The extreme to exceptional drought in California is likely to get worse this winter. La Niña, is predicted to redevelop this winter. La Niña involves intensified organized thunderstorm activity over Indonesia and the western tropical Pacific ocean and intensified subsidence of the east Pacific high pressure area west of California. A sea surface temperature pattern with warmer than normal water in the tropical western Pacific and in the oceanic region centered between Alaska and Hawaii is already in place that will tend to send the jet stream north of California and the southwest. The welling up of cold water in the equatorial eastern Pacific and intensified convection over Indonesia associated with La Niña will further increase the intensity of the eastern Pacific high, keeping the storm track north of California. The Climate Prediction Center has just issued a La Niña watch that forecasts a 70%-80% chance of La Niña developing this northern hemisphere winter. www.cpc.ncep.noaa.gov/…
Parts of California are already suffering from record drought conditions. The watersheds of the southern Sierra Nevada were extraordinarily dry last winter and last rainy season was the second year of very low rainfall. A third year in a row could be disruptive to water supplies for both cities and agriculture. Here’s a summary from the Californiawaterblog.com
Droughts and this drought in California
- California has more hydrologic variability than any state in the US, meaning that we have more drought and flood years per average year than any other state. This is a problem, but has also meant that we have designed for droughts, which are always testing us.
- 2021 is the 3rd driest year in more than 100 years of precipitation record. 2020 was the 9th driest year in the precipitation record.
- Much warmer temperatures are further reducing streamflows and aquifer recharge, and has lengthened and deepened the wildfire season.
- Large reductions are occurring in surface water available for agriculture, especially in the San Joaquin Valley, but also in the Sacramento Valley and smaller river valleys statewide.
- Much increased groundwater pumping greatly reduces agricultural impacts, but affects rural wells.
- Major forest and aquatic ecosystem impacts are occurring, especially for wildfires and salmon runs, particularly for winter-run salmon downstream of Shasta Dam.
- A growing number of small communities and towns are being affected, in addition to more common problems for rural household and community wells. Santa Clara Valley (San Jose area) is the most-affected major urban area, seeking 30% water use reductions.
Because of La Niña and the northern hemisphere pattern of ocean heat anomalies favors a third year of drought, the water supply situation in California is likely to get much worse and another year of devastating fires can be expected in 2022. The polar vortex disruption forecast for the coming winter is below the fold.
Reports will come out soon of an apparent recovery year for sea ice. A stormy, cloudy summer in the north polar region slowed melting in the central Arctic basin and dispersed ice towards Alaska. The minimum Arctic sea ice extent this September will be significantly higher than last year. However, that is not the whole story. The ice has been spread thin and very little multi-year ice remains. The thickness of the ice is at or near a record low.
Moreover, Warm water from the north Atlantic has pushed into the seas northwest of Greenland raising the heat content of waters there to exceptionally high levels.
Warm water and very low sea ice extent on the Atlantic side of the Arctic tends to displace the polar vortex towards the Atlantic in the late fall into midwinter and can lead to sudden stratospheric warmings and the breakdown or extreme displacement of the polar vortex in midwinter. The combination of La Niña and low ice in the Barents sea enhances the chances of a major stratospheric midwinter warming by amplifying temperature gradients across Eurasia. Click the link for a video by Dr. Judah Cohen and associates explaining recent research on how the polar vortex instability is connected to low sea ice and ocean heat on the Atlantic side of the Arctic www.aer.com/…
PBS did an excellent piece in understandable language on the paradox of extreme winter weather in the warming climate that explains the situation we may face this winter.
One detail of the PBS piece could be updated based on the recent research report by Cohen and associates. Energy gradients are actually increasing across Eurasia as sea ice melts because the oceanic heat north of Scandinavia leads to more Siberian snowfall and intensification of the Siberian high pressure area in late fall into early winter. It can cause a major ridge in the jet stream north of Scandinavia and a deep trough of very cold air to form downstream over Siberia. An early season version of this pattern may be seen in the 8 to 14 day forecast. This pattern favors early fall intensification of the polar vortex followed by midwinter destabilization. The vortex may break down or be displaced in midwinter because so much heat is sent upwards towards the top of the stratosphere by breaking atmospheric waves that the hot air displaces or breaks up the vortex.
The CFS model forecast made using today’s conditions to predict midwinter atmospheric dynamics is picking up on the potential for a stretched of destabilized polar vortex. The model made a similar forecast last winter and got it right. The extreme Texas cold wave was caused by a polar vortex destabilization event that the CFS forecast months ahead of time. The present CFS forecast for February is quite extreme in pushing the cold air towards central and eastern north America as the result of a forecast major weakening and displacement of the stratospheric polar vortex.
I have been tracking the CFS model forecasts since about 2015 and the impacts of ocean heat on weather and climate since 1980. There are many complexities to seasonal forecasting and all of the models don’t have the capabilities to get the timing of events right months ahead of time. The CFS model doesn’t work well in the tropical Atlantic where low density Amazon river water inhibits the upwelling of the water beneath it. It doesn’t work well around Antarctica where glacial melting has created a fresh water layer that has stabilized sea ice and kept Antarctica and its offshore surface waters cold. However, the CFS model has had success in predicting polar vortex destabilization events. Presumably, this is because the ocean heat anomalies associated with La Niña and the loss of sea ice north of Scandinavia involve massive amounts of energy that are so large that they impact the weather for the coming fall and winter.
Don’t expect the details of this CFS temperature forecast to be exactly right. I follow these forecasts from week to week and month to month and they are not necessarily consistent. Moreover, l look at a number of other models including the European ECMWF. Based on my experience of interpreting the model results integrated with my experience in tracking the impacts of ocean heat on weather, the displacement of cold air forecast towards north America by the CFS model for this coming February has enhanced odds (over normal) of happening.
The latest model run on the 12th of September shows the polar vortex disruption beginning in January with the intrusion of cold air into north America peaking in February, but much can happen between now and then to change the forecast. Expect the weather to get weird.
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