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Posted at 2:15 PM ET, 11/29/2010

Introducing the Snow Potential Index

By Jason Samenow

We know a lot of Capital Weather Gang readers are snow lovers, so starting tomorrow (November 30) and continuing into March, we'll publish a daily index of the snow potential over the next seven days. For brevity, we'll refer to it as the SPI.

The index will be on a scale from 0-10, much like our daily digit. A 10 would indicate a virtual certainty of accumulating snow in the next seven days and a 0 would indicate essentially no chance of accumulating snow. If there's potential for four or more inches of snow, we'll add a "+" to the SPI number and "++" for the potential for more than eight inches.

We'll also include the trend from the previous day, so if the potential increases, we'll include an up arrow, and if the potential decreases, a down arrow. The text "no change" conveys the same SPI value from the previous day.

The SPI will be accompanied by a line of commentary but will not go into the same level of detail as the Snow Lover's Crystal Ball.

Here's a sample SPI for November 29 (with the up arrow indicating the increase in likelihood relative to yesterday):

Snow Potential Index: 2 (↑) - Watching the slight chance of a little snow Sunday from a weak disturbance.

The SPI is a daily assessment of snow potential for the next week on a 0-10 scale. Get the 'SPI' on Twitter

The SPI will be published in the morning forecast post as well as on Twitter (@capitalweather) and Facebook the night before the forecast post is published - so be sure to follow us there...

By Jason Samenow  | November 29, 2010; 2:15 PM ET
Categories:  Capital Weather Gang, Latest  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: A look into early December: cold likely
Next: PM Update: Clouds increase tonight, not as cold


Great idea - thanks for adding it!

Posted by: josh28 | November 29, 2010 2:25 PM | Report abuse

I presume if there is more than one chance of snow during the 7-day period each will receive a separate value of the index: rather than a single value of the index representative the chances anytime during the 7 days.

The up/down arrow is great, since we want to see if the odds are increasing/decreasing as the event gets closer from one day to the next.

Posted by: SteveT-CapitalWeatherGang | November 29, 2010 2:49 PM | Report abuse

Awesome, I like it! Hopefully it won't bee too long before it gets to 10. :D

Posted by: oriolesfan2323 | November 29, 2010 2:57 PM | Report abuse

Great idea; thinking in terms of Walter's sculpting, a scallop means = inch, a snow shark = 10 inches or more and a great white whale = 20-plus inches?

Sunday, however, sounds more like planketon.

Posted by: JerryFloyd1 | November 29, 2010 3:17 PM | Report abuse

Love this...thank you for continuing to push for excellence.

Posted by: parksndc | November 29, 2010 3:35 PM | Report abuse

Thanks for the feedback (both now and when we first discussed this last year!). I think we would give more than one SPI if there was more than one threat. I added some language to the post to this effect. (edited comment at 18:30 p.m.)

Posted by: Jason-CapitalWeatherGang | November 29, 2010 3:38 PM | Report abuse

i like it too! here's hoping we see lots of 10++s...

thanks for the "shout out". i have no ideas yet for this year's menagerie... we'll see when the snow hits the ground.

Posted by: walter-in-fallschurch | November 29, 2010 4:03 PM | Report abuse

regarding the "+" signs. can we assume each + represents another 4"? so, before last year's storms we might have seen SPIs like 10+++++?

Posted by: walter-in-fallschurch | November 29, 2010 4:43 PM | Report abuse


I don't think we're going to do more than two pluses-- but yes, if we did 4" per plus, woulda needed a lot of characters last year :)

Posted by: Jason-CapitalWeatherGang | November 29, 2010 6:26 PM | Report abuse

Aren't you guys worried that 7, 6, and 5 day forecasts are often unreliable?

I'm concerned this is a form of pandering.

(But of course I'll be reading it!)

Posted by: jaybird926 | November 29, 2010 7:02 PM | Report abuse


The objective of the index is to give folks a general sense. The SPI in days 5-7 will be tend to be low except under highly unusual circumstances.

Posted by: Jason-CapitalWeatherGang | November 29, 2010 8:14 PM | Report abuse

Here's hoping the S.P.I. DOES NOT replace the Snow Lover's Crystal Ball.

Posted by: Bombo47jea | November 30, 2010 12:15 AM | Report abuse

I'm with bombo, this isn't replacing the snow lovers crystal ball right?

Posted by: paul-Sterling | November 30, 2010 7:50 AM | Report abuse

I'm with bombo, this isn't replacing the snow lovers crystal ball right?

Posted by: paul-Sterling | November 30, 2010 7:51 AM | Report abuse

Sorry about the double post, timed out and I hit submit again, I guess it went through tho

Posted by: paul-Sterling | November 30, 2010 7:52 AM | Report abuse

Folks- the post above says that this index will not go into the detail of the that means we're still doing the SLCB.

Posted by: Jason-CapitalWeatherGang | November 30, 2010 8:40 AM | Report abuse

We have GOT to name our snow events. I know they do it for every Low in Europe, but Im liking how we'll always remember which one was Snowpocalypse, Snowmageddon and Snoverkill. I really think we could start something here...and for us weather geeks, give us something to put our hat on, "historically" speaking...thoughts?

Posted by: DullesARC | November 30, 2010 11:09 AM | Report abuse

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