Primarily for general aviation discussion, but other aviation topics are also welcome.
#1872666
Looking at your first TAF it was accurate in that the TEMPO occurred as predicted. However it was late clearing.

The second TAF was spot on. It cleared exactly on time.

See https://www.ogimet.com/display_metars2. ... &send=send

What you may not know is that they cannot issue or reissue a TAF until they have had 3 actuals on which to base the new TAF.

Hence the hour delay that you are seeing.
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By TopCat
FLYER Club Member  FLYER Club Member
#1872739
The funny thing is, the first TAF turned out to be much better.

It was indeed (much better than) 9999, and pretty much exactly FEW 040 when I went flying briefly this afternoon to dry off my now sparkly clean aeroplane. It took quite a lot longer to clear up than the TAF suggested, but it turned out quite nice.

The TAF AMD was the aberration, interestingly.
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By kanga
#1873038
now no longer flying, so my 'these days' is the ~10 years up to ~5 years ago. In that period TAFs were much better (more accurate as well as more easily available) than they had been when I started flying 50+ years ago, despite there being fewer METARs available (presumably because of closures of military airfield with Met Office Observers at each). Have things got worse in the last ~5 years ?

Forecasting for British Isles (sitting on the windward side of a large ocean with both sea and air mixing warmer and cooler air) is always going to be difficult, especially for the phenomena which particularly affect GA - cloudbase and wind strength.
#1873042
TAFs got worse when they changed to a 24hr forecast period a few years ago. When there was a 0700-1600 TAF followed by a 10-19, the later one was more accurate after they had a chance to look out the window. They also used to issue TEMPOs for a 1hr duration now they don't bother. They can get away with doing less work.
#1873132
kanga wrote:
Forecasting for British Isles (sitting on the windward side of a large ocean with both sea and air mixing warmer and cooler air) is always going to be difficult, especially for the phenomena which particularly affect GA - cloudbase and wind strength.


Once in Gibraltar I was thanking the met man who, the previous week, had given us an impressively accurate forecast for a slow 3 day flight back to the UK.

I said “I suppose it’s a lot easier to make forecasts here in the Med?”

His reply was that UK forecasts are far easier because there were many more reporting airfield/ Airports and, more importantly, a lot of weather ships in the North Atlantic watching the approaching weather...all of which actually made forecasting here easier.

I was quite surprised...
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By PeteSpencer
FLYER Club Member  FLYER Club Member
#1873504
Today's TAF in E Angular was spot on

Sunny, strong winds straight down the chute in the morning > Flew home early pm spotting and dodging the easily visible but non transparent heavy showers, then after putting AC to bed, drove home through a torrential downpour with cloud down to the ground and vis less than 2miles across the fields.

I guess you win some and lose some..................... :wink:
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By BoeingBoy
#1873649
I am sure someone will correct me but as far as I am aware, all computer models are in essence based on historical records of what happened next when similar conditions appeared in the past. No doubt some clever tweaking is now done in the name of modern programming to justify getting rid of met forecasters but my experience of the met service over the last forty years would seem to indicate that once a forecast is published it's constantly updated until it matches the actual. That way you can't file a claim in litigation against the Met Office for it not being correct.

When I started out in airline flying, part of our briefing process was to visit the local met office where a little old man in horn rimmed glasses, wearing corduroy trousers complete with sandals and socks, and a baggy jumper would remove his pipe and tell us to the exact minute what time a cold front would ruin our return from the Greek islands in twelve hours time. Nowadays you're lucky if the computer can forecast an entire low pressure system to within the same time band!

The UK Met Office are constantly aware of their legal liability following the great storm of the eighties (I was flying that night). So much so that TAF's are merely best guesses, constantly updated until they are METARS.
#1873945
BoeingBoy wrote:I am sure someone will correct me but as far as I am aware, all computer models are in essence based on historical records of what happened next when similar conditions appeared in the past.


Actually they are based on actually weather dynamics at low scale levels where we measure initial conditions and we use physics to simulate things going forward while disregarding historical data, this does not allow for some historical seasonality effects or similarities in the past, but some of these are introduced on ad-hoc basis

The relationship between weather state at t & t+1 is based on physics law rather than historical data (t-265/t-266 from one year ago), it’s shame they don’t combine both, they can’t predict summers & winters from initial conditions :lol:
#1873976
PeteSpencer wrote:Today's TAF in E Angular was spot on

Sunny, strong winds straight down the chute in the morning > Flew home early pm spotting and dodging the easily visible but non transparent heavy showers, then after putting AC to bed, drove home through a torrential downpour with cloud down to the ground and vis less than 2miles across the fields.

I guess you win some and lose some..................... :wink:



Looked at TAF' for local Yarksheer aerodromes today and also the synoptic. Thought, ahaaaa, we have a window in our envelope so to speak. Needed to do a flight test on an RV8.

And so it came to pass.... 240/12, Sc2400, 14/12, 1005.

My training was not in vain :mrgreen:
#1873981
There are the formal TAFs, but there are more detailed reports/apps available (usually at a small cost).

If you’re using only free stuff, you’re likely on the GFS which is free for all. But there is also ECMWF, ICON, NEMS & AROME which will vary by applicability depending where you are and what type of flying you are doing.

Also any models output will vary with how close the dataset is to the mean. Example: three previous cool damp overcast 10C days (we’ve got that sorted in the UK; loads of data). Now what if there was aberrant weather blowing our way from across the Atlantic or just unusual (Example: 3 days over 35C with wind out of the north); how many prior examples do we have to run.
#1873985
Curiously just looking at weather to confirm dodgy weather as I've got 10 days of isolation re getting COVID.

I see there's a low in the North Atlantic at 955 hPa.

I remember in early 2020 we had some high pressure days at/near 1050 and many of us found that was the upper limit of our altimeters settings; what is the lowest QNH most altimeters can set?
By BoeingBoy
#1874035
what is the lowest QNH most altimeters can set?


Pinched from another forum:

There are actually multiple different answers depending on the specific type of altimeter system and what standard applies.

The stand-alone altimeters in older aircraft and small GA aircraft (panel mounted "steam gauge") are certificated to SAE AS392C, Altimeter, Pressure Actuated Sensitive Type. The specified scale range is "at least 28.1 - 30.99 inches of Hg (946 - 1049 millibars)".

This standard was updated in 2016 to require compliance with SAE AS8009C, Pressure Altitude Systems. Altimeters built to this standard have a specified range of 27.50 - 31.50 inches of Hg (931.3 to 1066.7 mb).

Aircraft with "glass cockpits" use Air Data Computers certificated to SAE AS8002A, AIR DATA COMPUTER - MINIMUM PERFORMANCE STANDARD. Barometric corrected altitude correction is covered by Table 2, which defines a range of 22.00 - 30.98 inches of Hg or 745 - 1049 millibars.