If you could get above our low cloud deck, there’s plenty of sunshine to be had.

The Great Lakes and the coastal Pacific Northwest tend to be among the cloudiest places on the continent beginning in later autumn into early spring. Often, a temperature inversion develops in lower levels of the atmosphere with a layer of warm air off the deck, trapping cool, moist air near the surface (without an inversion, temps drop steadily with an increase in altitude).

That’s what we’re going to be stuck with quite often this time of the year and over the next several days. Computer models are so tuned to this climatology they are even able to focus in on low cloud cover, along with mid and high-level cloudiness. This is a modeled depiction of low clouds at about midday this Friday.

In aviation, the issue of low clouds is largely separate from ground fog in making decisions on landings and takeoffs. Sophisticated airliners have instrumentation which allow landings in even rather dense fog, so long as pilots can see the runway just before wheel touchdown. Most instrument-equipped fixed wing aircraft can readily maneuver aloft through low cloud cover. It’s ground fog which complicates matters, especially for pilots with less experience and/or with aircraft without more advanced instrumentation. Most general aviators planning on a practice or pleasure ride will avoid flying when extensive fog is present or forecast to develop.

Fog is, simply put, a stratus cloud right on the ground. It occurs when the air at the surface is saturated, with the air temperature matching the dew point temperature. It often worsens in very stable conditions with little vertical mixing in the air and with very light surface winds. Here is an image of Air Force One on the ground in dense fog.

Fog is always a forecast challenge in meteorology. It might be a little less challenging, say, if we know sea fog is advecting/moving horizontally in off the foggy Atlantic, onshore into JFK. It becomes more of a challenge in irregular terrain with cloud bases above the ground, but still very low. The ceiling is the broken or solid base level of a cloudy layer. There may be perfectly acceptable visibility right down on the ground, with dense clouds looming not far from the deck.

For airline passengers on final approach, you may find yourself slipping into a white knuckles state if YOU can’t see the runway. Your cockpit crew, however, has advanced avionics which guide the aircraft with precision and safety to the runway. For takeoffs, certain visibility minimums are required. While the decision to take off is usually that of the pilots, if fog becomes extremely dense and visibility drops below Federal Aviation Administration minimums, the airport itself may do a ground stop and cease operations until conditions improve.

With helicopters, low ceilings and fog present more serious hazards for safe operation. While we can’t touch on all the variables in the scope of this article (and shouldn’t, since I’ve flown many hours in mostly Army copters only as a passenger in training exercises, not as a pilot), there are some more clear-cut hazards I can cover.

Good visibility on the ground with very low ceilings may be fine for an Airbus 320, but those conditions are not fine for most helicopters and their pilots. Very low ceilings give less pilot reaction time in helicopters when attempting to land in an area with obstacles, such as towers and power lines. Helicopters need to stay out of flight paths used by fixed wing aircraft and tend to follow more irregular paths, such as highways. When flying in dense clouds, the absence of visible ground markers, even if there is decent instrumentation, increases the risk of pilot disorientation, even for experienced pilots.

The climatology of southern California, especially in the winter, combines mixed very hilly terrain with incursions from the Pacific marine layer. It appears in the Kobe Bryant tragedy, ground visibility wasn’t bad, at 3-4 miles. But FAA ceiling reports from instruments and other pilots had broken ceilings as low as 1,500 feet away from the takeoff point but in the proposed flight path. The terrain includes hills which exceed 1,500 feet in numerous locations.

If a pilot were to be embedded in dense low clouds not anticipated or not forecast, his/her situational awareness would be quite inadequate. Sometimes such meteorological conditions are not in a pilot’s weather briefing and develop unexpectedly. Other helicopter pilots have speculated they would not have flown at that time, stating the broken low ceilings were either already in place in the flight path, or were forecast to develop.

From the National Weather Service Jetstream educational site, here is a short primer on the marine layer, which is a key element in California near coastal weather and for aviation.

At this point, the National Transportation Safety Board has much investigative work to do, which will include attempts to gauge the pilot’s situational awareness concerning weather and terrain on that day. There is some evidence of pilot disorientation in those final moments, before which the pilot had done something of a rapid descent to a lower altitude, perhaps to find recognizable ground features. At that point, he was alerted by ground control he had dropped below radar by which he could be tracked on the ground.

It is all too easy to speculate on what caused this crash. The final reports will be a long time in coming, which is appropriate for a thorough investigation.

Finally, here are some thoughts from a former longtime police helicopter pilot on flying with restricted visibility. It is not directly relevant to this crash, but it illustrates some of the pilot issues.