WeatherArc

Im not surprised by the spcs upgrade for thursday although it is very rare for them to upgrade the day 3 risk. A lot of shorter range models have the dryline firing. Any discrete supercell that can sustain itself will be capable of golfball-baseball sized hail, 70+ mph straight line wind gusts and strong-violent tornadoes. I also think the spcs decision to upgrade was partly due to the csu machine learning showing the equivalent of a high risk for the area, never seen that before! 21z RAP very potent, two dryline bulges one in Texas panhandle and another in Northern Kansas. Soundings from Texas panhandle Soundings from Northern Kansas Wonder if we see a 30% upgrade for fri and sat tomorrow morning, looking at models at the min both days certainly meet the threshold.

If we dont see downtrends in the next few days saturday is going to be a problem, a significant trough ejection with strong flow rounding the base, negative tilt and ejection right at peak heating. At the minute everything synoptically speaking looks very favourable for a high end severe weather outbreak. A sub 997mb low is expected to develop with a strong (50-60 knot) low level jet. The existence of subtle confluence bands was also pointed out on twitter. In regimes with less forcing these bands can help give just enough lift for storms to fire off allowing for discrete convection. I do think its important to urge some caution though, differences do still exist in models. Look at the ukmets depiction, much less favourable with trough way behind. Weve had the wheels fall off the train before (especially our last setup) so lets see what the NAM and other short range models show when they get into range tomorrow/Thursday. Overall though, thursday, Friday and Saturday all are looking like good chase days with severe weather with all hazards possible. RRFS for thursday Nam 3km also for thurs NAM for friday SPC now upgraded Thursdays risk to a day 3 enhanced. "Severe thunderstorms are likely from late Thursday afternoon into Thursday night across parts of the central and southern Great Plains. Very large hail, severe wind gusts, and strong tornadoes will all be possible. Guidance continues to suggest strong buoyancy will be in place ahead of a negatively tilted shortwave trough ejecting across the southern High Plains. General forecast expressed in the previous outlook remains valid, but confidence in an area of greater severe-weather potential has become more apparent with the most recent guidance. Late afternoon development is anticipated across the TX Panhandle, with these storms quickly becoming severe and capable of large to very large hail up to 3" in diameter. Low-level moisture may be later to arrive in west-central/southwest KS, delaying convective initiation to a few hours later than farther south. Large to very large hail is anticipated with initial development across west-central/southwest KS as well. In both of these areas, storms are expected to move east-northeastward off the dryline, encountering strengthening low-level southerly flow and environment that is increasingly favorable for tornadoes. Low-level shear will continue to strengthening into the early evening, and the overall environment supports the potential for strong to intense tornadoes if a discrete mode can be maintained." Interestingly, CSU now predicting a very small area equivalent to a high risk for Thurs, i think it will be very conditional due to cap but a significant severe event is possible if storms can fire.

The upcoming period from April 25th to May 5th is likely to be the most active stretch we've had this year and possibly the most active the great plains has been since 2019. Starting with thurs night, a 'primer' negatively tilted shortwave will eject across the region, this trough will both bring the risk of supercells with all hazards and prime the atmosphere by doing the job of pulling up moisture for following troughs to use. A 993mb surface low will develop with an associated 35-42 knot low level jet. Despite being a primer ejection moisture should be plentiful with dewpoints in the mid 60s and a sharp dryline. Steep lapse rates should also aid instability. Cape should be in the range of 1,500-2,400 j/kg sufficient for severe thunderstorm development. Looking at hodographs i wonder if cells will start as hailers before transitioning to tornado producers as hodographs become more curved. As the shortwave ejects into friday night it will deepen further with a vortmax over South Dakota. The associated low level jet will continue to strengthen as surface low pressure drops to around 987mb. Due to the large warm sector and strong low level jet severe storms are possible from Iowa to Texas. On sat night the second trough arrives and ejects over the same areas as thursday nights risk. A trough that looks like that at 500mb ejecting at peak heating means trouble. 12z GFS gives me big May 24th 2011 vibes. Classic Colorado surface low develops and tracks along panhandle, pressure down to 989mb with low level jet in the 50-60 knot range. Relatively steep lapse rates and dewpoints in the upper 60s and low 70s should result in cape values of 2400-3000 j/kg. Curved/Inflated hodographs should foster a significant severe threat with any discrete supercell, with all hazards. However, some failure modes do exist. Firstly with the weak upper level shear, while low level shear should be more than sufficient. Mid-especially upper level is iffy could lead to more HP cells or supercells struggling, also would like to see bulk shear vectors more perpendicular to initiating boundary, the more parallel they are the less discrete the storm mode. Cloud cover may also be an issue but i never trust models on that and always look at satellite the day of. The main failure mode though is the trough being mistimed or not happening at all, the GFS has trended much faster with its timing with the trough moving in with peak surface heating unlike yesterday where it had it coming through at night, things could still trend back though. The 00z GDPS is the weirdest solution ive seen though with no large trough ejection and a more zonal flow, not sure i trust this model but its worth keeping an eye on. While the pattern looks favourable i think its incredibly important to stress how many times weve seen these events fall apart as we get into the 84 hour range. Overall though, a multi-day severe weather event is likely for portions of the plains and midwest as an active wave train pattern brings multiple trough ejections combined with good moisture. Looks like a very active stretch for storm chasing! Talking about May 24th 2011 im reminded of this good pecos hank vid. The footage 57 seconds in is some of the scariest tornado video ive seen. Apart from El Reno 2013 and Moore 1999 this is one of the strongest tornadoes ever to be captured on film, i believe peak winds in this thing were estimated to be 295+mph. Notice the rolling horizontal vortex on the left side of the tornado at 1 minute! Reed also made a twitter live covering this active stretch

Big time uptick in severe weather likely going into next week with a day 6 and 7 15% issued with another 15% likely to be issued for Saturday as well. Heres what our GEFS is showing, decent support for an initial shortwave on the 25th followed by a larger trough ejection around the 27th. Past few runs of the GFS have also shown this ejection, good moisture and instability in place The Euro/EPS seems to agree with the GFS, slightly different in how it ejects the trough in regard to timing but thats to be expected at this range. Tilt of trough, and surface features such as the surface low positioning and mass response all still unclear at this range.

Ben Sainsbury I do think we are starting to enter a much more active period for severe weather, late April May and even June should be this years main show. GFS/GEFS looking fairly active as we go into late april/early may

As noted by a few on twitter tomorrow in Texas is looking quite interesting, high-extreme cape but with very low cape. Storms firing on a stationary cold front/dryline intersection, could be a few storms 'zippering' along the boundary and moving to the south west. Heres a comparison between the HRRR and Nam 3k, the Nam usually over moistens the atmosphere while the HRRRs overmixing bias dries things out so expect a middle between these models to verify High dewpoint values should lead to large cape profiles developing. This bigtime cape will lead to explosive updrafts But shear will really be on the low side with bulk shear of only 30 knots and below and 3km inflow of less than 20 knots. Having said that i wouldnt rule out a tornado threat, low level instability and vorticity (especially aided by the boundary) combined with the general large instability profiles could foster a tornado threat with a cell that can latch onto the boundary and slide down it. In fact, looking at this setup im reminded of Jarrell 1997, NO we are not going to get an F5 or anywhere close to that day, but looking at tornado archives the setup does bare some resemblance although cape will be weaker than in Jarrells case. Heres a few soundings, all taken from south Dallas, near Waco. HRRR Nam 3km I think i enjoy these days over high shear low cape, very mesoscale driven. Certain boundaries, pockets of vorticity or even surges in the RFD can lead to interesting things. Certain fail modes relate to storms quickly becoming OFD due to dry air, a more clustered mode or the weak shear overall stunting tornadogenesis/cell development Apart from the tornado threat large hail and wind damage are all possible. As said earlier the tornado risk tomorrow will be completely down to the mesoscale, or even storm scale environment. Regardless, doesn't look like too bad of a day to chase, these Texas high cape storms are always absolutely beautiful.

Some amazing pics from Iowa last night, many extremely photogenic tornadoes Including this low topped beaut of a supercell Even an attempt at triplets! Also some great satellite views of the cyclone that caused this tornado outbreak Always good to see reed dominating those tornadoes, believe this is only his second intercept since he got the dominators back out in 2022. Looking forward a conditional risk for severe weather is in place today and especially tomorrow, hrrr has cells firing on a stalled cold front in a high cape low shear environment, could foster a tornado threat depending on the mesoscale conditions. After that we should get a brief quiet period before the CFS suggests a real ramp up in severe probabilities as we enter late April and early May.

Found this on twitter lmao Eagle Eye Had class first thing so couldn't stay up, never underestimate the ability of the great plains to do a blue sky cap bust Ben Sainsbury Not surprised that storm did nothing looking at that profile that 700mb dry punch is brutal, good job with that forecast earlier verified pretty well believe the storm went just west of dodge city. We have another enhanced risk today with a 10% hatched tornado risk, mostly over Iowa. This ones still a little conditional as well but imo much greater odds of sig tors today over yesterday. Our conditionality lies with how quickly the atmosphere can recover, radar shows a band of clustered severe thunderstorms (some with embedded circulations that i believe have already produced a few weak tors) over our target area, this band should clear to the east and allow for development of discrete supercells by around 21z Now normally, the distance between the first clustered band and the more discrete mode would cause concern due to cloud cover leading to slower recovery of temps and instability however satellite reveals that a large EML punch is apparent due to the cyclones relatively mature development, this upper level dry air should help aid quick recovery and subsequent destabilisation. We should get a 47-55 knot low level jet to develop with largely 250+ 0-3km SRH, adequate for strong tornadoes if cells can remain discrete. Cape doesnt look like a problem, that EML slot should clear clouds and allow for destabilisation with around 2000 j/kg of mlcape Elevated EHI and sig tor values just ahead of cells. Profiles from Southern Iowa Profiles from Northern Missouri Profiles from Central Missouri Abundance of 3cape, should help cell's mesocyclones out

Decided to stay up just to see if the 00z models would show anything. The first thing that becomes apparent is the HRRR is handling this event incredibly poorly, moisture return is much more extensive than previously thought. HRRR vs Actual observed sounding, 8 degrees off. Heres the dewpoint error from earlier today. In fact, it seems the NAM is handling this event much better than it usually does. So looking at the 00z 3k nam we get a storm to fire in central Kansas, close to areas such as Ness city. Taking a sounding from the inflow region of said storm the Nam has a very potent environment. Now compare that to a HRRR sounding from the same area Both these models have there biases and at the moment they are really showing, i do have a bit more confidence on tomorrow actually doing something though. Seems like its going to be a day of watching observed soundings and mesoscale data as well as taking the risk of chasing on the off chance you see a Kansas wedge.

Alderc 2.0 agreed, ill admit i overhyped it but ill blame it on boredom and my thoughts that we couldn't get another event to completely underperform Hrrr does fire storms but the environment has been severely downgraded from what it was, we could still see upgrades but im not particularly hopeful Maybe its due to how active this stretch was last year with the highrisk but pretty much all of the setups so far have been messy with the higher end potential overhyped by models then severely downgraded in the last 24 hours. Im just hoping May can give us a bit more action

When the top 2 analogs for mondays system are April 14th 2012 and May 3rd 1999 i start to get very interested. The amplification of the trough seems to be the biggest question at the moment, we'll see where we are at when the CAMS begin to come into range this weekend. 18z GFS is just a classic look for a tornado event in the southern plains, almost a sub 980mb low Also large wedge tornado earlier today in Florida! Not much in the way of damage reports at the mo but will try to see if any on twitter

wow 12z Euro coming in for Monday with a very high-end likely tornado outbreak for Oklahoma and Kansas, the gfs is now the only outlier with a slower trough ejection and i would expect it to cave to the other models soon. 983 mb low! Some soundings When you compare to other model runs apart from the GFS there's pretty decent agreement. Icon UKMet Still 132 hours, this may well fall apart but with all this agreement in models alarm bells for a significant severe weather episode in the southern plains are sounding. Alderc 2.0 Agreed, 9/10 times outbreaks in the deep south aren't great due to messy storm modes and lapse rates, hopefully we are starting to see a transition to classic tornado alley with its highly visible tornadoes.

A very rare day 6 30% severe has now been issued for portions of Northern Texas, Oklahoma and southern Kansas. Per the SPC "The actual severe weather setup appears substantial. Air mass modification will ensue northward from the western Gulf on D3, with multiple days to improve the low-level moisture profile amid well above-normal surface temperatures and a pronounced elevated mixed layer. With the likely flow field amplification through the troposphere, all ingredients appear present for a significant severe weather day on D6/Monday. The areal uncertainty of the synoptic features is the primary limiting factor. For now, have added a confined 30 percent highlight to indicate the higher-end potential and the most probable corridor, while broadening the previous 15 percent area." Its not often we see such confidence in severe weather this far out, the last day 6 30% in the plains was the May 20th 2019 high risk. Confidence still a little iffy due to differences in timing but both euro, gfs and icon have significant severe weather setups.

Yeah that could be an issue, HRRR now developing a discrete cell ahead of the line for Wednesday.

Our active period continues today and tomorrow with an enhanced and moderate risk. Tonight an elevated tornado threat will develop across eastern Texas, any cell that can develop and track across the warm front has increased likelihood of producing a strong or even violent tornado, significant hail is also possible alongside damaging wind gusts. For tomorrow, the SPC has upgraded the risk to a moderate as a powerful MCS (with potential to develop into a Derecho) will track across the Mississippi, Louisiana, Alabama regions. A rare 45% hatched wind risk for gusts exceeding 75mph as well as a 15% hatched risk for strong QLCS tornadoes that can spinup. Looking even further ahead, the spc has issued a day 7 15% for the system we've been watching since Saturday, a negatively tilted trough will eject into the plains with ample moisture, still some uncertainty on whether the ejection will occur during peak heating or not, could be a significant tornado day if all things line up but can swing either way at this range. AndrewHamm Early may still has that favourable look on the long range models, you know its pretty significant when people start mentioning 2011 and 2013 as analogues!

Reed timmers going up live in a plane

18z Gfs smoking some wild stuff tonight what an utterly ridiculous run Looking at ensemble runs its very clear there's decent support for another trough to move in next weekend, GEFS also showing a slight negative tilt to this system (much more favourable for severe weather) However it is important to remember we are still 180-200 hours out from this system, lots can and will change and many important factors such as surface low development and placement, moisture, lapse rates will not start getting resolved until we enter 80 hours out.

Not good to see so early in the season, Europe's had 2 catastrophic fire years and hopefully we wont see a third.

Yes, its one gfs run 210 hours out and will likely not verify but couldn't resist not posting Absolute dream of a look for a big plains tornado day

Robert1981 Essentially, yes. Ill try to explain it. Bad drawing here but the area in blue is what i would consider the most frequent area in the US for tornadoes, it includes the classic tornado alley (Oklahoma, Kansas, Texas, Colorado and Nebraska) Dixie alley (Alabama, Mississippi, Louisiana, Tennessee, Arkansas, Kentucky and Missouri) as well as the Midwest (Iowa, Illinois and Indiana) and the high plains (North and south Dakota and portions of Saskatchewan and Alberta) during spring large low pressure troughs swing in from the west, as they do they pull up moisture from the warm gulf of mexico. This typically results in dewpoints (the temperature at which water vapor can condense) of around 15-25 degrees Celsius, we in the Uk often struggle to get high dewpoints due to the cold waters surrounding us, its only really in August and September that our dewpoints can reach into the low 20s. Higher dewpoints and temps equal more cape/instability. Typically, cape values 500+ result in strong showers, 1000+ thunderstorms and 2000+ severe thunderstorms. In the summer areas of the US can reach 7-8000 j/kg of cape. Now in the UK we typically can reach values of around 2500-3000 in the height of summer, however look at this euro run from last year, 6000 mucape just south of Bristol! We of course never actually got close to that number but just proves that the UK does have the ability to have these explosive values (imo because our sea temps were so warm that year) Now the area i circled red on that map is what we call the EML (elevated mixed layer) source region, this region comprises of mountains and deserts, meaning dry air. When a trough moves over the plains it will advect this dry air to the north east and push it on top of the moist air being drawn in from the south creating a cap and raising instability further. A capping inversion acts as a lid on the atmosphere, often in the uk we will get storms firing at around 10/11 in the morning due to the lack of this cap, these storms then use up the little instability available at that time as well as ruin the atmosphere with cloud cover, in classic American tornado outbreaks a strong EML means storms wont fire till around 3-5pm when instability is at its highest. A strong cap also means only the strongest updrafts can develop, meaning storms are more isolated and available to take full advantage of the present conditions. Now we in the Uk/Ireland usually struggle to get that cap, however some of our best thunderstorm events the past few years have been when a cap is present. Another reason the us is so favourable is due to whats called Lee cyclogenesis, essentially as a trough moves over the Rockies a surface low will develop on the Leeward side of the mountains, this surface low enhances the 850mb winds as well as drawing in even more moisture. The winds at 850mb are known as the low level jet and as the sun goes down at around 5pm they will rapidly strengthen due to higher elevations (Rockies) cooling faster than lower elevations. This is why tornadoes are so common in the evening. In the uk, we dont have any mountain ranges like this to create Lee cyclogenesis, this means we often lack low level shear to really create much of a tornado threat. However, when we do get a surface low to either develop or pass over us we can get severe weather, especially in the summer. This is from the Birmingham 2005 EF2 tornado, very well positioned trough bringing us warm, moist air from the Mediterranean while also enhancing upper layer shear for supercells, meanwhile a surface low formed enhancing our low level jet just enough to become supportive of tornadoes, we had outbreaks of supercells across the country this day, mainly producing large hail. Theres also the 28th june 2012 supercells, while low level shear was much weaker than the Birmingham setup these things did produce large hail and a few weak tornadoes. Love this vid, shows that the uk can get severe supercells on par with those in the us. Hopefully ive explained that alright, any questions absolutely feel free to ask. I would also really recommend giving this channel a watch.

Robert1981 Thank you very much yeah i do sometimes wish our weather was a little more active, i would kill to see a beefy LP supercell like the ones below in person. Saying that though im looking forward to storm season, if we have a repeat of last year ill be very happy. Hopefully we get a few big cape days as well. Ill be keeping an eye on sea surface temps, the higher they are the higher the dewpoints. I think we'll enter a quieter period for severe weather until late april, GFS seems to of picked up on something. Long way out but something to look out for. Even GEFS has some support

Slow start to the season so far, however May is starting to show up in longer range models as a very active month for severe weather and tornadoes across the plains. We always thought this would be a back ended year with greater severe weather probs happening in late April, May and June.