As drone operators the weather is very important to our work. We have been operating an automated weather station since May 2019, however the current professional system was installed in January 2022 to replace an all-in-one unit that did not survive its third Shetland winter!

Our weather station is a Davis Vantage PRO2 Plus Integrated Sensor Suite (ISS) that transmits wirelessly to our WeatherLink Live (WLL) unit in our office. The ISS consists of a temperature and humidity sensor in a radiation shield, a 0.2mm "tipping spoon" rain gauge, a solar radiation sensor and a UV sensor. The anemometer is separate from the ISS, mounted on our roof at 8m above ground.

The WLL contains atmospheric pressure, inside temperature and humidity sesnors. It has built-in memory that can store several days of observations should the network be unavailable. It also uploads all weather observations to the Davis Cloud every minute, ensuring a complete backup.

The ISS transmits observation data to the WLL which is connected by ethernet to our network. These observations are then read by a backend application which processes these raw data, calculating derived observations such as "feels like" temperature, and quality checking that observations are within a defined range, then archives them in a database. Once archived various reports are generated for upload to a web server or for further processing. In addition observation data is sent to various weather sites such as Windy, PWS Weather, the Met Office and Weather Underground.

Our website displays the reports generated by the backend application using cards, charts and tables. It is fully responsive and designed for both desktop and mobile / tablet devices, however some pages (e.g. the stats page and live gauges) display better on a small screen mobile device rotated to landscape format.

The home page shows a hyperlocal forecast for the next three hours (see Local Forecast below), and cards with the current conditions (by default these are updated every five minutes, however you can turn this off using the switch under the logo) along with min, max and averages for the day. Below the cards is a pressure and wind map with a five day forecast for Lerwick, provided by Windy and the European Centre for Medium Range Weather Forecast (ECMWF). Below that is an animated satellite map provided by Eumetsat via Meteoblue. On the right (or below the satellite map on mobile or small screen devices) the interactive charts show observations for the last 24 hours.

Using the menu links you can find observations for yesterday, the current week, the current month and the current year. You will also find reports organised by year then month, a statistics page showing monthly highs, lows and averages along with all time highs and lows, and the almanac page which displays sun and moon phases, major planets, the tide times for Lerwick Harbour, an aurora forecast (courtesy of NOAA), and - new for 2026 - a live sun path diagram that displays the azimuth and altitude of the sun in Lerwick or your location (note that this requires browser location services to be enabled and that you grant the page access your location). It can also display the moon path, and you can download the diagram as a PNG or SVG file.

The interactive charts allow you to view observations at a specific time, zoom in and out on the observation timeline, zoom in to a selected timespan (click and drag with your mouse to select a region on the timeline), pan along the zoomed timeline, and download the observations in SVG, PNG and CSV formats. When analysing the charts on the current conditions page it is advisable to turn off the auto update feature. Note that on most mobile devices the select zoom and pan options are not available, however you can still zoom in / out and download the images or CSV files.

The CSV download option allows you to download the observation data for further processing in a spreadsheet application (however, please read the copyright, version info and disclaimer link at the bottom of the page for acceptable use). The CSV option is available on all interactive charts: current, yesterday, week, month and year, plus the charts in the reports pages. Charts with multiple observations (e.g. feels like and wind) will include all the data displayed.

Most of the observation cards are self-explanatory, showing current, maximum and minimum values for the time period, however there are four cards that deviate from this (as well as the 12 hour forecast card, see below): UV Index displays a colour-coded risk indicator from Low, Moderate, High and Very High; Solar Radiation displays the cumulative radiation of the period in Wh/m² or KWh/m², the current solar radiation (amber text if the sun is shining, otherwise blue), and the total sunshine for the period; Wind Run displays the wind run over the last hour, the cumulative total for the day and the maximum 5 minute observation; and on the current conditions page only, Drying Potential. On the Week, Month, Year and Year / Month reports these special observation cards will display averages, totals and highs similar to the standard cards.

Drying Potential is a derived observation that uses a proprietary algorithm to determine how well a damp or wet surface will dry under the current atmospheric conditions. This is a useful indication on how well laundry will dry, as well as roads, paths or anything else that requires air drying.

The algorithm uses temperature, pressure, humidity, solar radiation, wind and rain observations and trends to display the drying potential on a five point scale: Not Good, Poor, Good, Very Good and Excellent. It also displays the expected trend over the next two to three hours. Although the trend can predict the chance of rain (and improving or deteriorating conditions), the Drying Potential is based on a combination of current conditions and trends over the last three hours and can change every five minutes. It is recommended to use this observation in conjunction with the 12 hour forecast.

The 12 hour forecast card uses an algorithm developed from the Zambretti instrument (see below) to broadly determine the expected local conditions for the day. The forecast is issued at 09:00 every morning - which is considered the best time to use the instrument - and is valid until 21:00.

Tests with the real instrument have proven to be very accurate, and there is no discrepancy between the physical instrument and the algorithm used by this website.

The Zambretti Forecaster is a weather forecasting instrument used in conjunction with a barometer. It interprets the reading of a barometer into one forecast from 26 permutations after making allowances for variable factors. These include wind direction, a rising, falling or steady barometer, and the season.

Negretti and Zambra were scientific instrument makers based in London, noted for their barometers. Their instrument was first produced in 1915 as a portable forecaster which needed minimal instrumentation, a simple barometer and an observation of the wind direction, and was easy to calculate with. It was produced as a small circular sliderule made of overlaid discs of ivorine, an early plastic. Despite its simplicity, it can achieve over 94% accuracy for 12 hour forecasts in the temperate regions of the northern hemisphere.

The 26 possible forecasts use the letters A to Z which are read through one of three apertures on the dial, one for rising, one for falling and one for a steady barometer. Two letters show in each aperture, one for winter and one for summer, then you read the forecast using the corresponding letter on the rear of the dial.

Our hyperlocal forecast combines multiple realtime and modelled weather data, ROAB (upper-air) soundings, synoptic and local observations using an application called WXSim to simulate and model weather systems and the likely surface conditions up to seven days ahead. The forecast is generated seven times a day, every three hours from 03:00 until 21:00. There is no forecast issued at 00:00. Due to data availibility, forecasts for three and more days ahead are more accurate when issued after 12:00.

Feeding into the main forecast algorithms is a second application that uses machine learning to create bias corrections to ECMWF data modelled using current and historical observations from our local station. These correction data improve the overall forecast accuracy as much as 20% to 30%.

The forecast is presented in the European Weather Network format. The top section shows the issue time, next update and the forecast for the coming hour, with unit options on the top right. A six-day iconic forecast follows, with three tabs below: Overview (detailed day and night forecasts), Table (hourly conditions, selectable by day), and Graphs (visual forecasts for each day or the full period).

This website has been optimised to run as a standalone progressive web app (PWA) on mobile and tablet devices. A PWA runs full screen without the normal browser controls, address and tab bars, providing a native app-like experience. You can use the menu items for navigation, or swipe left / right between open pages.

For iOS and iPadOS tap on the share button (top right) in Safari or Chrome and select 'Add to Home Screen'. For Android devices, in Chrome tap on the three dot menu and select 'Install application' or 'Add to Home Screen' depending on the device. The PWA has been tested on various iOS (minimum supported version is iOS / iPadOS 15.1) and Android (minimum supported version 11) devices.