Point Forecast Matrices (PFM) FAQ

Question:
What is the PFM?

Answer:
PFM stands for the Point Forecast Matrices product. It provides another way to view WFO Charleston’s forecast for various specific locations in our geographic area of responsibility.

Question:
In what format is the PFM written?

Answer:
The PFM is written in a tabular format. Forecast parameters are listed down the left hand side of the product and forecasts are provided for each parameter and each location at 3-hour, 6-hour, and/or 12-hour intervals.

Question:
Who should use the PFM?

Answer:
While the PFM was initially designed to support large volume users of NWS products, the PFM product provides specific weather forecast information that can be used by everyone.

Question:
What are the benefits of using the PFM?

Answer:
The PFM allows for the user to rapidly scan weather forecast information and pick out the information that is most important to them. As an example, many users are interested in relative humidity information. The traditional NWS forecast does not provide this information. The user can access the PFM information for a specific city and get forecast relative humidity information at three-hour intervals. In addition, traditional NWS forecasts many times provide ranges of temperature and wind forecasts over an area the size of a county or a number of counties. The PFM provided specific numeric forecasts for specific locations. Advanced users will be able to parse out important PFM data and reissue this information in their own products.

Question:
When will the PFM data be updated?

Answer:
While the PFM will have a mandatory issuance twice daily of no later than 4 am and 4 pm daily, the PFM will be an event-driven, dynamic product. As weather changes and forecasts change, the PFM product will also be updated as needed. This means that the PFM product will always provide fresh information for anyone using it.

Question:
What time frame does the PFM cover?

Answer:
The PFM covers a 7-day period of time from the time of issuance.

Question:
When I look on the PFM, I see two different time lines below the date. What am I looking at?

Answer:
UTC stands for Universal Time Coordinate. Depending on the time of year, this time will differ from the local time by 4 or 5 hours. On the next line below the UTC line, you will see another line showing either EST or EDT (depending on the time of year). This will be your local time on a 24-hour clock. As an example, in local time, “03" would represent 3:00 am, “12" would represent noon, and “18" would be 6:00 pm.

Question:
When I look at the MX/MN line, I only see one number every 12 hours. What am I looking at?

Answer:
The MX/MN line of the PFM displays the high and low temperature forecast. The maximum temperature is valid between 7 am and 7 pm local standard time. The minimum temperature is valid between 7 pm and 8 am local standard time. The numbers you see indicate the forecast high and low temperature . The MX/MN temperature forecast is placed in the column at the end of the valid period, with the maximum or minimum temperature occurring sometime within the prior 12 hours (for the MaX temp) and 13 hours (for the MiN temp).

Question:
What units are used for the wind forecast and how many points on the compass are used?
Also, what does “00" mean?

Answer:
Wind information is provided in mph (miles per hour) as opposed to knots. WIND SPD represents a snapshot of the forecast sustained wind speed at the indicated hour through the first 2 ½ days. WIND GUST provides a snapshot of the wind gusts in mph (miles per hour) at the indicated hour. A gust is only indicated when the wind is expected to exceed the forecast sustained wind by at least 10 mph. “00" represents calm winds.

Beyond 60 hours, wind character codes (WIND CHAR) are used. Click here to see a table of Wind Character Codes

Question:
What does all this cloud information mean?

Answer:
During the first 60-hours, the PFM provides 3-hourly forecasts of opaque sky cover. This is done through a series of different cloud codes. Click here to access the Cloud Code Table.

After 60 hours, a different parameter, AVG CLOUDS, is used to indicate the average amount of all clouds during a 6-hour period ending on the hour indicated at the top of the column.

Question:
How does the PFM handle forecast information about precipitation?

Answer:
POP 12HR is a parameter that is used in the PFM to express the likelihood of measurable precipitation (1/100th of an inch) during the 12-hour period that ends at 6:00 am or 6:00 pm local time (0600 or 1800). The POP 12HR parameter is provided through Day 7.

Another parameter, QPF 12HR represents the total amount of precipitation in inches of liquid equivalent that is forecast at a specific point during the 12-hour period ending at 6:00 am or 6:00 pm local time (0600 or 1800). QPF will be provided as a range in hundredths of an inch and will be included out through the first 60 hours.

During the locally defined winter period defined by WFO Charleston, the PFM will also include the SNOW 12HR parameter which will provide users with specific total snowfall accumulation 12-hour point forecasts in whole inches of snowfall ending at 6:00 am and 6:00 pm local time. The SNOW 12HR parameter will appear as a single or double digit, or as a range (i.e. “2-4" meaning two to four inches of snow in a 12-hour period ending at the specified time). “00-00" is used to indicate no snowfall. “T” is used to indicate trace amounts (less than 0.1 inch of frozen precipitation). The SNOW 12HR is forecast out to 36 hours.

Precipitation types may also appear in the left hand column of the PFM. At 3-hour time intervals out to 60 hours and then during 6-hour time intervals between 60 hours and Day 7, specific probability of precipitation codes will be included when certain precipitation types are forecast.
Click here to access a table of PFM Precipitation types and Probability of Precipitation Codes.

Question:
What other types of information are in the PFM?

Answer:
Visibility forecasts are provided in the PFM at 3-hour intervals through 60 hours.
Click here to access a list of Obstruction to Visibility Codes used in the PFM.

Other information you might see on a PFM include wind chill and heat index information based on criteria locally defined by WFO Charleston. Six-hour forecasts of minimum wind chill and maximum heat index may also appear on the following line, again when local criteria are met.

Question:
The traditional NWS Forecast highlights long-fused watches, warnings, and advisories. Will the PFM provide this information as well?

Answer:
The answer to this question is “yes”. In the future, special codes will allow for specific input of long-fused watch, warning, and advisory information into the PFM product. Special codes for watches (“A”), warnings (“W”), and advisories (“Y”) will be applied to 3-hour time spans, matching the valid times of the event as possible. The specific watch, warning, or advisory will be provided in the left hand column, with the special codes appearing within the first 60 hours of the PFM.

Question:
What does “MM” mean on the PFM product?

Answer:
“MM” represents missing data in the PFM product.