SOMs Work

Analysis Region Top Widespread EventsLocation of Extreme Precipitation

DJF Master SOM

•Produced with ERA-Interim + SN WRF-50.hPa MSLP anomalies (1989-2007)•Widespread extreme days (99th percentile, w/ at least 25 grid points) from WRF mapped onto Master SOM

99th Percentile

Top 10 DJF Composite

Top 5 DJF Composite

Top DJF Event

Extreme Node Selection

• In some analysis regions, nodes are being accessed that don’t show favorable circulation for widespread precip. extremes

• Some regions may need a smaller Master SOM, as strong features far from region may confound node selection

Native WRF output vs. NCDC-based WRF output

Comparing Node Frequencies

1. Extracted WRF widespread extreme events from N. American analysis region

2. Extracted NCDC station extremes from same regions

3. Extracted WRF output from grid points closest to NCDC station

4. Compared node frequencies from the three sources

Native WRF: L-H-L signal seems to be the dominant circulation feature. Highly accessed nodes on the periphery of SOM space, in general.

NCDC observations don't really show the L-H-L pattern that we find in the model output; we find a strong Aleutian low and a region of relaxed high pressure over the eastern part

of domain.

Similar L-H-L as found in native WRF. Highest frequency node, however, shows a low pressure feature over Gulf of Alaska, with H pressure over the Bering Strait.