Tuesday, May 10, 2011

April Precipitation in Context

The National Climatic Data Center has released it's preliminary climate statistics for April and they are quite remarkable.  If you think it was a wet April here, consider the folks in the midwest.  It was the wettest April in the instrumented record for Illinois, Indiana, Ohio, Pennsylvania, Kentucky, and West Virginia.
Source: NCDC
Surrounding states such as Arkansas, Missouri, Michigan, New York, and Vermont were also near record levels.  What does this mean in terms of total precipitation?  How about 7.33-11.88" depending on the state.

Source: NCDC
Our state-averaged precipitation was "much above normal".  Of course, averaging on the scale of a state is convenient, but sometimes blurs reality.  According to the Advanced Hydrologic Prediction Service (AHPS) analysis, April precipitation in northern Utah and upper-elevation regions of southern Utah bore the brunt of the wet weather, with some areas of eastern Utah observing below average precipitation.

Source: NWS-AHPS
High resolution precipitation analyses are known to have a few warts, so let's have a look at some station data.  According to the recently released April climate summary from the National Weather Service Salt Lake City Forecast Office we received 4.06" of precipitation at KSLC, 201% above the 1971-2000 average of 2.04" and the fifth wettest April on record (since 1874).  Alta received 101.5" of snow and 14.25" of water, the latter 267% of the 1971-2000 average.  On the otherhand, Wellington (south of Price), compared to a long-term average of 0.68" (average from Western Region Climate Center), so perhaps there were a few areas in eastern Utah that snuck in below average.

Not surprisingly, the 30-Day mean 500-mb geopotential height departure from climatology shows anomalous troughing over the northwestern United States and ridging extending across northern Mexico and the southeast United States.  This places much of the soggy midwest in anomalous southwesterly flow and Utah downstream of anomalous flow that originates over the northeast Pacific.

Source: ESRL/PSD
In contrast, note the anomalous ridge over western Europe.  There are always winners and losers in the weather game and it appears they picked a good month for the Royal Wedding.


  1. I've found it remarkable that Lake Champlain in NY & VT is flooding and has exceeded its historical high mark.

    Further, Devil's Lake in ND is growing by leaps and bounds each year.

    This is certainly a trend for these 2 lakes but what does it mean beyond the decadal scale?

  2. I don't know enough about the hydrology of these areas to evaluate whether or not we're dealing primarily with the impact of this winter and spring's precip or a decadal scale phenomenon. The Lake Champlain atlas contains some info that might help: http://www.lcbp.org/Atlas/HTML/nat_lakefax.htm