The place for technical discussions about GA and flying.
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By flyingearly
#1897961
Not sure if weather questions belong here, but it is a technical question!

Other than 'the pressure contours are close together', is there a means of estimating forecast wind speed from the pressure gradient on a synoptic chart (e.g. I'm interested in understand how close together the pressure contours need to be to result in XX knot wind, for example)?

While the weather is a bit wet, I'm trying to throw myself into lots of learning and reading to further my met knowledge and - as part of this - I start my day looking at the synoptic charts and trying to put together my own forecast, which I'll then cross-reference against the actual produced forecasts.

Where I'm struggling is that I look at the chart for tomorrow - for example - and over the South-East the lines don't appear that close together (relatively!)...

https://www.metoffice.gov.uk/premium/da ... /161441274

...but then when I look at the forecast it's pretty breezy: 30 knot gusts!

https://www.windy.com/51.353/0.504?50.9 ... ,m:e4KagbZ

I can't see from this chart where the forecast of strong winds is coming from - is it just the case that my definition of 'close together' isn't the same as others?
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By GrahamB
FLYER Club Member  FLYER Club Member
#1897966
@flyingearly The geostrophic wind strength v. separation of isobars varies with latitude.

Previously the UKMO's forecast surface pressure charts were monochrome, but had a geostrophic wind scale in the top left hand corner. The newer supposedly better colour ones don't . :roll:

Google 'Geostrophic wind scale' and you'll find a number of them - pick and adapt the the one you like best.

Remember that surface wind velocity will be lower and backed from the geostrophic value.
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By FlightDek
FLYER Club Member  FLYER Club Member
#1897988
You can find the geostrophic wind scale on charts at this location

https://premium.weatherweb.net/models/ukmo-fronts/

Measure distance between isobars and superimpose on the scale at your latitude. I learned this from Simon Keeling's weather school - highly recommended.
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#1898107
Thanks all - very helpful.

One of my goals for this year is to really get into Met; I haven't yet done Simon's weather school (I will get round to it) but what I'd really like to do is a more structured qualification that is easy to get into initially, but I can build on over time.

I'm reading Weather Flying at the moment and lots of good nuggets, but I want to try and get a broad exposure to different tools, topics and approaches; perhaps I am a bit out of the loop, but I thought Simon's course was geared around interpreting Skew-Ts; I'm happy with that, but also looking at something more formal like the Met Office courses (https://www.metoffice.gov.uk/services/t ... g/calendar)

This is one of those scenarios where geeks like me like the theory as much as the practical; I'd like to take some time off, possibly a sabbatical, and get myself a really useful qualification (!!) if I can.
By Aerials
FLYER Club Member  FLYER Club Member
#1898166
I self taught Met for NPPL and since then, I have picked such a lot of information up on youtube and elsewhere. All extremely useful to either bring knowledge back to the forefront or to 'fill in the gaps' of my knowledge. I had my attention drawn to this course https://www.futurelearn.com/courses/learn-about-weather which is free for a month or at some cost with different access variations. I haven't got round to taking the course yet but I'm going to - promise!
User avatar
By Rob L
#1898337
flyingearly wrote:
Paul_Sengupta wrote:Alternatively just look out of the window and see how far the stone on the string is leaning over.


What stone? (tornado)

Almost...it's an old forecaster's joke:

By Rjk983
FLYER Club Member  FLYER Club Member
#1898782
flyingearly wrote:Thanks all - very helpful.

One of my goals for this year is to really get into Met; I haven't yet done Simon's weather school…

….but I thought Simon's course was geared around interpreting Skew-Ts…

This is one of those scenarios where geeks like me like the theory as much as the practical; I'd like to take some time off, possibly a sabbatical, and get myself a really useful qualification (!!) if I can.


All I knew about met was the rudimentary stuff I picked up in UAS many years ago (and subsequently forgot all bar BR=mist on a TAF) and what I tried to learn from Pooleys, but ultimately I learnt enough to pass the exams and then promised myself to get some education later.

Simon runs two courses, the second of which covers SkewT charts. The weather school part one covers how to read the synoptic charts (including working out the wind speed from the isobar spacing as described above) and an intro into the various types of weather mass, how to recognise them and what they mean for flying weather.

I did the course at the start of 2021 (online via zoom and it worked really well) and I really can’t recommend it enough. Especially if you want to get a basic understanding and then decide whether you need / want to take it further. There are loads opportunities to chat to Simon in coffee breaks etc and sound him out on your longer term goals.
#1898810
You have to separate the steady wind speed from gusts. Gusts are usually the result of thermic activity.

So the isobar spacing gives you your basic wind speed, but you need either to be able to read a forecast skewT or look up thermic forecasts via RASP UK. Stronger thermals = stronger gusts.
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By TopCat
FLYER Club Member  FLYER Club Member
#1898864
GrahamB wrote:Previously the UKMO's forecast surface pressure charts were monochrome, but had a geostrophic wind scale in the top left hand corner. The newer supposedly better colour ones don't . :roll:

The monochrome ones are still available, still with the geostrophic wind scale.

You can toggle between colour and monochrome on the Met Office site here, under Briefing Charts > Surface Pressure. There's a link for the toggle just above the chart.
GrahamB, NDB_hold liked this
User avatar
By GrahamB
FLYER Club Member  FLYER Club Member
#1898903
TopCat wrote:The monochrome ones are still available, still with the geostrophic wind scale.

You can toggle between colour and monochrome…

How did I not spot that? :oops:
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By StratoTramp
FLYER Club Member  FLYER Club Member
#1908919
profchrisreed wrote:
> You have to separate the steady wind speed from gusts. Gusts are usually
> the result of thermic activity.
>
> So the isobar spacing gives you your basic wind speed, but you need either
> to be able to read a forecast skewT or look up thermic forecasts via RASP
> UK. Stronger thermals = stronger gusts.

Thanks for that, that rasp link is handy.

[usermention=23747]@flyingearly[/usermention]

I did say 1 of weather school yesterday. Day 2 is where he covers skew-t's

I was expecting day one to be a bit of s rehash of stuff I'd already learnt but it was packed full of information to eke every ounce of information out of the pressure charts as well as many actionable rules of thumb. Found the whole thing very clarifying and cemented what I did know.

Will be returning for day 2. :thumleft: