IntermtnClimateSummaryJan2006

• Title: Intermountain West Climate Summary
• Date: 1/17/2006
• Description: Water Availability Task Force Meeting Presentation
• Basin: Statewide
• Drought Mitigation - Doc Type: Presentation

INTERMOUNTAIN WEST CLIMATE SUMMARY, JANUARY 2006

Precipitation Outlook January - May 2006

The winter and spring seasonal precipitation forecasts issued
December 15th by the NOAA Climate Prediction Center (CPC)
sho\:v the Intermountain West as having "equal chances" of
above-average, near-normal or below-average precipitation for
the Jan-March 2006 forecast periods (Figure lla-d). However, La
Nina conditions are associated with dry conditions in the winter in
the Southwestern U.S., and these conditions typically extend into
southern Colorado and Utah.
According to CPC, sea surface temperatures (SSTs) and
atmospheric conditions, which are currently neutral, are trending
toward weak La Nina conditions. CPC thinks that the Pacific
is close enough to La Nina conditions to impact the climate for
Jan-Mar 2006. However, the reliability of anticipated impacts is
lower than would be expected in a moderate or strong La Nina
event. The CPC will update the seasonal precipitation forecasts
on Thursday, January 19th, based on the latest observations of La
Nina and other factors.

Notes
The seasonal precipitation outlooks in Figures 11 a-d predict the
likelihood (chance) of above-average, near-average, and below-
average precipitation, but not the magnitude of such variation. The
numbers on the maps refer to the percent chance that precipitation
will be in one of these three categories, they do not refer to inches

Figure 11 a. Long-lead national precipitation forecast
for January 2006. (released Dec. 30, 2005)

Source: NOAA Climate Prediction Center

of precipitation.
The NOAA-CPC outlooks are a 3-category forecast based
largely on the status of EI Nino and recent trends. As a starting
point, the 1971-2000 climate record for each particular 1 or 3
month period is divided into 3 categories or terciles, each with a
33.30/0 chance of occurring. The middle tercile is considered the
near-average (or normal) precipitation range. The forecast indi-
cates the likelihood of the precipitation being in one of the wetter
or drier terciles--above-average (A) or below-average (B)--with a
corresponding adjustment to the opposite category; the near-aver-
age category is preserved at 33.30/0 likelihood, unless the anomaly
forecast probability is very high.
Thus, using the NOAA-CPC precipitation outlook, areas with
light brown shading display a 33.3-39.90/0 chance of below-aver-
age, a 33.30/0 chance of near-average, and a 26.7-33.30/0 chance
of below-average precipitation. A darker brown shade indicates a
40.0-50.00/0 chance of below-average, a 33.30/0 chance of near-
average, and a 16.7-26.60/0 chance of below-average precipitation,
and so on. Correspondingly, green shades are indicated for areas
with greater chances of above average precipitation.
Equal Chances (EC) indicates areas for which the models can-
not predict the precipitation with any confidence. EC is used as a
"default option" representing equal chances or a 33.30/0 probability
for each tercile, indicating areas where the reliability (i.e., 'skill') of
the forecast is poor.

A = Above
. 40.0-49.90/0

D 33.3-39.90/0

Figure 11 b. Long-lead national precipitation forecast
for Jan. - Mar. 2006. (released Dec. 15, 2005)

B = Below
. 40.0-49.90/0

D 33.3-39.90/0

Figure 11 c. Long-lead national precipitation forecast
for Feb. - Apr. 2006. (released Dec. 15, 2005)

EC = Equal
Chances

Figure 11 c. Long-lead national precipitation forecast
for Mar. - May 2006. (released Dec. 15, 2005)

On the Web
- For more information and the most recent CPC forecast images, visit: http://www.cpc.ncep.noaa.gov/products/predictions/ multi_season/13_
seasonal_outlooks/color/churchill.html. Please note that this website has many graphics and may load slowly on your computer.
- The CPC "discussion for non-technical users" is at: http://www.cpc.noaa.gov/products/predictions/90day/fxus05.html
- For IRI forecasts, visit: http://iri.columbia.edu/c1imate/forecast/net_asmt/.
- More information about temperature distributions at specific stations in Colorado, Utah, Wyoming, and across the West can be found at the
Western Regional Climate Center, http://www.wrcc.dri.edu/CLlMATEDATA.html.
- The CDC experimental guidance product, including a discussion and executive summary, is available on the web at: http://www.cdc.noaa.
gov /people/kla us. wolter/SWcasts/i ndex. html

FORECASTS 11 4