Flight weather

Weather forecast information is generated from the centroid of your project AOI — if necessary click a more appropriate location on the map to move the forecast point

Tiles © Esri

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About these readings

Moving the forecast point: The page opens on the project location passed in the link, shown as a green ring. Clicking the map moves the forecast to that spot — the red dot — and reloads everything below it. Drag to pan, scroll or use the buttons to zoom, and Reset returns to the project location. Useful when the project polygon is large enough that its centre is not where you will actually launch, or when you want to sample conditions at a ridge versus a valley floor. The NWS grid is about 2.5 km, so moves shorter than that will often return identical numbers.
Watches, warnings & advisories: Active National Weather Service alerts for the project coordinates, shown at the top when any are in force and omitted entirely when none are. A warning means the hazardous condition is occurring or imminent; a watch means conditions are favorable for it to develop; an advisory covers conditions that are inconvenient rather than dangerous. Colour follows that order — red, amber, blue. Alerts are polygon-based and issued for an area, so one can be in force across the county without affecting your specific site.
Wind & gust: The usual limiting factor. Gust matters more than sustained wind: a multirotor corrects continuously, and a gust that exceeds the aircraft's authority costs you position hold and battery at the same time. Reported at 10 m above ground — flow at altitude is normally stronger and less sheltered than the surface reading.
Temperature / dewpoint spread: The gap between air temperature and dewpoint, which is more useful than either number alone. A spread closing toward zero means the air is saturating: fog or low stratus is forming, and visibility can collapse quickly. A small spread near or below freezing also indicates icing potential. Highlighted at 4 °F or less.
Density altitude: The altitude the air feels like to a rotor, after correcting field elevation for pressure and temperature. High density altitude thins the air, so rotors generate less thrust: climb rate drops, payload margin shrinks, and endurance falls. On a hot afternoon at these elevations it commonly runs thousands of feet above the ground you are standing on, which is the failure mode that surprises pilots trained at lower elevation. Computed for the project site, not the reporting station. Highlighted when it exceeds site elevation by 2,000 ft or more.
Ceiling & maximum altitude: Ceiling is the lowest broken or overcast layer; scattered and few layers are not ceilings. Which cloud rule applies depends on how you are operating, and the badge beside the coordinates shows which set this page is using.
COA / part 91 (default). COA 2025-WSA-16323 authorizes Class G operations at or below 1,199 ft AGL. Under 14 CFR 91.155, Class G at or below 1,200 ft AGL by day requires 1 statute mile visibility and remaining clear of clouds, so the ceiling itself becomes the cap when it falls below 1,199 ft. Night minimums are higher.
Part 107. 400 ft AGL, 3 statute miles, and 500 ft below the clouds — add rule=107 to the URL to use these instead.
Either way the COA altitude applies in Class G only, and this page does not check which airspace the site sits in. Override the ceiling with the alt parameter.
Visibility: Threshold follows the rule set in force: 1 statute mile for daytime Class G under 91.155, 3 statute miles under 107.51. Highlighted below the applicable figure.
Weather minimums inside a TFR: The COA waives 91.155 only for operations conducted within a 91.137 TFR, where the incident or on-scene commander is responsible for airspace segregation and deconfliction between manned and unmanned aircraft. Outside a TFR the standard minimums above apply, and this page always displays the unwaived thresholds.
Low ceiling / visibility watch-out: Flags forecast hours where the ceiling or the visibility falls below the minimum for the rule set shown in the badge beside the coordinates — under the COA in Class G that is 1,199 ft AGL and 1 statute mile, under part 107 it is 900 ft and 3 miles. The cell reports whichever of the two is actually limiting. Restricted to the civil twilight window, because fog at 0300 does not affect a daylight operation; note that 91.155 night minimums are in fact higher, not lower, so this is an operating-window filter rather than a regulatory one. Raise either threshold for a planning buffer with the vis and cig URL parameters — setting vis=3 gives warning before you are at the legal floor.
Icing watch-out: Flags hours where the forecast temperature is at or below 35 °F with a temperature/dewpoint spread of 4 °F or less — freezing conditions plus enough moisture for ice to form on the airframe. Ice on rotors destroys lift and adds weight faster than most airframes can compensate, and small unmanned aircraft carry no anti-ice or de-ice equipment. The lower bound is −4 °F, below which the air generally holds too little moisture for meaningful accretion. The value shown is the coldest hour in the run.
Heavy precipitation watch-out: Flags a significant rain event in the forecast period, not a rain rate. The test is the total across every rolling 24-hour window: when any window reaches 0.50 in with at least a 50% probability of precipitation, the hours carrying that rain are flagged and split by day, so each cell shows how much falls that day and when. A slow-moving system is the reason it works this way — two inches spread across forty-eight hours never produces a large hourly rate, yet it is exactly the pattern that floods drainages and closes two-tracks. Short convective bursts are still caught, since a 24-hour window containing one also clears the threshold. The threshold is set for ground access rather than hydrology: in a region averaging about 14 in a year, half an inch in a day is a significant fraction of the annual total, and on bentonite soils it is more than enough to make two-tracks impassable. Adjust with the heavy and pop URL parameters. Note this looks forward only: rain that has already fallen never appears here.
Precipitation: Accumulation in the past hour at the reporting station. Most airframes are not rated for flight in precipitation, and water on the lens ends a mapping mission regardless of what the aircraft tolerates.
Kp index: Planetary geomagnetic activity, 0–9. Elevated Kp disturbs the ionosphere and degrades GNSS accuracy, which matters more for PPK and RTK survey work than for ordinary flight: it lengthens time to fix and can leave you with float rather than fixed solutions. Kp 5 and above is storm level and is highlighted. Below about 4 it is not worth thinking about.
Sun & lighting: Under the COA these times are a lighting trigger, not a hard stop. The Certificate of Waiver requires anti-collision lighting for civil twilight and night operations to increase the conspicuity of the aircraft, and the system must be operational at all times, day or night, unless operating in a TFR — the CoW waives 91.209(a)(1) only inside a TFR. A reminder appears here when the current time falls outside sunrise to sunset. Sun angle also drives shadow length: low-sun imagery produces long shadows and weaker tie points in photogrammetric processing. Computed from the site coordinates and today's date.
Weather cameras: Appears only when the popup passes a camera site in the URL. FAA WeatherCams give you a look at actual sky and surface conditions rather than a number, updated every ten minutes, with a clear-day reference image for comparison and a six-hour loop for trend. Montana is one of the earliest lower-48 states in the program, so coverage across the region is better than most. The nearest camera may still be well away from the project area — treat it as a regional look, the same as the station observations above.
Before you fly: Not weather, but on the same checklist. The COA requires a Distant (D) NOTAM not less than 24 hours and not more than 72 hours in advance of routine operations, cancelled when the operation is complete; first responder and prescribed fire operations may file as soon as practicable. Airport standoffs are 5 NM from a towered airport, 3 NM from an airport with a published instrument procedure, 2 NM otherwise, and 2 NM from a heliport. MTR and SUA deconfliction is the operator's responsibility.
Low temperature threshold: Set at 32 °F, freezing, because that is where the equipment gate actually sits: the X10 will not launch with a battery below 0 °C, and the Astro wants batteries above 10 °C at takeoff. Sun does little to close the gap — a grey case in full winter sun and still air gains only about 9 °F over ambient, so reaching the launch minimum by solar gain alone needs ambient near 23 °F, and any breeze erases most of that. Treat this row as notice that batteries need pre-warming and that endurance will be down, not as a no-fly call. It will fire on most winter mornings. Adjust with the cold URL parameter.
High temperature threshold: Set at 85 °F because the limiting factor is equipment, not crew comfort. A black battery left in still air under full sun runs roughly 40–60 °F above ambient at equilibrium, which puts it near the Astro's 50 °C (122 °F) ceiling somewhere between the low seventies and ninety, centred around eighty — so the threshold sits at the lower edge of that band rather than above it. The thermal time constant is around twenty minutes, so brief exposure is harmless and a full mission's worth is not. Shade spare batteries rather than trusting the ambient reading. Adjust with the heat URL parameter.
Forecast sections: Watch-outs and the day/night outlook come from the National Weather Service gridded forecast for the project coordinates. Current conditions come from the nearest station that is reporting, which may be a considerable distance and elevation away.