Weather

Weather Radar & SIGMETs

Two hours of precipitation radar you can scrub through, every active SIGMET, a warning of weather severe enough to matter to anyone flying, drawn as a hazard area you can filter by the level you will be at, the thunderstorms and pilot reports being filed around it, and the flight category each field is reporting right now. Click anywhere for the column of air over that point, from the ground to FL500. No live traffic: this is a weather map, and the aeroplanes are on their own one.

Loading the map

Radar frames, hazard areas and airfield reports arrive one after the other.

What the colours mean

Colour on the map always means weather. Airfield dots are sized by aerodrome class and never coloured by it, so nothing competes with the picture. The layer list beside the map says what each layer is, and with the radar on it names the band of echo that is not drawn at all. The keys below are the colours of everything else on the map.

Flight category, observed

VFR · Visibility more than 5 SM and no ceiling at or below 3,000 ft.
MVFR · Visibility 3 to 5 SM, or a ceiling of 1,000 to 3,000 ft.
IFR · Visibility 1 to under 3 SM, or a ceiling of 500 to under 1,000 ft.
LIFR · Visibility under 1 SM, or a ceiling under 500 ft.

Hazard areas

Thunderstorms and tropical cyclone
Volcanic ash
Turbulence and mountain wave
Icing
IFR conditions, mountains obscured and anything else

Drawn as hatched outlines rather than solid fills, so the radar underneath stays readable. The hatch angle and the dash of the outline differ by hazard family, so two families sharing a colour still separate.

Thunderstorm reports

Thunderstorm at the field, solid ring and bolt
Thunderstorm in the vicinity, dashed ring
Cumulonimbus reported, ring marked CB

Each one sits beside its airfield on a short leader, not on top of it, so the field stays visible and can still be opened.

Reading the map

The level filter asks the question a pilot asks first: does this affect me at my altitude. A SIGMET is a volume, and areas that publish no level are always kept on the map and labelled as such, because an unknown level is not the same as a level that does not apply.

Hazard areas and airfield reports are always current. Scrub the loop to a nowcast frame and they dim, because they were never part of that picture. The timeline says so on every frame.

Radar is full resolution to zoom 7 and upscaled beyond it, which the layer panel states where you can see it. Lower the radar opacity to read the coastline underneath.

The address bar carries the centre, zoom, layers, level band and open airfield, so a view can be sent to whoever you are flying with.

Where the data comes from

SIGMETs come from NOAA’s Aviation Weather Center, from both the international and the US domestic feed, so UK FIRs such as London and Scottish appear alongside the rest of the world. Movement is read from the numeric fields where the feed publishes them and from the report text where it does not, which is how the UK gets a vector at all.

G-AIRMETs are a United States product, so they are an optional layer rather than an always-on one: switch them on and you get turbulence, icing, IFR conditions, mountain obscuration, low-level wind shear and freezing-level contours, each with the flight levels it applies between. There is no equivalent outside the US, so for low-level hazards elsewhere use your national forecast, which in the UK is the Met Office F215.

Flight category and thunderstorm reports are what aerodromes are publishing in their own METARs, not a model and not a lightning-strike network. Radar comes from RainViewer, which composites national radar networks; the timeline shows the exact age of the frame you are looking at rather than asking you to assume one.

For training and reference only. Always use an approved briefing source for operational decisions.

The column over a point

Click anywhere on the map, including somewhere nothing has been reported, and the panel draws the air over that point from the ground to FL500. It is four things, and the chart is built so you can tell which of them somebody signed their name to.

Tropopause, dashed violet, with the temperature. Beside it is a whisker: the lowest and highest the tropopause gets within 300 nautical miles. A range wider than 8,000 feet gets a note, because that much variation over that distance is the signature of a fold rather than an ordinary slope. Narrower than that and nothing is said, so the note means something when it appears.
Freezing levels, from the model’s own temperatures rather than a lapse rate: 0 C solid, −20 C dashed, with the icing window shaded between them. Where an inversion produces more than one crossing, the one shown is the lowest, which is the one you meet first on the way up.
Turbulence, in two kinds that never share a treatment. A SIGMET over the point is a report, so it draws solid and at full strength and carries the forecaster’s own words. Shear worked out of the model’s winds draws faint and dashed and is labelled “forecast only, not a report” every single time. The index is only computed between 500 and 150 hPa, which is the band it was published for: run lower down it calls severe turbulence over any front or coastline, confidently and wrongly. Below that band the column is blank because nothing was computed there, which is not the same claim as smooth air.
Jet core, with its level, direction and speed, drawn only when the wind actually reaches jet strength rather than wherever the windiest level happens to be.

GFS 0.25 degree, from the most recent cycle published. The pin is rounded to half a degree, about 30 nautical miles, so moving around one region reuses one reading rather than asking for a new one per pixel. Anything that could not be read is named under the chart instead of being left as a gap.

How the list is ordered

With the feed set to most abnormal, the order is computed here and the arithmetic is published below so you can disagree with it. It is not a severity assessment and must not be read as one: a SIGMET says what a forecaster judged, and this only says which of them to look at first. Every row keeps the report behind it, unedited. Switch the control above the list to newest and none of this applies: the order is then simply when each report was issued.

A score is what the hazard is × how much sky it covers × how long it has left, multiplied rather than added, so something expiring or covering almost nothing falls down the list however severe its class.

Area counts up to 250,000 square nautical miles and stops there. Without a ceiling, one enormous oceanic advisory would own the page for ever, which is a statement about how FIRs are drawn rather than about the weather.
Time left counts up to 6 hours. Beyond that the distinction stops mattering to anyone planning today.
Volcanic ash and tropical cyclones are not scored on area at all. An ash cloud covers a thousandth of the ceiling and closes the airway anyway. Scoring them on size buried an erupting volcano beneath weather you can fly around, so they are scored on what they are and how long they last.
Reports of the same hazard within 250 nautical miles of each other are one outbreak for counting purposes: thirteen thunderstorm SIGMETs over one FIR are one thing happening, not thirteen.

Hazard	Worth	Why
Volcanic ash	10	closes airways outright and destroys engines; there is no flying through it at any level
Tropical cyclone	9	a named, tracked system with a forecast path
Thunderstorms	6	what actually brings aircraft down, with tops above most cruising levels
Turbulence	4	hurts, and is routinely avoidable by changing level
Icing	4	the same
Mountain wave	3	severe in the lee of mountains, local by nature
IFR conditions	2	an aerodrome condition rather than en-route air
Mountains obscured	2	the same

SIGMETs, AIRMETs and volcanic ash and tropical cyclone advisories from NOAA’s Aviation Weather Center. The ranking is computed by Pilotised for orientation and is not an official product. For information and training only: always brief from the official service for your area before you fly.