Monday, June 20, 2022

Precip Data

With some help from Rick Thoman, I've managed to get hold of the NWS daily Alaska precipitation analysis data, i.e. the precipitation estimates that are displayed by the Alaska-Pacific River Forecast Center at:

Here's how the last 30 days stack up against normal for the time of year (using PRISM 1981-2010 normals):

That's a lot of dry.  Fairbanks picked up its first measurable rain in over a month yesterday, amounting to 0.35", but most locations around the area didn't see that much.  Here are estimated totals from the last 7 days:

A couple of cautionary notes about the data: first, obviously, there are very large areas with little or no data, so don't be impressed by the level of detail on the maps.  The analysis method takes the often-scarce observations and uses the high-resolution PRISM normals to create a best guess of how the precipitation may have varied depending on elevation, terrain orientation, and so forth.

The other note is that the analysis uses only automated observations, because the daily analysis is valid for 1200-1200 UTC, or 3am-3am AKST.  Manual observations like co-op or CoCoRaHS are not included.

The 90-day maps show less than 0.75" of liquid-equivalent precipitation in the Y-K delta region, and less than 20% of normal near Bethel and a few other spots around the state.


  1. "Manual observations like co-op or CoCoRaHS are not included."
    That's too bad given the issues with some of the automated stations' precip reporting. PAHN for one only reports 73% of what I get at the HNS #2 coop site about a mile away (yearly average, not quite as bad in the summer).
    PS I looked at your CRN site you linked to in the previous post. You might want to check the precip normals for Utqiagvik, they seem way high.

    1. Yes, it's a pity. Given that most if not all of the automated stations report hourly, it seems it would be better if the Alaska precip analysis were run for 24 hours ending at 15Z or 16Z.

      Thanks very much for pointing out the problem with the Utqiagvik precip normals! It turns out there are highly erroneous values in 2004 and suspicious numbers for a few more years - I've no idea why these weren't removed by the quality control. I re-ran the Utqiagvik normals for 2010-present, and they look more reasonable: the annual normal of just over 7" is in line with the climate site in town over the same period.