Thursday, February 4, 2016

The Weakening of El Nino - Spring Outlook

Signs might be pointing to El Nino moving past it's peak intensity for this particular episode while moving toward a neutral phase by Spring. Below is an animation that showed the beginning of the 2015-2016 El Nino episode then toward the very end starts to show a drop in Sea Surface Temperature anomalies. This may very well be a signal of El Nino weakening.

This same trend has also been picked up in forecast computer models projecting a neutral phase by late Spring and even suggesting a weak La Nina phase by late Summer. Below is a look at the latest computer model projections all the way through the start of Fall 2016. Each line color represents a different model forecast. The closer the line is to "zero" the more neutral the phase is expected. The solid yellow line is the average of all the model forecasts. Most of the models agree on an El Nino phase (positive 0.5+) until the AMJ (April-May-June) time frame. This would suggest a slowly weakening El Nino through late Spring.

Many are wondering what that would mean for our weather here in the Mid-South. El Nino primarily has its greatest influence during the winter months for the Mid-South. We tend to see near average precipitation and warmer than average temperatures. With a weak El Nino signal taking us into Spring, we could see a slight uptick in severe weather events but also likely start to see a break from above average temperatures and continue with average rainfall. It all really depends on where the jetstream continues to set up for the remainder of winter.

Here is another look at how the weather pattern typically looks like during an El Nino event:

Friday, January 29, 2016

Tuesday Thunderstorms - Severe Potential

Monday AM Update:
This morning's look at the risk area from the Storm Pediction Center is still pretty close to what we've been seeing the past couple of days. Kentucky and Tennessee are included in the ENHANCED risk and everyone in the Local 6 area is covered under the SLIGHT risk area. To see how each risk area is defined, see the Sunday PM Update below. 

Sunday PM Update:
The Storm Prediction Center has updates their outlook and it still places KY/TN in the area for greatest risk for severe storms on Tuesday. A few showers and storms will be possible late tonight and early tomorrow as an initial weak front passes through the area. By Monday evening, a warm front will lift back north across the Local 6 area, bringing back the moisture needed for Tuesday storm development. 
Here is a closer look at timing of the main line of storms expected on Tuesday:

Friday PM Update: 
All signs have pointed to a major storm system developing in the heart of the central plains on Monday, moving east on Tuesday to bring the threat of strong/severe storms to the Local 6.
Since early this week, computer models have indicated the development of this storm system and the threat of severe weather associated with it. Over time the risk area has been more defined to include the Mid-Mississippi  and Tennessee Valleys. 
An initial chance of rain will arrive Sunday into Sunday night as a warm front lifts north across the Local 6 area. A weak front will pass through early Monday bringing a brief period of cooler, drier air. Another warm front will lift back north across the region late Monday night and early Tuesday allowing warmth and moisture to return to set the stage for the larger storm system. The timing of storm development will coincide with the heating of the day and any sunshine that might break through will further destabilize the atmosphere in Kentucky and Tennessee leading to the highlighted risk area above. 
Damaging winds will be the greatest concern with storms that move across the area. There will also be a threat of isolated tornadoes, particularly as storms begin to develop Tuesday afternoon. 
Of course this storm system is still several days away so timing may change a little but I wanted to give you a heads up going into the weekend. Updates will be forthcoming over the weekend and we'll see if a Weather Authority Alert Day will be necessary.
Our area is typically a target for organized lines of storms that bring embedded weak tornadoes and damaging winds. Here is a look at the average number of times we see these types of events during the cold season, each decade:
Courtesy: Storm Prediction Center

Here is a link to severe weather preparedness from The Weather Authority, WPSD Local 6.