Local Three-Month Temperature Outlook
by Jan Jackson
There is a suite of new climate products available from the National Weather Service. They are site-specific 3 month temperature forecasts for a few of the Cooperative Observing, (Coop), sites in each of the Weather Forecast Office County Warning Areas, (CWA). There are 14 sites with the new 3 month temperature outlooks in the Blacksburg CWA. They are:
West Virginia - Lewisburg.
Virginia- Appomattox, Blacksburg, Bluefield, Danville, Galax, Hot Springs, Lexington, Lynchburg, Roanoke, and Wytheville.
North Carolina- Boone, Jefferson and Mount Airy.
The forecasts are for average daily mean temperatures over a 3 month period. They are provided in graphical, tabular, and text formats for thirteen separate three month periods, (to cover a year's worth of time). These forecast periods begin at 0.5 months after the current month, to 12.5 months after the current month. The forecasts are updated once a month, after the 15th of each month. These new forecasts can be accessed from the National Weather Service, Blacksburg, Va homepage. Just select the local Climate link on the left hand menu (see below).
Then from the climate page, select the Climate Prediction folder (below).
The next page you will see is the main climate prediction web page, which has links to several national climate forecasts, but it also has a link at the top left (see below) for the Local 3-Month Outlook for the Blacksburg CWA. Select that link.
The next page you will see is a map with all of the available sites with 3 month outlooks. (See below).
Specific sites can be selected by clicking on the green dots on the map, or using the drop down menu at the bottom. Forecast products can be selected by using the drop down menu on the right, or clicking on the product windows on the bottom.
There are basically 4 ways of looking at the data. Examples of each, along with explanations, are listed below.
3 Category Outlook
This is an example of the 3 Category Outlook for Blacksburg, for the 3 month period of April through June. This product is a pie chart that shows the expected chance that the 3 month average temperature will be either Below Normal, Near Normal or Above Normal. The legend to the right shows the actual temperature ranges used, based on 1971 - 2000 normals. Note in this example, that Blacksburg is forecast to have the highest chance of being above normal (underlined in red).
For those that prefer their data in tabular form, or for a quick way to look at all of the 3 month periods for the next year, the 3 Category Outlook is also available as a table:
Note that in this example for Bluefield, Va, that the 3 month period with an enhanced chance of being above normal is highlighted in red.
Probability of Exceedance
Another way of looking at the 3 month temperature outlook is the Probability of Exceedance (POE). This product contains the most information at one glance. It is a graph that shows the expected chance (Y axis in percent), that the average 3 month temperature will exceed the temperatures shown on the X axis. The graph shows 2 curves: the one in red is the POE for the 1971 - 2000 reference period, and the one in green is the forecast POE. The colored vertical lines are the observed 3 month average temperatures for the past 5 years. Note in this example for Mount Airy NC for the 3 month period of June through August, that the forecast curve (green), is warmer than the 1971 - 2000 normal curve for corresponding probabilities. Note also the tab on the right "Customized Confidence Interval Worksheet". This percentage defaults to 99 percent, and the box below shows a spread of average temperatures for that percentage of confidence. It can be adjusted to show the temperature spread corresponding to 95, 90, 75 or 50 percent confidence levels as well. The Temperature Range product is a way to see a graphical view of this confidence spread. (See example below).
This is the same graph as the default POE graph, but with the temperature on the Y axis, and percent probability of exceedance on the X axis.
For those of you that prefer to think of the glass as half full, rather than half empty, you can select the "Switch To Probability of Non-Exceedance" button and the same data is displayed as the percentage probability that the temperatures will not be exceeded. (Example below).
This is still the June through August forecast for Mount Airy NC. Note that now the lower probabilities correspond to the cooler temperatures.
Finally, for those that prefer a tabular view of the the POE data, it is available in a table. The table has the added feature of showing any 3 month period that deviates from climatology by 0.5 degrees F or more by shading it. (See example below, and note the legend on the bottom.)
This is the final way that the 3-month outlook can be viewed, and is a quick way to see the the expected temperature spread for any 3 month period. The default graph is based on a 99 percent confidence level, but you can also choose from 95, 90, 75 or 50 percent confidence levels. Note in the example for Danville above, that the forecast has a higher temperature spread on the warm side compared to than the 1971 - 2000 Climate Median, (denoted by the +), for many of the 3 month periods.
Summer Temperature Outlook
The map above shows the 3 month temperature outlook for the country. Note that southern West Virginia, southwest Virginia, and northwest North Carolina all fall within the 33 to 40 % range for being above normal. This is an example of where the new Local 3-Month Temperature Outlook products can provide a lot more detail. Take a look at any of the 14 sites within the Blacksburg CWA, and you will see that while all of them have higher probabilities of warmer than normal temperatures this Summer, there is a wide range from site to site. Generally, the sites west of the Blue Ridge have higher probabilities of having above normal temperatures this Summer, and this is typical for a La Nina pattern.
Summer Precipitation Outlook
There are plans to develop a Local 3-Month Precipitation Outlook similar to the Local 3-Month Temperature Outlook, and for the same 14 locations in the Blacksburg CWA. For now, the best you can do for a long range precipitation outlook for your area is to view the national map (below), which indicates equal chances for the entire area, and means that there are no strong climate signals for either above or below normal rainfall for the area.