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Automated NAEFS 8-14 Day outlooks are currently issued once per day at roughly 8am, (Eastern Times). This is a strictly EXPERIMENTAL product and in no way should be mistaken for any offical NWS forecast.

As an experimental product, the information & graphics presented on this page will change (in number, type & presentation) as the product progresses through the developmental process. Commentary is always welcome.

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HOME> Outlook Maps>8-14 Day NAEFS Outlooks
North American Ensemble Forecast System
Extended Range Precipitation and Temperature Guidance [EXPERIMENTAL]
About these Products

Return to Temperature Forecasts
Return to Precipitation Forecasts

The North America Ensemble Forecasting System (NAEFS) is a multinational effort involving Canada, Mexico, and the United States to produce forecast guidance based on model ensemble forecasts run at Environment Canada and the National Centers for Environmental Prediction (NCEP). This product interprets an ensemble of 40 different numerical model forecasts to produce guidance for a probabilistic prediction of the mean surface temperatures and accumulated precipitation. Each model prediction is based on either slightly different estimates of the current state of the atmosphere or slightly different model physics. The ensemble of solutions represents the range of possible outcomes for a given forecast. A new set of ensemble forecasts is available every 12 hours from both the NCEP and Canadian models. These are based on initial conditions generated from observations at 1200 and 0000 UTC, corresponding to the morning and evening hours over North America. Details of the NCEP numerical weather prediction model used in NAEFS forecasts can be found in the following.

Precipitation Guidance Maps.

Maps displayed are based on NCEP and Canadian ensemble model forecasts of precipitation amount. Maps of North America show the probability of precipitation amounts falling into either the below normal or above normal categories. Below and above normal are defined as the lower and upper third of the observations from 1979-2007 for the same week of year. In dry regions during some periods, more than one-third of the observed 5 or 7 day periods have no precipitation. Even though these areas are "normally dry", zero precipitation is always placed in the below normal category. In very dry regions, where more than two-thirds of the observed 5 and 7 day periods from 1979-2007 have no precipitation, above normal is defined as the probability of precipitation and plotted when this probability exceeds one-third, even though lower probabilities can be greater than normal.

Global maps are provided showing an estimate of the probability of total precipitation for the period exceeding the specified amounts, 25 and 75 millimeters or approximately 1 and 3 inches. Probabilities are derived from the fraction of ensemble precipiation forecasts exceeding various thresholds.

Temperature Guidance Maps.

Maps based on model output of forecast near surface air temperatures (2 meters above the surface). Probabilities indicate the percent of ensemble members that predict temperatures significantly above normal, near normal, or significantly below normal. These probabilities are not calibrated, which means that they do not necessarily reflect the subsequent observed frequencies of above, near, or below normal temperatures, but can provide reasonable guidance for the true probabilities. Model forecasts have been corrected for the mean systematic errors (or bias) in the 2 meter temperatures in the immediate past.

Colors represent areas where the majority of ensemble members agree on a single temperature category. White areas indicate areas of substantial disagreement among ensemble members. Contours within the colored areas indicate the percentage of members forecasting the specified category. Forecast certainty increases as colors darken , indicating more agreement among ensemble members.

Definition of categories

Categories are based on the observations for a given time of year over many years. Temperatures and accumulated precipitation amounts are classified as "above normal" when they are greater than two-thirds of the distribution of observations that occurred in a given week over the last 30-years. Values in the lowest one-third are classified as "below normal" and in the remaining middle third as "near normal". The values that separate thirds of the range of observations (or distribution) are described as "tercile" boundaries. Terciles are shown on the NAEFS temperature guidance page under "Category Limits". A weekly mean temperature at any given location that is above the value listed on the map labeled "Upper Tercile" will be classified as above normal. A temperature is below normal when it is below the value listed on the "Lower Tercile" map. Temperatures in between the upper and lower tercile limits are classified as near normal.

Supplemental Forecast Information

The upper level circulation features that correspond to the NAEFS temperature and precipitation guidance is shown in the maps labeled "500-hPa Heights" and "500-hPa Anomalies" The 500-hPa heights indicate the height at which the atmospheric pressure is approximately half its normal surface value and is displayed in meters above sea level. The "500-hPa Height" map shows the mean value of all ensembles for the 8-14 day period, while the "500-hPa Anomalies" shows the forecast departure from the long term average value for that given week. Shaded regions indicate where the predicted heights are significantly higher or lower than normal.

NAEFS verifications

To provide information on how the temperature guidance has performed in the recent past, the verification page gives access to the forecasts issued within the last few months. The forecast that was issued on any given day can be recalled by clicking on the calendar date. The three maps displayed are: the NAEFS temperature guidance issued, if available, the observations corresponding to the forecast, and the official forecast issued by CPC forecasters. The official forecast includes additional information not included in the NAEFS guidance. The verifying observations are based on an analysis of the observations obtained in real-time. These values are analyzed to a 1 degree grid and contoured at intervals of 5 degrees F. Shading indicates areas of above or below normal temperatures, based on the same tercile limits used to classify forecasts. Because of sparse data in some regions, and occasional missing data received, the analysis values may be unreliable in some locations, such as sparsely populated or mountainous regions.

Related Topics:
Official Forecast 6 to 10 Day Outlooks, Official 8 to 14 Day Outlooks,
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Page last modified: Dec 15, 2005
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