Large Scale Summary
- For near term conditions, the longwave pattern supports rain dates in the near term May 6-9.
- We look for 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 Nino 3.4 zone, i.e. Baja California to Hawaii and 10N to 26N.
- Those functions that introduce increased variation in the westerlies occur at 32-43N for the most part as mentioned above. The increased variation tends to occasionally interrupt westerlies which occur along the usual development path in subtropics and midlatitude.
- While April precipitation continues above average, some heavy May precipitation is also of interest: occurring 3-5,16-17 May.
- In summary, 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 130-150W with a bias to maintain some occasional support for troughing into California and effect more rains into the near coastal areas or California for mid-May, and again in late May.
- Looking ahead to early summer: June and July see 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 early summer: As mentioned, late June and July see a maximum of rainfall in SW Mexico and Baja, as well as up the Sierra Madre and south portions of the California Sierras as mentioned. Some of rain in W and SW Mexico may be due to monsoonal moisture coming north towards the SW U.S. and SOCAL-Sierras in California. In July also the monsoonal influence could become robust, bringing a chance for more rains into California and SW U.S.
MAY 1-25
NORCAL
- PRECIPITATION DATES: 3-4,16-17 MAY
- MILD to WARM/DRY PERIODS: MOUNTAIN showers - rain 1,3-7 MAY
CENTRAL CALIFORNIA
- PRECIPITATION_DATES: 1,3-4,16-17 MAY
- MILD AND DRY: 2,5-8 MAY
- CENTRAL SIERRA: PRECIP: 1,3-5, 16-17 MAY
SOUTHERN CALIFORNIA
- PRECIPITATION DATES: MAY 3-5,16-17.
- COLD/FROSTS DRY WINDS:FROSTS VALLEYS.1,6-7 MAY.
- MOUNTAIN SNOW: SNOW IN MAINLY CENTRAL AND S SIERRAS. SHOWERY MOUNTAIN SNOW IN SOCAL MOUNTAINS/SAN BDNO CO MAY 16-17.
SOUTHERN CALIFORNIA DESERTS
- PRECIPITATION DATES. 29-30 APR SOUTHERN SIERRAS EAST SLOPE, AND SAN BDNO MOUNTAINS E SLOPES.
- MOUNTAIN SNOW: SNOW SHOWERS 3-5, 10-11, 16-17 MAY.
Medium Term Outlook: May 2026
NORCAL
- PRECIP Dates: MAY 1-2, MOUNTAINS AND EARLY (1-2 MAY) PSBLY COLD/SNOWY AGAIN IN EARLY MAY 3-5 AND 10-11, 16-17 MAY. MOSTLY NEAR AVERAGE IN EAST CALIF. BELOW IN WEST CALIF. ABOVE AVERAGE CALIFORNIA NORTH COAST. COLD SHOWERY 16-17 MAY.
- MOUNTAIN SNOWS: BELOW AVERAGE, MOSTLY HIGH SNOW LEVELS. OCCASIONAL LOW SNOW LEVELS 4000-4500 FT, EVEN IN EARLY AND MID MAY.
CENTRAL CALIFORNIA: MAY, JUNE, JULY 2026
- PRECIPITATION JUNE-JULY: MOSTLY COLD AND NEAR AVERAGE RAIN AND SNOW IN SIERRAS,INCL MID MAY.
SOUTHERN CALIFORNIA JUNE-JULY
- PRECIPITATION: NEAR AVERAGE. BEST CHANCES SHOWERS: MAY 15-17. POSSIBLE EARLY BURST OF THE MONSOONAL RAINS IN MID-LATE JUNE, AND ANOTHER BURST IN EARLY JULY.
SOUTHERN CALIFORNIA DESERTS May 15-31 2026
- PRECIPITATION: NEAR AVERAGE. BEST CHANCES SHOWERS: MAY 15-17. POSSIBLE EARLY BURST OF THE MONSOONAL RAINS IN MID JUNE, AND ANOTHER BURST IN EARLY JULY. TURNING WARMER THAN AERAGE IN JUNE AND JULY, WITH ABOVE AVERAGE RAINFALL FROM ACTIVE MONSOON AND TSTMS IN JULY.
Figures and Text: Alan Fox, Fox Weather, LLC
Copyright © 2026 Fox Weather, LLC.
Monthly Outlook Summary Maps are courtesy of (NOAA/NCEP/CPC/NWS).