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Dallas flooding is 5th 1-in-1,000-year flood event in US since late July

Thursday, August 25, 2022 19:12 UTC
Wyatt Loy, AccuWeather staff writer

In the last five weeks, five areas across the United States have all experienced what should have been very unlikely -- if not impossible -- one in 1,000-year flooding events.

The most recent historic flooding event occurred in Dallas on Monday, Aug. 22, where 8 to 16 inches of rain fell over a 24-hour stretch. The heavy rain flooded buildings, submerged cars on interstates and also caused the Trinity River to swell well beyond its normal water line. All of this resulted in billions of dollars worth of damage, according to an AccuWeather estimate.

AccuWeather Founder and CEO Dr. Joel N. Myers, who has for decades closely studied the economic impacts of extreme weather, estimated that the total damage and economic loss resulting from the catastrophic flash flooding would range between $4.5 billion and $6 billion.

This flooding occurred after a 67-day dry streak in the city, and according to Allen Li, a researcher at the University of Oklahoma, this weather whiplash is not only more common due to climate change but could happen again, even multiple times over the next 1,000 years.

"One in 1,000 [years] doesn't mean that only happened once over 1,000 years," Li told AccuWeather National Reporter Bill Wadell. It only means there's a 0.1 percent chance of it happening every year.

>>>>>Remember in a large set of data, if the mean changes by a little, the extremes change by a lot.         Once in every 'N Years' means a 63% of the event happening at least once in the time frame specified, here 1,000 years.   >>>>>> CIK62

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10 minutes ago, Rjay said:

No relief in sight.   I'm sure the usual areas will see some storms at some point over the next 2 weeks though. 

Can only hope the HRRR is on to something for tomorrow. Would certainly help bring some temporary relief

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The 12z EPS is correcting stronger with the WAR/SE Ridge through the Labor Day weekend. So a continuation of our 90°+ pattern on the warmer days. Some hint that a tropical system could make it close to the Bahamas or Gulf after Labor Day. That may be our best chance at something more than the hit or miss convection which has been dominating. 

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24 minutes ago, Rjay said:

And a bit over an inch came with that supercell in July if I recall correctly.  

This is the driest July 1st - August 25th period on record at ISP. 1966 had 2.91" by this day. FRG has only had 1.00" since July 1st.

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1 hour ago, CIK62 said:

Dallas flooding is 5th 1-in-1,000-year flood event in US since late July

Thursday, August 25, 2022 19:12 UTC
Wyatt Loy, AccuWeather staff writer

In the last five weeks, five areas across the United States have all experienced what should have been very unlikely -- if not impossible -- one in 1,000-year flooding events.

The most recent historic flooding event occurred in Dallas on Monday, Aug. 22, where 8 to 16 inches of rain fell over a 24-hour stretch. The heavy rain flooded buildings, submerged cars on interstates and also caused the Trinity River to swell well beyond its normal water line. All of this resulted in billions of dollars worth of damage, according to an AccuWeather estimate.

AccuWeather Founder and CEO Dr. Joel N. Myers, who has for decades closely studied the economic impacts of extreme weather, estimated that the total damage and economic loss resulting from the catastrophic flash flooding would range between $4.5 billion and $6 billion.

This flooding occurred after a 67-day dry streak in the city, and according to Allen Li, a researcher at the University of Oklahoma, this weather whiplash is not only more common due to climate change but could happen again, even multiple times over the next 1,000 years.

"One in 1,000 [years] doesn't mean that only happened once over 1,000 years," Li told AccuWeather National Reporter Bill Wadell. It only means there's a 0.1 percent chance of it happening every year.

>>>>>Remember in a large set of data, if the mean changes by a little, the extremes change by a lot.         Once in every 'N Years' means a 63% of the event happening at least once in the time frame specified, here 1,000 years.   >>>>>> CIK62

These were considered 1000 year events in our old climate. But they may actually be 10 to 100 year events in our warmer climate. So NOAA may be doing an update on the criteria soon. 
 

 

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Today was another hot day. Many locations from New York City to Philadelphia saw the temperature soar to 90° or above. The remainder of August will likely see generally above normal temperatures. Additional 90° or above days are possible in parts of the region.

The ECMWF seasonal forecast indicates that the summer will be warmer than normal throughout the region and across much of North America. Based on how the pattern has been evolving during the spring transition to summer, it is more likely than not that the warmest anomalies of the summer will likely occur in July and August with June being the coolest of the three months in the Northeast.

In addition, in the 6 past cases when the June AO averaged +0.750 or above (1950-2021), 67% of the following August and September cases featured above normal temperatures. The August ECMWF forecast shows a warmer than normal September in the Northeast. This warmth would be consistent with the ongoing warming that has been occurring in September.

On August 18, the SOI fell to -32.90. Since 1991, there were 8 cases when the SOI fell to -30 or below during the August 10-25 period. That outcome has often preceded a wetter than normal September in parts of the Northeast. Mean September rainfall figures for those 8 cases: Boston: 4.38" (normal: 3.55"); New York City: 5.08" (normal: 4.31"); and, Philadelphia: 5.12" (normal: 4.40"). Very wet years outnumbered very dry ones by a 2:1 ratio in Boston and 3:1 ratio in both New York City and Philadelphia. 63% of cases saw at least one day with 1" or more rainfall in Boston. 88% saw at least one day with 1" or more in New York City and Philadelphia. 50% of those cases saw at least one day with 2" or more daily rainfall in Philadelphia. In sum, the SOI may be offering a signal that there will be some drought relief for the northern Mid-Atlantic and southern New England regions in September.

The ENSO Region 1+2 anomaly was -0.8°C and the Region 3.4 anomaly was -1.2°C for the week centered around August 10. For the past six weeks, the ENSO Region 1+2 anomaly has averaged -0.83°C and the ENSO Region 3.4 anomaly has averaged -0.88°C. La Niña conditions will likely persist through the fall.

The SOI was -9.04 today.

The preliminary Arctic Oscillation (AO) was -0.728 today.

On August 23 the MJO was in Phase 2 at an amplitude of 1.586 (RMM). The August 22-adjusted amplitude was 1.229 (RMM).

Based on sensitivity analysis applied to the latest guidance, there is an implied near 100% probability that New York City will have a warmer than normal August (1991-2020 normal). August will likely finish with a mean temperature near 79.1° (3.0° above normal).

 

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Morning thoughts…

It will be partly  cloudy and very warm.  High temperatures will reach the upper 80s and lower 90s in most of the region. Likely high temperatures around the region include:

New York City (Central Park): 89°

Newark: 91°

Philadelphia: 92°

The remainder of August will likely see generally warmer than normal conditions.

Normals:

New York City: 30-Year: 82.1°; 15-Year: 81.9°

Newark: 30-Year: 83.5°; 15-Year: 83.4°

Philadelphia: 30-Year: 84.6°; 15-Year: 84.3°

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The last 6 days of August are averaging  83degs,(76/91) or +8.

Month to date is  79.2[+2.7].      August should end at  80.0[+3.9].

Reached 83 here yesterday.

Today:   82-88, wind w., p. cloudy, 74 tomorrow AM., slight chance of rain late.

75*(85%RH) here at 7am.      77* at 9pm.      80* at 10am.      82* at Noon.         80* at 2pm, sun shower.       84* at 4pm.       85* from 5pm-6pm with another sun shower.     Reached 87*,  6:30pm-7:30pm.

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75 / 68 and more humid.   More 90s for the area today and slight chance of pop up storms today.  Overall warm to hot at times through the end of the month.  Trough and cool down for a 2 day affair Sep 1 - 2.  Tropics remain active in some form or other on most guidance in the frist week of Sep.  The Gulf seems to be where things may be targting.

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