La
Niña Events and Effects on New
Mexico's Winter Precipitation and Spring Snowpack
During mid year 2007, sea
surface temperatures (SST) in the tropical east Pacific Ocean cooled
to below normal levels. This event is referred to as La Niña,
and while the tropical Pacific Ocean is a great distance from New Mexico,
a La Niña event often
results in a drier than normal precipitation across New Mexico, particularly
during the winter season.
In an attempt to determine what effect La Niña episodeshave
on winter precipitation in New Mexico, we looked back at previous
La Niña episodes and
associated precipitation as reported by climate division and stations.
We used La Niña events as defined by CPC,
and included the recent "cool" episode
of 2005-2006 during which near La Niña conditions were met for
a three month period.
Results for climate divisions are illustrated in the diagram below, and
statistics
for each of the sites are accessed from the map.
Percent of Normal
December-January-February Precipitation (for
Climate Divisions)
during
La Niña Events
since 1950
Results are available
for individual sites - click on a site to view details.
When a La Niña episode is in progress, the winter
season of December-January-February (DJF) is often drier than normal.
Climate
division
average precipitation
during
winter for 21 recent La Niña events ranged
from
77 percent of normal in the Southeastern Plains (division 7) to
88 percent of normal in the Northern Mountains (division 2). While all
climate divisions
averaged less than normal winter precipitation, there are years during
which a La Niña was in progress but the winter season had
above normal precipitation.
Using the same 21 La Niña winter events, we looked
at the variability of New Mexico statewide snowpack in early Spring. The
figure below illustrated the March 1st snowpack for each year since 1950.
La Niña winter events are denoted by the red bars.
About 70 percent of the
La Niña episode years (15 of 21) had below normal snowpack. Only
1962, 1965, 1968, 1975,
1985, and 2001 were La Niña winters during which March 1st statewide
snowpack, as measured by the USDA Natural Resources Conservation Service
(NRCS),
was greater than normal. Of the 21 La Niña winters in this study,
March 1st snowpack was less than 75 percent of normal during 10 years,
and less than 50 percent of normal during 9 of those 10 years. Following
the 21 La Niña winters, New Mexico snowpack as of March 1st was
less than 50 percent of normal 43 percent of the time.
In contrast, only 2 La Niña winters (1968 and 1985) resulted
in March 1st snowpack greater than 150 percent of normal. The winter
of 1968 featured a weak La Niña (-0.7 ONI) while the winter of
1985 featured a weak to moderate La Niña (-1.0 ONI).
In summary, La Niña generally has an impact on winter
precipitation and resultant early spring snowpack for New
Mexico.
However, each La Niña episode is likely to allow for a fairly
wide range in precipitation amounts, from a statewide average of 3.29
inches during the winter of 1984-1985 to 0.32 inches during the winter
of 2005-2006.
National Weather Service
Albuquerque Weather Forecast Office
2341 Clark Carr LP SE
Albuquerque, NM 87106
Ph: 505.243.0702
Web Master's Email: ABQ Webmaster
Page Author: WFO Albuquerque, NM
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