Anchorage sets record for snow

[skookerasbil]

Hey Bob..............

 

[bobgnote]

Current Alaska Weather Map

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National Weather Service, Alaska Region Headquarters, AK

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I wonder what will happen, during the coming El Nino?

National Weather Service, Anchorage Forecast Office The Weather Classroom -- El Nino, La Nina and Alaska

Weather in Alaska varies on a variety of timescales- from weeks, months to years. A considerable part of that variation but certainly not all of it is due to semi-periodic events like El Nino and La Nina. For example, the El Nino which occurred during the winter of 2002-2003 produced very warm temperatures across most of Alaska, while the El Nino of 1972-1973 produced cooler than normal conditions. Over the past several decades the national media has spent considerable time highlighting the impacts that these events have on North American weather. It is important to keep in mind that impacts differ greatly from one region of the continent to another.

*

There are additional affects produced by EN and LN besides the warming and cooling of the ocean in the tropics (strictly speaking within about 500 miles of either side of the equator). During EN's wind direction changes from east (normal direction in the tropics) to the west. In addition, the central and eastern tropical Pacific receives considerably more rainfall than in other years. This often results in flooding in coastal Ecuador and Peru. The western Pacific during an EN is most often drier than normal, leading to drought and an increase in wildfires in Indonesia and Australia. Although not as easy to observe, during EN there seems to be some type of modification to the ocean currents that transport warm water out of the tropical Pacific and cool water back into the tropics. This type of disruption in the 'normal' weather pattern (called 'anomalies') is important for short and long-term variation in the earths' climate. During a LN winds remain out of the east while rainfall over the western Pacific may be higher than normal. During neutral modes the weather in the tropics can still have significant anomalies.

These anomalies are a result of other physical processes that operate independently of EN and LN. One interesting aspect of the ENSO phenomena is the fact that LN's and EN's occur at irregular intervals. No one really knows at the present time how these events are initiated. The most commonly accepted theory for the creation of an El Nino for example, is that abnormally warm water in the Indonesia area is 'released' into the central and eastern Pacific. The body of warm water moves to the eastern Pacific over a period of two to four months. As noted earlier, this warm pool of water is typically several hundred feet deep. LN's occur as cool water moves into the central and eastern Pacific. Once in place, these warm or cool ocean water anomalies alter the winds, clouds and rainfall in and outside of the tropics.

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National Weather Service, Anchorage Forecast Office The Weather Classroom -- El Nino, La Nina and Alaska

There is considerable week-to-week variation in the strength and position of these jets. The sub-tropical jet for example is not continuous around the globe, but when it is present it is usually found over the eastern Pacific and Atlantic Oceans between 20° and 30° (in both hemispheres). The polar jet is the most continuous of the three in space and time, it typically ranges between 30° and 60° latitude. The arctic jet comes and goes and is much weaker than the other two jets. All of these jets are much stronger during the winter than at other time of the year.

Jet stream winds do not simply move along stationary tracks from west-to-east around the globe, rather they frequently follow 'wave-like' patterns. The crests of the waves are called 'ridges' (areas of high pressure) and the troughs of the wave are called something unique like 'troughs' (or a 'low' if the pattern is circular in nature). For the most part, large weather systems move along the northern edge of the polar jet stream. As you might imagine, storms moving along the western edge of a ridge transport warm and moist air from lower to higher latitudes. On the east side of a ridge (which maybe the west side of a trough), cooler and often drier air is transported from higher to lower latitudes. Over the course of a winter season there is a continual sea-saw between ridges to troughs over Aleutian Islands and Gulf of Alaska. Where a particular ridge or trough forms is very important to what type of weather Alaska will experience. In addition, due to the large size of our state, one type of weather pattern may not of course cover the entire state.

Above: A comparison of El Nino's warm strip in Dec. 1997 and Dec. 2002. Sea surface temperature anomalies in these maps were computed from measurements of sea surface temperature collected by the AVHRR sensor on the NOAA polar orbiting satellites.

A Quirky El Nino - NASA Science

 

[bobgnote]

Let's see if the coming El Nino involves warm temperatures, for Alaska.

Alaska might have just moved, to a trend, of warm El Nino weather.

National Weather Service, Anchorage Forecast Office The Weather Classroom -- El Nino, La Nina and Alaska

During most EN's there is a tendency during the winter for a higher frequency of ridges (when compared to the long-term average frequency) to form over western Canada and the eastern Gulf of Alaska, with fewer ridges centered over the Alaska Peninsula. This means that a higher frequency of storms move up the west side of the ridge into Southcentral Alaska, generating as you can imagine warmer temperatures. As a result, there is often an increase in cloud cover and possibly in precipitation (rain and snow) as well. In addition, we also find that in some locations, Anchorage for example, there is a higher number of windstorms (southeast winds) during El Nino winters.

During a LN winter ridging is favored between 170°W and 150°W (eastern Bering Sea to western Gulf of Alaska). The actual position of the ridge is important because it can mean the difference between either warmer or cooler than normal temperatures. For example, with a ridge centered near 160°W, western Alaska is often warm while the area east of the ridge center is cool. This weather pattern also tends to produce cloud free conditions over the region (one exception would be marine fog and stratus).

Keep in mind that the magnitude or impact of air temperature or precipitation anomalies is different from one location in the state to the next. The largest air temperature anomalies occur in the Interior while the smallest ones occur in the marine zones. Precipitation anomalies on the other hand are not as clear-cut in terms of percent of normal rain or snowfall- there is a considerable variation around the state. In terms of actual amounts, the coastal zone along the Gulf of Alaska usually experiences the largest anomalies. For any given EN or LN, the impact that it has on weather may or may not extend over the entire state. For example, there have been El Nino's which produce very strong anomalies over Southeast, Southcentral, and the Interior, with little or no impact in western Alaska and the arctic slope. In a similar manor, some ENSO events produce anomalies that have a significant impact on western Alaska and the arctic slope.

An additional point that needs to be stressed is that when an EN or LN does occur, the anomalies produced by that event are not constant throughout the life of the event. By way of example we will use monthly mean air temperatures at Juneau as seen in the following table. The weather during the winters of 1994-1995 and 2002-2003 were under the influence of an EN. There are a couple of things to notice from this data: there can be some large 'jumps' from one month to the next. Secondly, as illustrated by the 1994-1995 data, on occasions an EN does not produce the 'expected' warm temperatures. Thirdly, even during a strong EN, such as occurred in 2002-2003, there is considerable difference in the average monthly temperature anomalies.

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Summary

The largest impact on Alaska's weather from ENSO events occurs during the winter months.
El Nino's usually produce warmer than normal conditions over most of the state, while La Nina's frequently produce cooler temperatures. However, there is considerable variation in temperature (and precipitation) at all timescales.

The magnitude of a given anomaly is location dependent. Weather in western Alaska and along the arctic coast is not as influenced by ENSO events as the remainder of the state.

 

[bobgnote]

Alaskan temperatures are subject, to whatever happens, to the Arctic ice. If it melts, Alaska has to cool off, and more precip will fall:


NASA - NASA Finds Thickest Parts of Arctic Ice Cap Melting Faster


Danged if that isn't what happened! Back to skook's titties: