https://thebarentsobserver.com/en/ecology/2020/02/extreme-low-pressure-brought-down-air-traffic-northern-norway
The past months have seen extraordinarily rough weather along the north Norwegian coast. Early this week came another extreme. The air pressure dropped to a level not seen in several decades.
According to the Norwegian meteorological institute, the air pressure across major parts of the region was below 940 hectopascal, a level that makes flying unsafe.
940 hectopascal = 13.65 psi or 940 millibars.
"The low pressure also resulted in high waters levels along the Norwegian coast. In Tromsø, the north Norwegian town, the sea water was on Tuesday 354 cm higher than normal, the Meteorological Institute informs"
Circa 10 ft rise in sea level.
940 millibar = 27.76 inHg ... pretty amazingly low.
Using the rule-of-thumb that one inch of mercury is about a thousand feet of pressure altitude, that still only implies a pressure altitude of 2,000' at sea level, which isn't going to be stop a plane from flying. I assume the issues are primarily about instrumentation or automation limitations than anything else.
Quote from: NovemberWhiskey on February 15, 2020, 06:37:29 AMI assume the issues are primarily about instrumentation or automation limitations than anything else.
I'd agree... the adjustment range of my aircraft's altimeter is 28.10 - 30.99 so an ATIS report of 27.76 would keep me on the ground.
Pressure this low breaks the rule of thumb for reading metars: three digit millibar values less than five prefix with a ten, otherwise prefix with a nine.