, Issued at 158 AM PDT Mon Jul 20 2026 (Today and tonight)
A 581 decameter geopotential height low remains located 500 miles west of San Francisco. The southern branch of the polar/subtropical jet stream is just forward of this low with jet stream winds to our southwest through northeast. These jet stream winds have helped quickly transport high and mid level clouds away from TS Elida in the last 24 hours or so. GOES-West Geostationary Lightning Mapper showed lightning approx 600 miles southwest of Point Conception earlier Sunday, but since Sunday evening it's been quiet. This lightning activity was closer to the northward moving and weakening center of TS Elida.
KMUX has occasionally shown widely scattered high based showers over our forecast area, but there have been no measurable rain or lightning reports so far. A band of light high based rain is developing over the coastal waters as well. We're in a little bit of unknown territory here with mainly minor energy transformations taking place, complexities that occur whenever tropical moisture travels northward and interacts with the mid-high latitude synoptic pattern. At the moment, the high based showers/band of light rain correspond to an area of weaker 500 mb positive vorticity that is forecast to continue moving northward of our forecast area along with the aforementioned upper level jet stream. So in a way, the combination of parameters and the steady diffusing of mid and high level clouds (water vapor) with minimal to no organization so far appear to be self limiting, leaning the pattern toward stability, keeping convective potential at a minimum.
Cloud cover will be a mix of stratus and mid and high level clouds today. The Sun may break out over the southern interior today, possibly some sunny breaks farther north to the South Bay as well. Daytime highs today will be about the same it was on Sunday, varying from the mid to upper 60s along the coast to the 70s bayside to the 80s and 90s well inland. Tonight lows will cool to the 50s except in the 60s in the hills and mountains.
..issued at 158 AM PDT Mon Jul 20 2026 (Tuesday through Sunday)
With generally decreasing 500 mb positive vorticity Monday this will help keep convective potential at a minimum with exception of the North Bay Monday afternoon to early evening when there may be a brief uptick in positive vorticity. However, even the 00z NAM output for this timeframe shows minimal convective potential along with convective inhibition. The HRRR, RRFS and GFS show essentially no convective potential.
For Tuesday, 500 mb positive vorticity is essentially non-existant including in the 00z NAM cross sections. Residual mid to high level clouds may still be around, but there'll likely won't be a lifting mechanism left to destabilize an atmospheric layer or air parcels. The westerlies, wind shear and drier air is destructive to tropical origin convective development, but there can be the exception to this when a steep east to west moisture gradient helps temporarily destabilize a lifted layer or air parcels. Given model trends and further dissipation of TS Elida, this is unlikely Tuesday when the tail end of the moisture gradient moves across the forecast area. Stay tuned to the latest updates.
Otherwise it'll be summertime dry weather, warm to hot inland and coolest at the coast and bays mid to late week. The high pressure system over the interior west will gradually shift southward then slowly move to the Four Corners by the weekend.
(18z TAFS) Issued at 1049 AM PDT Mon Jul 20 2026
Mid to high level clouds continue to stream across the region from the southwest this morning. These clouds helped eroding the stratus deck below with most terminals having scattered out at this hour. Showers accompanying these mid/high clouds may produce a shower here and there however most will not hit the ground and fall as virga. VFR conditions and diurnal winds will prevail this afternoon. High confidence in the return of IFR conditions to coastal terminals tonight with low confidence elsewhere due to the shallow nature of the marine layer.
Vicinity of SFO, VFR conditions and northwesterly flow will prevail. Low confidence on the return of an IFR cigs tonight, however current thinking brings IFR cigs in around 05z over KOAK and between 13z-17z over KSFO.
SFO Bridge Approach, Similar to SFO.
Monterey Bay Terminals, VFR conditions will prevail with moderate northwesterly winds kicking in by this afternoon. Moderate to high confidence on IFR cigs returning tonight. Current thinking has IFR cigs returning around 02z.
(today through Saturday) Issued at 1049 AM PDT Mon Jul 20 2026
Light to locally moderate northwesterly winds will prevail through midweek, becoming moderate Thursday into Friday. Slight to moderate seas will prevail. Tropical cyclone activity in the Eastern Pacific Ocean will spur several rounds of moderate period southerly swells; hazardous conditions from mixed seas may result. Instability from the remnants of the tropical cyclone will also bring a slight chance of convection that may bring showers as well as gusty and erratic outflow winds that would be result in hazardous conditions to small craft.
Ca, None. PZ, None.
