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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 - PowerPoint PPT Presentation
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2011 Arklamiss Warm Season Outlook
NWS Jackson
NWS Southern Region
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
NWS Southern Region
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
NWS Southern Region
Why So Cold?
Negative NAO Persistent East Coast Trough
NWS Southern Region
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
CurrentForecast
NWS Southern Region
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
NWS Southern Region
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
NWS Southern Region
CPC Spring Outlooks
Temperatures Precipitation
NWS Southern Region
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
NWS Southern Region
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
NWS Southern Region
Spring Flooding – Miss River
NWS Southern Region
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
NWS Southern Region
Decadal Tornado Trends
41 strong tornadoes since 2006 – almost as many as the entire previous
decade
NWS Southern Region
Sea Surface Temperatures
Cooler than
Normal
NWS Southern Region
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
NWS Southern Region
Peek at Hurricane Season
Warmer than
Normal
NWS Southern Region
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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