Weather Outlook — June 17 - July 17, 2026

Large Scale Summary

• For the month of June rain dates are sparse in mid-June to mid-July.  July rains are mostly 26-30 in Central Sierras Yosemite NP to Lake Tahoe. 
• Showers increase in the tropical southern Mexico coast region (Jalisco to Oaxaca states during June through late July.
• Greatest variation in speed of the westerlies coming into NORCAL occur during 15-20 June. The greatestvariation in speed of the westerlies occurs at 33-40N. Most of this variation appears related to interruptions in the westerlies at 30 to 43N, and subtropical troughs in the Pacific between 16N and 25N and longitudes 120-135W.
• Interestingly, we are seeing an increase in rainfall for western Mexico north into Arizona/southern Rockies in June-July period.  
• There appears to be a continued development of August and September rains into W Mexico and Arizona and eventually California. 
• Regarding the emerging summer season and transition to autumn, it is more logical to remain with the guidance at hand from NOAA/CPC/NWS.  An increase in thunderstorm (TSTM) activity is reasonable as we transition into September, as we consider the overall pattern. It would be constructive to consider transition to a potentially aggressive period for wildland fires in California as we go into October. We prefer to see some more solid guidance before commenting further on the autumn fire season in November. 
• Certainly lightning and wind are important influencers of the autumn fire weather season.  So, even if some wet periods occur, presence of lightning/TSTMS and 
  gusty/fickle winds are certainly risk factors to consider, even in a "wet fall".

Special Guidance Summary

• The usual occurrences of breeze are suggested for the remainder of June as a risk factor for Fire Weather.
• July should be targeted as a month of TSTMS in the Central Sierras, but with local gusty winds in the Central Sierra foothills, near TSTMS. 
• July precipitation will tend to be below average except in the higher terrain areas of the Central Sierra. Rain-band mergers are greatest risk when convective cells in the foothills contribute to development of gusty afternoon-evening winds in addition to rains and TSTMS.
• August above average occurrence of TSTMS and cloud to ground lightning from strong convective systems that cover areas of minimal size.  These can be fire producers for mid to late July and August.
• September would be the month for squall lines and frontal systems that are better organized. But even with localized heavy rains, amounts of rain, region-wide would 
  still tend to be small, and heavy rains tend to focus in the Sierra crest. The September events that produce widespread rain are tropical cyclone remnants, or 
  interaction of those remnants with cutoff lows and associated frontal bands. 
• October will tend to be similar to September with small rain-cell size.  
   

CENTRAL CALIFORNIA

• PRECIPITATION DATES: Timing of rain events is difficult this time of year.  Systems are convective, with small areal coverage.  Upper lows occur, but depending on current flow regimes, the flow of moisture from the tropics into SOCAL can be very limited. These tend to result in very small cumulus cells, and limited moisture for precipitation. Convection can be present, with the usual ëthunderheadí or "popcorn-types" of clouds, but without rainfall. If moisture is present, then rain is more likely to occur, which is logical. 
• For Sierra SHOWERS/TSTMS with the cutoff low coming from the ESE across central California, moisture is limited.  Dates we saw have been June 21-22, 29-30,
  but those dates are not confirmed in the latest CFSv2 guidance. There is practically nothing in early July, but the CFSv2 prefers to show above average rainfall occurring in the Central Sierras from Yosemite NP to Lake Tahoe to Truckee in mid to late July.  Unfortunately, the precipitation can get "zeroed-out" pretty quickly in this type of early season dry pattern for summer. So there ís not much to report except, during lack of tropical cyclones, to go with the usual climatological patterns. So, except for Tahoe etc, thereís minimal or no rain in July for the Sierras, or North Coast beyond occasional coastal drizzle.  Tropical cyclone activity and monsoonal moisture is focusing in east winds across N and central Mexico.  Bottom line with that pattern is:  hot summer weather inland and over the mountains, and coastal fogs with low inversions over the California coast. More specific information will need to wait until July, August, and early September for those months.
      

SOUTHERN CALIFORNIA

• PRECIPITATION DATES:MOUNTAINS 29-30 JUNE SOUTHERN CALIFORNIA SAN BDNO/LA CO MTNS/ AND TEHACHAPI MTNS 21-22, and 29-30 June. Then in July: basically the same in SOCAL as well as in Central California/Sierras. Dry and hot, alternating with breezy and a little cooler as dry troughs occur with deeper marine layer at times. Again, high pressure continues to focus into California while easterly flow with tropical moisture and TSTMs focus in western Mexico and into SOCAL.

SOUTHERN CALIFORNIA DESERTS

• Lack of TSTMS, lack of showers, plenty of heat. Precipitation dates will tend to focus into late July and early August when the moisture reaches north into SOCAL from Mexico. VENTURA CO MOUNTAIN PRECIPITATION: RAIN SHOWERS/TSTMS will occur if there is moisture reaching northwestward from Mexico and Arizona. 

Outlook into August — October

• There may be an increased chance for rains in August and September as the monsoonal moisture reaches farther N into SOCAL and the Sierras.  Our best strategy at this point is to monitor tropical cyclone developments.  As the summer transitions into fall, we should expect more interaction from tropical (monsoonal) moisture with flow around cutoff lows and their associated fronts.  Those associations will occur. August-September are prime months for those. In addition, with the developing El Nino pattern expected to affect W Mexico, SOCAL, then push moisture further north into California, there will tend to be
  some more opportunities for rains to occur.
• The current synopsis is rains early in the fall season (August-September, and October. The NOA NCEP/CPC maps tend to show a break in the rain action in November, followed by an up-tick in December as the El Nino ñ fueled winter storms become active.

Figures and Text: Alan Fox, Fox Weather, LLC
Copyright © 2026 Fox Weather, LLC.