Wednesday, March 11, 2015

Is This a World Record Snowfall?

Capracotta, Italy.  Source:
Yesterday evening, reports of a world-record 100.8 inch snowfall in 18 hours in Capracotta, Italy went viral.  The original source of this report is the Italian weather site (click here to access).  94.5 inches was reported in Pescocostanzo.  This sort of thing is what the Wasatch Weather Weenies live for!  Let's have a look.

Capracotta is located in central Italy on the east side of the Apennine Mountains at an elevation of 1,421 meters (4,662 ft).  The Adriatic Sea lies to the east.  The Tyrrhenian Sea is to the west.

The storm occurred on the 5th of March when an intense cyclone developed over the region.  The storm was deepest over the Tyrrhenian Sea, but a secondary low center also developed over the Adriatic Sea (plots below based on 6-hour GFS forecast, red square indicates approximate location of Capracotta).

GFS SLP forecast valid 1200 UTC 5 March 2015
The overall pattern favored the transport and concentration of high integrated water vapor values (contours below, warmer indicating higher values) over the southern Adriatic Sea, which then wrapped cyclonically around the mesolow into the Apennines and to Capracotta.  Wind vectors below are for 850 mb, very near the altitude of Capracotta.

GFS integrated water vapor and 850-mb wind forecast valid 1200 UTC 5 March 2015
I couldn't access Italian radar for the event, so I'm going with the GFS 6-h precipitation forecast for mid-day just to show how this leads to heavy orographic precipitation over the eastern Apennines (Magenta is more than 1 inch of water equivalent in 6 hours - keep in mind that the GFS does not fully resolve the Apennines).  The sea level pressure analysis further above also shows a pronounced mesoscale pressure ridge upstream of the terrain, consistent with terrain blocked flow and typically accompanied by an pocket of colder air.

Thus, it is clear that a major snowstorm rocked the Capracotta area.

Now we get to the more difficult issue concerning snowfall amounts.  It is not uncommon for remarkable snow totals to be reported in the media after big events.  I did a quick Google search and was able to find another claim of a world-record 24-hour and storm-total snowfall in the Pyrenees just a few weeks ago.   Unfortunately, I haven't been able to find any discussion of who took the measurements in Capracotta or Pescocostanzo, or how those measurements were taken.  The current world record is 76 inches in 24 hours set at Silver Lake, Colorado, and we've discussed some of the issues even with this record previously (see Looking Back at the World 24-Hour Snowfall Record).

Although I believe the snowfall in Capracotta was exceptional, there are a few reasons why I'm a bit skeptical of the 100 inch report.  First, it is so far above anything that has been previously reported that I'm inclined to doubt it until I see some sort of analysis of how and where the measurements were taken (previous claims on the world record, such as a 77 inch total over the Tug Hill Plateau, have not survived such scrutiny, although they have almost always been exceptional events).

Second, my experience with extreme snowfalls is that they tend to be low-density events (i.e., the water content of the snow is low) and thus typically feature lots of dendritic crystals with little riming.  These crystals form at temperatures between -12 and -18 ºC.  The event in Capracotta was relatively warm (sea-level temperatures were 6ºC and forecast 850 mb temperatures were 0 to -5ºC, so this dendritic growth region would have been elevated.  Those crystals would have had to survive without being beaten to hell by atmospheric turbulence (tough given the strong flow) and also avoid riming in the warm environment.  However, it's possible that the damming of cold air along the Appennines helped in this regard.

Third, and consistent with the item above, this looks to have been a fairly high density snowfall.  The photos at show what looks to be high density snow.  It's balled up and supporting people who are walking on it.

Although I'm skeptical, I remain open minded about this event.  Surprises happen in meteorology, and I look forward to seeing a careful analysis of this event.  I guess the old Ronald Reagan line, trust but verify applies here.  One thing is for sure - they got pounded with a hell of a lot of snow and it appears that even if 100 doesn't hold up, they may likely have a big number in the end.  Jealous!

If you see any official reports or analyses, please post a comment below with a link.

Addendum @ 3:25 PM:

More discussion of this at the Capital Weather Gang.  They actually suggest that the world record is 90.6 inches on Mt. Ibuki, Japan in February 1927, which I was completely unaware of.  I sometimes wonder if we should just have a "do over" for all these snowfall records!


  1. Even low-density snow can ball up like that, especially when it is being compressed by snow on top of it. But with that said, I'm not sure I believe it either. Supposedly it fell in 18 hours which means an average snowfall of over 5" per hour. I guess we'll find out... Any idea who is tasked with "scrutinizing" the record assess its validity?

    1. In the United States, a potential record like this would be be investigated by NOAA, potentially using NOAA employees and/or outside experts. Here's the report they prepared on the potential Tug Hill Record:

      I don't know the Italian weather enterprise well enough to know if they would undertake such an investigation. I suppose it is possible that the World Meteorological Organization (WMO) could have a look, but they do not currently recognize snowfall records. Here's a quote from their climate extremes archive web site ( that pretty much summarizes the warty nature of these records, but already comments on the Italy event:

      "At the present time, the WMO Archive of Weather and Climate Extremes does not recognize or list any official world snowfall records. This is because, in the past, accurate and official snowfall measurements have proven to be rather limited in geographic space around the world and because accurate snowfall measurement have, in the past, proven markedly difficult to verify (for example, even making snowfall measurements too often can affect the total snowfall value as snow compression is a critical factor in snowfall measurement). However,the WMO is currently evaluating the addition of world snowfall extremes as a new category for the WMO Archive of Weather and Climate Extremes. We will likely be adding it to the Archive in the near future. When we do so, we certainly will be investigating March 2015 weather reports from Italy as a possible record snowfall extreme."