Explaining a ‘trace’ of rainfall

December 2nd, 2012 at 9:47 am by under Weather

The rainfall boards from this morning, referencing Saturday, December 1st. Notice that a ‘trace’ of rain was reported at Camp Mabry.

The last few mornings in central Texas brought the area plenty of low clouds, patchy fog, and even a bit of very light drizzle.

We have been reporting on the incredible dry streak Austin has seen this fall – with only 0.96″ of rain since Oct. 1 and a completely dry November.  With drizzle the past few mornings, and Camp Mabry reporting a ‘trace’ of rainfall both yesterday and today – you may wonder if this officially ends the dry spell.

Oftentimes, you hear meteorologists refer to ‘measurable rainfall’. For instance, today is the 37th day in a row that both Camp Mabry AND the airport have gone without measurable rainfall.

A ‘trace’ of rainfall means that very light rainfall was observed at the weather station that day – but it was not enough to “tip the bucket” and register one one-hundredth of an inch, and was therefore not measurable.

Because of this technicality, the streak without measurable rainfall in Austin continues…

2 Responses to “Explaining a ‘trace’ of rainfall”

  1. Ramon says:

    I believe we’ve had more than average rainfall at the two Austin official weather sites (Mabry & ABIA), but I’m sure that didn’t make up the two year deficit because 2011 was so extremely dry. My question is are we in a multi-year (e.g., decade long) deficit. It seems like we’ve been in drought most of the last ten years, but maybe, it all averages out over the ten years. Of course, evapotranspiration has probably been much higher than average, especially since 2008!

    1. davidyeomans says:

      Great question.
      Here’s a look at the last ten years of observed rainfall at Camp Mabry (the main reporting station for the city), and how it compares to the 30-year average yearly rainfall of 34.24″:

      2002: 36.00 (+1.76)
      2003: 21.41 (-12.83)
      2004: 52.27 (+18.03)
      2005: 22.33 (-11.91)
      2006: 34.70 (+0.46)
      2007: 46.95 (+12.71)
      2008: 16.07 (-18.17)
      2009: 31.38 (-2.86)
      2010: 37.76 (+3.52)
      2011: 19.68 (-14.56)
      2012: 32.67 to date (+0.45 to date)

      Judging by these numbers, we are in a total rainfall deficit of -23.4 inches over the past 10 years (averaging a deficit of 2.34″ each year).

      Perhaps more importantly, we’re in a deficit of 31.62 inches since 2008. That’s almost a deficit of one entire year’s rainfall accumulated in only 4 years!

      I hope that helps.