The main factors that usually influence the seasonal climate outlook include: 1) El Nino and La Nina – which together comprise El Nino/Southern Oscillation or ENSO. Impacts of these events are summarized by separating 3-month observations from 3 or more decades into El Nino, Neutral, and La Nina sets, averaging each separately, and then computing anomalies. These are called “ENSO Composites”, which are used at times to subjectively modify the forecast. 2) Trends – Approximated by the OCN tool as the difference between the most recent 10-year mean of temperature or 15-year mean of precipitation for a given location and time of year and the 30-year climatological period (1981-2010). 3) The Madden-Julian Oscillation (MJO) – affects climate variability within seasons. 4) The North Atlantic Oscillation (NAO) and the Pacific – North American (PNA) patterns – which affect anomaly patterns especially during the cold seasons. These phenomena are considerably less predictable on a seasonal timescale than ENSO. 5) The Pacific Decadal Oscillation (PDO) – an ENSO-like pattern of climate variability affecting the Tropics and the north Pacific and North American regions, but which varies on a much longer timescale than ENSO. 6) Persistently dry or wet soils in the spring and summer and snow and ice cover anomalies in the winter. These factors tend to persist for long periods and act as a kind of memory in the climate system. 7) Statistical Forecast Tools – Canonical Correlation Analysis (CCA), Screening Multiple Linear Regression (SMLR), Constructed Analogue (CA) and Ensemble CCA (ECCA). 8) Dynamical forecast models – Including the NCEP Climate Forecast System (CFS). An experimental model forecast system, the North American Multi-Model Ensemble, comprised of several models and designated NMME, may also be used experimentally and subjectively until it is included into the consolidation. An international multi-model ensemble designated IMME is also available. 9) Consolidation (CON) – An objective, skill-weighted combination of the OCN, CCA, SMLR, ECCA, AND CFS forecasts is used as a first guess in preparing the forecast maps. This technique makes optimum use of the known skill of forecast tools.
Current atmospheric and oceanic observations are consistent with ENSO-neutral conditions with the likely transition to El Nino conditions in autumn and winter. A weak El Nino event is most probable, however there is a chance of either a moderate event or continued ENSO-neutral conditions into winter. A strong El Nino event is not likely to occur this year. Most dynamical and statistical model forecasts of east-central equatorial Pacific sea surface temperatures (SSTs) in the Nino 3.4 region (170W to 120W longitude and 5S to 5N latitude) indicate a weak El Nino (+0.5C to +0.9C) with peak anomalies in the early winter.
The temperature outlook for October-November-December (OND) 2014 indicates elevated probabilities of above-normal mean temperatures west of the Rocky Mountains, across the Northern U.S. from the Northern Rockies to the Northeast, in most areas east of the Mississippi, and for all of Alaska. Below-normal mean temperatures are more likely over areas of the Southwest including eastern Arizona, New Mexico and western Texas.
The OND 2014 precipitation outlook indicates enhanced probabilities of below-median precipitation over the Pacific Northwest including parts of Northern California and Nevada and over the Northern Rockies. Increased probabilities for above-median precipitation amounts are forecast from southern California eastward across the Southern Rockies and the Southern Plains, and along the Gulf and Southern Atlantic coasts up to North Carolina. The probabilities for above-median precipitation are also enhanced over southern Alaska.
In areas where the likelihoods of seasonal mean temperatures and seasonal accumulated precipitation amounts are similar to climatological probabilities, equal chances (EC) is indicated.
Basis and Summary of the Current Long-Lead Outlooks Note: For Graphical Displays of the Forecast Tools Discussed Below See: http://www.cpc.ncep.noaa.gov/products/predictions/90day/tools/briefing
Current Atmospheric and Oceanic Conditions
Atmospheric and oceanic conditions in the tropical Pacific are consistent with current ENSO-neutral conditions, while indicating the potential development of an El Nino. Observations for the second week of September show SST anomalies of +0.5C in the Nino 3.4 region, +0.7C in Nino 4, +0.4C in Nino 3, and +0.7C in Nino 1+2. SST anomalies increased in the east-central Pacific during the last month. The equatorial upper ocean heat content as indicated by the subsurface temperature anomalies to a depth of 300 meters has increased steadily during the last two months.
An area of suppressed convection represented by positive OLR anomalies was observed near the Date Line mostly north of the equator, and enhanced convection and negative OLR anomalies were observed over the Maritime Continent. Low-level (850-hPa) winds were near-average across most of the equatorial Pacific during the last month, and upper-level (200-hPa) easterly anomalies were observed over the east-central Pacific.
Persistent, strongly positive SST anomalies were observed over the North Pacific, along the Pacific Coast of North America, and westward across the subtropical Pacific Ocean. This SST pattern projects weakly onto a positive PDO. Positive SST anomalies were also observed along the Atlantic Coast and in the North Atlantic.
Prognostic Discussion of SST Forecasts
Most statistical and dynamical models continue to predict that an El Nino event will develop within autumn. Nino 3.4 anomalies are predicted to peak as a weak El Nino in early winter in many forecasts, with some model forecasts indicating a moderate or a strong event and some ensemble members remaining below +0.5C. The CFS Nino 3.4 ensemble members are similar to the multi-model ensemble forecasts of the NMME, currently indicating a peak anomaly of about +0.8C in winter of 2014/2015. Very few ensemble members predict a strong El Nino event. While few ENSO events have developed at this time of year, it is not unprecedented, and considered together, model forecasts and current observations continue to support the consensus ENSO forecast indicating a 60-65% chance of El Nino development in autumn or winter.
Positive North Pacific SST anomalies are forecast to persist through the boreal winter by many dynamical models including the NMME as an El Nino is forecast to develop. Positive SST anomalies along the Atlantic Coast are forecast to persist into winter. These sub-tropical and tropical SST anomalies are likely to impact the climate of North America in the next several seasons.
Prognostic Tools USed for U.S. Temperature and Precipitation Outlooks
The temperature and precipitation outlooks were influenced by potential impacts of an El Nino beginning with OND 2014 and continuing through MAM 2015. The seasonal outlooks are based primarily on dynamical model forecasts from the NMME and IMME, including the CFS, with adjustments made for potential model biases. The shift in probabilities related to positive Nino 3.4 anomalies in the range of 0.5C to 1.0C were considered. For outlooks from AMJ through OND 2015, decadal trends due to changes in the climate base state are the primary source of temperature and precipitation signals. The temperature forecasts of the NMME models appear generally to indicate a greater likelihood of above-normal temperatures across much of the U.S., while few areas of below-normal temperatures are indicated by the dynamical model forecasts.
Prognostic Discussion of Outlooks – OND 2014 to OND 2015
The OND 2014 through MAM 2015 temperature outlooks indicate enhanced probabilities of above-normal temperatures for much of the west, particularly along the Pacific Coast. Temperature outlooks indicate enhanced probabilities of above-normal temperatures across the Northern U.S. through DJF 2014/2015, for parts of the Southeast through NDJ 2014/2015, and for parts of the Northeast throughout the year. These areas of enhanced probabilities for above normal temperatures are supported by most dynamical model forecasts, and are also consistent with impacts of a potential El Nino. Decadal temperature trends have enhanced the chances of above-normal temperatures in much of the Southwest, the Northeast, and the Southeast in the forecasts from MJJ through OND 2015. Enhanced probabilities of above-normal temperatures are forecast for Alaska through OND 2015. Through FMA 2015, this Alaska forecast is due in part to dynamical model forecasts for the persistence of above-normal North Pacific SSTs. The anomalous delay in Arctic Ocean and Bering Sea sea-ice cover for October and November in the last decade relative to the 1981-2010 climatology period results in greatly enhanced probabilities of above-normal temperatures for parts of Northern and Northwestern Alaska. An area of enhanced probabilities of below-normal temperatures is forecast for parts of the Southwest in OND 2014, extending across Texas into Southern Louisiana by DJF 2014/2015 and across parts of the Gulf Coast states in JFM and FMA 2015. The increased likelihood of below-normal temperatures continues into MAM 2015 for Southern New Mexico and Texas. This forecast is supported by the average impacts of positive Nino 3.4 SST anomalies during these seasons. Dynamical model forecasts for the same seasons indicate only weaker probabilities of above normal temperatures or near-normal temperatures, with few forecasts of below-normal. The outlooks were made by adjusting dynamical model forecasts by the most likely impacts of a potential warm ENSO event.
The OND 2014 through FMA 2015 precipitation outlooks indicate enhanced probabilities of above-median precipitation from parts of Southern California, across most of the Southwest and the Southern Plains, and along the Gulf and Southern Atlantic Coasts. Enhanced probabilities for below-median precipitation are indicated for the Pacific Northwest through FMA 2015, and from the Central Mississippi Valley into the Great Lakes region from NDJ 2014/2015 into FMA 2015. Probabilities of above-median precipitation are enhanced for Southern Alaska and parts of the Alaskan Panhandle through FMA 2015. These precipitation outlooks are supported by dynamical forecasts from the NMME and IMME, as well as by the potential impacts of an El Nino.
Probabilities of below-median precipitation are enhanced for parts of the Pacific Northwest in the JAS and ASO 2015 seasons due to decadal trends resulting from a changing climate.
Forecaster: Dan Collins
The Climatic normals are based on conditions between 1981 and 2010, following the World Meterological Organization convention of using the most recent 3 complete decades as the climatic reference period. The probability anomalies for temperature and precipitation based on these new normals better represent shorter term climatic anomalies than the forecasts based on older normals.
For a description of of the standard forecast tools – their skill- and the forecast format please see our web page at http:/www.cpc.ncep.noaa.gov/products/predictions/90day/disc.html (Use Lower Case Letters) Information on the formation of skill of the CAS forecasts may be found at: http://www.cpc.ncep.noaa.gov/soilmst/forecasts.html (use lowercase letters) Notes – These climate outlooks are intended for use prior to the start of their valid period. Within any given valid period observations and short and medium range forecasts should be consulted.
This set of outlooks will be superseded by the issuance of the new set next month on Oct 16 2014
1981-2010 base period means were implemented effective with the May 19, 2011 forecast release.