Thursday, September 4, 2014

Wet August in Jackson and Snow in Tetons

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


Friday, August 8, 2014

July Not as Hot as it used to be....

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

Wednesday, August 6, 2014

The Monsoon Explained

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

Thursday, July 31, 2014

What does Probability of Precipitation Mean?

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.


Tuesday, July 22, 2014

How to keep from getting Zapped in a Thunderstorm

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.

Tuesday, July 15, 2014

Thunderstorms and Cool Clouds from July 14, 2014

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

Saturday, May 24, 2014

What makes the wind blow?

Meteorologist Jim Woodmencey
(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

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