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Severe Severe weather threat April 17-19

PEA_RIDGE said:


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Our saving grace may be the fact that it's in the overnight hours so CAPE is lower & critical angles are far from ideal plus drier air in a large-scale sense leads to cooler downdrafts that are capable of disrupting the parent mesocyclones in these supercells.
 
That is true but heck the way it's been lately I dunno

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Close range models should come in range of this tomorrow for some of the southeast. So we should have a better idea tomorrow im guessing
 
Haven't had a chance to look at the setup because of the system that just went through. But the weather people on the news keep talking about it.
 
From NWS BMX on their latest AFD



THURSDAY THROUGH SATURDAY. HAVE CONTINUED TO MONITOR TRENDS WITH THE CONSISTENT SYNOPTIC SIGNAL OF SEVERE WEATHER HEADING INTO THURSDAY. GOOD FORECAST CONFIDENCE REMAINS WITH THE DEEP-LAYER TROUGH AMPLIFYING & THEREAFTER OCCLUDING ON THURSDAY ACROSS THE GREAT PLAINS WITH GUIDANCE SUGGESTING A ~545 DECAMETER MID-LEVEL LOW NEAR NORTHEAST KANSAS THURSDAY MORNING. AS A RESULT, ONGOING DOWNSTREAM RIDGING & SOUTHWEST FLOW ALOFT DEVELOPS OVER THE GULF COAST STATES. WARM, MOIST ADVECTION ACROSS THE LOWER MRV AND SOUTHEAST SUGGESTS AN UNSTABLE BOUNDARY LAYER WITH ~2,000+ MLCAPE DURING THE AFTERNOON, ALONG WITH 40-50+ KTS 0-6 KM BULK SHEAR. LATEST GUIDANCE SUGGESTS LEE CYCLOGENESIS ACROSS THE PLAINS WITH A DEEPENING SURFACE LOW HEADING NORTHEASTWARD INTO IL BY FRIDAY MORNING. TO THE SOUTH, A TRAILING FRONTAL BOUNDARY AND 90-100KT H5 JET MAX SHOULD MOVE INTO THE LOWER MRV BY THURSDAY AFTERNOON. CONSIDERING INDICATIONS OF FAVORABLE WARM SECTOR INSTABILITY, ASSOCIATED SHEAR PROFILES & BROAD HODOGRAPH CURVATURE, ALL MODES OF SEVERE WEATHER REMAIN ON THE TABLE. WILL CONTINUE TO ADVERTISE THE LOW-MEDIUM CONFIDENCE FOR SEVERE WEATHER IN THE HWO. AS ALWAYS, TRENDS WILL BE ACTIVELY MONITORED WITH NECESSARY FORECAST UPDATES PASSED ALONG. WEATHER CONDITIONS FRIDAY/SATURDAY WOULD GENERALLY SHOW IMPROVEMENT AS EXPECTED NVA/CAA SPREADS ACROSS THE REGION BEHIND THE EXITING SYSTEM.

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PEA_RIDGE said:
From NWS BMX on their latest AFD



THURSDAY THROUGH SATURDAY. HAVE CONTINUED TO MONITOR TRENDS WITH THE CONSISTENT SYNOPTIC SIGNAL OF SEVERE WEATHER HEADING INTO THURSDAY. GOOD FORECAST CONFIDENCE REMAINS WITH THE DEEP-LAYER TROUGH AMPLIFYING & THEREAFTER OCCLUDING ON THURSDAY ACROSS THE GREAT PLAINS WITH GUIDANCE SUGGESTING A ~545 DECAMETER MID-LEVEL LOW NEAR NORTHEAST KANSAS THURSDAY MORNING. AS A RESULT, ONGOING DOWNSTREAM RIDGING & SOUTHWEST FLOW ALOFT DEVELOPS OVER THE GULF COAST STATES. WARM, MOIST ADVECTION ACROSS THE LOWER MRV AND SOUTHEAST SUGGESTS AN UNSTABLE BOUNDARY LAYER WITH ~2,000+ MLCAPE DURING THE AFTERNOON, ALONG WITH 40-50+ KTS 0-6 KM BULK SHEAR. LATEST GUIDANCE SUGGESTS LEE CYCLOGENESIS ACROSS THE PLAINS WITH A DEEPENING SURFACE LOW HEADING NORTHEASTWARD INTO IL BY FRIDAY MORNING. TO THE SOUTH, A TRAILING FRONTAL BOUNDARY AND 90-100KT H5 JET MAX SHOULD MOVE INTO THE LOWER MRV BY THURSDAY AFTERNOON. CONSIDERING INDICATIONS OF FAVORABLE WARM SECTOR INSTABILITY, ASSOCIATED SHEAR PROFILES & BROAD HODOGRAPH CURVATURE, ALL MODES OF SEVERE WEATHER REMAIN ON THE TABLE. WILL CONTINUE TO ADVERTISE THE LOW-MEDIUM CONFIDENCE FOR SEVERE WEATHER IN THE HWO. AS ALWAYS, TRENDS WILL BE ACTIVELY MONITORED WITH NECESSARY FORECAST UPDATES PASSED ALONG. WEATHER CONDITIONS FRIDAY/SATURDAY WOULD GENERALLY SHOW IMPROVEMENT AS EXPECTED NVA/CAA SPREADS ACROSS THE REGION BEHIND THE EXITING SYSTEM.

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Wow sounds like a decent severe threat from BMX wording
 
The low pressure is far away from the southeast that'll be helpful. although mississippi and alabama had a tornado outbreak back in 2014 when there was a very deep low sitting in Nebraska.
 
Zander98al said:
The low pressure is far away from the southeast that'll be helpful. although mississippi and alabama had a tornado outbreak back in 2014 when there was a very deep low sitting in Nebraska.
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From Fred Gossage, “I will provide a word of caution preemptively in case this starts coming up in discussion in places:

Don't get too hung up on the surface low being pretty far to the north. Low-level winds are still backed way down in the warm sector, there are still significant surface pressure falls through the MS/AL/GA/TN portion of the warm sector, and the actual upper-level energy Thursday is more directly aimed here. To the thunderstorms, it still "feels" like the surface low is closer because of all that. They don't check the GFS, or Euro, to see what the surface low position is before they decide to rotate. We have had MANY outright violent tornado events over the decades here in Alabama with surface low positions a good bit north of what is considered that "classic" track from central Arkansas into Kentucky.”
 
Day 5 severe probabilities per Cips past analogs similar to the upcoming one.
Screenshot_20190414-204912_Samsung Internet.jpgScreenshot_20190414-204854_Samsung Internet.jpg
 
VegasEagle said:
Looking like a bad few days ahead. Can you post the next time frame please
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Don't have access to those graphics. That was a picture from alabama forecast facebook page. Although this is later at around 10 oclock. From the euro.Screenshot_20190414-212854_Samsung Internet.jpg
 
Zander98al said:
Don't have access to those graphics. That was a picture from alabama forecast facebook page. Although this is later at around 10 oclock. From the euro.View attachment 19050
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I personally prefer this color table for modeled precipitation specifically for severe weather over other maps that are offered by weathermodels or weatherbell.
 
Zander98al said:
The low pressure is far away from the southeast that'll be helpful. although mississippi and alabama had a tornado outbreak back in 2014 when there was a very deep low sitting in Nebraska.
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Low pressure location is fine for a big event. The issue with this one is about the same thing that we had with the last one, a sharp trough with quick height falls along with 500mb winds out of the SSW will lead to a QLCS with embedded supercells.

Any isolated supercell out front could cause issues, but it doesnt appear the Euro shows much instability ahead of the complex.
 
Arcc said:
Low pressure location is fine for a big event. The issue with this one is about the same thing that we had with the last one, a sharp trough with quick height falls along with 500mb winds out of the SSW will lead to a QLCS with embedded supercells.

Any isolated supercell out front could cause issues, but it doesnt appear the Euro shows much instability ahead of the complex.
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If it happens during the day that would be a problem much bigger warm sector now that were in mid april. Maybe a stupid question but don't you want winds around 500 mb to be coming from the west not southwest for supercells? Or does it also matter were the front is located? I know you need veering winds with height southeast winds at the surface and so on. Ive never understood what direction you would want the winds to come from at 500mb and 200mb
 
Zander98al said:
If it happens during the day that would be a problem much bigger warm sector now that were in mid april. Maybe a stupid question but don't you want winds around 500 mb to be coming from the west not southwest for supercells? Or does it also matter were the front is located? I know you need veering winds with height southeast winds at the surface and so on. Ive never understood what direction you would want the winds to come from at 500mb and 200mb
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Yes, you want winds aloft perpendicular to the front or dry line. It can depend on the front as well. If the front is N/S you want bulk shear coming from the WSW or W. That said if you have a more east to west boundary you can get messy convection if the upper level winds are also from a more westerly vector.

The funny part is as Fred Gossage showed me years ago, you generally dont want surface winds out of the SE as that will normally pull in lower dew points off the Atlantic. For the southeast, you generally need surface winds out of the south, 850s out of the SW and 500mb winds out of the WSW or W with a low amp, broad based trough.
 
Arcc said:
Yes, you want winds aloft perpendicular to the front or dry line. It can depend on the front as well. If the front is N/S you want bulk shear coming from the WSW or W. That said if you have a more east to west boundary you can get messy convection if the upper level winds are also from a more westerly vector.

The funny part is as Fred Gossage showed me years ago, you generally dont want surface winds out of the SE as that will normally pull in lower dew points off the Atlantic. For the southeast, you generally need surface winds out of the south, 850s out of the SW and 500mb winds out of the WSW or W with a low amp, broad based trough.
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Absolutely correct. Some of our worst outbreaks have occurred with surface winds from the south or even, in some cases, a little from the SSW. There are so many ways to get tornadoes in Alabama and many of them aren't the "classic" set-ups you see in the textbooks.
 
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