Beginning April 1st - One Inch Hail New Severe Criterion

[Dave]

The National Weather Service will be making a change to one of the criterion on which it issues Severe Thunderstorm Warnings.

Beginning on or around April 1 2009 the NWS will change the hail-size criterion from 3/4 inch to 1 inch in diameter for the Central Region.

In more common terms, this means the criterion will change from around "Penny size" to around "Quarter size" hail.

There will be no change in the wind speed criterion, which will remain 58mph.

This change will likely result in fewer Severe Thunderstorm Warnings being issued. The NWS will no longer issue warnings when hail less than 1 inch in diameter is occurring or expected.

Studies have shown the structural damage rarely occurs when hail is less than 1 inch.

Click for more information in regards to this change:

http://www.crh.noaa.gov/crh/One_Inch_Hail_Podcast.wmv

[RL3AO]

A started a thread on it Monday but no one seemed interested.

[Dave]

I've been out since last saturday, flu, so didn't see your thread RL at all. Just now starting to feel human again.

[CrazyC83]

Is that a national standard or a regional standard?

[RL3AO]

Just the central region for now.

[Dave]

Actually my county here in Indiana isn't included yet, southeastern part because our nws office is Wilmington OH but I pull weather from Indy & Louisville. I do it because we are the western most county in the WIL district and I like to know what's going to hit us long before it gets here. IN & KY offices give me that info.

Edit: From the WARN office in Cincinnati OH:

"This does not affect us at this time. No decision has been made on when or if the change will be made by the Eastern Region NWS offices. For now, it’s business as usual."

[RL3AO]

Everything I've heard is Central Region only.

[vbhoutex]

Everything I've heard is Central Region only.

I find that hard to believe(not doubting you) that only the central region would change something like this. I haven't had time to check it further, but the hail size is one of the basic things taught during Skywarn classes.

[RL3AO]

From what I understand, it has been tested by the WFOs in Kansas since 2005 or something and is now being spread to every Central Region WFO.

EDIT: From the Green Bay WFO site.

Hail Size for Severe Thunderstorm Warnings Increased to One Inch

The National Weather Service (NWS) Central Region conducted a demonstration in the state of Kansas and nearby areas over the past four years, utilizing a hail size criterion for issuance of Severe Thunderstorm Warnings of 1" in diameter, rather than the historical 3/4" threshold. This experiment was based on feedback from local partners, as well as scientific research conducted by Texas Tech University which demonstrated that significant property damage does not occur until hailstone sizes reach 1" in diameter. The NWS Central Region, along with the NWS Office of Climate, Weather and Water Services (OCWWS), is now taking steps to expand the demonstration area to encompass all Central Region weather offices, including the NWS offices that serve Wisconsin.

No change in minimum severe wind (58 mph or 50 knots) is being made. The new hail criteria is scheduled to be implemented this April 1.

[Extremeweatherguy]

Kind of strange that Oklahoma will not be included in this.

[srainhoutx]

My understanding is that most but Southern Regional has adopted this change. Correct me if I'm wrong.

[Dave]

I emailed our WARN office a few minutes ago to see if they have any info on other regional offices including ours at Wilmington OH on this subject.

[RL3AO]

I guess the stats showed that around 50% of SVR are issued for .75" hail.

[Dave]

Here's the answer I just received from the WARN network out of Cincinnati OH/Wilmington OH NWS:

"This does not affect us at this time. No decision has been made on when or if the change will be made by the Eastern Region NWS offices. For now, it’s business as usual."

From that, it looks like RL3AO's right, Central Office only so far.

[srainhoutx]

Here's the answer I just received from the WARN network out of Cincinnati OH/Wilmington OH NWS:

"This does not affect us at this time. No decision has been made on when or if the change will be made by the Eastern Region NWS offices. For now, it’s business as usual."

From that, it looks like RL3AO's right, Central Office only so far.

Thanks ai9d. That clears that up.

[vbhoutex]

The fact that it is still in "demonstration" mode is what cleared it up for me besides this official answer. Thanks Dave for helping clear this up.

[CrazyC83]

I think it should at least be increased to .88" (nickel size) if not 1" (quarter size).