Rain Starts and Stops in AS16 and ASP4
Posted by Robert Halmich, Last modified by Robert Halmich on 03 September 2020 01:18 AM

Keywords: Rain, starts, stops, precip, AS16, ASP4, ASN

Related Product(s): Active Sky 2016 for FSX and Prepar3D v3, Active Sky for Prepar3D v4, Active Sky Next


We often receive technical support requests regarding the unexpected starting and stopping of rain/precip in FEW and SCT (scattered) cloud coverage conditions when rain is reported even though SH (showers) are not indicated.  This is working properly and as designed according to our advanced precipitation and radar simulation which accurately considers actual cloud depiction in sim and applies the realistic behavior/rule that precip cannot fall from clear air.  Clouds move with wind in FSX and P3D, and in FEW and SCT conditions, it is normal for rain to start and stop accordingly as occasional nimbus clouds pass overhead, regardless of SH (showers) element existing in the METAR string.


The effect is described in the AS16 (pg 35) and ASP4 (pg 33) User's Guide - Generic Precipitation Display.

AS16 and ASP4 include advanced precipitation and radar features which constantly monitor the cloud positions as actually depicted within the simulator.  The occurrence, type and intensity of precipitation will thus change depending on the existence, type, thickness and convection properties of the simulated cloud that is overhead the aircraft.

Users will experience what may appear as "showery precip" as "few" or "scattered" nimbus (rain) clouds pass overhead, so it will be normal for rain to start and stop or change intensity over time.

Steady rain will occur when the area is covered in overcast cloud layers or fast moving broken layers (typical with nimbostratus).

METARs are a glimpse in time, showing conditions at the time of observation, using equipment such as ceilometers (measuring cloud base heights and coverage) and rainfall sensors (if equipped).  The measurement location and scope is very specific and small, and does not account for change over time even as short as a few seconds/minutes.  The use of the SH (showers) METAR element is generally associated with convective precipitation i.e. cumulonimbus and not indicated in the more stable non-convective nimbus clouds. 

If you require further assistance please visit the forum or feel free to submit a ticket.

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