BASIC PATTERN:
Large Scale Pattern –
- We had extremely hot conditions on 6-7th through areas of California away from the immediate coast/beaches, with offshore winds.
- The large scale pattern of recurrent troughs in the northcentral Pacific encourages additional risk of such hot occurrences in California during the mid to late spring, before the onset of the summertime pattern. This pattern is forced by the current pattern of sea surface temperature anomalies.
- Bottom line for growers of avocado and other sensitive orchards and crops in coast, and coastal hills-valleys of central and S California, watch for a higher than usual occurrence of hot days…mid 90s to 100 during these normally cool spring months. Highest probability of near 100 degree temperatures are in the coastal hills and “coastal and intermediate valleys” of S California, and south-facing coastal areas (Santa Cruz, San Luis Obispo Co coast, and Santa Barbara Co. We will also in general see more cold events, possibly frosts, with larger than normal oscillation between abnormally warm and abnormally cold conditions.
- Precipitation trend: Approximate dates of precipitation are: Showers or rains Apr 16, 19-20, 22-23, 29-30, and May 6-8.
- April: Below normal sea surface temperatures are suggested by the latest guidance from the North American Multi-Model Ensemble (NMME) for Apr – June, inclusive. This will tend to support the risk of frost in Apr, on occasion, for NW California coastal valleys, including Mendocino and Sonoma Co’s, and early April in upper Salinas Valley, and San Luis Obispo Co coastal valleys.
- For the N California forests, a key issue is timing of dry-off of seasonal grasses in the Sierras and foothills, and coastal mountains of N California. On satellite imagery, we are already seeing evidence of early onset of seasonal dry-off of grasses bordering the Central Valley on Apr 10. More specifically, we refer to the west side of the Valley: Glenn County south through the Delta and the coastal mountain ranges south of the Delta.
- As we head into May, the combination of colder than normal sea surface along the California coast, and well above normal temperatures in inland valleys of California, including mountains and deserts, may tend to contribute to stronger onshore flow and persistent or recurrent marine fog. For the north and central California coast, this encourages unusually persistent or recurrent conditions for fog drip in the coastal forests beginning in late April and continuing in May, as the spring fog-and-stratus season arrives.
- For May: It turns much warmer than normal away from the coast, and in coastal hills above the marine inversion (1500 ft), and valleys (interior Salinas Valley, Central Valley-both Sacramento and San Joaquin portions, and Delta. Again, the Redwood Coast will tend to be cool and drippy with above normally recurrent onshore flow.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
NORCAL Rains: Apr 16, 19-20, 22-23, 29-30, and May 6-8.
CENTRAL CALIF Rains: Apr 16 (N areas), 20, 23, 30 and May 6-8.
WARM SPELLS: Apr 17-18, 25-27, May 2-3 and 15-17.
COLD SPELLS: Apr 16, 19-23, 29-30 and May 6-8.
FRONTS WITH RAINS: Apr 16, 19, 22 29.
FROST RISK: Apr 15, 17-18, 21, 24-26, May 1-3.
Forecast for S California:
SOCAL RAINS: Apr 16 (Ventura Cnty N), 20 (Ventura Cnty N), 23, 30.
SOCAL WARM SPELLS: Apr 17-18, 25-28.
SOCAL COOL OR COLD SPELLS: Apr 16, 20-23, 30-May 1 and 6-8.
SOCAL FROST PERIODS: Apr 18 21, 24-25, May 1-2.
FRONTS WITH RAINS/DRIZZLE: Apr 16 (drizzle), 20 (drizzle), 23 (drizzle), 30 (drizzle). Light rain possible Ventura Co with these systems.
Central Sierra Nevada:
Dates of mountain rains and snows are: Apr 15, 16-17, 20, 23-24, 30-May 1, and 6-8.
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The listing of dates normally included for hot and cold spells, and precipitation are based on our CFSDaily and CFSDailyAI forecast products, and present expected trends in precipitation and temperature (CFSDailyAI) to 4km. Our system gives some consideration of 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 Apr 15- May 15, 2022
Highlights: Turning consistently warmer than normal for most of mid Apr to 5 May.
Looking Ahead – Long Range Outlook
May 15- June 15, 2022... N and Central California: NORCAL and Central California: Trend toward warmer conditions. We should see a turn to higher snow levels than normal in the Sierras, and above normal temperatures for mid-Apr and May 2022. Near normal rainfall in the Delta and Northern California. Consistently warmer than normal in mid-May onward with some hot conditions (highs in the mid to upper 90s possible around May 15th and also later in the month.
For SOCAL May 15 - June 15, 2022, mountains westward to coast: Progressive trend towards above normal temperature and below normal rainfall for May. There is potential to turn hot and dry again in mid-May, with foothill and coastal valley highs (avocado areas) peaking into the u90s on occasion before a persistent marine layer pattern becomes well established.
In summary, despite a couple of upticks of rains in mid Apr in northcentral and N California, a drier than normal rainy season, overall, is likely, with some seriously low reservoir levels at the beginning of the long dry hot season. Watch for some 100+ hot spells early in the summer season for end of May and in June while cool fogs hang at the immediate coast/beach through most of the days from the end of May through June.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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