Aspen Airport TAF Forecast Explained for Travelers

A METAR tells you what the weather at Aspen is doing right now. But your flight is hours away, and what matters is what the weather will be doing when you are on final approach. That forecast is the TAF, and it is the single document airline dispatchers lean on hardest when they decide whether to launch a flight to Aspen.

This guide explains what a TAF is, how to read one for Aspen-Pitkin County Airport (KASE), and how the KASE Weather dashboard turns it into the hourly forecast you see on the home page. If you have read our guide to reading a METAR, this is the natural next step. The two reports use almost the same shorthand.

What a TAF is and how it differs from a METAR

TAF is short for Terminal Aerodrome Forecast. Where a METAR is an observation of current conditions, a TAF is a prediction of future conditions in the airspace around an airport. Think of the METAR as a photo and the TAF as the weekend forecast.

A TAF covers a five-mile radius around the airport and looks ahead a fixed number of hours. It uses the same field-by-field codes as a METAR (wind, visibility, weather, clouds), so once you can read one, you can mostly read the other. The big difference is that a TAF is broken into time periods, because the forecaster expects conditions to change over the day.

For Aspen, the TAF matters more than the METAR for trip planning. A clear METAR at 6:00am tells you nothing about the afternoon north winds or evening snow that actually cause the day's delays and cancellations. The TAF is where those expected changes show up hours in advance.

How often the TAF updates and how far ahead it looks

The National Weather Service issues a routine TAF for Aspen four times a day, at 0000, 0600, 1200, and 1800 Zulu time (UTC). Each Aspen TAF is valid for the next 24 hours. When the forecast changes significantly between scheduled issues, the office puts out an amended TAF (marked TAF AMD) rather than waiting for the next slot.

That 24-hour window is the key planning horizon. If your flight is tomorrow afternoon, the TAF issued this morning already covers it. As your departure gets closer, each new TAF sharpens the picture, which is why the forecast for a flight 20 hours out is less trustworthy than the one issued 6 hours out.

A real Aspen TAF, decoded

Here is what a typical winter TAF for Aspen looks like. It is longer than a METAR because it covers a whole day in pieces:

TAF KASE 021130Z 0212/0312 32006KT P6SM SCT080
     FM021800 35010G18KT 5SM -SN BKN050
     FM030000 36015G25KT 2SM SN OVC020
     FM030600 33008KT P6SM SCT060

Each piece has a fixed meaning. Reading the header first, then each time period:

TAF KASE 021130Z: the header

TAF says this is a forecast, not an observation.
KASE is the ICAO code for Aspen-Pitkin County Airport (the FAA short code is ASE).
021130Z is when the forecast was issued: the 2nd of the month at 11:30 Zulu (UTC).

0212/0312: the valid period

This is the window the forecast covers, written as two day-and-hour stamps. 0212 means the 2nd at 12:00 Z, and 0312 means the 3rd at 12:00 Z. So this TAF is good for 24 hours, from noon Zulu one day to noon Zulu the next. Mountain Time runs 6 or 7 hours behind UTC, so in winter that is roughly 5:00am one day to 5:00am the next, Aspen time.

The base period: 32006KT P6SM SCT080

The first line after the valid period describes conditions at the start of the window. These are the same codes a METAR uses:

32006KT: wind from 320 degrees (northwest) at 6 knots.
P6SM: visibility greater than 6 statute miles. A TAF maxes out at P6SM ("plus 6"), where a METAR can report up to 10SM. Both just mean "clear and far."
SCT080: scattered clouds at 8,000 feet above the ground.

Light wind, great visibility, high clouds. A calm start to the day.

FM021800: the first change

FM stands for "from." It marks a new period that replaces everything before it, starting at the listed time. FM021800 means a change starting the 2nd at 18:00 Z (around 11:00am Mountain Time in winter).

35010G18KT 5SM -SN BKN050 reads as: wind from 350 degrees at 10 knots, gusting to 18, visibility down to 5 miles in light snow, with a broken cloud layer at 5,000 feet. Conditions are starting to slide.

FM030000: the rough patch

FM030000 starts the 3rd at 00:00 Z (around 5:00pm Mountain Time). This is the period that should get your attention:

36015G25KT 2SM SN OVC020 reads as: wind from 360 degrees (due north) at 15 knots, gusting to 25, visibility down to 2 miles in steady snow, overcast at 2,000 feet. The north wind matters at Aspen. Every commercial flight lands on Runway 15, and a north wind becomes a direct tailwind on that approach, which is the airport's most common wind problem. Pair that tailwind with 2-mile visibility and a 2,000-foot ceiling and you have a forecast for holds, diversions, and cancellations. For why the runway direction drives so much of this, see our Aspen winter weather patterns guide.

FM030600: the clearing

FM030600 starts the 3rd at 06:00 Z (around 11:00pm Mountain Time). 33008KT P6SM SCT060 means the wind backs to the northwest at 8 knots, visibility opens back up beyond 6 miles, and the clouds lift to scattered at 6,000 feet. The system has moved through and conditions recover overnight.

The change groups: FM, TEMPO, BECMG, and PROB

The example above only uses FM groups, but a TAF has a few other ways to describe change. You will see these in busier forecasts:

FM (from): a lasting change that starts at a specific time and replaces the previous conditions. The cleanest kind of change.
TEMPO (temporary): short-lived fluctuations expected to come and go, each lasting under an hour, within the listed window. Think a passing snow shower that drops visibility for 20 minutes.
BECMG (becoming): a gradual change that settles in over a span of time, rather than flipping at one moment.
PROB30 or PROB40 (probability): a 30 or 40 percent chance of the conditions that follow. Forecasters use this when a disruptive event is possible but not likely enough to commit to.

For a traveler, the takeaway is simple. An FM line is the forecaster's best single guess for that block of time. A TEMPO or PROB line is a heads-up that the day could get worse than the main forecast suggests, which is exactly the uncertainty a dispatcher weighs when deciding whether to carry extra fuel or delay a departure.

How the dashboard turns the TAF into an hourly forecast

Reading a raw TAF is a skill, but you do not have to. The KASE Weather dashboard fetches the latest Aspen TAF, breaks each forecast period into hourly slots, and scores every hour the same way it scores a live METAR. The result is the color-coded "KASE Local Forecast" strip on the home page: a row of green, yellow, and red bars, one per hour, that you can tap for the underlying numbers.

The scoring uses the same thresholds the dashboard applies to current conditions:

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 on Runway 15. Tailwind at or above 10 knots, or crosswind at or above 30 knots, is red. Values that approach those limits are yellow.

Run our decoded TAF through that logic and you get a clear story: green through the calm morning, yellow as the light snow arrives late morning, red through the evening when the north wind, low visibility, and low ceiling stack up together, then back to green overnight. The same colors the airlines are effectively working from, without the alphabet soup. For why visibility and ceiling carry more weight than wind in that score, see why Aspen flights get delayed.

What a TAF can and cannot tell you

A TAF is a forecast, so it comes with the usual limits of any forecast. Worth keeping in mind:

It is a five-mile picture, not a route forecast. The TAF describes the airport area, not the mountain passes the flight crosses on the way in. A clean Aspen TAF can still pair with a rough ride en route.
Closer is better. The forecast for a time 20 hours out is a rougher guess than the one issued 6 hours out. Check again the morning of your flight.
Amendments happen. When the forecast shifts, the office issues a TAF AMD. The dashboard always pulls the newest one, so a refresh gives you the current version.
It does not know your airline's decision. The TAF describes weather. Whether a specific flight delays, diverts, or cancels is a separate call the dispatcher makes using the TAF plus fuel, crew, and curfew limits.

The bottom line

If the METAR answers "what is the weather doing now," the TAF answers "what will it be doing when I land." For a destination as weather-sensitive as Aspen, that second question is the one that decides your trip. Learning to spot a north wind, a dropping ceiling, or a snow period a few hours out in the TAF is the fastest way to know a tough day is coming before the airline sends the delay notice.

The dashboard reads the TAF for you and lays it out hour by hour, so you can see the day's risk at a glance. It also now blends the TAF with hub weather, FAA ground stops, and more; see how the new v2 risk model works. For frequent Aspen travelers, KASE Weather Premium watches the forecast and emails you when an upcoming hour crosses into yellow or red, so the warning reaches you before your plans are already in trouble.