powderfreak
New member
I get asked this often so figured I'd share, plus a little extra fun stuff.
Its been a fun 24 hours of consistent light to moderate snow which this
pattern seemed to be ripe for. Another one on Wednesday night possibly into Friday and accums should be higher than this last snowfall.
>how well does the yellow and orange bands on the radar translate into
>snowfall? i'm seeing bands around bolton and mansfield that are showing a
>solid color (indicative of snow)
>
>how much of this actually makes it to the ground???
This is the general rule of thumb for BTV's radar (not other New England
one's, as BTV's radar is the closest to a 4,000ft wall than any other
radar):
Base Reflectivity only works for the Champlain Valley and down the Bolton
Flats/I-89 corridor but for only so long. If you select the Composite
Reflectivity, 90% of the time in my experience that accurately shows what
is going on in the Green Mountains and snowfall usually lines up with it.
This was most noticable last March when we had several upslope heavy snow
events along the Green Mountain Spine.
9pm is a perfect example of the differences:
Composite: http://tinyurl.com/tm3ek
Base: http://tinyurl.com/uawjt
If you look at it closely, the max returns right on I-89 (lowest elevation
in there) is between 25-30dbz which depending on fluff factor can be
anywhere from a coating to .75" per hour. My guess is the I-89 corridor
right now is getting a dusting to a quarter of an inch per hour because
the coverage of those 25+dbz is very low and no one area would see them
for more than 10 minutes at a time. Meanwhile, the composite radar shows
30-35dbz over the I-89 corridor which is only one level higher than the
base.
BUT, what it does show is even more interesting...this snowfall is likely
being produced not that far off the deck and we are seeing quite
fascinating NW to SE convergence zones setting up in applicable areas.
Moisture is getting forced through the gap between Camels Hump and the
higher terrain north of Bolton...even more interesting is the convergence
occuring over Smugglers Notch/RT108. You can see RT 108 on the map there
just to the east of Morrisville...and my bet is the highest elevation
through the notch on RT 108 is seeing some light to moderate snow, along
with adjacent mountain terrain...but very quickly as you move away from
the notch it is likely only flurries. For Stowe skiers, this is what
often causes enhanced snowfall over past Chin Clip, or over between the
Long Trail and Hellbrook. Not sure what happens at Smuggs but my bet is
its the reason why the backbowls are often talked about as being
especially deep. Also not sure where App Gap is but could be those
returns just north of Bristol south of I-89.
Very interesting meso-scale radar picture right there with snowfall
localized and focused on NW-SE mtn passes.
Composite radar shows the heaviest returns of any area from all of its
scans at different angles. During the winter, it works pretty well
because snow producing clouds are significantly lower than they are vs.
summer-time convective thunderstorms. So a Base Scan (.5 degrees tilt I
think) doesn't make it over the mountains or even hills surrounding the
airport, overall, it is pretty useless because the one area it can scan
(Burlington, South Burlington, Williston, etc) is too close to the radar
giving it the broken up look, though it can help up to St. Albans and down
to Rutland County.
General Rule of Thumb is...30-35dbz on base reflectivity is roughly 1"/hr
in the valleys. Now, for 1" to fall, you need to be under those for an
hour or at least 3/4ths of an hour if the snow is fluffy. Those same
returns on the composite show 1"/hr or greater along the Green Mountain
spine.
Last night at 130am the composite looked like this for 2-3 hours,
producing the 2-5" that Stowe reported and the 3-6" at Jay. Jay got
caught up in the front as it sagged southward and was in a better
developed band but in this imaged you can see the orographic effect kick
in as likely the leading boundary of cold air was forced up as it hit the
mountains. Then when the deeper cold air moved through there was an
additional burst of snow which is the band that ran from Jay Peak into
Essex County, NY.
1:30am: http://tinyurl.com/y46f6o
2:20am: http://tinyurl.com/y6jqy3
Front stalling along the Green Mountains at 2am, must've been snowing
pretty good above 2,000ft from Camels Hump to Mansfield. 1hr estimated
precip totals support that with .1" or greater along the west slopes in
that area; assuming a 10 to 1 ratio, between 1:30-2:30am: 1"-1.5"
http://tinyurl.com/y4lvo7
Then this afternoon at 3pm, still chugging along.
http://tinyurl.com/y5lpw4
Then at 7pm the focus looked to be on Bolton Valley Ski Area.
http://tinyurl.com/y6p8zu
Here are a few pics from downtown Burlington last night between that 1:30-
2:30am time frame:
http://tinyurl.com/y5msn9
http://tinyurl.com/y48fxs
http://tinyurl.com/vtzzo
http://tinyurl.com/t8xul
http://tinyurl.com/y8kh82
http://tinyurl.com/yy3gpa
http://tinyurl.com/y5hd5f
-Scott
Its been a fun 24 hours of consistent light to moderate snow which this
pattern seemed to be ripe for. Another one on Wednesday night possibly into Friday and accums should be higher than this last snowfall.
>how well does the yellow and orange bands on the radar translate into
>snowfall? i'm seeing bands around bolton and mansfield that are showing a
>solid color (indicative of snow)
>
>how much of this actually makes it to the ground???
This is the general rule of thumb for BTV's radar (not other New England
one's, as BTV's radar is the closest to a 4,000ft wall than any other
radar):
Base Reflectivity only works for the Champlain Valley and down the Bolton
Flats/I-89 corridor but for only so long. If you select the Composite
Reflectivity, 90% of the time in my experience that accurately shows what
is going on in the Green Mountains and snowfall usually lines up with it.
This was most noticable last March when we had several upslope heavy snow
events along the Green Mountain Spine.
9pm is a perfect example of the differences:
Composite: http://tinyurl.com/tm3ek
Base: http://tinyurl.com/uawjt
If you look at it closely, the max returns right on I-89 (lowest elevation
in there) is between 25-30dbz which depending on fluff factor can be
anywhere from a coating to .75" per hour. My guess is the I-89 corridor
right now is getting a dusting to a quarter of an inch per hour because
the coverage of those 25+dbz is very low and no one area would see them
for more than 10 minutes at a time. Meanwhile, the composite radar shows
30-35dbz over the I-89 corridor which is only one level higher than the
base.
BUT, what it does show is even more interesting...this snowfall is likely
being produced not that far off the deck and we are seeing quite
fascinating NW to SE convergence zones setting up in applicable areas.
Moisture is getting forced through the gap between Camels Hump and the
higher terrain north of Bolton...even more interesting is the convergence
occuring over Smugglers Notch/RT108. You can see RT 108 on the map there
just to the east of Morrisville...and my bet is the highest elevation
through the notch on RT 108 is seeing some light to moderate snow, along
with adjacent mountain terrain...but very quickly as you move away from
the notch it is likely only flurries. For Stowe skiers, this is what
often causes enhanced snowfall over past Chin Clip, or over between the
Long Trail and Hellbrook. Not sure what happens at Smuggs but my bet is
its the reason why the backbowls are often talked about as being
especially deep. Also not sure where App Gap is but could be those
returns just north of Bristol south of I-89.
Very interesting meso-scale radar picture right there with snowfall
localized and focused on NW-SE mtn passes.
Composite radar shows the heaviest returns of any area from all of its
scans at different angles. During the winter, it works pretty well
because snow producing clouds are significantly lower than they are vs.
summer-time convective thunderstorms. So a Base Scan (.5 degrees tilt I
think) doesn't make it over the mountains or even hills surrounding the
airport, overall, it is pretty useless because the one area it can scan
(Burlington, South Burlington, Williston, etc) is too close to the radar
giving it the broken up look, though it can help up to St. Albans and down
to Rutland County.
General Rule of Thumb is...30-35dbz on base reflectivity is roughly 1"/hr
in the valleys. Now, for 1" to fall, you need to be under those for an
hour or at least 3/4ths of an hour if the snow is fluffy. Those same
returns on the composite show 1"/hr or greater along the Green Mountain
spine.
Last night at 130am the composite looked like this for 2-3 hours,
producing the 2-5" that Stowe reported and the 3-6" at Jay. Jay got
caught up in the front as it sagged southward and was in a better
developed band but in this imaged you can see the orographic effect kick
in as likely the leading boundary of cold air was forced up as it hit the
mountains. Then when the deeper cold air moved through there was an
additional burst of snow which is the band that ran from Jay Peak into
Essex County, NY.
1:30am: http://tinyurl.com/y46f6o
2:20am: http://tinyurl.com/y6jqy3
Front stalling along the Green Mountains at 2am, must've been snowing
pretty good above 2,000ft from Camels Hump to Mansfield. 1hr estimated
precip totals support that with .1" or greater along the west slopes in
that area; assuming a 10 to 1 ratio, between 1:30-2:30am: 1"-1.5"
http://tinyurl.com/y4lvo7
Then this afternoon at 3pm, still chugging along.
http://tinyurl.com/y5lpw4
Then at 7pm the focus looked to be on Bolton Valley Ski Area.
http://tinyurl.com/y6p8zu
Here are a few pics from downtown Burlington last night between that 1:30-
2:30am time frame:
http://tinyurl.com/y5msn9
http://tinyurl.com/y48fxs
http://tinyurl.com/vtzzo
http://tinyurl.com/t8xul
http://tinyurl.com/y8kh82
http://tinyurl.com/yy3gpa
http://tinyurl.com/y5hd5f
-Scott
