NCEP Extended Forecast
Every month the Climate Prediction Center (CPC) issues maps showing the probability of exceeding thresholds of above and below normal conditions for temperature and precipitation. The CPC also makes available versions of these outlooks giving temperature (degrees Fahrenheit) and precipitation (inches) for the lower 48 states by climate regions (Probability of Exceedence). Our office will post the most recent one-month and three-month (seasonal) outlooks on this page. Outlooks ranging in length from 2 weeks to 13 months can be found at the CPC homepage, http://www.cpc.ncep.noaa.gov/index.html
Monthly Outlook:
The first map represents a monthly temperature forecast. An "A" on the map means that the temperature field, within the colored region, is predicted to be above the normal average, whereas a "B" represents below average conditions. "EC" represents an equal chance for above or below normal, essentially stating that it is indeed normal. The actual colorings represent the certainty of the particular forecast for the area (See Table 1 below).
Table 1
The second map on each month represents departure from normal average for precipitation data. the characters represent the same thing as on the temperature forecast, with "A"s above, "B"s below the average, and "EC"s signifying an equal chance of above or below average conditions.
The numbers following the border of each color represent, as stated above, the probability of the forecast's accuracy. Table 1 explans in greater detail the meaning of each number and color. After finding the color of the region, next find the head of the column with the appropriate letter in the "Probability of occurrence for each Equal" section, to determine the magnitude of probability (confidence) for the forecast.
September 2004
Seasonal
Outlook:
September-October-November 2004
Probability of Excedence (POE)
The POE charts below are paired by region, with the first graph of every section representing temperature, and the second graph showing precipitation data. POE charts are used to document the probability that a data point for a season will be exceeded, using a set of 4 different plotted lines to expand on this idea. The graphs maintained on this page will show information for the next three month period.
The four lines, as noted above, show different aspects of the probability of our forecast data. The first line, which happens to be black, is the climatological normal, meaning that it is the average observed temperature or precipitation data taken over our recorded history of the data of interest. Next is yello, 'observed data' line. This line shows the actual unfitted observed data for the period of interest. If one were to take the average of the curves in this line, and them compare it to the black climatological line, this would give an idea of the accuracy of our chart. If the line matches up perfectly then the chart is accurately created, if below or above the curve, or with a different general shape of slope, then the chart may not hold the most accurate information. The next line is the forecast line, which typically will overlap the black or normal line. This occurs because the forecast takes into account a great deal of different data, which will nearly always correspond, after averaging it out, with what normally will happen for that year. When we have even more specific data for our forecast, then one might see a deviation from normal accounted for by increased certainty. The final line is the "error envelope" represented by the thin red line. This line shows the possible deviation from current position of the forecast line. It is possible that the line, with the same slope and shape, might be shifted within the two thin red error lines. This is due to several errors that could possibly be found within the forecasts calculations, such as inaccurate data or forecaster misjudgment.
So, now to actually use this chart, observe the point on the X-axis of interest, then trace a vertical line up from that data point until it matches your forecast or whatever line your wish to observe. Then trace a horizontal line to the percentile on the left or right margin. This is the probability of "exceedence," the probability that the value you choose on the X-axis will be exceeded during the forecasted season. There are also several points about the POE made in blue at the top and right of the lines within the chart for quick reference.
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Climate Division 5 (Eastern Great Lakes)
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Climate Division 8 (Northern Appalachians)
Climate Division 7 (Mid-Atlantic Coast)
