BASIC PATTERN:
Large Scale Pattern –
- We note that the sea surface temperature anomalies and IVTinit, there is support for a tendency for occasional troughing near the coast of California…Central, south as well as in the north. There is support for upper lows to develop near Pt Arguello-Morro Bay, to maintain a cool onshore flow with alternating drizzle and a few showers and a frost or two for central coastal valleys.
- The sea surface temperature anomaly pattern (SSTA)suggests a continuation of troughing near the California coast, and the cool or briefly cold conditions continuing through Apr 30 and into first part of May. We still see the active cold fronts arriving from the N Pacific/off the Washington coast, with snow in NORCAL mountains and Sierras. Occasional frosts could reappear a few times into N and Northcentral California areas to interfere with spring bloom.
- Precipitation Trend Precipitation Dates for N and Central California: Apr 19, 23, 30-May 1, May 5-6.
- Seasonal….Longer term trend. Both NOAA/Climate Prediction Center, and the Australian Bureau of Meteorology are in “El Nino Watch” status for next winter season. This means That for the upcoming rainy season late 2023 through Spring 2024, and possibly the next season of 2024-2025, we may be looking again at above normal rainy seasons for California, as well as NW Mexico, Arizona. For Australia, the seesaw is in the opposite direction…below normal rainfall, drought, and more dangerous fire conditions throughout the year, comprised of multiple hot-dry-windy seasons for Australia.
FORECASTS FOR CALIFORNIA
Forecast for Northern and Central California:
Norcal PRECIPITATION: Apr 19, 23, 30-May 1, 5, 10-11.
Norcal MILD SPELLS: Apr 22-23, May 3-4, 8-9, 13-14.
Norcal COLD/COOL SPELLS: Apr 24-26, 30-May 2, 5, 10-11 and 15-16.
Norcal FROSTS/FREEZES: Apr 20-21, 26-27, May 2 and 6.
Central Calif PRECIPITATION: May 1
Central Calif MILD SPELLS: Apr 22-23, May 3-5, 8-10.
Central Calif COOL SPELLS: Apr 24, May 1-2, 12.
Central Calif DRY COLD WINDS/FREEZE RISK: Apr 20 and 26.
Forecast for Southern California:
SOCAL RAINS: Latest models show dry other than occasional drizzle.
SOCAL MILD TO WARM SPELLS: Apr 22-25, 28-May 2, 4-6.
SOCAL COOL OR COLD SPELLS: Apr 26, May 3 and 11.
SOCAL FROSTS/FREEZES: None.
SOCAL SANTA ANAS: Apr 27-28, May 2-3, 5-7 and 12-13.
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 try to experience some of the seasonal warmup.
Forecast for Central Sierra Nevada:
Central Sierra Nevada Precipitation: Dates of rain or snow: Apr 25-26, 30,May 4-6 and May 11.
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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 May 15 - June 15, 2023
Highlights: Generally near normal rainfall in most areas. Colder than normal.
Looking Ahead – Long Range Outlook - May 22 - June 30, 2023
NORCAL and Central California: In general, during this period, CFSv2 continues to show cool and showery conditions in the N and Central Sierras, Siskiyou’s/Cascades, and cool showery conditions in the NE Plateau. After some cool and showery periods in early to mid May (per NMME), we finally emerge to a very brief warmer than normal (hot) period sometime about the beginning of June for interior N and Central California. There continues risk of abnormal cool periods with showers and thunderstorms central Sierras early to mid June, then turning warmer in late June to first part of July.
Long Range Outlook SOCAL: This period currently appears to turn cool in May due to intermittent deep marine layer coast-coastal valleys. This is forced by currently below normal sea surface temperatures and a tendency for troughing with cooler than normal airmasses aloft. Interior valleys have a better chance to recover to near normal warmth for brief periods by late May, but then turn breezy and cool or cold again in June due to abnormally strong upper lows or troughs.
Precipitation in SOCAL mountains and deserts: Below normal for higher mountain areas except near normal in some or perhaps a little above normal in some lower mountain and foothill spots!
For SOCAL coast and valley areas: Watch for below normal temperatures in May and through mid June…cool days with drizzly coastal eddy conditions on the windward slopes, but about normal nighttime temperatures in SOCAL from coastal marine clouds in May through mid June. Turning warmer by end of June,with transition to warmer conditions but still with the breeze that is more typical of May. You’ll notice the cool difference this May and June in the degree day data. Would not expect summer monsoonal conditions until July and August when the mountain/desert TSTMS of midsummer finally get going.
For the Sierras: After the cool May with showery conditions in the Central Sierras, we have a cool and showery June too, with mountain showers and a few Thunderstorms (TSTMS)…but non-monsoonal… possible. It appears that surface moisture from residual snow and moist soils and fuels may persist through May and most of June. From there, the expected cold sea surface temperature anomaly pattern appears to focus over Baja and SOCAL, favoring troughs with SE flow aloft into central and N California in most of June, per NMME (Ensemble) forecast map guidance. At some point, this could launch us into an active mid-summer TSTM season in July and August. To follow the wet season, we should consider the possibility of a robust late May through June growth of fuels, i.e. dry brush understory in the forests. As the subsequent seasonal dry-off of these understory fuels “greenup” occurs in late June-early July we could launch quickly into a robust fire season sometime in July.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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