Difference between Radar precipitation data stage 2 and stage 4

Zhuotong Nan ([email protected])

Stage II

Be produced directly from the real-time gauge and WSR-88D radar data received at NCEP.


  • from ~1450 ASOS sites from near-real time METAR file
  • and from ~5500 HADS automated gauge reports via the GEOS data Collection Platform.


  • Hourly real-time Digital Precipitation Arrays (DPAs) from 140 ConUS WSR-88D radar sites.

The primary input to the ETA/EDAS precipitation assimilation before 2003.

Stage IV

A mosaic of regional multi-sensor analysis produced by NWS River Forecast Centers (RFCs) and benefits from the RFCs’ manual quality control step

mosaicked from the regional multi-sensor 1h and 6h analyses produced by the 12 ConUS RFCs.

The primary input to the ETA/EDAS precipitation assimilation after 2003. Stage II is only used when Stage IV is unavailable.

In summary,

Since Stage IV benefits from manual QC at the local RFCs, it is generally better than Stage II, which has no manual QC. There are a number of other issues for your consideration:

1. Coverage period: Stage II began to be archived at NCAR on 1 May 1996. Stage IV did not began to be archived until 1 Jan 2002. (NOTE: we have data from 1997 on for OHIO river basin. I guess this statement is for entire continuous continental, rather than for an individual RFC. -Zhuotong)

2. Do you need hourly or 6-hourly analysis? For 6-hourlies, Stage IV is the one to use (if you don’t need the pre-2002 data). Stage IV hourlies have some coverage problem since we do not receive the local analyses from all the RFCs for all hours.

3. How soon do you need the analysis to be available? Stage II hourly analysis is made at 35 minutes after the top of the hour, then re-made twice at 6 hours and 18 hours later. Stage VI runs each hour at approximately 35 minutes past the top of the hour.

4. If I choose Stage II, which type should I use? We recommend the multi-sensor analysis with the exception of early spring – early Aug 2000, when the radar coverage was bad. You might want to use the gauge-only analysis for that time period.

Validation examples:

clip_image004 clip_image006

figure 1 24 hour precipitation accumulative amount on OCT 10, 2004, Stage II (left) and Stage IV (right).


figure 2 Left: Stage II; Right: Stage VI. On Jun 28 2005. Here we can see the variance between them.


1. http://nanzt.info/wp-content/uploads/2008/05/stage2-4.19hydro.pdf
2. http://www.emc.ncep.noaa.gov/mmb/ylin/pcpanl/QandA/
3. http://www.emc.ncep.noaa.gov/mmb/ylin/pcpverif/daily/

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