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Weather Question from a viewer:

16 Dec 2009, 2:14 pm

Hello and happy Wednesday everyone, hope you are having a good week. I wanted to share a weather question with everyone that I got from a viewer/emailer:

> Message: I am curious to know if there is a particular
> radar (link) out
> there that picks up snow (light vs heavy). Each time I view
> any radar I have a
> hard time detecting if the snow is even falling, or if it
> is light or heavy.
> Thanks

Of course, I couldn’t just make it a quick response, so here’s what I wrote – Enjoy:

>>>>

yes, it can be difficult to determine snow intensity by radar. The simple fact is that radar reflectivity is A LOT lower in a snow vs. rain.

i.e. in a heavy rain event, you’ll see oranges and reds vs. in a snow event you’ll see light blues/greens/sometimes yellow.

Why does this happen?? Analogy for you. Pretend a flashlight is the radar beam and shine that light at a basketball (raindrop) and a whiffleball (snowflake). The amount of light captured by those different “items” differs greatly. (imagine the basketball and the whiffleball were made of mirror and reflected the light back to the flashlight) When the radar receives it’s “pulse” (signal) from the those items, the basketball would reflect all of the light back and the whiffleball would only reflect SOME of the light, the other percentage would go through the whiffleball.

OK – now that we’ve got that covered… raindrop vs. snowflake – now you know why it’s harder to pick out heavy snow on a radar. Unfortunately, radar available to the public isn’t as high resolution as we’d like it to be. Also, many free online sites don’t have “Winter Masks” to show snow vs. rain and the ones that do are very course.

This is what I do:

Go to the NWS Radar here:
http://nws.noaa.gov/radar_tab.php

Click on a specific location you are looking for – I’ll do the radar out of western NY by the Lake Effect Snow today:
http://radar.weather.gov/radar.php?product=NCR&rid=TYX&loop=yes

You can loop this image by clicking the “Loop” link on the left under “Reflectivity“. Composite Loop is the radar slices combined as a whole and Base Loop is the lowest tilt of the radar, useful for tornadic signatures on velocity mode.

**LIGHT snow** will show up at a light blue color or light green color. (up to 25dbz)
**MODERATE snow** will show up as a darker green color. (30dbz)
**HEAVY snow** will show up as a yellow color, but that is quite rare. (35dbz or perhaps 40dbz.

Basing snow intensity by radar is tough. Snow intensity is actually based on visibility, so if you can tell what the visibility is, then you’re good to go:

**LIGHT snow** visibility is greater than 1/2 mile
**MODERATE snow** visibility is 1/2 mile or less, but greater than 1/4 mile
**HEAVY snow** visibility is 1/4 or less

Other Radar sites:
COD Weather: http://weather.cod.edu/analysis/satrad.regional.html
COD Weather 1KM: http://weather.cod.edu/analysis/analysis.radar.html

There a wonderful HIGH RESOLUTION radar available if you are willing to pay for it ($250 for an individual license) – we use it here at WeatherNation – it’s called GR2 Analyst. Great for tornadic storms, but you can download “Winter Masks” to get better resolution of heavy snow vs. light snow. See here: http://www.grlevelx.com/gr2analyst/

Sorry for the long-winded response, but I hope that helps!

Cheers,
Meteorologist Todd Nelson – WeatherNation LLC

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