BASIC PATTERN:
Large Scale Pattern –
- We start with a dry period of the last week of April. There are few periods of showers in May…5-7 and 10-12 in the nearest term.
- The large-scale pattern of recurrent troughs in the northcentral Pacific encourages additional risk of short hot events in California during the late spring, until the onset of the summertime pattern. This pattern is forced by the current sea surface temperature anomalies, which are colder than normal off the California coast for 100-150 miles.
- Bottom line for growers of avocado and other sensitive orchards and crops in the coastal hills-valleys of central and S California, watch for a higher than usual occurrence of hot days…low to mid-90s during the periods of late May and June. The highest probability of near 100-degree temperatures is in the warmest intermediate valleys as high pressure rebuilds behind cold fronts. Some highs of 110-115 are possible in SOCAL inland valleys and inland foothill areas during the June heat waves. This includes highs in the 103-108 range in hilly areas near Escondido-Fallbrook, and 110-116 in Riverside, Perris, Hemet, as well as the southern Deserts (Imperial and Coachella Valleys) of S California. Other areas that are more normally hot in such early summer heat waves are: counties of Kings, Kern, Tulare, and the lower Sierra foothills region areas during high-sun periods when there is lack of the cooling Delta breeze.
- Precipitation trend: Approximate dates of precipitation are: May 5-7,10-12, 13-15, 18, and 21-23.
- For the N California forests, a key issue is the timing of dry-off of seasonal grasses in the Sierras and foothills, and coastal mountains of N California.
- In 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 will eventually contribute to stronger onshore flow and persistent or recurrent marine fog. For the north and central California coast, this will eventually encourage persistent or recurrent conditions in May for fog drip in the coastal forests especially at elevations at or below 1300 feet on the windward slopes (facing W or NW), as the springtime fog-and-stratus season becomes established.
- During periods of stronger fronts that break the marine inversion (mainly early May), we expect episodes of sunny, very warm conditions, followed by redevelopment of a marine layer with fog-drip events in coastal forests.
- For May: It turns much warmer than normal away from the coast, and in coastal hills above the marine inversion (1200 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 recurrent onshore flow.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
NORCAL Rains: May 5-7, 10-12, 13-15, 18 and 21-23.
CENTRAL CALIF Rains: May 7 (light rain N areas), 11-12 and 22-23.
WARM SPELLS: May 1-4, 16-17, 20, 25-29.
COLD SPELLS: May 6-7, 11-12, 14-15, 18 and 21-23.
FRONTS WITH RAINS: May 5, 10, 13, 18 and 21.
FROST RISK: Apr 27-28, May 8-9, 16, 19.
Forecast for S California:
SOCAL RAINS: May 7, 12, 15, 23.
SOCAL WARM SPELLS: May 1-5, 8-9, 16-18 and 25-29.
SOCAL COOL OR COLD SPELLS: May 7, 11-15 and 22-23.
FRONTS WITH RAIN/DRIZZLE: May 7, 12, 15 and 23.
Central Sierra Nevada:
Dates of mountain rains and snows are: May 6-7, 11-15, 18 and 22-23.
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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 29- May 29, 2022
Highlights: End of April – late May is a changeable time, with periods of gusty NW winds and cool nights, followed by less wind, but sharply warmer days.
Looking Ahead – Long Range Outlook
May 29- June 29, 2022... N and Central California: NORCAL and Central California: Consistently warmer than normal in May 20 onward with some hot conditions (highs in the mid to upper 90s possible around May 15-20 and also near end of May. Above normal temperatures are expected for June, with a well established, although shallow marine layer.
For SOCAL May 29 - June 29, 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 for end of May and June, with foothill and coastal valley highs m90s (avocado areas), and intermediate valleys peaking into the u90s to L100s on occasion before a persistent but shallow marine layer pattern becomes well established.
In summary, due to the drier than normal rainy season, watch for seriously low reservoir levels at the beginning of the long dry hot season. Watch for some 100+ hot spells early in the summer season (late May and end of May) and in June while cool fogs hang at the immediate coast/beach through most 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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