Point Forecast Matrices
What are the POINT FORECAST MATRICES?
|How to read/interpret the PFM
There are several forecast parameters which appear in the PFM product. Some of these values are forecast in 12 hour intervals while others are forecast in 3 and 6 hour intervals. Listed below is an example of an PFM product and a description of each of its parameters.
| MAX/MIN. (Alternatively labeled as MIN/MAX for afternoon issuance)
A forecast of maximum or minimum temperatures in degrees Fahrenheit (F)The MAX temperature is valid for the period 7:00 a.m. through 7:00 p.m. local standard time, and “MIN” is valid for 7:00 p.m. through 8:00 a.m. local standard time (note that due to a 3-hour minimum time resolution, this element is right justified in the column beneath the approximate ending time of the MAX/MIN period). The nighttime MIN and daytime MAX may be displayed as single integer (e.g., -2, 8, 53, 102) as a range (e.g., 54 56 60) if the MAX/MIN temperatures are expected to vary across the area. In area forecasts, the middle number within the range is the representative single digit value for that area. MAX/MIN is forecast out through Day 7.
A snapshot of the expected temperature in degrees F valid at the indicated hour. The temperature is right justified in the column below the hour to which it refers. TEMP is forecast at 3-hour intervals through 60 hours, then 6-hour intervals through Day 7.
A snapshot of the expected dew point temperature in degrees F for the same time periods as its corresponding temperature forecast. DEWPT is located directly below the temperature line.
The relative humidity (RH) is a snapshot of the expected RH for the same time periods as its corresponding temperature and dew point forecast. The RH row is located directly below the “DEWPT” row. RH is available at 3-hour increments through 60 hours.
| WIND DIR
A snapshot of the expected wind direction forecast to occur at the indicated hour, using the 8 points of a compass (i.e., N, NE, E, SE, S, SW, W, NW). If a calm wind is forecast, double zeros (00) will be listed in place of a wind direction. WIND DIR is located below the hour to which it refers. WIND DIR is available in 3-hour increments out to 60 hours.
In the 6HRLY block, PWIND DIR is the “predominant” wind direction for the zone(s) during the 12-hour period between 6:00 a.m. and 6:00 p.m., or 6:00 p.m. and 6:00 a.m. local time. PWIND DIR is valid beyond 60 hours through Day 7.
Wind Character Codes
| WIND GUST
A wind gust row will appear in the 3HRLY block whenever forecasted wind gusts exceed the sustained wind speed (WIND SPD) by at least 10 MPH. WIND GUST is a snapshot valid on the hour indicated at the top of the corresponding column. WIND GUST is a snapshot of gusts of wind occurring at the indicated hour and is valid in 3-hour increments through 60 hours.
Sky Cover Codes
|Code||Stands for:||Traditional Text Equivalent||Percent of Sky Covered with Clouds|
|FW||Few||Mostly Clear/Mostly Sunny||7%-31%|
|SC||Scattered||Partly Cloudy/Partly Sunny||32%-69%|
Probability of Precipitation (POP), is defined as the likelihood, expressed as a percent, of a measurable precipitation event (1/100th of an inch) at any given point within the forecast area(s) covered by the PFM. The “12HR” refers to the 12-hour valid time ending at 6:00 a.m. or 6:00 p.m. local time (0600 or 1800). The POP 12HR value is right justified in the column beneath the hour defining the ending time of the valid period.
MAX QPF (optional)
The value for MAX QPF value is the estimated maximum amount of precipitation, in inches occurring at any point within the zone(s) during the12-hour period ending at 6:00 a.m. or 6:00 p.m. local time. This amount is presented as either a single value or a range, and is based upon a 75% confidence level of the QPF forecaster(s). MAX QPF is right justified below the hour defining the ending time of the expected precipitation, and is available out to 60 hours.
PRECIPITATION TYPE AND CATEGORY
The PFM may list several types of precipitation. Precipitation types only appear in the PFM if they are forecast to occur at any point within the zones(s) during the seven day forecast. Precipitation type codes are listed in the far left column of the PFM. For each type of precipitation that is forecast, an associated POP category is specified within the body of the product. The POP expression for the indicated precipitation type is valid at the hour specified by the column header. Precipitation type expressions are forecast at three hour time intervals out to 60 hours, then 12-hour time intervals beyond 60 hours through Day 7.
Probability of Precipitation Codes
If an obstruction to visibility (OBVIS) is forecast for the zone, a row labeled OBVIS will be listed underneath any forecast of precipitation. If no precipitation is forecast, then OBVIS will be listed under the row labeled AVG CLOUDS. In the Figure 19 example, “K” implies that smoke is restricting visibility during the 6-hour period from 3:00 a.m. - 9:00 a.m. EST on Monday 2/12/01. OBVIS is forecast at 3-hour intervals through 60 hours.
|PF+||Patchy Dense Fog|