Marine Weather and Tide Forecast for Penn Valley, CA

DISCUSSION

...Today & Thursday...
Upper level ridging continues to dominate the synoptic pattern across interior NorCal this morning. High pressure aloft will remain the primary driver for our hot temperatures and light surface winds through Thursday, with highs expected to be in the mid to upper 90s with some triple-digit readings continuing.
Moderate HeatRisk and areas of Major HeatRisk also continue today and Thursday. Synoptic pattern will begin to break down by early Friday however, ushering in cooler temperatures and breezy to gusty winds.

Friday
Upper level trough in the PacNW, with a weak offshore low will develop on Friday, ushering in lower heights aloft and increasing onshore flow. While daytime temperatures will still be 6 to 12 degrees above normal, the overnight relief will help mitigate the HeatRisk for much of the area. Pockets of Moderate HeatRisk will remain in the thermal belts of the foothills, but with the downward trend of HeatRisk we have removed Friday from the current Heat Advisory and it will now end at 10 PM on Thursday. Onshore flow with winds gusting up to 30 mph Friday evening/night will certainly provide a break from the summer like heat.

...Saturday - Monday...
This weekend we will start to see the true pattern change and the resultant sensible weather effects. By Saturday, PacNW troughing, weak offshore low, and remnants of Hurricane Rachel will begin to merge across our region and push onshore. Breezy to gusty onshore winds Saturday morning are possible, cloud coverage, increased daytime humidity values will lead to cooler high temperatures around the area, with highs in the upper 70s to low 80s (warmest in the northern San Joaquin Valley). By Sunday, an area of low pressure should form over the region, track close to the coast, continuing to provide locally breezy winds with further cooling, as highs are forecast to be in the low to mid 70s. Recent NBM model runs continue to suggest enough moisture from the remnants of Hurricane Rachel will advect into the area, bringing shower chances and a less than 10% chance for thunderstorms developing mainly over the mountains. North winds will also develop in the Valley, with gusts forecast to be around 25-35 mph.

Similar weather conditions will continue into Monday as well, with highs in the low to mid 70s, cooler upper 50s to mid 60s in the higher elevations. Currently have a non-zero chance of seeing some accumulating snow, mainly south of HWY-50 Monday morning, but not expecting significant impacts at this time. Low pressure moves further onshore Monday afternoon and begins to move eastward and out of the area by Tuesday night, where upper level ridging will begin to build over the region.

There is still a high level of uncertainty regarding moisture, thunderstorms, overall wind speeds, and potential impacts to the region this weekend and into early next week. Biggest question at this time will be how much moisture advects into the area, will it make it into lower elevations, and how much can precipitation could we get. Uncertainty regarding wind gusts speeds is high as well for Saturday morning in the Delta, then Sunday and Monday in the northern Sacramento Valley. We can say confidently a pattern change is going to occur, we just are still highly uncertain on the precipitation and wind impacts at this time.

AVIATION

VFR conditions prevail across interior NorCal next 24 hours, with light surface winds generally below 12 knots. East wind gusts up to 15 to 20 knots in the higher elevations through 17z Thursday.

STO WATCHES/WARNINGS/ADVISORIES
Heat Advisory until 10 PM PDT Thursday for Butte County Below 1000 ft-C. San Joaquin County including Stockton-C. Solano County including Fairfield-C. Stanislaus County including Modesto-C. Yolo/NE Solano including Woodland-Central Colusa County Incl. I-5-Central Glenn Co & Interstate 5-Central Motherlode 1000-3000 ft-E. Diablo Range Above 1000 ft-Eastern Colusa County-Eastern Glenn County-N. Motherlode 1000-3000 ft-N.
Sac Valley in Tehama County-NE San Joaquin Valley Below 1000 ft- SW Solano County including Vallejo-Sac Metro/W. El Dorado/Amador County-Sacramento County Delta-San Joaquin County Delta-Shasta County Foothills 1000-3000 ft-Shasta Metro-Sierra (Tehama- Plumas) 1000-3000 ft-Southern Motherlode 1000-3000 ft- Sutter/Yuba counties below 1000 ft-Tracy Triangle Below 1000 ft- W Tehama Co Foothills 1000-3000 ft-W. Glenn/Colusa Foothills 1000-3000 ft-W. Shasta County 1000-3000 ft-W. Stanislaus County Above 1000 ft & I-5-W. Yolo County including Capay/I-505-Yolo / Solano County Hills.