Weather

Red tells the story: California drought still big and bad


On this map above of precipitation so far during the water year that began Oct. 1, red is bad — under 25 percent of normal. Those splotches of darkest, scary red you see out in the lower desert and a few other places — that means under five percent of normal. This is after the heavy rainfall last week in Northern California. Orange areas are creeping up toward 50 percent of normal. Better, but still not green or blue.

drought-secerity-map-noaa.jpgAnother way to view the situation is on this drought monitor map from NOAA. The blanket of red across much of Califronia marks the area of extreme drought. The brown swath is classified as "exceptional drought." You can check out both maps larger and with their explanatory legends at the California Weather Blog, which notes the likely return of the Ridiculously Resilient Ridge of high pressure that the blogger named earlier in the state's current epic dry cycle.

Here is an excerpt of the blog's latest take:

While the recent atmospheric river did bring much-needed precipitation to parts of Northern California, California is unquestionably still in the midst of an extraordinary drought. The most recent update of the Drought Monitor depicts a slight (and likely temporary) reduction in the severity of the drought over parts of NorCal that received heavy precipitation from the atmospheric river, but the core of the drought region remains in “exceptional” territory–the most severe categorization....


Many readers may be wondering about the fate of the RRR, which has been a frustratingly persistent feature of our weather over the past 14 months. It’s certainly true that the ridge in the northeastern Pacific has weakened considerably over the past two weeks, and the portion over the Gulf of Alaska has essentially disappeared. At the same time, the semi-permanent East Pacific subtropical high has remained unusually strong for this time of year, which is the primary reason that Southern California has remained high and dry even as far northern parts of the state have recently received substantial precipitation.

Unfortunately, it now appears that the RRR may try to make a comeback during the second half of February. Recent model solutions are bringing considerably drier and more stable conditions back to California after the coming week’s light rainfall, and the ensembles are starting to hint at an all-too-familiar pattern of geopotential height anomalies over the northeastern Pacific.

The RRR, as defined back in December, is not a categorically monolithic feature–it has waxed and waned considerably during its period of relevance, shifting around between the central North Pacific east of the Aleutian Islands in the Gulf of Alaska in the west and the Pacific Coast of North America in the east. In general, though, a region of high-amplitude ridging and associated highly-anomalous wind patterns have been present somewhere within this box more often than not since last January. Despite slight breaks in the ridge’s dominance and longitudinal shifts in its primary axis, this atmospheric pattern has ultimately resulted in the extraordinary persistence of record-dry conditions throughout California. For this reason, I’m reluctant to announce the “death” of the RRR until we’ve experienced at least a month of more typical atmospheric conditions.

Unfortunately, it now appears that the RRR may try to make a comeback during the second half of February. Recent model solutions are bringing considerably drier and more stable conditions back to California after the coming week’s light rainfall, and the ensembles are starting to hint at an all-too-familiar pattern of geopotential height anomalies over the northeastern Pacific.


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