INTRODUCTION
The National Weather Service Forecast New Orleans/Baton Rouge Area Office is now providing detailed forecasts in a matrix format known as "Point Forecast Matrix" or PFM. The detailed digital forecasts are routinely issued around 430 am and 430 pm local time, with updates issued as needed. The PFM is issued under the NEWPFMLIX header This guide will explain how to read and interpret the new product. This product will be replacing the Area Forecast Matrix or AFM which was issued under the NEWAFMLIX header after 430 AM Friday, December 19, 2003.
The Point Forecast Matrix presents nearly the same information in an identical format as the Area Forecast Matrix.
WHAT IS THE POINT FORECAST MATRIX?
The Point Forecast Matrix displays forecast weather parameters in 3-hour, 6-hour and 12-hour intervals. These intervals, combined with a matrix format, create a detailed forecast of various weather parameters. In the Point Forecast Matrix you will find 3-hourly and 12-hourly forecasts for up to 48 hours into the future. 6-hourly and 12-hourly forecasts are provided between 3 and 7 days into the future. The product is available via all NWS routine distribution channels, and is available on our website at http://www.srh.noaa.gov/lix by selecting the Digital Forecasts link.
HOW TO READ AND INTERPRET THE DETAILED POINT FORECAST MATRIX PRODUCT
An example of the Detailed Point Forecast Matrix product is displayed below. There are several forecast parameters which appear. Some of these values are displayed in 12-hour intervals while others are displayed in 6-hour or 3-hour intervals. At the top is the local time and date that the forecast was issued. In the case illustrated, the forecast was issued on Monday, May 12th, and the time of issuance was 1:05 p.m. Central Daylight Time (CDT). The matrix format is below the time and date, and a forecast timeline is established in 3 hour increments for 48 hours (2 days) into the future. Listed on the far left of this timeline is the local time zone. In this example, CDT is listed, which means the hours in the timeline are in Central Standard Time. Another timeline in "UTC" or Universal Coordinated Time (sometimes called "Z" time or "Zulu", or "GMT" - Greenwich Mean Time) is provided for reference. Whether using UTC or CDT, the hours of the day use the 24-hour clock system, where "00" is "midnight" and "18" is 600 pm. The time lines are organized under a line called "DATE" which lays out the day of the week and the calendar date.
Note that the Point Forecast Matrix product is organized into two blocks of data. The upper matrix includes forecast parameters for the first 48 hours out into the future, while the lower matrix includes data for days 3 through 7 into the future. The lower matrix can be identified by locating a second set of "timelines". The lower matrix is the "extended forecast".
000FOUS54 KLIX 290950PFMLIX POINT FORECAST MATRICESNATIONAL WEATHER SERVICE NEW ORLEANS LA350 AM CST FRI FEB 29 2008 MSZ070-292215-MCCOMB-PIKE MS 31.18N 90.46W350 AM CST FRI FEB 29 2008 DATE FRI 02/29/08 SAT 03/01/08 SUN 03/02/08UTC 3HRLY 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00CST 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 71 52 72 52 75TEMP 45 44 55 65 67 58 53 52 52 52 58 66 69 61 58 56 53 52 60 69 72 64DEWPT 45 44 49 53 53 51 52 50 50 49 53 50 51 51 52 52 51 52 54 56 55 56RH 100100 80 65 61 77 96 93 93 89 83 56 53 70 80 86 93100 81 63 55 75WIND DIR SE SE S S SE SE S S NW NE E SE E E SE SE E E SE SE SEWIND SPD 6 11 14 11 5 3 2 2 2 3 4 4 3 4 4 4 4 6 13 14 14CLOUDS B1 B1 B2 B2 B2 B2 B2 B2 SC SC SC SC SC SC B1 B1 B1 B1 B1 B1 B1POP 12HR 30 20 10 10 20QPF 12HR 0.02 0.01 0 0.01 0.02SNOW 12HR 00-00 00-00 00-00 RAIN SHWRS C C S S S S S S S S CTSTMS S S S S C DATE MON 03/03/08 TUE 03/04/08 WED 03/05/08 THU 03/06/08UTC 6HRLY 06 12 18 00 06 12 18 00 06 12 18 00 06 12 18 00CST 6HRLY 00 06 12 18 00 06 12 18 00 06 12 18 00 06 12 18 MIN/MAX 58 71 44 51 40 67 50 65TEMP 61 58 71 57 47 44 49 46 43 40 60 62 55 50 60 57DEWPT 57 58 66 57 47 34 33 35 32 31 47 49 48 47 52 49PWIND DIR SE S NW W SW S S NWWIND CHAR GN BZ BZ GN LT GN GN GNAVG CLOUDS B1 B2 OV OV OV B2 SC SC FW FW FW FW SC SC B2 B2POP 12HR 30 70 60 10 10 10 10 20RAIN SHWRS C C L L L C S STSTMS C C L L L C
FORECAST PARAMETERS
Taken line by line ... the upper matrix ...
1) MN/MX - The forecast maximum or minimum temperature. MN/MX is located near the ending time of each 12 hour period for which it is forecast out to 48 hours. The maximum temperatures are forecast from 6:00 a.m. to 6:00 p.m. Local Time. Minimum temperatures are forecasted from 6:00 p.m. to 6:00 a.m. Local Time, but on occasion the low temperature for the night may occur after 6:00 a.m.
2) TEMP - The expected temperature at a specified time, in degrees Farenheit. The temperature is forecast in 3 hour intervals.
3) DEWPT - The expected dewpoint temperature at a specified time, in degrees Farenheit. The dewpoint temperature is forecast in 3 hour intervals.
4) RH - The relative humidity based on the expected temperature and dewpoint.
5) WIND DIR - The expected direction from which wind should blow at 3 hour intervals. The 8 point compass is used (e.g., W, NW, N. . . etc.) Dashes (- -) represent no wind direction forecast due to a calm wind.
6) WIND SPD - The expected average wind speed in miles per hour, during each three hour time period.
7) CLOUDS - The expected cloud cover during each 3-hour time period. The contractions used and their meanings are as follows:
CL = CLEAR SKIES (0-6% CLOUD COVER)
FW = MOSTLY CLEAR SKIES (7-31% CLOUD COVER)
SC = PARTLY CLOUDY SKIES (32-69% CLOUD COVER)
BK = MOSTLY CLOUDY SKIES (70-94% CLOUD COVER)
OV = CLOUDY SKIES (95-100% CLOUD COVER)
8) POP 12HR - The probability of precipitation is for a 12-hour "daytime" period, or a 12-hour "nighttime" period. This percentage probability is listed toward the ending time of each period for which it applies. In the example, there is a 20% probability of precipitation during the day Sunday. There is an 80% probability of precipitation overnight Sunday night.
9) QPF 12HR - The amount of rainfall expected in each 12-hour period ("daytime"/"nighttime"). The values given are in inches, and may be in ranges. For example: ".01-.10" means between a hundredth and a tenth of an inch during the 12-hour period.
10) SNOW 12HR - The amount of snowfall expected in each 12-hour period ("daytime"/"nighttime"). The values given are in inches.
Additional lines, such as "RAIN", "WIND CHILL", and "MIN CHILL" in the example above, are included in the upper matrix if any of the following are in the forecast for that 48-hour period:
WIND CHILL = "How it feels" based on temperature and wind each 3 hours
MIN CHILL = Lowest wind chill over last 6 hour period
HEAT INDEX = "How it feels" based on temperature and relative humidity each 3 hours
MAX HEAT = Highest heat index over last 6 hour period
RAIN = Precipitation type for each 3 hour period is RAIN
RAIN SHWRS = Precipitation type for each 3 hour period is RAIN SHOWERS
SPRINKLES = Precipitation type for each 3 hour period is SPRINKLES
TSTMS = Precipitation type for each 3 hour period is THUNDERSTORMS
DRIZZLE = Precipitation type for each 3 hour period is DRIZZLE
SNOW = Precipitation type for each 3 hour period is SNOW
SNOW SHWRS = Precipitation type for each 3 hour period is SNOW SHOWERS
FLURRIES = Precipitation type for each 3 hour period is SNOW FLURRIES
SLEET = Precipitation type for each 3 hour period is ICE PELLETS
FRZNG RAIN = Precipitation type for each 3 hour period is FREEZING RAIN
FRZNG DRZL = Precipitation type for each 3 hour period is FREEZING DRIZZLE
EACH PRECIPITATION PARAMETER IS CLASSIFIED AS FOLLOWS...
IS = ISOLATED (10-20% COVERAGE)
S = SLIGHT (10-20% PROBABILITY)
SC = SCATTERED (30-50% COVERAGE)
C = CHANCE (30-50% PROBABILITY)
NM = NUMEROUS (60-70% COVERAGE)
L = LIKELY (60-70% PROBABILITY)
O = OCCASIONAL (80-100% PROBABILITY)
D = DEFINITE (80-100% PROBABILITY)
OBSTRUCTIONS TO VISIBILITY ARE CLASSIFIED AS FOLLOWS...
F = FOG
PF = PATCHY FOG
F+ = DENSE FOG
PF+ = PATCHY DENSE FOG
Taken line by line ... the lower matrix or "Extended" Forecast ... (after the time lines)
1) MN/MX - The forecast maximum or minimum temperature. MN/MX is located near the ending time of each 12 hour period for which it is forecast. The maximum temperatures are forecast from 6:00 a.m. to 6:00 p.m. Local Time. Minimum temperatures are forecasted from 6:00 p.m. to 6:00 a.m. LocalTime, but on occasion the low temperature for the night may occur after 6:00 a.m.
2) TEMP - The expected temperature at the specified time, in degrees Farenheit. The temperature is forecast in 6 hour intervals.
3) DEWPT - The expected dewpoint temperature at the specified time, in degrees Farenheit. The dewpoint temperature is forecast in 6 hour intervals.
4) PWIND DIR - Primary wind direction for each 12 hour period
5) WIND CHAR - Wind characteristic for each 12 hour period, where
LT = LIGHT (< 8 MPH)
GN = GENTLE (8-14 MPH)
BZ = BREEZY (15-22 MPH)
WY = WINDY (23-30 MPH)
VW = VERY WINDY (31-39 MPH)
SD = STRONG (>40 MPH)
HF = HURRICANE (>=74 MPH)
6) AVG CLOUDS - Average cloud cover for each 12 hour period, where
CL = CLEAR SKIES (0-6% CLOUD COVER)
FW = MOSTLY CLEAR SKIES (7-31% CLOUD COVER)
SC = PARTLY CLOUDY SKIES (32-69% CLOUD COVER)
BK = MOSTLY CLOUDY SKIES (70-94% CLOUD COVER)
OV = CLOUDY SKIES (95-100% CLOUD COVER)
7) POP 12HR - The probability of precipitation is for a 12-hour "daytime" period, or a 12-hour "nighttime" period. This percentage probability is listed toward the ending time of each period for which it applies.
Additional lines, such as "RAIN", in the example above, are included in the lower matrix if any of the following are in the forecast in the extended period:
WIND CHILL = "How it feels" based on temperature and wind each 3 hours
MIN CHILL = Lowest wind chill over last 6 hour period
HEAT INDEX = "How it feels" based on temperature and relative humidity each 3 hours
MAX HEAT = Highest heat index over last 6 hour period
RAIN = Precipitation type for each 6 hour period is RAIN
RAIN SHWRS = Precipitation type for each 6 hour period is RAIN SHOWERS
SPRINKLES = Precipitation type for each 6 hour period is SPRINKLES
TSTMS = Precipitation type for each 6 hour period is THUNDERSTORMS
DRIZZLE = Precipitation type for each 6 hour period is DRIZZLE
SNOW = Precipitation type for each 6 hour period is SNOW
SNOW SHWRS = Precipitation type for each 6 hour period is SNOW SHOWERS
FLURRIES = Precipitation type for each 6 hour period is SNOW FLURRIES
SLEET = Precipitation type for each 6 hour period is ICE PELLETS
FRZNG RAIN = Precipitation type for each 6 hour period is FREEZING RAIN
FRZNG DRZL = Precipitation type for each 6 hour period is FREEZING DRIZZLE
EACH PRECIPITATION PARAMETER IS CLASSIFIED AS FOLLOWS...
IS = ISOLATED (10-20% COVERAGE)
S = SLIGHT (10-20% PROBABILITY)
SC = SCATTERED (30-50% COVERAGE)
C = CHANCE (30-50% PROBABILITY)
NM = NUMEROUS (60-70% COVERAGE)
L = LIKELY (60-70% PROBABILITY)
O = OCCASIONAL (80-100% PROBABILITY)
D = DEFINITE (80-100% PROBABILITY)
OBSTRUCTIONS TO VISIBILITY ARE CLASSIFIED AS FOLLOWS...
F = FOG
PF = PATCHY FOG
F+ = DENSE FOG
PF+ = PATCHY DENSE FOG