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 wet for California with continued occurrence of troughing in April. A cool, moist pattern is across the Pacific from 175W to 130W…26-44N. There continues support for troughs coming into California from the west. We should expect to see the cool and wet conditions continuing in April.
- The sea surface temperature anomaly (SSTA) pattern across the equatorial Pacific continues to show support for active westerlies into California to bring troughs onshore.
- The sea surface temperature anomaly pattern (SSTA) suggests a continuation of troughing near the California coast, and cold conditions continuing into April, while warmer than normal conditions are in the Central US and Rockies.This pattern supports active cold fronts from NW Canada coming into California from the north, to continue the cold pattern with late season showers and snows in the Sierras and N California mountains. This suggests an active frost season in N and Central California valleys during the spring bloom period in those regions.
- Precipitation Trend: Rain dates March: 28-29, April 1-3, dry periods mid Apr. 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 showers in this late season period on occasion.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
Norcal PRECIPITATION: Apr 1, 4-6,9-11,13, 17-21.
Norcal MILD SPELLS: Apr 3, 8, 15-17 and 26-29.
Norcal COLD/COOL SPELLS: Apr 1-2, 4-6, 9-14, 17-21, 22-25.
Norcal FROSTS/FREEZES: Mar 31, Apr 2-3, 7-8, 12, 14, 21 and 25.
Central Calif PRECIPITATION: Apr 1, 4-6,9-11, 17-21.
Central Calif MILD SPELLS: Apr 8, 13-15 and 21-22.
Central Calif COOL SPELLS: Apr 1, 4-7, 9-12, 17-19 and 23-24.
Central Calif DRY COLD WINDS/FREEZE RISK: Apr 2, 7, 12-13 and 20-21.
Forecast for Southern California:
SOCAL RAINS: Mar 30, Apr 1, 5,10, 18-19.
SOCAL MILD TO WARM SPELLS: Apr 3-4, 7-9, 12-16 and 20-21.
SOCAL COOL OR COLD SPELLS: Apr 1, 5-6, 10-11 and 18-19.
SOCAL FROSTS/FREEZES: Apr 2, 7-8 and 12.
SOCAL SANTA ANAS: Cold dry winds are possible, hot and dry are unlikely.
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: Apr 1, 5, 9-10, 17-20.
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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 April and 2023
Highlights: Generally near normal rainfall in most areas, or a little below normal. Colder than normal, with risk of frosts or light freezes for April, and isolated in first week of May.
Looking Ahead – Long Range Outlook - May 1 - June 30, 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 (per NMME), we finally emerge to brief warmer than normal (hot) period about beginning of June for interior N and Central California. There continues risk of cool periods with showers and thunderstorms central Sierras early to mid June, then much warmer late June to first part of July.
For SOCAL mountains westward to coast: This period currently appears about normal to cool for Apr in SOCAL, but cool in May due to intermittently deep marine layer out at the 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 near to below normal daytime temperatures in May, cool days with drizzly coastal eddy conditions on the windward slopes, but cool to near normal nighttime temperatures in SOCAL for most of May. Showers and TSTMS in mountains mid to late June. Much warmer by late June, with transition to summer monsoonal conditions and mountain/desert TSTMS late June-into July.
For the Sierras: After the cool May with showery conditions in the Central Sierras, we have a cool and showery June too, with mountain thunderstorms (TSTMS). It is possible that surface moisture from soils and fuels may persist well through mid to late May. From there, the expected sea surface temperature anomaly pattern tends to focus over Baja and SOCAL, favoring troughs with SE flow aloft into central and N California in early to mid June, per NMME (Ensemble) forecast map guidance. If this occurs, it could launch us into an active early summer TSTM season in June. To follow the wet season, we should consider a robust mid to late spring growth of fuels/grasses. Following this is the seasonal dryoff of fuels “greenup” by mid to late June, then with an active concurrent period of TSTMS, we could launch rather quickly into a robust fire season by early July.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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