It seems as though our most vivid memories come from some of our worst experiences in life. While many pilots don't remember their first exposure to structural icing, they probably will never forget their worst. For many, it remains etched in their brain forever. But, we can avoid making painful lasting memories if we do some careful preflight planning and use some street smarts to negotiate the system to our advantage during this icing season.
The icing environment in and around the Great Lakes region is not a place where you want to cut your teeth with respect to icing. Any instrument pilot that has experience flying in this region during the early winter is probably nodding his or her head right about now. Three years ago I helped one of my former instrument students avoid making any bad memories for a cross-country flight from Springfield, Illinois (KSPI) to Williamsport, Pennsylvania (KIPT).
It was early November, and this would be Rick's first exposure of the season. This time of the year, convective sigmets seem to morph into icing airmets as we become prisoners within our own airspace. After five months of ice-free flying, I could tell he was apprehensive about this flight. I was more than happy to help him sort it out.
Rick flies a normally aspirated Cirrus SR22 mainly for pleasure. With the promise of a decent tailwind, he would be able to easily make a nonstop flight with plenty of fuel in reserve should he need to divert. Fuel in the tanks will give you more options if things don't go as planned. His biggest challenge was trying to decipher the icing environment through the Ohio Valley on that early November day.
His plan was to depart Springfield in the late morning. This would put him in Williamsport by midafternoon. Springfield is located in central Illinois a bit upwind of the Great Lakes ice-breeding ground. Williamsport is located in north central Pennsylvania, a definite downwind target of the Lake Erie and Lake Ontario ice blast zone.
Shift in Thinking
The sun was just starting to rise when Rick joined my online session. Since his SR22 does not have a certified ice protection system (IPS), I thought it would be useful to do a bit of review to shift his thinking from dodging thunderstorms to ice avoidance.
We started with the basics. If you are flying in visible moisture and the air temperature is at or below 0 degrees C, there's a good chance you'll encounter some kind of structural icing down to a temperature as cold as -25 degrees C. Visible moisture includes cloud drops, rain or drizzle. Below -25 degrees C, supercooled liquid water becomes increasingly scarce outside of any deep, moist convection.
I also wanted to point out to Rick that many nonconvective weather systems are layered. However, if a climb or descent fails to take him out of visible moisture or out of the freezing temperature band, the chance of continued structural icing is still very likely, and a change of altitude could place him in a region where the liquid water content is higher.
The Big Picture
So it was time to look at the weather for his proposed flight. Even though Rick was eager to jump right to the details, I convinced him to first take a look at the big picture, or what meteorologists refer to as the synoptic-scale weather.
Here's what we saw. The latest surface analysis chart valid at 1200 UTC showed a cold front located near the Eastern Seaboard. By looping the surface analysis over the last 24 hours, it was apparent that this front had marched to the east, pushing through the upper and lower Great Lakes and Ohio Valley regions during the previous day and overnight hours.
A deep, occluded low pressure was located over Georgian Bay, well to the north of Detroit. A fairly strong pressure gradient extended hundreds of miles outward from the center of this low, creating brisk surface winds that were generally from the west. Rick was quite relieved to learn that his entire proposed route was located behind the cold front with favorable tailwinds.
What Does It All Mean?
The area behind a strong, fall-season cold front is not where you generally find deep, moist convection or thunderstorms. However, in November the warm water of the Great Lakes can be quite the ice machine when it is coupled with a cold Canadian air mass as it picks up surface moisture and transports it south and east. Moisture-rich, post-cold-frontal stratus and stratocumulus clouds are the usual result. With surface temperatures in the mid- to upper 30s and a cold air mass moving in aloft, that means these clouds are guaranteed to be dominated by supercooled liquid water.
The trends in the analyses and forecasts all implied the icing would remain around for the remainder of the day. In fact, the clouds and icing potential were forecast to continue to push south and east through the afternoon.
Of course, this prompted the Aviation Weather Center (AWC) to issue an icing airmet at 1445 UTC from 2,000 feet through 13,000 feet valid through 2100 UTC. The airmet encompassed most of the northern two-thirds of Ohio and also included the western half of Pennsylvania, anticipating the south and eastward push of these clouds.