Fig. 1-3: The 3rd warmest (on record) “warm blob” in the northeast Pacific Ocean during late summer has weakened with the attendant ocean warming shifting to the North America West Coast well-correlated to the early autumn upper level high pressure ridge causing the California fires.
Discussion: Possibly the greatest influence on North America climate during the past 7 years is the evolution of the persistent very warm waters of the northeast Pacific Ocean referred to by climate scientists as the “warm blob”. The “warm blob” caused the 2013-14/2014-15 “polar vortex” winter seasons and the persistent Western U.S. drought of recent years plus many other high impact climate regimes most perilous to North America and particularly the U.S.
During late summer 2020 the “warm blob” reached its 3rd strongest signature on record. However, due to a recently persistent presence of an upper level cold trough across the Gulf of Alaska the “warm blob” has cooled and the attendant warm ocean has shifted east to the waters off the West Coast of North America (Fig. 1). The 2-week SSTA change identifies the much cooler trend south of Alaska and the much warmer change off the West Coast (Fig. 2).
The upper air pattern has a tendency to ridge over water waters and trough over cool waters for long periods of time. The most recent northeast Pacific Ocean change has foreshadowed a resurgent intense upper ridge pattern on the West Coast (Fig. 3) which has inspired high wind, dry weather and anomalous heat in California as a new round of wildfires develops and expands.
West U.S. traders/risk managers: The SSTA changes identified pose an interesting question for western U.S. autumn climate. If the trough pattern in the Gulf of Alaska were to amplify the southwest energetic fetch in the upper atmosphere would cross the warm waters off the U.S. West Coast and entrain the high low atmosphere water to unload rain on the Western U.S. drought area (including northern California to the Canadian West Coast). But! If the upper trough does not strengthen and the upper ridge on the West Coast is sustained the dry pattern will continue.
Forecast models showed signs of trending toward the wetter scenario in late September but are now backing off as some models are now maintaining the West Coast ridge and preventing the Gulf of Alaska low pressure area from producing rainfall on the U.S. West Coast and limiting the duration of will be briefly heavy rain on the West Coast of Canada.
Short-term dangerous conditions continue California: NOAA/NWS offices have expanded the Heat Advisory and Red Flag Warning for most of the California Coast which includes San Francisco, Los Angeles and San Diego. Excessive heat, 15-25F above normal in some locations and high wind will continue to cause existing fires to spread and new fires to form today. The extreme weather conditions ease only slightly tomorrow.