**[El Nino Weather In The Greater Anchorage Area]{.underline}:**

**What the data indicates could occur this winter.**

With the advent of a new El Nino in the Tropical Pacific, it is
worthwhile considering what weather anomalies might be expected this
winter in the greater Anchorage area. Figure One shows the average
winter (defined as November through March) temperature as observed at
Ted Stevens International Airport. The data ranges from 1976 through
2005 (in 1976 there was a significant climate shift across the North
Pacific so older data is not used). Notice that there is considerable
variation from one

El Nino winter to the next. The blue horizontal line shows the 30 year
average which corresponds to 21.5^o^ F. This figure indicates that three
events were significantly warmer than normal (1976/1977, 1986/1987,
2002/2003) while five events were 'near' normal.

![](media/image1.wmf){width="4.013888888888889in"
height="2.564583333333333in"}Only one event (1994/1995) generated
temperatures that were well below the long-term average. From this we
may conclude that for any given El Nino, there is a reasonable high
probability that air temperatures will tend to be warmer than normal
(how much warmer cannot be determined). Conversely there is only a
slight chance that temperatures will be below the long-term average.

![](media/image2.wmf){width="4.25in" height="2.75in"} Snowfall amounts
during El Nino winters are shown in Figure Two. The main point of
interest is that the seasonal snowfall is highly variable (note that
this figure only shows snowfall, not snow on the ground). During some El
Nino winters snowfall is well above normal (1987/1988, 1991/1992,
1994/1995) while other winters it is well below normal (1982/1983,
1986/1987, 2002/2003). Snowfall in Anchorage tends to be a function of
the position of the North Pacific storm track as well as air
temperatures ([sometimes]{.underline} we receive rain instead of snow
due to the warmer than normal temperatures). Since the data does not
indicate any clear signal, there is no predictability- in other words
there is equal chance that snowfall across Anchorage will be above
normal, near normal or below normal. \[Note that the same conclusion is
reached when November-March precipitation (snowfall and rain) data is
considered.\]

The third weather element that people want to know about is the wind.
Thirty years of surface wind data from Ted Stevens Int. Airport
indicates that the frequency of southeast wind events during El Nino
winters is the same as it is during non-El Nino winters. However, twenty
years of data collected on Anchorage Hillside by a cooperative observer
does seem to indicate a slight increase in southeast (downsloping) wind
events during El Nino winters.

El Nino conditions in the equatorial Pacific (warmer than normal sea
surface temperatures, enhanced (reduced) rainfall east (west) of the
Dateline, stronger subtropical jetstream over eastern Pacific), tends to
force the Aleutian Low pressure system eastward from its 'normal'
position. At the same time high pressure over western Canada is
enhanced. The net result is that during most (but not all) El Nino
winters, the frequency of storms that move into the Gulf of Alaska is
increased. During the winter of 1994/1995 for example, the Aleutian Low
shifted so far east that Anchorage and most of Alaska experienced cooler
(slightly) temperatures than normal.

[Conclusions]{.underline}:

Temperatures- most likely will be warmer than normal (degree of
departure is unknown)

Note that there will still be periods of cold temperatures, however the
[seasonal]{.underline}

[average]{.underline} will most likely be on the warm side of normal.

Snowfall- no forecast skill, equal chance of above, near or below normal
amounts. The

amount of snow on the ground at any given time is a function of snowfall
and

air temperatures. We have had some El Nino winters where snowfall was
well

above normal, however, warmer temperatures and enhanced downslope winds

(Chinooks) produced a thin snowcover across Anchorage.

Winds- slight increase in frequency of southeast winds along the
Hillside.