四月改善的味道？尽管SoCal保持干燥
最干燥，最温暖的1月至4月中旬在加利福尼亚
从天气和气候的角度来看，这是加利福尼亚州日历年的一个非凡开始，而不是很好。降水量如此之低，以至于它已经破坏了北部和加利福尼亚州中部几乎所有地方的1月 - 中期降水量的所有记录，因此也在全州范围内。此外，相对于历史记录，CA的历史记录中，创纪录的热量已将平均温度提高到非常高的水平 - 除了低降水记录外，日历年还经历了记录的前5个最温暖的开始。结果，内华达山脉的积雪以创纪录的速度下降 - 在全州范围内，日期的平均水平低至平均水平的22％。野火现已在全州范围内进行了几个月，而萨克拉曼多的NWS本周早些时候发布了最早的春季危险警告。
ph。
但是至少在短期内，我确实有一些更好的消息要报告（至少在该州的北部地区）！
短期内某些（意外的）好消息：某些地区可能会入站。
Multi-model ensembles have now converged on a North Pacific weather set-up that will favor wet conditions over the northern third of California for the next 7-10 days. In fact, the ensembles have trended slightly wetter as the potential event has come into focus–a welcomed change from the trend during much of this winter. As it currently stands, it appears that an anomalously deep NE Pacific trough will set up shop off the West Coast later this week, allowing 2 or 3 weather systems to cycle through over the next 7 days or so. While these systems will probably be confined to NorCal, with nearly all precipitation staying north of Monterey Bay, some spots along the North Coast and in the Northern Sierra could end up seeing pretty substantial accumulations of 2-3 inches of liquid equivalent (locally 5+ inches in the very wettest spots over the course of 7-10 days). While these precipitation totals are still quite small relative to accumulated annual precipitation deficit (which is running as high as 25-35 inches in some of these wetter NorCal spots), they will be pretty notable for an event occurring this late in the season. And while these will not be particularly cold storms, nor will they be particularly warm storms: it appears that there could be some pretty decent snow accumulation above 5,500 feet or so. In fact, I do expect statewide SWE to recover (though only modestly), perhaps getting back up as high as 30-35% of average for the date by Apr 20th or so (which is still, needless to say, really low–but better than it was).
Lower elevation areas away from the North Coast will be a bit more of a wildcard. Much of the Bay Area and Sacramento Valley stands a good shot at soaking rainfall from this pattern as well–probably 0.5 to 1 inches in many spots (although with the caveat that there could be substantial rain shadowing in some inland valleys). SoCal will mostly remain dry–perhaps completely so–though the period, so it is mainly the northern third (and to a lesser extent, the northern half) of CA that will reap the benefits of this upcoming pattern shift.
罪魁祸首：重新定居西太平洋台风（是的，又是其中之一）
这背后的罪魁祸首是什么明显unexpected mid-April reprieve (perhaps leading to, given the apparent imperative to give an alliterative name to it, April Ameloriation)? As far as I can tell, it appears that the unusually deep West Coast trough/low that will be proximally responsible for the wet conditions in NorCal can be traced to the indirect effects of a recurving West Pacific Typhoon (Malakas).
这可能是一个老调r为长期的博客eaders: a significant fraction of “surprising” early and/or late season (autumn and/or spring) precipitation events (even in extreme drought years) in California appear to be driven by the perturbation of the North Pacific jet stream by the injection of moisture and vorticity well upstream. Often, these ingredients are contributed by strong tropical cyclones (drawing their energy from the warm oceans) that rapidly weaken and transition into extratropical cyclones (drawing their energy from the latitudinal temperature gradients in the atmosphere) as they move over much colder waters and become injected into the usually powerful jet stream over the NW Pacific. In doing so, these moisture/spin injections can pump up ridging over the Central Pacific in such a way that can cause either a strong ridge (with warm and dry conditions over CA) or a strong trough (with cool and wet conditions over CA), depending on the exact longitude at which it occurs. Fortunately, in this case, it appears that a wetter/troughier outcome will come to pass. It is worth noting that such occurrences–where a significant fraction of the seasonal (in this case, spring) precipitation falls essentially during a single event–are virtually impossible to foresee at seasonal prediction scale. (So there can be, and probably always will be, the potential for these kinds of events to “surprise” us in the final hour even during the driest years.)
长期仍然暗示着加剧干旱和不良的火灾季节，但模式仍可能带来切实的短期缓解
From an ecosystem and wildfire perspective in NorCal, all this late season precipitation will be good news. It will probably contribute some modest transient streamflows and will measurably bolster mountain snowpack, perhaps taking the edge of now-extreme drought conditions in many of these areas. It will also put a damper on fire season for a 2-3 week period in many parts of NorCal–no small thing these days, and perhaps extending the window for prescribed burning and ongoing fuels reduction projects further into May. One downside may be from an agricultural perspective: substantial late season rainfall can damage a number of crops that are commonly grown in the Central Valley (though it does look like the San Joaquin will mostly likely be too far south to see much precipitation out of this). But overall, it is nice to be able to report that a substantial swath of the state will see some quite respectable precipitation over the next 7-10 days. Thereafter, things do appear likely to dry out again by late April, with a return to ridging and somewhat warmer conditions.
新研究：在美国西部极端野火条件下，气候变化正在增加极端降水的风险
我的同事和我有最近发表了一些新研究查看在温暖气候下极端野火燃烧条件下极端降水事件发生的变化。我们发现，气候变化正在增加整个美国西部的极端危险造成的火灾状况，尽管在某些地方比其他地方更快。有趣的是，极端降水事件的增加同样重要（如果不是在本地！），而极端火灾的增长在推动整体趋势方面的增长 - 强调考虑放大水文硬币两面的重要性温暖的气候。
The original paper, led byDr. Danielle Touma，，，，所有人都可以在科学进步中完全开放访问权限。
有关我们的发现，方法和更广泛含义的更详细概述，请查看几周前的Twitter线程：
