Can weather groups contain multiple descriptors in a METAR?

Question

I understand that a weather group in a METAR is composed of qualifiers (intensity, descriptor) and the weather phenomenon: precipitation, obscuration and other phenomena.

My question is can weather phenomena have multiple descriptors? Eg: Are TSSH or TSSHRA valid in a METAR?

Answer 1

No, a METAR descriptor can only appear once in a METAR or line of a TAF. That is because METARs and TAFs report weather phenomena in the format of

[Intensity][Proximity][Descriptor][Precipitation][Obstructions to Visibility].

Thunderstorms, for example, are one descriptor; therefore, thunderstorms (TS) will only appear once.

1. Intensity

   Applies only to the first type of precipitation reported. A “−” denotes light, no symbol denotes moderate, and a “+” denotes heavy.

2. Proximity

   Applies to and reported only for weather occurring in the vicinity of the airport (between 5 and 10 miles of the point(s) of observation). It is denoted by the letters “VC.” (Intensity and “VC” will not appear together in the weather group.)

3. Descriptor

   These eight descriptors apply to the precipitation or obstructions to visibility:

   TS = Thunderstorm
   DR = Low drifting
   SH = Showers
   MI = Shallow
   FZ = Freezing
   BC = Patches
   BL = Blowing
   PR = Partial
   

4. Precipitation

   There are nine types of precipitation in the METAR code

   RA = Rain
   DZ = Drizzle
   SN = Snow
   GR = Hail (1/4" or greater)
   GS = Small hail
   PL = Ice pellets
   SG = Snow grains
   IC = Ice crystals
   UP = Unknown precipitation
   

5. Obstructions to Visibility There are eight types of obscuration phenomena in the METAR code

   FG = Fog
   HZ = Haze
   FU = Smoke
   PY = Spray
   BR = Mist
   SA = Sand
   DU = Dust
   VA = Volcanic ash
   

Answer 2

Your question brought to my mind the following question. Since TS and SH are both descriptors that indicate the intensity of precipitation, can they both exist simultaneously? Sort of like when does fast become slow? Or, in the case of the weather phenomenon RA, at what point does gray become black or white instead of both? A quick google search turned up the following article from a local meteorologist.

Thunderstorm, Thundershower...What's the Difference?  
March 16, 2001 at 1:51 AM EST - Updated July 1 at 10:45 AM  
What's the difference between a
thundershower and a thunderstorm?  That is
a question that has a technical and
psychological answer.  Technically, any
cloud producing lightning is considered a
thunderstorm, even if there is no rain
falling.  The National Weather Service
reports it as "TS" in their hourly
observations at the airport.  TSRA means a
Thunderstorm with a Rain Shower, which is
what most of us think of when we think of
thunderstorms...Thunder, Lightning and
Rain.  But, when meteorologists (Mainly on
TV and Radio) want to indicate that
thunderstorms with light rain are expected,
they will call them Thundershowers, even
though there is no technical abbreviation
for a thundershower.  It's just a good way
of taking the much stronger sounding word
"storm" out of the mix, and adding the
gentler sounding description of "shower". 
Properly, thunderstorms have either no rain
(TS), light rain (TSRA-), moderate rain
(TSRA), or heavy rain (TSRA+).  But, for a
viewer, it's tough to explain all that, so
we generally talk about weaker
thunderstorms as thundershowers, even
though there is "technically" no such
thing.

With this type of argument, TS and SH remain completely separate (eg. TSRA vs. SHRA). The + or - would be added to indicate intensity.