If you are a frequent Weather Channel watcher, you have probably heard the terms they use to describe a variety of winter storms, such as, “Atmospheric Rivers”, “Polar Vortexes” and “Bomb Cyclones”. All of which sound quite ominous! It reminds me of that line in the Wizard of Oz, “Lions and Tigers and Bears, Oh My!”

From my perspective, these terms are used to create a state of panic, to get you to stay tuned-in. It’s what some meteorologists refer to as, the “atmosfear”. If you can make it sound like some sort of weather Armageddon is coming, then perhaps more people will keep watching.

In this week’s column, I’ll explain some of these fearsome terms you might hear about this winter and perhaps calm some of your fears.

Atmospheric River

An “Atmospheric River” is simply a continuous feed of moisture, for example, from the eastern Pacific into the western United States. Generally, that moisture is carried along in a strong jet stream flow. If that river of moisture lines up over you, expect several days in a row of continuous precipitation, in the form of rain or snow, depending on temperatures.

Another term you may have heard in the past is, “Pineapple Express”.  That doesn’t sound too bad, could be a name for a tropical drink you might order in a bar. The pineapple express is also an atmospheric river.

Atmospheric river sounds much more threatening, thus the recent switch in terminology used in the media.

Polar Vortex

The “Polar Vortex” is more often an eastern United States phenomenon.  All it is really, is a deep, cold trough of low-pressure in the atmosphere, which brings very cold air much further south than normal. But that’s too many words and doesn’t sound nearly as sexy as just saying, “Polar Vortex”.

Cold air that originates up near the north pole, is the polar part. The low-pressure is the vortex part of the name. All low-pressure systems or storm systems are vortexes. That is, any cyclonically rotating (counterclockwise) area of lower pressure in the Northern Hemisphere is a vortex. Again, that isn’t a very catchy way to describe it.

If you wanted to, you could call it a “Polar Cyclone” and make it sound even scarier.

Bomb Cyclone

Cyclone is yet another term used to describe a low-pressure system or any storm. The term “Bomb Cyclone” refers to a center of low-pressure that has a precipitous drop in its central pressure in a short time. The criteria for calling it a bomb is, 24 millibars of pressure decrease in less than 24 hours. An average drop in pressure for a developing storm is about half that rate.

A bomb cyclone, or “bombogenesis”, as it is also known in meteorology, is simply a rapidly intensifying low-pressure system. They usually form along either the Northwest or Northeast Coasts of the United States. A bomb cyclone hit the Oregon Coast this past Thanksgiving.

Don’t be Scared

All of these three terms I just described have been around and known to meteorologists since about the 1950’s. Media outlets, like The Weather Channel, love to use them to help sensationalize the weather. Having catchy monikers helps reel you in.

The Weather Channel has also adopted the practice of naming winter storms, in the same manner the National Weather Service names hurricanes during the summer. The NWS does not give official names to winter storms, by the way.

Often times, all it amounts to is just another a winter storm, like many winter storms that we get in Wyoming, or anywhere else in the country for that matter.

Don’t be afraid, it’s just the weather, doing what weather does. There is nothing new or more severe about it just because it has been given a sexy name.

The National Weather Service issues watches and warnings, those are what you should pay attention to this winter season. They will let you know when the potential exists for severe weather that might hamper travel. Those are the days when it is best to just stay home and hunker down by the fire instead of heading outside where there might be lions and tiger and bears, oh my!

Post by metetorlogist Jim Woodmencey

This article originally appeared in the Jackson Hole News & Guide on December 31, 2019.

Low-pressure systems have been swinging across the Southwestern U.S. this past week or so, but leaving the northern & central Rockies to catch the fringes of those weather systems. That is about to change, for the start of the New Year.

Current Weather Pattern

This series of 700mb maps (@10,000-ft.) shows the transition of the weather pattern over the next few days, A dry & cold Northerly flow over the northern Rockies today, December 30th, gives way to more of a Westerly flow aloft Tuesday and then a Northwesterly flow New Year’s Day. The blue shows areas of moist air and the orange is dry air.

Short-term Snowfall Forecasts

Here are two short-term snowfall forecasts for Dec. 30th to Jan. 2nd.
The NAM Model (North American Mesoscale) is first. The WRF Model (Weather Research & Forecasting) is next from the CAIC (Colorado Avalanche Info Center).

Longer-term Snowfall Forecasts

Next are two model forecast that take us out 10 to 14 days, respectively. The European Model is the weakest for snow accumulation over the next 10 days (Dec. 30 to Jan. 8). The GFS (Global Forecast System) goes pretty big with snow accumulation for the next two weeks in the Rockiess, between Dec. 30 and January 14th, 2020. Good news for the start of the New Year, if it all comes true!

Happy New Year Everyone!

Post by meteorologist Jim Woodmencey

The outlook for fresh powder in the Western United States between Christmas and New Year’s Day is not looking too cheery for many locations.

A split jet stream flow in the Pacific will send three separate Low pressure systems on a southerly track across the Southwestern U.S. That will favor the southern Sierra Nevada (Mammoth) and the San Juan Mountains (Telluride) for snowfall.

In the northern Gulf of Alaska, more of a West to Sw flow wil bring plentiful moisture & the biggest snow accumulations across British Columbia, Canada’s mountains.

Current Satellite map Monday morning Dec. 23rd, 2019:

SNOWFALL FORECASTS

Short-term and longer term forecasts below for total snow accumulations.

First up is from The Colorado Avalanche Information Center’s WRF model, with snow accumulations through Christmas Night. Looks like theirs is the most optimistic, with 4 to 7 inches for the Teton Mountains & about 3 to 4 inches for the Jackson Hole Valley.

A little more for the Wasatch Mountains & Yellowstone Park. The Uinta Mountains of Utah, Southern Sierra & San Juan Mountains of Colorado look to get the most, with a foot or more.

Looking just beyond New Year’s Day, the 10-day snowfall forecast from the European model shows only a little more snow most places in the West. British Columbia scores the most snow.

The weather patter looks like it finally changes to something more favorable for the northern Rockies by the end of the first week in January 2020.

Below is the GFS model snowfall accumulation forecast for Dec. 23, 2019 to Jan. 7, 2020. The bulk of that snowfall for the Tetons comes between January 5th & 7th.

Merry Christmas & Happy New Year!

Post by meteorologist Jim Woodmencey

This Saturday is the Winter Solstice and the official start to the winter season, according the calendar at least. Next week is Christmas and then it’s a whole New Year!

To help you plan you your travels, or your ski destination, or to just to get a sense of how white your Christmas is going to be this year, I have compiled the best short and longer-term snowfall forecasts for you to consult. Looks like some places do better than others, by a large measure.

The Short Story

Current weather situation shows Low-pressure systems in the Pacific that weaken and/or split as they move inland this week and Christmas week. Jet stream not continuous or too strong coming out of the Pacific right now.

Solstice Snowfall Forecasts

From today, Wednesday Dec. 18, into Saturday Dec. 21, here are two short-term forecasts that tell a similar tale for new snow accumulation:

Snowfall Through Christmas Week

Smaller weather disturbances follow after Christmas and into New Year’s Day. Best bet for big snowfall accumulations this week and next are the Washington Cascades (Mt. Baker) and Southwestern British Columbia’s mountains (Whistler).

Caution: Differences in snow accumulation between the two models below due to the Euro model going out 10 days and the GFS out 14 days. Biggest difference between models is seen over Northwest Wyoming and the Colorado Rockies, due in part to more snowfall after Dec. 28th.

I’ll update this post again in a few days to see if there is any significant change to the snowfall outlook for the Holidays.

Post by meteorologist Jim Woodmencey

A West to Northwesterly flow aloft over the Western U.S. will yield additional snowfall through this coming weekend. A large area of Low pressure in the Gulf of Alaska, combining with a smaller Low-pressure center currently further out in the Pacific will rotate Pacific moisture across the Cascades, Sierra Nevada, and the northern & Central Rockies.

An area of High pressure also sits off the southern California coast, with a strong jet stream between this High and the Low’s to the north. (Jet Stream is yellow line).

These two Low pressure centers hang around out in the Pacific into the weekend and the jet stream relaxes a bit & winds decrease. Pacific moisture will continue to pulse inland through this weekend. Best periods of snowfall in the mountains appears to be Thursday night and again overnight Friday into Saturday. Best break in precip is during the day Friday.

As time goes on , a Ridge of High pressure builds along the West Coast and more Northwesterly flow aloft brings cooler temperatures over the Rockies this weekend. Extending light snow over the northern & central Rockies through Sunday into Monday.

700mb Maps with Forecast Clouds (gray) & Precipitation (blue-green). Maps from Windy.com

Snowfall Forecasts

Models differ slightly about how much snow will accumulate, but it looks like some mountain areas are favored by this West-NW flow. A few of these models predicted snowfall amounts are shown below.

The first is the high resolution WRF from the Colorado Avalanche Information Center, which shows the greatest amounts in the mountains. Their regular WRF model follows, both examples show snowfall totals from Thursday afternoon to Sunday morning.

The NAM (North American Model) below with total snow accumulations from Thursday afternoon through Sunday afternoon.

Post by MountainWeather meteorologist Jim Woodmencey

Back in early September I did my first outlook for the winter season in this blog. That was just after the Farmer’s Almanacs came out with their predictions. Two of those Almanac forecasts had most of the Mountain West painted under cooler and snowier conditions, overall. Those forecasts don’t change, once they are published in late August. (See their maps below).

The Climate Prediction Center (CPC) forecast that I reviewed from NOAA, that was issued in mid-August, revealed that the western U.S. would be warmer than normal, but was undecided about precipitation. That outlook was non-committal about it being above, below, or normal for precipitation for the three-month period, they gave it “equal chances” for each. No help there. However, the latest update looks a little different.

Latest Look

The newest three-month long-range outlook from the Climate Prediction Center, issued on November 21, 2020, still has western Wyoming under warmer than normal conditions for December, January and February. This is still in direct contrast to both Farmer’s Almanac temperature forecasts.

The precipitation forecast from the CPC has now shifted to placing Northwest Wyoming & western Montana under about a 55-percent chance of having above normal precipitation. That’s somewhat more encouraging.

Most of the Pacific Northwest, northern Utah & northern Colorado are riding the 50-percent chance of above normal precip line.

El Nino Situation

The El Niño Southern Oscillation, or ENSO, is one of many indicators long-range forecasters use to decide what the general conditions for the winter season might be across the Northern Hemisphere.

The ENSO actually has three different phases: El Niño, La Niña and Neutral. Sea surface temperatures in the Equatorial Pacific determine the current phase of the ENSO.

An El Niño is occurring when sea surface temperatures are warmer than normal. A La Niña is occurring when temperatures are colder than normal. Neutral ENSO conditions (No Niño) occur when temperatures are near normal, usually when transitioning between the El and La phases.

In general, during an El Niño Winter the northern tier of the United States experiences warmer than normal temperatures and below normal precipitation. At the same time, the southern tier of the United States is usually cooler with above normal precipitation.

During a La Niña Winter the opposite is true, the northern tier of the United States usually experiences a cooler and snowier winter, while the southern tier is usually warmer and drier.

Neutral or No Niño Winters, could go either way. And the ENSO forecast for this winter is for Neutral conditions in the Equatorial Pacific.

ENSO Current status: “Surface temperatures in the east-central tropical Pacific were near to above average in October 2019, but the atmosphere did not react to the warmth. Sub-surface heat that spread across the basin in mid-September was dispersing. Thus, of the three possible outcomes—return of El Niño, La Niña, or neutral—forecasters give neutral the highest odds (70% chance) of continuing through winter.”

What’s it all Mean for JH?

Last winter was a weak El Niño, and pretty much the entire western U.S had a cooler and wetter winter. Jackson Hole was above normal for snowfall, after a record February. That wasn’t supposed to happen.

Historically, from snowfall data for the past 44 winters at the Jackson Hole Mountain Resort, El Niño’s have produced more below normal snowfall winters here than above normal (10 below and 4 above). La Nina’s have produced more above normal snowfall winters than below normal (10 above and 4 below).

Neutral or No Niño’s have also produced more below normal snowfall winters than above normal snowfall winters, but by a smaller margin (9 below and 6 above).

What’s really interesting is, two of those six above normal No Niño winters were the two snowiest winters on record at the Jackson Hole Mountain Resort, the winter of 1996-97 and the winter of 2016-17.

Based on those stats, an optimist would be rooting for another one of those record-breakers during this winter’s No Niño. The pessimist would say chances are less than 50/50 for an above normal snowfall winter.

I already know how many optimists there are in Jackson, just count how many season ski passes have been sold so far.

Post by: Meteorologist Jim Woodmencey