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Severe Threat May 15-16, 2025

So, just for fun, I asked Chatgpt about the new SPC outlook, "What would you interpret the ceiling of the event to be based on all the different possibilities they outline?"

Here was its response:

Based on the SPC outlook, the ceiling of this event — i.e., the worst-case realistic scenario — is a significant and widespread severe weather outbreak with multiple high-end impacts across several regions. Here's what that ceiling could look like:



Upper-End Scenario (Ceiling):​


  1. Multiple strong (EF2+) tornadoes, including a couple of long-tracked, potentially violent tornadoes, especially from southeast Missouri into western Kentucky and southern Indiana — areas where supercells may remain discrete for longer.
  2. Very large hail, potentially up to 3.5 inches in diameter, particularly in the early, more isolated supercell phase.
  3. Widespread destructive wind damage, including gusts over 80 mph (70+ kt), associated with a mature bow echo/MCS sweeping from the Ohio Valley into the Mid-Atlantic overnight. This line could maintain severe intensity for hundreds of miles.
  4. Significant nocturnal tornadoes, especially embedded within the bowing line — a particularly dangerous scenario due to reduced visibility and lower public response at night.
  5. Additional severe weather "nodes" farther south (ArkLaTex) and east (Mid-Atlantic) may flare up, adding to the complexity and scope of the event, though these are more conditional.

Interpretation:​


The ingredients — strong instability (up to 3500 J/kg MLCAPE), intense shear (including 70–90 kt mid-level flow), enlarged hodographs, and multiple convective modes — all point to a volatile environment. If storms remain semi-discrete longer before consolidating into a line, the tornado and hail threat becomes more pronounced. Once linear, the wind threat could become widespread and damaging, extending into the overnight period across multiple states.



So, while not guaranteed, the ceiling includes:

  • A regional tornado outbreak (with a few strong ones),
  • Scattered instances of baseball-sized hail,
  • A long-lived derecho-like wind event,
  • Dangerous nocturnal severe weather over a broad area.

This is the kind of setup that could lead to high-end impacts over a large population area, especially if storms evolve toward the most aggressive possibilities outlined.
 
Grand Poo Bah said:
So, just for fun, I asked Chatgpt about the new SPC outlook, "What would you interpret the ceiling of the event to be based on all the different possibilities they outline?"

Here was its response:

Based on the SPC outlook, the ceiling of this event — i.e., the worst-case realistic scenario — is a significant and widespread severe weather outbreak with multiple high-end impacts across several regions. Here's what that ceiling could look like:



Upper-End Scenario (Ceiling):​


  1. Multiple strong (EF2+) tornadoes, including a couple of long-tracked, potentially violent tornadoes, especially from southeast Missouri into western Kentucky and southern Indiana — areas where supercells may remain discrete for longer.
  2. Very large hail, potentially up to 3.5 inches in diameter, particularly in the early, more isolated supercell phase.
  3. Widespread destructive wind damage, including gusts over 80 mph (70+ kt), associated with a mature bow echo/MCS sweeping from the Ohio Valley into the Mid-Atlantic overnight. This line could maintain severe intensity for hundreds of miles.
  4. Significant nocturnal tornadoes, especially embedded within the bowing line — a particularly dangerous scenario due to reduced visibility and lower public response at night.
  5. Additional severe weather "nodes" farther south (ArkLaTex) and east (Mid-Atlantic) may flare up, adding to the complexity and scope of the event, though these are more conditional.

Interpretation:​


The ingredients — strong instability (up to 3500 J/kg MLCAPE), intense shear (including 70–90 kt mid-level flow), enlarged hodographs, and multiple convective modes — all point to a volatile environment. If storms remain semi-discrete longer before consolidating into a line, the tornado and hail threat becomes more pronounced. Once linear, the wind threat could become widespread and damaging, extending into the overnight period across multiple states.



So, while not guaranteed, the ceiling includes:

  • A regional tornado outbreak (with a few strong ones),
  • Scattered instances of baseball-sized hail,
  • A long-lived derecho-like wind event,
  • Dangerous nocturnal severe weather over a broad area.

This is the kind of setup that could lead to high-end impacts over a large population area, especially if storms evolve toward the most aggressive possibilities outlined.
Click to expand...
Lol, I asked it "what is the current day 2 risk level for the SPC" and here's how it responded:

"As of Thursday, May 15, 2025, the Storm Prediction Center (SPC) has not issued a Day 2 Convective Outlook, which typically covers the period from 12:00 PM (CDT) on Friday, May 16, to 12:00 PM (CDT) on Saturday, May 17). Therefore, there is currently no designated risk level for severe thunderstorms for that timeframe."

False alarm, guys, no risk for tomorrow! :D (I'm being sarcastic)
 
And just to cover the bases I asked what a realistic floor would look like

Lower-End Scenario (Floor):​


  1. Morning convection lingers longer than expected, stabilizing the atmosphere over key risk areas (especially Kentucky/Indiana), which would limit daytime heating and reduce instability.
  2. Supercells struggle to form or remain discrete, possibly due to early messy convection, weaker surface convergence, or unexpected inhibition (e.g., lingering capping). This would significantly reduce the large hail and tornado potential.
  3. The bowing MCS forms earlier, which could limit the tornado risk by quickly transitioning storms into a linear mode. A fast evolution into a line would also constrain the time window for the most dangerous hail-producing storms.
  4. Damaging winds remain more scattered, with fewer gusts exceeding 60–70 mph, and the MCS weakens more quickly as it crosses the Appalachians into more stable air.
  5. Southern and eastern areas (ArkLaTex, Mid-Atlantic) remain mostly quiet, due to weaker forcing, capping, or displacement from primary jet dynamics.


Interpretation:​


In the best-case realistic outcome, this event still brings some severe storms — especially damaging winds and a few hail reports — but the widespread outbreak and strong tornadoes are muted or highly localized. Impacts would still occur, but they would be:
  • More isolated and less intense,
  • Focused within a shorter time window,
  • And less widespread geographically.

There could be only a few brief or weak tornadoes, hail mostly under 2 inches, and scattered wind reports, rather than a full-blown regional outbreak.


Summary Range:​

  • Ceiling = Significant, widespread tornadoes, hail, and wind — possibly a derecho.
  • Floor = A mostly linear event with isolated severe reports and minimal tornado activity.
 
US_Highway15 said:
Yes, from 2000-2025, there have been I believe three to five years where there were 5 High Risks issued, but 2010 takes the cake with 6 of them issued that year.
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It’s hard to compare then vs now. The SPC has absolutely raised the bar for what a high risk is and forecasting had gotten better leading to fewer high risks. Also, they used to issue high risks for wind, and while they still can, I’ll be stunned if we ever see another. The SPC has basically said as much.
 
ChatGPT is not a reliable source of information. It outputs text based on probabilities connected to how often words go together in its training information. It does not comprehend the data you have provided to it. I can share more information on this elsewhere, but there are studies that show it is not even reliable for summarizing information, let alone synthesizing it.
 
notsoencrypted said:
ChatGPT is not a reliable source of information. It outputs text based on probabilities connected to how often words go together in its training information. It does not comprehend the data you have provided to it. I can share more information on this elsewhere, but there are studies that show it is not even reliable for summarizing information, let alone synthesizing it.
Click to expand...

ChatGPT is a very reliable source of information if you use it correctly.
 
HRRR is not budging with developing a strong tornadic supercell right over north-central Cook county. It's been modeling that since the early morning runs. Similar to the NAM. Remarkable consistency and very worrying.
 
notsoencrypted said:
ChatGPT is not a reliable source of information. It outputs text based on probabilities connected to how often words go together in its training information. It does not comprehend the data you have provided to it. I can share more information on this elsewhere, but there are studies that show it is not even reliable for summarizing information, let alone synthesizing it.
Click to expand...
I'd be interested in more information about this if you want to message it to me! I think it's a pretty useful tool, and it's especially good at pattern recognition, which makes it fun to use for weather.
 
For fun I asked ChatGPT the same question. Looks perfect to me:

what is the SPC's day 2 convective outlook (issues today, may 15th 2025)

ChatGPT said:​

As of May 15, 2025, the Storm Prediction Center (SPC) has issued a Day 2 Convective Outlook indicating a significant severe weather threat for Friday, May 16, 2025.

⚠️ Risk Overview​

A Moderate Risk (Level 4 of 5) is forecast across portions of the middle Mississippi and Ohio Valleys, including parts of southeast Missouri, southern Illinois and Indiana, and central and western Kentucky. This setup suggests a regional outbreak of severe thunderstorms is likely Friday afternoon into Friday night. Storm Prediction Center+1Big Rapids Pioneer+1

Tornado Risk​

There is a 10% probability of tornadoes within 25 miles of a point across areas including Indianapolis, St. Louis, Cincinnati, Louisville, and Evansville. Some of these tornadoes could be strong (EF2 or greater). Storm Prediction Center+10Storm Prediction Center+10Storm Prediction Center+10Storm Prediction Center+2Big Rapids Pioneer+2Wikipedia+2

️ Damaging Wind Risk​

A 30% risk area for damaging winds (60 mph or greater) encompasses cities such as Indianapolis, Nashville, Cincinnati, Louisville, and Lexington. Additionally, a significant severe wind area (hatched) indicates potential for wind gusts exceeding 75 mph. Storm Prediction Center+4Storm Prediction Center+4Big Rapids Pioneer+4Storm Prediction Center+1Storm Prediction Center+1

️ Large Hail Risk​

A 30% risk area for large hail (1 inch or greater) includes cities like St. Louis, Evansville, Bloomington, Jonesboro, and Terre Haute. A significant severe hail area (hatched) suggests potential for hailstones 2 inches in diameter or larger. Big Rapids Pioneer+8Storm Prediction Center+8Storm Prediction Center+8

Local Impact: Chicago Area​

While Chicago is not within the Moderate Risk area, it is included in a 15% risk area for severe thunderstorms, indicating the potential for damaging winds and large hail. Residents should remain alert and monitor local forecasts.Big Rapids Pioneer+4Storm Prediction Center+4Storm Prediction Center+4

⏰ Timing and Hazards​

Severe thunderstorms are expected to develop Friday afternoon and continue into the evening and overnight hours. Initial supercells may pose risks for large hail and tornadoes, with storms potentially organizing into a bowing line capable of producing widespread damaging winds and additional tornadoes. Storm Prediction Center+4Storm Prediction Center+4Big Rapids Pioneer+4
For the most current information and updates, please refer to the SPC Day 2 Convective Outlook.
 
If there's one bad thing about metros in the U.S., it's gotta be that huge sprawling metros and bad weather usually make for a deadly mix. If you had a Tokyo-size metro in Oklahoma, I'm sure they'd see hundreds of tornado deaths over the years due to the sheer amount of people that live there.
 
lake.effect said:
For fun I asked ChatGPT the same question. Looks perfect to me:

what is the SPC's day 2 convective outlook (issues today, may 15th 2025)

ChatGPT said:​

As of May 15, 2025, the Storm Prediction Center (SPC) has issued a Day 2 Convective Outlook indicating a significant severe weather threat for Friday, May 16, 2025.

⚠️ Risk Overview​

A Moderate Risk (Level 4 of 5) is forecast across portions of the middle Mississippi and Ohio Valleys, including parts of southeast Missouri, southern Illinois and Indiana, and central and western Kentucky. This setup suggests a regional outbreak of severe thunderstorms is likely Friday afternoon into Friday night. Storm Prediction Center+1Big Rapids Pioneer+1

Tornado Risk​

There is a 10% probability of tornadoes within 25 miles of a point across areas including Indianapolis, St. Louis, Cincinnati, Louisville, and Evansville. Some of these tornadoes could be strong (EF2 or greater). Storm Prediction Center+10Storm Prediction Center+10Storm Prediction Center+10Storm Prediction Center+2Big Rapids Pioneer+2Wikipedia+2

️ Damaging Wind Risk​

A 30% risk area for damaging winds (60 mph or greater) encompasses cities such as Indianapolis, Nashville, Cincinnati, Louisville, and Lexington. Additionally, a significant severe wind area (hatched) indicates potential for wind gusts exceeding 75 mph. Storm Prediction Center+4Storm Prediction Center+4Big Rapids Pioneer+4Storm Prediction Center+1Storm Prediction Center+1

️ Large Hail Risk​

A 30% risk area for large hail (1 inch or greater) includes cities like St. Louis, Evansville, Bloomington, Jonesboro, and Terre Haute. A significant severe hail area (hatched) suggests potential for hailstones 2 inches in diameter or larger. Big Rapids Pioneer+8Storm Prediction Center+8Storm Prediction Center+8

Local Impact: Chicago Area​

While Chicago is not within the Moderate Risk area, it is included in a 15% risk area for severe thunderstorms, indicating the potential for damaging winds and large hail. Residents should remain alert and monitor local forecasts.Big Rapids Pioneer+4Storm Prediction Center+4Storm Prediction Center+4

⏰ Timing and Hazards​

Severe thunderstorms are expected to develop Friday afternoon and continue into the evening and overnight hours. Initial supercells may pose risks for large hail and tornadoes, with storms potentially organizing into a bowing line capable of producing widespread damaging winds and additional tornadoes. Storm Prediction Center+4Storm Prediction Center+4Big Rapids Pioneer+4
For the most current information and updates, please refer to the SPC Day 2 Convective Outlook.
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Huh, weird.
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