Go or No Go: Rocky Mountain mess

After 20 years of living in Colorado, you know that March weather in the Rockies means anything from blizzards to warm, spring-like days. Unfortunately the weather is closer to the first extreme for your planned trip tonight, a 1:30 flight from your home in Denver (BJC) to Provo, Utah (PVU), to visit your son in college. Your Cessna 421 is a capable airplane, with two turbocharged engines, pressurization, full deice boots, and a glass cockpit. Looks like you might need all that gear today.

You are fully IFR qualified and proficient, and the plan is for an IFR flight today. Departure is scheduled for 2330Z, which means you’ll be arriving just before sunset in the Salt Lake City area. Read the weather forecast below, then tell us if you would go or cancel. Remember – there’s no right or wrong answer here. The goal is to practice your decision-making skills and share your thinking with other pilots.

Overview

A look at the Maps page in ForeFlight shows a rainbow of colors, with rain, snow and mixed precipitation north of Denver, another patch of rain over western Colorado, and more rain to the north of your destination.

The surface analysis shows a low parked over Colorado and another one in eastern Nevada.

The satellite image shows solid clouds all along your route of flight, with the thickest parts in the middle. It does look like the clouds break up as you get towards Salt Lake City.

Prog charts

So far you have an idea of current conditions. What about the future? Unfortunately, the forecast doesn’t show much of an improvement, as a look at the first prog chart shows:

The next one shows the low moving slowly off to the northeast, but leaving plenty of rain and snow behind:

Icing

The biggest concern today is proabably in-flight icing. While your 421 is approved for flight into known icing (FIKI), no airplane can linger in serious icing for long. The easiest way to evaluate the threat is to use ForeFlight’s icing layers. It looks like you’ll be mostly-ice free for takeoff and landing, since the 8,000 ft. icing chart is mostly clear:

By 14,000 feet there is definitely some ice to tangle with, although mostly light.

Same story at 20,000 feet, with icing in the middle of your flight. Again, it’s mostly light:

The good news is that you can get on top by 22,000 feet today. That’s definitely doable in your 421, which you regularly fly in the low to mid-twenties.

Turbulence

Winter and mountains often mean turbulence too, so a quick look at the turbulence forecast is in order. Those charts show the expected bumps down low, especially over the Front Range, but they persist up to 18,000 feet.

How about once you’re out of the ice (hopefully) at 22,000 feet – is it any better? A little:

PIREPs

So far you’ve looked at forecast products; now it’s time to see what pilots are saying. There are plenty of icing PIREPs out there, including this one between 13,000 and 9,000 feet near your destination.

Here’s another one that shows light rime and moderate turbulence at 13,000 feet near Denver.

Another one near Denver shows light icing from 14,000 to 16,000.

South of your route there’s a report of moderate ice at 15,000:

The scariest PIREP is well south of your route, but shows severe icing at 13,000 feet.

Skew-T

Given all the weather and the potential for icing, a look at the skew-T diagrams is a good idea today. First up is Denver, which shows a bit of a temperature inversion and seemingly endless clouds. The winds are steady out of the west:


And here’s the diagram for Salt Lake City:

Text weather

Now it’s down to the METARs and TAFs. Finally there’s some good news. Conditions at your departure are good VFR with light winds, and it’s forecast to stay that way for a while:

Your destination is also reporting good VFR weather and calm winds, although the forecast isn’t quite so good:

En route weather is much more varied. 20V, closer to Denver, is windy but VFR, while 4V0 and VEL are IFR:

Decision time

It’s time to decide whether you’re going flying today or not. It’s certainly an IFR day, with rain, snow, icing and probably some turbulence – not an easy flight. On the other hand, you are an experienced IFR pilot with a high performance airplane and it looks like you can get on top of the ice today.

Add a comment below and tell us what you would do. Then tell us why you reached that conclusion.

20 Comments

  • Until I’ve had some experience with icing in the 421 and how it handles it, I’d be avoiding ice as much as possible.

    With the deteriorating forecast at destination, leaving earlier is worth consideration.

    And I’d be checking out airports en route for bolt holes.

    • Looks like a long unpleasant flight at best and potentially dangerous if conditions change. Conditions are worse to the south and that seem likely to move up into our flight path. Also, there’s two lows and multiple fronts converging, there’s not much chance of forecast is going to be right. I’d say not worth the risk. If I did go, I’d try and flight plan a route to the north, weather is more stable and terrain is less severe.

  • I’ve flown in enough icing to know that if your plane can handle light icing you’ll probably encounter moderate. That being said it’s March, in the Rockies, which means there’s more moisture than say January. Combine that with the fact that the route is over some very unforgiving terrain I’d say hold off. If it were an east coast or midsection of the country flight where you can get lower to get out of icing or divert I might be more inclined.

  • While we don’t have any real experience in a C421, we do have plenty of pressurized Aerostar experience which generally performs better. Getting on top is the key, even with the headwind. Could go to FL 240 as necessary. The other key is mountain flying experience which for us is limited. Like Mike, in the Midwest or the Northeast, we’d definitely go – lots more enroute options than on this route. Here, I think we’d be discussing the flight with other local pilots if possible as well as trying to leave earlier in the day. Bottom line – for an experienced C421 pilot, it’s a likely go. For me, I’d wait it out.

  • I would personally scuttle this trip. The existing conditions (terrific head winds, icing in the mid-teens, moisture, temperature inversion with possibility of clear icing and run-back which is not affected by de-icing boots, destination weather and lows over a large area) make you a bold pilot. We all remember the old saw about old and bold pilots. A bit of wisdom I learned from Richard Collin’s books is that the only relevant hour is the “next hour.” It does not matter how many hours are in one’s log book, the only one that matters are the decision making and judgment we use for our next flight-hour.

  • I have no C421 time. Would I make this flight in a capable piston single engine such as a P210? No. Lose an engine in the 421 (not unheard of!) and that’s what we’d be flying. Single engine over high rugged cloud obscured terrain trying to (in vain) stay out of the ice. Naw, I too vote for Skype or phone calls and teach/demonstrate good judgment to my son.

  • Wow … great article! Thank you for the great example of the importance of doing a complete pre-flight weather assessment. This is a great example of how it is not good enough to just do a quick “what is the weather here … what is the weather there” look.

    I definitely would NOT go on this one. While my JetProp certainly would get on top of the weather – “everything that goes up, must come down” – and I just see bad, bad, and bad when looking at every other factor.

  • No point in pushing the weather and putting yourself through that type of flight for a quick visit!

    However, I really enjoyed this article and am looking forward to similar ones in the future!

  • I would file for fl250 and plan for the ILS 13 Provo. As long as I had a little more confidence from flight service that 250 was clear or clouds.

  • Back in the 60’s I flew that route 3x in a comanche 180, in March, in snow. The 4th time there was a break in the snow squalls and I saw what was below me. I have never flown that route again. I have no time in a C421 and that might make a difference, but not with the weather described. Buy a ticket on Southwest.

  • No way, with those forecasts of ice and turbulence in a route near mountains, even with an aircraft with de-icing gears (not anti-icing) and proficient pilot.

  • Not for me. I went flying today and had light icing that continued to pick up and landed with 1/4 inch. Even with deicing equipment and a plane like the Cessna 421 when there is moderate ice in the forecast it is better to stay on the ground. Looking at the PIREPs with icing and the icing forecast, I would not go. “Better to be on the ground wishing you were in the air than in the air wishing you were on the ground.”

  • I’d pass on this flight for a few reasons. The ice reports indicate that this is probably doable in the 421, but I’d prefer a jet or turboprop where I could get a much better climb to get above the turbulence. A 737 would do. One reported moderate, which for a short time in a 737 is ok…. probably not in a 421 because with it’s lesser climb could be a lot of turbulence. And with moderate, west of Denver, there’s a likelihood of worse.

    Now, the 421 is not really a “bad” ice plane, but with pistons ya just don’t have that climb rate which could be needed. And a hot wing would be much better that boots.

    With 27000 hours, I’ve done many flights like this one, however, this IS a challenge and not a comfy flight. Most likely not unsafe, but most likely not comfortable. There’s lots of “outs” with planning for a 421 flight.

    But, I don’t think the hassle and work for a flight just to see my son is warranted. Now, if her were getting married, I’d launch.

  • ATC once rerouted us mid flight to avoid ice and wound up flying us through the midst of it. We landed after a tumultuous roller coaster ride, our experienced Navy PIC and CFI-instrument had called ATC to report we were out of control. We fortunately reached at our destination, but with no paint left on all leading edges and prop.

    In your example above, just because you can get on top of ice doesn’t mean you don’t have to climb or descend through it.

  • What’s the single engine service ceiling of a 421? Would imagine if one engine conked out you could be in for a world of hurt- icing, high terrain, turbulence, etc. Not for me.

    Also feel like doing this before nightfall adds another layer of risk, as if you have any delays along the way you’re now dealing with all of the above in the dark.

    Also worth noting that all of the icing pireps were from more capable turbine aircraft. Light icing to a 737 might be something different to a 421.

  • Most of the weather (icing, precip, etc.) can be avoided very easily by filing for FL220 and climbing toward KHDN (Yampa Valley). This will skirt the north side of the weather that is showing (especially at FL220) and once past the Yampa area, a turn to the southwest toward Provo might be a VMC descent. There is no need to plow through whatever weather is west of KBJC — just divert around it. Why make it hard when there is a simple alternative.

    You have a very capable aircraft and the deviation would add very little to the time encounter, plus it’s likely to be a much more comfortable and pleasant flight. Isn’t that what general aviation is all about?

  • Since it looks like it will be difficult or impossible to stay on top, and with the amount of moisture and turbulence in the enroute weather system, I’d stay home. even with a well-equipped airplane and solid IFR skills.

    One thing is for sure. If you do go, you are gonna get bounced around really good and be dodging icing for the whole trip.

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