Large Scale Summary
- For near term conditions, the longwave pattern supports rainí dates in the near term (May 12-19) and beyond are: May 14-15, 29-31, and June 4-6,9. Best dates for rain appear to be 14-15 and 29-31 May, and 4-5 June.
- Look for the greatest variation in speed of the westerlies at 30N and 40N. Most of this variation is due to interruptions in the westerlies at 32 to 43N, to the north of the 16N to 25N and longitudes 130-135W.
- Those functions that introduce increased variation in the westerlies occur at 30-40N for the most part as mentioned above. The increased variation tends to occasionally interrupt westerlies which occur along the usual development path in subtropical and midlatitude areas, including south to 25N.
- After the rains in April, May precipitation is smaller and covers less territory in the California region. As mentioned above, the May precipitation is of some interest: occurring 14-15,29-31 May.
- In summary, subtropical troughs and associated variations in speed of the westerlies can still develop near the end of mid and late spring periods.
- The favored locations of troughs continue to be mid Pacific around 130-135W and 155WÖwith a bias to maintain some occasional support for troughing into California and possibly N Baja, and effect more rains into the near coastal areas or California for mid-May, and again in June.
- Looking ahead to early summer: mostly July there appears to be a maximum of rainfall SW-W Mexico to Baja, as well as north along the Sierra Madre Occidental, and in the California Sierras from southcentral California to SOCAL.
- Looking ahead to mid-July-August: As mentioned, these early to mid summer months, the summer monsoon and usual hurricane season in southern Baja and western Mexico become more dominant sources of precipitation. As these occur, they make their way north through the Sierras, showing a maximum of rainfall in the Central and Southern Sierras. In July and August the monsoonal influence can become robust, and closely associate with persistently above average temperatures. This suggests an influence from thunderstorms (TSTMS) bringing a chance for more rains into California and SW U.S.
NORCAL
- PRECIPITATION DATES: 14-16, 29-31 MAY, and 4-5, 15 JUNE.
- MOUNTAIN showers Örain 3-5, 15-18, 29-31 MAY, and 3-5, and 15 June.
CENTRAL CALIFORNIA
- PRECIPITATION DATES: May 15-17, COOLER WITH RAINS 29-31 MAY, and SHOWERS 3-5, AND 15 June in SIERRAS.
- MOSTLY DRY WITH SOME HOT PERIODS: BEST CHANCES FOR RAINS: 15-18 MAY. TURNING BRIEFLY COOLER WITH RAINSON 29-31 MAY.
- CENTRAL SIERRA: PRECIP: 15-18,BRIEFLY COOLER WITH RAINS 29-31 MAY, and 3-5 JUNE.
SOUTHERN CALIFORNIA
- PRECIPITATION DATES: MAY 15-18, 28-31.
- SOUTHERN CALIFORNIA DESERTS PRECIPITATION DATES. 29-30 APR SOUTHERN SIERRAS EAST SLOPE, AND SAN BDNO MOUNTAINS E SLOPES.
- MOUNTAIN PRECIPITATION: RAIN SHOWERS/TSTMS 15-18, 29-31 MAY, 3-5,15 JUN.
Medium Term Outlook: JUNE 15-JULY 15
NORCAL
- PRECIP Dates: JUNE 15,25, includes MOUNTAINS PRECIPITATION: MOSTLY NEAR AVERAGE IN EAST CALIF. BELOW IN WEST CALIF. SHOWERY 3-5 JUNE. MOUNTAIN SNOW OR RAIN: PRECIPITATION IS MOSTLY RAIN BY JUNE 1 ONWARD THRU JULY.
CENTRAL CALIFORNIA
- PRECIPITATION JULY-AUGUST: Turning warmer than average with TSTMS accompanying the precipitation.
SOUTHERN CALIFORNIA
- PRECIPITATION: NEAR AVERAGE. BEST CHANCES SHOWERS: Possible early burst of monsoonal rains in in early JUNE, and some robust monsoonal bursts
in July and again in August. SOUTHERN CALIFORNIA DESERTS: PRECIPITATION: NEAR AVERAGE. BEST CHANCES SHOWERS: June 3-5. POSSIBLE EARLY BURST OF THE MONSOONAL RAINS IN early to mid-JUNE, AND ANOTHER BURST IN EARLY TO MID JULY. TURNING WARMER THAN AVERAGE IN JUNE AND JULY, WITH ABOVE AVERAGE RAINFALL FROM ACTIVE MONSOON AND TSTMS IN JULY. FOR WESTERN MEXICO, THE MONSOONAL INFLUENCE DECREASES AFTER LATE JUNE, CONTINUING ON THROUGH AUGUST.
Figures and Text: Alan Fox, Fox Weather, LLC
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