MSFS moves
the weather
in steps
AloftWX is what happens in between.
A Windows desktop app and a small MSFS 2024 package, linked over loopback on your own machine. It builds a layer stack from surface observations, terminal forecasts and model winds aloft, integrates toward it ten times a second under a ceiling on how fast each value is allowed to change, and writes to the simulator at most once a second — then reads the simulator’s own weather back out and compares it to what it asked for.
Slower than the real atmosphere, on purpose. A smooth wrong answer flies better than a correct discontinuity.
Surface wind — one step, and the chase
Illustrative geometry, not a capture. The shape is the claim: the commanded value is a staircase because observations arrive as discrete reports, and the written value is a curve because every change is bounded by a maximum rate. The gap between them is the product.
- Simulator
- MSFS 2024 — and only 2024
- Platform
- Windows x64
- Licence
- One-time · lifetime updates · 5 machines
- Price
- Announced at launch
- Release
- No date announced
A weather update is a cut, not a transition
What the simulator actually does
MSFS 2024’s live weather refreshes on its own schedule. When it does, the new state replaces the old one. Wind veers thirty degrees between one frame and the next; a layer appears at altitude with no approach to it; the altimeter setting jumps and the aircraft settles through it.
None of that is a bug. It is what “apply this weather now” means, and the simulator has no concept of getting there gradually. The atmosphere it hands you at any instant is defensible. The path between two of them is not.
The step you feel
An instantaneous wind change is an instantaneous change in relative airflow. The autopilot corrects, the aircraft yaws, and on approach it arrives as a lurch that has no meteorological cause.
The step you fly through
A layer that materialises rather than builds gives you no shear to anticipate and nothing to trim for. Turbulence modelling downstream of it inherits the discontinuity.
The step you cannot plan for
If the sky can change completely at an unannounced refresh, a briefing has no predictive value. The weather stops being something you fly and becomes something that happens to you.
Five stages, and a ceiling on every one of them
The loop below runs continuously while the simulator is up. Nothing in it is clever; the whole design is in the rate ceiling at stage three and the read-back at stage five.
Read the sources
METAR for surface conditions, TAF for where the terminal forecast is going, and model winds aloft for the layers above it. Each source is fetched on the schedule it is actually published on — polling a METAR every ten seconds does not make it newer.
Build one layer stack
The three inputs are reconciled into a single vertical profile: surface wind and pressure, temperature and dewpoint by altitude, cloud layers with bases and tops, and visibility. One coherent atmosphere, not three feeds fighting.
Integrate toward it
The engine does not jump to the new profile. It moves toward it a hundred times over ten seconds, and every quantity carries its own ceiling on how fast it may change — wind direction in degrees per second, pressure in hectopascals per second, and so on. That ceiling is the product.
Write to the simulator
The current integrated state is handed to the in-sim package once a second. Writing faster does not make the sky smoother — the integration is already continuous — it only spends frame time and risks the simulator coalescing the writes.
Read it back and verify
After each write the engine reads the simulator's own weather state back out and compares it against what it asked for. A write that did not land is logged as a write that did not land, not assumed to have worked.
Why the ceiling is the product
Any add-on can push a new weather state into the simulator. The difficult part is refusing to — holding a value back when the source data says it should already have changed, and accepting that the sky you are flying is a few seconds behind the sky that was reported. That lag is not a limitation being apologised for. It is the entire reason the aircraft stays flyable through a frontal passage.
Why the read-back matters
Weather injection is a request, not a command — the simulator can clamp a value, round it, or ignore it outright, and it does not report when it has. Reading the state back out after every write is the only way to know whether what you asked for is what is being flown. When the two disagree, the log says so.
What it drives, and what state each part is in
Surface wind and gust
BuiltDirection, speed and gust, rate-limited independently. Direction interpolates the short way around the compass, so a north-westerly backing through north does not sweep 340° the wrong way.
Pressure and temperature
BuiltQNH and MSL temperature from the nearest reporting station, with a temperature profile by altitude rather than a single surface value.
Cloud layers
BuiltBases, tops and coverage per layer, built from the observation and extended upward with model data. Layers fade in and out across their rate ceiling rather than appearing whole.
Winds aloft
BuiltA full vertical wind profile from model data, not a surface wind copied upward. This is the part a briefing is actually about.
Visibility and precipitation
PartialVisibility in metres and a precipitation rate, both rate-limited. Precipitation type follows the temperature profile rather than being set independently.
Write log and verification
BuiltEvery write, its echo read-back, and any disagreement between the two, timestamped and exportable. This is how a bug report against AloftWX gets written.
What it will not do, stated before you buy it
This section exists because the alternative is a support queue full of people who expected something the product never claimed. Every item here is either a constraint of the simulator or a decision we made on purpose.
- The sky is global, not localSimulator limit
- MSFS 2024 applies weather to the whole world at once. There is one atmosphere, and it is the one at your aircraft. Fly two hundred miles and the weather follows you rather than being waited for. No add-on can change this; it is how the simulator's weather system is built.
- MSFS 2024 onlyBy design
- Not MSFS 2020, not X-Plane, not P3D. The injection path AloftWX uses does not exist in 2020, and supporting a second simulator properly is a second product, not a checkbox.
- Windows onlyBy design
- The desktop app is Windows x64. There is no macOS or Linux build and none is planned, because the simulator it drives does not run there either.
- It runs alongside the sim, not inside itArchitecture
- A desktop application plus a small in-sim package, talking over loopback. If the desktop app is not running, the simulator's own weather is untouched — AloftWX is not a mod that changes files you would have to undo.
- Not a forecasting productScope
- AloftWX transports published meteorological data into the simulator smoothly. It does not model weather, generate weather, or improve on the sources. If the METAR is wrong, so is your sky.
- Real-time only, for nowNot built
- Historical weather replay and a scripted-scenario mode are both plausible and neither is built. They are not on a roadmap with dates because there is no release date to hang dates off.
One payment, five machines, no subscription
What the licence is
AloftWX is bought once. Updates are included for as long as the product exists, and there is no subscription, no seat renewal and no server that has to stay up for the software you paid for to keep working.
One licence activates on five machines, which you can release and reassign yourself — a rebuild, a new PC, or a laptop for the road should not require an email to support. Entitlement is checked once at startup and pinned for the life of the process, and it fails open on any server error: if our licensing service is down, your simulator session is not.
There is no price on this page because the price is not decided, and there are no pre-orders because taking money for an unshipped product with no date is not something we are willing to do.
Licence — as it stands today
- Model
- One-time purchase
- Updates
- Lifetime, included
- Machines
- 5 per licence
- Subscription
- None
- Price
- Announced at launch
- Trial
- Free closed beta first
Where the product actually is
“In development” is doing a lot of work on the rest of this page, so here is what it means. No percentages — a percentage on a software project is a guess wearing a number’s clothes.
| Subsystem | What it covers | State |
|---|---|---|
| Weather engine | Source ingest, layer-stack reconciliation, 10 Hz integration and per-quantity rate ceilings. The core loop runs. | Built |
| Simulator package | The in-sim half that receives state over loopback and applies it, plus the read-back that verifies each write landed. | Built |
| Licensing and entitlement | Validate once at startup and pin for the life of the process, fail open on any server error, five machines per licence with self-service release. Under test. | Built |
| Desktop application | The window you actually use: live state, the write log, source health and the rate-ceiling controls. Functional, not finished. | In progress |
| Installer and updates | Signed installer and a silent updater. The signing chain is solved; the packaging is not wired up end to end yet. | In progress |
| Closed beta | A small invited group, free, before any paid release. Not open, and not scheduled — it starts when the desktop app stops changing under it. | Not started |
There is no release date on this page. When there is one it will appear here first, and it will be a date we already believe rather than one we are aiming at.
The eight we are actually asked
- Does this replace the simulator's live weather?
- It drives it. MSFS 2024's own live weather is switched off and AloftWX becomes the thing setting the atmosphere, using the same published sources the simulator would have used — just applied continuously instead of in steps.
- What happens if AloftWX is not running?
- Nothing. The in-sim package sits idle and the simulator behaves exactly as it did before you installed anything. There is no file to restore and no setting to put back.
- Will it work with MSFS 2020?
- No, and it is not planned. The injection path AloftWX depends on does not exist in 2020. Supporting it would mean a materially different product built against a different mechanism.
- Does it work online, on VATSIM or IVAO?
- AloftWX sets your simulator's weather from real-world sources, which is what those networks assume you are flying. It does not talk to the networks and it is not a network client.
- Can I have different weather in different places?
- No. MSFS 2024 has one global atmosphere, so the weather at your aircraft is the weather everywhere. This is a simulator constraint, not an AloftWX one, and no add-on can work around it.
- How much will it cost?
- Not decided. It will be a one-time purchase with lifetime updates and five machines per licence, and the number will be published here before it is charged anywhere.
- Can I pre-order or reserve a beta place?
- No pre-orders. The closed beta is free and invited, and the way to be considered is to send an email — there is nothing to pay and nothing to reserve.
- What was this called before?
- ArcusWX. Same product, same people, same code — the name changed and the domain moved to aloftwx.com. Anything published under the old name still applies.
Two emails, and then nothing
There is no waitlist form on this page yet. Until there is, an email does the same job: say you want to hear about the closed beta and you will get exactly two messages — the beta invitation and the release notice. No newsletter, no partner mail, and the list is not shared with anyone.
What we would rather hear
If a claim on this page is wrong, or a limit is stated in a way that would still surprise you after reading it, say so. That correction is worth more to us now than a sale is later.