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 and N California.This includes San Luis Obispo Co from Pt Arguello north through the Bay Area to most of NORCAL coast and mountains, including Mendocino-Humboldt Co’s, Siskiyou’s, Trinity Co, NE California Plateau and Lassen Co, and the Sierras from Butte Co to Yosemite And the Redwood Parks (Sequoia etc).
- There continues support for troughs and upper lows to develop near Pt Arguello-Morro Bay. These maintain cool onshore flow with coastal drizzle alternating with showers. There may be a frost in coastal valleys of the central coast/Monterey/San Benito Co’s in May on multiple dates.
- 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 May and even into the first week or two of June. There continue 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: Rain and showers May 2-6, 7-11,most dates May 15-30. Prospect for onset of summer in June… Both May and June are shown by CFSv2 as rainy, late-spring-type months…abnormally cool and wet.
- Seasonal….Longer term trend. Both NOAA/Climate Prediction Center, and Australian Bureau of Meteorology have “El Nino Watch” status for next winter season Northern Hemisphere. This means: for the upcoming rainy season late 2023 through Spring 2024, and possibly next wet season of 2024-2025, we may be looking again at a wetter than normal rainy seasons for California, aswell as NW Mexico, Arizona. For Australia, the seesaw is in the opposite sense…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 Trend: May 2-6, 7-11, 15th off-on until 30th.
Norcal MILD SPELLS: May 12-14, 17-18 and Jun 1-4.
Norcal COLD/COOL SPELLS: May 2-5, 15-16 and 20-29.
Norcal FROSTS/FREEZES: May 6 and 8 (M30s to U30s).
Central Calif PRECIPITATION: May 3-5, 22, 25 and 28.
Central Calif MILD SPELLS: May 11-15, 18-20 and Jun 1-5.
Central Calif COOL SPELLS:May 3-6, 15-17 and 22-28.
Central Calif DRY COLD WINDS/FROST RISK: May 6 and 17.
Forecast for Southern California:
SOCAL RAINS: May 3-5.
SOCAL MILD TO WARM SPELLS: May 11-14, 18-21, 26-28 and May 30-Jun 5.
SOCAL COOL OR COLD SPELLS: May 3-9, 16 and 23-24.
SOCAL FROSTS/FREEZES: Unlikely.
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: May 3-6, 14-18, 21-22, 26, 28-30 and Jun 1-4.
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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 June 5 - July 5, 2023
Highlights: Generally near normal rainfall in most areas, focused in early May (2-3,5-7). Colder than normal with windy periods.
Looking Ahead – Long Range Outlook - June 5 - July 5, 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 cold, 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 warm or hot day for interior N and Central California. There continues risk of abnormal cool periods with showers and a thunderstorm central Sierras early to mid June, then turning warmer in last week of June to first part of July with seasonable showers.
Long Range Outlook SOCAL: This period currently appears to turn cool in May due to intermittent showery events, and a deep marine layer coast-coastal valleys. This is forced by currently below normalsea surface temperatures and a tendency for troughing with cooler than
normal airmasses aloft. Interior valleys may have a better chance to recover to near normal warmth for brief period 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: For May and most of June…near normal precipitation for higher mountain areas, except a little above normal in some. Wetter than normal in lower mountain and foothill spots due to active moist marine layer.
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 breezy...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 late 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 foothill-mountain showers. 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, upper lows and southeast flow should finally launch us into an active mid-summer TSTM season in late July and August.
To follow the wet winter and spring, 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 occurs in late June-July, we could launch quickly into a robust fire season about late July or August.
(Terms and Definitions Used In This Weather Outlook)
Alan Fox & Zane Stephens...Fox Weather, LLC
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