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Weather Discussion

This weather discussion provides an update on the recent evolution of Equatorial Pacific sea surface temperature (SST) departures, along with other relevant atmospheric and oceanic conditions. It includes information on ENSO neutral conditions, SST outlook, atmospheric circulation over North Pacific and North America, U.S temperature and precipitation departures, and a summary of current weather phenomena.

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Weather Discussion

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  1. Weather Discussion 4/24/12

  2. ENSO UPDATE

  3. Recent Evolution of Equatorial Pacific SST Departures (oC) Time From September 2011- January 2012, below-average SSTs were evident across much of the equatorial Pacific Ocean. Since February 2012, above-average SSTs have persisted in the eastern Pacific, while negative anomalies have gradually weakened in the central Pacific. Longitude

  4. Niño Region SST Departures (oC) Recent Evolution The latest weekly SST departures are: Niño 4 -0.3ºC Niño 3.4 -0.4ºC Niño 3 0.1ºC Niño 1+2 1.5ºC

  5. SST Departures (oC) in the Tropical Pacific During the Last 4 Weeks • During the last 4-weeks, equatorial SSTs were below average in the central and east-central Pacific and above average in the eastern Pacific.

  6. Weekly Central & Eastern Pacific Upper-Ocean (0-300 m) Average Temperature Anomalies Positive subsurface anomalies were evident from March-July 2011. Negative anomalies developed in late July 2011. The negative anomalies began weakening in January 2012 and have recently become positive.

  7. Sub-Surface Temperature Departures (oC) in the Equatorial Pacific • During the last two months, negative subsurface temperature anomalies became near-average to above-average across the eastern equatorial Pacific. • During the recent period, near-surface positive anomalies are evident in portions of the eastern equatorial Pacific. Time Most recent pentad analysis Longitude

  8. Pacific Niño 3.4 SST Outlook • The majority of models predict ENSO-neutral conditions (Niño-3.4 SST anomalies between -0.5°C and +0.5°C) during the Northern Hemisphere spring, continuing through the remainder of 2012. • The average dynamical model forecast is slightly warmer than the statistical models and favor El Niño conditions during the last half of 2012. Figure provided by the International Research Institute (IRI) for Climate and Society (updated 17 April 2012).

  9. Official Probabilistic ENSO Outlook(updated 5 Apr 2012) ENSO-neutral is favored during the Northern Hemisphere spring and summer.

  10. SST Outlook: NCEP CFS.v2 Forecast Issued 23 April 2012 The CFS.v2 ensemble mean (black dashed line) predicts El Niño conditions to develop by JJA 2012. (not PDF corrected)

  11. Atmospheric Circulation over the North Pacific & North America During the Last 60 Days 200-hPa Wind 500-hPa Height & Anoms. 925-hPa Temp. Anoms. (oC) From mid-February to mid-April, above-average 500-hPa heights persisted over central and eastern North America, accompanied by above-average temperatures. During most of the period, below-average 500-hPa heights and temperatures were evident near the western coast of North America.

  12. U.S. Temperature and Precipitation Departures During the Last 30 and 90 Days Last 30 Days 30-day (ending 21 Apr 2012) temperature departures (degree C) 30-day (ending 20 Apr 2012) % of average precipitation Last 90 Days 90-day (ending 20 Apr 2012) % of average precipitation 90-day (ending 21 Apr 2012) temperature departures (degree C)

  13. Big Convective Outbreak east of the Cascades 6 PM

  14. Satellite • http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?vis1km_west+/24h/2h • http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?ir4km+/24h/

  15. Lightning • http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?ltnw+36 • http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?ir_ltng_common+48

  16. Radar • http://www.atmos.washington.edu/weather/radar.shtml • http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?pdt_ncr+/24h/60m • Otx • http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?pdt_n0v+/24h/60m

  17. Storm Total • http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?ir_ltng_common+48

  18. 24-h precip

  19. Heppner, June 14, 19033rd deadliest flash flood in U.S. history (247)

  20. Not a great forecast by WRF

  21. http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d3_pcp3+2012042312///3http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d3_pcp3+2012042312///3 • Good cape http://www.atmos.washington.edu/~ovens/loops/wxloop.cgi?mm5d2_mcape+2012042312//84/3

  22. Nam only slightly better

  23. HRRR Impressive • http://rapidrefresh.noaa.gov/hrrrconus15min/jsloop.cgi?dsKeys=hrrr_15min:&runTime=2012042318&plotName=cref15min_t1sfc&fcstInc=15&numFcsts=61&model=hrrr&ptitle=HRRR%20Model%20Fields&maxFcstLen=15&fcstStrLen=-1&resizePlot=1&domain=t1&wjet=1

  24. But no obvious trigger…

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