DCA Snowfall Total Controversy

[Deck Pic]

Sometimes a remark might get copied into the next one inadvertently, so they really might not have meant to send that in the ob twice.  Its uncertain.  Like all of this.

 

it was over the phone...while none of this might be certain, the circumstantial evidence is overhwhelming.  We know this would never stand at IAD/LWX...ever...hope DCA is held to the same standard

[famartin]

Has anyone here every recorded 0.04" from moderate snow in an undermeasuring bucket at 27 degrees with 17.8" depth and the snow didn't stick?

A couple points:

1 - Its not a tipping bucket.  Climate ASOS's like DCA have weighing gauges now.

2 - Its not impossible snow clung to the orifice and fell in later, which could erroneously put precip which fell earlier into that hours ob.

3 - With severe blowing and drifting, ratios could be quite low.  You're right though, probably not zero. 

[Deck Pic]

A couple points:

1 - Its not a tipping bucket.  Climate ASOS's like DCA have weighing gauges now.

2 - Its not impossible snow clung to the orifice and fell in later, which could erroneously put precip which fell earlier into that hours ob.

3 - With severe blowing and drifting, ratios could be quite low.  You're right though, probably not zero. 

 

Plus it is hard to tack on more snow when you don't measure.  Next time it snows until midnight, I am going to post my final total at 5pm and stop measuring

[Stebo]

Sometimes a remark might get copied into the next one inadvertently, so they really might not have meant to send that in the ob twice.  Its uncertain.  Like all of this.

The problem with this is that they had 2 SPECI that came out between the 2 obs in question, if they had locked in the remarks it would have shown that. They didn't but then included it in the next METAR then corrected, to me it shows someone who didn't know what they were doing.

[Stebo]

A couple points:

1 - Its not a tipping bucket.  Climate ASOS's like DCA have weighing gauges now.

2 - Its not impossible snow clung to the orifice and fell in later, which could erroneously put precip which fell earlier into that hours ob.

3 - With severe blowing and drifting, ratios could be quite low.  You're right though, probably not zero. 

Considering part of the hour was at 1/16SM visibility with snow falling I would imagine the .03" being legit and in reality more probably fell but because of the wind it blew over the collection sensor.

[Inverted_Trough]

You would think that the observers at DCA - an airport that is under higher scrutiny because of its litany of dubious temperature and snow observations in the past - would be especially careful to take good measurements, given that higher scrutiny.  But clearly, they're not.  Instead, we have people who are more interested in protecting their own or self-preservation, rather than the integrity of the process.  That's why this has been going on for 40 years.

 

I'm of the belief that bad information is worse than no information.  Scrap the record.  Or put a big fat asterisk next to it, with the footnote: *This data is garbage, please disregard 

[famartin]

You would think that the observers at DCA - an airport that is under higher scrutiny because of its litany of dubious temperature and snow observations in the past - would be especially careful to take good measurements, given that higher scrutiny. But clearly, they're not. Instead, we have people who are more interested in protecting their own or self-preservation, rather than the integrity of the process. That's why this has been going on for 40 years.

I'm of the belief that bad information is worse than no information. Scrap the record. Or put a big fat asterisk next to it, with the footnote: *This data is garbage, please disregard

I'm going to point out again that snowfall data is inherently full of errors. Particularly during big windy blizzards.

[Ian]

Not to mention we just pay a whole lot of attention to DCA. Various similar data-screwing issues occur at obs locations all across the world. Anyway, possibly having a May record month that was inflated by 1-2 degrees by a bad sensor is probably still the bigger offense in the grand scheme.

[nw baltimore wx]

Not to mention we just pay a whole lot of attention to DCA. Various similar data-screwing issues occur at obs locations all across the world. Anyway, possibly having a May record month that was inflated by 1-2 degrees by a bad sensor is probably still the bigger offense in the grand scheme.

BWI has to be high, pun intended. I had 25", took a core and ended up with 3.15" liquid. BWI gets 29" with 2.13"? Of course, I didn't use a snowboard but that's still quite a discrepancy.

[famartin]

BWI has to be high, pun intended. I had 25", took a core and ended up with 3.15" liquid. BWI gets 29" with 2.13"? Of course, I didn't use a snowboard but that's still quite a discrepancy.

The observer gauge suffered from too much wind so, as with at DCA, we were forced to use the ASOS reading. It may be reviewed.

[Deck Pic]

I'm going to point out again that snowfall data is inherently full of errors. Particularly during big windy blizzards.

 

And particularly when protocol isn't followed and the observers don't care.  

[WinterWxLuvr]

I'm going to point out again that snowfall data is inherently full of errors. Particularly during big windy blizzards.

Stick four 16 foot poles in the ground in a 20 x 20 rectangle, wrap a tarp around it on all sides, put a 3 x 3 board in the center, walk out and measure the snow every 6 hours. It shouldn't be that hard. Might not be perfect but it would be pretty close.

This whole thing is like a Bad News Bears movie.

[famartin]

You guys fail to account for blowing and drifting which can make a single snow board unrepresentative. It's not so simple.

To have a decent measurement you will want multiple boards and depth measurements. Also consider that an airport observer has other data to colect and then code for the observation.

[Amped]

I'm going to point out again that snowfall data is inherently full of errors. Particularly during big windy blizzards.

Exactly, we'll never know how much fell. It's best to average surrounding measurements but there's still no fool proof way of telling.

[HighStakes]

Just call it 20 inches and end this insanity.

[ravensrule]

Apparently its like rocket science.

If the folks at DCA would just let RR show em how to do it, there would be no controversy .

My ruler is too big to measure such paltry snowfall.

[ravensrule]

BWI has to be high, pun intended. I had 25", took a core and ended up with 3.15" liquid. BWI gets 29" with 2.13"? Of course, I didn't use a snowboard but that's still quite a discrepancy.

I think your measurement was low though. A trained spotter in Pimlico 4 miles to your SE measured 27".

[isohume]

Plus it is hard to tack on more snow when you don't measure.  Next time it snows until midnight, I am going to post my final total at 5pm and stop measuring

 

Lol...I know you're just joking (hope so anyway), but that made me laugh!

[nw baltimore wx]

I think your measurement was low though. A trained spotter in Pimlico 4 miles to your SE measured 27".

Yeah, I always compare my totals to that observer in Pimlico, but they may be measuring "more correctly" than I do. I don't use a snowboard and obviously, error increases as snow accumulation increases.

Also, my ratio was about 8:1 which also might indicate my total may be a little low. But it's the way I've always measured snow, and my measurements are generally for my own records so no big deal.

If we get another decent snow event this winter, maybe I'll try to set up a couple of snow boards and see what kind of discrepancy I get.

[North Balti Zen]

Yeah, I always compare my totals to that observer in Pimlico, but they may be measuring "more correctly" than I do. I don't use a snowboard and obviously, error increases as snow accumulation increases.

 

 I was at 27" not that far from you and I am now within a few miles of Pimlico - I think you are low.

[Deck Pic]

You guys fail to account for blowing and drifting which can make a single snow board unrepresentative. It's not so simple.

To have a decent measurement you will want multiple boards and depth measurements. Also consider that an airport observer has other data to colect and then code for the observation.

 

agreed....yet DCA has only one, and they lost it......This "measuring is hard" trope is a red herring.  It is hard, but it is particularly hard when you lose your one snow board, and you quit measuring before the storm is over. 

[ravensrule]

Yeah, I always compare my totals to that observer in Pimlico, but they may be measuring "more correctly" than I do. I don't use a snowboard and obviously, error increases as snow accumulation increases.

Also, my ratio was about 8:1 which also might indicate my total may be a little low. But it's the way I've always measured snow, and my measurements are generally for my own records so no big deal.

If we get another decent snow event this winter, maybe I'll try to set up a couple of snow boards and see what kind of discrepancy I get.

Lol could you imagine had I actually posted my measurements that yielded between 25-30" and averaged it at 27.5". I would have been called a huge slant sticker. That's why I'm using your measurements this winter .

[nw baltimore wx]

Lol could you imagine had I actually posted my measurements that yielded between 25-30" and averaged it at 27.5". I would have been called a huge slant sticker. That's why I'm using your measurements this winter .

Oh, don't do that. My totals are admittedly conservative, always. Besides, your location is normally a location that is colder and gets more snow. The NWS map definitely illustrates my total is low, and one of the reasons I don't report totals to any authority is because I am not a trained spotter, nor am I willing to do what Matt and others do to measure snow accurately as defined by NWS or even COCORAHS. I applaud those that do, but it's obvious that it requires a commitment prior to and for the full duration of a storm that I am not willing to make.

I also agree with Ray that snow totals are filled with error for many scientific reasons (wind, location of measurement, etc), and I also think that it's just human nature for average folks to over inflate their totals. But, in the end, I think all of this discussion supports the argument that there needs to be a consistent standard for the airport reporting stations. Those reporting stations should use the same outlined, trained process and even though there will still be some unavoidable errors, it should be as accurate as possible.

[mappy]

Lol could you imagine had I actually posted my measurements that yielded between 25-30" and averaged it at 27.5". I would have been called a huge slant sticker. That's why I'm using your measurements this winter .

 

OR, stop being so passive aggressive and just post what you think you got. Trust me, I'll see it later in the data if your totals are a joke.

[nw baltimore wx]

OR, stop being so passive aggressive and just post what you think you got. Trust me, I'll see it later in the data if your totals are a joke.

My guess is that over the years, you have come to know the tendencies of your sources and are able to smooth over the differences when making your maps.

[mappy]

My guess is that over the years, you have come to know the tendencies of your sources and are able to smooth over the differences when making your maps.

 

Yes. The differences are obvious is someone inflates or under reports their totals. Not to derail this thread.. but your 25" would stick out for this storm if I did an individual map. 27" makes more sense given what others around you have reported. 

[ravensrule]

Oh, don't do that. My totals are admittedly conservative, always. Besides, your location is normally a location that is colder and gets more snow. The NWS map definitely illustrates my total is low, and one of the reasons I don't report totals to any authority is because I am not a trained spotter, nor am I willing to do what Matt and others do to measure snow accurately as defined by NWS or even COCORAHS. I applaud those that do, but it's obvious that it requires a commitment prior to and for the full duration of a storm that I am not willing to make.

I also agree with Ray that snow totals are filled with error for many scientific reasons (wind, location of measurement, etc), and I also think that it's just human nature for average folks to over inflate their totals. But, in the end, I think all of this discussion supports the argument that there needs to be a consistent standard for the airport reporting stations. Those reporting stations should use the same outlined, trained process and even though there will still be some unavoidable errors, it should be as accurate as possible.

I am the same as you. I go out when i feel like it and measure either on top of a garbage can, top of my air conditioning unit, patio table or grill cover. So it may not be accurate but i am reporting exactly what my stick shows. I will just stick with your measurements since people seem to get their drawers in a snitch about my measurements.

[ravensrule]

OR, stop being so passive aggressive and just post what you think you got. Trust me, I'll see it later in the data if your totals are a joke.

According to you my totals are always a joke. So no need to overexert my precious ruler.

[Inverted_Trough]

Has it always been the FAA that measures snow at DCA (i.e., for the past 40 years at least?).  Or have those responsibilities changed hands over the years?  And if those responsibilities have changed - then who used to measure it?

 

Of course all measurements have errors.  You can use spatial statistical methods to identify anomalies and adjust for them.  It's done all the time in any engineering or scientific field.  Weather has strong spatial and temporal autocorrelation, i.e., if everyone within a 1-mile radius is reporting 20% more snow than you, then your measurement is suspect.  

[famartin]

Has it always been the FAA that measures snow at DCA (i.e., for the past 40 years at least?).  Or have those responsibilities changed hands over the years?  And if those responsibilities have changed - then who used to measure it?

 

Of course all measurements have errors.  You can use spatial statistical methods to identify anomalies and adjust for them.  It's done all the time in any engineering or scientific field.  Weather has strong spatial and temporal autocorrelation, i.e., if everyone within a 1-mile radius is reporting 20% more snow than you, then your measurement is suspect.  

 

I think that at some point there was a NWS Airport Office at DCA, but it was closed and the current FAA Contract Weather Observing station was established in its place.  I couldn't tell you when, maybe the 80s?