BASIC PATTERN:
Large Scale Pattern –
- We have had a cold beginning to May. However, some much warmer periods are expected at times during the second half of May.
- There are few periods of cold showers on May 10-12 in the nearest term. However, this pattern will be shifting to a warmer one.
- The large-scale pattern of recurrent troughs in the northcentral Pacific encourages the risk of short hot events in California during the late spring, until the onset of the summer fog and stratus pattern. The large scale 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… mid to upper 90s during the hotter periods of June. The highest probability of 100-108 degree temperatures is in the warmest intermediate valleys as high pressure rebuilds behind cold fronts during the periods of high sun angle in June.
- Some highs of 110 to 115 are possible in SOCAL inland valley and inland foothill areas during the June heatwaves. This includes highs in the 103-108 range in hilly areas near Escondido-Fallbrook, and 108-115 in Riverside, Perris, Hemet, and 112-120 in southern Deserts (Imperial and Coachella Valleys) of S California. Other areas that are more normally hot in such early summer heatwaves are the counties of Kings, Kern, Tulare, and the lower Sierra foothills region areas during high-sun periods when there is a lack of the cooling Delta breeze.
- Precipitation trend: Approximate dates of showers or light rain in N California are: Heaviest amounts for the North coast and Sierras appear to be today NW California mountains. On 12 May, the heaviest rains focus in Oregon and far NW coast (Del Norte Co). Some possibly significant rains occur during 19-25 May in Sierras and most of NORCAL, and NORCAL coast. A series of smaller rains occur about 14-16 June.
- 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. Rains have persisted through the first 10 days of May, and more are expected in N California until midmonth.
- 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 contribute to stronger onshore flow and persistent or recurrent marine fog immediate coast.
- For the north and central California coast, this will eventually encourage persistent or recurrent conditions for fog drip in the coastal forests, especially at elevations at or below 1300 feet on windward slopes (facing W or NW), as the early summer fog-and-stratus season becomes established.
- During periods of stronger fronts that break the marine inversion (mainly in May), we expect episodes of sunny, very warm and effective drying conditions, followed by redevelopment of a marine layer with fog-drip events in coastal forests.
- For late May: There are more of the dry north wind events through N and Central California, typical for May at coast, coastal mountains, and Sierras. For the coastal foothills, this actually brings a higher risk of drying conditions in this recurrently dry and windy pattern.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
NORCAL Rains: May 11, 23-25 (scattered showers), Jun 4-5.
CENTRAL CALIF Rains: May 11, 24-25 (showers N areas).
WARM SPELLS: May 13-16, 19-22, 27-Jun 3 and 7-12. .
COLD SPELLS: May 11, 24-25, Jun 4-6 and 13-14.
FRONTS WITH RAINS: May 10, 23 and Jun 4.
FROST RISK: May 11-12 (None after 17 May).
Forecast for S California:
SOCAL RAINS: None.
SOCAL WARM SPELLS: May 13-23, 28-Jun 4 and 7-13.
SOCAL COOL OR COLD SPELLS: May 24-26 and Jun 5-6.
FRONTS WITH RAIN/DRIZZLE:. May 25 (coastal drizzle).
Central Sierra Nevada:
Dates of mountain rains and snows are: May 12, 23-25 and Jun 4-6.
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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 May 13- June 13, 2022
Highlights: May is a changeable time, with periods of gusty dry winds, and some episodes of blowing dust and sand. The colder nights as wind speeds decrease are often followed by sharply warmer days.
Monsoon considerations: Both short term climate models (NMME and CFSv2)are suggesting a dry beginning to the summer monsoon season for SOCAL, western Arizona, and NW Mexico through June. The NMME model suggests anomalously dry conditions continuing well into the first month of the monsoon season (July). NMME is currently predicting anomalously dry conditions continuing into the middle of the hurricane season (Aug and Sep) this year. This is worthy of note, and a reason for including the NMME precipitation anomaly maps through the summer in this report.
Looking Ahead – Long Range Outlook
June 15-July 31, 2022... NORCAL and Central California: Consistently warmer than normal in June, with some hot conditions (highs in the mid-90s to m100s during the hot spells. For the coastal hills, above-normal temperatures are expected for June, with a well-established, although shallow marine layer. The lack of monsoonal moisture (see comments about this year’s North American Summer Monsoon above) would tend to argue for warmer than normal during the periods of high sun and lack of clouds and usual thunderstorms (TSTMS).
For SOCAL June 15- July 31, 2022 mountains westward to coast: Progressive trend towards above normal temperature. There is potential to turn hot and dry in mid-June and all of July above or away from the marine layer and lack of monsoonal clouds. Foothill and coastal valley highs m90s (avocado areas), and intermediate valleys persistently into the u90s to m100s on occasion before a persistent but shallow marine layer pattern becomes well established.
In summary, due to the drier than normal rainy season, we have seriously low reservoir levels at the beginning of the long dry hot season. Watch for some 100+ hot spells early in the summer season (early June), and in June while cool fogs hang at the immediate coast/beach through most days, except those dates with offshore flow in June.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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