End of Month Storm Threat Could Precede Active February Pattern…
Old man winter has returned in a big way over the past week, complete with severe cold, bitter wind chills, and significant snow across much of the Northeastern US. Our brief January thaw has transitioned into a highly amplified, meridional pattern, as the EPO continues strongly negative. This north Pacific / Alaskan block has been a mainstay of winter 2013-14, and if one examines the SSTA profile in the Pacific, ocean temperature anomalies persist well above normal south of Alaska. Thus, the signaling remains for a positive feedback cycle of building the mid level ridge over Alaska, and maintaining the cross polar flow from Siberia/Arctic into Canada.
There are indications that some of the global indices will undergo a significant change mid/late next week, and this should play a large role in the end of January storm thread which will be discussed here. Prior to that potential, we have a light snow accumulation event coming Saturday, the 25th, with potentially (as it stands now) another light accumulation early next week. The threat for a more moisture laden, Miller A storm exists beyond the middle of next week, particularly in the January 27th-February 2nd. Let’s put together the meteorological pieces for why this potential does in fact exist.
Tropical forcing has recently awakened as the latest MJO wave is progged by most model guidance to progress through phase 7. MJO phase 7 in January generally argues for the development / persistence of -EPO blocking, PNA ridging, and Arctic/NAO blocking as well. MJO phases 7, 8, and 1 are the most conducive for sub tropical jet activation and so I wouldn’t be surprised to see models beginning to detect a stronger southern stream short wave for later next week. So far this winter, the dominant snow producer has been northern stream Miller B type short waves. These are systems which can provide significant to major snows given the surrounding synoptics are favorable for tilting and deepening near the east coast. Miller A type storms, however, originating in the sub tropical jet stream, often are moisture laden and bigger snow makers.
Below is the MJO phase 7 500mb composite. Notice the ridging in the West, across the arctic, and in the NAO regions.
