26 inch Fort Lauderdale rainfall

[bigtenfan]

I am not sure that I am putting this in the correct forum.

Do any Mets on the board have a scientific explanation as to the cause of the biggest single day rainfall in Florida history?  I almost had a very personal stake in this as my wife's flight  out of FLL got off the ground an hour before they stopped all flights in and out. She said that the ascent was very turbulent.

I have seen very little discussion of what was truly a history making event.

Thanks in advance

 

[It's Always Sunny]

I worked that day. Looking back on everything, it was a very rare occurrence (1 in every 200 years). Stationary front was slow to lift north however given vertical wind profile, an embedded supercell was able to develop. During the time of development, storm motion vectors (Bunkers) yielded a fairly stationary cell that anchored to the frontal boundary and just spun like a top over FLL for hours. 

[GaWx]

2 hours ago, bigtenfan said:

I am not sure that I am putting this in the correct forum.

Do any Mets on the board have a scientific explanation as to the cause of the biggest single day rainfall in Florida history?  I almost had a very personal stake in this as my wife's flight  out of FLL got off the ground an hour before they stopped all flights in and out. She said that the ascent was very turbulent.

I have seen very little discussion of what was truly a history making event.

Thanks in advance

 

More on this huge Ft Lauderdale rain:

- Records go back to 1913.

- 25.91", which fell mainly within just a 12 hour period, far exceeds the greatest there on record in one calendar day. The old record was 14.59" on 4/25/1979 from a weak low in the NE GOM.

 

 Here are prior 10"+ 2 calendar day rains:

- 16.74" 10/19-20/1924 from hurricane moving NE from NW Caribb.

- 15.79" 4/24-5/1979 from weak NE GOM low

- 13.72" 6/2-3/1930 with no tropical system anywhere nearby

- 13.10" 10/11-12/1947 from hurricane moving NE from NW Caribb.

- 12.25" 10/31-11/1/1969 near stationary front

- 11.00" 10/4-5/1948 from hurricane moving NE from NW Caribb.

- 10.89" 5/27-28/2003 (nothing tropical).

- 10.75" 3/14-15/1919 (nothing tropical).

- 10.68" 11/19-20/1973 (nothing tropical).

- 10.14" 6/7-8/1999 (nothing tropical).

 
 The THREE day record is "only" 18.24" set 10/19-21/1924 per this:

https://www.newsweek.com/fort-lauderdale-third-annual-rainfall-only-7-hours-1794169?amp=1

 Interestingly, no 10"+ event has occurred from a tropical cyclone since way back in 1948! If someone had told me before I did this research that it had been 75 years since the last from a TC, I would have wondered if that was accurate.

  Is there any clearcut evidence that GW was a major factor? No clearcut evidence imho. Why?

 - It occurred with dewpoints in the low 70s and offshore SSTs no higher than the low 80s. Yes, those are above average for mid April. However, SSTs get into the mid to upper 80s and dewpoints into the upper 70s every summer and yet nothing even close to this heavy an event has occurred most years in S FL summers.

- Look at the decades for the listed 11 heaviest Ft Lauderdale events since 1913:

1910s, 1920s, 1930s, 1940s (2), 1960s, 1970s (2), 1990s, 2000s, 2020s

 This looks like a pretty even distribution. If these records had been heavily influenced by the 3 or so degree F warmer globe, I would have expected a heavier concentration since the 1980s (and especially in summer/early fall). Yet, there have been only 3 of 11 since then.

[Ed, snow and hurricane fan]

Tops the one day 17 inch rain totals in a non-tropical system, the 2016 Houston Tax Day Floods.  I remember 2015, before I flew to ISP, record non-tropical floods there.  No matter what the SSTs were, something may be changing. I suspect in the PWATs.  All else being equal, S Florida should have higher single day rainfalls than anywhere in Texas just based on sub-tropical water in almost all compass directions.

 

https://abc13.com/houston-flooding-april-tax-day-flood-24-inches-of-rain-three-brothers-bakery/11752788/#:~:text=HOUSTON%2C Texas (KTRK) --,and around the Houston area.&text=Meyerland resident Dr.,two days all too vividly.

[bluewave]

https://www.weather.gov/owp/hdsc_aep

https://www.weather.gov/media/owp/oh/hdsc/docs/202304_FtLauderdale.pdf

 

 

 

 

 

[GaWx]

2 hours ago, bluewave said:

https://www.weather.gov/owp/hdsc_aep

https://www.weather.gov/media/owp/oh/hdsc/docs/202304_FtLauderdale.pdf

 

 

 

 

 Due to how extreme this event was, I feel this is quite possibly not just a 1 in 1,000 year event but also perhaps a once in several thousand year event as Erich Fischer suggests above. However, I also maintain for the reasons I already stated that there's no indication that AGW/CC had much, if anything, to do with the set of freak factors that lead to this.

 Keep in mind that this occurred over only a small area relatively speaking. Ft Lauderdale is 34 sq mi. I estimate that as much as 35 sq miles had 20+" of rain. And that's probably conservatively high. So, that's 35 sq miles out of 3.5 million sq miles in the entire US. So, there are 100,000 parcels of land the size of Ft Lauderdale in the US. Even though it is obviously a huge deal wherever it occurs, a 1 in several thousand year event occurring over 1/100000 of the US isn't hard to fathom. For that matter, the expectation is that on average several of these 1 in several thousand year events would occur somewhere in the US each year.

 Whereas I believe that events such as the extreme rains from Hurricane Harvey (covered a much larger area) for example, were made more probable due to AGW, I see no evidence of that for this event for the reasons I stated in my earlier post. But there are certain folks that do their best to blame AGW/CC for as many extreme events as possible even without ample evidence. Imho, that actually leads to more folks denying the existence of AGW.

[bluewave]

3 hours ago, GaWx said:

 Due to how extreme this event was, I feel this is quite possibly not just a 1 in 1,000 year event but also perhaps a once in several thousand year event as Erich Fischer suggests above. However, I also maintain for the reasons I already stated that there's no indication that AGW/CC had much, if anything, to do with the set of freak factors that lead to this.

 Keep in mind that this occurred over only a small area relatively speaking. Ft Lauderdale is 34 sq mi. I estimate that as much as 35 sq miles had 20+" of rain. And that's probably conservatively high. So, that's 35 sq miles out of 3.5 million sq miles in the entire US. So, there are 100,000 parcels of land the size of Ft Lauderdale in the US. Even though it is obviously a huge deal wherever it occurs, a 1 in several thousand year event occurring over 1/100000 of the US isn't hard to fathom. For that matter, the expectation is that on average several of these 1 in several thousand year events would occur somewhere in the US each year.

 Whereas I believe that events such as the extreme rains from Hurricane Harvey (covered a much larger area) for example, were made more probable due to AGW, I see no evidence of that for this event for the reasons I stated in my earlier post. But there are certain folks that do their best to blame AGW/CC for as many extreme events as possible even without ample evidence. Imho, that actually leads to more folks denying the existence of AGW.

All we know at this point is that a warmer atmosphere holds more moisture and has been producing heavier precipitation events across the world and US. We will need an attribution study for this one to see how all the various factors came together. So what was considered a 1000yr recurrence interval in our older climate may have a shorter reoccurrence interval in our warmer climate. Plus land use changes can enhance flooding in extreme rainfall events.

https://glisa.umich.edu/resources-tools/climate-impacts/extreme-precipitation/

Five weeks. Five instances of 1,000-year rain events. 

https://www.washingtonpost.com/climate-environment/2022/08/23/flood-united-states-climate-explainer/

Nowadays, however, our climate is evolving rapidly enough that previously defined recurrence intervals based on historic data might no longer apply. 

 

Event

AEP map duration(s)

Shapefile

Fort Lauderdale, Florida, 12 April 2023	12-Hour	link
Hurricane Ian, Florida, 28-30 September 2022	6-Hour, 24-Hour
Post-Tropical Depression Ida, Northeast, 31 August - 2 September 2021	3-Hour, 6-Hour, 12-Hour, 24-Hour	link
West Central Tennessee, 20-22 August 2021	12-Hour, 24-Hour	link
Imelda, 16-20 September 2019	12-Hour, 24-Hour, 48-Hour	link
Remnants of Barry, Arkansas, 15-16 July 2019	24-hour	link
South-Central Nebraska, 8 July 2019	6-hour	link
Arkansas River Basin, April - May 2019	30-day	link
Hurricane Florence, 13-18 September 2018	72-hour	link
Michigan and Wisconsin, 14-18 June 2018	6-hour, 24-hour, 72-hour	link
Ellicott City, Maryland, 27 May 2018	3-hour
Hurricane Maria, 20 September 2017	12-hour	link
Hurricane Harvey, 25-31 August 2017	4-day
Missouri, 28 April - 2 May 2017	48-hour	link
Hurricane Matthew, 6-10 October 2016	12-hour	link
Louisiana, 11-13 August 2016	48-hour
Ellicott City, Maryland, 30 July 2016	3-hour
Northern Wisconsin, 11-12 July 2016	6-hour
West Virginia, 23-24 June 2016	24-hour
Lower Mississippi River Valley, 8-12 March 2016	48-hour
Corsicana, Texas, 24-25 October 2015	24-hour
Austin, Texas, 30 October 2015	3-hour, 6-hour
South Carolina, 2 - 4 October 2015	24-hour, 72-hour
Central Texas, 23-24 May 2015	3-hour, 6-hour
Oklahoma, April - June 2015	20-day,30-day, 60-day
Phoenix, Arizona, 19 August 2014	12-hour
Islip, New York, 13 August 2014	3-hour
Pensacola, Florida, 29-30 April 2014	6-hour
New Mexico, 9-16 September 2013	7-day
Colorado, 9-16 September 2013	24-hour, 48-hour, 7-day
Southern Missouri, 29 July - 8 August 2013	10-day
San Antonio, Texas, 25 May 2013	6-hour
Oklahoma City region, 31 May-1 June 2013	4-hour, 6-hour
Tropical storm Debby, 24-27 June 2012	48-hour
Duluth, Minnesota, 19-20 June 2012	24-hour
Tennessee, 1-2 May 2010	48-hour
Southeastern New England, March 2010	20-day

[Jns2183]

Smethport, pa July 1942. There are a few others like this roughly once ever 20 years. I believe last one was 1995 Madison county. These happen. They have been happening for awhile. It may just be how they analyse recurrence intervals in a specified area. But a 1000 year recurrence intervals is just bad wording. I'm sure if we had data for multiple locations within a specified grid for many thousands of years the smoothed probability distributions for entire region would be more similar to the models. But at no point do those graphs actually state that is the atmospheric maximum for such location. Because a podoke mountain town in north central pa had more rain than this in I believe less time, back in 1942.

Sent from my SM-G970U using Tapatalk

[Jns2183]

If my memory is correct they did a relanaysis of it based on stream gauges at the time and estimated the hills just east of town received upwards of 40" in under 6hours.

Sent from my SM-G970U using Tapatalk

[bluewave]

The local NWS office did a nice presentation on that event.

http://weather.mynetgear.com/severe/1942/17Jul1942.pdf

The rainfall analysis was literally based on a bucket survey with Short Run, PA having 11.9+ inches in a crock, 11.3+ in a wooden bucket, and 8.2+ inches in a milk pail. Pans, tubs, buckets, paint cans, coffee pots and similar devices rounded out the instrumentation set. Emporium, PA had 25.6 inches in a crock and Coudersport, PA had 25.5 inches of rainfall in a Milk Can. Official NWS COOP data analysis of this event indicates no 24 hour records and the official gage Coudersport recorded 8.48 inches. Far less than the Milk Can.
The gage at Smethport “reported 6.68 inches before the gage was lost” (Gelber, 2002). Smethport reportedly set the 24 hour rainfall record of 30.60 inches on 17 July with an event total rainfall estimated to be 34.50 inches. There were no official rain gages within 40% of these values and as noted the Smethport gage was lost before the event ended. The official gage data indicated that when combining 17-18 July data rainfall, amounts over 8.48 inches were recorded and values much over 10 inches were difficult to find. Clearly, there was a large discrepancy between rain gage and bucket analysis. Gelber (2002) argues that the official 24 hour rainfall record for Pennsylvania is 19.81 inches set in Park Place, PA in July 1947.
The impacts of the heavy rain were significant (Gelber, 2002) and similar to those one might associated with an intense widespread 6-10 inch rainfall event. The flooding claimed 16 lives, 6 of which occurred in Port Allegany. McKean County had damage to our lost 16 bridges.

 

 

[Stormchaserchuck1]

I'll just say it, someone probably did mushrooms. 

The odds of it only over a city (looking at radar totals) are like 1/1000.

If not now, then another point in time. [matter of factly lol]

 

[csnavywx]

On 4/17/2023 at 10:48 PM, GaWx said:

More on this huge Ft Lauderdale rain:

- Records go back to 1913.

- 25.91", which fell mainly within just a 12 hour period, far exceeds the greatest there on record in one calendar day. The old record was 14.59" on 4/25/1979 from a weak low in the NE GOM.

 

 Here are prior 10"+ 2 calendar day rains:

- 16.74" 10/19-20/1924 from hurricane moving NE from NW Caribb.

- 15.79" 4/24-5/1979 from weak NE GOM low

- 13.72" 6/2-3/1930 with no tropical system anywhere nearby

- 13.10" 10/11-12/1947 from hurricane moving NE from NW Caribb.

- 12.25" 10/31-11/1/1969 near stationary front

- 11.00" 10/4-5/1948 from hurricane moving NE from NW Caribb.

- 10.89" 5/27-28/2003 (nothing tropical).

- 10.75" 3/14-15/1919 (nothing tropical).

- 10.68" 11/19-20/1973 (nothing tropical).

- 10.14" 6/7-8/1999 (nothing tropical).

 
 The THREE day record is "only" 18.24" set 10/19-21/1924 per this:

https://www.newsweek.com/fort-lauderdale-third-annual-rainfall-only-7-hours-1794169?amp=1

 Interestingly, no 10"+ event has occurred from a tropical cyclone since way back in 1948! If someone had told me before I did this research that it had been 75 years since the last from a TC, I would have wondered if that was accurate.

  Is there any clearcut evidence that GW was a major factor? No clearcut evidence imho. Why?

 - It occurred with dewpoints in the low 70s and offshore SSTs no higher than the low 80s. Yes, those are above average for mid April. However, SSTs get into the mid to upper 80s and dewpoints into the upper 70s every summer and yet nothing even close to this heavy an event has occurred most years in S FL summers.

- Look at the decades for the listed 11 heaviest Ft Lauderdale events since 1913:

1910s, 1920s, 1930s, 1940s (2), 1960s, 1970s (2), 1990s, 2000s, 2020s

 This looks like a pretty even distribution. If these records had been heavily influenced by the 3 or so degree F warmer globe, I would have expected a heavier concentration since the 1980s (and especially in summer/early fall). Yet, there have been only 3 of 11 since then.

Good stats listed here, but I would debate this portion and some of the interpretation. I'll agree it's complex and difficult to tease out. However -- you're generally not going to get environments favorable for supercells in S FL in summer and fall, esp for the kind we saw with long duration. This strikes me as a combination of mid-spring setup overlapping with higher SSTs than should have been available. 1-2C warmer than normal temps/dews temps into a skinny CAPE-high shear profile will absolutely make a difference in both updraft maintenance and precip output, esp if warm cloud layer is deep enough. A few degrees cooler at the surface and in the inflow layer and I'm not even sure you get an event anywhere near this magnitude -- probably several inches less. But in a marginal situation like this? The persistent maintenance of a mesocyclone alone could've contributed up to 50% of the updraft speed.

Obvs. it falling over a metro area and the expanding bullseye effect have some blame here too.

[bigtenfan]

13 hours ago, csnavywx said:

Good stats listed here, but I would debate this portion and some of the interpretation. I'll agree it's complex and difficult to tease out. However -- you're generally not going to get environments favorable for supercells in S FL in summer and fall, esp for the kind we saw with long duration. This strikes me as a combination of mid-spring setup overlapping with higher SSTs than should have been available. 1-2C warmer than normal temps/dews temps into a skinny CAPE-high shear profile will absolutely make a difference in both updraft maintenance and precip output, esp if warm cloud layer is deep enough. A few degrees cooler at the surface and in the inflow layer and I'm not even sure you get an event anywhere near this magnitude -- probably several inches less. But in a marginal situation like this? The persistent maintenance of a mesocyclone alone could've contributed up to 50% of the updraft speed.

Obvs. it falling over a metro area and the expanding bullseye effect have some blame here too.

Did the fact that was worst at the airport itself have anything to do with heat generated from all of the jet engines?

[csnavywx]

2 hours ago, bigtenfan said:

Did the fact that was worst at the airport itself have anything to do with heat generated from all of the jet engines?

Probably coincidence. The amount of heat generated by condensation from ocean fluxes dwarfs anything we can generally produce *directly* (and flights would've been shut down, anyways). Exception is generally from retained solar heat in buildings/concrete, etc -- but wasn't much solar heating going on before that.

[Eskimo Joe]

On 4/21/2023 at 9:52 AM, bigtenfan said:

Did the fact that was worst at the airport itself have anything to do with heat generated from all of the jet engines?

No