MSFS moves
the weather
in steps

• Licensing and entitlementValidate once at startup and pin it for the life of the process, fail open on any server error, five machines per licence with self-service release. Under test.Built
• Engine processThe weather engine runs crash-isolated from the interface and is respawned in a few hundred milliseconds with the window and session intact.Built
• Stall watchdogTrips at ten seconds and stops writing rather than accumulating a correction it would dump into the sim the moment the link came back.Built
• Capability listEvery weather concept MSFS 2024 cannot do, with the reason, shipped in the product and enforced by tests.Built
• In-sim packageConfirmed in a running MSFS 2024 — the toolbar button appears, the panel renders, the loopback link is reachable, and the package encoder is byte-checked against Asobo's own compiler. The automatic copy into the Community folder is not written yet.Partial
• SmoothingThe per-parameter rate table and the control loop are real code. The arithmetic that walks each value toward its target at those ceilings is not done. This is the single most important thing in the product and it is not finished.In progress
• Data planeScheduled ingest of METAR, TAF and GFS winds aloft. Specified, scheduled, and absent — there is no provider code in any repository yet.Not built
• Air effects (turbulence)The SimConnect writer exists behind a feature flag and currently emits zeroes. The model is not written and the axis mapping is not yet confirmed in the sim.Not built
• Installer and updatesA signed per-user Windows installer with signature-verified automatic updates. Specified, not proven end to end.Not built

NEXT MILESTONE — A free closed beta, invitation only, from the waitlist. No pre-orders and no paid early access at any point before release.

1. 01

   Every change is an instant step

   The sim does not interpolate. Hand it a new weather state and it applies the whole thing on the next frame: the wind snaps forty degrees on short final, the cloud deck teleports two thousand feet, the altimeter jumps. Anything that updates the weather while you fly has this problem, including the sim's own live weather.

   ArcusWX integrates ten times a second under a fixed ceiling per parameter and writes at most once a second. The step becomes a ramp.

2. 02

   Writes are clamped and ignored in silence

   Send a value outside the sim's range and it is clamped or dropped. No error, no return code, no log line. The write reports success and the sky does something else.

   ArcusWX reads the sim's own copy of the weather back out after every write and compares it to what it sent. A success without an echo is not a success.

3. 03

   The wind ceiling is 150 knots

   MSFS silently clamps wind speed at 150 kt. The strongest winds aloft are unreachable — not by us, not by anyone, not with any tool.

   ArcusWX honours the ceiling, tells you when it has been hit, and shows the clamped value beside the one it asked for. That is the whole of the honest answer.

4. 04

   The weather is global, always

   MSFS has one weather state and it is the weather everywhere in the world at once. There is no latitude, no longitude, no station, no radius, no per-cell anything. Nobody can place a storm over the ridge ahead of you, and any product that says otherwise is describing something the simulator cannot do.

   ArcusWX keeps that one global sky correct where your aircraft actually is, and rebuilds it as you move.

5. 05

   The sky is built around the surface report

   Stock live weather leans heavily on the surface observation, which is why a BKN report gives you a broken deck and very little above it, and why the high cloud a real sounding would put at twenty thousand feet is frequently just absent.

   ArcusWX builds the whole column — layered wind and cloud from the surface upward — rather than stretching one surface report across the sky.

6. 06

   There is no cloud type, no visibility, no temperature aloft

   The weather API has no cloud-type input, no visibility field, no temperature layers and no dewpoint. The renderer infers cumulus or cirrus from the altitude, thickness, density and coverage it is given, and the entire temperature column is derived from one sea-level number.

   ArcusWX shapes the four values the renderer actually reads, and states the rest as gaps instead of selling them. The full list ships inside the app.

7. 07

   Custom weather takes the sim out of live weather

   The moment any tool selects a custom weather state, MSFS live weather is off and that tool owns one hundred per cent of the sky — including every artefact you see. There is no blending and no partial ownership. Run one weather engine at a time.

   When ArcusWX is driving, it is ours to get right, and ours to fix.

8. 08

   Preset lists that fill up

   Weather written through a preset can leave a preset behind, and users have reported preset lists running into the thousands.

   ArcusWX creates exactly one weather preset in your simulator, ever, and never modifies or overrides a core simulator file.

A note on the mechanism, because technically literate simmers already know it: MSFS has no supported weather-writing API. SimConnect’s was removed and the MSFS 2024 SimConnect reference contains no weather symbols at all. Every weather add-on for MSFS 2024 goes through the same undocumented in-sim JavaScript route. ArcusWX assumes it will change — it probes every call before using it, reads the sim’s own limits at runtime instead of hardcoding any, and preserves fields it does not recognise rather than dropping them.

1. 01ReadNot built

   Surface observations, terminal forecasts and global model winds aloft — METAR, TAF and GFS. Fetched on a schedule and delivered to the app, with the age of every feed shown on the face of the interface and a manual refresh you can hit yourself. When a source is unreachable the last good value is held and marked as held, never silently substituted.

2. 02ResolvePartial

   Build the column, not the headline. Wind layers with their own altitude, direction, speed and per-layer gusts; cloud layers with base, tops, coverage, density and scattering. The profile is rebuilt as you move, so the sky above you matches where you actually are. Then, because MSFS takes one global state, it is collapsed to a single answer before it goes anywhere near the wire.

3. 03IntegrateIn progress

   The part that matters. ArcusWX moves toward the resolved state ten times a second, with a ceiling on how fast every parameter may change: 2 kt/s of wind speed, 2 °/s of direction, 0.5 °C/s, 0.5 hPa/s, 0.02/s of cloud coverage and density, 30 m/s of cloud altitude with a 60 m deadband so a layer does not chase noise. Direction takes the shortest arc — 359° to 001° is a two-degree change, not a three-minute sweep of the windsock.

4. 04WriteBuilt

   Into the running simulator, at most once a second, through the in-sim package's weather listener. No file swaps. No preset menu. No reload, no repositioning, no pause. One durable preset is created on first install and never again, and nothing Asobo ships is patched or overridden.

5. 05VerifyBuilt

   Read the sim's own weather back out, compare it to what was sent, and show both. Clamped values are reported as clamped. If the echoes stop, the watchdog trips after ten seconds and ArcusWX stops writing rather than accumulating a correction it would dump into the sim the moment the link came back. Failure is surfaced, not hidden.

Five of them are rate-limited on the way in — wind, cloud, pressure, temperature and precipitation rate, the ones you can watch change from the cockpit. The other five are set outright, because a step change in snow depth or humidity is not something anybody can perceive mid-flight and smoothing it would buy nothing. All ten are read back out and compared. Nothing here is claimed to be finished before the data plane and the integrator are.

• Wind layersUp to sixteen on our wire, each with its own altitude, direction and speed, and a gust carrying its own direction, interval and peak multiplier. A gusty surface layer can sit under smooth air aloft.Built
• Cloud layersUp to sixteen on our wire, each with base and tops, coverage ratio, density and light scattering. Tops must exceed base; the schema refuses anything else.Built
• MSL pressureSea-level pressure, in hectopascals. Rate-ceilinged at 0.5 hPa/s so your altimeter does not jump.Built
• MSL temperatureOne mean-sea-level temperature. This is the only temperature in the protocol — see the limits below.Built
• Precipitation rateIntensity, driven live. MSFS decides rain or snow itself from the surface temperature, so ArcusWX gets the temperature right and lets the sim make that call.Built
• Snow coverGround snow depth. Carried on our wire; the mapping onto the sim's own scale is a placeholder until it is measured.Partial
• Aerosol densityThe only atmospheric-obscuration lever MSFS exposes. It is not visibility and it is not calibrated — see the limits below.Planned
• HumidityA humidity multiplier on the sim's own model.Built
• Thunderstorm ratioA single global value between zero and one. It is not a storm cell and it has no position.Built
• Zulu timeThe simulator's clock, driven to match the observation being flown.Built

• Cloud typeThere is no cloud-type input. The renderer infers cumulus, stratus or cirrus from a layer's altitude band, thickness, density and coverage. ArcusWX shapes those four so the sky the renderer builds is the one the observation implies.Not supported
• Visibility distanceThere is no visibility field at all. The only lever is a 0–1 aerosol density on an undocumented nonlinear extinction curve that has never been calibrated. ArcusWX will fit reported visibility onto it, together with a low dense layer for fog. That fit is not written yet, and we will never print a visibility distance as a product output.Not supported
• Precipitation typeMSFS chooses rain or snow itself from the surface temperature. You cannot force snow above freezing.Not supported
• Temperature layersMSFS takes exactly one mean-sea-level temperature. There are no layers to set.Not supported
• DewpointThere is no dewpoint input.Not supported
• Lapse rateThe whole temperature column is derived from that one sea-level value with a fixed standard lapse rate. No inversion, no set freezing level. Upper-air temperature fidelity is permanently capped.Not supported
• Turbulence (weather API)The weather system has no turbulence input. ArcusWX writes body rotation rates to the airframe over SimConnect instead.Not supported
• Wind shearThere is no shear model. Discontinuities between wind layers are smoothed by the sim's own interpolation. Stacked layers with differing directions imply shear; that is the most that can honestly be said.Not supported
• IcingStructural or engine icing cannot be driven through the weather API. There is no workaround.Not supported

Simulator

Microsoft Flight Simulator 2024. Only 2024. Not MSFS 2020, not X-Plane 12, not Xbox — those are not partially supported or best-effort, they are not built. Advertising a simulator we do not test is how a product ends up owing people something it cannot deliver.

Operating system

Windows 10 or 11, x64. There is no macOS or Linux target and none planned. The desktop app must be running for weather to flow, so there is no in-sim-only version.

Install shape

Two halves, one product: a Windows desktop app, and a small package in your MSFS 2024 Community folder. Steam and Microsoft Store installs are both supported, including a relocated Community folder. Folder detection is written; the automatic copy into it is not yet, so today installation is a manual copy. The sim must be closed while the package is installed, and it will not appear until the sim restarts.

The sim's own live weather

Off, while ArcusWX is driving. Selecting a custom preset takes MSFS out of live weather entirely — from that moment ArcusWX owns 100% of the sky, including every visual artefact you see, which makes anything that looks wrong ours to fix. There is no blending and no partial ownership.

Air effects are the exception

MSFS's weather system has no turbulence input at all, so turbulence is written straight to the airframe over SimConnect instead — independent of the weather system. That makes it the one part of ArcusWX that works with MSFS live weather left switched on. In development: today it is a feature-flagged writer emitting zeroes.

Weather is global

MSFS applies one sky to the whole world at once. There is no lat/lon, no station, no radius, no per-cell anything — and no add-on for MSFS 2024 can give you otherwise. ArcusWX follows your aircraft and keeps that one global sky correct where you actually are. We would rather tell you now than sell around it.

What it touches in your sim

Nothing that Asobo ships. Everything lives inside the ArcusWX package's own folder; no core simulator file is patched or overridden, and the manifest carries no override key at all. ArcusWX creates exactly one weather preset in your simulator, ever. It adds one toolbar button.

Other weather engines

Run one at a time. The in-sim weather listener is shared and the outcome is last writer wins, so two engines fighting produces nonsense rather than a merge. Our plan is to detect a foreign engine and tell you, not to interoperate with it.

VATSIM, IVAO and online ATC

ArcusWX drives your simulator. It does not drive the network. Controllers read the network's own weather feed, and two feeds sampled at different times will sometimes disagree — usually by a few degrees and a couple of knots, occasionally by more. Anyone promising your sim and the ATIS will always match is describing something they do not control.

Multiplayer and group flights

Each copy injects into its own simulator. Other pilots see whatever their sim is doing, whether or not they run ArcusWX. Guaranteed identical conditions across a group flight is not a v1 feature and we are not going to imply otherwise.

Other add-ons

Not yet tested. We have not run ArcusWX alongside the usual immersion and traffic add-ons in a controlled way, so we are not going to publish a compatibility list we have not earned. When we have, it goes here.

Internet

Live weather needs a live connection. The licence does not: activate once online, and after that the app carries a signed entitlement good for weeks without a successful check-in. If our servers are slow, down or unreachable, it runs on what it already has and says nothing.

Performance

Not measured, so not claimed. What we can state is the architecture it will be measured against: the weather engine runs in its own process, it writes to the simulator at most once a second, and sim telemetry never reaches the interface above 1 Hz. When we have a frame-time number we will publish the method used to get it alongside it.

Payment model

One-time purchase. No subscription, no annual fee, no per-simulator upsell — there is one simulator.

Updates

Lifetime, including major versions. That is not a promise we can quietly revise: the licence database has no expiry column and the update feed has no version gate. There is currently no mechanism in the product to sell you a paid v2.

Machines per licence

Five. The sim PC, the networked second PC, the laptop, and two spare.

Releasing a seat

From the Devices pane in the app, any time, no cooldown and no support ticket. Reinstall Windows, swap an SSD, upgrade a GPU: the same machine is recognised as the same machine and no seat is consumed. Seats that have not been seen for 45 days are reclaimed automatically.

Your hardware

Raw hardware identifiers never leave your machine. Each component of the device fingerprint is hashed before it is sent, and the server stores it under a secret it keeps outside the database.

Offline

Activate once online. After that the app carries a signed entitlement with a seven-day window and a further thirty-day grace, and it never locks a session that is already running. The licence is checked once at startup and pinned in memory for the life of the process — a sixteen-hour flight will never see a licensing dialog.

If our servers are down

Nothing happens. Any timeout, DNS failure or 5xx runs on the cached entitlement, silently. Our uptime is not your uptime.

Where it is sold

Direct from arcuswx.com at launch, through a merchant of record who handles payment, VAT and invoicing. The licence itself is issued and enforced by us.

Refunds

The full policy is published before the first sale. It will honour the EU and UK fourteen-day right of withdrawal rather than hiding behind “digital goods are final”.

1. Now

   Injection and install

   The app copies the in-sim package into your Community folder, and a full weather write runs end to end on a machine that is not the developer's. This is the milestone that proves the product is possible.

2. Next

   The data plane

   Scheduled ingest of METAR surface observations, TAF terminal forecasts and GFS model winds aloft, served to entitled clients. Until this lands there is nothing real to inject — everything before it is plumbing with test values in it.

3. Then

   The integrator

   The arithmetic that walks every parameter toward its target at a ceilinged rate, ten times a second, and writes to the sim at most once a second. The rate table and the control loop already exist. This is the reason the product exists and it is the one part that will not be rushed to hit a date.

4. Then

   Air effects

   Body rotation rates written to the airframe over SimConnect. The first job is not a turbulence model — it is proving the aircraft moves convincingly at all, and confirming which axis is which. Until that is answered we will not describe what it feels like.

5. Then

   Installer, signing and updates

   A signed per-user Windows installer that needs no administrator prompt, and automatic updates that verify the signature of what they download before running it.

6. Before launch

   Free closed beta

   Invited from this list. Free, with no obligation and no discount attached to taking part — a paid beta is a pre-order with a different name.

7. Policy

   When Asobo ships a sim update

   Sim updates have broken weather integration for every product in this category before and will again. We will not promise a fix window we do not control. We will promise a statement: within 48 hours of a sim update landing, this page says whether ArcusWX is affected, what specifically broke, and whether there is a workaround.

8. After v1

   Not being built

   Historical replay, a manual weather editor and other simulators are not in v1 and are not being built. If any of them start, they appear on this list before they appear in a feature bullet.

No percentage bars, no quarters, no dates. The absence is the argument.

Do I turn the sim's live weather on or off?

Off, while ArcusWX is driving the sky. Selecting a custom preset takes MSFS out of live weather and there is no in-between. The single exception is air effects: turbulence is written to the airframe over SimConnect, independently of the weather system, so it works with live weather left on.

How does the injection actually work — presets, file swaps, or a direct write?

A direct write into the running simulator. No file swaps, no preset menu, no reload. MSFS 2024 has no supported weather-writing API — SimConnect's fourteen weather functions were removed and the 2024 reference contains none of them — so every weather add-on for 2024 uses the same undocumented in-sim JavaScript route. ArcusWX reads the sim's own limits at runtime instead of hardcoding any, and reads the weather back out after each write to compare it with what it asked for.

Is the weather only in a bubble around my aircraft, or the whole world?

The whole world, because that is the only thing MSFS offers. One weather state is the weather everywhere at once — no lat/lon, no station, no radius. ArcusWX keeps that one sky correct where your aircraft is, and rebuilds it as you move. Nothing sold for MSFS 2024 does otherwise, whatever the marketing says.

Where is the Community folder, and will the installer find it?

MSFS 2024 puts it in a different place depending on whether you installed from Steam or the Microsoft Store, and it lets you relocate it. ArcusWX detects all three cases — that detection is written and works. The automatic copy of the package into the folder is not written yet, so until it is, installation is a manual copy with the sim closed, and the package appears when the sim restarts.

Will my weather match what VATSIM ATC is using?

Usually close, not guaranteed. ArcusWX drives your simulator; controllers read the network's own feed. Two feeds sampled minutes apart will sometimes disagree. We are not going to claim control over a system we do not run.

Does it work in multiplayer? Will other pilots see the same sky?

Each copy writes into its own simulator, so other pilots see whatever their sim is doing. Guaranteed identical conditions across a group flight is not a v1 feature.

What does it cost me in frame rate?

We do not know yet, and we are not going to guess. The engine runs in a separate process from the interface, writes to the sim at most once a second, and sends nothing to the UI above 1 Hz — but that is architecture, not a measurement. When there is a number there will be a method printed beside it.

Does it handle thunderstorms and CB cells?

Partly, and here is the limit. MSFS takes a single global thunderstorm value and decides the rest itself; there is no way to place a cell at a position, so no product can put a storm forty miles ahead of you on your route. ArcusWX drives the levers the sim exposes and tells you which ones the sim silently clamped.

Can I set visibility, fog, or a cloud type?

Not directly — none of the three is an input MSFS accepts. There is no visibility field at all; the only lever is an atmospheric aerosol value on an undocumented nonlinear curve. There is no cloud-type setting either: the sim's renderer infers cumulus, stratus or cirrus from the altitude band, thickness, density and coverage it is handed. ArcusWX shapes those four so the sky the renderer builds is the one the observation implies, and fits reported visibility onto the aerosol curve. That fit is not written yet, and we will never print a visibility distance as a product output.

What about icing, wind shear, temperature aloft and dewpoint?

None of them are settable. MSFS takes exactly one mean-sea-level temperature and derives the whole column with a fixed lapse rate, so there is no dewpoint, no inversion and no freezing level you can set. There is no shear model, and structural or engine icing cannot be driven through the weather API at all. The app ships this list itself, in the interface, with the reason next to each entry.

Is there a passive mode that leaves the sim's clouds alone?

There is one honest version of it: leave MSFS live weather on and run air effects only, because turbulence goes to the airframe over SimConnect and never touches the weather system. What you cannot have is ArcusWX driving the winds while MSFS draws its own clouds — selecting a custom preset takes the sim out of live weather entirely. There is no partial ownership of the sky, for anyone.

Can I turn it off mid-flight?

ArcusWX stops writing the moment you disengage or close it. What it will not do is put MSFS back into live weather for you — selecting a custom preset is a sim-side state, and returning to live weather is a setting you change in the sim's own weather menu. That is the specified behaviour; it has not yet been proven end to end in a running sim, so it carries an in-development mark until it has.

Does it conflict with other add-ons?

We have not tested them yet, so we are not going to publish a compatibility list. The one conflict we can state with certainty is with another weather engine: the in-sim weather listener is shared and the outcome is last writer wins. Run one at a time.

How many PCs, and can I move my licence?

Five machines per licence. Release a seat yourself from the Devices pane at any time — no cooldown, no support ticket. Reinstalling Windows, swapping an SSD or upgrading a GPU does not consume a new one, and a seat unseen for 45 days is reclaimed automatically.

Can I replay historical weather or build my own conditions by hand?

No, and not in v1. There is no reanalysis archive and no manual weather editor anywhere in the plan. If either is built it will appear on the roadmap before it appears in a feature list.

Who is building this, can I pre-order, and when does it release?

Downwind Studios. No pre-orders, no paid early access, and no release date — a free closed beta comes first, then launch. Support will be email plus a public issue tracker, because “injection stopped” needs to become a reproducible ticket with a log attached, not a message that scrolls away in a chat channel.