Strong storm headed for California this week; compelling signs of developing El Nino...
but will the RRR return in the meantime?
http://www.weatherwest.com/
Recent Weather Summary
Unusually dry and warm conditions have returned to California over the past week. In the wake of the atmospheric river event two weeks ago, high pressure built back over the far eastern Pacific and has acted to deflect most storm activity to the north of California, which is a pattern very reminiscent of the one that has been seemingly locked in place for many months over the same general geographic region. What differentiates the present atmospheric ridging from the much-maligned “Ridiculously Resilient Ridge,” however, its is lack of persistence. The fairly high-amplitude ridge currently in place will be undercut by an impending surge in strong westerly winds over the coming week, which is something that hasn’t happened to any meaningful extent in over a year
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Strong storm for all of California on Friday/Saturday
It’s not all doom-and-gloom, however. A drastic, high-impact pattern change is on the way that is likely to affect the entire state of California this week, bringing an excellent chance of soaking rainfall all the way from San Diego to the Oregon border. In fact, it currently appears that two storm systems will move ashore this week, though the first one will bring only light to moderate precipitation to the northern part of the state on Wednesday. All eyes are currently focused on the second storm, scheduled arrive on Friday. For the first time since December 2012, a deep, well-developed trough will arrive just west of the California coast and direct a deepening low pressure center over the Golden State. This trough and associated surface low pressure system will coincide with the appearance of a temporarily enhanced East Pacific jet stream, which together will set the stage for a substantial statewide precipitation event.
GFS depiction of impressive Friday/Saturday storm. (NOAA/NCEP)
California will be located underneath a region of strong upper-level divergence in the favorable left exit region of a strong jet streak rounding the base of this deep trough, which will allow the surface low to deepen as it approaches the coast on Friday. Given the presence of a sub-1000mb surface low near the NorCal coast, a strong Pacific jet overhead, strong upper-level divergence, and the presence of more than adequate lower tropospheric moisture, most of the necessary ingredients will be in place for a pretty impressive storm event across much of California, especially by the middling standards of the past year or so.
Heavy precipitation can be expected for at least brief period in many locations, especially near the time of cold frontal passage. Strong upward vertical motion and modest near-surface instability suggest the potential for convective activity as well, with possible high rainfall rates and thunderstorms (especially across Southern California). Strong and gusty winds may also be an issue, especially given the proximity of the surface low to the California coast and the potential for convection to mix strong winds aloft down towards the surface. I actually expect precipitation amounts to be surprisingly uniform from north to south, with generally 1-3 inches both along the coast and inland all the way from Eureka to Los Angeles, with areas to the south potentially seeing somewhat less than that but orographically favored regions (especially the Transverse Ranges in SoCal) locally seeing 3-5 inches. While these totals are well under the highly localized extreme 10+ inch values observed in NorCal during the recent atmospheric river event, I expect that this storm will bring more water to California overall given the widespread nature of the precipitation. Brief flooding of vulnerable urban areas and small streams will be possible given the potential for high rain rates. This will be a fairly cold storm system, and hugely beneficial snowfall on the order of 2-3 feet can be expected at pass level in the Sierra Nevada.
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keeping my fingers crossed
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