LARGE SCALE SUMMARY
- Troughing continues in the central North Pacific from about 135-150W (mainly NNE to NE of Hawaii), and at 160W to near the Dateline NW of Hawaii. CFSv2 suggests showery conditions in late Apr per the map discussion above, then dry and warmer conditions for 2-8 May.
- Rains develop per CFSv2 model for 10-15 May.
- Rainy periods in end of Apr ñ first week of May have been inconsistent from CFSv2.
- The monthly outlook maps from the CFSv2 model (monthly time step Apr ñ June 2025) are posted at the end of this report (pdf version). Watch for some typically showery periods in April through most of central and N California, unsettled through early to mid May (1 and May 9-15), showers 17-18 and showers 24-26 May, then transition to a hot June.
NEAR TERM OUTLOOK — April 17 - May 17
- NORCAL precipitation dates are April 16-17, and about 30 Apr-1 May. Cool to near seasonally average temperatures. Cool with occasional low snow levels. North Sierra Precipitation: Apr 16-18,27-30, and May 1. Central Sierra Precipitation: Apr 16-18,27-30.
- CENTRAL California precipitation in Sierras on 16-18 another windy cold front comes south into NORCAL with cold showers. Other cold showers are indicated Apr 27-30-May1 (Central California and north). After May 10-11 with few showers central Sierras, more showers occur on 11-18 May, again cold or cool. It appears that the emerging IVTinit pattern is starting to support the wetter pattern for ORWA and NORCAL around the 16-17Apr, and again 24 followed by showers 25-30 Apr. There is a possibility of some other wet fronts with showers currently suggested for 15-18 May.Mild dry periods alternate with cold and (snow showers or flurries in Sierras). Warn breezy dry 22-24 Apr. Showers mid Apr and again 25-29 Apr.
- SOCAL precipiation appears to be sparse and disorganized at this time for mid to late Apr.
- SOCAL COLD/FROST PERIODS: Several nights may have isolated frosts in the normally colder valleys, on nights if clearings occur for a time overnights/early mornings between fronts/rain events.
- SOCAL DRY/WARM (SANTA ANA) type events: Apr 22-24.
- Southern California Deserts colder than average during a few showery periods mid Apr and again mid May. Rainfall amounts near average. Shower dates in SOCAL Deserts: Rain sparse in April, occurring mainly 16,17, in a few light desert showers.
MEDIUM TERM OUTLOOK — June 17 - July 17
- Northern California: Below average rainfall. Highest precipitation anomaly will be at the North Coast Mendocino Co north from coastal drizzle and light rains from weak end-of-season cold front or trough around June 1. For valleys and mountains of Northern California, turning hotter and drier than average during late spring and first month of summer (10-30 June).
- Southern California: 10 June -30 June: Near average precipitation with near average temperature. Watch for interspersed hot periods accompanied by shallow coastal marine layer conditions at times during mid to late June. Transition to dry hot conditions by mid June. 30 Day Precip/Temp maps for June and July suggest a return to near average rainfall (monsoonal TSTMS) but continue above average temperatures. Please note that well above normal temperatures are suggested in the NCEP/CPC guidance for June suggest heat wave conditions in the Sierra Nevada foothills and west slope areas from El Dorado Co south in June. For the valleys of Southern California: Turning warmer and drier than average at times during June. We note from the NCEP monthly guidance included next page that significant hot spells are a possibility in June for inland SOCAL citrus and avocado regions. There is risk of highs reaching to near 105 in the Ramona-Temecula areas and 95-100 in Fallbrook during mid to late June.
Figures: Alan Fox, Text: Alan Fox, Fox Weather, LLC.
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