IntermtnClimateSummaryJan2008

• Title: Intermountain West Climate Summary
• Date: 1/22/2008
• Description: Water Availability Task Force Meeting Report
• Basin: Statewide
• Drought Mitigation - Doc Type: Reports

INTERMOUNTAIN WEST CLIMATE SUMMARY, JANUARY 2008

EI Nino Status and Forecast

A moderate La Nina continues in the tropical Pacific,
with below-average sea surface temperatures (SSTs)
extending from 160DE to the South American coast. SST
indices in the NINO 3.4 region averaged 1.5 DC below
average during December, where a value of 1.0 -1.5 DC
below average indicates the existence of moderate La
Nina conditions (Figure 13a). The recent SST forecasts
(dynamical and statistical models) for the Nino 3.4 region
indicate a continuation of La Nina conditions into North-
ern Hemisphere spring 2008 (Figure 13b). Over half of
the models predict at least moderate La Nina conditions to
continue through February-April, followed by weaker La
Nina conditions. Current atmospheric and oceanic condi-
tions and recent trends are consistent with a likely con-
tinuation of La Nina into the Northern Hemisphere spring
2008. According to the International Research Institute
for Climate and Society, a NOAA partner, based on the lat- 205
est observations and forecasts, there is a 96% probability
of maintaining La Nina conditions over the January-March
2008 season, and a 50% probability that it will continue
through the May-July season. The probability of an EI
Nino developing by May-July is less than 10%.
During January-March 2008, the potential impacts La
Nina over the continental U.S. include above-average pre-
cipitation in the Northern Rockies, the Pacific North\vest,
the Ohio and Tennessee Valleys, and parts of the Great
Lakes region. Belo\v-average precipitation is expected
across the southern tier, particularly in the southeastern
states where there is an ongoing severe drought.
The CPC ENSO Diagnostic Discussion will be updated
next on February 7th, and the IRI ENSO "Quick Look" on
February 21st.

Notes
Two NOAA graphics in Figure 13a show observed SST (up-
per) and SST anomalies (lower) in the Pacific Ocean, averaged
over a recent 5-day period. Data are from satellite observations
and the NOAA TAO array of 70 moored buoys spread out over
the Pacific Ocean, centered on the equator. The buoys measure
temperature, currents, and winds and transmit data in real-time.
NOAA uses these observations to predict short-term (a few
months to one year) climate variations.
Figure 13b shows forecasts for SST in the Nino 3.4 region
for nine overlapping 3-month periods. "Nino 3.4" refers to the
region of the equatorial Pacific from 1200W to 1700W and 50N to
50S, which is used as an SST-based index for defining ENSO.
Abbreviations represent groups of three months (e.g. SON =
Sept-Nov). The expected skills of the models, based on histori-
cal performance, vary among the models, and skill generally
decreases with lead-time. Forecast skill also varies over the
year because of seasonal differences in predictability of the
system, e.g., forecasts made between June and December are
generally better than those made between February and May.
Differences among forecasts reflect both differences in model
design and actual uncertainty in the forecast of the possible
future SST scenario.

Observed Sea Surface Temperature (CO)

20N

~

10N

30

EQ

105

205

160W
I I
23 24

140W
1 I
25 26

120W 100W
I I, ~
27 28 29

80W

Observed Sea Surface Temperature Anomalies (CO)

20N

80W

~

10N

.--------- -.._..../..

EQ

~ I

105

______.... __ L:- ----__.

100W
I~I

-5

" I
-2

-1 -0.5 0.5

-4

-3

Figure 13a. Observed SST (upper) and the observed SST anomalies
(lower) in the Pacific Ocean. The Nino 3.4 region encompasses the area
between 120oW-170oW and 50N-50S. The graphics represent the 7-day
average centered on January 9, 2008.

Model Forecasts of ENSO from January 2008

3 I

2

I

2.5

o
e- 1.5
~
ro
E
o
c
<(
~ 0.5
(f)
(f)
~ 0
cry
o
~~ -0.5
z

-1

-2

Observdd

: Forecast

-2.5
OND Dee DJF JFM FMA MAM AMJ MJJ JJA
2007 2008

JAS ASO SON

Figure 13b. Forecasts made by dynamical and statistical models for sea
surface temperatures (SST) in the Nino 3.4 region for nine overlapping
3-month periods from January through November 2008 (released January
16, 2008). Forecast graphic is from the International Research Institute
(IRI) for Climate and Society.

On the Web
· For a technical discussion of current EI Nino conditions, visit: http://www.cpc.ncep.noaa.gov/products/analysis_
mo n itori ng/enso _advisory I.
· For updated graphics of SST and SST anomalies, visit this site and click on "Weekly SST Anomalies": http://www.cpc.
ncep. noaa. gov Iprod ucts/precip/CWli n k/MJO/enso .shtml#cu rrent.
· For more information about EI Nino, including the most recent forecasts, visit: http://portal.iri.columbia.edu/climate/ENSOI.

FORECASTS 11 6