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The Official 2014 Fall Discussion Thread


jburns

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Could have some strong storms for the South, mainly Monday into Tuesday. Typical low CAPE high shear type of set up.

Agreed, GFS is showing some +500 m2/s2 helicity Monday in E Tenn and parts of the TN/AL border. Little cape showing up, but with helicity and shear being as high as modeled.. I could see a few EF-0 to EF-2 tornado's.

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It must have been 90 then because car thermometers are very accurate.

It might not have been 90 but it certainly felt that way with the oppressive humidity. We had cooler days in July than we had yesterday.

 

I think there should be different criteria for a heat advisory in the fall as opposed to summer. Anything over 85 with dp over 65 should meet the criteria for a heat advisory in the fall. Your body gets used to the cooler weather and it doesn't take much heat to make it feel really hot.

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Agreed, GFS is showing some +500 m2/s2 helicity Monday in E Tenn and parts of the TN/AL border. Little cape showing up, but with helicity and shear being as high as modeled.. I could see a few EF-0 to EF-2 tornado's.

I wonder if there will be enough forcing out ahead of the system to get discrete convection. GFS shows the winds backing a bit more. I still think main mode will be linear damaging winds. In Dixie alley, it doesn't take those raging CAPE values to get tornadoes. But I'd like to see a little more consistency between the models.
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It might not have been 90 but it certainly felt that way with the oppressive humidity. We had cooler days in July than we had yesterday.

 

I think there should be different criteria for a heat advisory in the fall as opposed to summer. Anything over 85 with dp over 65 should meet the criteria for a heat advisory in the fall. Your body gets used to the cooler weather and it doesn't take much heat to make it feel really hot.

 

Is this a serious comment?

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I wonder if there will be enough forcing out ahead of the system to get discrete convection. GFS shows the winds backing a bit more. I still think main mode will be linear damaging winds. In Dixie alley, it doesn't take those raging CAPE values to get tornadoes. But I'd like to see a little more consistency between the models.

Yeah forcing looks to lag a little so we will see but nonetheless, widespread 50+kt winds should accompany the line. Would love to see some descrete cells pop up in E Tenn for chase potential (of course not in hopes of distruction). I am thinking the best shot embeded in the line Monday night would be where Tn/Al/Ms meet with good veering showing up but hey we are discussing the GFS here so that could all change quick.
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12z gfs not nearly as impressive, cuts the low off much farther north then what was previously modeled.  Thus this run at least looks to be less of a severe threat and more of a rain event.  Time will tell and I expect the models (or at least the GFS) to continue to flip flop a few more times as to whether or not the low cuts off when the storm is farther south.

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12z gfs not nearly as impressive, cuts the low off much farther north then what was previously modeled.  Thus this run at least looks to be less of a severe threat and more of a rain event.  Time will tell and I expect the models (or at least the GFS) to continue to flip flop a few more times as to whether or not the low cuts off when the storm is farther south.

The threat is still very real for the low/mid Mississippi River Valley and points just east into Alabama and West/Central Tennessee.  Looks like the GFS has the surface winds backing and the LLJ looks very impressive.  Could be a rough day Monday for those aforementioned places.        

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The threat is still very real for the low/mid Mississippi River Valley and points just east into Alabama and West/Central Tennessee.  Looks like the GFS has the surface winds backing and the LLJ looks very impressive.  Could be a rough day Monday for those aforementioned places.        

 

No doubt, certainly still a severe threat.  Best play Monday may be to sit on the Tennessee/Alabama border and watch for where the best shear pops.  LLJ like you mentioned is impressive across the area so the next fews days of model runs will be very telling.

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70 kt winds at 850 and 80+ kt winds at 500mb slamming into the Southern Apps Tuesday morning...first off that would have my attention in the mountains for even non-convective winds being mixed down to the surface. And second...its a very strong upslope signature for the So Apps as that jet will be doing a squeeze play with a ridge off shore...

The potential is there for a wind and rain maker!

 

GFS_3_2014100912_F120_WSPD_850_MB.png

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WxSouth is sounding the alarm on facebook.

 

The newly released run of GFS shows a trend toward what European Model shows...which is a strongly negative tilting system that blasts through the Southeast, Tennessee and lower Ohio Valleys, then much of the East Coast. This is an image of rain totals ahead of the storm ending Tuesday night (its just beginning then for eastern VA, MD, DE) The storm forms a strong 850 jet through the TN Valley Monday night , the Apps Tuesday and then strengthens this jet in Virginia and Maryland with a strong 75 knot wind. This evolution usually means severe weather along this line as it comes through with unfortunately, tornadoes in that line. Remember Fall can be another period of Severe Weather, like Spring, since we're changing the seasons.

 

 

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The 12z Euro continues the trend of cutting the upper low off farther north now.  I think this is a trend to be cognizant of as we head into the winter.  That model seems to have a SE bias with these features.  I have seen numerous anomalous cutoffs over the SE in the 5-8 day range, only to trend weaker and farther north as we close in.  Kinda goes back to the convo the other day about why models tend to trend away from the big, anomalous stuff rather than toward.  Still, should be a pretty powerful system and a good weather-maker.  The farther west you are, the better the chance for interesting weather.

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The 12z Euro continues the trend of cutting the upper low off farther north now.  I think this is a trend to be cognizant of as we head into the winter.  That model seems to have a SE bias with these features.  I have seen numerous anomalous cutoffs over the SE in the 5-8 day range, only to trend weaker and farther north as we close in.  Kinda goes back to the convo the other day about why models tend to trend away from the big, anomalous stuff rather than toward.  Still, should be a pretty powerful system and a good weather-maker.  The farther west you are, the better the chance for interesting weather.

 

 

Yep should be a good soaker for everyone!  Euro also has a tropical disturbance near Miami on the 10 day.  Lets see if it keeps that feature for the next few runs, might be something to watch if it persists.  I was doing some research on these low CAPE, high shear events and came across a good link that sheds light on how these events evolve.  Thought it was interesting.

 

http://www.theweatherprediction.com/weatherpapers/116/index.html

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Yep should be a good soaker for everyone!  Euro also has a tropical disturbance near Miami on the 10 day.  Lets see if it keeps that feature for the next few runs, might be something to watch if it persists.  I was doing some research on these low CAPE, high shear events and came across a good link that sheds light on how these events evolve.  Thought it was interesting.

 

http://www.theweatherprediction.com/weatherpapers/116/index.html

 

That's a good read.  Thanks for linking to it.  D10 tropical threats have shown up on the GFS all season.  The Euro has been much more bearish.  It'll be interesting to see if it maintains the entity.

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