SVR Warning Winds

[Robert Dewey]

I remember several years ago seeing a SVR warning for Wayne County (Michigan)... Instead of the typical "DAMAGING WINDS UP TO 70MPH", it said something to the effect of "DESTRUCTIVE WINDS IN EXCESS OF 90MPH". I was quite stunned that the NWS would go that high, especially after seeing a glimpse of the cell on radar. I'm not sure whether there were spotter reports within that wind range (thus prompting the high-end warning)...

What criteria does the NWS use to determine wind speeds? Some warnings say "DAMAGING WINDS UP TO 60MPH", while others say "DAMAGING WINDS UP TO 70MPH", and for high-end warnings "DESTRUCTIVE WINDS IN EXCESS OF 70MPH".

 

[Jayson Prentice]

I think it is basically determined by the reports and radar image that they have available to them. I would assume if they get a spotter report or a reading from a station that winds gusted above 70 mph then they would put that into the warning. I think any general severe thunderstorm pretty much gets the 'DAMAGING WINDS UP TO 60 MPH', but anything higher probably has to come from that spotter/report.

I suppose strong radar images can also do the trick and that maybe another good source for it.

 

[rdale]

Looking for a MARC signature - if there's a good one that would make the text a little stronger. Or if we see a good bowing indicating rear inflow increasing or headed towards the surface.

Usually it takes ground truth though to get more dramatic in a warning.

 

[Stan Rose]

There are countless factors that go into the decision. Some have just been mentioned.
Here's a few more:
1) the strength of the environmental winds, and the overall strength of the storm itself (if you have a strong supercell with well-defined rfd it's a good bet you may see higher winds).
2) DCAPE.
3) Microburst potential, which a sounding will help with. We didn't hesitate recently to mention 90 mph winds when we had sfc dewpoint spreads of 60+ degrees (!). It didn't take long for spotter reports to verify that. And some of those cells looked totally innocuous on radar--we were getting 60 mph gusts with 45 dBZ cells!
Incidentally, the 60 mph phrase sometimes doesn't make it into the warning, since a storm can have 30 mph winds and still be severe.

 

[rdale]

I can't recall ever seeing a warning that didn't have that blanket statement - even on elevated storms where there was no way the winds were getting to the surface...

 

[Robert Dewey]

I can't recall ever seeing a warning that didn't have that blanket statement - even on elevated storms where there was no way the winds were getting to the surface...
[/b]

Actually, I see that quite often. Here at DTX, it will state something like "HAIL UP TO 1 INCH IN DAMETER", but make no mention of winds. A bit further down, it might say something to the effect of "LARGE HAIL AND DAMAGING WNDS ARE LIKELY", but no actual speed is given.

 

[rdale]

That's what I'm referring to - always keeping that in the CTA even when it's not a risk. But nobody really reads that part anyways so it's not that big of a deal...