Fire Weather Products and Services – Wiki Page


In support of the NWS mission to issue weather forecasts and warnings for the protection of life and property, the NWS tailors fire weather forecasts and services to provide support for federal, state, and local agencies that are responsible for fire control and land management.  Forecasts and tools are described below to help customers decide which products and services best suit their planning needs.  Additional details of the NWS fire weather program may be found in the NWS Directives System.    

The Fire Weather Planning Forecast (defined below) covers basic fire weather forecast information and can be useful for those needing a text printout.  The main fire weather page also links to additional resources that can be utilized for specific needs, including the Weather Activity Planner, Spot Forecast Request Page (and Spot Forecast Info page), Fire Weather Point Forecast Matrices, the Fire Weather Planning Forecast for neighboring NWS forecast offices, and the Texas Fire Weather Operating Plan (identifies, contacts, services and local Red Flag Criteria for NWS offices that serve Texas) .   Toward the bottom of this page, a small glossary is provided to explain some of the basic parameters and terminology used in the fire weather program.

Fire Weather Planning Forecasts (product identifier list SATFWFEWX, MND header FNUS54 KEWX)

The Fire Weather Planning Forecast, or FWF, is issued daily to provide weather forecasts tailored to support any fire related operations in South Central Texas. The FWF is issued at least twice daily, with morning and afternoon issuances at around 7:00 a.m. and 3:30 pm respectively. Updates to the FWF may be updated more frequently than twice a day, especially during active fire seasons and other periods of rapidly changing weather conditions.

Primary components:

Headlines. Headlines will always first indicate if Red Flag Warnings and/or Fire Weather Watches (defined below) are in effect.  Other headline statements indicate significant weather patterns that could promote the spread of fires and any other major weather changes that would impact the planning of fire control operations.  These significant fire weather conditions are often described as elevated, near critical, critical, or extreme, based on the severity of the wind and relative humidity values expected.  These fire weather condition classifications are identified in more detail in the glossary section of this page below.

Discussion. The discussion should be a brief, clear, non-technical description of weather patterns that influence the weather in the forecast area.

2-Day Tabular Forecasts.  The FWF product has a minimum of three 12-hour time periods in the morning forecast, and four 12-hour time periods in the afternoon forecast.  Each time period includes the following weather elements:

CLOUD COVER - expressed in terms similar to those used in the zone forecast product.
PRECIP TYPE - expressed in terms similar to those used in the zone forecast product.
CHANCE PRECIP (%) - rounded to the nearest 10 percent and should be the same as Probability of Precipitation (PoP) used in the zone foreast product.
TEMP - expressed in terms similar to those used in the zone forecast product.  Based on Automated Surface Observing System (ASOS) measurement standards.
RH (%) - relative humidity is expressed in terms of maximums and minimums for the day.
20FTWIND/AM (MPH) - morning forecast portion of the daytime winds. Derived from (ASOS) measurement standards used in conventional forecasting operations to simulate RAWS reporting standards. The winds will be indicated as 20-foot level, which is estimated by multiplying the 33-foot wind forecast (derived from model data) by a factor of 0.8.  Use the 8-point compass for the wind direction.
20FTWIND/PM (MPH) - either the afternoon portion of the daytime winds or both the evening and early morning portions of the nighttime winds.
LAL - lightning activity level. See glossary for details.
CWR - chance of wetting rain.  Similar to Probability of Precipitation (PoP), but a wetting rain is defined as 0.10 for South Central Texas.
HAINES - defined as Low Level Haines Index for South Central Texas. See glossary for details.
MIXING HGT (FT-AGL) - the forecast maximum mixing height for an afternoon in South Central Texas. Nighttime minimums are not included in the forecast.
TRANSPORT WINDS (MPH) - The average direction and speed of the wind during the time of maximum afternoon mixing.  Nighttime transport winds for minimum mixing are not included in the forecast.

Extended Forecast.  In this section, a forecast period is broken down into 24-hour blocks of time beginning at 12 midnight and ending at 12 midnight the next day. Weather elements in the outlook period will include Sky/Weather, Temperature, and 33-foot winds. 

Extended portions of these fire weather forecasts show a slight resemblance to local or zone forecast products.  Due to automated formatting procedures, there may be slight discrepancies between the zone forecast and the fire weather forecast.  However, the experimental graphical wind and humidity forecasts provided on the Austin/San Antonio NWS homepage should represent both forecasts.


Other Fire Weather Forecast Output Available on the Austin/San Antonio NWS Web Pages

Fire Weather Point Forecast Matrices (product identifier list SATPFWEWX, MND Header FOUS54 KEWX)

The Fire Weather Point Forecast Matrices product is an experimental tabular forecast data output product generated automatically from the digital forecast database.  The output, which uses selected locations of Remote Automated Weather Stations (RAWS), is intended for general planning purposes only.  The product format is designed to replicate the numerical model output style of the Model Output Statistics (MOS), which provides forecast values every 3 to 6 hours for up to 7 days.  Forecast parameters used include, temperature, dew point, relative humidity, heat index, cloud coverage, Probability of Precipitation (PoP), quantitative precipitation forecast (QPF), lightning activity level (LAL), Haines Index, mixing height, and transport winds.

 

 

Weather Activity Planner

This data output tool allows the user to extract specific data from the digital forecast database.  Additional details are provided on the Weather Activity Planner page.

 

Graphical Forecasts

Fire weather related data is available in graphical format as a part of the National Digital Forecast Database.  The user needs to be zoomed into the Weather Forecast Office in order to see the maximum available fire weather forecast parameters available.  Additional information on the National Gridded Forecast Database is located at http://www.weather.gov/ndfd/.

 


Glossary

ASOS:  The Automated Surface Observing System is the predominant weather observing unit used for verification of NWS forecasts.

Critical Fire Weather Conditions:  These weather conditions indicate the presence of winds and relative humidity values that will likely promote the aggressive spread of fires over dry vegetation fuels.  Typically, a Red Flag Warning or Fire Weather Watch is issued for critical fire weather conditions, dependent on how far into the future the weather event is forecast.

Elevated Fire Weather Conditions:  These weather conditions indicate the presence of winds and relative humidity values that are capable of promoting the aggressive spread of fires over dry vegetation fuels, but with a low potential for the fire weather conditions to escalate to critical levels.

Extreme Fire Weather Conditions:  These weather conditions indicate the presence of winds and relative humidity values that will promote the aggressive spread of fires over dry vegetation fuels on a scale that is only experienced a few times per decade.  Red Flag Warnings and Fire Weather Watches are always issued for extreme fire weather conditions, dependent only on how far into the future the weather event is forecast.

Fire Weather Watch:  Fire weather watches are issued to alert fire and land management agencies to the possibility of red flag conditions beyond the first forecast period (12 hours). The watch is issued generally 18 to 96 hours in advance of the expected conditions if the forecaster is reasonably confident.  Once the timing of the forecast event falls to within one day of the current time, the Fire Weather Watch is expected to be upgraded into a Red Flag Warning.

Haines Index (HI):  An atmospheric index used to indicate the potential for wildfire growth by measuring the stability and dryness of the air.

The HI numbers are computed for 3 different elevations using the following parameters:
HI = STABILITY TERM (A) + MOISTURE TERM (B)

The Austin/San Antonio NWS Office uses low elevations to compute the moisture and stability terms for HI where:
A = 950-850 MB TEMP
B = 850 MB TEMP-DEW POINT

Moisture and stability terms are categorized as follows:

A=1 when 3 deg C or less

B=1 when 5 deg C or less

A=2 when 4-7 deg C

B=2 when 6-9 deg C

A=3 when 8 deg C or more

B=3 when 10 deg C or more

Haines Index classifications are assigned to values 2 through 6 as shown below:

 Haines Index

Potential for Large Fire Growth

2 or 3 

Very Low

Low

Moderate

High

Lightning Activity Level (LAL):  A number, on a scale from 1 to 6, which reflects frequency and character of cloud-to-ground lightning.

LAL Guide for Fire Weather Observers:  Cloud-to-ground lightning discharges in individual storm cells (cg)

 

Cloud & Storm 
LAL Development 

Areal Coverage

Counts cg / 5 min

Counts cg / 15 min

Average cg / min

1

No thunderstorms

-

-

-

-

2

Cumulus clouds are common but only a few reach the towering stage.  A single thunderstorm must be confirmed in the rating area.  The clouds mostly produce virga but light rain will occasionally reach ground.  Lightning is very infrequent.

<15% 

1-5 

1-8 

<1

3

Cumulus clouds are common.  Swelling and towering cumulus cover less than 2/10 of the sky.  Thunderstorms are few, but 2 to 3 occur within the observation area.  Light to moderate rain will reach the ground, and lightning is infrequent.

15% to 24% 

6-10 

9-15

1-2

4

Swelling cumulus and towering cumulus cover 2-3/10 of the sky.  Thunderstorms are scattered but more than three must occur within the observation area.  Moderate rain is commonly produced, and lightning is frequent.

25% to 50%

11-15 

16-25 

2-3

5

Towering cumulus and thunderstorms are numerous.  They cover more than 3/10 and occasionally obscure the sky.  Rain is moderate to heavy, and lightning is frequent and intense.

>50%

>15

>25

>3

6

Dry lightning outbreak.  (LAL of 3 or greater with majority of storms producing little or no rainfall.)

-

-

-

-

Mixing Height:  Mixing height is defined as the height above the surface through which relatively vigorous mixing will take place due to convection.  The mixing height is generally found at the base of a temperature inversion.  Units used by the Austin/San Antonio NWS Office are above ground level (agl).

Near Critical Fire Weather Conditions:  These weather conditions indicate the presence of winds and relative humidity values that are capable of promoting the aggressive spread of fires over dry vegetation fuels, with a moderate potential for the fire weather conditions to escalate to critical levels.

Probability of Precipitation (PoP):  The 12-hour probability of measurable precipitation (0.01 or greater) at any given location within an area defined by a forecaster.

RAWS: Remote Automated Weather Stations are owned and operated by wildland fire agencies.  More information on the RAWS network is provided at http://raws.fam.nwcg.gov/.

Red Flag Criteria:  Red Flag Criteria are based on winds and relative humidity values reaching certain thresholds based on an assumption of pre-existing dry vegetation fuels and areal climatology as analyzed by fire behavior specialists.  Details on specific criteria for a given area can be found in the Texas Fire Weather Operating Plan.

Red Flag Warning:  A Red Flag Warning is used to alert fire and land management agencies that critical (or extreme) fire weather conditions exist or are imminent in the next 24-48 hours. In many cases, a Fire Weather Watch is issued for forecast periods beyond 1 day and is upgraded into a Red Flag Warning once the critical fire weather conditions are considered imminent.

Transport Winds:  The mean wind speed and direction of the layer between the surface and mixing height.  The Austin/San Antonio NWS Office uses the unit of miles per hour (mph) for speed and a 16 point compass to describe wind direction.  However, graphical viewing of this data is provided in knots (mph multiplied by 1.15).

Wetting Rain:  The amount of rainfall considered sufficient to effectively moisten vegetation fuel beds, defined as 0.10 inches for South Central Texas.  Wetting rain chances are for 12-hour periods, similar to the PoP.
 


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