Harvey Rain / Snow Comparison

Hurricane Harvey has produced incredible amounts of rain in Texas and Louisiana and other parts of the southwest. Particularly, parts of Houston have experienced incredible flooding. For those looking for local organizations to support, the New York Times has provided links to several local nonprofits serving this region. See Christina Caron, Where to Donate to Harvey Victims (and How to Avoid Scams) (New York Times, Aug. 28, 2017), available at www.nytimes.com/2017/08/28/us/donate-harvey-charities-scams.html (last visited Aug. 30, 2017).

Matthew Cappucci wrote an interesting article to help illustrate the sheer volume of water that had fallen across Houston and Southeast Texas at the time, 9 trillion gallons (now 14 trillion gallons). See Matthew Cappucci, Texas flood disaster: Harvey has unloaded 9 trillion gallons of water (Washington Post, Aug. 27, 2017), available at www.washingtonpost.com/news/capital-weather-gang/wp/2017/08/27/texas-flood-disaster-harvey-has-unloaded-9-trillion-tons-of-water (last visited Aug. 30, 2017). One of the examples he gave to put a finer point on the perspective was this: "If we averaged this amount of water spread equally over the lower 48 states, that’s the equivalent of about 0.17 inches of rain — roughly the height of three pennies stacked atop each other — occupying every square inch of the contiguous United States. Imagine one downpour large enough to cover the entire country!" Id.

Here in Delaware and on the east coast, snow is more common than flooding (and fortunately we have not had too many instances of blizzards dropping 3' or 4' of snow over the past couple of years, although parts of New York and Boston have certainly had incredible snowfalls over the past few winters). So how much snow would 48" (4 feet) of rain be?

Generally speaking and under ideal snow conditions, 1 inch of rain is approximately 13 inches of snow. See National Severe Storms Laboratory, Frequently Asked Questions About Winter Weather, available at www.nssl.noaa.gov/education/svrwx101/winter/faq (last visited Aug. 30, 2017). As a straight conversion, if 1 inch of rain is 13 inches, then 48 inches of rain would be 624 inches, or 52 feet of snow. To illustrate the size of Houston (627 square miles) compared to Delaware (2491 square miles), this would be a lot of snow covering about half the state, including New Castle County and half of Kent County from Dover north. 

So we tweeted about this using the same graphic above along with a text box that effectively illustrated the point - 48" inches of rain in Houston would be the same as roughly 52 feet of snow covering this part of Delaware. 

As was pointed out (thank you to Matthew Cappucci), it is scientifically impossible to have this much snow, a principal called the Clausius–Clapeyron relationship, which a google search can explain far better and in far more depth than is necessary here. 

Adopting this analogy to make it more realistic, we can spread this snowfall out over a wider area. So 52 feet of snow over a 627 square mile area is the same as spreading 26 feet of snow over a 1,254 square mile area. It would be the same as spreading 13 feet of snow over a 2,508 square mile area, which put another way, 48" inches of rain would be like having 13 feet of snow fall over the entirety of the state of Delaware (2,491 square miles). 

Spread out even further (and somewhat more realistically), 48" rain in Houston (627 square miles), or 52 feet of snow over 627 square miles would be approximately equal to 6" snow over 65,000 square miles (65,208 to be exact). Put another way, 48" rain would be roughly the same as 6" of snow covering slightly less than the entirety of Pennsylvania, Maryland, Delaware, and New Jersey (roughly 69,000 square miles). 

The more visual way to understand the amount of rain that has fallen and impacted Houston and Southeastern Texas and parts of Louisiana is with snow in feet though. Since we have had snowstorms and blizzards more than once over the past few years that have dumped as much as 2-3 feet of snow in as many days (e.g., Feb. 2010 - back to back storms dumping more than 30" of snow across all three counties, Jan. 2016 - 1-2' throughout the state and more north, March 2017 - a foot or so here but far worse north of Delaware), people on the east coast (or us anyway), recognize and can appreciate how much 1 or 2 feet (or 3 feet of snow) is and how much inconvenience that causes, even if only for a few days. The flood and water will impact that part of our country for far longer. (See reference to local organizations that can help above).

To close out the point with three final illustrations:

48" rain in Houston is roughly the same as 52' snow over 627 square miles is roughly the same as 1' snow over 32,604 square miles (roughly illustrated on the map here).

Imagine a foot of snow covering this area (approximately 32,600 square miles)

Imagine a foot of snow covering this area (approximately 32,600 square miles)

48" rain in Houston is roughly the same as 52' snow over 627 square miles is roughly the same as 3' snow over 10,868 square miles, or about the same areas as the states of Delaware and New Jersey (11,220 square miles).

48" of rain in Houston or 52' of snow over 627 square miles would be approximately the same as 2 feet of snow over an area of 16,302 square miles, approximately the same area as the States of Delaware and Maryland plus Philadelphia, Chester, and Delaware Counties in Pennsylvania. 

The map below (covering Delmarva and a good chunk of Maryland, New Jersey, and parts of southeastern Pennsylvania) also covers about 16,300 square miles and hopefully helps show the point.

A #harvey #perspective - if 1" rain ≈ 13" snow→48" rain in #Houston ≈ 52' snow over 627 sqmi ≈ 2' snow over 16k sqmi.

A #harvey #perspective - if 1" rain ≈ 13" snow→48" rain in #Houston ≈ 52' snow over 627 sqmi ≈ 2' snow over 16k sqmi.

That is a lot of snow! And Houston (and many other surrounding areas) have had a lot of rain and related flooding issues the likes of which they have never seen. Please consider helping by donating directly to one of the local organizations referenced in the New York Times article here and which we have also linked to our on Facebook page here.