation or thunderstorms can happen when the POP is 20-percent, and they can miss you completely or never materialize when the POP is 70-percent.

Especially in the mountains, I would treat any mention of showers or thunderstorms in the forecast to mean, “be-on-the-lookout” that day. The higher the percentage, the more likely you will get wet, but I still carry my raincoat on a 20-percent PoP day.

Probability of Precipitation (POP)
Probability Value
“Uncertain” Term
10 to 20 %
Slight Chance
30 % to 50 %
Chance
60 % to 70 %
Possible or Likely
80 % to 100 %
(usually no term used,
certainty is high)

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.

How to keep from getting Zapped in a Thunderstorm

Mountain Weather Blog
Meteorologist Jim Woodmencey

 (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.

Thunderstorms and Cool Clouds from July 14, 2014

Mountain Weather Blog
Meteorologist Jim Woodmencey

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