Archive for February, 2012

Updated Tornado Stats….
February 29, 2012

These are some great stats provided by John Robinson from the NWS in Little Rock.  Here is an explantion below….

Things to keep in mind:  On the map showing the number of verified tornadoes, if a tornado passed through more than one county, it is counted in each county that it entered (in other words, it appears on the map more than once); thus this map is referred to as “tornadoes by county.” Counties with the largest populations are likely to have the largest tornado counts, since almost all tornadoes will be observed and reported. More rural counties, especially those with large areas of timber and small populations, tend to have smaller tornado counts since some tornadoes may go unreported.
 
On the map of tornado deaths:  The number of fatalities in White County heavily reflects the Judsonia tornado on March 21, 1952 (as does the number in Woodruff County).  That day was the deadliest tornado day in Arkansas history with at least 111 lives lost.  In 1952 when the Judsonia tornado occurred, TV stations were just coming on the air in Arkansas, there was no weather radar, and the warning program in this country was just getting underway. In those days, unless you saw the tornado or someone else saw it and called you on the phone, virtually all tornadoes hit by surprise. So, the death toll tended to be much larger in those days. Such large loss of life nowadays is less likely, but not impossible — just look at the tornadoes in Tuscaloosa, Joplin, and other places last year.
 
Drew Michaels
 
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Severe Weather Recap
February 29, 2012

 A couple potent thunderstorms moved through Benton, Washington and Madison counties last night. Two of these cells had significant rotation and had tornado warnings in effect for them. The cell in northern Benton county is the same storm that produced a tornado in Branson, MO. The second cell did put down a path of hail and wind damage. Winds were gusting to 60 mph with some ping-pong ball size hail.

Ross Ellet

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Tornado Watch Until 5:00 A.M.
February 28, 2012

A strong to severe line of thunderstorms continues to move in our direction.  The SPC has issued a Tornado Watch across the area until 5 a.m.

The wind shear remains extremely strong tonight, so it’s possible to get a few storms within the line that rotate.  Those storms will be capable of producing isolated tornadoes.

Drew Michaels

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10:00 P.M. Update
February 28, 2012

A line of strong to severe thunderstorms has developed to the northwest of the Tulsa metro area.  This line of storms will move in between Midnight and 3 a.m.

The overall tornado threat remains low within the line; however, an isolated tornado is possible with the amount of wind shear present in the atmosphere.  Quarter hail and gusty winds to 60 mph are the primary threats.  Currently there are no watches or warnings in effect across our viewing area.

Drew Michaels

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6:00 P.M. Update
February 28, 2012

All remains quiet across the area this early evening.  The weather should remain quiet through 10 p.m.  Showers and storms will move in between 11 p.m. and 3 a.m.  Now it’s looking more like the storms will arrive closer to midnight.

The clouds have limited the overall instability this afternoon.  The cloud cover has helped to weaken the overall severe weather chances; however, the wind shear remains high tonight, so storms will still have to be watched closely for rotation.

Wind shear will continue to strengthen after dark as a ribbon of air around 5,000 ft increases.  You can see that depicted above.  We call that the low-level jet.  That low-level jet will also help to create elevated instability which will also help to fuel showers and storms.

Quarter hail, gusty winds to 60 mph, and a small tornado threat.

Drew Michaels

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2:30 P.M. Update
February 28, 2012

The clouds have filled back in across the area this afternoon as expected.  This stratus indicates of the warm moist air being transported from the Gulf of Mexico.  Isolated showers are possible across the area this afternoon and evening.

The warm front is slowly creeping north across the Ouachitas.  The models still indicate that the front will push north across our entire area by this evening.  Dewpoints will continue to increase into the middle to upper 50’s and lower 60’s.  

The dryline across western Oklahoma/Texas will be the focus for shower and thunderstorm activity late this afternoon and early evening.  Those storms along the dryline/cold front will head in our direction toward the late evening.  The storm timeframe has been pushed back even further.  10 p.m. till 3:00 a.m. is more realistic.

Right now the instability is really lacking across the area.  That’s something that would help to limit the overall tornado threat.  Winds and hail are still possible with the strong to severe storms.

Drew Michaels

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10:00 A.M. Update…Increasing Moisture
February 28, 2012

The forecast will quickly evolve this afternoon and evening with showers and thunderstorms developing.  One of the necessary ingredients for severe thunderstorms is surface based moisture.  We look at dewpoints to indicate where the deep moisture resides.

This is a surface map made up of many station plots.  The bottom green number represents the dewpoint temperature.  Notice that the dewpoints across NW AR and the River Valley are low; however, just to our south, dewpoint are in the upper 50’s to near 60.

Dewpoints in the middle to upper 50’s and lower 60’s would help support strong to severe thunderstorms.  A warm front sits just to our south this morning along the Red River.  South of the warm front is where the greatest moisture sits.  The warm front will lift north throughout the afternoon allowing the deeper moisture to move into eastern Oklahoma and western Arkansas.

You should notice the humidity will increase throughout the afternoon.  Some other ingredients will need to come together for severe weather; however, the moisture part of the equation won’t be an issue.

Drew Michaels

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It All Comes Down To The Sunshine
February 28, 2012

We are still under a slight risk for severe thunderstorms for tonight. This is what we call a high shear low instability set up. In other words, the winds in the atmosphere will be very supportive of severe weather later on tonight, but there won’t be a lot of instability available to help get violent storms started. We are expecting a mostly cloudy sky today, if we do get more sunshine then the instability will be much higher and the threat for severe weather will also climb.

The biggest thing that we are concerned about is that an increase in sunshine will quickly erode a very weak inversion. That would allow tonight’s thunderstorms to be surfaced based instead of elevated. In other words the storm’s cloud base will be much closer to the ground and that is where the strongest wind shear is located. This would not only lead to an increase in hail, and damaging winds but the tornado threat would also climb much higher. So it all comes down to the sunshine…and it is a wait and see game at the moment.

Ross Ellet

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Tuesday’s Severe Weather Update
February 27, 2012

I really have no major changes from Ross’ thinking from earlier today.  The entire viewing area remains under a slight risk for severe weather for Tuesday evening. 

The severe storm potential will mainly be from 6p.m. until Midnight.  Storms will develop out west during the late afternoon and early evening, and head in our direction toward the late evening.

A warm front will race north by Tuesday morning.  Low level moisture will  increase from the south.  We’re expecting dewpoints in the 50’s and 60’s, so low-level moisture won’t be in question with this event.

The tricky part of the forecast is how severe will the storms be.  This is a tough forecast because we’re expecting low clouds to be with us throughout the morning and afternoon.  A low cloud deck will limit the amount of available instability; in other words, storms would be weaker and less severe.

If the clouds can break and the sky goes partly cloudy, the hail and tornado threat would increase dramatically.  Right now the models are keeping the CAPE low, but that could be altered if sunshine returns.

Sunshine would increase the updraft speed which would support larger hail stones.  Sunshine would also help to promote surface based storms.  If surface based storms can become rooted in the boundary layer, the chance for tornadoes would also increase.

We will watch the conditions closely throughout the day tomorrow.  Keep checking the weather blog for more updates.

Drew Michaels

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Severe Storms Possible Tomorrow Night
February 27, 2012

As Drew mentioned last night, severe thunderstorms are possible Tuesday evening. A few showers and storms are possible in the morning hours along the warm front but the biggest severe weather threat will be between 6pm and Midnight on Tuesday. The biggest threats will be damaging winds. Large hail and isolated tornadoes are also a big concern as well. At this time, the area is under a slight risk for severe thunderstorms. I wouldn’t be surprised if that risk area is upgraded to a moderate risk in future outlooks…especially if more sunshine is able to break out on Tuesday afternoon.

Ross Ellet

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