Climate discussion: The winter 2017-18 climate pattern is locking in. Here are the contributing factors.
- ENSO: La Nina develops. HOWEVER, La Nina will have limited intensity. Why? Lack of inflow from the cold water currents off the West Coast of North America arcing southwestward into the equatorial Pacific to enhance cooling. The NMME DEC/JAN/FEB 2017-18 global SSTA forecast indicates strong warming in the subtropical southeast Pacific Ocean negating the cool inflow and also implying the Pacific decadal oscillation does not transit to the cool phase which typically happens when La Nina is present.
- Pacific decadal oscillation: As mentioned the neutral phase is present now and a shift toward cool phase is not expected. The slightly cool northeast Pacific coupled with the warm SSTA pattern to the immediate south does imply where the jet stream axis is located which supports a wet fetch into the Northwest U.S.
- The warm southeast North Pacific will propel a steady and reliable warm fetch of air into the U.S. causing warm periods south of snow cover.
- Madden Julian oscillation is active! But! The strongest influence on climate is when the MJO is located across the anomalous warm water of the tropical West Pacific. During these episodes an upstream upper ridge forms over Alaska with the polar vortex amplifying downstream over central to northeast Canada. However, due to the warm influence of the southeast North Pacific a full latitude cold trough will not form.
- The northwest North Atlantic is super warm and likely a contributor to a developing snow belt across Quebec. This region is possibly sneaky cold this winter and the nearby Northeast U.S. to the Ohio Valley is at risk for storms and following cold due to this development. Most likely is high volatility for this region as storms and following cold caused by the polar vortex are separated by periods of mild Pacific influence.
- Research published in The Journal of Climate recently indicates MJO influence on climate during winter is increasing. One result of that assessment is the ability for warming feeding the MJO intensity in the tropics becomes so strong that energy is propelled pole ward and into the stratosphere increasing the risk of sudden stratospheric warming (SSW) episodes. These regimes are what cause the sudden emergence of frigid arctic air in the northern latitudes which inevitably release into the middle latitudes. The U.S. is at risk for one (maybe 2) of these events this winter season.
