Answer: The short answer is no. Echo top height is a volume product that originates from the NWS WSR-88D NEXRAD Doppler radars.

This is the same network of radars that is used to build the familiar radar mosaic pilots readily use in the cockpit. While not provided in the FIS-B broadcast, the echo top height product, however, is arguably the most misused data that is broadcast by SiriusXM to your satellite-based weather receiver.

Despite what many pilots are taught, this product does not represent the height of the cloud tops and should never be used as such since it is often likely to produce unreliable and inconsistent results.

When looking at any ground-based radar depiction, the colors you see are mapped to a quantity in decibels of Z, often abbreviated dBZ, where Z is the reflectivity parameter. As the name implies, reflectivity is the amount of energy that is returned (reflected) back to the receiver after hitting a target.

For precipitation, these targets are called hydrometeors that include rain, snow, ice pellets, and hail. There are a few exceptions, but generally speaking, the higher the dBZ value, the heavier the precipitation.

All deep, moist convection or thunderstorms have both a cloud top (the highest point of the cloud as measured from sea level) and top of the precipitation core within the convection. The “top” of the precipitation core is defined as the msl height of the highest radar reflectivity of 18 dBZ. This altitude is referred to as the echo top height.   

For example, imagine taking a vertical “slice” through a typical thunderstorm, such as the one shown above. The white dashed line shows the west-to-east slice with the echo top height shown on the left and the base reflectivity from the lowest elevation angle shown on the right. The radar depiction on the right is the view most familiar to a pilot.

However, to better illustrate how the echo tops are determined, the depiction below is this same slice from above that is shown as a vertical cross section of the radar reflectivity. In other words, it depicts all possible elevation angles from the radar’s volume scan through this slice.

The colors are the reflectivity values in dBZ. The highest values shown in the precipitation core are about 55-60 dBZ and are all below about 7 kilometers (about 23,000 feet). As height increases in the core, notice the values drop off to less than 15 dBZ.

By connecting the points where the values in the core drop off to the 18 dBZ value, this represents the echo top height (shown by the white squiggly line). For this cell, the highest point in this cross-section is 17 kilometers or roughly 56,000 feet msl.

Cloud top height, on the other hand, is higher than the echo top height. In fact, it can be 5,000 to 10,000 feet higher in some of the most intense storms.

The visible satellite image below is a good example of thunderstorms with overshooting tops. Given the time of day, the highest tops actually cast a shadow on the thunderstorm anvil. This is the column of air in the thunderstorm that will usually have the highest echo tops due to the vigorous updraft. 

Echo top heights are specifically used by forecasters to identify the most significant storms by locating the highest echo regions. Stronger updrafts are seen in regions where the highest echo tops are located.

Moreover, the parameter that has the highest apparent correlation with lightning is not the highest cloud top but rather the highest detected radar echo top of 30 dBZ or greater.

Shown above is the SiriusXM composite radar mosaic shown with the Garmin Pilot app. In addition to the radar reflectivity, storm cell identification tracking (SCIT) markers are shown.

These attempt to identify the movement and echo top height of various cells in the radar mosaic. The height provided is measured in hundreds of feet. If there’s an arrow, this defines the direction of movement, and the end of the arrow represents where the cell might be located in the next 60 minutes given its current speed and direction of movement.  

Lastly, this may seem obvious, but echo tops are not going to help identify the vertical extent of many weather systems unless those clouds are producing some kind of precipitation in the form of rain, snow, hail, or ice pellets.

Therefore, a stratus deck, even one that has some depth, won’t likely be picked up by the radar. In fact, it’s not likely you will see echo tops shown below 20,000 feet because of this. Echo tops are more appropriate for convective precipitation where the clouds have significant vertical depth.  

The post What Are Echo Tops? appeared first on FLYING Magazine.

Answer: You’re in luck. The paper student pilot certificate was issued by the aviation medical examiner (AME) and not done through IACRA as we know it, so it is doubtful the learner already has an IACRA account.

• READ MORE: Is There an Official Weather Briefing

All you have to do is sit down with the learner and create a new application. Simply follow the prompts and fill out the application. In a few weeks he will get a plastic student pilot certificate in the mail.

Also, don’t forget to also verify the learner’s citizenship and give him a TSA endorsement, which have become requirements since 2002.

Do you have a question about aviation that’s been bugging you? Ask us anything you’ve ever wanted to know about aviation. Our experts in general aviation, flight training, aircraft, avionics, and more may attempt to answer your question in a future article.

The post How Do You Obtain a Student Pilot Certificate After a Break in Training? appeared first on FLYING Magazine.

• READ MORE: What Is the Rudder Used for in Flying?

Answer: According to an FAA spokesperson:  “Generally speaking, the FAA will accept [a pilot’s] last airman certificate application (Form 8710-1) or what they reported on their last medical application (Form 8500-8).” You should have access to at least one of those documents.

Pro tip: Moving forward, you may want to invest in an electronic logbook and save the information to the cloud, or at least record a digital image of each page of the paper logbook when you fill it up. If you rent aircraft, sometimes you can re-create your experience by cross-referencing your receipts. 

• READ MORE: Is There an Official Weather Briefing?

Do you have a question about aviation that’s been bugging you? Ask us anything you’ve ever wanted to know about aviation. Our experts in general aviation, flight training, aircraft, avionics, and more may attempt to answer your question in a future article.

The post What to Do When You Lose Your Logbook appeared first on FLYING Magazine.

Answer: Rudder controls the side-to-side motion of the nose of the airplane—the technical term for this is yaw.

To make the airplane turn (bank), the pilot moves the yoke or stick in the direction they want to turn. This activates the ailerons, which are the outboard, moveable panels on the wings.

The downward-deflected panel is on the outside of the turn, and as the downward deflection increases the surface area of the wing, it generates more lift. The aircraft nose yaws toward the side with the wing generating more lift. From the pilot’s perspective, that yaw is in the opposite direction of the turn. As this turn is opposite to the direction of the turn the pilot wants, the technical term for this is adverse yaw. 

In the airplane, banking without using the rudders feels a little bit like someone pulling you sideways by the seat of your pants. It is poor airmanship as it results in an uncoordinated turn.

In an aircraft with a turn coordinator or slip skid indicator (the instrument that has a tube and ball in it that acts in response to lateral motion), note that if the airplane is banked only with aileron, the ball will be to the outside of the turn. To correct this, the pilot steps on the rudder on the same side the ball is deflecting to. This corrects the adverse yaw.  “Step on the ball” is the phrase you often hear. When flying an aircraft with a glass panel that has a triangle with a lateral moving base, the phrase “step on the line” is used.

The rudder controls the adverse yaw, and when correctly applied results in a coordinated (smoother) turn.

For more information refer to the Pilot’s Handbook of Aeronautical Knowledge (available on the FAA website or at brick-and-mortar stores) in Chapter 6, Flight Controls.

The post What Is the Rudder Used for in Flying? appeared first on FLYING Magazine.

Answer: It depends on your mission and how many Ben Franklins you have to spare. Your sferics (short for radio atmospherics) equipment may represent the only real-time weather you’ll ever see in your cockpit.

Sure, panel-mounted and portable weather systems deliver their product in a timely fashion, but it will never be as immediate as your sferics device. Once you understand how to interpret your real-time lightning guidance, it can become a valuable asset in your in-flight aviation toolkit. 

Choices in the Cockpit

You have two options if you want lightning data in the cockpit: You can choose from ground-based lightning sensors or onboard lightning detection from a sferics device such as a Stormscope.

A Stormscope provides real-time data but does require some basic interpretation. Ground-based lightning, on the other hand, is a bit delayed and is only available through a data link broadcast at this time. Ground-based lightning is normally coupled with other weather guidance, such as ground-based weather radar (NEXRAD), surface observations, pilot weather reports, and other forecasts.   

Ground-Based Lightning

The ground-based lightning that’s now available through the Flight Information System-Broadcast (FIS-B) comes from the National Lightning Detection Network (NLDN). This network of lightning detectors has a margin of error of 150 meters for locating a cloud-to-ground strike. The ground-based lightning sensors instantly detect the electromagnetic signals given off when lightning strikes the earth’s surface.    

With 150-meter accuracy, I’d choose ground-based lightning any day. Don’t get too excited, though. Ground-based lightning is expensive (the data is owned by private companies like Vaisala), and you’ll not likely see a high-resolution product in your cockpit anytime soon.

SiriusXM satellite weather pulls from a different lightning detection network and includes both cloud-to-ground and intracloud lightning. It produces a 0.5 nm horizontal resolution lightning product. This means that you will see a lightning bolt or other symbol arranged on your display in a 0.5 nm grid.

Even if 50 strikes were detected minutes apart near a grid point, only one symbol will be displayed for that grid point. Same is true for the FIS-B lightning.

Stormscope Advantages

A Stormscope must be viewed as a gross vectoring aid. You cannot expect to use it like onboard radar.

Nevertheless, it does alert you to thunderstorm activity and will provide you with the ability to see the truly ugly parts of a thunderstorm.  Where there’s lightning, you can also guarantee moderate or greater turbulence.   

No lightning detection equipment shows every strike, but the Stormscope will show most cloud-to-ground and intracloud strikes. This allows you to see the intensity and concentration of the strikes within a cell or line of cells with a refresh rate of two seconds. It also lets you see intracloud electrical activity that may be present in towering cumulus clouds even when no rain may be falling.

Even if no cloud-to-ground strikes are present, intracloud strikes may be present. The Stormscope can detect any strike that has some vertical component (most strikes do). This is important since there are typically more intracloud strikes than cloud-to-ground strikes.

To emphasize this point, most of the storms in the Central Plains have 10 times more intracloud strikes than cloud-to-ground strikes. Moreover, during the initial development of a thunderstorm, and in some severe storms, intracloud lightning may dominate the spectrum. 

Also keep in mind that a sferics device does not suffer from attenuation like onboard radar. That is, it can “see” the storm behind the storm to paint cells in the distance out to 200 nm, but it does not see precipitation or clouds.     

Stormscope Disadvantages

It doesn’t take a full-fledged storm, complete with lightning, to get your attention.

Intense precipitation alone is a good indicator of a strong updraft (or downdraft) and the potential for moderate to severe turbulence in the cloud. Consequently, the Stormscope does not tell you anything about the presence or intensity of precipitation or the absence of turbulence.

Never use the Stormscope as a tactical device to penetrate a line of thunderstorm cells. Visible gaps in the cells depicted on the Stormscope may fill in rapidly. Fly high and always stay visual and you will normally stay out of any serious turbulence.        

A Stormscope display is often difficult to interpret by a novice. Radial spread, splattering, buried cables, and seemingly random “clear air” strikes can create a challenge for the pilot. It may take a couple years of experience to be completely comfortable interpreting the Stormscope display. Often what you see out of your window will confirm what you see on your display.    

Radial Spread

As the name suggests, the biggest Stormscope error is the distance calculation along the radial from the aircraft.

The placement of the strike azimuthally is pretty accurate. However, how far to place the strike from the aircraft along the detected radial is a bit more complicated and prone to error.

Lightning strikes are not all made equally. When the sferics devices were invented back in the mid-1970s, they measured the distance of the cloud-to-ground strike based on the strength of the signal (amperage) generated by the strike. An average strike signature of 19,000 amperes is used to determine the approximate distance of the strike.

Statistically, 98 percent of the return strokes have a peak current between 7,000 and 28,000 amperes. That creates the potential for error in the distance calculation. This error is a useful approximation, however, in that strokes of stronger intensity appear closer and strokes of weaker intensity appear farther away. 

In strike mode on the Stormscope, strikes are displayed based on a specific strike signature, whereas cell mode on the newer Stormscope models uses a clustering algorithm that attempts to organize these strikes around a single location or cell.

Cell mode will even remove strikes that are not part of a mature cell. Most thunderstorm outbreaks are a result of a line of storms. Cell mode provides a more accurate representation to the extent of the line of thunderstorms.

Radial spread is not necessarily always a bad thing. You can use it to your advantage to distinguish between false or clear air strikes and a real thunderstorm. Most of the strikes of a real storm will be of the typical strike signature and be placed appropriately.

As mentioned above, stronger than average strikes will be painted closer to the airplane. Looking at this in strike mode, a line of these stronger strikes will protrude toward the aircraft.  The result is a stingray-looking appearance to the strikes.    

You can confirm this by clearing the display.  The same stingray pattern should reappear with the tail protruding once again toward the airplane.

Clear Frequently

Clearing the Stormscope display frequently is a must.  How quickly the display “snaps back” will provide you with an indication of the intensity of the storm or line of storms.

You should be sure to give these storms an extra-wide berth.  Clearing the Stormscope in “clear air” will also remove any false strikes that may be displayed allowing you to focus on real cells that may be building in the distance.

Aging

Both ground-based and onboard lightning use a specific symbol to indicate the age of the data.

For Stormscope data shown on the Garmin 430/530, a lightning symbol is displayed for the most recent strikes (first six seconds the symbol is bolded). The symbol changes to a large plus  sign after one minute followed by a small plus  sign for strikes that are at least two minutes old. Finally, it is removed from the display after the strike is three minutes old.

Cells with lots of recent strikes will often contain the most severe updrafts and may not have much of a ground-based radar signature. Cells with lots of older strikes signify steady-state rainfall reaching the surface that may include significant downdrafts. 

Flight Strategy

A nice feature of a Stormscope is that you can quickly assess the convective picture out to 200 nm while still safely on the ground. Same is true for lightning received from the SiriusXM datalink broadcast.

However, for those with lightning from FIS-B, you won’t receive a broadcast until you are well above traffic pattern altitude unless your departure airport has an ADS-B tower on the field.  

As soon as your Stormscope is turned on, within a few minutes you’ll get a pretty good picture of the challenging weather ahead. If you are flying IFR, you may want to negotiate your clearance or initial headings with ATC to steer clear of the areas you are painting on your display. I’ve canceled or delayed a few flights based strictly on the initial Stormscope picture while I was still on the ramp. 

Another goal is to fly as high as allowable. You will benefit from being able to get above the haze layer, and the higher altitude will allow you to see the larger buildups and towering cumulus from a greater distance.

If you are flying IFR and you are continually asking for more than 30 degrees of heading change to get around small cells or significant buildups, then you should call it quits. You are too close, or you are making decisions too late.

Visual or not, the goal is to keep the strikes (in cell mode) out of the 25-mile-range ring on your Stormscope. If one or two strikes pop into this area, don’t worry. Just keep most of the strikes outside of this 25-mile ring.      

Don’t discount the value of a sferics device.  Add one of the data link cockpit weather solutions as a compliment, and you will have a great set of tools to steer clear of convective weather all year long.

The post Is Sferics Equipment Still Needed in the Cockpit? appeared first on FLYING Magazine.

Answer: In general aviation, one of the most cumbersome things to do while in flight is to file a pilot weather report, more commonly known as a PIREP. This has created the unfortunate situation that on any given day 98 percent of the PIREPs in the system are typically describing weather conditions at or above 18,000 feet.

It wasn’t all that long ago that the Enroute Flight Advisory Service (EFAS) was available primarily for pilots to receive weather updates while they were flying to their destination. More importantly, EFAS was the main outlet to file a PIREP such that it was guaranteed to be input into the system and become available for other pilots to see. This service was also called Flight Watch.

Given that EFAS was organized by Air Route Traffic Control Centers (ARTCC), you simply put 122.0 MHz into your radio, keyed the mic, and referenced them by a particular center’s airspace you were located within. For example, if you were in the Jacksonville Center’s airspace in Florida, your initial call might have been, “Jacksonville Flight Watch, Skyhawk One Two Three Whiskey X-ray, 30 miles southwest of the Brunswick V-O-R at five thousand five hundred.” Then as long as you were more than 5,000 feet above the ground, someone from Flight Watch came on the frequency, and you engaged in a two-way conversation to file your PIREP.

• READ MORE: The Ins and Outs of Pilot Weather Reports

However, EFAS was terminated on October 1, 2015. This now leaves the arduous task of finding the right Flight Service Station (FSS) frequency, making contact, and hoping someone on the other end responds to your call. The frequency you use to transmit and receive is dependent on your location. Pull out your VFR sectional (paper or electronic version), find the nearest VOR to your location, and look for the frequency located on the top of the VOR information box.

Of course, the correct frequency to use may also be available through your avionics or one of the many heavyweight electronic flight bag apps.

This is the frequency you will use to transmit and receive. Below the box is the name of the particular FSS to use in your initial call. For example, if you are near the Brunswick VORTAC in Georgia, your initial call may be, “Macon Radio, Skyhawk One Two Three Whiskey X-ray, transmitting and receiving on 122.2, over.” This is the easy case.

• READ MORE: How to Wrap Your Head Around Weather

If there’s an “R” shown at the end of the frequency (e.g., 122.1R), then that means FSS will receive on this frequency and you will transmit on this frequency. And you’ll need to be sure you listen for its response over the VOR frequency. Make sure your volume is turned up and not muted on your VOR radio.

This column first appeared in the May 2024/Issue 948 of FLYING’s print edition.

The post How Do I File a Pilot Weather Report Online? appeared first on FLYING Magazine.

Answer: According to the FAA, aircraft used by Part 141 pilot schools must be maintained under the same requirements as aircraft operated under Part 91. FAA regulations allow someone who does not hold a mechanic or repairman certificate to perform certain preventive maintenance under Part 91.

• READ MORE: Is There an Official Weather Briefing?

The regulation you are referring to applies to a certificated pilot. That is a private pilot, sport pilot, or higher—a student pilot is not a certificated pilot, therefore the student pilot doing preventative maintenance on an aircraft would not be permitted. In addition, 14 CFR Part 43 notes that maintenance can only be done when the aircraft is not used under 14 CFR Part 121, 127, 129, or 135. If the flight school also uses the airplanes for charter operations (Part 135), that’s another reason you cannot touch them.

The post Can Student Pilots Perform Preventative Maintenance on Aircraft? appeared first on FLYING Magazine.

I have been using 1800WXBRIEF.com and Aviation Weather Center for years since they don’t require a paid subscription. But according to the CFIs at the school I just started flying with, these are not considered legal weather briefings. 

Answer: The question asked begs another one: Legal to whom? 

FAA regulations, notably FAR 91.103, require pilots to obtain weather reports and forecasts. However, according to an FAA spokesperson, “the FAA does not prefer one weather source over another, nor do we define a ‘legal weather briefing.’ It is up to the pilot in command (PIC) to use a weather source that best suits their needs and allows them to meet the preflight planning requirements.“

That being said, there are some CFIs and flight schools that advocate paid subscriptions, such as ForeFlight, and free discreet login services, such as 1800WXBRIEF, because in addition to providing information, they also allow the pilot to file a flight plan. They also require an account, which means it’s easier to prove the pilot obtained a weather briefing prior to the flight because there will be a record of the login.

The latter is often one of the first things the National Transportation Safety Board checks when it investigates an accident or incident.

At the very least, a pilot should check TAFs, METARs, winds aloft, and NOTAMs prior to a flight. It is distressing how many pilots and pilots in training believe that listening to the ATIS/ASOS/AWOS at the airport or along their route constitutes a weather briefing. They don’t. 

Nor does looking out the window at the FBO. Any more than “pretty good” is a PIREP. 

The post Is There an Official Weather Briefing? appeared first on FLYING Magazine.

Answer: You have just described knowing the top of descent—that is, knowing how much time and distance it will take you to reach the predetermined altitude, such as the pattern.

• READ MORE: What Is an Outflow Boundary Shown on a Surface Analysis Chart? 

There are two basic means to do this.

First, determine how much altitude you need to lose. Let’s say you are at 3,500 feet and the traffic pattern altitude (TPA) is 1,000 feet. 3,500 – 1,000 = 2,500, so you need to lose 2,500. If you are descending at 500 feet per minute, 2,500/5 = 5 minutes to get to TPA.

Next, determine distance for descent. Take your current altitude: 3,500 feet. Subtract the traffic pattern altitude of 1,000 feet = 2,500. Multiply the altitude to lose by 3, so 3 x 2,500 = 7,500.  Divide this by 1,000 and get the approximately distance to the airport  = 7,500/1,000 = 7.5 miles.

• READ MORE: Should I File an Initial Approach Fix?

Looking at the VFR sectional, put a mark that is at the distance from the airport, especially if it is over a landmark like a lake, fairgrounds, etc., or if using GPS, refer to that. You can adjust your rate of descent if you are coming down too quickly when you have the distance in mind. 

Make a point to practice this. You don’t want to be that pilot who flies pattern altitude (or accidentally lower) miles from the airport, nor do you want to be the pilot who forgets to start a descent and dives into the pattern. But don’t worry. We have not had an aircraft stay stuck up there yet.

The post How Do You Know When to Descend? appeared first on FLYING Magazine.

Answer: When looking at the surface analysis chart issued every three hours by meteorologists at the Weather Prediction Center (WPC), you may have seen a tan dashed line with a label “OUTFLOW BNDRY” nearby. This is what meteorologists call a convective outflow boundary.

You may view North American surface analysis here.

Convective outflow boundaries emanating away from thunderstorms are generated as cold, dense air descends in downdrafts then moves outward away from the convection to produce a mesoscale cold front also known as a “gust front.” 

• READ MORE: Should I File an Initial Approach Fix?

Some gust fronts can be completely harmless or may be a precursor for an encounter with severe turbulence and dangerous low-level convective wind shear. The direction of movement of the gust front isn’t always coincident with the general motion of the thunderstorms. If the gust front is moving in advance of the convection, it should be strictly avoided. The pilot’s best defense is to recognize and characterize the gust front using METARs, ground-based radar, and visible satellite imagery.

According to research meteorologist and thunderstorm expert Charles Doswell, “cold, stable air is the ‘exhaust’ of deep, moist convection descending in downdrafts and then spreading outward like pancake batter poured on a griddle.” 

As a pulse-type thunderstorm reaches a point where its updraft can no longer support the load of precipitation that has accumulated inside, the precipitation load collapses down through the original updraft area. Evaporation of some of the rain cools the downdraft, making it even more dense compared to the surrounding air. When the downdraft reaches the ground, it is deflected laterally and spreads out almost uniformly in all directions, producing a gust front.

• READ MORE: How Do You Check NOTAMs?

Gust fronts are normally seen moving away from weakening thunderstorm cores. Once a gust front forms and moves away from the convection, the boundary may be detected on the NWS WSR-88D NEXRAD Doppler radar as a bow-shaped line of low reflectivity returns usually 20 dBZ or less. Outflow boundaries are low-level events and do not necessarily produce precipitation. Instead, the radar is detecting the density discontinuity of the boundary itself along with any dust, insects, and other debris that may be carried along with the strong winds within the outflow. The gust front in southwest Missouri shows up very well on the NWS radar image out of Springfield as shown below.

An important observation is to note the motion of the gust front relative to the motion of the convection. In this particular case, the boundary is steadily moving south while the thunderstorm cells that produced the gust front are moving to the east. This kind of outflow boundary is usually benign, especially as it gains distance from the source convection. On the other hand, a gust front that is moving in the same general direction in advance of the convection is of the most concern. These gust fronts often contain severe or extreme turbulence, strong and gusty straight-line winds, and low-level convective wind shear.

As mentioned previously, gust fronts are strictly low-level events. As such, even the lowest elevation angle of the radar may overshoot the boundary if it is not close to the radar site. 

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Shown below at 22Z, the NWS WSR-88D NEXRAD Doppler radar out of Greenville-Spartanburg, South Carolina, is the closest radar site and clearly “sees” the gust front (right image). However, the NEXRAD Doppler radar out of Columbia, South Carolina (left image), is farther away and misses the gust front completely. As the gust front moves away from the radar site, it may appear to dissipate, when in fact, the lowest elevation beam of the radar is simply overshooting the boundary. As a result, it is important to examine the NEXRAD radar mosaic image before looking at the individual radar sites.

Not all gust fronts are easy to distinguish on visible satellite imagery; the gust front could be embedded in other dense clouds, or a high cirrus deck may obscure it. It is also possible that the boundary may not have enough lift or moisture to produce clouds. In many cases, however, it will clearly stand out on the visible satellite image. When the gust front contains enough moisture, as it was in this situation, cumuliform clouds may form along the boundary and move outward as can be seen in this visible image below centered on Charlotte, North Carolina. This is very common in the Southeast and coastal regions along the Gulf of Mexico given the higher moisture content. 

As this particular gust front passed through my neighborhood located south of Charlotte, strong, gusty northerly winds persisted for about 10 minutes. As is common, the main core of the precipitation didn’t start to fall for another 10 minutes. When a gust front such as this appears on satellite or radar, it is important to monitor the METARs and ASOS or AWOS closely for the occurrence of high winds. Several airports in the vicinity reported wind gusts peaking at 30 knots. The sky cover went from being just a few scattered clouds to a broken sky with these cumuliform clouds shown below moving rapidly through the region.

These cumuliform-type clouds were the result of a strong convective outflow boundary that moved through Fort Mill, South Carolina.  [Courtesy: Scott Dennstaedt]

As mentioned earlier, a gust front moving away from thunderstorms is a low-level event that can contain strong updrafts and downdrafts. The graph shown below is a time series, plotting the upward and downward motion or vertical velocity in a strong gust front as it moves over a particular point on the ground. 

The top half of the graph is upward motion and the bottom half is downward motion. Time increases from left to right. As the gust front approaches, the vertical velocity of the air upward increases quickly over a one- or two-minute period. While the maximum vertical velocities vary with height in the outflow, a common maximum number seen is 10 meters per second (m/s) at about 1.4 kilometers or 4,500 feet agl (25 knots is roughly 12 m/s for reference). 

• READ MORE: Is a Medical Certificate Required for a Private Pilot Check Ride?

As the gust front moves through, the velocities abruptly switch from an upward to a downward motion, creating strong wind gusts at the surface. Most outflow boundaries don’t extend above about 2 kilometers or 6,500 feet agl. What is remarkable is that upward-to-downward motion changes in just about 30 seconds over the ground point where this was observed. But imagine flying an aircraft at 150 knots through this— the up-and-down exchange will happen in just a few seconds, producing a jarring turbulence event.

Just in case you were wondering, gust fronts are conveniently filtered out by your datalink weather broadcasts as shown below for XM-delivered satellite weather. This is because the broadcast only provides returns from actual areas of precipitation. Often outflow boundaries or gust fronts produce low reflectivity returns that fall below the threshold used to filter out other clutter not associated with actual areas of precipitation. 

When in flight, pay particular attention to surface observations, looking for strong, gusty winds, before attempting a landing at an airport when storms are approaching. 

The post What Is an Outflow Boundary Shown on a Surface Analysis Chart? appeared first on FLYING Magazine.