VayuMet User Guide

01 Introduction

What this guide covers, who it is written for, and how to move through it.

Purpose of this guide

VayuMet presents a large amount of meteorological data — rainfall, wind, temperature, cloud, aviation reports, hazard alerts, seasonal outlooks, satellite imagery and air quality — on a single interactive map, turns that data into impact-based advisories telling you what the weather will actually do to your sector, and adds a set of focused standalone tools including the Rain Futures Index Desk and the VIMI monsoon index. This guide explains how to operate all of it in a logical order: get in, find your way around, use a feature, then fix problems if they appear.

Every instruction here describes behaviour that is live on the site today. Where a feature is experimental or partially populated, it is labelled as such rather than quietly omitted.

Who this guide is for

How to use this guide

Sections are numbered and ordered by when you are likely to need them. You do not have to read it end to end — the contents list on the left links directly to any subsection, and each section stands on its own.

▚ End module 1 — introduction

02 Getting Started

Reaching the platform, what your device needs, and what you should see on a successful first load.

2.1 Opening VayuMet

1. Go to the site

   Visit www.vayumetweather.com in any modern browser. The interactive forecast map is the home page — nothing further is needed to begin.

2. Wait for the first data load

   A loading indicator appears while the current model run is fetched. First load takes a few seconds because forecast rasters are decoded in your browser.

3. Check the frame time

   The timeline at the bottom shows the valid time of the frame you are looking at, in UTC. Stepping the timeline changes this; it is not the model run time.

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2.2 What you need

2.3 Your first map

On a successful load you should see India centred in the map canvas with a default rainfall layer active, a colour legend along the timeline bar, and the control panel available from the right edge.

1. Pan and zoom

   Drag to pan. Scroll or pinch to zoom. Double-click zooms in one level.

2. Open the control panel

   Use the tab on the right edge of the map to slide the layer panel open, then closed again when you want the full map.

3. Step through time

   Use the timeline at the bottom to move forward through the forecast. Section 3.3 covers this in full.

▚ End module 2 — getting started

03 Navigating the Interface

The five regions of the screen, what each control does, and how to move through forecast time.

3.1 Screen anatomy

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Capture: full interface, control panel open, rainfall layer active. Annotate: number five callouts — ① logo, ② map canvas, ③ control panel, ④ legend and timeline, ⑤ map actions.

3.2 The control panel

The panel is the primary control surface. It is organised top to bottom as basemap, overlay toggles, then layer groups.

Basemap

Four combinations let you set the map tiles and label colour independently, which matters when a bright raster washes out place names:

Overlay toggles

Three switches sit directly under the basemap row. These stack on top of whichever main layer is active, so you can combine information rather than switching back and forth:

Layer groups

Everything below the toggles is a collapsible group — click a heading to expand it. Fourteen groups cover Live Observations, Precipitation, Cloud Cover, Wind Animation, Air Quality, Renewable Energy and Agriculture, alongside headings that link out to the standalone tools in section 4.8. Only one raster layer is active at a time; selecting a new one replaces the last.

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Capture: control panel open, scrolled to show the basemap row and overlay toggles together. Annotate: bracket and label each group.

3.3 Timeline & playback

The main forecast covers 10 days in 41 frames at 6-hour steps. The timeline adapts to the active layer — daily layers step a day at a time, seasonal layers step a month at a time, and live layers hide the scrubber because there is only one current observation.

1. Read the current frame

   The valid time is displayed above the scrubber. All forecast times are UTC — add 5 hours 30 minutes for IST.

2. Step frame by frame

   Use the previous and next buttons for precise stepping, or click the track to jump.

3. Play the animation

   Press play to auto-advance and watch a system move. Press again to pause.

4. Use the keyboard

   Focus the scrubber, then use the arrow keys and space bar as listed below.

3.4 Key icons

▚ End module 3 — navigation

04 Using Core Features

Task-based walkthroughs for each layer group, in the order most people need them.

4.1 Rainfall forecast

Goal: find out how much rain a district will get, and when.

1. Open the panel and choose a rainfall layer

   Under the precipitation group, pick Total Rain · 6h for timing detail or Total Rain · 24h (Daily) for daily totals.

2. Zoom to your area

   Scroll in on your district so the colour bands are clearly separated.

3. Read the legend

   The colour bar sits above the scrubber with values in millimetres. Deeper colours are heavier rain.

4. Step forward in time

   Advance frame by frame to see when the rain band arrives and clears.

5. Check the total

   Switch to Total Rain · Cumulative to see the accumulated storm total rather than any single step.

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Capture: an active monsoon day with a strong west-coast rain band, legend visible. Annotate: point to the legend and to one heavy-rain core with its mm value.

4.2 Wind and wind barbs

Goal: see wind speed and direction at the level you care about.

1. Pick a level

   Choose a wind layer from 10 m (surface) up through 100 m, 850, 500, 300 and 200 hPa.

2. Add barbs for direction

   Enable the matching barbs layer to overlay direction symbols on the speed field.

3. Read the barbs

   The staff points into the wind. Each full barb is 10 knots, each half barb 5 knots, and a filled pennant 50 knots.

4. Check gusts separately

   Wind Gust shows peak gusts, which matter far more than mean wind for damage and aviation.

4.3 Aviation weather

Goal: assess flight conditions from live reports.

1. Open the Aviation Dashboard

   Expand the ✈ Aviation-SigWx Dashboard group in the panel and follow its link, or go straight to the dashboard.

2. Start with flight category

   METAR Flight Cat colours each station by current conditions; TAF Flight Cat does the same for the forecast.

3. Click a station

   Open a station to read its decoded report and, for TAF, a period-by-period forecast chart.

4. Check hazards and ceilings

   SIGMET Hazards shows affected airspace; Cloud Base AGL (ft) and Visibility METAR cover approach minima; Fog Probability flags fog risk.

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Capture: Aviation Dashboard with METAR flight-category dots and one station popup open. Annotate: label one dot per flight category.

4.4 Hazard alerts

Goal: see which districts face which hazard, day by day.

1. Open the alerts map

   Expand the 🚨 Alerts & Warnings group in the panel and follow its link, or go straight to the alerts map.

2. Start with the composite

   Composite Alert merges all hazards into one severity view — the fastest overall picture.

3. Isolate a hazard

   Switch to a specific alert to see only that threat.

4. Step through the days

   The timeline moves a day at a time across the alert period.

4.5 Seasonal outlook

Goal: understand the months ahead, not the days ahead.

1. Open the seasonal forecast

   Expand the 📅 Seasonal Forecast group in the panel and follow its link, or go straight to the seasonal forecast.

2. Choose anomaly or absolute

   Anomaly layers show departure from normal. Forecast layers show the predicted value itself.

3. Step by month

   The timeline advances one month per step across the outlook period.

4. Click a district

   Opens a month-by-month chart for that district so you can see the shape of the season.

For monsoon performance against actuals, the Monsoon 2026 Monitor compares forecast rainfall with observed rainfall to date on a side-by-side swipe map.

4.6 Air quality and visibility

Goal: assess haze, particulate load and fog risk.

4.7 Satellite and live observations

Goal: see what is actually happening right now, not what is forecast.

1. Enable satellite imagery

   Choose Himawari-9 TRM/B13 for infrared cloud-top temperature, or Himawari-9 SND for the sandwich IR/RGB product.

2. Check the status badge

   Where the frame time normally sits, the timeline shows ⬤ SAT followed by the imagery timestamp, for example ⬤ SAT 31 Jul 2026 06:30Z. The panel repeats it as Updated:. Error states are covered in section 6.

3. Add station reports

   Turn on 📡 Live Observations for Wx Icons (METAR) and Temperature (METAR) at reporting stations.

4. Compare with the forecast

   Switch between satellite and forecast rainfall for the same time to judge how well the model is tracking reality.

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Capture: Himawari-9 infrared imagery with the Live Observations group expanded. Annotate: highlight the active satellite layer and its timestamp.

4.8 Standalone tools

Several features are separate focused pages rather than layers on the main map. Each is reachable from its named group in the control panel, and from the links below.

4.9 Rain Futures index desk

Goal: see where an exchange-traded rainfall index has been, and where two independent models say it is heading.

NCDEX lists India's first exchange-traded weather derivatives. RAINMUMBAI tracks the southwest monsoon over Mumbai from 1 June to 30 September; RAINCHNNAI tracks the northeast monsoon over Chennai from 1 September to 31 December. Each settles on a running Cumulative Deviation Rainfall (CDR) number: the index opens the season at that city's seasonal normal — 2,206.7 mm for Mumbai, 998.25 mm for Chennai — then each day adds the rainfall actually recorded at its two IMD observatories and subtracts the normal for that date. Rising means wetter than normal, falling means drier. One millimetre is worth Rs 50 per lot on both contracts.

The Rain Futures Index Desk is a standalone page — it is not a map layer. It reproduces the official published spot and runs it forward 14 days.

1. Read the header strip

   Each panel opens with the official spot in millimetres and its rupee value per lot, the departure from the season anchor, the model spread at the end of the projection window, and where the season currently ranks against previous seasons on the same date.

2. Follow the solid line

   That is the CDR spot as NCDEX publishes it — observed, not forecast. The shaded band behind it is the same index over its published back-computed seasons, 10th to 90th percentile, with the median as a dashed grey line.

3. Read the two dashed lines

   VM-AIFS is ECMWF's machine-learning model; VM-IFS is ECMWF's physics model. Both start from the latest published spot. They are separate models, not two members of one.

4. Use the gap as your uncertainty

   The Gap column in the table under each chart is the distance between the two projections. Where they diverge, that divergence is the honest uncertainty on the call.

5. Check the verification table

   Below both panels, yesterday's projections are scored against what the exchange actually published, by city, by model and by lead day. Nothing is hidden when it misses.

4.10 VIMI monsoon index

Goal: know whether the monsoon is about to go active or break, and why.

Most monsoon diagnostics measure an ocean signal that influences the monsoon. The VayuMet Indian Monsoon Index (VIMI) measures the monsoon itself. It is a seven-component weighted index built on the semi-permanent circulation features that constitute the Indian summer monsoon, computed on GFS output to 16 days.

1. Read the composite index

   A single value combining all seven components. High means a strong, well-organised monsoon circulation; low means a weakening or broken one.

2. Read the forward curve

   The index is projected on GFS output to 16 days, so a turn in the curve is an early signal of an approaching active or break spell.

3. Break it into components

   When the index moves, the component breakdown shows which feature moved it — a collapsing low-level jet and a weakening trough mean different things for where rain will fall.

4. Read the paper for the method

   The full derivation, weighting and verification are in the VIMI scientific paper (PDF).

4.11 Impact-based advisories

Goal: stop reading a forecast and start acting on one.

A conventional warning tells you the weather: heavy rain, orange, 15–17 July. It does not tell you what that rain will do to you — and the answer is completely different for a district officer, a farmer with a standing crop, a dispatcher planning fuel, and a wind-farm operator. VayuMet takes the extra step: every district forecast carries advisories that name the consequence, the recommended action and the exact dates affected.

They appear in two places, and both are driven by the same rules:

1. On the district forecast page

   Open the District 10-Day Forecast, pick a district, then use the four tabs at the top — Weather, Agriculture, Aviation, Energy. Each tab redraws the charts for that sector and swaps the advisory card beneath them.

2. On the main map

   Click a district to open the meteogram tray. The advisory column is the final column, spanning every row — the same guidance without leaving the map.

3. Read the dot colour first

   Each bullet is dotted in its IMD warning tier — red for severe or extreme, orange for warning, yellow for watch, green for all-clear, blue and grey for information. Scan the colours before the words.

4. Read the dates, not just the hazard

   Dates are collapsed into readable ranges — 15–17 Jul, 20 Jul — so you can plan around the specific days rather than the whole period.

5. Print or export it

   The forecast page has 🖨 Print and ⬇ PNG buttons, so an advisory can go straight into a briefing pack or a field bulletin.

What each sector tab tells you

▚ End module 4 — core features

05 Advanced Options

Customising the display, getting views out of the platform, and where the data comes from.

5.1 Customisation settings

5.2 Sharing and export

1. Share a link

   Press ↗. On mobile this opens the system share sheet; on desktop the page URL is copied to your clipboard with an on-screen confirmation.

2. Save an image or PDF

   Press 📷, then use your browser's Print → Save as PDF to capture the current view.

3. Present fullscreen

   Press ⛶ to remove browser chrome for meetings and briefings.

5.3 Integrations and data sources

VayuMet integrates several external data streams. Understanding which model sits behind a layer tells you how much to trust it and how often it refreshes.

Comments on articles

Blog articles use giscus, which threads discussion through GitHub. Reading comments requires nothing; posting one requires a free GitHub account and is the only place on VayuMet where any sign-in exists — it belongs to GitHub, not to us.

▚ End module 5 — advanced options

06 Troubleshooting & FAQs

What the on-screen messages mean, and what to do about them.

Common messages and fixes

Frequently asked questions

The map is blank or stuck loading.

Hard-reload the page (Ctrl+Shift+R, or Cmd+Shift+R on Mac). Confirm JavaScript is enabled and that an ad blocker is not blocking map tiles. First load of a layer is always slower because rasters are decoded in your browser.

The data looks older than it should.

The model run time is not shown on the map — only the valid time of the frame you are viewing. Runs publish four times daily and take time to process, so several hours of lag between real time and the newest frame is normal. If the earliest frame is more than a day behind today, hard-reload to clear a cached copy.

Why do the forecast times not match my clock?

All forecast times are UTC. Indian Standard Time is UTC + 5:30 — so 06:00 UTC is 11:30 IST.

Two rainfall layers disagree.

They almost certainly use different accumulation windows. Re-read the callout in section 3.3 — 6-hourly, daily and cumulative totals are not comparable to each other.

Labels are unreadable over a bright layer.

Change the basemap combination (section 3.2). The mixed options exist precisely for this — they let you flip label colour independently of the tiles.

It does not work well on my phone.

The map works on mobile, but layer-heavy views are demanding. Close the panel after choosing a layer, turn off overlays you are not using, and prefer the district meteogram or a state forecast page for a quick answer on a small screen.

Can I download the underlying data?

Not directly today — see section 5.3.

The Rain Futures projection does not match the futures price I see on my terminal.

It is not meant to. The desk projects the rainfall index (the CDR spot), not the traded price of any contract. The futures table on that page also carries a footnote worth reading: the exchange's daily series publishes one value per calendar day and releases the current day's only once it settles, so those prints can predate the live spot shown above them. Section 4.9 has the full explanation.

Where do the advisories on the forecast page come from?

They are generated from that district's own meteogram by a shared rule set based on IMD warning criteria, ICAO practice and agromet guidance — not written by hand per district, and not a generic national bulletin. Section 4.11 explains what each sector tab covers.

The advisory says spraying is favourable but it looks windy outside.

The advisory is built on the forecast, not on current conditions, and it works at district scale. Local wind at your field can differ from the district value. Check section 4.11's caveat and use the live observations in section 4.7 for what is happening right now.

Why do VM-AIFS and VM-IFS disagree?

Because they are genuinely different models — one machine-learning, one physics — and that disagreement is the point. The Gap column is published as the honest uncertainty on the call. See section 4.9.

VIMI says the monsoon is active but my district is dry.

VIMI is a circulation index for the monsoon as a system, not a district rainfall forecast. A strong circulation still leaves rain-shadow and orographically sheltered districts dry. Use section 4.1 for where rain actually lands.

Contact and support

When reporting a problem, please include the page URL, the frame time shown on the timeline, the layer you had selected, and your browser and device. That is usually enough to reproduce it.

▚ End module 6 — troubleshooting

07 Versioning & Updates

How this document is structured so it can be maintained without rewriting it.

How to update a section

1. Locate the module

   Find the banner comment naming the module, for example MODULE 4 — CORE FEATURES.

2. Replace between the markers

   Edit or swap everything between the banner and the matching ▚ End module line. Leave surrounding modules untouched.

3. Update the contents list

   The sidebar is the only cross-reference — mirror any added, removed or renamed section there.

4. Verify layer names

   Feature names in section 4 must match the label fields in js/config.js exactly, so the guide and the interface always agree.

5. Record the change

   Add a row to the revision history below and update the revision number in the masthead and sidebar footer.

Maintenance checklist

Screenshot placeholders

Placeholder frames mark every image this guide should carry. Each names its target file under /guide-img/ and states what to capture and annotate.

The only reason to edit the markup is to revise the alt text, which should describe what the screenshot shows for readers using a screen reader.

Revision history

▚ End module 7 — versioning