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April 15-16 Severe Weather threat


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Wow, what an incredible storm here in Dunwoody (where I'm visiting). 1"+ hail falling for 10 minutes followed by extremely heavy rain.

Wow, amazing stuff larry. I have never experienced anything like that. I know large hail is not something you exactly wish for but I'm somewhat envious.

Wind here is blowing awfully hard...almost as hard as it was before that severe line that went through a while back. Several gusts into the low to mid 30mph range and it's been getting progressively higher. Not expecting anything like what happened with that line, unless a stray severe storm is able to develop. But this wind is impressive on it's own.

Robert, you are sure right about the rainfall amounts. Models not handling it well at all.

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looks like the models are going to bust way too low on rain amounts. I'm not surprised. The backbuilding convection will probably continue through the night until the front comes through for GA and then the Carolinas.

Yep, it looks like the radar is setting up well for some significant rainfall overnight into the first half of tomorrow. I was noticing how the low level southeast flow never got any precip developing, infact during the afternoon hours the dewpoints here mixed out into the 40's. But since early evening, the rainfall has picked up a lot of steam in advancing northeast into the Southern Appalachians.

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Yep. We are easily going to break 2 inches again here. It is raining to beat the band right now. Seems like every storm system in the past month has dropped at least 2 inches here. Some over 3 inches.

Wow, amazing stuff larry. I have never experienced anything like that. I know large hail is not something you exactly wish for but I'm somewhat envious.

Wind here is blowing awfully hard...almost as hard as it was before that severe line that went through a while back. Several gusts into the low to mid 30mph range and it's been getting progressively higher. Not expecting anything like what happened with that line, unless a stray severe storm is able to develop. But this wind is impressive on it's own.

Robert, you are sure right about the rainfall amounts. Models not handling it well at all.

Yep, it looks like the radar is setting up well for some significant rainfall overnight into the first half of tomorrow. I was noticing how the low level southeast flow never got any precip developing, infact during the afternoon hours the dewpoints here mixed out into the 40's. But since early evening, the rainfall has picked up a lot of steam in advancing northeast into the Southern Appalachians.

Yes, this is an anomalous situation, with the 4 contour cutoff so far south and west, and slow moving, I didn't think the models were handling the building and rebuilding convection properly. Even with the southeast winds, severe will probably make it into the Carolinas overnight, and for GA and Ala and eastern TN, the constant diffluence right over rich air inflow will equal continuous re-development of rain and storms. The RUC has it finally pushing through around 9 to 11 am for CLT region, and thats when the veering flow will be the worst , so another squall line with discrete should have developed by then, if not quasi linear. Once that pushes to near RDU the models have it much stronger. Either way you slice it , heavy rain and discrete supercells through the night likely, not to mention the geostrophic winds howling and increasing, esp. as the front nears, with the low level jet increasing, as Lookout noted. High winds here already blew more limbs down, and its only going to get worse. One look at the radar shows rain filling back in under eastern TN where the strongest diffluence is, probably some 3"+ amounts there to western NC and northern third of GA, considerig the best lift will still be several hours away. Another amazing event really all around.

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It has been awhile since I can remember an event like this across the southern U.S. - perhaps that 1990s? Unsure. Defin one for the books and an incredible day. Incredible amount of rotating storms.

I guess it depends on where you live really. At my house, I've had nothing but rain and some lightning. Nothing to remember at all. Are you saying this event is bigger than the Super Tuesday tornado outbreak in 2008 ?

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Yes, this is an anomalous situation, with the 4 contour cutoff so far south and west, and slow moving, I didn't think the models were handling the building and rebuilding convection properly. Even with the southeast winds, severe will probably make it into the Carolinas overnight, and for GA and Ala and eastern TN, the constant diffluence right over rich air inflow will equal continuous re-development of rain and storms. The RUC has it finally pushing through around 9 to 11 am for CLT region, and thats when the veering flow will be the worst , so another squall line with discrete should have developed by then, if not quasi linear. Once that pushes to near RDU the models have it much stronger. Either way you slice it , heavy rain and discrete supercells through the night likely, not to mention the geostrophic winds howling and increasing, esp. as the front nears, with the low level jet increasing, as Lookout noted. High winds here already blew more limbs down, and its only going to get worse. One look at the radar shows rain filling back in under eastern TN where the strongest diffluence is, probably some 3"+ amounts there to western NC and northern third of GA, considerig the best lift will still be several hours away. Another amazing event really all around.

Yeah I think the strongest shot of severe storms here in northeast/east ga and western carolinas will be at least 3am or after...which is worrisome for obvious reasons. There are two strong storms near to me but one will go north of here and the other is the long tracked supercell that started way back in alabama and it will go south of here. Pretty amazing to see how long it has held together.

Dewpoints are finally starting to rise here. They have been stuck in the low 50s most of the evening but it has risen to 57 here of late.

As you noted, I have also had a few small limbs come down with these winds. Seems like we have had a lot of wind this spring, certainly of late.

As I'm finished typing this, starting to hear some thunder for the first time. Rain started a few minutes ago.

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Here's a frontal map Met Tech just shared with me on Yahoo Messenger...

Discussions we had included occluded fronts, triple points, shear, low pressure troughs

It's neat to have a monster event like this one that I get to watch and not actually have a direct hit (like Hurricane Gustave)

post-6115-0-30285900-1302924278.gif

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Strong line of storms representing the back edge of precipitation is still back just east of Birmingham. Given the trajectory of the storms I think metro Atlanta is in for another round. I fully expect to be woken up in a few hours to thunder and flashes of vivid lightning. I just hope the tornadoes if any stay away from my area.

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Strong line of storms representing the back edge of precipitation is still back just east of Birmingham. Given the trajectory of the storms I think metro Atlanta is in for another round. I fully expect to be woken up in a few hours to thunder and flashes of vivid lightning. I just hope the tornadoes if any stay away from my area.

So you think they may need to re-issue a tornado watch for areas in which the watch was dropped ? Along I-20 in particular.

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So you think they may need to re-issue a tornado watch for areas in which the watch was dropped ? Along I-20 in particular.

no, I just looked at the Mesoscale Analysis and the risk of significant tornadoes and hail is well south of metro Atlanta. Most of the high values are down in southern Alabama and the Florida panhandle. I wish I knew how to read the Wind Shear maps they have there but I just don't have enough experience or knowledge to interpret them for you.

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New MSD out.

FARTHER NORTHEAST INTO NORTH GA...THE 00Z PEACHTREE CITY SOUNDING

DEPICTED MARGINAL INSTABILITY THOUGH A FAVORABLE HODOGRAPH FOR

SUPERCELLS/TORNADOES -- I.E. STRONG CLOCKWISE CURVATURE IN THE LOW

LEVELS YIELDING AN EFFECTIVE SRH VALUE OF 575 M2/S2.

HOWEVER...WIDESPREAD PRECIP ACROSS NRN GA HAS AIDED IN THE

DEVELOPMENT OF A COLD POOL...WITH DEEPER CONVECTION FOUND ON ITS ERN

PERIPHERY. NEVERTHELESS...CONVECTION DEVELOPING UPSTREAM ACROSS NERN

AL CONTINUES TO BE SUSTAINED INVOF MORE NOTABLE SFC PRESSURE FALLS

REFLECTING SOME ASCENT. DESPITE THE STABILIZATION EFFECTS OF THE

COLD POOL OVER NRN GA...THE EFFECT OF STRONG DEEP-LAYER VERTICAL

WIND SHEAR WILL ENHANCE UPDRAFT POTENTIAL IN THIS AREA...AND STRONG

LOW-LEVEL VERTICAL WIND SHEAR WILL YIELD A TORNADO POTENTIAL ACROSS

NRN PORTIONS OF WW147.

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New MSD out.

FARTHER NORTHEAST INTO NORTH GA...THE 00Z PEACHTREE CITY SOUNDING

DEPICTED MARGINAL INSTABILITY THOUGH A FAVORABLE HODOGRAPH FOR

SUPERCELLS/TORNADOES -- I.E. STRONG CLOCKWISE CURVATURE IN THE LOW

LEVELS YIELDING AN EFFECTIVE SRH VALUE OF 575 M2/S2.

HOWEVER...WIDESPREAD PRECIP ACROSS NRN GA HAS AIDED IN THE

DEVELOPMENT OF A COLD POOL...WITH DEEPER CONVECTION FOUND ON ITS ERN

PERIPHERY. NEVERTHELESS...CONVECTION DEVELOPING UPSTREAM ACROSS NERN

AL CONTINUES TO BE SUSTAINED INVOF MORE NOTABLE SFC PRESSURE FALLS

REFLECTING SOME ASCENT. DESPITE THE STABILIZATION EFFECTS OF THE

COLD POOL OVER NRN GA...THE EFFECT OF STRONG DEEP-LAYER VERTICAL

WIND SHEAR WILL ENHANCE UPDRAFT POTENTIAL IN THIS AREA...AND STRONG

LOW-LEVEL VERTICAL WIND SHEAR WILL YIELD A TORNADO POTENTIAL ACROSS

NRN PORTIONS OF WW147.

That's interesting.

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Just pushed out a 05Z Severe Weather Threat analysis. Showing S. Alabama into Florida Panhandle with the highest instability at this hour for tornadoes, with Pensacola, FL with the highest threat of all. Still seeing surface CAPE's holding around 1200(j/kg), 0-3KM Shear around 60 knots, and 0-3KM SRH around 358 m/s. Further up into GA, showing stronger potential for winds of 60 knots and hail up to 1.5" in diameter. Analysis can be viewed here http://smartwxmodel.net/severe.pdf and city specific forecasts are also updated at http://smartwxmodel.net.

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