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Severe Weather April 23rd 2021


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SPC D5 15% highlighted outlook

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Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0354 AM CDT Mon Apr 19 2021

 

 

..DISCUSSION...
   A shortwave trough should move eastward across the Southwest on Day
   4/Thursday. Low-level moisture return appears likely across parts of
   the southern Plains into Day 5/Friday, as lee cyclogenesis occurs
   across the southern High Plains ahead of the approaching upper
   trough. Run-to-run consistency over the past several runs of the
   deterministic ECMWF lends confidence that the shortwave trough
   should eject eastward over the southern Plains on Friday. Increasing
   low-level moisture to the east of a dryline/cold front and steep
   mid-level lapse rates should support at least moderate instability
   in a corridor across parts of OK and TX by Friday afternoon. Strong
   mid-level flow and related deep-layer shear appear more than
   sufficient for organized severe storms, including supercells. As
   mid-level height falls/ascent overspread the warm sector, robust
   convective development should occur, with at least isolated severe
   storms potentially spreading eastward towards southeast TX Friday
   evening/night. Confidence in this scenario occurring has increased
   enough to include a 15% severe area for Friday.

   
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The trend appears to be feeding better instability and moisture up to I-40 now. It’s in weenie NAM land, but the fact that the 12km shows very sparse convection with minimal CIN in central/southern Oklahoma toward 00z, catches your attention.

Without getting into specifics, as the forecast will evolve, it definitely bears watching from roughly the DFW - OKC area. 

Could see isolated convection farther south as well, as we’ve seen a few times this month. 

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Day has some similarities to 4/22 (Springer/Madill) last year being right at the base of the trough with cold air aloft promoting a lot of 0-3 km CAPE and strong updraft accelerations. Ingredients that I'd look for more of are low level flow/moisture depth and also the eastward extent of the warm sector. I'm wondering if some warmer temps closer to I-35 could promote a threat closer to the main LLJ axis, which would raise the tornado threat for DFW north to OKC.

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Most models have a cluster of storms in east Texas, with possible higher storm-relative helicity and higher dew points around 68F. This part could be quite messy, but it could result in several tornadoes reports. Otherwise, models show convection near the cold front, possibly 00z-06z, which could be somewhat significant as well. Perhaps one of the more interesting questions is if any storms will go up near the dryline. So, overall, kind of a complicated scenario.

Ld0tlVh.jpg

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It’s definitely complicated. Reminds me of a tamer version of 5/9/16. Recall that SPC and some others (like me) thought the warm sector looked better. The dryline went nuts in what was almost a colossal bust on my end. Also seeing some shades of Springer as well.

The new HRRR has a late CI bias, but other models also show limited QPF/CI signals. I actually like that. If you do get an isolated storm or two, then they have a chance to go bonkers. Forecast soundings ahead of the dryline show classic thermodynamic profiles and while hodographs may not be extremely large, I’d gather they’d support a photogenic supercell. 

CI near the triple point seems to have the best model support, but that might get undercut by the cold front. 

I pulled some warm sector soundings and low-level lapse rates look rather anemic.

The dryline south of the Red River seems like the biggest wild card that could go boom or bust in a big way. 

At the very least, the Plains is waking up!

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At this point, it's looking like (per usual) the widespread convection tomorrow will be just east of DFW.

But it's a much closer call than we've had all season. CINH looks to be non-existent and the forcing will be stronger. If things slow down slightly or initiate a bit earlier, it could be a different story. 

I don't expect anything along the dryline if the warm sector storms blow up and work over the atmosphere. 

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It looks like a lead, subtle perturbation in the warm air advection regime sets off a mess of convection by midday across central/eastern Texas into eastern Oklahoma. 

While the HRRR lacks CI away from the triple point area in NW OK (which gets undercut by a cold front), the 3km NAM and WRF/ARW members are much more active in SW OK.

Looking at the HRRR forecast soundings, I’m not quite sure why it doesn’t initiate convection there. It shows virtually no CIN, temperatures reaching convT and large CAPE profiles. I’m guessing it has to do with overzealous mixing and/or the tendency for HRRR to be too late with CI.

The setup does seem a bit off. Maybe a touch too slow as some have mentioned, at least in comparison to 4/22/20. The HRRR is furthest north, while the 3km NAM places the triple point the farthest southwest.

At this juncture, I’d say Texas is mostly out of any dryline action, with the only possible exception being if the low tracks farther south. If the 3km were onto a trend, maybe you see storms initiate in far NW Texas. 

The surging cold front looks like it will undercut storms closer to the surface low in western OK. 

We may have to wait until morning to really get a better idea of specifics, but I wouldn’t write this setup off yet. 

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000
FXUS64 KFWD 230112 AAA
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
812 PM CDT Thu Apr 22 2021

...New Short Term, Aviation...

.SHORT TERM... /NEW/
/Through Friday Night/

The primary weather concern over the next short term forecast
period revolves around chances for severe convection across North
and Central Texas. Friday will be a day that individuals should
monitor the weather closely from a trusted source as severe
weather will likely strike quickly. In addition, there will be a
risk for areas of fog/drizzle that could reduce visibility down to
below 1 mile.

Surface analysis in tandem with satellite imagery indicated a
conveyor of richer near surface moisture extended from South
Texas northwestward toward western reaches of the Hill Country.
Ceiling observations in tandem with aircraft data (AMDAR) from
Dallas Love Field and our presently ascending 00 UTC weather
balloon showed a large amount of dry air from near 5,000 feet
toward the surface across North and Central Texas. While the
radarscope has slowly continued to illuminate thanks to increased
mid-upper level ascent (implied by increasing high clouds), I
think we`ll be hard pressed to measure any rainfall over the next
6 to 12 hours thanks to the aformentioned dry air. As a result,
I`ve opted for a mention of sprinkles as opposed to rain showers
for many areas through 12 UTC Friday, though a few areas may
measure south of I-20 and west of US HWY 281 as ceilings fall
below 1,000 feet during the pre-dawn hours on Friday.

A warm front extended from near Del Rio to Victoria this evening
and thanks to observed surface pressure falls between 2-4 mbar
over the past several hours, this boundary should have no problem
lifting northward tonight. As it does, we`ll see an increased
advection fog potential between 3 am and sunrise across western
Central Texas and likely our initial shower and thunderstorm
development after sunrise Friday. While advective in nature, fog
processes may be hindered some as 925mb flow is expected to remain
quite turbulence and as a result of this, I`ll omit the mention
of "dense" fog from the worded forecast. However, we`ll monitor
this potential during the overnight hours.

One of the more significant changes made to the forecast (though
I`m still very cautious about this) was to delay the wording of
"severe" in the zones until the afternoon. Initial glances at
some of the hi- res model guidance would suggest that deep
convection could fire as early as 15 UTC. However, taking a look
at some of the synoptic guidance, it doesn`t appear that
appreciable height falls associated with the main PV anomaly
currently across western Arizona will not impinge upon our area
until closer to 17-18 UTC. Moreover, there`s still a little bit of
remnant capping evident in forecast soundings so the potential
for surface based convection in the morning looks low at this
time.

I still show high chance PoPs (50%) through 16 UTC for areas
near/southwest of a Jacksboro to Waco to Temple line, but I
believe the potential for a larger coverage of severe weather may
not occur until Friday afternoon...closer to 18-19 UTC (more in
accordance with the NSSL WRF and NCEP WRF ARW core). It`s possible
that even this timing may be a little too early. Does that mean
that we won`t have severe weather across our area in the morning?
NO! In fact, IF elevated convection gets going along the
northward lifting warm front, it`ll certainly have a large hail
potential given 0-6km bulk wind differences of 50 knots and
700-500mb lapse rates closer to 8 C/km. Because this activity
is expected to be elevated, I believe the damaging wind and
tornado threat will be low. Any surface based storm near the warm
front, however, will need to be monitored closely for a damaging
wind and/or tornado threat!

As stronger forcing for ascent emerges from the west, I do
believe that both newly formed and any ongoing convection will
strengthen very, very quickly. While widespread cloud cover will
likely dampen what would otherwise be much higher instability
values, CAPE is still progged to average out to around 2000 J/kg
across our area in a strongly sheared environment (supportive of
supercellular structures). Forecast soundings suggest that the
high shear and steep lapse rates would facilitate large to
potentially significant hail sizes (2+ in diameter), along with
damaging winds. 0-1 km shear values from hi-res guidance suggest
that these values will be maximized to the south and east of the
Metroplex, and thus I would anticipate a greater tornado risk
here. However, low level SRH may also increase farther north
across Northeast Texas (near and east of US HWY 75) depending on
where the frontal boundary stalls and any storm interacting with
the warm front (or any additional boundary) will have an enhanced
wind and tornado threat.

Storms will likely exit East Texas between 03-06 UTC, but the
dryline appears that it`ll lag back to the west. A cold front is
expected to crash southward from Oklahoma Friday night and
normally this would present another opportunity for additional
convection to fire. However, we`ll be on the subsident side of the
upper trough and this will likely suppress any deep convection.
However, they`ll likely be attempts along the boundary and if an
updrafts can realize what should still be unstable air, there
could be a brief strong to severe weather threat after midnight.

Bain
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41 minutes ago, Powerball said:

That said, I'm still concerned most of the widespread/organized convection will miss DFW just to the south and east. 

Last year on 4/22, here in DFW we were sandwiched between the two modes, with the northern mode producing strong tornadoes along the Red River into southern OK, and the southern mode producing the long-track supercell from east/southeast TX into LA and even into MS(?), dropping sigtors along parts of its path. We ended up with a cap bust here.

Given the comparisons to that day (I am aware that nobody is necessarily calling for a repeat of that by any means), it seems like we might once again be sandwiched in that spot between the two main focuses for severe weather. Obviously that's not to say that we won't see any ourselves (we may or may not), but it does seem like we're getting caught in between two higher probability corridors again. One difference (of many) between tomorrow and 4/22/20 also lies in the surface temperatures. I remember last year, we were like in the mid-to-upper 80s, but this time around we well likely be 10+ degrees cooler.

Frankly, I could see an upgrade to enhanced by SPC, but probably for portions of eastern TX where the coverage of severe storms might warrant higher probabilities (in my opinion). Obviously would not be surprised to see storms get pretty grungy there though.

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22 minutes ago, TexMexWx said:

Last year on 4/22, here in DFW we were sandwiched between the two modes, with the northern mode producing strong tornadoes along the Red River into southern OK, and the southern mode producing the long-track supercell from east/southeast TX into LA and even into MS(?), dropping sigtors along parts of its path. We ended up with a cap bust here.

Given the comparisons to that day (I am aware that nobody is necessarily calling for a repeat of that by any means), it seems like we might once again be sandwiched in that spot between the two main focuses for severe weather. Obviously that's not to say that we won't see any ourselves (we may or may not), but it does seem like we're getting caught in between two higher probability corridors again. One difference (of many) between tomorrow and 4/22/20 also lies in the surface temperatures. I remember last year, we were like in the mid-to-upper 80s, but this time around we well likely be 10+ degrees cooler.

Frankly, I could see an upgrade to enhanced by SPC, but probably for portions of eastern TX where the coverage of severe storms might warrant higher probabilities (in my opinion). Obviously would not be surprised to see storms get pretty grungy there though.

Hi-Res models have been mixed on convection coverage locally. Some go bonkers (like the 3km NAM and RGEM), and others give us the middle finger (NMMB and ARW)

This time though, the cap won't be an issue. It's going to be where the best forcing and convergence sets up.

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6 minutes ago, Powerball said:

Hi-Res models have been mixed on convection coverage locally. Some go bonkers (like the 3km NAM and RGEM), and others give us the middle finger (NMMB and ARW)

Yeah, I wanted to give some meaningful model analysis, but models are still pretty inconsistent even under 24 hours out (for DFW area, specifically), so I just didn't want to bother haha

7 minutes ago, Powerball said:

This time though, the cap won't be an issue. It's going to be where the best forcing and convergence sets up.

Agreed on this as well

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1 hour ago, TexMexWx said:

Last year on 4/22, here in DFW we were sandwiched between the two modes, with the northern mode producing strong tornadoes along the Red River into southern OK, and the southern mode producing the long-track supercell from east/southeast TX into LA and even into MS(?), dropping sigtors along parts of its path. We ended up with a cap bust here.

Given the comparisons to that day (I am aware that nobody is necessarily calling for a repeat of that by any means), it seems like we might once again be sandwiched in that spot between the two main focuses for severe weather. Obviously that's not to say that we won't see any ourselves (we may or may not), but it does seem like we're getting caught in between two higher probability corridors again. One difference (of many) between tomorrow and 4/22/20 also lies in the surface temperatures. I remember last year, we were like in the mid-to-upper 80s, but this time around we well likely be 10+ degrees cooler.

Frankly, I could see an upgrade to enhanced by SPC, but probably for portions of eastern TX where the coverage of severe storms might warrant higher probabilities (in my opinion). Obviously would not be surprised to see storms get pretty grungy there though.

Good call on the day 1 enhanced risk from the SPC.

 

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The East Texas and Louisiana threat looks pretty dang messy and will be in questionable to poor chase terrain. The extreme NW Texas threat looks like a pretty good bet to at least see 2-3 isolated supercells. The tornado threat may be a tad bit lower but from a storm chasing perspective, that's where I would target.

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Combo of SDS and FOMO today was real with me today. Left KC prior to 8am for somewhere between Childress to Wichita Falls. Like my chances of a photogenic supercell. Ingredients *could* materialize for a decent tornado threat from 23-01z.

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On the latest outlook from the SPC, the enhanced risk areas have been shuffled around a bit.

The one covering Eastern TX / LA was shifted SW and now extends into all of far southern MS, and the one covering south central OK was expanded westward.

Otherwise, I don't see any other major changes

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6 minutes ago, Powerball said:

On the latest outlook from the SPC, the enhanced risk areas have been shuffled around a bit.

The one covering Eastern TX / LA was shifted SW and now extends into all of far southern MS, and the one covering south central OK was expanded westward.

Otherwise, I don't see any other major changes

Correction: A 30% hail area was added in SW OK.

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The discussion also mentions that an increase in tornado probabilities could be deemed necessary in the next outlook for the eastern enhanced risk area. Still yet to be determined how each threat area unfolds, obviously

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 Mesoscale Discussion 0405
   NWS Storm Prediction Center Norman OK
   1129 AM CDT Fri Apr 23 2021

   Areas affected...portions of northern and central Texas

   Concerning...Severe potential...Watch likely 

   Valid 231629Z - 231800Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Thunderstorm activity is expected to increase over the
   next couple of hours. Large hail and locally damaging wind gusts
   will be possible with this activity through the afternoon/evening. A
   severe thunderstorm watch will likely be needed by 18z.

   DISCUSSION...An area of deepening, midlevel convection atop the EML
   across west-central TX is evident in radar and visible satellite
   imagery as of 16z. This is indicative of increasing large-scale
   ascent now spreading into western TX, in conjunction with continued
   warm advection/increasing moisture beneath the weakening EML. Over
   the next couple of hours, convection is expected to continue to
   increase with a slow erosion of the cap. This may result in a mix of
   elevated storms, transitioning toward surface-based convection
   through the afternoon. 

   Very steep midlevel lapse rates (7.5-8.5 C/km) and favorable,
   elongated hodographs will support large hail. PW values increasing
   to around 1.5-1.75 with northward extent, and increasing low level
   flow will also promote strong/locally damaging gusts.

   ..Leitman/Hart.. 04/23/2021

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...HGX...FWD...OUN...EWX...SJT...

   LAT...LON   29309832 29519883 29789911 30589935 31169932 31449930
               34059863 34319832 34409769 34349711 34259672 33769649
               33179633 32929633 30459625 29629661 29319716 29269775
               29309832 

image.png

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RGENT - IMMEDIATE BROADCAST REQUESTED  
SEVERE THUNDERSTORM WATCH NUMBER 98  
NWS STORM PREDICTION CENTER NORMAN OK  
1240 PM CDT FRI APR 23 2021  
  
THE NWS STORM PREDICTION CENTER HAS ISSUED A  
  
* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF   
  SOUTHERN OKLAHOMA  
  NORTH-CENTRAL AND CENTRAL TEXAS  
  
* EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 1240 PM UNTIL  
  800 PM CDT.  
  
* PRIMARY THREATS INCLUDE...  
  SCATTERED LARGE HAIL AND ISOLATED VERY LARGE HAIL EVENTS TO 2  
    INCHES IN DIAMETER LIKELY  
  SCATTERED DAMAGING WIND GUSTS TO 70 MPH LIKELY  
  A TORNADO OR TWO POSSIBLE  
  
SUMMARY...THUNDERSTORMS ARE EXPECTED TO INTENSIFY THIS AFTERNOON  
ACROSS THE WATCH AREA, WITH A FEW STORMS BECOMING SEVERE.  LARGE  
HAIL AND DAMAGING WINDS WILL BE THE MAIN THREATS, ALTHOUGH A TORNADO  
OR TWO IS ALSO POSSIBLE.  

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