The Ins and Outs of Pilot Weather Reports

Pilot weather reports, more simply known as PIREPs, are those rare commodities that general aviation pilots yearn for during preflight planning or while en route using datalink weather. They are vital since they answer these basic questions: At what altitude will I likely encounter ice? What is the severity of those icing conditions? What is the severity of turbulence at my planned altitude? And the most frequently asked question: What altitude will I find the cloud tops?

Perhaps there’s a PIREP or two out there that might just fill the void and answer one or more of these basic questions.

It’s important to know that pilots are not the exclusive consumers of your reports. Meteorologists, air traffic controllers, dispatchers, briefers, and researchers are all extremely interested in your PIREPs. On a visit to the Aviation Weather Center (AWC) in Kansas City,

Missouri, nearly two decades ago, I asked one of the forecasters if PIREPs were important to him. He responded without hesitation, “Oh, god, yes!” as if his job depended on it. While he could continue to do his job without PIREPs, a forecaster can do his job better with more of them in the system.

Some meteorologists that issue terminal aerodrome forecasts (TAFs) examine the latest PIREPs before constructing their forecast. By far, the forecasters that depend on PIREPs the most are those located at the Center Weather Service Units (CWSUs) and those at the AWC. Let’s say an urgent pilot weather report from a Boeing 767 comes in for severe icing. An audible alarm will sound on the forecaster’s terminal at the AWC alerting them to the urgent report. They must click the alarm to silence it. AWC forecasters affectionately call this the “blue light special” since the alarm button turns that color.

Such a PIREP will likely trigger the AWC meteorologist to pick up their “bat phone” and start a conversation with a CWSU meteorologist. They put their heads together to determine if there’s a need for a SIGMET or perhaps just a simple center weather advisory (CWA). The goal is to avoid advisories that may conflict and create confusion for pilots, although it does happen from time to time, especially when the weather is rather extreme.

As such, SIGMET advisories for severe or extreme turbulence and severe icing literally live and die by PIREPs. An urgent PIREP (UUA) of severe icing or severe or extreme turbulence may trigger an AWC forecaster to issue a SIGMET based solely on the conditions reported by a single pilot or aircrew. In fact, if you read the SIGMET or CWA text carefully, you will likely notice it often says, “RPTD BY ACFT” or “RPTD BY B767,” which tells you the SIGMET was issued due to one or more PIREPs of severe conditions.

At the other extreme, the AWC forecaster may cancel a SIGMET because there are no longer reports of severe icing or turbulence in the area. It may just be mostly moderate reports. Again, the decision to let the SIGMET die or extend it largely comes from PIREPs.

There’s nothing inherently wrong with a forecaster issuing a SIGMET without pilots reporting severe conditions. However, many forecasters want to see “ground truth” before issuing one. This is because issuing a SIGMET for severe ice, for example, makes the area a no-fly zone for most GA aircraft. Your TBM 960 can no longer legally fly through this area since it is not certified for flight into severe icing conditions. The FAA will no doubt pull the SIGMET as evidence that you should have known better if you turn yourself into a flying popsicle and need assistance.

Your PIREPs are incorporated by weather guidance such as the Current Icing Product (CIP) and Graphical Turbulence Guidance (GTG) product found on aviationweather.gov. Both of these use PIREPs for icing and turbulence, respectively, to build the product’s analysis.

For example, a positive icing report helps CIP to increase the confidence there’s icing at the altitude reported by the pilot at the time the guidance is valid. Conversely, if the report is for negative icing, it might decrease the icing probability at that altitude.

But don’t try to fool the algorithm. If you were to report moderate ice in an area where the sky is obviously clear, it will be able to toss out your bogus report since it also relies on other observational data, such as satellite and surface observations (METARs). Sure, it’s unlikely any pilot would file a bogus report on purpose, but at times turbulence PIREPs are miscoded as reports for icing or the VOR identifier provided in the report for the location is miscoded (e.g., ODG instead of OGD).

If you are like me, you undoubtedly find it difficult to file a pilot weather report. This is especially true when flying in busy terminal airspace, where it often matters the most. Whether flying IFR or VFR with flight following, it’s a challenge.

First, you need to leave the frequency. That involves asking the controller permission to switch frequencies so you can make that call to flight service. Once you’ve received permission, then you have the chore of finding the correct frequency and hoping someone on the other end will answer. When the weather is challenging, expect to hear, “N1234B, you are number four, standby.”

Can you just give the controller your PIREP and skip the call to flight service? Sure, but the controller’s primary job is not to file your report—it is to separate IFR aircraft from other IFR or special VFR aircraft.

In other words, there’s no requirement for that controller to take your report and forward the details to flight service so the rest of the stakeholders in the aviation industry can take advantage of it. If you are reporting severe conditions, such as severe or extreme turbulence, severe ice, or low-level wind shear, the controller should be passing this along. However, in busy airspace, the controller may just say, “Thanks!” and that’s as far as it goes.

If you are lucky enough to have an internet connection in the cockpit, there are resources to file the report online. You may find that some of the heavyweight apps provide this service. There is one such portal on the aviationweather.gov website.

Just be aware that you have to create an account and then make direct contact to provide your name, airman’s certificate number, and specific affiliation (e.g., airline, flight school, government, military, etc.) for validation purposes. Once this validation is complete, you can sign in and file a report directly online. Those reports are appended with “AWCWEB” in the remarks like this one:

OVE UA /OV KCIC/TM 1515/FL260/TP B737/TB MOD/RM 180-260 AWC-WEB

However, to make the process even easier, download the Virga app (search for “Fly Virga” in the App Store or Google Play Store). This is a great option since it is fully integrated with the aviationweawther.gov PIREP portal. Visit www.flyvirga.com for more information. Note that you still must have a Wi-Fi or cellular connection to file the report.

When making a PIREP, be sure to be specific. Avoid general terms, such as “icing during the climb” or “turbulence during descent,” unless you specify the altitudes you experienced icing or turbulence in the climb or descent. This is critical since nobody knows what altitude you climbed to or descended from. Moreover, the CIP and GTG analyses depend on these specifics in order to utilize your report effectively.

Also, for turbulence reports, add details such as whether or not you were in or outside of the cloud boundary. This is to differentiate turbulence related to convection (i.e., cumuliform-type clouds) versus clear air turbulence.

How long is a PIREP useful? While it’s difficult to pick out a particular length of time, reports of icing conditions more than 75 minutes old are typically useless to a pilot and to the CIP algorithm. Not unlike thunderstorms, icing conditions and intensity can change rapidly in time and space. Precipitation and clouds come and go as the synoptic, or big weather picture, changes. Clouds become supercooled due to rapid cold-air advection, and other clouds become glaciated (all ice crystals) as temperatures fall below minus-20 degrees Celsius.

From an aging perspective, turbulence PIREPs have an even shorter shelf life than icing PIREPs. Turbulence is highly transitory. An eddy of air might be propagating to a lower altitude after a pilot encounters it. Twenty minutes later, the next pilot at that same altitude may not see any bumps since the cause of the turbulence is now at a lower altitude. Again, it’s hard to agree on a specific time, but after about 45 minutes an isolated report of severe turbulence is probably too old to trust.

According to 14 CFR § 91.183 (b), a pilot flying under IFR in controlled airspace must report “any unforecast weather conditions encountered” by radio to ATC. Given this broad-brush regulation, you should limit your report to any forecast errors strictly significant to aviation operations. Unless it is urgent, there’s no need to make a big deal out of it either.

For example, let’s say you depart an uncontrolled field that has a TAF issued, and the forecast suggests that ceilings will be 2,000 feet at the departure time. As you climb out, you penetrate the lowest cloud deck at 900 feet AGL—this is significant to aviation, and you should report it to ATC. “Cirrus 1WX, one thousand two hundred, climbing four thousand, ceiling niner hundred overcast” is all you need to say.

While ATC may make use of this report for its own purposes, it is highly unlikely it will assemble your report into an official PIREP. To be sure this is relayed to the rest of us inquiring pilots, take a moment to file that report with flight service when you have the time.

One of the comments I repeatedly hear from pilots is, “If I report icing, won’t I be admitting guilt if I’m piloting an aircraft not certified for flight into known icing conditions?” I’m not an attorney, however, I believe the answer is yes and no.

There was a similar concern from pilots when cockpit voice recorders (CVRs) were first introduced. Could the FAA use the recording against a pilot? The FAA said that wasn’t the intention, and CVRs were strictly added to improve safety of flight to learn why mistakes are made—not to bust the pilot during some random audit.

Similarly, there are no PIREP police waiting to nab you at the FBO in random fashion. Now, if you reported icing conditions and then had a hard landing that caused a prop strike due to a load of ice on the airframe, it’s likely the FAA will use your own PIREP against you.

Controllers are there to help you out of a bad situation. As always, confess to them that you are quickly becoming a flying popsicle. Be assertive with your request— tell them exactly what you need. For example, “1WX is in moderate icing and needs an immediate descent to four thousand.” If necessary, don’t hesitate to declare an emergency because doing so will likely get you priority handling.

Just remember that PIREPs are not just a private conversation between you and flight service. They are broadcast to the world. So, try to challenge yourself on each and every flight to file at least one PIREP.

So it doesn’t matter if the weather is extremely challenging or “oh-so boring.” Sometimes the best report is one that states smooth conditions and negative icing. There may be a pilot out there getting their back fillings jarred, and your report of glassy smooth conditions just 2,000 feet above them will help make their flight more enjoyable.

The hardworking folks at the AWC only complain when they don’t get enough PIREPs. So, let’s file those reports and not give them a reason to complain. I can tell you from firsthand experience, there’s nothing worse than a whiny meteorologist.

This column first appeared in the April 2024/Issue 947 of FLYING’s print edition.