Forecast conditions and Leeway table
When you have completed the data capture of the Datum Header information (described in LKP information and Time at Datum), and you have clicked on the Save button, the following screen will be displayed -
•A : the drift time is displayed - this is the total time from time at LKP to time at Datum.
•B : the Datum calculation method options are displayed and they default to using the forecast conditions and the Leeway table
•In the input box for the forecast conditions are three main sections
•C : Forecast model - SearchWell offers to download forecast files from two different sources /models (also see Forecast Info). The insert shows the available options :
oEUR - The main European source downloading
▪Wind from ECMWF
▪Current from CMEMS (Copernicus)
oUSA - the main USA source downloading
▪Wind from GFS
▪Current from HYCOM
•D : Where the forecast conditions are to come from -
oDownload (default) - the wind and current forecasts will automatically be downloaded and stored on your computer
oI have a file - the forecast has already been downloaded by SearchWell, so we don't have to download them again, we can just use them
▪A : when you select the "I have a file" option
▪B : SearchWell asks you to find the previously downloaded forecast file. It starts looking in the main "SearchWell Output Files" folder on your hard drive
▪C : You will find the forecast files in a sub-folder that has the date that the files were downloaded followed by the words "Condition Forecasts".
When you double click on the required sub-folder the following window will be displayed -
•A : in this example I opened the sub-folder with forecasts that were downloaded on 2024-09-19
•B : the wind and current forecast files stored in the sub-folder are displayed. The file name tells you -
oThe local time the forecast was downloaded - in this case 07h02
oThe date and time range of the forecasts - in this case the forecast was for 2024-09-18 from 07:00 until 10:00
owhether the file contains WIND or CURRENT information
So, in the above illustration, the forecasts were downloaded on the 19th of September, but they were the forecasts of the conditions experienced on the 18th September between 07:00 and 10:00
oI will enter my own forecast - the user does not want (cannot) to download the forecasts and will look them up himself and enter them
▪A : the "I will enter my own forecast" option is selected
▪B : the date and time of the required forecast (the LKP time)
▪C : the position at which the forecast is required
▪D : you must enter a wind speed and a wind bearing
▪E : if you click on this Windy icon SearchWell sends you to the Windy.com web site using the location displayed on the input form, and you can read the wind and current forecasts from Windy
▪F : if you click on this button the help information will be displayed
▪G : you must enter a wind speed and a wind bearing
▪H : you must enter the current speed and current bearing
▪I : this message tells you how many hours you have entered forecast for and also the total number of drift hours
▪K : click on the OK button to continue - SearchWell will continue to the next hour of the drift, or, if all the forecast information has been entered it will display the results of the drift on the screen
oAutomatic (default) - if the forecast is/has been downloaded by SearchWell, just accept them as correct
oCheck the forecast information - if the forecast is/has been downloaded by SearchWell the user wants to see them and be able to change them. This might be done if the rescue crew on site have more accurate input particularly with the wind information
▪A : when the Check forecast information is clicked
▪B : Datum date and time is displayed
▪C : Datum position in decimal degrees that can be copied and pasted into a forecast site
▪D : when you click on this button the help screen will be displayed
▪E : displays the wind forecast information for the hour which you can change
▪F : displays the current forecast information for the hour which you can change
▪G : gives an indication of how many hours you have checked in relation to the total number of drift hours
▪H : click on the OK button to continue
•E : Probability - if this is selected (there is a double ring in the circle - which is the default) then random points will be generated and Probability of Detection (POD) can be used as a guideline to where the rescue crew should be looking
oThe default number of points is 500, but this number can be changed
oThe confidence levels can be selected from the following list (see Forecast Confidence in the Important Information section). The default is moderately confident in both the wind and the current forecast information
•F : Casualty type - all the casualty types listed in the Leeway Table are displayed and you need to click on the one that best describes your casualty
•G : There are three items of information that are defaulted
oLand Check - toggling this on/off allows you to define whether or not you want the system to check if the casualty or random points are on land. The datum calculation is substantially faster if the land check is not done - not selected is the default state. The option will be "grayed out" and unavailable if the file containing land information is unavailable.
oSearch Error - this defines how confident one is in the information used for the calculation and it is used when creating the circle around the Datum point that defines the Search Area. 30% is the recommended number and it means that we will go back (up-drift or towards the LKP) 30% of the total drift distance, and we will draw a circle around the Datum Point with that 30% as the radius. This is not used if you use the Probability Search Areas.
oPosition Error nm (optional) - This distance is added to the radius of the circle around which the search area is defined and it depends upon how confident you are with the coordinates you are using for the LKP. IAMSAR recommends that this is 0.1nm if the LKP location comes from a GPS, but if it is an observation by a person, this should be 1nm. The bigger the number given here, the bigger the search area.
The need for this falls away if one considers the random particles.
•H : The calculate button which is clicked when you have entered all the required input information
•I : The help button which, when clicked, displays quick in-form assistance
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