High Wind Warning criteria?

[Robert Dewey]

I thought high wind warning criteria was categorized as sustained wind speeds of 40 MPH or greater lasting for 1 hour or longer, and/or winds of 58 MPH or greater for any duration of time?

Is the criteria different for northern GA? The warning outlines sustained winds of 20-35mph, which is still short of warning criteria... unless by "gusts at or above 45mph" implies >=58mph.

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
443 PM EST WED DEC 2 2009

GAZ001>009-013>016-030300-
/O.CON.KFFC.HW.W.0004.000000T0000Z-091203T0300Z/
DADE-WALKER-CATOOSA-WHITFIELD-MURRAY-FANNIN-GILMER-UNION-TOWNS-
PICKENS-DAWSON-LUMPKIN-WHITE-
INCLUDING THE CITIES OF...DAHLONEGA...CLEVELAND
443 PM EST WED DEC 2 2009

...HIGH WIND WARNING REMAINS IN EFFECT UNTIL 10 PM EST THIS
EVENING FOR THE NORTH GEORGIA MOUNTAINS...

A HIGH WIND WARNING REMAINS IN EFFECT UNTIL 10 PM EST THIS
EVENING.

STRONG WINDS ARE EXPECTED ACROSS MOST OF GEORGIA THIS AFTERNOON
AND EVENING AS A LOW PRESSURE SYSTEM MOVES FROM WESTERN TENNESSEE
INTO THE OHIO VALLEY. SOUTHEAST WINDS AT 20 TO 35 MPH WITH HIGHER
GUSTS AT OR ABOVE 45 MPH ARE EXPECTED...ESPECIALLY IN THE HIGHER
ELEVATIONS OF NORTH GEORGIA. THE WINDS WILL BEGIN TO SUBSIDE AFTER
SUNSET THIS EVENING.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A HIGH WIND WARNING MEANS A HAZARDOUS HIGH WIND EVENT IS EXPECTED
OR OCCURRING. SUSTAINED WIND SPEEDS OF AT LEAST 35 MPH OR GUSTS
OF 45 MPH OR MORE COULD TOPPLE TREES AND POWER LINES AS WELL AS
CAUSE PROPERTY DAMAGE. WINDS THIS STRONG WILL MAKE DRIVING
EXTREMELY DIFFICULT...ESPECIALLY FOR HIGH PROFILE VEHICLES.
PLEASE USE EXTRA CAUTION TODAY.

 

[rdale]

http://www.weather.gov/directives/sym/pd01005015curr.pdf

"Wind speeds forecast to meet or exceed locally defined warning criteria. (Typical values are sustained wind speeds of 40 mph or greater lasting for 1 hour or longer, or winds of 58 mph or greater for any duration)."

 

[Jay McCoy]

Sounds like a golf day in the Texas panhandle...lol

I always get a chuckle when I see places like Austin anywhere in Georgia/ Mississippi talking about high winds in the 20-25 range.. But I guess when your used to stagnant calm air anything about 15 is a bad wind day.

 

[Tim Stoecklein]

No kidding Jay, I always chuckle when I see Cat 1 hurricane wind speeds, and then we have high wind warnings for the same speeds

 

[Robert Dewey]

http://www.weather.gov/directives/sym/pd01005015curr.pdf

"Wind speeds forecast to meet or exceed locally defined warning criteria. (Typical values are sustained wind speeds of 40 mph or greater lasting for 1 hour or longer, or winds of 58 mph or greater for any duration)."

Thanks Rob. I guess this falls under "locally defined." We have several events per year here in the Great Lakes area that are 45-55mph (max gusts) with nothing more than the standard advisory (sometimes being issued last minute as the reports stream in), this caught me off guard.

 

[B Ozanne]

Sounds like a golf day in the Texas panhandle...lol

I always get a chuckle when I see places like Austin anywhere in Georgia/ Mississippi talking about high winds in the 20-25 range.. But I guess when your used to stagnant calm air anything about 15 is a bad wind day.

It's not that people are used to calm winds, it's the forested canopy that is. 40 mph sustained winds (hasn't happened in years here) or 50+ gusts tend to wreak havoc in my part of the world, and that's in the winter. Local conditions are obviously a big factor. Just like a foot of snow in Alta, UT may only generate a winter weather advisory.

 

[Jay McCoy]

It's not that people are used to calm winds, it's the forested canopy that is. 40 mph sustained winds (hasn't happened in years here) or 50+ gusts tend to wreak havoc in my part of the world, and that's in the winter. Local conditions are obviously a big factor. Just like a foot of snow in Alta, UT may only generate a winter weather advisory.

Thasts what I was implying.. What some of consider a normal day is a wild day to somebody esle. I am sure folks in the Dakotas laugh at folks in Dallas where a few inches of snow closes schools.

In the early spring it is common to have days with winds here in Amarillo of 40-50mph with gusts of 70+.

 

[Brett Adair]

With trees....etc.....around here we generally get alot of damage with those kind of winds after the ground has been very saturated from the significant amounts of rainfall picked up within the last few months. FFC always issues watches/warnings it seems based on different criteria than most.

 

[Chris Nuttall]

Thasts what I was implying.. What some of consider a normal day is a wild day to somebody esle. I am sure folks in the Dakotas laugh at folks in Dallas where a few inches of snow closes schools.

In the early spring it is common to have days with winds here in Amarillo of 40-50mph with gusts of 70+.

I'll take the 45mph and raise you 10 more. I'm holding a full house with lee-side cyclogenesis and a dry slot.

 

[Glenn Rivers]

High Wind Criteria

One factor that may be in play here is that winds over arodynamicaly rough terain or even tall forests tend to have much more turbulance and short term (second to minute) variability than winds blowing over open grassy plains or water, at the same average wind speed.

Wind damage to buildings and trees can be very sensitive to high frequency turbulence. I remenber reading about the devastating wind damage to a large woodlot in Germany caused by one the great winter gales of the last decade. The study found that the trees at the upwind edge of the woodlot facing the highest wind speeds suffered relatively little damage while trees some distance inside the woodlot suffered far worse damage. This was attributed to the very energetic spectrum of high frequency wind gusts that caused destructive amplification of the swaying motion of the trees, despite the fact that these trees were subject to lower wind speeds than the trees at the upwind edge of the forest.

I think that one might find the experience of a wind prevailing during an ASOS report of 40 G 50 Knots in Amarillo an invigorating experience, while an outing in a windstorm in a wooded or urban area in New England or in the Southeast giving an ASOS report of 40 G 80 Knots would be a thoroughly terrifying experience.

 

[beaudodson]

Interesting presentation on high wind warnings - to issue then or not to issue them - criteria and other

http://ams.confex.com/ams/39BROADCAST/flvgateway.cgi/id/18132?recordingid=18132

 

[Mike Johnson]

interesting presentation, but that audio is TERRIBLE!

 

[rdale]

Hey - it was a conference that cost hundreds of dollars to go to... I can't complain that much that they are doing it for free NWA has yet to follow suit with their conferences...