Question on high level SIGWX chart

[Kiwi]

Can you nice folks settle an argument - there's beers riding on the outcome...

On a high level sigwx forcast the jetstream is predicted.

My question is - What does the level indicated for the jetstream represent. Is it;

A) the center core of the jetstream ie it's strongest point. or,

B) the top of the jetstream. or,

C) Something else entirely.

Cheers

 

[Computer Geek]

Jet Streams​

Jet streams with a maximum speed of more than 80 knots are identified by bold lines. Jet stream lines lie along the core of maximum winds. Arrowheads on the lines indicate the orientation of each jet stream.​

Double hatched lines positioned along the jet core identify changes of wind speed. These speed indicators are drawn at 20-knot intervals and begin with 100 knots. Wind speed maximums along the jet core are characterized by wind symbols and altitudes. A standard wind symbol (shaft, pennants, and
barbs) is placed at each pertinent position to identify velocity. The altitude in hundreds of feet prefaced with "FL" is placed adjacent to each wind symbol.​

Jet Delta​

Changes to High and Medium Level SIGWX

In response to approved ICAO requirements, the World Area Forecast Centers (WAFCs) have enhanced jet stream forecasts on all significant weather (SIGWX) forecasts. WAFC Washington, Aviation Weather Center, and WAFC London added the vertical depth of the jet stream information to the jet element. This change was implemented with the 00 UTC forecast valid November 25, 2004.​

This jet forecast enhancement was presented and approved at the seventh meeting of the World Area Forecast System Study Group in September 2002.​

Forecast Strategy​

The jet stream flight level text are placed along the wind barb shaft on the opposite side of the wind barb pennants and barbs. The vertical depths to the 80 knot wind field above and below the jet steam are determined. This new forecast information has been added directly below the flight level text.
Two critical forecasts elements are available. First, the vertical depth forecast above the jet maximum which is depicted as "+XXX". Second, the vertical depth forecast below the jet maximum is depicted as "-XXX".​

EXAMPLE:​

FL350​

+300/-020​

At this maximum jet wind speed the distance to the 80 knot wind field is 30,000 feet above flight level 35,000 feet and 2000 feet below flight level 35,000 feet. These values are altitude distance values and are not flight level values.
On rare occasions when jet streams cross from one hemisphere to the other, the wind flags and associated text placement conform to the method used in the hemisphere containing the majority of the jet stream line.
The jet stream vertical depth forecast adheres to these guidelines:​

• Jet stream vertical depth forecasts are added when the maximum speed is 120 knots or more.
• Jet stream height information are placed at the maximum speed point only, normally at one point on each jet stream.
• When the jet stream is very long and there are several wind maxima, then each maxima should include forecasts of the vertical depth.

Wind change bars

Wind change bars occur at intervals of 20 knots from the spot of the maximum wind.
The jet stream vertical depth forecast is omitted when wind change bars are used.​

Hope this is what you are looking for, I was always under the impression the Hi lvl sig chart showed the 100 knt core altitude.

CG