Weather station question

[Jonger]

I'm starting to look for a weather station to replace the low end unit I have now. Anyone know of a unit that doesn't have a warm bias during sunlight hours. My current unit has a solar shield, but it still reads high temps about 3 degrees high at peak sun. Anyway to avoid this problem besides parking it in the shade?

[wxmeddler]

Yes, their are options, but a few questions first.

1. What was your previous station?

2. Do you have any trees or other obstructions from the sun to the station during the day? (ex. There is a tree to my SE and blocks the sunlight from 10-11 am)

3. How ventilated (windy) is your station location? Is the wind blocked by something?

4. Whats your budget?

Which leads to #5. How redneck are you? (aka. Your wiring and ductape abilities.)

Ps. A picture (or even better, a panorama) starting from the east to west via south would suffice for questions 2 and 3.

[NeffsvilleWx]

I threw my stations thermometer inside a 3" pvc pipe with an 80mm PC fan at the top to draw in fresh air. No more daylight temp problems.

[MN Transplant]

Davis VP2 w/fan-aspirated shield. It is supposed to go in full sun. Actually, if you are snooping around for different stations, most of them should have owners manuals online. You can see what they think the siting should be.

[famartin]

Davis VP2 w/fan-aspirated shield. It is supposed to go in full sun. Actually, if you are snooping around for different stations, most of them should have owners manuals online. You can see what they think the siting should be.

 

Actually, a close read of the VP2 console manual reveals that they think there will be a bit of a warm bias at peak heating even on aspirated models:

 

"***Outside temperature accuracy is based on the temperature sensor itself and not on the sensor and

the passive shielding together. The solar radiation induced error for standard ration shield: +4F (2C)

at solar noon; for fan aspirated radiation shield: +0.6F (0.3C) at solar noon (insolation = 1040 W/m2,

avg. wind speed =< 2 mph (1 m/s), reference: RM Young Model 43408 Fan-Aspirated Radiation

Shield)."

[Jonger]

Davis VP2 w/fan-aspirated shield. It is supposed to go in full sun. Actually, if you are snooping around for different stations, most of them should have owners manuals online. You can see what they think the siting should be.

 

Actually, a close read of the VP2 console manual reveals that they think there will be a bit of a warm bias at peak heating even on aspirated models:

 

"***Outside temperature accuracy is based on the temperature sensor itself and not on the sensor and

the passive shielding together. The solar radiation induced error for standard ration shield: +4F (2C)

at solar noon; for fan aspirated radiation shield: +0.6F (0.3C) at solar noon (insolation = 1040 W/m2,

avg. wind speed =< 2 mph (1 m/s), reference: RM Young Model 43408 Fan-Aspirated Radiation

Shield)."

Lots of NWS sites use these solar shield type setups now.... I always wondered how anyone is getting a true record without solar contamination.

[famartin]

Lots of NWS sites use these solar shield type setups now.... I always wondered how anyone is getting a true record without solar contamination.

Exterior and interior designs of the shield are not the same between the NWS Coop sensor and Davis'. 

[wxmeddler]

Exterior and interior designs of the shield are not the same between the NWS Coop sensor and Davis'. 

 

The CRS shelters are the classic Stevenson screens with min/max alcohol/mercury thermo's from 1890-1970's and look nothing like the new MMTS (digital) shelters. However, the MMTS shelters and the Davis shelters are pretty similar on the exterior.  I found some schematics of both instrument housings online:

 

MMTS: http://www.srh.noaa.gov/srh/dad/coop/mmts_images/ShelterAssemblyDrawings1.pdf

Davis FARS (See Page #7): http://www.davisnet.com/product_documents/weather/manuals/VP2_Fan_Aspirated_ISS_Rev_C.pdf

[famartin]

The CRS shelters are the classic Stevenson screens with min/max alcohol/mercury thermo's from 1890-1970's and look nothing like the new MMTS (digital) shelters. However, the MMTS shelters and the Davis shelters are pretty similar on the exterior.  I found some schematics of both instrument housings online:

 

MMTS: http://www.srh.noaa.gov/srh/dad/coop/mmts_images/ShelterAssemblyDrawings1.pdf

Davis FARS (See Page #7): http://www.davisnet.com/product_documents/weather/manuals/VP2_Fan_Aspirated_ISS_Rev_C.pdf

 

Note the interior design on page 7 of the Davis specs.  Essentially, the "louves" have nothing to do with air flow or protecting the sensor from radiation; they're almost decorative.  They perhaps shield the interior cylinder, through which the air actually flows from bottom to top (much more like ASOS HO-1088 than the MMTS), from excessive heating. 

 

In the MMTS, the air actually flows through those "louves" into the interior where the sensor lies.

[Met1985]

Good info on here but I am also in the hunt for a weather station. My budget is $200 or less. I have done a lot of research but I am not really coming up with anything that really impresses me or something that is pretty accurate. Thanks.

[Jonger]

Good info on here but I am also in the hunt for a weather station. My budget is $200 or less. I have done a lot of research but I am not really coming up with anything that really impresses me or something that is pretty accurate. Thanks.

Unless it is fan cooled, don't bother unless you like to record high temps 2 degrees warmer than reality on sunny days.

[NeffsvilleWx]

http://www.ambientweather.com/amws2090.html

 

Couple this with cumulus software and you should be able to achieve reasonably accurate measurements. Cumulus has software calibration settings that allow you to fine-tune the accuracy of your measurements.

[famartin]

http://www.ambientweather.com/amws2090.html

 

Couple this with cumulus software and you should be able to achieve reasonably accurate measurements. Cumulus has software calibration settings that allow you to fine-tune the accuracy of your measurements.

Important note from a reviewer on Amazon:

"Of course, the temperature sensor cannot be installed in the sun where heat will reflect off walls, etc., "

[NeffsvilleWx]

Most low end units have this problem. It can be solved with a little ingenuity and a trip to Lowe's, and even after a homemade active solar shield, it's well within his budget.

 

I have a station from the same manufacturer. Out of the box, it had solar heating problems to the point where it was failing MADIS QC. After building a radiation shield, it's within a few tenths of a degree of KLNS.

 

Another note: placement is extremely important, CWOP has a good guide on station placement.

[Disc]

Good info on here but I am also in the hunt for a weather station. My budget is $200 or less. I have done a lot of research but I am not really coming up with anything that really impresses me or something that is pretty accurate. Thanks.

 

Even though this is a little over your budget, I think you'd be better off with a Davis. http://www.archertradingpost.com/atp/index.php?main_page=product_info&cPath=1_6_7&products_id=78 ..The only caveat of this unit is that everything is all in one and you can't customize/add stuff to it in the future.

 

I've also had bad experiences with the WS-model AmbientWeather weather stations in the past and it really is worth a little extra money for something that won't cause headaches in the future.

[Met1985]

Hey thanks for all the info and help. I am looking at the ambient WS 2080 or the all in one 2090. I was looking at the Davis Vantage Vue. I was thinking of getting getting the ambient WS for this winter because it is pretty cheap then Make a run to get the Davis this spring after the holidays and such.

[NeffsvilleWx]

Even though this is a little over your budget, I think you'd be better off with a Davis. http://www.archertradingpost.com/atp/index.php?main_page=product_info&cPath=1_6_7&products_id=78 ..The only caveat of this unit is that everything is all in one and you can't customize/add stuff to it in the future.

 

I've also had bad experiences with the WS-model AmbientWeather weather stations in the past and it really is worth a little extra money for something that won't cause headaches in the future.

I agree, if one can afford a little extra, the Davis is definitely the way to go.

[Jonger]

Couple this with cumulus software and you should be able to achieve reasonably accurate measurements. Cumulus has software calibration settings that allow you to fine-tune the accuracy of your measurements.

Does the software use a solar sensor to adjust the temp down during high solar hours?

[NeffsvilleWx]

Does the software use a solar sensor to adjust the temp down during high solar hours?

 

No. It's merely a manual calibration factor. You can either add or subtract from the measured data, or multiply. You can dial it in within a few degrees to compensate for solar heating, but an active solar shield works much better.

 

It really shouldn't take much to add a small fan to your shield to overcome the solar heating problems. PC fans are easy enough, and you could either tap into the power supply for the unit itself or use an old cell phone charger to power it, provided the fan is rated for 5 volts.

 

Just curious, what software are you currently using? Cumulus is free and works with most weather stations on the market.

 

http://sandaysoft.com/products/cumulus

[Jonger]

No. It's merely a manual calibration factor. You can either add or subtract from the measured data, or multiply. You can dial it in within a few degrees to compensate for solar heating, but an active solar shield works much better.

 

It really shouldn't take much to add a small fan to your shield to overcome the solar heating problems. PC fans are easy enough, and you could either tap into the power supply for the unit itself or use an old cell phone charger to power it, provided the fan is rated for 5 volts.

 

Just curious, what software are you currently using? Cumulus is free and works with most weather stations on the market.

 

http://sandaysoft.com/products/cumulus

 

My current station is garbage, I'm just trying to figure out the best solution for solar contamination to my temp records before I spend much on a new unit.

 

I'm thinking a Vantage Pro 2 with fan aspiration should improve accuracy enough for the sake of record keeping.

[famartin]

My current station is garbage, I'm just trying to figure out the best solution for solar contamination to my temp records before I spend much on a new unit.

 

I'm thinking a Vantage Pro 2 with fan aspiration should improve accuracy enough for the sake of record keeping.

It will.  I have two, both of which are about 2 miles from the nearest ASOS's (one here near EKO, the other back in NJ near TTN).  Average differences for highs and lows between the Vantage Pro 2's and the respective ASOS's are less than a degree.

[GramaxRefugee]

Even though this is a little over your budget, I think you'd be better off with a Davis. http://www.archertradingpost.com/atp/index.php?main_page=product_info&cPath=1_6_7&products_id=78 ..The only caveat of this unit is that everything is all in one and you can't customize/add stuff to it in the future.

 

I have used one since they came out a few years back. A wonderful gadget to have, and I have never tired of it, but.....It is loaded with warm bias if not sited in shade. Partly because, as you mention, it is all in one. The radiation shield/stevenson screen is a tiny little thing that allows about 5 F extra on sunny days.

[NeffsvilleWx]

My current station is garbage, I'm just trying to figure out the best solution for solar contamination to my temp records before I spend much on a new unit.

 

I'm thinking a Vantage Pro 2 with fan aspiration should improve accuracy enough for the sake of record keeping.

 

That's the key for most hobbyist level stations. The included screens are often too small to function properly.

[famartin]

That's the key for most hobbyist level stations. The included screens are often too small to function properly.

Even though the exterior of the Davis screen looks like the MMTS/Nimbus units NWS COOP stations use (which are not aspirated), the interior design is much more like the ASOS HO-1088 thermometer (which IS aspirated), so it really needs aspiration to function properly.

[GramaxRefugee]

I should've also mentioned, (for the benefit of any youngsters that wander across this thread), that mixing wind, temp, and rain in one unit is a major compromise. If in shade for the temp, the rain gauge can't work. If low enough for proper temp, the wind can't work well.

 

But, I love having the dew point, and I guess that works anywhere.

[famartin]

I should've also mentioned, (for the benefit of any youngsters that wander across this thread), that mixing wind, temp, and rain in one unit is a major compromise. If in shade for the temp, the rain gauge can't work. If low enough for proper temp, the wind can't work well.

 

But, I love having the dew point, and I guess that works anywhere.

Well the rain gauge CAN work in the shade, unless its under a roof   If its under a tree it just won't work well. 

 

Dew point can be a problem if it is near water or heavy vegetation, which would artificially raise it beyond what the "ambient" readings are.  Dew point is also one of the things Davis doesn't do that great, it tends to have a wet bias even with aspiration, especially when readings get fairly high (60s-70s).

[Jonger]

I should've also mentioned, (for the benefit of any youngsters that wander across this thread), that mixing wind, temp, and rain in one unit is a major compromise. If in shade for the temp, the rain gauge can't work. If low enough for proper temp, the wind can't work well.

 

But, I love having the dew point, and I guess that works anywhere.

Well the rain gauge CAN work in the shade, unless its under a roof   If its under a tree it just won't work well. 

 

Dew point can be a problem if it is near water or heavy vegetation, which would artificially raise it beyond what the "ambient" readings are.  Dew point is also one of the things Davis doesn't do that great, it tends to have a wet bias even with aspiration, especially when readings get fairly high (60s-70s).

Doesn't the Davis have wireless add on components? I wonder if you can purchase a more accurate hygrometer.

[famartin]

Doesn't the Davis have wireless add on components? I wonder if you can purchase a more accurate hygrometer.

I think we're focusing on the Vantage Vue, which is an all-in-one.  The Pro 2 does have add-on ability though I'm not sure if non-Davis components can be added.

[GramaxRefugee]

Well you're right; there are occasions that the rain gauge agrees with my official funnel tube gauge. Usually in winter when the leaves are off. It is nice to have an electric gauge to estimate the rainfall without going outside.

 

There are other threads elsewhere that refer to the battery and contact problem that the Davis Vantage Vue had. They have a solar cell (PV), but mine, and others, ate batteries until I learned that there is a corrosion issue inside which can be overcome with dielectric grease. Haven't had to replace a battery since making the repair.

[dendrite]

Davis VP2 w/ FARS is the way to go, but if it's over your budget you can get creative and make your own FARS as some have mentioned. I run my FARS with 3 VAC with an AC-to-DC converter 24/7 rather than relying on the solar panels. That way I get the same aspiration rate throughout the day and night.

 

Here's a study Davis did on their FARS years ago...

 

http://www.davisnet.com/news/ars_vs_c.pdf