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2011 Arklamiss Warm Season Outlook

2011 Arklamiss Warm Season Outlook. NWS Jackson. Winter Outlook - Recap. Precipitation: South of US Highway 82: 50% chance of below normal, 30% chance of near normal, 20% chance of above normal

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2011 Arklamiss Warm Season Outlook

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  1. 2011 Arklamiss Warm Season Outlook NWS Jackson

  2. Winter Outlook - Recap • Precipitation: • South of US Highway 82: 50% chance of below normal, 30% chance of near normal, 20% chance of above normal • Verification since December 1: Jackson 3” below normal, Meridian 6” below normal, Tallulah-Vicksburg 5” below normal, Hattiesburg 6” below normal • US Highway 82 and North: 30% chance of below normal, 40% chance of near normal, 30% chance of above normal • Verification since December 1: Greenwood 5.5” below normal, Greenville 8” below normal

  3. Temperatures • Highly variable, but expected to average out above normal for temperatures • Verification: Bust! Temperatures have averaged below normal everywhere • Severe weather: • 50% chance of above normal severe weather, 30% chance of near normal, 20% chance of below normal • Verification: Above normal tornadoes, primarily November 29 and New Year’s events • Winter Weather • Below normal likelihood of a significant snow event, Near to somewhat above normal risk for a significant icing event • Verification: Icing correct, snowfall wrong

  4. Why So Cold? Persistent East Coast Trough Negative NAO

  5. ENSO Status • Currently in a moderate to strong La Nina episode • As is typical, the La Nina should weaken through the spring • Expected to become neutral this summer El Nino La Nina Forecast Current

  6. Spring Outlook - Methodology • Look for years in which the La Nina phase was similar to this year • 1976, 1989, 1999, 2000 were the best matches • Look at other key atmospheric and oceanic indices to see how they match • Use typical La Nina impacts for the region, CPC forecasts, and impacts during the analog years and extension of recent trends, to give some probabilities as to what the spring may bring

  7. La Nina Impact • El Nino/La Nina is the prime driver of the global atmospheric pattern, although there are other important processes at work • The La Nina impact is clearest during the winter season (and the tropics in the summer); not as defined during the rest of the year • Overall, trend toward warmer and drier than normal, particularly in the southern sections of the Arklamiss Typical Spring La Nina Rainfall Patterns

  8. CPC Spring Outlooks Temperatures Precipitation

  9. Spring Flooding – Arklamiss Rivers • Rainfall has been below normal nearly everywhere last 90 days • Combined with forecast near to below normal spring rainfall – below normal spring flood threat % of Normal Precipitation Last 90 Days

  10. Spring Flooding – Miss River 2-4” of liquid water in the upper MS Valley Most of the snow in the OH and mid-MS valleys has melted in the last 5 days This reduces the risk to the lower MS valley Above normal rain forecast in Ohio Valley, but below normal in Arkansas/Red Overall, expect near normal flood threat for the lower Mississippi River Snow Water Equivalent in Inches

  11. Spring Flooding – Miss River

  12. Severe Weather • Average number of tornadoes (Feb through May): • All years: 28 total, 11 strong • Analog years: 36 total, 12 strong • Three of the four years were above normal for tornadoes and strong tornadoes • Some notable severe weather events occurred during the analog years • March 26, 1976 “Simpson County” • March 29-30, 1976 • April 14, 1999 Moss Tornado Event

  13. Decadal Tornado Trends 41 strong tornadoes since 2006 – almost as many as the entire previous decade

  14. Sea Surface Temperatures Cooler than Normal

  15. Spring Outlook • Temperatures: 50% chance of above normal, 30% chance of near normal, 20% chance of below normal • Precipitation: 50% chance of below normal, 30% chance of near normal, 20% chance of above normal • Slightly higher chances of near/above normal rainfall in northern parts of area • Severe Weather: Equal chances of near/above/below normal (no clear signal) • Flooding: Below normal on area rivers; near normal on the lower Mississippi

  16. Peek at Hurricane Season Warmer than Normal

  17. Peek at Hurricane Season • Warmer than normal Atlantic sea surface temperatures • Favors above normal tropical season • Neutral or weak La Nina conditions expected this summer • Favors above normal tropical season • Active period of “multi-decadal” signal favors more active than normal conditions • Gray-Klotzbach December forecast: 17 named storms, 9 hurricanes and 5 major hurricanes (normal is 11, 6, 2) • NOAA forecast will be issued in May

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