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.

• 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

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.

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.

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.

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

Meteorologist Jim Woodmencey

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

Weather Map Examples of Northerly Wind over Rockies
Source: MeteoStar	Source: NCAR
Surface Map	Jet Stream Map