Virginia Deluge Was an “Off the Charts Above a 1000-year Rainfall,” Says National Weather Service

JR:  The disinformers like to say the extreme weather we are seeing today is nothing unusual.  They don’t live in Texas, where “No One on the Face of This Earth has Ever Fought Fires in These Extreme Conditions.” Or my hometown area around the Catskill Mountains, where Hurricane Irene was “the most devastating weather event ever to hit the region.”  Or around Binghamton, NY, where “An Extreme Rainfall Event Unprecedented in Recorded History Has Hit.”

Rainfall rates observed in southern Fairfax county around 6:00 p.m. on September 8. Some places saw rates between 3 and 4” per hour.

Capital Weather Gang Chief Meteorologist Jason Samenow has the details on one more record-exploding extreme event in this repost.

On Thursday, September 8, Ft. Belvoir received an astounding 7.03” of rain in three hours. According to the National Weather Service (NWS), that amount of rain in that amount of time was an “off the charts above a 1000-year rainfall (based on precip frequency from Quantico).”

Chris Strong, warning coordination meteorologist for the NWS in Sterling, emailed media a note on the frequency of rain return from last week’s event, for locations in Maryland and Virginia. It’s extraordinarily impressive and reproduced in full below…

National Weather Service note:

For our DC and Baltimore media colleagues…Some interesting stats that our hydrologist Jason Elliott passed on to us that you may find useful in your broadcasts/bloggings. Based on precipitation frequency computations, for last week’s rainfall:

Maryland (Wednesday)

* The Bowie IFLOWS gauge recorded 4.57 inches in 3 hours, which is about a 200-year rainfall (based on precip frequency from Glenn Dale).

* For Upper Marlboro and near Ellicott City, Wednesday’s rains were a roughly one in 50-100 year event.

* For Westview (near I-70 and the Baltimore Beltway), Wednesday’s rains were a roughly one in 10-25 year event.

Virginia (Thursday)

* The Kingstowne IFLOWS gauge (near Franconia) in Fairfax County recorded 5.47 inches in 3 hours, which is approximately a 500-year rainfall for that timeframe (based on precip frequency from Vienna & Clarendon).

* The Reston IFLOWS gauge in Fairfax County recorded 6.57 inches in 6 hours, which is also approximately a 500-year rainfall (based on precip frequency from Dulles).

* The Fort Belvoir AWOS (KDAA) reported 7.03 inches in 3 hours, which is off the charts above a 1000-year rainfall (based on precip frequency from Quantico).

For a wide swath in the heavy rain axis thru the DC and Baltimore metro areas, rainfall was at least a one in 10-25 year event.

Of course return period doesn’t mean that we won’t see that kind of rain in those locations for several decades (or centuries). A 1 in 100 year rain means that there is a 1% chance of seeing that amount of rain in any given year. A 0.1% chance is true for a 1 in 1000 year event.

Chris Strong
NWS Baltimore/Washington

Causes of the excessive rainfall event?

Last week, I wrote a piece on how different streams of moisture set up to converge over the D.C. region (as well as locations to the north). Not to be left out of the discussion is the potential effect of climate change, which is very likely already enhancing heavy rain events. As Andrew Freedman wrote earlier this year:

The physical mechanism behind the link between warming global average land and ocean temperatures and more frequent heavy precipitation events is rather simple to understand – as air warms, it can hold more water vapor, which means that more water can then be squeezed out of the atmosphere as liquid or frozen precipitation.

While this event cannot be blamed on climate change, warming probably gives existing rain events some added intensity and will most likely increase the frequency of very heavy rain episodes into the future.

— Jason Samenow

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31 Responses to Virginia Deluge Was an “Off the Charts Above a 1000-year Rainfall,” Says National Weather Service

  1. The common phrasing “this event cannot be blamed on climate change” makes it sound like either climate change was the main cause or not involved at all.

    The reality is that climate change is a constant contributing factor in most weather events now. The question is how big a role it played.

    Better phrasing might be “it is hard to tease out exactly how much climate change contributed to this specific event, however this is the kind of extreme precipitation event predicted to occur more often by climate science.”

  2. Interesting Times says:

    Agreed. Otherwise you just given deniers more cherry-pick material.

    Also, I believe James Hansen has said that we wouldn’t be seeing such extreme weather events if CO2 levels were still at the pre-industrial 250ppm or so.

  3. Dennis says:

    Even better: “This is the kind of extreme precipitation event predicted to occur more often because our CO2 emissions are warming up the atmosphere.”

  4. Lewis Cleverdon says:

    Barry – I’d agree the phrasing is poor to lousy, in that it’s potentially misleading.

    A better alternative would be:

    “While no single extreme weather event can be attributed solely to climate destabilization,
    we are now seeing exactly the increase of extreme weather events that science has long predicted as the outcome of continued greenhouse gas pollution.
    And, by the way, the warming powering the present extreme weather impacts is the time-lagged outcome of the greenhouse gas pollution of the 1970s.”

    If scientists don’t tell it like it is, who will ?



  5. Colorado Bob says:

    The meteorological department says average rainfall across Sindh is three times normal, with the worst-affected districts of Badin, Mirpurkhas and Thar seeing eight times the usual levels.

    Chief meteorologist Mohammad Riaz told AFP the figures were a 51-year record, and the rains would continue for the rest of the week.

  6. Colorado Bob says:

    Government officials say at least 5.3 million people and 1.2 million homes have been affected, with 1.7 million acres of arable land inundated.

  7. Daron says:

    I think its important to be more clear. Just say “We have changed the world climate system by our actions, all weather events happening today are impacted by our actions.” Just keep hammering in something like that over and over again in public statements. You need short, easy to understand statements to get through on the media these days.

  8. Paul magnus says:

    While … There is currently no proof that…. no single extreme weather event can be attributed solely to climate destabilization

  9. Merrelyn Emery says:

    You may have only 10-15 seconds on TV so it is critical to make it snappy and strategic, e.g. “extreme events – as predicted by climate scientists” and just keep on repeating the “as predicted”.

    This makes the link between the disasters and the science which is necessary to penetrate the layers of denial and disbelief, ME

  10. MemphisBill says:

    I think “evidence” is a better word then “proof” in this context. “Evidence” is for science, “proof” is for math.

  11. Pangolin says:

    How about….. a small shift in average temperatures or rainfall can result in much more frequent occurrences of extreme heat events and/or extreme precipitation events. The new “normal” effected by observed Climate Change will have many more of these events than we have seen in the past.

    Stealing shamelessly from:

  12. David B. Benson says:

    Keep it short and snappy for the Twitter generation.

  13. Lewis Cleverdon says:

    Something more like:

    “Burn the planet – and we’re all toast –
    Piss on it – and we drown !”

    Vague enough ???



  14. The wording may not be the best, and I wrote it in haste, but I always try to make a clear distinction between the causal factors for extreme weather events and enhancing factors. Whereas greenhouse warming is a key enhancer or intensifier of extreme weather events like heat waves and heavy precip, it’s a very big stretch to list it prominently as a causal factor. Might greenhouse warming alter the atmospheric circulation in some modest ways to be a causal factor? Sure. But that’s very poorly understood and almost certainly a very minor player compared to the prevailing jet stream patterns, internal modes of climate variability, etc. I want to be clear that the enhancement from greenhouse warming is important, but you actually provide ammunition for the disinformers when say greenhouse warming “causes”, “results in”, “drives” because it’s kind of easy to shoot down. Better to say, IMO, climate warming “enhances”, “intensifies”, “loads the dice”, “stacks the deck”, “changes/increases the frequency”, etc.

  15. David B. Benson says:

    Well, maybe one needs to avoid utterances such as “lack of statistical stationarity makes even probabilistic predictions unreliable, but based on the Clausius–Clapeyron equation…”

  16. Wyoming says:

    A farmer friend of mine in Westmoreland County (2 hours south of DC and 1 hour east of Fredricksburg) recieved 10 inches of rain from the remenants of tropical storm Lee and a neighbor of his recieved 20 inches. The pictures of the damage to the fields were astonishing. Their totals from Irene and Lee were 16 inches and 30 inches respectively. Huge amounts of top soil were washed into the river.

  17. Merrelyn Emery says:

    Using the terminology of the ‘new normal’ is a serious strategic mistake which can only encourage acceptance which is far from the very active collective effort we now need.

    We need to be emphasizing just how ABnormal this is and exactly what it presages for all of us, ME

  18. Lewis Cleverdon says:

    Agreed !

  19. David B. Benson says:


    Many more people need to know such vivid reminders.

  20. Robert In New Orleans says:

    Is there a physical limit as to the amount of rain that can fall in a given time span?

  21. David B. Benson says:

    Good question and yes, there is a limit.

    But rather than attempt an aproximate answer, I’ll just relate BBC news items I recall from the devastating rains in Pakistan in the summer of 2010: in the Swat valley it rained at least 12 feet in 12 days. It rained so hard, at least at intervals, that two men standing out in the rain talking to one another could not see each other.

    Pakistan has not yet fully recovered; there were two intresting articles about Pakistan in a fairly recent issue of The Nation.

  22. Colorado Bob says:

    A maximum 140mm of rain till 5pm on Tuesday was recorded at the Meteorological Department’s observatory at the PAF Base Faisal while this measurement was followed by 131mm of rain recorded since Monday at PAF Base Masroor.

    In Saddar, 114mm of rain was recorded, 111mm of rain was recorded in Nazimabad, 108mm in North Karachi, 108mm on University Road, 100mm in Landhi, and 89mm rain in North Karachi. On Tuesday alone, the Karachi Airport received 40mm of rain while the old area of the airport received 47.5mm of rain.

  23. Lewis Cleverdon says:

    Jason – thanks for responding to comments above.

    It’s not quite clear what your perception of the influence of global warming on extreme weather events may be. I take it we’d agree that there is no container from which ‘natural’ weather is released, of which only a fraction gets affected by AGW –

    The reality is therefore that to some extent all weather reflects both the increased planetary temperatures that AGW has achieved, and the raised atmospheric moisture capacity that allows, as well as a host of other influential marine, terrestrial and atmospheric changes. The Lorenz thesis of outcomes’ ‘sensitivity to initial conditions’ is clearly of central relevance here.

    With the rate of extreme weather disasters having tripled – according to that most scrupulous of commercial authorities, Munich Re, – it follows that if AGW has not empowered that increase, some other phenomena have.

    So, short of proposing some new driver of the increase of those extreme events, perhaps we might agree that AGW has, via a host of linkages, now begun to drive climate destabilization, of which the increasing frequency of increasingly extreme weather events are but the symptoms ?



  24. Lewis Cleverdon says:

    Topping that event was Hurricane Mitch, that delivered about 12ft in a week to parts of Honduras and Nicaragua – which, according to the BBC & the Independent, caused some of the ordinary country rivers to rise by 120 feet. Again, as in the Swat valley too, huge amounts of the fertile valleys’ topsoil was lost, along with countless casualties.

    Apparently Clinton remarked that this was a ‘10,000-year’ event, though I don’t know if his source for that view was Robert Watson or someone else.



  25. Raul m. says:

    Game over as a phrase might refer to what happens when a rental agent tries to rent a place that has been destroyed by weather in a day to someone who has to go to work the next day and is looking for a place that is nice. The rental agent may not have the opportunity to have the place ready and the viewer may not be interested in “whatever”. So, from a rental arrangement it
    Might be said to be game over.

  26. Joan Savage says:

    I hope the NRCS comes up with updated information on topsoil loss. Soil fertility was declining due to conventional farming practices, even before extreme weather led to more wind-blown soil, burn-off, or runoff.
    One of the outcomes of the 2010 Pakistan megaflood was damage to acreage that was over-topped with less-fertile flood mud, and it would be useful to know how many acres in the US lost fertility to mud.

  27. Joan Savage says:

    Premptive note – I’m not assuming your farmer friend in Wyoming County used conventional farming practices. Ten to twenty inches of rain can obviously overwhelm even the most diligent efforts of a farmer to improve the soil.

  28. Raul m. says:

    Prevention of flood damages may be as simple as adding a glass door that has magnetic stripping at edges and a metal striping around the door frame to the outside of a doorway. The water pressure of low level flooding would press the glass door even tighter to the framing and keep water intrusion outside of the building. Just a thought.

  29. Wyoming says:


    I farm organically, but both of the farms I was speaking of are “conventional”. But in the case of these off the chart storms it really makes little difference what farmong methods you are using. Westmoreland County is mostly very flat ground. But if you get 20 inches of water on saturated ground fast nothing is going to help you. I saw pictures of flat fields which were cut with fresh gullies 4 feet deep and as wide as roads. There is no extra dirt to fix this kind of damage.

    Some of the folks I know that have friends or relatives farming in upstate NY and Vermont have stories that make mine seem tame. One was telling me today that her brother said that water during Irene coming down a nearby creek went over the deck of the highway bridge near his place. The kicker is the bridge deck is 50 FEET above the creek!

  30. David B. Benson says:

    Thanks. I’ll try to keep Hurricane Mitch in mind.

  31. Lewis Cleverdon says:

    It’s worth avoiding the double negative – so if we go further than introducing ‘solely’ and ‘climate destabilization’ perhaps a better statement would be:

    “While we cannot yet attribute an extreme weather event solely to climate destabilization . . .”

    But the third new component does seem likely to strain the listener’s capacity to assimilate new info from a single sentence.