Last Night's Storms

Wow, last night was an incredible night covering severe weather. Normally hail is not as big of a deal around here. That wasn't the case last night. Hail definitely lead the night with hen egg and tennis ball size hail reports coming in from central and south Mississippi. Golf ball size hail was common in just about all of the thunderstorms. More on the hail later.

As I expected, the tornado and wind threats were very small. There was wind damage in parts of Hinds, Copiah and Simpson counties. The National Weather Service sent teams into some of those areas to survey the damage. Their report came down this afternoon. Here it is:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE JACKSON MS
332 PM CST WED MAR 30 2011

...STORM SURVEY DETERMINES THAT WIND DAMAGE IN SIMPSON AND COPIAH
COUNTIES WAS DUE TO STRAIGHT LINE WINDS...

...PRELIMINARY STORM SURVEY INFORMATION...

COUNTY: SIMPSON
SUMMARY OF WIND DAMAGE: A MACROBURST OCCURRED IN NORTHWEST SIMPSON
COUNTY ALONG AND NEAR OLD PEARL ROAD. THE DAMAGE WAS WIDESPREAD
ACROSS THE AREA WITH THE WORST DAMAGE OCCURRING FROM CRISCO ROAD TO
LEWIS ROAD SOUTH. NUMEROUS HARDWOOD AND SOFTWOOD TREES WERE UPROOTED
AND SNAPPED IN THE DAMAGE AREA. SEVERAL TREES FELL ON HOMES AND
OUTBUILDINGS CAUSING SOME STRUCTURAL DAMAGE. MAXIMUM WINDS WERE
ESTIMATED TO BE 110 MPH FROM CRISCO ROAD TO LEWIS ROAD SOUTH.

SUMMARY OF HAIL: REPORTS INDICATE THAT HAIL AT LEAST AS LARGE AS
GOLF BALLS FELL IN THE SAME AREA FOR A SIGNIFICANT PERIOD OF TIME.
HAIL ACCUMULATED 4 INCHES DEEP ACROSS THE AREA WITH A FEW SPOTS
ESTIMATED TO BE AROUND 1 FOOT DEEP. SOME ROOF AND SIDING DAMAGE WAS
CAUSED BY THE WIND DRIVEN HAIL. THE HAIL CAUSED WIDESPREAD LEAF AND
PINE NEEDLES TO BE STRIPPED FROM THE TREES.

COUNTY: COPIAH
SUMMARY OF WIND DAMAGE: NUMEROUS TREES WERE UPROOTED AND SNAPPED IN
AND TO THE NORTH OF CRYSTAL SPRINGS. SEVERAL OF THE TREES FELL ON
HOMES CAUSING STRUCTURAL DAMAGE. TO THE NORTH OF CRYSTAL SPRINGS...A
METAL BUILDING HAD TWO WALLS BLOWN OUT. MAXIMUM WINDS WERE ESTIMATED
TO BE 90 MPH IN THE COUNTY.

As word got out that the storm surveys concluded the wind damage was caused by straight-line winds, I heard some complaints from people.

No doubt trying to determine if the damage was due to a tornado or straight-line winds can be hard. There was a tornado warning out. There was, albeit a weak, circulation in the storm. Determining the damage to be caused by a tornado would actually would help verify the tornado warning. But, in this case, the survey team from the weather service looked at the damage, compared it to the radar images, and ultimately decided that straight-line winds and wind driven large hail caused the damage in the Crystal Springs and in northwest Simpson County. Now, it is easily overlooked, but this damage survey is PRELIMINARY, so there is always a chance if new damage is discovered and checked out, there could be some changes made to the report. This is why it is very important that if you have damage or you have strong winds or hail, you should report it either to WLBT, the NWS, or your local emergency management officials.

Let's go with assuming that the damage was all straight-line wind or hail. Straight-line winds can be over 100mph. Heck, winds in a hurricane are a type of straight-line wind. We all know how strong those can be. In the Simpson County case, the straight-line winds were believed to be caused by something called a macroburst (more on that in a second) and are estimated to have been about 100-110mph in Simpson County. To put that in perspective, those winds are what you'd find in a strong Category 2 hurricane!

A macroburst is a large scale downburst. Downbursts are common in thunderstorms. Downbursts are created when rain-cooled air falling in the downdraft part of a thunderstorm helps to bring the strong winds inside the storm down to the ground. When those strong winds hit the ground, they fan out. The net result is very strong winds at the surface, just like what happened last night. The intensity of last night's downburst is rare for this part of the country. In fact, I'm not sure in my 7 years in Mississippi I've seen straight-line thunderstorm winds that strong. Downbursts are a big threat to air planes landing or taking off as well.

This graphic helps to illustrate downbrust winds. You can click it to make it larger.

When storm surveys are done, meteorologists look at the damage pattern to determine if the damage was done by a tornado, straight-line winds, or even hail.

Damage from straight-line winds, like from a microburst (small scale) or macroburst (larger scale), will generally be pointed in the same direction and have a diverging pattern to the damage. Tornadic damage, on the other hand, will have a cyclonic (in most cases) pattern to the damage. Sometimes survey teams have to look at the damage from an airplane to get a better idea. I do not know if that was done in the Copiah and Simpson county cases.

Below are two examples of each kind of damage. Can you see the difference?
Regardless of if it was tornado damage or straight-line wind damage, insurance policies will cover it. If you have one that doesn't or the insurance company tries to tell you it won't cover straight-line wind damage, but it will tornado damage, I'd advise you to read over the fine print in your policy and do some investigating of your own.

The wind driven hail also caused a lot of the damage. That may have an impact on some insurance policies? I'm not really sure.

Let's talk about the hail....it was INCREDIBLE. Not only the size, but the amount. Check out this picture from Simpson County. This was taken after sunrise and hail was still on the ground!

There are several reports of hail drifts up to a FOOT deep. WLBT's David Kenny, who covered Simpson County today, says that hail was still on the ground this afternoon. That's nuts! I will be interested to see how that compares to other hail storms in Mississippi. Let me tell you, it is rare ANYWHERE!

By the way, I still want hail pictures. If you have anything, especially hail coating the ground, please send them to me at elaw@wlbt.com. I will be able to use them in future weather talks and the National Weather Service would also like to look at them.

Suffice to say, if this storm had moved over a populated area, like the Jackson Metro, we'd be talking about hail damage in the multi-millions of dollars.

I'm planning to blog on some more things tomorrow. Probably about the complaints from our weather coverage.

Eric - elaw@wlbt.com