You mention here--"Typically in my experience, the "visual" part of the gust front will be nearly upon you before the serious winds hit (if they are any)"--so, are you referring to the shelf cloud specifically or something else in addition?
I should've described this in my original reply, but it's basically the shelf cloud you mention. I kind of think of it as a wide "arrow" because visually, both ends of it seem to taper down into a point...maybe "wing" is a better word than arrow, but yeah you've basically got the point.
Regarding shelf clouds I've been told two opposing views: one, that you can't conclude from an intimidating shelf cloud that there will be high winds, two, that yes, you can, that the more organizedand striated and impressive generally the shelf cloud is the greater the chance of having some potent straight-line winds coming up and that the height off the ground of the ridges/striations in it might make a difference and how high into the storm that organization proceeds
Both answers seem reasonable, but as with all things weather, you can never depend on either LOL. I've seen a lot of impressive gust fronts visually that didn't even produce severe winds (58mph or greater) let alone really intense severe winds. On the other hand, the visual structure of a gust front (as with any visual part of a storm)
can be clues to its nature. The easiest way to decide what type of winds you'll be dealing with is to monitor weather radio and keep track of warnings and any reports from anyone who may have already experienced the GF passage. The high winds in a gust front are not always neatly "packaged" and there may be smaller pockets of really intense winds within the overall severe windfield.
Are RFD cuts perceptible in multi-cell storms? And does one expect RFD winds exactly when one is in the clearer scoured out area, or a bit before and after? Should one generally take the presence of that appearance of lightened cloud or even sky and sunlight peeking through with an RFD cut to indicate stronger RFD winds?
I can't say for sure either way about the multi-cell RFD cut, I've honestly never thought about it. Theoretically it would seem that any RFD would be noticeable because it erodes cloud material, but then the multi-cell structure lends itself to competing updrafts, which are always in the cycle of building and dying, and this would (IMO) seem to preclude any chance of a significant RFD occurring (because RFDs co-exist with single, dominating updrafts). These ideas may be completely wrong, as I've never really considered this. Excellent question, perhaps someone more schooled can answer this.
One should expect to experience RFD winds when they are immediately south of the RFD region, i.e. SE/S/SW. Generally all storms move north or east so the RFD wrap descends upon the southern portion of the updraft (backside). You need to be fairly close to the RFD region (within a mile or less) to feel the effects of it, and really close to actually be in danger of high winds. (It's important to note that the RFD region is separate from the tornado itself; you can be a safe distance from the tornado but still be in the direct path of an intense RFD punch...which can sometimes be
worse than the tornado).
Usually if you can see the RFD clearly, you're far enough back to where you won't feel it too intensely. But if you're positioned south (or on the backside relative to the storm's forward motion) of a close tornado, you will begin to feel RFD effects as the tornado moves by, and again, these can be worse than the tornado itself. If you're close enough to be in danger from RFD winds, visual clues no longer apply; you need to be aware of your position relative to the tornado.
How will a gustinado first manifest itself? Will you see a rotating in the cloud above you followed by a gust without any condensation funnel ever? Or might there be a slight funnel sometimes? And would the funnel come after the winds have already been established on the ground?
To be a true gustnado, the surface circulation can not be connected to the cloud base; gustnado "spin" is generated by inflow/outflow interactions along gust fronts. Typically gustnadoes form within a concentrated area of dust, kicked out by the storm's outflow, or along a gust front. Sometimes you will see gustnadoes develop in the clear, alone, with only the circulation itself visible, no other dirt is seen. These are often mistaken as tornadoes.
However, as I mentioned in my first reply, there are situations where the inflow/outflow interface can generate cloud base rotation along a gustfront, and produce a tornado. Granted, the circulations within these type of circulations/tornadoes is certainly not "deep", but it's convective and extends to the ground and is, by definition, a tornado.
What are the thresholds for you as the chase or spotter to modify your behavior in terms of safety with these severe winds as well as stimulating you to pick a different part of the storm to chase? Generallly everyone tends to give up on a storm "lining out" into a linear gust front as you mentioned above and yet there was that tornado that emerged as you describe from "tight rotation on the leading edge" of the gust front. Did a shelf cloud identify this "leading edge" or were there other features there? After this experience, are you more reluctant to give up on a storm?
My general threshold for abandoning a storm or not is "do I think this can produce a tornado?" As long as the answer is "yes" I will stay with the storm. When I feel a storm is losing its supercellular characteristics I will abandon it immediately, unless there is no other game in town (as on June 1, 2007). There really wasn't any visual clue about this gust front rotation except the rotation itself; it appeared as a typical gust front but on the nose of it there was this vigorous cloud swirl where the rotation was concentrated. I do not believe that my chances of seeing a tornado from this type of storm/structure are nearly as high as from a typical supercell; I consider 6-1-07 to be the exception not the rule, and it's a shame I botched getting it on video.
What's the highest you'd consider safe for standing in vs. driving in? Doesn't the human body tend to go airborne around 120 or so? And by 90-100 can't one get knocked down? Assuming there aren't trees right nearby or powerlines, where would you advocate drawing the line? (And at what point might you consider lying down on the ground to avoid being picked up or thrown around) [Sorry if this starts to seem silly, but I would like to know some of these precise thresholds]
I would not advise standing outside in severe winds ever, regardless of the speed. Being knocked down is the least of your worries in high winds; airborne debris can seriously injure you, even in "low end" severe winds. Now as far as being inside a vehicle, if there are no trees or powerlines around, I'd say go for it. With nothing around for the wind to bring down on you, the only worry you really have is the wind itself. I've been in sustained winds around 100mph, with a gust to around 125mph. The 100mph winds pushed our small truck (extended cab Toyota) across dry pavement about a foot, and the 125mph gust at the end lifted the rear tires off the ground briefly and pushed the back end sideways a few feet. That was one time in almost 12 years. The typical severe thunderstorm rarely produces winds of that magnitude for that duration, so I'd say it's very unlikely you'll encounter thunderstorm winds strong enough to flip a vehicle.
How much do you trust your estimate of non-supercell tornados in terms of their power and damage potential while witnessing them away from objects? So, for example, if you're witnessing what will later be classifed anything from an EF-0 to an EF-3 out in a field, are there some particular cues?
Typically the tornadoes I've seen along gust fronts are weak, you could probably stand through one if you had something to hold onto. Visually estimating tornado windspeeds is subjective, and is "picked up" over time.
With a multi-cell severe storm, does one sometimes encounter visually more than one wall cloud at the same time?
Again, I've never really thought about this, as I typically don't chase multi-cell storms. But with multiple updrafts, the potential for multiple wall clouds seems reasonable.
