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cheese007

Severe Weather April 28-29th 2020

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I wonder what the odds of getting a tornado are for north-central Texas if there happen to be discrete storms around?  I know the supercell composite, helicity, and significant tornado values often do go up in the evening and at night (RAP on SPC Mesoanalysis shows this happening over north-central TX prior to the arrival of storms), but that storms often become more elevated at night as well.  The HRRR model also has the DFW area at the tail-end of the line of storms.

It always concerns me to see forecast values that high over a highly-populated area (DFW) with what could be some semi-discrete activity, but I have seen this happen before in the late spring and summer with few-to-no tornado reports.  This is also a northwest-flow scenario and there tend to be fewer tornadoes with that.  That said, I do wonder if we will see a derecho this evening.

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4 minutes ago, BrandonC_TX said:

I wonder what the odds of getting a tornado are for north-central Texas if there happen to be discrete storms around?  I know the supercell composite, helicity, and significant tornado values often do go up in the evening and at night (RAP on SPC Mesoanalysis shows this happening over north-central TX prior to the arrival of storms), but that storms often become more elevated at night as well.  The HRRR model also has the DFW area at the tail-end of the line of storms.

It always concerns me to see forecast values that high over a highly-populated area (DFW) with what could be some semi-discrete activity, but I have seen this happen before in the late spring and summer with few-to-no tornado reports.  This is also a northwest-flow scenario and there tend to be fewer tornadoes with that.  That said, I do wonder if we will see a derecho this evening.

Yeah, I've been wondering about that too. Being on the western/southwestern edge of the line (most likely) got me wondering if we could see a broken line of cells impacting our area rather than the squall, but I still think that with this being a northwest-flow scenario (as you said), and really not much shear in the area, I'm not very concerned about anything more than maybe a few weak tornadoes (then again, there's a lot of built-up areas here and it'll be late at night), but trends will continue to be monitored. The threat may very well increase, it's just not looking that way to me as of now. If DFW ends up getting in on a derecho, that'll probably result in a lot of power outages and damage in its own right. 

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Definitely getting similar vibes to the June wind storm from last year in DFW. Took out a ton of trees and knocked a crane onto an apartment buildin

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Your mid level lapse rates are great and low levels not too shabby either.  Shear and helicity values could be better for tors but as the LLJ ramps up wait and see what happens.  Watch those two cells to the north in OK coming down I-35.

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High winds of 60-70mph have been reported west of Springfield MO, and also high winds detected by radar in this area.

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2 minutes ago, cheese007 said:

Definitely getting similar vibes to the June wind storm from last year in DFW. Took out a ton of trees and knocked a crane onto an apartment buildin

Ah yeah I remember, did we have a couple tornadoes with that one? We actually had a few storm systems and tornadoes in June. My family and cousins got the bright idea to go to a community swimming pool that day, storm took everyone by surprise and the leading edge of the line was ominous and rotating in front of me. We got some gusts of 60+ mph there.

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There has already been a significant wind report out of Tulsa (65-75 mph wind gust at 51st/Harvard; listed as a 75 mph significant wind report by SPC).  If we get a derecho that might be where it starts, so I would expect areas to the east of DFW to be at the highest risk for getting a derecho today (the OK/AR/MO border region is also a climatological hotspot for derecho activity per SPC).  Remember that severe winds have to extend for at least 250 miles to get a derecho; that said, you can have an MCS with destructive winds that does not persist long enough to meet derecho criteria.

DFW itself will be impacted by the activity (either ongoing or yet to form) over central Oklahoma.  So far this activity has remained more discrete than that over northeastern Oklahoma (which has formed into a solid line).  Also note that helicity may increase between 01z and 03z based on RAP guidance (as seen on the SPC Mesoanalysis page), which also forecasts effective SigTor values as high as 9 over the DFW area as the storms arrive.  I'm not saying that there will be tornadoes (it seems unlikely, and SPC has only put DFW and much of north-central Texas in a 2% contour after all), but it might be a possibility with any discrete or semi-discrete cells once that helicity ramps up in a few hours.

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 Mesoscale Discussion 0492
   NWS Storm Prediction Center Norman OK
   0702 PM CDT Tue Apr 28 2020

   Areas affected...southwest through central Oklahoma

   Concerning...Severe Thunderstorm Watch 151...

   Valid 290002Z - 290130Z

   The severe weather threat for Severe Thunderstorm Watch 151
   continues.

   SUMMARY...Threat for very large hail and locally strong to damaging
   wind gusts will persist through mid evening from southwest through
   central OK.

   DISCUSSION...Early this evening isolated severe storms including
   some with supercell structures continue developing across central OK
   along a southeast-advancing cold front. The atmosphere is very
   unstable in this region with 3000-3500 J/kg MLCAPE along with steep
   lapse rates and 35-40 kt effective bulk shear. These storms have a
   history of very large hail and damaging gusts. Despite the increase
   in convective inhibition due to boundary-layer cooling, forcing from
   near the front/dryline intersection over southwest OK and northeast
   along the cold front will remain sufficient for thunderstorm
   development through at least mid evening.

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17 minutes ago, TexMexWx said:

MD on the segment of the bowing segment impacting Springfield, MO says 60-80 mph wind gusts possible as it moves east

I live within the MD. The worst seems to have gone just north of me. Winds on the leading edge were decent probably in the  40-60 range, but the back side was just as strong, if not stronger. 

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Critical angles are expected to be absurdly large (approaching a full 180º) which may keep the tornado threat fairly low even with a discrete cell since there won't be much streamwise vorticity to ingest. Give the instability/shear combo, especially as the low level jet ramps up around sunset, the damaging wind threat does look very real.

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Watch coming soon including DFW area 

Mesoscale Discussion 0494
   NWS Storm Prediction Center Norman OK
   0806 PM CDT Tue Apr 28 2020

   Areas affected...north central through northeast Texas into
   southwest Arkansas and northwest Louisiana

   Concerning...Severe potential...Watch likely 

   Valid 290106Z - 290200Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe storms with a threat for mainly damaging wind and
   large hail are expected to develop southeast into north-central and
   northeast Texas, southwest AR and northwest LA this evening into
   tonight. A WW will likely be issued prior to 0130Z.

   DISCUSSION...Severe storms continue developing along a
   southeast-advancing cold front from eastern through south-central
   OK. The downstream warm sector across north-central and northeast TX
   is very unstable with the 00Z RAOB from Fort Worth indicating 3500
   J/kg MLCAPE and 9 C/km 700-500 mb lapse rates along with 35-40 kt
   effective bulk shear. An inversion was evident near 800 mb at the
   base of an EML, and convective inhibition will increase as the
   surface layer cools. However, deep forcing and convergence along the
   southeast-advancing cold front should remain sufficient for
   additional thunderstorm development this evening into tonight. Both
   multicell line segments and some embedded supercell structures will
   be possible with large to very large hail and widespread damaging
   wind gusts the main threats, though a tornado or two cannot be ruled
   out.

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We have gotten hammered with rain here in SELA!! It looks to have caught all of the Mets by surprise.

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8 minutes ago, rnj79 said:

We have gotten hammered with rain here in SELA!! It looks to have caught all of the Mets by surprise.

Looks like SELA has the only tornado report of the day so far as well

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90%/70% severe wind probabilities on that new severe thunderstorm watch, high odds but not enough for PDS.  If those odds were slightly higher (let's say >95/80) then I think they would have gone PDS.

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20 minutes ago, TexMexWx said:

Looks like SELA has the only tornado report of the day so far as well

Yes, there was one east of us, in Hammond.

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8 minutes ago, BrandonC_TX said:

90%/70% severe wind probabilities on that new severe thunderstorm watch, high odds but not enough for PDS.  If those odds were slightly higher (let's say >95/80) then I think they would have gone PDS.

Yeah, does PDS for severe t-storm watches have a different criteria than TOR watches (with regard to probabilities)? I want to say yes but I can't remember for sure

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2 minutes ago, Chinook said:

Three possible tornadoes in southeast Oklahoma

8J1x2oQ.jpg

Those signatures came up pretty quickly, but moving east so they'll likely be taken over by the line soon?

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1 minute ago, Buckeye05 said:

That's actually a fairly intense couplet near Clayton, OK. Wouldn't be surprised if that put down a substantial tornado.

It certainly stuck out to me as well as the strongest out of the three in that image.

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Denton, TX currently in the path of a severe thunderstorm, with other SVR warned storms to the west and southwest, out of the cells that have crossed the Red River

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Definitely an area of strong winds southwest of Gainesville, moving towards the Metroplex.  I’m also wondering if that might be some rotation near Valley View?

 

 

80413300-B200-4DD3-8471-432543DDCC99.png

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With the storms moving towards the Metroplex being more discrete, there is likely an increased threat for hail from them. As for tornadoes, currently meh (which is good news). Latest MD states that the best threat for a tornado or two is NE TX/SE OK/SW AR

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Northern Little Rock metro looks to get hit by a strong part of the squall with a TOR warning there and definitely strong winds

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Starting to see lightening in the distance from my vantage point in far north Dallas

EDIT: May see a direct hit from the hail core. If not from the first storm then the one behind it

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Yep, hearing rumbles of thunder now. Looks like a sort of line has congealed from Denton County down to Fort Worth, 2 severe warnings cover the line. Winds for the northern warning up to 70 mph possibly, large hail mentioned as well.

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