Winter blast heading for the Pacific Northwest

It has been mild recently across the Pacific Northwest. In fact, Seattle tied their record high temperature of 60 degrees yesterday (11/12/13), also set in 1953. That is all about to change as we head into the weekend.

A mid-level trough will cut across the area Thursday, initiating a slight cooling trend in temperatures. Precipitation with this initial trough will be very light and portions of the Washington Cascades will see anywhere from 1 to 3 inches of snow above 3,500 feet.

Mid-level trough position late Thursday afternoon (denoted by dashed lines).

Mid-level trough position late Thursday afternoon (denoted by dashed lines).

The trough of interest will start diving into the Pacific Northwest Friday and will likely bring some of the coldest air yet this season to the region. Precipitation will start Friday morning/afternoon across western Washington and will continue progressing south and east through much of the rest of Washington and into Oregon by Friday night.

The trough of interest enters the Pacific Northwest.

The trough of interest enters the Pacific Northwest.

Snow levels will initially start out around 3,000 feet in Washington, but will fall to around  2,000 feet by late Friday night or Saturday. Farther south, across the Oregon Cascades, snow levels will start out around 4,000 feet or so and will fall to near 2,700 feet by Saturday night.

Snow will be heaviest across the Washington Cascades late Friday through Friday night and will begin to taper off Saturday afternoon. Snowfall totals of 3 to 6 inches are expected above 2,500 feet and 6 to 12 inches appears likely above 3,000 feet. Of course, mountain peaks and favored upslope regions could see more than a foot of snow.

The Oregon Cascades will see their heaviest snow late Friday night through Saturday before it tapers off Saturday night. Totals of 1 to 3 inches are expected above 3,000 feet with amounts of 3 to 6 inches likely above 4,000 feet. As you get above 5,000 feet in elevation, totals may exceed 6 inches, especially in favored upslope regions.

In addition to snow falling in the Cascades, snow will fall across the Blue Mountains of Oregon and portions of the Northern Rockies and eventually across the Wasatch Range and Central Rockies. I am not going to talk about totals here just yet, though it does appear pretty safe to say these areas will see accumulating snow.

As far as temperatures go, Seattle will likely see lows in the middle 30s or perhaps even lower 30s Saturday and Sunday night. Portland will see temperatures dip into the upper, perhaps even middle, 30s Sunday night.

A majority of the precip will fall before the coldest air arrives, so there is an extremely small chance of there being any lowland snow. Sorry, snow lovers in Portland and Seattle.

The cold blast won’t last long as the ridge across the eastern Pacific shifts east a bit early next week significantly warming things up.

Avalanches Kill 17 Soldiers in Indian Kashmir

According to the AP, two massive avalanches struck portions of Indian-controlled Kashmir late Wednesday night killing 17 soldiers, and injuring 17 others.

Sonamarg, a location of one of the avalanches, is marked by the "A" pin above.

“Dawar, in the frontier Gurez region, remains cut off from the rest of Kashmir for nearly five months every year as heavy snowfall and rains block road links to the region.”

Rescue efforts were hampered for a time last night as dense fog and moderate snow continued to affect these regions. A winter storm is ongoing across Sonamarg and Dawar and will continue through the day today. After the storm is all said and done, 10-15 inches of fresh snow will coat the mountainous terrain. There will be a brief break in the weather Friday with only light snow or flurries expected, but more accumulating snow is expected Saturday.

“Amir Ali, a state government disaster management official, warned of more avalanches across mountainous parts of Indian Kashmir.”

How the MJO Affects Weather Across the Western US

The Madden-Julian Oscillation (MJO) is a coupling between atmospheric circulation and deep tropical convection. In other words, it is an eastward progression of large regions of both enhanced and suppressed tropical rainfall, observed mainly over the Indian and Pacific Oceans. Variations in wind and temperature produced by the MJO can have a significant influence on global atmospheric and oceanic circulations. The MJO is also known as the 30-60 Day Tropical Wave since it typically circles the globe along the equator in about 30-60 days, or 45 days on average.

590x794_11282010_pineapple

MJO activity in the pacific is greatest during weak La Ninas (such as we are currently in) and ENSO-neutral conditions. During moderate to strong El Ninos, MJO activity is minimal or even absent. The MJO plays an important role on the patterns of tropical and extratropical precipitation, atmospheric circulation, and surface temperature around the global tropics and subtropics, but for the purposes of this blog, I am only going to tell you how it affects the weather across the western US.

The greatest affects from the MJO in the United States are felt during the winter months along the west coast. As the MJO propagates eastward across the Pacific Ocean, subduction in advance of this oceanic tropical wave (Kelvin wave) anomalously warms the sea waters.

As this Kelvin wave, and its associated deep convection, nears the central Pacific Ocean, it encounters the sub-tropical jet. This sub-tropical jet will then transport this moisture northeastward into the mid-latitudes. This is also known as the Pineapple Express. A perfect example of this (that I happened to document) occurred last winter during the week of December 19, 2010. Below is the picture I posted in the blog “The Pineapple Express“.

A clear depiction of the MJO and the Pineapple Express from December 19, 2010.

The large cluster of thunderstorms (the reds and yellows) over the central Pacific Ocean is actually the MJO. The sub-tropical jet is then tapping into this moisture and transporting it northeastward, as is depicted by the arrow. This particular event brought extremely heavy rain to the vallies of California, and over 10 feet of snow to the Sierras.

When the MJO is affecting the western United States, effects typically seen are:

  • Unusually heavy precipitation
  • Greater cloud cover
  • Warmer than normal nighttime temperatures

The MJO recently peaked in late November and early December of 2011. Perhaps you can recall, during this time, multiple upper level mid-latitude troughs (Rossby waves) formed or passed over the western US, and often remained over this area for several days at a time. This resulted in periods of moderate to heavy rain/snow over portions of the southwest during this time.

Time series of daily MJO Index. Data supplied by the CPC and graph supplied by the Boulder NWS.

The pattern in early December of 2011 was more like what we see during an El Nino as opposed to what we typically see during a La Nina. This was due to the MJO peaking during that time. After the MJO passed, the southwestern US saw dry conditions, which is what we expect to see during La Nina winters.

Currently the MJO is becoming better organized once again across the Indian Ocean, however, it does not yet appear to be propagating eastward. This will be something to keep an eye on, because if it does strengthen and begin to move eastward, this will have a significant impact on the weather across the western US in the next month or so.

The MJO also influences the frequency and intensity of cold air outbreaks across the eastern US, along with tropical cyclone activity in both the eastern Pacific and Atlantic basins during the Northern Hemisphere summer. I will save this for another time.

January 1-3 Forecast Lake-Effect Snowfall Totals for OH and MI

Click here to see the final snowfall totals from this event

Here are my forecasted snowfall totals for Michigan for the entire lake-effect snow event. The higher amounts will be found wherever the lake-effect bands persist the longest. If you are not under one of these bands, then the total snowfall in that area will be closer to the lower end of the amounts shown.

Forecast lake-effect snow totals for Michigan for areas that will receive at least 3" of snow.

Here are my forecasted snowfall totals for Ohio for the entire lake-effect snow event. The higher amounts will be found wherever the lake-effect bands persist the longest. If you are not under one of these bands, then the total snowfall in that area will be closer to the lower end of the amounts shown.

Forecast lake-effect snow totals for Ohio for areas that will receive at least 3" of snow.

January 1-3, 2012 Preliminary Snowfall Map for Ohio

Here is a preliminary snowfall map for Ohio for the impending lake-effect snow. It is important to note that the snow will not be spread evenly throughout the areas highlighted. For instance, wherever the heaviest band sets up in far northeast Ohio, there will likely be 12-18″ of snow, but outside of this band, there may be even less than a foot of snow. It is still too far out to pinpoint where the snow bands will set up, but as the event draws nearer, I will post an updated snowfall map.

Preliminary lake-effect snowfall forecast for Ohio.

January 1-3, 2012 Lake Effect Snow

There has been a lot of talk lately about a significant lake-effect snow event for the Great Lakes, and for good reason. We haven’t really had any significant lake-effect snow events so far this season, but it looks like the first good lake-effect snows will occur from January 1-3. In my blog yesterday I talked about the necessary ingredients for lake-effect snow, so I will be referring to that frequently.

I am going to break this down by lakes. I will talk about the potential for lake-effect snow off of Lake Michigan and Lake Erie. If you would like a detailed break down for any other lake, just let me know and I will see what I can do.

Lake Michigan

A strong cold front will move across Lake Michigan Sunday night, bringing an end to the relatively mild weather. Due to the lack of cold so far this winter, the surface water temperature of Lake Michigan is a relatively warm 3-4 degrees Celsius. The temperatures at 850 mb will be -12 to -14 Celsius, so the temperature difference of 15-18C is plenty for lake-effect snow.

The winds behind the front will start off westerly on Sunday and will then turn more northwesterly Sunday night into Monday. The directional shear from the surface to 700 mb will tend to be less than 30 degrees throughout the duration of this event, which as I mentioned yesterday, is ideal for heavy lake-effect snow. One factor that may limit the overall intensity of the snow bands will be the excessive wind speed throughout the boundary layer. The wind speed from 925 mb up to 700 mb will range anywhere from 45-60 knots (~52-70 mph). Considering the ideal average wind speed throughout the boundary layer is less than 40 mph for heavy lake-effect snow, this will likely minimize the potential for snow bands producing snowfall at rates of greater than 1.5″/hr. One exception may be up across far northwestern Michigan where the lake fetch is essentially from Lake Superior and northern Lake Michigan.

All in all it looks like areas east of Lake Michigan should still receive a good amount of lake-effect snow just due to the duration of the event. It will last from Sunday through Monday night before ending. The winds will be shifting quite a bit from the west to the northwest and eventually almost to the north. This will help to spread the snow out over a greater area, which will also limit the total amount of snow. It is too hard to forecast snowfall amounts at this time, however the heaviest snow will fall across portions of far northern and northwestern Michigan and across far southwestern Michigan (from Allegan county on southward). The area in northwestern Michigan (near Otsego and the surrounding counties) has the best *potential* to receive a foot or more of snow. Something else to keep in mind is that with such strong wind speeds, the heaviest snow will not fall along the lake shore, but rather 10-20 miles inland. The strong winds will also make for blizzard-like conditions at times. Below is a county map of Michigan so you can reference the counties I was talking about.

Michigan counties.

 

Lake Erie

The cold front will move across lake Erie during the day Sunday. The water temperatures and 850 mb temperatures will be nearly the same as for Lake Michigan, so we know that there will be potential for lake-effect snow. The lake-effect event off of Erie will run from Sunday night through the first part of the day on Tuesday.

The winds behind the front will initially be westerly and this will continue through Sunday night. The winds from the surface to 700 mb will tend to have less than 30 degrees of directional shear, which is ideal for heavy lake-effect snow. As we head into Monday, the winds will turn more out of the northwest and will remain this way through much of Monday night. Early Tuesday morning into the early afternoon hours, the winds will try to become more north northwesterly.

The winds throughout the boundary layer will average between 30 and 40 knots (~35-45 mph), quite a bit weaker than the winds over Lake Michigan. This will greatly enhance the chance of significant lake-effect snow. Much like Lake Michigan, the wind direction does shift quite a bit throughout the entire event. This will be the one limiting factor as far as snowfall totals go off of Lake Erie. Sunday night into Monday will be when the heaviest snow falls in this area, since drier air will move in after this timeframe.

The heaviest snow off of Lake Erie will fall across far western New York (south of Buffalo), far northwestern Pennsylvania (just inland from Erie), and across far northeastern Ohio (east of Cleveland). In Ohio the hardest hit counties will likely be Lake, Geauga, Ashtabula, and Trumbull. As the winds turn more out of the north Monday and Monday night, counties farther to the west and south will have the potential to pick up some accumulating snow as well. This includes Portage, Cuyahoga, and Summit counties. It would not surprise me if some places in Ashtabula and far northwest Pennsylvania pick up 1-2 feet of snow. The strong winds at the surface may also make for blizzard-like conditions at times. Below is a county map of Ohio for reference.

Ohio counties.

 

Here is a great map from accuweather.com to help you visualize what areas downwind of the lakes have the best chance at lake-effect snow.

The map represents the areas that will likely see lake-effect snow from Sunday through Tuesday morning. Courtesy accuweather.com.

Ideal Setup for Lake Effect Snow

Lake-effect snow events occur most commonly in the Great Lakes region and can produce extremely heavy snow. Snowfall rates can reach several inches per hour and there are many reports of 2 or more feet of snow falling in a 24-hour period from lake-effect snows.

Lake-effect snow generally occurs from November to February, and tends to be most intense in the late Fall and early Winter because the temperature gradient between the lake and the cold air is relatively high. So what factors need to come together to produce a lake-effect snow event?

  • You want the temperature difference between the lake surface and 850 mb to be at least 13 degrees Celsius. (i.e. you need a wave of cold air to be moving over the lakes) This wave of cold air should be deep, at least to 850 mb for lake-effect snow, but deeper than 700 mb for heavy lake-effect snow. This is because shallow arctic air limits the amount of convection that can take place.
  • You want very little directional shear from the surface to 700 mb. Less than 30 degrees is ideal, but you can still get weaker lake-effect bands with up to 60 degrees of directional shear. Any more than 60 degrees and you will tend not to get anything more than some flurries. This is because directional shear decreases the moisture convergence out over the lake and causes the snow to spread over a larger area.
  • You want a lake fetch of at least 60 km for lake-effect snow showers, and of at least 100 km for heavy lake-effect snow. The “lake fetch” is the distance the air must travel over the water before reaching land.
  • You don’t want the winds that blow across the lake (in the boundary layer) to be too strong. They need to be light enough for moisture convergence to occur. If the winds are too strong, say 50 mph, enough moisture may not be able to evaporate to produce heavy lake-effect snow. The ideal wind speed is between 10 and 40 mph.

Below is a sketch from theweatherprediction.com of a typical lake-effect snow event.

Sketch of a typical lake-effect snow event.

Those are the key ingredients needed for lake-effect snow. Of course, depending on just where you are compared to the lake will make a huge difference. Lets take Lake Erie for example. If you have a northwesterly wind and all the above criteria is met, where would you expect the heaviest snow off of Lake Erie to occur?

If you guessed across far northeastern OH, especially in Geauga and Ashtabula counties, you would be correct. We can use December 14, 2010 as an example. During this day, the winds were generally out of the northwest and up to 2 feet of snow fell across portions of northeast Ohio. Below is a map of some of the snowfall totals that I posted last year. You can see just how sharp some of the gradients were. Central Trumbull County received nearly 2 feet of snow, while the southern portion of the county only received 3 inches!

Lake-effect snow totals from December 14, 2010.

The terrain also plays an important part in lake-effect snow. Once the air traveling over the water hits land, frictional convergence plays a big role. Essentially, the air gets “piled up” just inland from the lake shore and this helps to intensify snow bands. You will rarely see the heaviest snow occur right along shore, but rather a few miles inland. The winds will blow the developing snow downwind from the lake shore.

Max 24 Hour Snowfall Totals this Winter

Here is a list of the top 24 hour snowfall totals per state so far this winter (October 20th – December 23, 2011). The 24 hour time frame runs from 6Z – 6Z. NOTE: Only states with totals over 12″ are included.

  1. Alaska – 37″
  2. Washington – 34″
  3. Colorado – 30″
  4. Wyoming – 25″
  5. Arizona – 25″
  6. New Mexico – 24″
  7. New Hampshire – 19″
  8. Montana – 16″
  9. Texas – 15.5″
  10. Utah – 15″
  11. South Dakota – 15″
  12. Minnesota – 15″
  13. Maine – 15″
  14. Kansas – 15″
  15. New York – 14″
  16. Vermont – 13.7″
  17. Michigan – 13.1″
  18. California – 12″

**All data is unofficial**


Science Blogs
Science links

Aftermath of December 19-20, 2011 Plains Blizzard

I was out in Garden City, Kansas during this blizzard, and I can honestly say, I have never experienced anything quite like this before. I was born and raised near Akron, OH, so getting a foot of snow was not too unusual, but getting a foot of snow with winds gusting to 50+ mph, now that was crazy. At times, it was hard to even keep your balance with the combination of 50 mph wind gusts and the ice and snow under your feet.

Courtesy NOAA: A map of the snow depth after the blizzard. As you can see, I was in one of the heaviest bands of snow in Kansas. (Click image for full NOAA resolution)

I arrived in Garden City around 3 PM, just about the time the rain changed to freezing rain and was mixing with a little sleet. I checked in to my hotel room and began to prepare for the long night ahead of me.

For nearly two hours the precipitation was a mix of a little bit of everything. For brief periods of time it would change to all snow, but then it would mix right back with sleet again. By 5 PM the snow/sleet was beginning to accumulate, but very slowly.

Snow/sleet beginning to accumulate.

By 9 PM there was only 2 inches of snow/sleet on the ground. The sleet was really cutting down on accumulations, and I began to worry I hadn’t driven far enough west/north.

About 2 inches of snow/sleet had fallen by 9 PM.

Finally, by 10 PM or so, the precipitation had changed to all snow. Around 11 PM the snow really began to pick up in intensity and the winds continued to consistently gust above 45 mph. The snow began to accumulate quickly (in the somewhat sheltered areas) and the drifts began to pile up. For a time, mainly between 11 PM and 2 AM, the combination of the high winds and heavy snow was so intense that the Comfort Inn sign in the above pictures was barely visible.

Below is some footage I took during the blizzard. This was taken around 11 PM.

 

By the morning, all the snow had come to an end. The winds were still gusting to 35 mph and blowing some snow around, but nothing too severe. This is what I woke up to.

What I woke up to the morning after the blizzard.

I took multiple measurements around the hotel that morning, and the average snow depth was 13 inches (in sheltered locations), with drifts of 2 – 3 feet. I began my trek home around 10 AM, and below is a little of what I saw along the way. Roads were completely snow packed with a layer of ice underneath. While driving east on US 400 that morning, I did not see one other vehicle for nearly an entire hour, a moving vehicle that is. There were probably 30-40 vehicles stranded along the highway between Garden City and Dodge City, some were even on their sides. The average snow drifts outside of town were 4 – 5 feet, while a few isolated snow drifts reached 7 FEET in remote locations just east of Garden City. When I arrived in Pratt, Kansas, about 1 hour west of Wichita, trees and power lines were coated in about 1/4 inch of ice.

A truck was flipped on its side off of US 400.

The average snow drifts outside of Garden City, KS were 4 - 5 feet.

A few isolated snow drifts reached 7 FEET!

Trees and power lines were coated in approx. 1/4 inch of ice near Pratt, Kansas.

This was definitely an experience I will never forget, and hopefully I will get to go blizzard chasing again sometime soon!

December 19-20, 2011 Winter Storm

A stalled low over southern California, the same one that brought hail, funnel clouds, and Santa Ana winds to So Cal the last two days will be ejecting eastward over the southwest US and eventually the southern Plains. Ample moisture will be advecting northward out ahead of this storm, while cold air will filter into the southern Plains from the north.

Nearly all locations will start out as rain during the day Monday. The first area to change over to snow (not including the mountains in New Mexico) will be northeastern New Mexico/southeast Colorado eastward into the western Oklahoma and Texas panhandles. As the storm progresses eastward Monday night, northwest Oklahoma and much of Kansas will transition over to all snow.

Below is a map of my forecast snowfall accumulations for this event. It is possible that the entire swath of snow could shift a little south, however, I believe the models will trend back north a bit by the time of the actual event. A coating to two inches of snow will fall outside of the bands drawn. This would include cities such as Wichita, KS, Kansas City, MO, and much of northern Missouri.

Snowfall forecast for the upcoming winter storm in the southern Plains.