Meteorologist Jim Woodmencey

Jackson Hole and the Tetons are going to be in for some decent snowfall the rest of this week. Snow Thursday will get things going with a somewhat weaker storm moving across the Northern Rockies. Then a second storm system that is looking much more powerful, moving across the southern Gulf of Alaska Friday will punch inland for the weekend.

The higher elevations of the Cascades of Washington and Oregon stand to get some significant snowfall. The central Idaho mountains will also benefit with some heavier snowfall.

In the Tetons of western Wyoming, two-feet or more of snow and between 2 and 3 inches of water could accumulate between Thursday morning and Sunday morning. This will be accompanied by strong  winds. And then finish off with a little more snow & wind, and cooler temps, on Sunday.

Forecast Weather Map for Saturday 11 January 2014

Forecast Total Snowfall Amounts Thursday a.m thru Saturday p.m. (Jan 8 to 11)

CAUTION!

PLEASE be careful to not get so jacked-up for skiing powder in the backcountry that you forget to pay attention to the avalanche conditions. Remember, all this new snow is falling on a weak snowpack, and avalanche danger is going to rise, especially with the wind helping to add additional load those slopes!

PAY ATTENTION to the AVALANCHE FORECAST for the areas you like to go to. Get avalanche info for all areas of the Western US on the Skier’s Page of mountainweather.com

If you are going to your favorite ski area, please exercise some patience for ski area workers as they may need extra time to open the mountain and make it safe for you. And also highway avalanche control workers who will doing the same this weekend.

Post by Meteorologist Jim Woodmencey
Graphics from NOAA

Allow me to officially welcome you to the start of Winter! Even though it has been snowing and relatively cold here in Jackson Hole for three months already! Remember those first snow storms in the mountains at the end of September?

Despite that,

This creates the shortest days of the year in Jackson Hole at about 43.5 degrees North Latitude, or 67 degrees of latitude further north from where the sun is shining directly overhead.

There is less than nine hours of daylight, and just over 15 hours of darkness this time of year.  Exactly the opposite is true in the Southern Hemisphere, where they will be having their Summer Solstice on December 21.

During the week or two around the Solstice, the length of each day is very similar. The days won’t start getting much longer until well into January. After that, the days will steadily lengthen as we progress towards the Spring Equinox, which is another 90 days away in March.

Post by Jim Woodmencey, meteorologist

Meteorologist Jim Woodmencey

After a pretty good drought the last week or so, it looks like the weather pattern is finally changing to get the Pacific Northwest & the Rockies back into some new snow.

Low pressure center developing over British Columbia on Sunday, December 1st, will favor the Washington Cascades and northern Idaho & Montana initially. But some snow will fall in the mountains of SW Montana and western Wyoming.

The jet stream position is a little too far north to bring the best energy further south until Sunday night and Monday, when it drives right over western Wyoming and favors Jackson Hole & the Tetons. Low pressure center over BC moves east along the Canadian border and puts the Teton Mountains under a strong Westerly flow on Monday, finishing up on Tuesday with a colder Northwesterly flow and lighter winds and lighter snowfall.

Snow Amounts

Snowfall amounts should be rather impressive, especially in the Washington Cascades when you include snow accumulations this weekend and through Monday evening. Around 2 feet of new snow should be expected at around the 9,000-ft. elevation, more at higher elevations and in some favored locations. (See snowfall forecast maps below).

Then on Tuesday & Wednesday the focus will shift over the northern & central Colorado Rockies.

Water Amounts

Models are showing impressive water amounts also, with 4 to 5 inches of water forecast through Monday night for the Cascades, and 2 to 3 inches of water content for the Tetons.

It will be interesting to follow this storm and see how much we get. Certainly enough to make some good powder skiing again, and certainly enough to up the ante on the avalanche danger this week….especially combining the amount of wind, water, and snow.

Word of Caution: Be careful how you manage your enthusiasm for powder with the impending hazard in the backcountry!

Forecasted Snowfall Amounts Northwest US thru Monday evening, Dec. 2

Zoom in on same Forecasted Snowfall Amounts Western WY area

Total Forecasted Water Amounts Nov. 30 thru Dec. 2

Jet stream position on Monday December 2 (Red core is over 120 mph)

Posted by meteorologist Jim Woodmencey
Graphics from NOAA, NEXLAB, & LEADS On-line

Meteorologist Jim Woodmencey

Usually by now, I will hear some utterance to the effect, “Oh, it’s an El Nino year”, or, “I heard we are gonna have another La Nina”.

“El Nino” and “La Nina” have become buzzwords for ski towns like Jackson Hole El Nino has become synonymous with low-snowfall winters and La Nina with above normal snowfall winters.  No Nino doesn’t seem to have its own buzz, although if you looked at the No Nino winters we’ve had in Jackson Hole over the years, you might tag it as a buzz-killer.

First, let’s get some definition as to what El Nino, La Nina, and No Nino really mean. Collectively, these are known as the El Nino Southern Oscillation (ENSO), a phenomena that is happening down in the Equatorial Pacific. ENSO affects weather patterns around the globe, and these effects are more prevalent during Northern Hemisphere winters.

The ENSO phase we are in is determined by sea surface temperatures found across the Pacific, between the coast of South America and Indonesia.

El Nino is when sea surface temperatures are warmer than normal. La Nina is when temperatures are colder than normal. No Nino is when temperatures are normal, otherwise known as the neutral phase of ENSO.

Generally during El Nino winters, the Pacific Northwest and Northern Rockies experience warmer than normal temperatures and below normal precipitation, while the southern tier of the United States is usually cooler with above normal precipitation.

During La Nina winters, the opposite is true: the northern tier of the U.S. experiences a cooler and snowier winter, while the southern tier is usually warmer and drier.

This is why when we hear El Nino in Jackson, we think, “no snow”. And when we hear La Nina we think, “mo’ snow!” We came out of a weak La Nina last winter and have been stuck in neutral ever since.

Statistically here in Jackson Hole, El Nino winters are evenly split between above and below normal snowfall winters; 50/50. La Nina winters are snowier than normal more like 70-percent of the time. That’s why we get excited about them. But 30% of La Nina’s have had below normal snowfall.

You might surmise that No Nino winters (or Nada Nino) should then be “normal” or “average” winters. An average winter is difficult to define because our averages are created by our extremes. Almost every single winter is either above or below the average, some more than others. Besides, who is going to run around shouting, “Woody said we are going to have average winter!”

In Jackson Hole, winters that were spent in the No Nino phase more often than not produced below normal snowfall; about two-thirds of the 15 winters I analyzed in this category were drier than normal winters. That means that a third of the No Nino winters had above normal snowfall. Most notably was the winter of 1996-97, which was a very big snowfall year.

El Nino Southern Oscillation

Send in the Arctic Oscillation

ENSO isn’t the only thing that can disrupt weather patterns in the winter months. Another phenomenon that is closely monitored is the Arctic Oscillation, or AO.

AO is a measure of the difference in pressure between the Northern Polar Regions & the mid-Latitudes (where we live). This difference creates either a positive or a negative phase.

Positive AO occurs when there is lower pressure over the Arctic Circle and higher pressure over mid-Latitudes. This forces the jet stream and the storm track further north. The result is more ocean storms and wetter weather for Alaska, and warmer temperatures in the mid-latitudes.

Negative AO occurs when there is higher pressure over the Arctic Circle and lower pressure over the mid-latitudes. This forces the jet stream and storm track further south. The result is colder air and more storms in the mid-Latitudes, at the same time warmer air moves up into Alaska.

The problem is that the Arctic Oscillation fluctuates more regularly, from week to week, whereas ENSO fluctuations take longer to switch from one phase to another, on the order of months.

Given the current No Nino outlook for this winter, I will be turning my attention to the North Pole and looking for some “Negative AO” action to drive the storm track further south and right over Jackson Hole. Not sure that’s gonna have the same buzz as La Nina does.

Arctic Oscillation

The content of his week’s blog is excerpted from the Mountain Weather Column I wrote for the Jackson Hole News and Guide in October.
Graphics courtesy of NOAA.

Meteorologist Jim Woodmencey

Nice dump of snow for Jackson last night, with about 5 inches in a couple of hours at my house near Snow King Mountain.  At 7:00 pm there was no snow, by 9:00 pm I was shoveling the deck. As I write this at 5:00 a.m. on Tuesday morning, there is another 4 or 5 inches on the deck. Total of 8 to 10 inches in less than 12 hours. (It is still October, isn’t it?)

This snowstorm was courtesy of a slow moving and very large Low pressure system that moved into the Western U.S. on Sunday. It basically parked itself over the Great Basin Monday and wrapped some cold air from Canada into itself.

For the most part, the flow aloft was out of the South overnight, a flow which favors Snow King Mountain and the Town of Jackson for orographic snowfall, that is, the extra lift the mountains provide to boost the snowfall. The jet stream was also in an optimal position to give an extra boost, as well.

Looking around at other mountain instruments, it seems that 6 to 8 inches overnight was the norm, even up at elevation in the Tetons. So a fairly even distribution from what we received in Town and what fell at 8 to 10,000-ft. in the Teton Range.

After a week of High pressure and sunny weather last week, we switched gears pretty quickly on Monday.

Even though technically I a supposed to be on my “Fall Break” right now, I couldn’t resist looking at this storm. Now our 5th snowstorm in the Tetons since late September.

I am off to Alaska this coming week to teach a weather course. Back to forecasting for JH on Nov. 11th.

Surface Map

700mb Map (around 10,000-ft. elevation)

Jet Stream Map (@ 30,000-ft.)

Post by Jim Woodmencey
Graphics from NOAA

Meteorologist Jim Woodmencey

Pretty good snowstorm for the western Wyoming mountains Thursday/Thursday night. But a really good snowstorm for the rest of Wyoming for Friday & Friday night. Winter Storm Warnings and Blizzard Warnings issued for much of the eastern half of Wyoming.

Some snow for the Colorado Rockies with this storm, but the Plains of Nebraska and South Dakota really get hammered by this weather system as it moves east Saturday.

From NWS Office Cheyenne Issued Friday morning Oct. 4

NWS Nationall Forecast Map for Friday Oct. 4

Snowdepths Getting Deep for Early October
Up in the Teton mountains there is now a foot or more of snow up around the 9,000 to 10,000-ft elevation being reported on the few instruments that are up and running. For instance, the Snotel sensor at Grand Targhee at an elevation of 9260-ft. is showing a 13 inch snow depth.

The Snotel sensor on Togwotee Pass at the 9850-ft. elevation is showing 16 inches of settled snow depth at 8:00 a.m. on Friday, October 4th. 

Over in the Wind River Range, which stands to get the most snow from this storm as it is now more of an “upslope” event for areas along and east of the Continental Divide (as the Low pressure center moves into Central/Eastern Wyoming), there dis even more snow on the ground now. Hobbs Park Snotel is at 10,100-ft., along the eastern side of the Winds, and it shows a 20 inch sow depth this morning.

Oh, and by the way, the temperature up at around the 10,000-ft. elevation this morning is 18 degrees. I guess we are skipping Fall and heading right into Winter.

RAP Snowfall forecast map of total snow accumulation Friday morning thru Friday Evening

WRF Total snow accumulation forecast for Friday morning thru Saturday morning.

Keep track of Jackson Hole & Wyoming Weather & Snowfall

If you want a quick way to check out all the local weather instruments, go to the “WAM” (Weather Access Map) for the Jackson Hole & Yellowstone area…..click here: WAM Tetons

There is also a “WAM” for the State of Wyoming……click here: WAM Wyoming

Both of thees maps will get you to the latest data and also the latest forecasts for those same locations.
(Note: Utah & Colorado WAM’s will be available soon, hopefully soon enough!)

Post by meteorologist Jim Woodmencey
Maps courtesy of the NWS

Meteorologist Jim Woodmencey

The big storm that brought rain and snow this week to the Northwest and the Northern Rockies will be moving across the central Rockies and the northern Plains the next 24-hours or so.

What it left behind was fairly impressive, with record September snowfall at Crater Lake National Park in Oregon of 8 inches in 24-hours Tuesday into Wednesday, above about the 6,000-ft. elevation.

At the Jackson Hole Mountain Resort there was also about 8 inches of snow reported up there at about the 9500-ft. elevation, which accumulated from just before midnight Tuesday through Thursday morning Sept. 26th. Togwotee Pass had about 10 inches at the same elevation. And the higher elevations in the Wind River Range had more than that, and appear to have the deepest snow accumulations from this storm.

Rain in the Town of Jackson was also significant, at the automated rain gauge in town 1.26 inches of rain fell in less than 24-hours. Significant because the average rainfall for the month is 1.29 inches.

See precip and snowfall coverage maps below from this storm.

One Day’s Precip on September 26th across the Western US

Zoom on Northwest US One-Day Precip Sept. 26

Zoomed into Wyoming One-Day Precip Totals Sept 26.

US Snow Depth Map on morning of Sept. 27th

Zoomed in Snow Depth Map for Western WY

Meteorologist Jim Woodmencey

Seasons are definitely changing this week, with word of a “big storm” heading our way, which began its hype on Monday. Sometimes the mere mention of the word “snow” in the forecast will set off a 4-alarm warning, among skiers especially, even in September!

This will actually be the second storm this September to bring snow to the Tetons. The first one was on September 18th, and most of that snow has melted off except for a skiff on north faces above 10,000-ft.

This incoming storm will bring even colder air with it and snow levels will get down near the valley floor, probably by Thursday the way it looks right now. It will be selective about where it deposits the bulk of the snow, as the whole weather system divides as it crosses the Rockies.

Best moisture comes over western Wyoming when snow levels are still fairly high during the day on Wednesday.

Certain areas in Western Wyoming will be favored as this large Low pressure Trof appears to split up as it moves across the Rockies, with the main center of that Low going north into Montana and eventually Southern Canada by the end of the week. And the southern part swinging across Nevada & Utah and eventually Colorado.

The higher elevations of Yellowstone Park (especially the SW corner of the Park) and the Wind River Range will potentially receive the most snowfall. As snow levels lower progressively Wednesday thru Thursday in western Wyoming, the lower elevations pick up some snow, as well. I also expect the Tetons will see a brief period of enhanced snowfall when that Low is over us and moving across Southwest Montana.

Who Gets It?

This is also a good looking set-up for Central Idaho’s Mountains, as they get into the colder air sooner, when the storm is still intact as it moves inland Tuesday night/Wednesday. And then another swath of snow will be likely across Southwest and Central Montana, initially with a SW flow as the Low approaches for west of the Divide, and then east of the Divide (central Montana) with decent upslope flow once the Low moves into eastern Montana.

A variety of different computer models depict the variability of the snowfall accumulation & distribution across the Northwestern US and NW Wyoming with this storm, and a few of those are shown below for comparison. Note that they each cover a different time period. So, which one is correct?

(Hint: A skier will pick the one that shows the greatest amount of snow where they like to go, every time!)

Don’t pull on your snow pants just yet, it will warm up over the weekend and melt a good portion of what accumulates in the mountains this week.

NAM 48-hour Total Snow Accumulation Tues. a.m thru Wed. p.m.

MFF Total Snow Accumulation Tues. a.m. thru Fri. a.m.

WRF Total Snow Accumulation Tues. a.m. thru Thursday evening.

Same Map as Above (WRF) zoomed in on Western Wyoming

Post by meteorologist Jim Woodmencey
Graphics courtesy of LEADS On-Line
and USDA-FS Fireweather

Meteorologist Jim Woodmencey

The First Day of the Fall Season doesn’t get here until Sunday, September 22nd,  but we will see a change in the weather pattern from what has been relatively warm to relatively cooler beginning Wednesday.

There will be a series of storm systems of different sizes and shapes working out of the Gulf of Alaska and moving across the Northwestern US over the course of the next 7 to 10 days, and each of these will be cold enough for some white stuff in the higher elevations, at least above 10,000-ft.

The first Low pressure system moves thru Tuesday night and early Wednesday. Then a break in the weather and warming Thursday & Friday. Next weather system looks weak but may bring some showers to the mountains later Saturday and on Sunday. Then another break between weather systems Monday & Tuesday of next week, with a larger and even colder looking Low pressure system moving into the Western US Thursday and Friday of next week, with snow levels may be down even lower.

Not to the valley floor, and not huge amounts of snow up high, but enough for a reminder that it ain’t summer anymore.

We also could see below freezing temps in the Jackson Hole valley this week, especially Friday morning with clearer skis overnight Thursday.

Wednesday Sept. 18 Weather Map

Sunday Sept. 22 Weather Map

Freeze-free Days in Jackson

With high temperatures still reaching into the 70’s this week (78 in town on Monday!) and lows only in the 40’s most mornings, it may seem like we have had a long “frost-free” season this summer. But actually it was probably not as long as you might think.

According to the thermometers at the Jackson Climate Station the last day below freezing overnight low temps in the Spring was on June 23rd (28 degrees). And the next time it got below freezing was on September 1st ( 30 degrees). That’s 69 days, by my math, of “frost-free” or “freeze-free” days.

Although, there was one day in mid-August that it got down to 32 degrees for a morning low……if that qualifies as a “freezing” day, then our growing season was split in two!

Post by meteorologist Jim Woodmencey
Maps from NWS