Marine Weather and Tide Forecast for Port Costa, CA

DISCUSSION

...Rest of Today-Friday...
Mostly clear skies observed across interior NorCal at the time of this writing. Upper level pattern reveals a ridge of high pressure deepening inland and weak troughing developing to the southeast of the area. Pattern will continue to allow for gusty north to east winds in the Sierra Nevada and adjacent foothills, north winds in the Valley, and low humidity values. Some observation points in the higher elevations have recorded wind gusts of 40 to 45 mph this morning, as well as morning RH values in the teens to low 20s, creating critical fire weather conditions. As the ridge and low deepen, winds will once again increase as we move into the evening and overnight areas. The Red Flag Warning will continue in the Sierra and adjacent foothills through at least 10 AM Friday.
NBM probabilities of wind gusts greater than 40 mph in the mountains are around 70-90% this evening and overnight, as the resultant pressure gradient will be the strongest. Overnight RH recoveries will remain in the low 20s to 30s, similar to what we saw this morning.

Elsewhere in the Valley, periods of breezy north to east winds will develop; strongest along and west of the I-5 corridor today and Friday. Locally stronger wind gusts of 30 to 40 mph in Colusa, Yolo, and northwestern Solano Counties will develop Friday as well. Elevated fire weather conditions will continue in the Valley and areas listed above tomorrow when winds are the strongest and humidity values are at their lowest. High temperatures will continue to warm today and Friday, with highs reaching the low 90s across much of the Valley. Ridge axis will begin to slowly move to the east, while a weak cut-off low forms in SoCal by Friday, keeping those dry and breezy to gusty conditions lingering through the afternoon/evening.

Weekend into Next Week
By Saturday, the ridge moves further east, and cut-loff low remains off the coast of SoCal. Pattern will allow for slight cooling to begin across the region, but only by a few degrees keeping temperatures above normal with continued dry conditions.
Offshore winds will ease as well as the upper air pattern continues to evolve. Sunday, a notable pattern change will begin as the aforementioned SoCal cut-off low will factor more into our weather pattern, allowing onshore flow to return to the area. High temperatures will cool to the low 80s across NorCal on Sunday and humidity values will see much better recoveries. Low pressure will also develop in the PacNW and begin to dig further south Sunday afternoon/evening.

Further southerly movement of the PacNW low and associated offshore troughing will cool temperatures further Monday through Wednesday, as well as introduce some slight shower chances to the region. Uncertainty remains relatively high on where the PacNW low will track, but recent ensemble runs are trying to keep the parent low offshore. Pattern would suggest better precipitation chances in the mountains and foothills, and the NBM probabilities reveal the best chances (50-70%) of 0.10" of measurable rain will be in the higher elevations. We will continue to monitor the track and strength of this system, but overall a cooldown and return of onshore flow are very likely early next week.

AVIATION

VFR conditions continue across interior NorCal next 24 hours.
Light to locally breezy north winds less than 12 knots at Valley TAF sites. North wind gusts up to 15 to 20 knots at RDD and RBL beginning roughly 20z today and continuing through the forecast period Friday. East to northeast wind gusts of 30-45 knots along the Sierra next 24 hours. Additional north wind gusts of 20-30 knots in Yolo and Colusa counties 20z today.

STO WATCHES/WARNINGS/ADVISORIES
Red Flag Warning until 10 AM PDT Friday for Central Motherlode 1000-3000 ft-N. Motherlode 1000-3000 ft-Sierra (Cal-Tuo) 3000- 5000 ft-Sierra (Cal-Tuo) Above 5000 ft-Sierra (El Dorado-Amador)
Above 5000 ft-Sierra (Sierra-Placer) Above 5000 ft-Sierra (Tehama-Plumas) 1000-3000 ft-Sierra (Tehama-Plumas) Above 3000 ft-Sierra (Yuba-Placer) 3000-5000 ft-Sierra 3000-5000 ft- Southern Motherlode 1000-3000 ft.