BASIC PATTERN:
Large Scale Pattern –
- May started colder than normal but high pressure will bring some very warm days later in the month. Occasional weak fronts will bring brief cooling.
- With the warmer high pressure comes a very dry pattern. Weak fronts at times will brush to the north but for the most part minimal rain is expected. June will start off very dry with well below normal precipitation expected to continue. Some subtropical moisture around June 5 and 7th could bring scattered showers into southern California mountains.
- The large-scale pattern of recurrent troughs in the northcentral Pacific encourages risk of short hot events in California during the late spring, until the onset of the summertime 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 100-110 degree temperatures is in the warmest intermediate valleys as high pressure rebuilds behind cold fronts in June.
- Some highs of 110 to 115 are possible in SOCAL inland valleys and inland foothill areas during the June heatwaves. This includes highs in the 102-109 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. Even in late May we are expecting some highs in the 102-108 range on May 25 in the San Joaquin Valley and Delta when the Delta breeze stops for a day.
- Precipitation trend: Approximate dates of showers or light rain in N California are: May 28-29 (light showers N), Jun 3-5 (Sierra scattered showers), 5 (few showers into S Calif) and 7 (scattered light showers S Calif).
- 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. The weather pattern is turning dry now with warmer than normal temperatures bringing a fast drying of the vegetation. A high fire danger is expected by late May with extreme fire dangers in many areas in June.
- 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.
- For late May: There are some dry north wind events through N and Central California, typical for coastal areas, coastal mountains, and Sierras. For the coastal foothills, this actually brings a higher risk of drying conditions in this recurrently dry and windy pattern.
- For June, the models show a drier than normal pattern with warmer than temperatures. Weaker fronts will bring some light rain northern-most California at times near the border. The GFS model is showing a surge of subtropical moisture with some showers into southern California on the 5th and again on the 7th. This is a bit early for subtropical moisture into that region and might be optimistic, with a dry pattern likely continuing.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
NORCAL Rains: May 28-29 (light showers N areas), and June 2-6 (mostly on 5th).
CENTRAL CALIF Rains: May 28 (coastal drizzle). Dry in June.
WARM SPELLS: May 24-25, Jun 9-12, 15-22, and 25-28.
COLD SPELLS: May 28-29, Jun 4-5 and 13-14.
FRONTS WITH RAINS: May 28, and Jun 4-5.
FROST RISK: Frost/freezes are unlikely.
Forecast for S California:
SOCAL RAINS: GFS model shows possible showers June 5 and 7.
SOCAL WARM SPELLS: May 24-27, 31- Jun 12, and 15-20.
SOCAL COOL OR COLD SPELLS: May 28-29 and Jun 13.
FRONTS WITH RAIN/DRIZZLE: Coastal drizzle May 28, and June 13.
Central Sierra Nevada:
Dates of mountain rains and snows are: May 29-30, and June 2-5.
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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 27 - June 27, 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. The end of May looks dry with warmer than normal temperatures. Summer begins with June with a very dry month expected across the state as high pressure will dominate the weather pattern. Some troughs will slide to the east into the Great Basin with brief cooling but dry across California.
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.
Looking Ahead – Long Range Outlook
June 27-Aug 14, 2022... NORCAL and Central California: Becoming 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). Some monsoonal showers should creep into the region by late July but models continue to show below-normal monsoonal moisture during the typically wet monsoonal season.
For SOCAL June 27- Aug 14, 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. Monsoonal moisture looks below normal early in the season with possible normal monsoonal showers around the start of Aug.
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 (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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