Tuesday, March 18, 2014

St. Patty's Day Storm

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

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

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

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

Surface Map from Monday Afternoon. Courtesy of MeteoStar.

Jet Stream Monday morning. Courtesy of MeteoStar.

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

Post by meteorologist Jim Woodmencey
Maps from MeteoStar LEADS On-Line

Wednesday, March 5, 2014

A Rare "Thundersnow" Event in Jackson Hole

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

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

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

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

Lightning Strike Map from Tuesday evening

Infra-red Satellite Image
Base Relectivity Radar Image

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

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

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

Tuesday, February 25, 2014

Stationary Front Divides the Warm from the Cold

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

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

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

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

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

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

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

Post by meteorologist Jim Woodmencey
Map from NOAA

Friday, February 7, 2014

The Next Big Winter Storm for the West & Jackson Hole

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

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

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

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

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

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

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

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

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

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

Forecasted Water Amounts for same time period.

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

Wednesday, January 29, 2014

Winter Storm Warning...and other Weather Alerts

Meteorologist Jim Woodmencey

Good timing on the weather!
In last week's Jackson Hole News & Guide I primed you with an article about NWS
Winter Weather Advisories, Watches, and Warnings….what they mean to you.......and here we go, with a "Winter Storm Warning" for Jackson Hole issued Wednesday mroning, which was upgraded from a "Watch" that was issued on Tuesday morning.

Mountain Weather Column
Jackson Hole News & Guide
January 22, 2014 Issue
During the course of the winter season we will see a number of different weather alerts issued by the National Weather Service Office in Riverton, which is responsible for issuing weather warnings for all of western Wyoming.

In this week’s column I will delineate for you the different types of Advisories, Watches, and Warnings you may come across during the winter season, what the criteria is for issuing them, and what they really mean to you.

The National Weather Service will issue Winter Weather “Advisories” to alert the public to weather situations that may present a hazard, but do not meet the “Warning” category criteria. “Advisories” are for weather that may cause significant inconvenience or difficulty to travelers. 

The earliest type of advisory you may see is a “Hazardous Weather Outlook”, which may be issued several days ahead of time if a large storm system is expected, which might affect travel. Other wintertime advisories and their criteria are listed below.

Winter Weather Advisory:  Most commonly issued for snow events or when a combination of precipitation is expected; such as: snow, sleet, freezing rain, or blowing snow, is in the forecast.

A Snow Advisory would be a more specific type of Winter Weather Advisory that would be issued when snowfall is expected to be between 3 and 6 inches in 24 hours in valley locations. Mountain locations have snow advisories issued when between 6 and12 inches of accumulation is expected in 24 hours.

Blowing Snow Advisory:  Issued when wind-driven snow intermittently reduces visibility to ¼ mile or less. Travel may be hampered.  Strong winds can create blowing snow by picking up old or new snow.

Other winter advisories you might see are: Wind-Chill Advisory (-20F) or a Dense Fog Advisory (¼ mile visibility).

Watches and Warnings

“Watches” and “Warnings” are more serious than “Advisories”.

A “Watch” is issued when conditions are favorable for the development of a particular weather event that meets certain threshold criteria.  A “Warning” is issued when a particular severe weather condition is imminent or actually occurring. “Watches” & “Warnings” are usually reserved for weather situations that will make travel impossible, or could pose a threat to life and property.

Note: Be aware that the criteria used for Advisories and Warnings is different for different locations across the country.

“Watches” are intended to provide enough lead-time so that people can adjust their schedules. “Watches” may be issued up to 48 hours in advance of the event and generally will precede a “Warning”. 

When a Watch is upgraded to a Warning, you should take it very seriously. Listed below are the most common Warnings you may see issued in western Wyoming.

Winter Storm Warning: Issued when heavy snow and/or strong wind are possible.

Winter Storm Warning for Heavy Snow: Issued when snowfall is expected to exceed 6 inches per event in the valley. For mountain locations it is 12 inches or more per event.

Blizzard Warning: 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. And these conditions are expected to last for 3 hours or longer.

Other Warnings might include: Wind-Chill Warning (-30F) or an Avalanche Warning (High to Extreme Avalanche danger rating).

Winter Weather Advisory & Warning Criteria for Heavy Snow in Western Wyoming
Per Event or Time Period

3 to 6 inches
6 inches or more
5 to 12 inches
12 inches or more
From NWS Central Region

While a "Winter Storm Warning" may not necessarily translate to copious powder for skiers, it should at least mean that we are in for some nasty weather involving snow, wind, bad visibility, and sporty driving conditions.

Blizzard, Winter storm, and Avalanche Warnings are serious enough to be sent out on the Emergency Alert System (EAS), and if you subscribe to NIXLE alerts, you should see them show up there, as well.

On the MountainWeather.com website on the Jackson Hole Forecast page, a flashing box will appear at the top of that page above the forecast content whenever the National Weather Service in Riverton has issued any sort of weather alert specifically for Teton County. Read these carefully, and don’t just assume the flashing box means a big dump is on the way!

Post by Meteorologist Jim Woodmencey
Republished with permission from JH N&G

Tuesday, January 21, 2014

Jackson was Colder & Drier than Normal in 2013

Meteorologist Jim Woodmencey
This article first appeared a week ago in the Jackson Hole News & Guide's Mountain Weather column, by meteorologist Jim Woodmencey and is republished here on the mountainweather blog.......

To characterize the entire year 2013 in Jackson as “colder and drier” than normal, does not adequately describe the actual ups and downs of weather that we experienced here over the previous 12 months. So, in order to give you a better feel for what transpired weather-wise here in Jackson Hole in 2013, I will “break it down”, like an ESPN post-game analyst, quarter by quarter, or season by season.

Winter 2013: January- February

The winter of 2012-13 ended up with below normal precipitation and snowfall in town. Below normal precipitation would a recurring problem until the Fall of 2013.

Temperatures were also colder than normal to start the year, a theme that would also continue throughout the year. The coldest day of 2013 was on January 3rd, with a morning low of 22-degrees below zero.

Spring 2013: March-April-May

For the spring months, temperatures and precipitation stayed very close to average. April was the standout month, with colder than normal temps and above normal precip. The month of May was the snowiest of the three months, with just over 5 inches of snow in town. That was more snow than we had in March and April combined, which is a little out of whack.

Summer 2013: June-July-August

We had less than 50-percent of our normal precipitation in town for the three months of summer. June and August were especially dry. July actually registered a few hundredths of an inch above normal in the climate station rain bucket.

There were also a few notable days with severe thunderstorm activity, large hail, gusty downdraft winds, and one particularly large cell that passed over town in mid-June that looked like it could spawn a tornado at any moment.

Temperatures each month of the summer were about as close to the historic average as you can get. The hottest temperature of 2013, recorded at the Jackson Climate Station thermometer, was 86 degrees. That actually occurred twice in August, twice in July, and also one day at the end of June. We never “officially” hit 90 degrees all summer.

Big thunderstorm cell over Snow King Mountain in mid-June. Nice shot Chris!

Fall 2013: September-October-November

Wet, cold, and snowy would be the best way to describe the fall season. Abundant precipitation in town helped make up for the low water amounts from summer. And snow was accumulating in the mountains by late September.

September was the wettest month this past year, with 2.91 inches of precip in town. The average in September is 1.27 inches. In October we had over 2 inches of precip, and 9 inches of snow was counted in town. That was more snow than we would get in November, and also more than we received in December!

Not surprisingly, September and October were much colder than normal. November was the only month in 2013 that recorded above normal temperatures, just barely. The average high in November 2013 was 40-degrees, which is normal. Average low in November 2013 was 19, the normal is 16 degrees.

Early Winter 2013: December

You could count the snowstorms we had in December on one hand: A good dump in early December, another decent snowfall a couple days before Christmas, and a few extra inches on New Year’s Eve to ring in 2014.

We had about half of our normal precipitation this past December, and less than half of our normal snowfall. Only 7 inches of snow recorded in Town, average December snowfall is 17 inches. (Note: some observations were missing, so this number may be misleading).

One thing is for sure, December 2013 was colder than average, with the month’s average high at 26 degrees, or two degrees below normal. The average low for the month of one degree was six degrees below normal.

Summary of 2013

If you compare 2013’s annual precipitation totals and the average temperatures for the year to the historic averages, then “colder and drier than normal” does sum it up for Jackson’s weather in 2013.

The average annual high temperature was three degrees colder than normal, and average annual low temperature was right at normal. Precipitation was 86-percent of normal for the year and annual snowfall, for the calendar year in town, was 58% of normal.

Annual Weather Stats for 2013 compared to Historic Averages

High Temp
Low Temp
Annual Snowfall
The Year
13.69 inches
45 inches
Historic Averages
15.83 inches
77 inches
Note: Historic data is from the Jackson Climate Station 1905-2012

 (Note: This post is from the Jackson Hole News and Guide Mountain Weather Column, January 8, 2014)

Monday, January 13, 2014

Jackson Hole's Snowstorm & Western US Snowdepths

Meteorologist Jim Woodmencey
The storm from this past weekend brought snow, along with a lot of wind to the Jackson Hole area. Around two feet of snow to the higher elevations of the Tetons, containing over 2 inches of water snow from Friday night thru Monday morning. Winds were averaging around 30 mph at ridgetop level, with gusts over 60mph, helping to load leeward slopes and creating dangerous avalanche conditions.

With all the wind we had, it is difficult to get a completely accurate reading of snow or water amounts. It's hard to chase that snow down when it is falling horizontally!

The Bridger-Teton National Forest Avalanche Center reported on Monday morning that some areas at the higher elevations received as much as 45 inches of snow over the past 4 days, along with 4.5 inches of water.

A summary of data reported during this past week’s storm cycle, taken from the Rendezvous Bowl and Raymer weather plots located at around 9500-ft. at JHMR, is shown in the table below. Almost 3 feet with more than 3 inches of water!

Summary of Snow and Water Accumulation
24-Hour and Storm Totals
Rendezvous Bowl

Snow (in.)
H2O (in.)
Snow (in.)
H2O (in.)
Thursday, Jan. 9
Friday, Jan. 10
Saturday, Jan. 11
Sunday Jan. 12
4-Day Storm Totals:
Data from BTNF morning weather summaries of preliminary data from these stations.

USA Snow Depths

For many parts of the west, especially the Sierras, it has been a slim snow year, so far. However, parts of West are doing just fine. The North Cascades, Central Idaho mountains, western Montana’s mountains, the mountains of NW Wyoming, and the higher elevations of the north-central Colorado Rockies have some of the deepest snowdepths in the United States as of Monday morning, January 13, 2014. (See maps below).

USA Snowdepths as of January 13, 2014

Zoom on Western US Snowdepths

Post by Meteorologist Jim Woodmencey
Data from BTNF
Graphic from NOAA

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