Passing of a legend Richard (Dick) Collins

I was very sad to hear the news this morning that Dick Collins passed away.  As I was learning to fly in the 1990s, Dick became an inspiration to me both as a writer and as a student of the weather.  As a newly minted private pilot, I read as many of Dick’s articles as I could get my hands on…I have stacks of his magazine articles still neatly packed away in my closet in a dozen or so boxes.

Even though my profession is in the field of meteorology, I didn’t have – and will never have – the weather flying experience that Dick so carefully wrote about in many of his articles.  You could tell with each and every paragraph he crafted that Dick was also a student of the weather and had utmost respect for the mysteries Mother Nature bestowed.   It takes a gifted and talented person to write to express, not to impress.   Even as Dick aged, he continued to impart his wisdom even just one month ago in his last piece in the Air Facts Journal.

I only met Dick once, very briefly at the Cumberland Airport in Maryland about 15 years ago.  As I reached out to shake his hand, he put on a big, but humble smile.  Even though we never exchanged business cards or emails, even though he never got a chance to attend one of my live aviation weather workshops, I felt he was a good friend and colleague simply through is stories.  He promoted safety in so many ways and his long aviation career demonstrated his passion for it.   There’s no doubt that his wisdom through his penmanship saved many a human life…not just those of pilots, but passengers as well.  As you have educated a countless number of pilots about weather over the last 50 or more years, I will continue to carry your torch Dick.  You will be missed!

Newest enhancements to WeatherSpork – version 4.3.0

WeatherSpork just got even better! WeatherSpork version 4.3.0 is now available in the App Store.  In addition to a few bug fixes, we are excited to tell you that we raised the roof of WeatherSpork to FL450.  You’ll now enjoy in the Route Profile view a depiction of clouds, wind and en route advisories from the surface to 45,000 feet MSL.  In this release we also added cross track distance to the Route Profile view allowing you to see the distance from fly-by airports to the proposed route.  Lastly, we added the High Resolution Ensemble Forecast (HREF) guidance for ceiling and flight category to the WeatherSpork Imagery view.

Watch the video below to see an overview of these enhancements to WeatherSpork. Enjoy!

“Most pilots are weatherwise, but some are otherwise.”

Scott Dennstaedt
Weather Systems Engineer
Co-founder, WeatherSpork

 

Just raised the roof on WeatherSpork!

With WeatherSpork version 4.3.0, you now have the option of selecting FL450 as the upper limit on the clouds and weather display.  The upper limit on earlier releases was restricted FL200.  This will allow you to see winds (speed and direction) as well as clouds and advisories (G-AIRMETs and SIGMETs) that extend higher in the flight levels or FL450.

To change the altitude limit, go to the Route Profile view and simply tap or click on the black route button at the top.  That will bring up the Route Profile settings.  Scroll down in the settings window (shown below) to find the Maximum Altitude setting and select FL450 and tap or click Save. The other selections of 6,000 ft MSL, 12,000 ft MSL and FL200 will remain available.

This enhancement only affects the Route Profile view.  The Meteogram view will still remain limited to a maximum altitude of FL200.

“Most pilots are weatherwise, but some are otherwise.”

Scott Dennstaedt
Weather Systems Engineer
Co-founder, WeatherSpork

Cross track distance from fly-by waypoints

When you’ve defined a proposed route in WeatherSpork you may notice that it picks a number of “close” fly-by stations (airports) to include along that route.  These show up on the Map view as rounded square icons like those shown below.  But how far is KMSV off of your great circle route from KBOS to KCLE to KORD?  That’s known as cross track distance (abbrevated XTK) and is defined as the closest distance from the station to the route as shown below.

Now in WeatherSpork version 4.3.0 we’ve added a cross track distance (abbreviated XTK) to the route progress strip at the bottom of the Route Profile view.  These fly-by stations along with those defining your route (departure, midpoints and destination) will be added to this view.   This gives you a quick indication of just how far this station is off of the route.  For example, in the Profile view below, KMSV is 27 nm from the route identified in the blue oval.  To decrease clutter in the route progress strip, cross track distances are not shown for the departure, destination and midpoint stations as shown by the red Xs below; it’s assumed that the cross track is 0 nm.

Keep in mind that the weather can be quite different at these fly-by stations as compared to stations right over the actual route.  The greater the distance, the more likely the variation in weather.  Keep that big weather picture in mind.

“Most pilots are weatherwise, but some are otherwise.”

Scott Dennstaedt
Weather Systems Engineer
Co-founder, WeatherSpork

 

New static Imagery from the HREF model

With WeatherSpork version 4.3.0, we’ve extended the static Imagery to include aviation forecasts from the High Resolution Ensemble Forecast (HREF) model.  The HREF is updated four times a day and provides a forecast lead time of 36 hours at one hour time increments.  In WeatherSpork you can find these in the Imagery view right below Graphical MOS under HREF Model as shown below.

These six choices provide the probability of a flight category of Marginal VFR (MVFR), IFR and Low IFR (LIFR) as well as the probability of a ceiling below 3,000 ft, 2,000 ft and 1,000 ft AGL.  In the sample below, the colors represent probabilities shown on the scale at the bottom of the chart.  Colors such as red and purple are indicative of ceilings that are forecast to be less than 3,000 feet as they are in northern Ohio; of course, they could be much less than 3,000 feet in this area.  Keep in mind that non-filled areas do not mean clear skies per se.  This simply means that there is a very low chance the ceiling will be less than 3,000 feet in these areas. This 21 hr forecast is valid at 1500Z on April 28, 2018.

The probabilistic ceiling forecasts above are additive in nature.  In other words if there’s a high probability of a ceiling less than 1,000 feet, there’s also a high probability of a ceiling less than 2,000 feet and 1,000 feet respectively.

Flight category combines both the ceiling and visibility as shown in the table below. These flight categories are sometimes improperly referred to as flight rules in many flight planning apps.

In addition to the probabilistic forecasts for ceiling, the HREF also provides a probabilistic forecast for specific flight categories that include LIFR, IFR and MVFR.  The example below has a forecast lead time of 22 hours and is valid at 1600Z on April 28, 2018.  Similar to the probabilistic ceiling forecasts above, higher probabilities of a MVFR flight category are shown in red and purple colors like you see in Indiana and Ohio in the example below.  Non-filled areas simply mean that the chances of a MVFR flight category are very low.  Unlike the probabilistic ceiling forecasts above, these forecasts are not additive.  That is, in an area where there’s a high probability of a MVFR ceiling, there may be a very low probability of a LIFR ceiling.

“Most pilots are weatherwise, but some are otherwise.”

Scott Dennstaedt
Weather Systems Engineer
Co-founder, WeatherSpork

An introduction to Model Output Statistics or MOS

A majority of certificated pilots have never heard of Model Output Statistics or what is referred to as MOS (pronounced moss).  MOS isn’t new and has been around since the 1960s, but is just starting to be leveraged by many pilots.  Back in 2016 the FAA added a brief description of MOS to the Aviation Weather Services advisory circular AC 00-45H Change 1 so it is now officially recognized by the FAA as supplemental guidance for preflight planning. WeatherSpork makes heavy use of this automated guidance which drives the signature feature in WeatherSpork called the Wheels Up Departure Advisor (WUDA) found in the Map, Grid and Route Profile views.  MOS is also used by meteorologists as one of several tools to issue terminal aerodrome forecasts (TAFs).

This video below was an audio and screen recording of a presentation given by Scott Dennstaedt to a local flight school in Charlotte.  Watch this video to learn a bit more about MOS and its advantages as flight planning guidance.

“Most pilots are weatherwise, but some are otherwise.”

Scott Dennstaedt
Weather Systems Engineer
Co-founder, WeatherSpork

Dangers of airframe icing in stratocumulus clouds

Normally pilots look forward to improving weather conditions after the passage of a cold front. The cold, dense air behind the front becomes negatively buoyant and sinks which tends to dry out the air. Moderate northwesterly winds will often prevail on the cold side of the front making for moderate mechanical turbulence sometimes extending up to 8,000 feet AGL. Other than some turbulent air, we don’t typically encounter much in the way of adverse weather behind such a cold front with few clouds, no precipitation and unlimited visibility.

During the spring, how many pilots think about the airframe icing threat that can occur in an overcast stratocumulus deck after the passage of cold front? Even a thin stratocumulus cloud deck like the one shown above can contain a liquid water contents approaching 0.5 g/m3 – especially near the tops. When the temperature is just right, these harmless-looking clouds can surprise a pilot with some moderate or even severe icing while climbing or descending through them.  This is especially concerning to those pilots flying aircraft without certified ice protection systems (IPSs).

Stratocumulus decks have very distinct characteristics from other clouds. Although not completely smooth on top like a stratus deck, they have rather even tops with a quilted-like or lumpy appearance when viewed from above. While a stratocumulus deck can be broken or even scattered it is quite common for these cloud decks to be overcast when they occur after the passage of a cold front. They are rooted in the boundary layer near the surface similar to other cumuliform clouds, but an overcast stratocumulus deck can extend for hundreds of miles making them difficult to avoid.

Let’s examine a case in the middle of April near Atlanta, Georgia where many pilots were reporting moderate icing in one of these stratocumulus decks.

This story starts out in the prior day.  A strong cold front moved through the Atlanta area during the late morning, bringing with it severe thunderstorms with tornadoes and microbursts in the afternoon from northern Virginia down to the peninsula of Florida as shown above. Temperatures ahead of the front climbed into the low 80s.  As the cold front (shown below) moved off the southeastern Atlantic coast the following day, this set the stage for a cold northwesterly wind to push a cold air mass over a fairly warm and wet ground in the Atlanta metro area.  A warm and moist surface with cold air moving in aloft is the perfect recipe for the genesis of a juicy stratocumlus cloud deck.

Skies were generally overcast all morning throughout the Atlanta area as can be seen by the surface observations below.  Ceilings were marginal VFR ranging from 2,100 feet to 2,600 feet.  In an overcast cloud deck, there’s no real way to know its depth from looking at the clouds from below.  Depending on the sun angle, a darker cloud base is indicative of more condensate, but this was early in the morning where the bases will generally be darker.  But in the Atlanta region, this was definitely an overcast stratocumulus deck like the one shown in the picture below.

KPDK 161453Z 30013G21KT 10SM OVC021 04/M01 A3000 RMK AO2 SLP167 T00391011 53014
KPDK 161353Z 27011G18KT 10SM OVC021 03/M01 A2998 RMK AO2 SLP160 T00331011
KPDK 161253Z 26013KT 10SM OVC022 03/M01 A2996 RMK AO2 SLP156 T00331011
KPDK 161153Z 28011KT 10SM BKN021 OVC028 04/M01 A2995 RMK AO2 SLP151 60000 70060 T00391006
KPDK 161139Z 26010KT 10SM BKN026 OVC033 04/M01 A2996 RMK AO2 T00391006

Temperatures at the surface during the morning were a chilly +3°C to +4°C.  But one characteristic of stratocumulus clouds is that there is very unstable air below.  This means the temperature decreases at the dry adiabatic lapse rate of 3°C for every 1,000 feet gain in altitude.  Except for right at the surface, this lapse rate is the most unstable that unsaturated air can be.  This is best seen on a thermodynamic chart called a Skew-T log (p) diagram.  The Skew-T analysis below for Dekalb-Peachtree Airport (KPDK) captured through the WeatherSpork Airports view demonstrates a textbook stratocumulus signature.

As can be seen above, the stratocumulus clouds extend from the bases at 2,500 feet MSL where the temperature and dewpoint converge with saturated conditions to the tops at roughly 5,500 feet MSL or where the temperature and dewpoint diverge.  That’s a depth of roughly 3,000 feet at 14Z (they likely varied in depth over the region).  Notice the large lapse rate below the cloud bases with nearly moist absolute instability within the actual cloud deck itself.  This is the most unstable lapse rate that can occur in saturated air. Remember that this area had received a fair amount of rain, so there was plenty of fuel being pulled into these clouds from below.

The tops are capped by a very strong temperature inversion which limits vertical cloud growth which is the classic signature to stratocumulus clouds.  So you can think of this “system” as a lid on a pot of boiling water.  The unstable air ascends, expands and cools to produce these clouds and given that the clouds are also unstable inside, the momentum in the capped updrafts gives those clouds the lumpy appearance when viewed from above.  In fact, taking a closer look at this sounding analysis shown below with a parcel lapse rate added, there is a fair amount of convective available potential energy (CAPE) that allows for efficient transfer of water vapor into condensate (liquid drops).  It’s like squeezing the water out of a sponge.

While not specifically shown on the Skew-T diagram, the graph below is a trace of the liquid water content of an instrumented research aircraft that climbed through one of these cloud decks.  The liquid water content is shown increasing to the right on the X-axis.  Height is shown on the Y-axis.  Because these clouds are rooted in the boundary layer, the have a median volumetric diameter drop size of less than 50 microns (small-drop icing scenario).  A liquid water content value at the top of this cloud deck shown in the graph below of 0.5 g/m3 is huge.  The liquid water content can be significant enough to overwhelm many aircraft when flying in the tops of these clouds.

Temperature is also important.  The cloud top will typically exhibit the coldest temperatures in these clouds.  In this case for Atlanta, the cloud top temperature is in the perfect range at -7°C if you want to see icing conditions.  That guarantees an all-liquid process making for a juicy cloud containing no ice crystals.  You can also see the cloud top temperature in the color-enhanced infrared satellite image below.  Colors in the image are based on temperature in degrees Celsius.  When clouds are present, this is the temperature of the cloud top, otherwise it’s the temperature of the surface of the earth. The stratocumulus deck shows up nicely over northern Georgia as a yellow color implying a cloud top temperatures of -8°C which matches what is shown in the Skew-T diagram.

Some of this cloud cover in extreme northwest Georgia was covered under an icing G-AIRMET valid at 15Z for widespread moderate icing from the surface to 10,000 feet MSL (shown below).

Lastly, there were a number of pilot weather reports for icing in and around the Atlanta region that included an urgent pilot report from a Boeing 737 at 5,000 feet MSL south of Atlanta.  The moderate ice reports during the morning tended to be around the tops of this cloud deck.

ATL UUA /OV ATL085020/TM 1245/FL050/TP B737/TA -3/IC MODERATE RIME

If you are not a member of WeatherSpork, your best online source for aviation weather and education, please consider becoming part of the WeatherSpork family.

“Most pilots are weatherwise, but some are otherwise.”

Scott Dennstaedt
Weather Systems Engineer
Co-founder, WeatherSpork

Thunderstorm planning with WeatherSpork, Part 3

Part 1 and Part 2 of this three video series showed a window of opportunity to depart Savannah, Georgia during the morning hours between 14Z and 15Z arriving in Charlotte, North Carolina before 17Z.  Was this guidance on the money?  Watch Part 3 of this video series to see how it all played out.  And stop back to this post and read some of the final thoughts below…

As shown below this was a very dangerous weather system that included many tornado and severe thunderstorm warnings up and down the Piedmont regions of North and South Carolina.  The line of relatively low-topped thunderstorms began to impact the Charlotte terminal area around 19Z and that matched the guidance from earlier in the day.

As I mentioned in the video, very strong winds at the surface were possible as heavy rain showers transferred the momentum of that strong low level jet down to the surface.  In fact, the wind gusted to 59 knots (68 mph) at the Charlotte Douglas Airport at 1913Z based on the METAR remarks below.

KCLT 151916Z 21035G59KT 1/4SM +TSRA BR BKN037CB BKN050 OVC065 21/17 A2980 RMK AO2 PK WND 20059/1913 LTG DSNT ALQDS RAB12 TSE01B02 PRESRR FRQ LTGICCCCG SW-W TS SW-W MOV NE P0000 T02110172 RVRNO

You can see in this color-enhanced IR satellite image below two patches of dark blue.  These were coincident with the two tornado warnings (red polygons) shown in the image above.  This satellite depictions shows cloud top temperatures in degrees Celsius.  The colder the temperatures, the higher the cloud tops.  In many cases, these overshooting tops are cells that will exhibit severe characteristics. These two cells within this line of thunderstorms likely spawned a tornado.

These two cells show up as well on the visible satellite (below), although not as good as the IR satellite image given the time of day.  If this occurred during sunset, you would have seen the higher tops cast a shadow on the clouds below. Nevertheless, the red arrows point to those two cells and the orange arrows show their approximate track.  The red X is there I live.   As this southernmost cell moved north-northeast, there was a heavy rain-wrapped circulation that passed through my neighborhood.  The driving heavy rain ended very abruptly as the backside of that cell passed…very typical of these kinds of mesoscale events.

Well I hope this video series was useful.  Feel free to send a link of these videos to all of your pilot friends and post them through your social media accounts or to your favorite aviation forums.

“Most pilots are weatherwise, but some are otherwise.”

Scott Dennstaedt
Weather Systems Engineer
Co-founder, WeatherSpork

 

Thunderstorm planning with WeatherSpork, Part 2

Part 1 of this series of three videos focused on how to use WeatherSpork to find the best time of departure for a trip the following day given a threat of thunderstorms along the proposed route.  Part 2 of this series takes place on the morning of this flight.  Watch this 20 minute video below to see if yesterday’s guidance was still on track.

“Most pilots are weatherwise, but some are otherwise.”

Scott Dennstaedt
Weather Systems Engineer
Co-founder, WeatherSpork

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