ASOS thunderstorm observation and possible false reports

Dan Robinson

How do the ASOS stations discern the presence of lightning for a thunderstorm observation? Is there some sort of integration with the NLDN, or do they have their own lightning sensors?

The reason I ask is that on three separate occasions this winter, the Beckley, WV (BKW) ASOS station was reporting thundersnow. I immediately checked radar and lightning data and found little to support that possibility (no cellular snow showers or significantly heavier reflectivities). Last night, the radar was still in clear air mode with a large shield of light precip (snow) over most of the state when a thundersnow ob came in from BKW. No strikes on the NLDN (I'm aware that intracloud discharges may not register). I wondered if there was something that might cause a reporting station to have a false alarm for lightning.
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Lightning Detection

I am stationed at NAS Jacksonville, FL Towers Field. We have a relatively new ASOS system with a lightning detector. It's rather lengthy to explain, but follow this link for a thorough explination. It says only 80-90% of all lightning strikes are detected, so not all are reported, hence it could have been thundersnow, w/o detection.

FAA/NWS ASOS units that have lightning reports are integrated with NLDN, it is not a local sensor.
Albany, NY is an ASOS station and it reports occurrences such as LTGCCCG or LTGCC and TSB08E49. How can that really be determined by a local sensor? There has got to be some other means of observation to get that specifc..... ????

BTW...This is a great thread for ST.
Albany, NY is an ASOS station and it reports occurrences such as LTGCCCG or LTGCC and TSB08E49. How can that really be determined by a local sensor? There has got to be some other means of observation to get that specifc..... ????

BTW...This is a great thread for ST.

No, the sensor can not determine the type of lightning in any form, it just detects the electrical discharge. The type of lightning is manually inputted into the remarks section for a Metar(hourly) or Speci(special in between hourly) observations. Unmanned/automatted stations will only say TS. Most manned stations are military instillations(i.e. Tinker AFB, NAS Jacksonville, Fort Sill, and Camp Pendleton, major airport(KBNA, KATL, KMIA etc), and other airports during operational hours, manned staffing permitting.Stationed at NAS JAX, we do this almost EVERY day from Memorial Day thru Labor Day. Hopefully that answers your question.
As I mentioned above, non-Navy ASOS sites utilize NLDN data. Which is why they can indicate where the lightning is at in relation to the station.

It's called ALDARS - some info at

That is what we use, but not all military sites are manned 24/7. NAS JAX is one, I'm on watch right now, but sites like Mayport,FL and Willow Grove,PA are manned from 12am to 8am, I know Keesler AFB,MS is the same way.
Dan, I can tell you that the first two thundersnow reports this year were correct. I had viewers call into the station saying they heard thunder during the snow. Even my station GM witnessed it. Have not heard any reports from Tuesday night yet, but there was an heavier band of snow that set up over south Beckley, snowfall went from 5" north to up to 9" over a very short distance. I wish I would have seen it. Only witnessed thundersnow twice, once in AL in March '93, and once in DC in Oct of '00.
ALDARS is for unmanned sites, it is not a local instrument. It's a link to NLDN.

aldars is also available at a number of manned sites. many observers will turn off aldars as it tends to get in the way. aldars will only report distant lightning. between 5 and 10 miles from the site it will report a tstm in the vicinity (VCTS) and from 0 to 5 miles it will report a tstm (TS). aldars will not report lightning within 10 miles nor will it give the location of a tstm within 10 miles of the station. manned sites (except sites manned by the ATCT) are required to report the frequency...type...and direction of the lightning: FRQ LTGIC DSNT NW... aldars will only report: LTG DSNT NW. also, except for ATCT sites, the direction and movement of the tstm is required: TS SW MOV E. So...a manually added remark at an augmented ASOS site might look like: OCNL LTGIC SW TS SW MOV E. aldars would only report a tstm TS in the present weather field of the metar and NO remarks.
Had some great thunder snow and sg, sn in 2010 near Ksea, 2 Alaska jets were hit and one horizon plane. I'm pretty sure all three strikes were ac triggered. Watched come through the convergence zone line on short final, landing runway 16L.
I've seen TSSN probably 6 times in my life here in the puget sound. All associated with the puget sound convergence zone, or close proximity upper low.

The observer here at Ksea missed the most recent strikes, and have been notoriously bad at catching weather since the move to the new tower. It's a shame.
Is there a time criteria for a TSRA ob regarding the last observed lightning flash? Say, lightning within the previous 5, 10, 15 minutes? 60 seconds? Currently (04z 10/14) there are large convective stratiform precip shields across MO and IL, with many of the stations reporting rain (no TS) where I am sure there is at least intermittent lightning in progress. A convective stratiform shield that is still producing lightning will have flash intervals of no more than 4-5 minutes, typically less (based on my experience). Any longer than 5-6 minutes without lightning means that the shield is done producing it, at least 99% of the time. So, a weaker electrified stratiform (in theory) might register no TSRA on an ASOS/AWOS if the time criteria for a lightning flash observation is less than 3-4 minutes from the time of the ob.

EDIT: Well, in this case, the "no TS" obs in MO/IL are because there really is no lightning with this system up here. I just fired up my ThreatNet display in my truck (my only way of getting realtime lightning) and there have been no strikes around the stations reporting rain.
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