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Decoding the Point Forecast Matrices

WMO : FOUS51 KAKQ
AWIPS: WBCFMAKQ

Latest Tabular PFM

INTRODUCTION

An increasing number of National Weather Service offices are now providing detailed digital forecast data products known as the Point Forecast Matrices (PFM) and the Area Forecast Matrices (AFM). This document will explain how to read and interpret the PFM. An example of a complete PFM is also included.

WHAT IS THE POINT FORECAST MATRICES?

The Point Forecast Matrices (PFM) displays various forecasted weather parameters at a specific point or geographic location in 3-hour and 6-hour intervals. These intervals combined with a matrix format create a detailed forecast, allowing quick procurement of forecast parameters. The PFM is available to disseminators of National Weather Service products,
and is available on the internet.

Currently, the PFM provides 3-hourly and 12-hourly forecasts up to 60 hours into the future. An extended portion of the PFM provides 6-hourly and 12-hourly forecasts 7 days into the future.

HOW TO READ AND INTERPRET THE PFM PRODUCT

An example of the PFM product is displayed below in Table 1. There are several forecast parameters which appear in the PFM. At the top of each product is the time and date that the PFM was issued. In the case of Table 1, the forecast was issued on February 1, and the issuance time was 9:01 a.m. Easternl Standard Time (EST). Below the time and date, two forecast time lines are provided in 3 hour increments for 60 hours (2 and one half days) into the future. Listed on the far left of the first time line is UTC (the abbreviation for Universal Coordinated Time). Below that line and more familiar to most users, the local time zone that the PFM is created in is displayed. In this example, EST is listed, which means the hours in the time line are in Eastern Standard Time. Note that in the bottom segment of the PFM, there are similar time lines displayed. This forecast time line is broken down into 6 hour increments, providing an extended forecast 3 to 7 days into the future. Reference dates are located above each time line.

901 AM EST THU FEB 1 2007

MDZ022-012115-
SALISBURY/OCEAN CITY WICOMICO REGIONAL AIRPORT-WICOMICO MD
38.35N  75.50W
901 AM EST THU FEB 1 2007

DATE             THU 02/01/07            FRI 02/02/07            SAT 02/03/07
UTC 3HRLY     08 11 14 17 20 23 02 05 08 11 14 17 20 23 02 05 08 11 14 17 20 23
EST 3HRLY     03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18
MAX/MIN                      37          32          44          30          43
TEMP                   35 36 35 34 33 33 33 36 41 41 39 36 34 33 31 35 40 39 36
DEWPT                  26 28 31 31 31 31 32 33 34 33 31 29 28 26 23 22 20 19 19
RH                     69 72 85 89 92 92 96 89 76 73 73 75 78 75 72 59 44 44 50
WIND DIR                S SE  E  E NE NE  N  N NW NW  W  W NW NW  W  W  W  W  W
WIND SPD                8  5  3  6 10 11 10 12 14 12  8  5  6  6  8 11 14 12  6
CLOUDS                 OV OV OV OV OV OV OV B2 B2 B1 B1 SC SC SC SC SC SC SC SC
POP 12HR                     70         100          90          10          10
QPF 12HR                   0.09        0.28        0.13           0           0
SNOW 12HR                 00-00           1       00-00                        
DRIZZLE                                      C  C                              
FRZG RAIN                           L  D  D                                    
RAIN                    C  C  L  L  L        C  C                              
SLEET                   C              D  D                                    
SNOW                    L  C  L                                                
WIND CHILL             28       28 25 24 25 28 33 34 33    28 27 24 27 32 31 30
MIN CHILL              26    29    24    23    25    32    28    24    24    29
WINTER WEATH                  Y  Y  Y  Y  Y      
Table 1. Sample PFM Product Output

PFM FORECAST PARAMETERS
Below are forecast parameters in the PFM.

1) MAX/MIN - A forecast of maximum or minimum temperatures during the daytime or nighttime hours, respectively. The maximum temperatures are forecast from 6:00 a.m. to 6:00 p.m. Local Time. Minimum temperatures are forecast from 6:00 p.m. to 6:00 a.m. Local Time. The overnight lows and daytime highs are displayed as a single number for the specific point or geographic location.

MAX/MIN is forecast out to 7 days. MAX/MIN is located near the ending time of each 12 hour period forecasted out to day 7.

2) TEMP - The temperature is forecast in 3 hour intervals. It is an average temperature within the specific geographic location for the time in question. The TEMP is generally forecasted 48 hours into the future.

3) DEWPT - The expected dewpoint temperature forecast for the same time period as its corresponding forecast temperature, forecast out to 48 hours.

4) RH - The relative humidity is based on the expected temperature and dewpoint. The RH is forecast for the same time as its corresponding temperature, and is forecast out to 48 hours.

5) WIND DIR - The expected wind direction forecast for the corresponding time using the 8 points of a compass (e.g., W, NW, N. . . etc.). WIND DIR is available out to 48 hours into the future.

6) WIND SPD - The expected average wind speed in miles per hour for the time in question.

7) CLOUDS - The expected cloud cover forecast for every 3-hour time period out to 60 hours. Cloud cover is then forecast in 6 hour time periods out to day 7. The contractions used and their meanings are as follows:

CL - Clear FW - Mostly Clear
SC - Partly Cloudy
BK - Mostly Cloudy OV - Cloudy

8) POP 12HR- This parameter is forecast for all 7 days of the PFM. The probability of precipitation is for a 12-hour period ending at 6:00 a.m. or 6:00 p.m. Local Time. This percentage probability is listed towards the ending time of each period out to day 7.


9)QPF 12HR- This parameter is forecast out to 60 hours in the PFM. A quantitative precipitation forecast, QPF 12HR lists the average precipitation expected if precipitation falls. QPF 12HR is listed under POP 12HR, and is forecast in 12 hour periods ending at 6:00 a.m. or 6:00 p.m. Local Time. QPF 12HR is located towards the ending time of each 12 hour period, and amounts are given in a range.

10) SNOW 12HR- Seasonal element. The expected range of snowfall accumulation (in whole inches) during a 12-hour period ending at 6:00 a.m. or 6:00 p.m. Local Time. SNOW 12HR is available out to 36 hours, located near the ending time of each 12 hour period for which it is forecast.

11) PRECIPITATION- The PFM may list several types of precipitation. Precipitation types are only shown in the PFM if they are forecast to occur at any point in the 7 day forecast, and are listed in the far left column of the RDF underneath CLOUDS.

For each type of precipitation that is forecast, a probability of precipitation is specified for 3-hour time periods out to 60 hours, then in 6 hour increments ending at 6 a.m. or 6 p.m. Local Time out to 7 days. The types of precipitation that may be forecast in the PFM are listed below.

RAIN- Rain

RAIN SHWRS- Rain showers

TSTMS- Thunderstorms

DRIZZLE- Drizzle

SNOW- Snow

SNOW SHWRS- Snow showers

FLURRIES- Flurries

SLEET- Sleet (ice pellets)

FRZNG RAIN- Freezing rain

FRZNG DRZL- Freezing drizzle

The probability contractions and their meanings are as follows:

S - Slight Chance (< 20%)

C - Chance (30%-50%)

L - Likely (60%-70%)

O - Occasional (80%-100%)

D - Definite (80%-100%)

12) OBVIS- An obstruction to visibility. If this is forecast at any point out to 48 hours, a row titled OBVIS will be listed underneath any forecast precipitation. If no precipitation is forecast, then OBVIS will be listed under the row titled QPF 12HR. OBVIS is forecasted in 3 hour intervals. The contractions used and their meanings are as follows:

F - Fog PF - Patchy Fog F+ - Dense Fog PF+ - Patchy Dense Fog

H - Haze BS - Blowing Snow K - Smoke BD - Blowing Dust


13) WIND CHILL and HEAT INDEX

When the Wind Chill Index is forecast to be 20 degrees F or lower with a 5 mph or greater wind speed, a row titled WIND CHILL will be listed under any forecast precipitation types, OBVIS or QPF 12HR. The Wind Chill Index is forecast out to 48 hours.

When the heat index is forecast to be 100 degrees F or higher, a row titled HEAT INDEX will be listed under any forecast precipitation types. Like Wind Chill, the Heat Index is forecast up to 48 hours into the future.



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