Thursday, February 16, 2017

Strangely Warm Outlook Toward Spring

March Update:

Winter 2016-2017 has officially gone down in the record books as warmest on record (along with the month of February) and the Spring severe weather season is now underway as March roared in loudly. A tornado/severe weather outbreak unfolded from February 28 - March 1st leaving a trail of damage across every state in the Local 6 area (KY, IL, TN, MO). It was exactly 5 years to the date and hour that we were covering a tornado ravaging Harrisburg, IL and  would later hear of its EF4 rating. The same night 5 years later another violent EF4 tornado in Perryville, MO and an EF3 in Crossville, IL from the same parent storm.
One of the main reasons I wrote this particular post is to give us an idea of what we can expect for Spring/Summer 2017. Looking back through historical data it was pretty clear that 2012 was a correlation too close to ignore and might give us the best insight to what may come this season. A weak La Nina episode continues dissolve and a trend toward a neutral signal is expected. 2012 was noted as the 3rd warmest La Nina year on record. In addition to the role of La Nina paying attention to the Arctic Oscillation influence during the transitional seasons (Spring & Fall) tends to produce a more accurate glimpse of possible outcomes. As detailed in the previous update in this post, a negative AO signal allows for arctic air to spill south into the lower 48. That hasn't happened much since December, at least to the point where it impacted the Mid-South. It also makes it more likely that moisture-rich warm air will travel further north from the Gulf of Mexico to fuel storms. When the jet steam does make a dip southward it makes for some wild temperature swings. Much like 2012 the growing season has begun WEEKS earlier than normal and La Nina weakened to a neutral signal by late Spring. It lead to an unrelenting drought and record low river levels.

Warm season lovers are rejoicing with an outlook for a much warmer than average rest of February. "Historically warm" may end up being the case for much of the country's mid-section. A weak La Nina influenced weather pattern has left us with near normal precipitation but the much warmer than average temperatures have been somewhat of a surprise. (Weak La Nina typically brings slightly cooler than average temperatures to the Paducah area for the winter months of Dec-Feb.)

Courtesy NOAA
There is one big exception to this and it was the Winter of 2011-2012. The 2012 calendar year started off very warm leading it to be the warmest year on record and second driest. Highs reached into the 80's during the month of March and drought settled in during the early summer months. Similar to the Winter of 2011-2012, this winter has been under the influence of a weakening La Nina episode. The current outlook is for La Nina to continue to weaken and go Neutral. Another global steering pattern is known as the Arctic Oscillation (AO). It determines if cold air is able to drain south into the north central United States. When the AO is in a negative phase, cold air is funneled southward. Alternatively a positive phase keeps an active jet stream further to our north. This was a large contributor to the record warmth of 2012. We are seeing similar signs of positive signal setting up at least into the beginning of March and the start of Spring.

Land Between the Lakes, KY & TN
Why compare the two? It may give us a hint to what is expected for the Spring and Summer months here in the Mid-South. Our region is already prone to extreme periods of heat and drought and when they occur it leads to devastating results. Brush fires, water loss, insects/pests worsen are just a couple. We should always be ready for heat and drought but expect a higher risk of the occurrence this warm season. As a normal part of combating fire risk, Land Between the Lakes has already planned several prescribed burns to eliminate dry brush fuel.

It won't take much for us to achieve record status wrapping up this Winter (Dec-Feb). December ran just above average at 0.6, January soared above average at 7.8 and so far February is sitting at 5.9 above average. If Winter were to end today, we would finish in 5th for warmest, still shy of the all-time record warm Winter of 1949-1950. The outlook for the rest of February remains well above average. The graphic to the right shows an "average" winter season compared to the noted of the past along with where we are today.
Paducah Area - Courtesy Climate Central 
In the short term a much warmer start to Spring will be great for getting outdoors and for the local recreational economy.  On the down side an erratic weather pattern could bring a late frost or freeze after many of our area crops emerge if they are planted too early during the enticing warmth. Mosquitoes, ticks and fleas will emerge much sooner and will reproduce more in a longer warm season. Long term impacts are more focused on extreme heat and drought. If warm, dry conditions persist long enough it contributes to a positive feedback mechanism, where dry conditions propagate even drier conditions. This usually is a result of a dominant area of high pressure blocking rain-producing weather systems. This is when crop loss, water shortages and wildfire risks increase rapidly.

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