The KASE Weather dashboard scores every flight risk at Aspen against the same data the airlines use: the METAR, a one-line weather report issued by the airport every hour. To a pilot, the METAR is second nature. To a passenger, it looks like alphabet soup.

This guide breaks down a real Aspen METAR field by field, in plain English. By the end, you will be able to look at a raw METAR and tell roughly whether your flight is in good shape.

What a METAR is and how often it updates

METAR is short for METeorological Aerodrome Report. It is the standard one-line weather report issued at airports worldwide. Aspen-Pitkin County Airport (KASE) issues a fresh METAR every hour, usually within a few minutes of the top of the hour. When conditions change quickly, the airport issues a SPECI (a special METAR) without waiting for the next scheduled time.

Each METAR is the source of truth for what the airlines are looking at when they decide whether to send a flight to Aspen. The KASE Weather dashboard parses every new METAR and scores it against the operational limits of the E175 jets that fly the route.

A real Aspen METAR, decoded

Here is what a typical Aspen METAR looks like on a winter day with light snow:

KASE 021653Z 33015G22KT 6SM -SN BKN040 OVC080 M03/M06 A3018

That looks like nonsense at first. But each piece has a fixed meaning. Reading left to right:

KASE: the station

KASE is the ICAO code for Aspen-Pitkin County Airport. The shorter FAA code is ASE. Both refer to the same airport in Aspen, Colorado. ICAO codes are used by airlines and weather services worldwide.

021653Z: the time stamp

This is when the report was issued, in three pieces:

  • 02 is the day of the month.
  • 1653 is the time in hours and minutes (16:53, or 4:53 PM).
  • Z means Zulu time, which is the same as UTC (Coordinated Universal Time).

Mountain Time is 6 or 7 hours behind UTC, depending on whether daylight saving time is active. So 16:53 Z is 9:53 or 10:53am in Aspen. The KASE Weather dashboard converts the time to Mountain Time automatically.

33015G22KT: the wind

Wind direction and speed:

  • 330 is the direction the wind is coming from, in degrees. (0 or 360 is north, 90 is east, 180 is south, 270 is west.) So 330 is from the northwest.
  • 15 is the steady wind speed in knots (about 17 mph).
  • G22 is the peak gust speed (22 knots, about 25 mph). The G piece only appears when there are gusts.
  • KT stands for knots (the unit).

If the wind direction is shifting around, you may see VRB instead of a number. If the wind is calm, you may see 00000KT.

At KASE, wind direction matters more than wind speed. The runway is fixed at 15/33, oriented from northwest to southeast, and every commercial flight lands on Runway 15. When the wind blows from the north, it becomes a direct tailwind on the landing direction, which is the main wind problem at the airport. For the full picture, see our Aspen winter weather patterns guide.

6SM: the visibility

Visibility is reported in statute miles (SM). 6SM means six statute miles. You may also see:

  • 10SM or P6SM: visibility is at or above the maximum reportable (10+ miles).
  • 1 1/2SM: one and a half miles.
  • 1/2SM: half a mile.

At KASE, 3 statute miles is the rough cutoff between landable and risky. Below 3 miles, flights start to hold or divert. The why Aspen flights get delayed post has the deeper explanation of why this number matters.

-SN: the weather phenomena (if any)

This is the "what is happening in the air" code. Each weather event has a letter pair:

  • RA rain
  • SN snow
  • DZ drizzle
  • FG fog
  • BR mist
  • HZ haze
  • TS thunderstorm
  • SH showers
  • FZ freezing (used as a prefix, so FZRA is freezing rain)

Intensity is shown with a prefix:

  • - light
  • (no prefix) moderate
  • + heavy

So -SN is light snow. +SHRA is heavy rain showers. FZRA is freezing rain (the worst kind for an airport). When skies are clear and dry, this field is missing entirely.

BKN040 OVC080: the clouds and ceiling

Cloud layers, from lowest to highest. Each entry has a coverage code and an altitude:

  • CLR or SKC: clear, no clouds
  • FEW: few clouds
  • SCT: scattered (about a quarter to half the sky)
  • BKN: broken (more than half the sky)
  • OVC: overcast (entire sky covered)

The three-digit number after each coverage code is the cloud altitude in hundreds of feet above ground. BKN040 means broken clouds at 4,000 feet. OVC080 means an overcast layer at 8,000 feet.

The ceiling is the altitude of the lowest broken or overcast layer. In this example, the ceiling is 4,000 feet. At KASE, a ceiling below 3,000 feet above ground is the rough cutoff for landable commercial operations. Below that, pilots cannot see the terrain they need for the approach.

M03/M06: temperature and dewpoint

Two two-digit numbers separated by a slash, both in degrees Celsius. The M prefix means minus. So:

  • M03/M06 = temperature -3°C, dewpoint -6°C.
  • 12/05 = temperature 12°C, dewpoint 5°C.
  • M03/M03 = temperature and dewpoint both -3°C, which means fog is likely.

The closer the temperature is to the dewpoint, the more likely fog will form. When they meet, fog is essentially guaranteed. At Aspen the temperature is often well below freezing in winter, which can also mean freezing fog (a quick way for ice to build up on an aircraft on the ground).

A3018: the altimeter setting

The A prefix is followed by four digits that represent inches of mercury (inHg). A3018 means 30.18 inHg. Standard sea-level pressure is about 29.92 inHg. This setting is mostly meaningful for pilots calibrating their altimeters. As a traveler, you can skip it.

How the dashboard turns this into a color

The KASE Weather dashboard reads each new METAR and scores three factors against E175 operating limits:

  • Visibility: 5+ statute miles is green, 3–5 is yellow, under 3 is red.
  • Ceiling: 5,000+ feet above ground is green, 3,000–5,000 is yellow, under 3,000 is red.
  • Wind: the dashboard calculates the crosswind and tailwind components on Runway 15 (the landing runway). Crosswind at or above 30 knots, or tailwind at or above 10 knots, is red. Lower values that still approach the limits are yellow.

Visibility and ceiling are weighted twice as heavily as wind in the overall risk score, because they drive cancellations at Aspen more reliably than wind does.

In the METAR above (6SM visibility, 4,000 ft ceiling, NW wind at 15 kt gusting 22), visibility is yellow (close to the 5SM threshold), ceiling is yellow (below 5,000 ft), and wind is green (the NW direction makes it mostly a crosswind on Runway 15, not a tailwind). Overall: moderate risk.

Three example METARs to practice on

A good day:

KASE 021753Z 35008KT 10SM CLR M01/M10 A3024

Wind from nearly due north at 8 knots, 10+ mile visibility, clear sky, temperature -1°C with dewpoint -10°C (well separated, no fog risk). The dashboard scores this all green. Flights run on time.

A marginal day:

KASE 021653Z 33015G22KT 6SM -SN BKN040 OVC080 M03/M06 A3018

Northwest wind 15 knots gusting 22, six mile visibility in light snow, ceiling at 4,000 feet, cold but not at dewpoint. The dashboard scores this yellow overall. There may be some delays on a day like this.

A bad day:

KASE 021453Z 36018G28KT 2SM SN BKN015 OVC025 M05/M07 A2998

North wind 18 knots gusting 28 (a direct tailwind on Runway 15), two mile visibility in moderate snow (below the 3SM limit), ceiling 1,500 feet (well below the 3,000 ft limit), temperature close to dewpoint. The dashboard scores this all red. Expect cancellations and diversions.

Where to find KASE METARs

Several sources publish METARs in real time:

  • The KASE Weather dashboard parses the latest METAR and scores it against E175 limits, in plain English. It refreshes automatically.
  • The NOAA Aviation Weather Center at aviationweather.gov publishes the raw METAR plus a TAF (the forecast version of a METAR).

The official update cadence is hourly, near the top of each hour. When conditions are changing fast, the airport issues a SPECI between scheduled times. The dashboard catches both.

The bottom line

A METAR is one line of weather data, but every airline dispatcher and pilot flying to Aspen reads it before launching the flight. Once you know what each piece means, you can do the same. The dashboard does the math for you, but reading the raw METAR yourself is the fastest way to develop an instinct for which kinds of days are going to be tough at Aspen.

For frequent travelers, KASE Weather Premium emails you when the METAR crosses from green into yellow or red, so you get warning before the airline sends a delay notice.

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