[wxqc] Measuring Snow
Dave Helms
dshelms at comcast.net
Wed Jan 4 23:44:17 EST 2006
Hi Darren,
Pretty much, but swapping out a rain gauge will be expensive. I know of
one person who used a heated pipe wrap to warm up his gauge enough to
melt the snow in close to real-time. My Peet heated gauge has two
capacitors under the funnel along with the wired AC voltage to drive the
capacitors.
Dave
CW0351
Darren Echelmeier wrote:
> Dave,
> This is interesting advice, being fairly new to weather reporting I
> was wondering how the snowmelt effected reporting. I assume I should
> either cover my gauge during snow periods or buy a heater.
>
> Darren
> CW2314
>
> ----- Original Message -----
> *From:* dshelms at comcast.net <mailto:dshelms at comcast.net>
> *To:* Discussion of weather data quality issues
> <mailto:wxqc at lists.gladstonefamily.net> ;
> wxqc at lists.gladstonefamilynet <mailto:wxqc at lists.gladstonefamily.net>
> *Cc:* Neil Hunt <mailto:nhunt at tamarackmountain.com>
> *Sent:* Wednesday, January 04, 2006 7:54 AM
> *Subject:* Re: [wxqc] Measuring Snow
>
> Hi Neil,
>
> The potential cross-section of the tube is very large relative to
> the catch area of the Peet Pro gauge which may account for the
> overcatch. Maybe as snow fall diagnally (which is going to be the
> case at your elevation even with some tree wind blockage), the
> snow strikes the side of the tube, slides down the tube, and
> enters the Peet Pro gauge through the connection between the tube
> and the gauge.
>
> The other possibility is the Peet Pro gauge is hosed!
>
> I am not a big fan of measuring "melt out" precip. I see
> after-the-fact precip in Maryland from the unheated gauges days
> after the snow has fallen (why I advocate non-heated gauge owners
> to cover their gauges during winter precip situations). For
> climate and hydrologic applications, the amount and timing of
> precip is very important so a timing error of hours and days will
> cause problems which may be very difficult to identify once that
> are in the data record.
>
> I know your station's remote location and power constraints have
> pushed you towards you tube innovation (which is very creative
> solution); however, we should try to melt and measure within
> minutes of the actual snowfall whenever possible. Hopefully, the
> group will offer some suggestions to this technology challenge
> (this is in fact a big issue for all remote precip measurement
> observing systems).
>
> Dave
> CW0351
>
>
>
> -------------- Original message ----------------------
> From: "Neil Hunt" <nhunt at tamarackmountain.com
> <mailto:nhunt at tamarackmountain.com>>
> > Here's an interesting instrument design problem... My rain gauge is
> > modified to collect snow for passive solar melting, but now
> apparently
> > over-reads by 2-4 *times*. I'm looking for insight on my
> modification, or
> > advice on how to modify it to collect snow for melting, but not
> over-read
> > rainfall. Details below.
> >
> > I'm operating a remote solar powered weather station reporting
> via amateur
> > packet radio (KG6PPD-9), on top a 7200 foot peak about 15 miles
> west of the
> > Sierra crest. The station is based on the Peets U2100 with the
> pro rain
> > gauge (parabolic shaped collector with drip formation and
> counting). The
> > solar panels don't have sufficient power to heat the rain gauge,
> so I
> > modified it by adding a passive solar melting tube to the gauge:
> pictures
> > at:
> http://tamarackmountain.com/TamarackMountain/Weather/Pictures.html
> >
> > The solar melting tube is a piece of black plastic 3-inch drain
> pipe. The
> > Peets pro rain gauge has an 8-square-inch collection area (about
> 3.19 inch
> > radius). The inner diameter of 3-inch drain pipe is 3 inches,
> and the outer
> > diameter is about 3.3 inches. Some careful shaping yields a
> pipe with a
> > razor-edge with the same 3.19 inches diameter as the unmodified
> rain gauge
> > collector
> >
> (http://tamarackmountain.com/TamarackMountain/Weather/Images/DSC_7821.jpg).
> > Snow that collects in the pipe melts slowly when the sun comes
> out and the
> > drips are directed into the raingauge by means of a 3-inch to
> 2-inch reducer
> > fitting, and a 3-inch to 3-inch coupler makes a sleeve to
> prevent snowmelt
> > or rain from the outside of the collector from tricking into the
> collection
> > bucket:
> >
> (http://tamarackmountain.com/TamarackMountain/Weather/Images/SnowCollector.j
> > pg). The lip of the gauge is about 12 feet above the ground,
> currently
> > about 6 feet above the snow. The site is generally not windy -
> average
> > winds of 2-5 mph are common during major rain events. The
> design of my
> > collector was motivated by the CA dept of water resources
> sensors, which
> > appear to be a similar vertical tube, albeit of much larger
> diameter and
> > height.
> >
> > 3 Teaspoons of water slowly dripped from a small nozzle yields a
> measured
> > .11 or .12 inches of rain, as expected.
> >
> > However, in a large storm, the gauge routinely reads 2-4 *times*
> more rain
> > than nearby stations, often showing improbably high figures of 3
> or 4 inches
> > of rain in a day while my neighbors are reading 1.5 inches.
> It's possible
> > that the orography at the site really does extract a lot more
> water from the
> > atmosphere, or it is possible that the design of the snow
> collector somehow
> > funnels much more rain than the cross-section of the pipe might
> indicate.
> > Note that it isn't a case of measuring 1/100 cms instead of
> 1/100 inches,
> > since the 3-Teaspoon test comes out correct, and the multiplier
> between my
> > measurement and neighbor's varies quite significantly from one
> event to the
> > next.
> >
> > Unfortunately, the site is about 3.5 hours drive away from home,
> and right
> > now is about 30 minutes of snow-shoeing from the nearest vehicle
> access - so
> > access is strictly limited. But I was able to visit on one
> occasion while
> > it was raining hard, and during that 30 minutes or so, the
> 2/10ths collected
> > in a jar on the ground corresponded closely to the measurement
> from the
> > instrument.
> >
> > I made a temporary modification by adding a secondary collection
> vessel to
> > the instrument drain. Snowfall, freezing, and inability to
> access until the
> > collection vessel overflowed made this calibration effort
> useless, but a
> > side effect was that there was no path for wind to suck through
> the drip
> > counter (since the drip tube was underwater). The gauge still
> counted
> > significantly more rain than nearby stations.
> >
> > My station data can be viewed at
> > http://findu.com/cgi-bin/wxpage.cgi?call=KG6PPD-9&last=240
> <http://findu.com/cgi-bin/wxpage.cgi?call=KG6PPD-9&last=240> (or,
> if you are
> > patient, at
> http://tamarackmountain.com/TamarackMountain/Weather/Index.pl)
> > while the nearest neighbor is at
> > http://findu.com/cgi-bin/wxpage.cgi?call=CW4253&last=240
> <http://findu.com/cgi-bin/wxpage.cgi?call=CW4253&last=240>. Note
> that CW4253
> > is not solar powered, and accordingly was subject to an extended
> power
> > failure this past weekend. That rain gauge isn't heated
> either. We had a
> > major snow event (4-6 feet) over the weekend, which has barely
> started
> > melting through either of our gauges - judging from the
> readings. The
> > nearest CADWR sensor is about 5 miles East at
> > http://cdec.water.ca.gov/cgi-progs/plotReal?staid=BLD. This
> season I've
> > measured 54 inches plus probably about 5 more still to melt,
> while the CADWR
> > measurement is currently showing 34.4 - that's x2 for season total.
> > However, on Dec 21, 22, 23, I measured a fantastic 9 inches,
> while BLD shows
> > only 3.22 inches - which is x8!
> >
> > Question: Can anyone share details of modification of rain
> gauges to collect
> > snow for passive melting?
> >
> > Question: Is this vertical tube design likely to somehow trap
> 2-4x as much
> > rainfall as the same cross-section of rain-gauge?
> >
> > Question: How likely is it that my site actually gets 3 or 4
> inches of rain
> > in a 24 hour period, while my neighbor 2 miles away only gets
> 1-2 inches in
> > the same period? My hilltop at 7200 feet is on the edge of the
> Stanislaus
> > river valley as the first groud over about 6900 feet in the
> prevailing storm
> > direction (from the SW); CW4253 is at a similar height, but is
> behind my
> > ridge and one other also at 7200 feet. BLD is also at 7200
> feet, but is in
> > an even more protected location about a mile East of a ridge of
> about 7300
> > feet.
> >
> > Neil/.
> >
> >
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