ASOS questions

[Chinook]

I have looked at METARs for many years. I am wondering why some airports near me only report in degrees C. Here are two examples

KFNL 022135Z AUTO 35014G21KT 10SM CLR 36/08 A2994 RMK AO1

KGXY 022135Z 14007KT 10SM CLR 38/08 A2993 RMK AO1

Other stations show fractional degrees C, which actually indicate whole numbers of degrees fahrenheit, if you convert it. So, in the "full ASOS" case, it's obvious the computers are programmed to measure temperature in degrees F. But why not FNL and GXY (and perhaps lots of others?)

another question:

why can't FNL report rain or snow??

June 24, late in the day, it was raining, with a thunderstorm indicated in this observation. See any RA in the METAR? No! No Rain.

KFNL 250315Z AUTO 26011KT 10SM TS OVC002 29/08 A3011 RMK AO1 LTG DSNT N TSB02

here's another example. May 23, we got about 0.5"-0.6" of rain across the whole area over a period of hours. FNL indicated very light rain, 0.05" (60005) in 6 hours. Here's the list of METARs with precipitation indicated on May 23 and 24. The thing did not have RA in any of the METARs. What kind of a weather station is this? Not detecting rain? The thing had a 6-hour precip clause at 00z, but did not have a 6-hour precip clause at 06z or 12z, nor did it have a 24-hour precip clause at 12z. It should have shown something at 6z and 12z.

daytime observations:

KFNL 232115Z AUTO 34011KT 5SM SCT048 OVC050 13/08 A2969 RMK AO1 P0001

KFNL 232155Z AUTO 00000KT 10SM FEW047 SCT060 OVC070 12/09 A2967 RMK AO1 P0003

00z observation:

KFNL 232355Z AUTO 17006KT 10SM OVC060 13/10 A2965 RMK AO1 P0002 60005 10190

20120 403100120 57007

other evening observations:

KFNL 240055Z AUTO 16010KT 10SM BKN060 OVC070 11/09 A2967 RMK AO1 P0001

KFNL 240155Z AUTO 11005KT 6SM SCT042 OVC050 11/09 A2967 RMK AO1 LTG DSNT E

P0006

KFNL 240235Z AUTO 31009KT 9SM TS SCT006 BKN015 OVC041 11/09 A2971 RMK AO1

LTG DSNT S TSB28 P0013

06z observation:

KFNL 240555Z AUTO 16004KT 10SM SCT120 09/07 A2968 RMK AO1 10130 20090

12z observation:

KFNL 241155Z AUTO 00000KT 10SM CLR 08/06 A2968 RMK AO1 10090 20070 52010

[Ellinwood]

The difference between precip. reports can be seen within the METAR... namely the AO1

http://weather.cod.e...otes/metar.html

AO2 means that the site is automated and HAS a precipitation sensor. If it were AO1, there would be no precip sensor. This does not mean the site is un-manned. If there is an AUTO after the ID in the metar ob, then there is no observer.

There's also several types of reporting stations between ASOS/AWOS/AWSS: http://en.wikipedia....weather_station

I can't remember off-hand the specific difference between which METARs reports the T group and which don't. EDIT: I think it's just the difference of AWOS not having it and ASOS having it, but I'm not sure.

[Chinook]

Ok, so it is an AO1 type station. Perhaps there are many of these around the country. I don't know. Why would you install a station that doesn't detect precipitation? Apparently this particular station also does not have correct rain gauge readings, although it has a rain gauge. This baffles me that this station does not have:

3-hour and 6-hour precipitation amount (6####)

24-hour precipitation amount (7####)

[dendrite]

The difference between precip. reports can be seen within the METAR... namely the AO1

http://weather.cod.e...otes/metar.html

There's also several types of reporting stations between ASOS/AWOS/AWSS: http://en.wikipedia....weather_station

I can't remember off-hand the specific difference between which METARs reports the T group and which don't. EDIT: I think it's just the difference of AWOS not having it and ASOS having it, but I'm not sure.

Most AWOS sites don't report the T group. You can find some here and there that do (like 1P1 up here). And yeah, many don't report precip type either. Apparently the FAA doesn't really care enough to have every site reporting ptype.

This link will show you what station each is...

http://www.faa.gov/air_traffic/weather/asos/

[dendrite]

Ok, so it is an AO1 type station. Perhaps there are many of these around the country. I don't know. Why would you install a station that doesn't detect precipitation? Apparently this particular station also does not have correct rain gauge readings, although it has a rain gauge. This baffles me that this station does not have:

3-hour and 6-hour precipitation amount (6####)

24-hour precipitation amount (7####)

I believe the FAA handles the AWOS stations and NOAA the ASOS. Therefore you have different reporting criteria for the two. The ASOS is more meteorologically/climatologically in design whereas AWOS is more from an aviation perspective and you tend to see them at smaller airports. From my experience AWOS precip reading tend to be terrible...I only look at totals from ASOS sites.

[famartin]

I think most questions have been answered already but I'll take a crack just in case something was missed.

I have looked at METARs for many years. I am wondering why some airports near me only report in degrees C. Here are two examples

KFNL 022135Z AUTO 35014G21KT 10SM CLR 36/08 A2994 RMK AO1

KGXY 022135Z 14007KT 10SM CLR 38/08 A2993 RMK AO1

Other stations show fractional degrees C, which actually indicate whole numbers of degrees fahrenheit, if you convert it. So, in the "full ASOS" case, it's obvious the computers are programmed to measure temperature in degrees F. But why not FNL and GXY (and perhaps lots of others?)

FNL and GXY are AWOS sites. The dead give-away is the standard reporting interval of 20 minutes, which is the normal AWOS interval. Many AWOS sites only report in Celsius. On the flip side, there have been a few which have been programmed to report T groups with no regard to Fahrenheit, so you get output which is to the nearest degree Celsius and doesn't round to the nearest degree Fahrenheit.

ASOS is programmed to report to the nearest degree Fahrenheit using the T group. That only applies to hourly observations, though. Special obs will only report to the nearest Celsius, no T group.

another question:

why can't FNL report rain or snow??

June 24, late in the day, it was raining, with a thunderstorm indicated in this observation. See any RA in the METAR? No! No Rain.

KFNL 250315Z AUTO 26011KT 10SM TS OVC002 29/08 A3011 RMK AO1 LTG DSNT N TSB02

here's another example. May 23, we got about 0.5"-0.6" of rain across the whole area over a period of hours. FNL indicated very light rain, 0.05" (60005) in 6 hours. Here's the list of METARs with precipitation indicated on May 23 and 24. The thing did not have RA in any of the METARs. What kind of a weather station is this? Not detecting rain? The thing had a 6-hour precip clause at 00z, but did not have a 6-hour precip clause at 06z or 12z, nor did it have a 24-hour precip clause at 12z. It should have shown something at 6z and 12z.

daytime observations:

KFNL 232115Z AUTO 34011KT 5SM SCT048 OVC050 13/08 A2969 RMK AO1 P0001

KFNL 232155Z AUTO 00000KT 10SM FEW047 SCT060 OVC070 12/09 A2967 RMK AO1 P0003

00z observation:

KFNL 232355Z AUTO 17006KT 10SM OVC060 13/10 A2965 RMK AO1 P0002 60005 10190

20120 403100120 57007

other evening observations:

KFNL 240055Z AUTO 16010KT 10SM BKN060 OVC070 11/09 A2967 RMK AO1 P0001

KFNL 240155Z AUTO 11005KT 6SM SCT042 OVC050 11/09 A2967 RMK AO1 LTG DSNT E

P0006

KFNL 240235Z AUTO 31009KT 9SM TS SCT006 BKN015 OVC041 11/09 A2971 RMK AO1

LTG DSNT S TSB28 P0013

06z observation:

KFNL 240555Z AUTO 16004KT 10SM SCT120 09/07 A2968 RMK AO1 10130 20090

12z observation:

KFNL 241155Z AUTO 00000KT 10SM CLR 08/06 A2968 RMK AO1 10090 20070 52010

Many AWOS (and in fact, a handful of ASOS) stations do not have present weather sensors. Technically, for aviation you don't need to know WHAT, if anything, is falling, just the visibility and ceiling. The remark AO1 indicates that the station has no present weather sensor. AO2 indicates that there is a present weather sensor.

[famartin]

Ok, so it is an AO1 type station. Perhaps there are many of these around the country. I don't know. Why would you install a station that doesn't detect precipitation? Apparently this particular station also does not have correct rain gauge readings, although it has a rain gauge. This baffles me that this station does not have:

3-hour and 6-hour precipitation amount (6####)

24-hour precipitation amount (7####)

AWOS sites are strictly for aviation purposes only, which means that if something isn't necessary for flying, the station probably won't have it. If it does, the purchaser was being a bit of a weather weenie when they bought it

The basic needs of an aviation site are ceiling, visibility, pressure, temperature. Anything else is extra.

[famartin]

I believe the FAA handles the AWOS stations and NOAA the ASOS. Therefore you have different reporting criteria for the two. The ASOS is more meteorologically/climatologically in design whereas AWOS is more from an aviation perspective and you tend to see them at smaller airports. From my experience AWOS precip reading tend to be terrible...I only look at totals from ASOS sites.

The standard FAA AWOS has precipitation accumulation, but not T-group temp reporting.

However, these days there are many non-FAA AWOS sites. There are a whole lot in some states, like Minnesota and Virginia, which are non-FAA. These sites are owned by the state government, local governments, or private entities.