Frequently Asked Questions

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What is Heat Load?

If heat into the system is greater than heat out of the system then heat will be stored. This is called a heat load.


All animals have a need to maintain core body temperature within a small range, so that body cells and tissues can function optimally.

For humans the range is 36.5 to 37.5°C, for cattle it’s in the range of 37.9 to 40.2oC depending on the cattle breed/genotype.


Cattle Heat Energy Balance

For feedlot cattle the major source of heat into the system is from the conversion of food into energy (Internal Metabolic Heat). This source of heat is generated in the core of the body and therefore any excess energy needs to be dissipated to the surrounding environment. Problems can occur when the environment’s ability to cool the animal is not enough to keep up with the internal heat generation. In this situation an animal will start to store heat.

How are the Heat Load Alerts defined?

The ALERT issued for your AHLU alert level is defines as follows:

  • AHLU event today: AHLU >50 units for today
  • AHLU event tomorrow: AHLU >50 for tomorrow and AHLU = 0 for less than 6 hours
  • Extended AHLU event: AHLU >50 units for more than 3 consecutive days
  • Incomplete nighttime recovery: AHLU = 0 for less than 6 hours for more than 3 consecutive days in 7 day forecast period
  • Rapid HLI change*: change in HLI >40 units over 4 hours. (Please Note: This alert is likely to change when more research becomes available)

  • How is my cattle’s heat risk calculated?

    The overall risk of a heat event occurring at your site is calculated using a combination of three factors; animal, environment and weather. The interaction and change of these three factors (some on an hourly basis) is crucial to an accurate heat event forecast.


    To quantify your cattle’s heat load risk you need to find out which HLI threshold applies to your feedlot site’s location and each type of cattle. Use the HLI Threshold calculator (found in the sidebar on your Site Summary and Toolbox page) to enter all the animal and environment factors for your cattle. 

    How do I use the HLI Threshold Calculator?


    HLI Threshold Calculator with sample data

    Select the characteristics and conditions of your highest risk cattle via the dropdowns. Once complete the HLI Threshold Calculator will generate the HLI Threshold for your operation, which provides you with the reference point for interpreting AHLU forecasts relevant to your site.

    For example, the AHLU80 forecast refers to the AHLU where the HLI threshold = 80.

    CHLT forecasts are provided for AHLU80, AHLU83, AHLU86, AHLU89, AHLU92 and AHLU95.

    Where your HLI threshold falls between two AHLU reference points, you need to either estimate the AHLU, or, for a conservative approach, refer to the AHLU for the HLI threshold that is closest to, but less than, the calculated HLI threshold.



    How do I reduce my site’s risk of a heat event?

    There are many things you can do to reduce your risk of a heat event occurring.

    Understanding your risk from the Risk Analysis Program (RAP) is a good start. The RAP provides a method to determine what measures need to be in place for your site. For example, if the RAP indicates a risk of more than 2 extreme events per year you may decide to reduce your risk by installing shade or alternatively not run high risk cattle genotypes at your feedlot during the summer months. You can find the Risk Analysis Program (RAP) in the  Toolbox or by clicking here.

    Preparing a Heat Management Plan and training your staff to identify the early signs of cattle experiencing heat stress can also reduce your risk of an event occurring. Download the Cattle Panting Score reference guide and Cattle Observations Log from the Toolbox.

    Monitoring the weather via your weather station and/or your forecast on your Site Summary page, and using the Daily Monitoring tool (coming soon) to keep track of conditions during the summer will also reduce your risk.

    All these tools and more are available to CHLT account holders on the Toolbox page:

    Where does the weather forecast come from?

    The Katestone Numerical Weather System (K-NWS) is an advanced weather forecasting system that is initialised daily from the Global Forecasting System (GFS). K-NWS models the complete atmosphere/land/ocean dynamics for a 12-km grid across Australia using the WRF-ARW dynamic core.

    This means you get a forecast for your location not some other location that may have different land uses characteristics or terrain features. The K-NWS uses high resolution terrain (90 m) and land use (900 m) data sets to derive the most accurate representations of Australian conditions. We then run our model out to 7 days, providing high resolution weather information for every hour.

    Analysis has shown our weather model to be highly accurate in forecasting the evolution of weather patterns that directly influence the development of high heat stress events. Continuous performance reviews of this forecasting system are made by Katestone’s scientists to ensure ongoing improvements to its performance and delivery of data into the future.


    What is the Heat Load Data Network?

    The Heat Load Data Network (HLDN) is an initiative of Katestone and the MLA which allows you to integrate your sites weather station data into your online forecast. By registering on this site and requesting to be part of the Heat Load Data Network here, you will receive all the assistance you need to get your weather station data uploaded and displayed as observations alongside your site specific forecast. The HLDN data is used to initialise the AHLU for your site. Initialisation time is the last time stamp in the supplied data. For example if your station uploads data to the HLDN at 4 am then the AHLU at 4 am will be used to initialise the predicted AHLU.



    I can’t login. What do I do?

    If you are having difficulty logging in, please double check you are using the correct user name and password.

    PLEASE NOTE: If you enter your user name and password incorrectly more than 5 times you will be locked out for 60 minutes.

    Otherwise you will get an error message like the ones below: 


    To regain access, please do the following:

    STEP 1: 
    Click ‘Lost Your Password’
    The next screen will ask for your username OR email address (see below). 


    STEP 2:
    1) Enter your email or username (whichever one you can recall).
    2) Enter the Captcha code.
    3) Click the ‘Get New Password’ button.

    Note: If you are unable to read the Captcha clearly, click the refresh button next to it to change it until you do.

    Once you enter the correct email or username, you will see the Confirmation Message (below);


    Confirmation Message

    STEP 3: Go to your email program and look for an email with the subject ‘[Cattle Heat Load Toolbox] Password Reset’ from
    The email will contain both your username and a link. Click the ‘reset your password’ link at the bottom of the email (or copy and paste the URL into a new browser window).  


    [Cattle Heat Load Toolbox] Password Reset email

    STEP 4: In the new browser window, set your new password to whatever you like. 
    Please do try to make it memorable AND strong. Enter it twice, then click RESET PASSWORD.


    You will be prompted to ‘Log in’. Enter your retrieved username (as per the reset password email) and your new password.
    If you still aren’t able to login after following all of the steps above, please contact your Site Supervisor to make sure you are registered for CHLT.

    If you are the Site Administrator and you still can’t login, please contact the CHLT Team via our contact form here.

    How can I add Town Forecast Locations to My Site Summary page?

    You can add any of the Town Forecast locations to your My Site Summary page by going to Account -> Manage Sites and selecting a location from the State drop down lists. You can also review the sites that you are associated with and remove yourself from those sites that you no longer wish to be associated with. Remember that any site you are associated with you can also set alerts for.

    HLI calc

    How do I change my details?

    You can change your username, email, phone number and password by going to Account -> My Account
    update the fields you wish to change and click the submit changes button

    set alert
    set alert
    set alert

    How do I set Heat Load Alerts?

    Alerts can be configured for any user who is associated with a site. Users can be associated with multiple sites and can set separate alerts for each site. To set your alert for a site go to Account -> Manage Alerts. The alerts are based on the AHLU and the HLI threshold that is representative of your site. Use the HLI Threshold Calculator to determine the risk threshold you want to manage your cattle to.

    HLI calc

    Then use the calculated HLI Threshold set your AHLU alert level, round it down to the closest AHLU alert level. Select the delivery method: Email, SMS or Both and click Submit.

    set alert
    Note: Consider changing your alert threshold throughout the summer to reflect cattle condition.

    What’s the difference between a site user and a site administrator?

    The first person to register their feedlot with CHLT is the default nominated Site Administrator. Site Administrators are able to view, add, update, and delete contact details and alert preferences of all users registered to their site on CHLT.

    Site Users are added to existing CHLT sites by their Site Administrator. Site users are able to view and update their contact details and alert preferences.

    How do I add users to my site?

    Step 1: Login and go to ‘Account’ > ‘Manage Users’

    Step 2:
    Click ‘Add User’

    Step 3: Fill in your new Site User’s details (Choose carefully as usernames cannot be changed)

    If you see an error message the system usually corrects it for you automatically, but do check the form details before Step 4.


    Step 4:
    Click the ‘Add New Site User’ button. If you have added a new site user correctly they will appear in the list (as below) on the site that you added them to.

    Additional Features:

    • To edit a user’s details, click on their username.
    • To send them an email message, click on their email.


    What are the correct equations for calculating HLIs and AHLUs?

    Heat Load Index Calculation

    Calculation of the Heat Load Index (HLI) requires Temperature (T) in °C, Relative Humidity (RH) expressed as a percentage, Wind Speed (WS) in m/s and Black Globe Temperature (BGT) in °C. Of these, T, RH and WS are routinely measured by the great majority of weather stations. Although sensors for measuring BGT exist, these are not normally included as part of the standard weather station and must be ordered from a suitable supplier. In the absence of a BGT sensor, the BGT can be inferred from measurements of T and Solar Radiation (SR).

    The equation for calculating BGT from T and SR is:

    BGT = 1.33 x T – 2.65 x sqrt(T) + 3.21 x log(SR + 1) + 3.5
    • log is the logarithm (base 10) function
    • sqrt is the square root function

    In the past, the HLI was calculated using one of two equations, depending on whether the BGT is above or below 25°C as follows:

    if ( BGT is below 25 ) then
    HLILO = 1.3 x BGT + 0.28 x RH – WS + 10.66
    HLIHI= 1.55 x BGT + 0.38 x RH – 0.5 x WS + exp (2.4 – WS) + 8.62
    • exp is the exponentiation function
    and the HLI value was taken as either HLIHI or HLILO depending on the BGT value.

    One issue that has been identified is that large jumps in HLI occur under some circumstances when the BGT passes through 25°C – for example from 24.9°C to 25.1°C. To overcome this, a blending function – S(BGT) – is used to produce a smooth transition in HLI values calculated using the two different equations. The blending function is:

    S(BGT) = 1 / (1 + exp(-(BGT – 25) / 2.25))

    Using this blending function, a value of the HLI is calculated as follows:

    HLI = S(BGT) * HLIHI + (1 – S(BGT)) * HLILO
    where HLIHI and HLILO are defined above.

    Finally, the HLI value is not allowed to decrease below 50. HLI values smaller than 50 are set to 50.

    if ( HLI < 50 ) HLI = 50

    download-pdf Download the HLI Calculator spreadsheet to try it out for yourself.

    Accumulated Heat Load Unit Calculation

    The Accumulated Heat Load Unit (AHLU) represents the amount of heat accumulated in cattle over a period of time. The rate of accumulation depends on the current HLI value. Large HLI values result in a more rapid increase in AHLU, conversely, low HLI values result in a decrease of the AHLU (ie the cattle cool down and recover). Whether cattle recover or become stressed depends on the value of certain thresholds. The first threshold occurs at a HLI value of 77. For HLI values below 77, the cattle cool down and recover. The second or UPPER_THRESHOLD depends on the type and condition of the cattle and their pen environment. Its value ranges from about 80 for unacclimatised (and possibly compromised) black angus cattle to about 95 for acclimatised Brahman cattle. The range of HLI values between 77 and the upper threshold is called the thermo-neutral zone. For this zone, cattle neither recover nor become stressed.

    It is important that the correct UPPER_THRESHOLD is used otherwise the AHLU values will erroneously indicate the state of the cattle.  The UPPER_THRESHOLD can be calculated using the Katestone on-line calculator at:

    The equation for calculating AHLU is as follows:


    For example, the AHLU at 2pm is calculated by adding an INCREMENT to the AHLU at 1pm. The INCREMENT is calculated as follows:

     If (HLI is between 77 and the upper threshold) then INCREMENT = ZERO

    If ( HLI < 77) then INCREMENT = INTERVAL * (HLI – 77) / 2


    INTERVAL is the time interval between successive HLI measurements. Its value is 1.0 for an interval of one hour, 0.5 for an interval of 30 minutes, 0.25 for an interval of 15 minutes and so on.

     Some points worth noting:

    • The INCREMENT can be positive or negative.
    • If HLI is below 77, then INCREMENT is halved (ie the rate of recovery or heat loss is half of the rate of heat accumulation.
    • AHLU values do not go below zero. If any calculation results in an AHLU value below zero, it is set to zero.

    The following table contains sample data that you can use to test your implementation of the HLI equations above:

    Relative Humidity = 33%
    Black Globe Temperature
    Wind Speed20o25o30o
    2 m/s 50.0 55.4 67.1
    4 m/s 50.0 53.3 64.8
    6 m/s 50.0 51.7 63.5
    Relative Humidity = 66%
     Black Globe Temperature
    Wind Speed20o25o30o
    2 m/s 54.3 66.3 79.3
    4 m/s 52.3 64.2 77.0
    6 m/s 50.4 62.6 75.8
    Relative Humidity = 99%
     Black Globe Temperature
    Wind Speed20o25o30o
    2 m/s 63.9 77.2 91.5
    4 m/s 61.9 75.0 89.2
    6 m/s 59.9 73.5 88.0

    The following table contains data that you can use to test your implementation of the AHLU equations:


    download-pdf Download this FAQ as a PDF

    What is the Heat Load Index (HLI) and how is it calculated?

    The Heat Load Index, referred to as the ‘HLI’, is an index that brings together all the weather factors into one number to allow easy interpretation of the cooling capacity of the environment. The Heat Load Index has been developed in Australia from over 10 years worth of research into assessing heat events in Australian feedlot conditions for Australian cattle.

    The basic weather information required to determine the capacity of the environment to cool a body consists of:

    • radiative temperature – a combination of temperature and radiation called Black Globe Temperature (BGT)
    • air movement (Wind Speed)
    • a measure of the moisture in the air (Relative Humidity)

    As you can see above, the HLI is calculated from measurements of BGT (°C), relative humidity (%) and wind speed (m/s) using a simple relationship. A tool is available on CHLT to calculate a HLI from the available input parameters.

    For the most part the HLI on its own does not indicate the likelihood of heat stress in feedlot cattle. This is done by calculation of the Accumulated Heat Load Unit (or AHLU). The only time when heat stress may be indicated by the HLI alone is when there is a rapid change in the HLI over a short period of time.


    What is an Accumulated Heat Load Unit (AHLU) and how is it calculated?

    The Accumulated Heat Load Unit (or AHLU) is a measure of the amount of heat that may be stored a body. An animal’s ‘heat energy balance’ is determined by the duration of exposure above the Heat Load Index (HLI) Threshold. Cattle may accumulate heat during the day (the body temperature rises) and dissipate this heat during the night. If there is insufficient night cooling, cattle may enter the following day with an accumulated heat load (AHL; Hahn and Mader, 1997).

    On CHLT, Accumulated Heat Load Units are calculated every hour, using the HLI for that hour, and the HLI Threshold.

    For every hour that the HLI is above the HLI Threshold, heat will be stored in lot cattle and will progressively increase without intervention if the conditions remain the same.

    Figure 1: Relationship between HLI and HLI Threshold

    Figure 1: Relationship between HLI and HLI Threshold

    As illustrated by Figure 1, for every 1 hour period that the HLI (green contour lines) is greater than HLI Threshold (orange line), heat load increases (red areas) at a rate equal to the difference between HLI and the HLI Threshold. (Note: The HLI Threshold can move up and down).

    For example, around 10am on Day 1, the HLI Threshold = 86 and the HLI = 98. Therefore the heat load is accumulating at a rate of 12 AHLU/hr.

    Figure 2: Relationship between HLI and heat dissipation

    Figure 2: Relationship between HLI and heat dissipation

    Heat will only begin to dissipate when the HLI decreases to below the lower threshold (shown by blue areas in Figure 2). Current research indicates that this threshold is 77 for most breeds, but may be higher for BosIndicus.

    The HLI Threshold is important to understand as it tells you at what point your cattle may start accumulating heat. The HLI threshold will change for even one beast as they go through the feedlot process.

    To understand how the HLI Threshold changes use the HLI Threshold calculator (right sidebar of the CHLT Toolbox).

    Undertaking activities when the environment is cooler may not necessarily mean the cattle have a lower heat load (see Figure 3).


    Figure 3 shows the HLI (green contour line) and the AHLU (red vertical lines) over a three day period. The high HLI on Day 1 and minimal recovery time overnight means that the heat load on Day 2 is actually higher than on Day 1, even though the HLI is lower.

    Note: AHLU86 means an AHLU with a HLI Threshold of 86.


    What is the WRF Model?

    The WRF Model is a next-generation meso-scale numerical weather prediction system designed to serve both atmospheric research and operational forecasting needs. It features two dynamical cores, a data assimilation system and a software architecture allowing for parallel computation and system extensibility. 

    The model serves a wide range of meteorological applications across scales ranging from metres to thousands of kilometres. In addition, WRF provides extensive physics options on parameterisation. The WRF model is used in a growing number of applications, which includes national meteorological services, militaries, governments and universities worldwide.

    WRF was developed as a collaboration partnership principally among;

    The WRF Model is run twice a day, initialised by the GFS data, in order to generate a four-day three-dimensional meteorological dataset. The WRF model downscales the GFS data to a much higher resolution, temporally and spatially. This method is optimised to produce a more accurate representation of local meteorology, taking into account influences that occur on a smaller scale such as land use and terrain. The Katestone NWS setup is a result of extensive research and is configured specifically to simulate and forecast Australian weather, following best practice. 

    The configuration of the WRF model was based on detailed studies, ensuring that the settings selected are appropriate in forecasting weather over Australia.