Monday, January 5, 2015

Big Snow & Blow in the Tetons

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

Friday, December 26, 2014

Understanding Winter Weather Warnings

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 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:


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 and has been forecasting the weather in Jackson Hole and the Teton Mountains for over 20 years.

Wednesday, November 26, 2014

Winter Outlook 2014-15

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
Above (33%)
Above (40%)
Above (40%)
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 and has been forecasting the weather in Jackson Hole and the Teton Mountains for over 20 years.

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 and has been forecasting the weather in Jackson Hole and the Teton Mountains for over 20 years.

Posted by meteorologist Jim Woodmencey

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 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.


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 %
60 % to 70 %
Possible or Likely
80 % to 100 %
(usually no term used,
certainty is high)

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

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