BASIC PATTERN:
Large Scale Pattern –
- We note that the sea surface temperature anomalies and IVTinit, with a circulation Center near 140W 44N maintain a pattern that is intermittently very wet for California with unusual back to back atmospheric river (AR) systems. A mild, moist pattern is across the Pacific from 175W to 130W…26-35N. There is even a recurrent storm track that keeps recurring just north of Hawaii! There continues support for troughing into California from the west. We should expect to see the highly unusual rains recurring to the end of March, and at times during the first part of April.
- Combined with the rains in Dec 2022, and Jan – Feb 2023 the Sierra Nevada range has some impressive positive departures in the snow amounts. California, and southern portions of the state have had some of the wettest periods for snowfall and snowpack water equivalent, with low snow levels recorded in California. The state snowpack water equivalent stood at 215% of normal on 12 March.
- Deep troughing (GFS) and the sea surface temperature anomaly pattern (SSTA’s suggests a resumption of above normal rainfall for northern California, Bay Area north, and in the Sierras from about Lake Tahoe as well as central Sierras northward. The current pattern supports more late season rains and mountain snowfall at the higher elevations through the end of March.
- Southern California has seen record precipitation events, both rain and snow. San Bernardino County mountain areas, and the Santa Barbara and west Ventura County foothills and mountains have received intense rainfall, and we expect this pattern to continue.
- Precipitation Trend: Rain dates March: 20-23. 24, and 29 for the general trend.
- For the rest of Mar, and into first part of Apr: below normal temperatures in most of California and the Pacific Northwest states from NMME and CFSv2 models. Above normal precipitation continues possible in Humboldt-Del Norte Co’s of NW California. Cyclogenetic zones near the California coast, and near S California suggest recurring support for significant rains in this late season period on occasion.
- At some point we will, according to the CFSv2 and NMME, transition to a drier and warmer trend. These short term climate models were suggesting that to begin in Feb, but it did not.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
Norcal PRECIPITATION: Mar 20-23, 24-25, 29-30 (shwrs), Apr 2-3,6-7,16.
Norcal MILD SPELLS: Mar 27-28 and Apr 9-14.
Norcal COLD/COOL SPELLS: Mar 20-25, 29-Apr 3, 6-8 and 16.
Norcal FROSTS/FREEZES: Mar 26-27, 31-Apr 1, 4 and 8-9.
Central Calif PRECIPITATION: Mar 20-23, 25-26, 29-30, Apr 6.
Central Calif MILD SPELLS: Mar 28, Apr 4-5 and 10-14.
Central Calif COOL SPELLS: Mar 20-27, 29-31, Apr 6-7.
Central Calif DRY COLD WINDS/FREEZE RISK: Mar 28, Apr 1-2 and 8.
Forecast for Southern California:
SOCAL RAINS: Mar 20,21,22, showers 24, rain 29.
SOCAL MILD TO WARM SPELLS: Mar 27-28, Apr 1-3, 5-6, 9-14, 17-18.
SOCAL COOL OR COLD SPELLS: Mar 20-24, 29-30, Apr 7-8, 16.
SOCAL FROSTS/FREEZES: Mar 25 and 31.
SOCAL SANTA ANAS: Mar 23, 25 and 30.
In May the thermal forcing for strong and persistent coastal onshore flow is normally near its seasonal maximum, with the sea surface still cold, while inland temperatures by end of May experience the seasonal warmup.
Forecast for Central Sierra Nevada:
Central Sierra Nevada Precipitation: Dates of rain or snow: Mar 20-22, 25-27, 29-30, Apr 3, 6-7.
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The listings of dates normally included for hot and cold spells, and precipitation are very approximate. They are based on our CFSDaily and CFSDailyAI products; and present expected trends in precipitation and temperature (FoxCFSDailyAI) to 5km. Our system gives some consideration to terrain and coastal influence. We consider the CFSv2 as one of the better ways to represent basic weather down in the sub-monthly time scale beyond the 15 –day GFS or monthly maps from CFSv2 or NMME.
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Southern California Deserts Outlook for Mar 12 - April 15, 2023
Highlights:Generally near normal rainfall in most areas, or a little below normal.
Looking Ahead – Long Range Outlook - Apr 18 – May 31, 2023
NORCAL and Central California coastal valleys, and Central Valley: In general, during this period, CFSv2 emerges from the abnormally cold conditions of March for N and Central California. After some cool and showery periods in early to mid May, we finally emerge to warmer than normal (hot) periods by the beginning of June for interior N and Central California. There continues risk of a cool period with showers central Sierras mid June.
For SOCAL mountains westward to coast: This period currently appears about normal for temperature in Apr for SOCAL, but turning cool in May due to intermittently deep marine layer coast-coastal valleys. This is forced by currently below normal sea surface temperatures.
Precipitation in mountains and deserts: Below normal for most areas except near normal in some mountain spots.
For SOCAL coast and valley areas: Watch for below normal temperatures in Apr, cool days with drizzly coastal eddy conditions on the windward slopes, but about normal nighttime temperatures in SOCAL for May. After the cool May with showery conditions in the Central Sierras,and recurrent deep marine layer/drizzle coast and coastal valleys, we turn to warmer conditions in June as high pressure builds aloft in early summer.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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