Tuesday, June 24, 2014

Precipitation Update

Earlier in the month we noted that Fairbanks precipitation had amounted to only about half of normal for the year to date, but the recent heavy rainfall has now completely erased this deficit; so 2014 is back to near-normal based on the mean climatology.  The median precipitation by this date is a little less - just under 3 inches.

Heavy rain has also occurred in Barrow: 0.49 inches yesterday, which is the second highest daily amount ever reported there in the month of June.  This continues a pattern of above-normal precipitation in Barrow that has persisted since March of last year; in the nearly 18 months since 2013 began, Barrow has seen nearly twice its normal precipitation.  The wettest periods relative to normal were March through September of last year, November and December of last year, and May 2014 through the present.  I've plotted the sea level pressure anomaly in each of these periods below; note the strong similarity in terms of the above-normal pressure in the Bering Sea.  It appears that this recurring anomaly has helped create a favored path for weather disturbances across the North Slope.







Update: the map below shows the correlation of annual mean sea surface temperature with annual mean sea level pressure at St Paul Island, which is located close to the center of the high pressure zone in the three maps above.  This is a negative PDO pattern, and indeed the annual mean PDO index values are correlated at -0.47 with the annual mean pressure at St Paul Island.  A negative PDO phase favors high pressure in the Bering Sea, although the correlation is only found in November through April.

The PDO was negative throughout 2013, so this may explain the high pressure in the Bering Sea last year, but it doesn't explain the recent persistence of the pattern, because (a) the PDO is now positive, and (b) the correlation goes away in summer.  So I don't have an explanation for the remarkable persistence of the pressure anomaly; and I would suggest that the profound seasonal changes in climate dynamics make it unlikely that a single cause can be identified.


7 comments:

  1. Thank you for the update Richard. A month or two ago I ran the numbers for precipitation at all airport stations in the U.S. since the beginning of 2012 and Barrow is the nationwide leader in precipitation departure as a percentage or normal (163% in a 30-month period).

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  2. More Interior rain statistics: http://pafg.arh.noaa.gov/wmofcst_pf.php?wmo=NOAK49PAFG&type=public

    Almost another 0.50" in my gauge here in Fairbanks

    During the 1967 flood water came out of the city sewers into homes with low connections preceding the overall inundation (Pers. Com.). Also in 1967 the Little Chena River downstream of the main Flood Control dam project contributed significantly to the overall flooding. That's according to co-workers that later studied that event in preparation for the building of the dam.

    I'm monitoring the downstairs head for water signs, and my flood insurance is paid up.

    Gary

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  3. From the CPC June 19th:

    ...EL NINO IS FORECAST TO DEVELOP DURING THE NEXT SEVERAL MONTHS, WITH THE LATEST CONSENSUS CPC/IRI FORECAST PLACING PROBABILITIES OF EL NINO OVER 70% FOR JAS.

    THE CURRENT NORTH PACIFIC SSTS PROJECT QUITE STRONGLY ONTO THE POSITIVE PHASE OF THE PDO (INDEX VALUE OF +1.80). IT IS REASONABLE TO EXPECT THIS BOUNDARY FORCING TO PERSIST THROUGH JULY GIVEN THE CURRENTLY FAVORED EMERGENCE OF EL NINO CONDITIONS..."

    How do the SST's relate to the red area spanning the Aleutian Islands above, if at all?

    Gary

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  4. Gary, good question. I added a few sentences onto the post discussing this. There is no easy answer!

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    Replies
    1. Yes. I wondered if the correlation was clear, or obfuscated. But that's what science is devoted...hypothesizing and maybe discovering. Thank you for the reply.

      Gary

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    2. I really, really like the map you added Richard. Nice job.

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    3. Gary - my pleasure. The challenge of trying to understand seasonal climate variability is ever enticing, but we're always just scratching the surface. So much more to learn!

      Brian - thanks. I think I learned about the ESRL correlation page from you, but this is the first time I've used it.

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