Marine Weather and Tide Forecast for Colma, CA

SHORT TERM
(This evening through Wednesday)
Issued at 218 PM PDT Tue Apr 29 2025

Splendid day today with nearly cloudless skies, sans a few areas along the immediate coast. Temperatures as expected today with temperatures ranging from the upper 60s to upper 70s. Some locations along the coastline held on to marine stratus for a bit longer today, so these locations are just getting out of the upper 50s as of writing. Shifting focus a bit to tomorrow since there some more interesting things to talk about. A subtle upper level trough is progged to move through the region tomorrow which will bring a low chance of very isolated showers and thunderstorms to the North Bay and areas near Monterey and San Benito counties in the vicinity of the Gabilan Range. Cold air advection in the upper levels with the passage of the trough and hi res guidance depicting sufficient low level moisture advection result in moderate instability of ~1,000 J/Kg. Rather impressive for this time of the year, but not unheard of. Areas of interest in this event would be favored areas of terrain-enhanced convection, such as interior portions of the North Bay and the interior Central Coast along the Gabilan Range. Limiting factors for severe modes will be the relative lack of a lifting mechanism and overall low degree of instability throughout the layer (slightly unstable through a deeper column as opposed to highly unstable through a shallower column). Should our available instability be realized through lifting via diurnal heating over these isolated terrain areas, we could see brief heavy showers and perhaps some small hail...again emphasizing isolated to the aforementioned areas.

LONG TERM
(Wednesday night through next Monday)
Issued at 218 PM PDT Tue Apr 29 2025

Once again not much to talk about between Wednesday and Friday, so shifting focus to the weekend. We have increased attention towards the weekend event regarding windy conditions. A deep upper low progged to enter the NEPac by Friday afternoon will bring quite a contrast to what we are going through mid-week. Increased cloudiness and breezy conditions will begin affecting the region late Friday. Winds increase on Saturday as a stout 75-80 kt 500 mb jet streak digs south along the West Coast. Behind the cold front we can expect wind gusts into the 40-50 mph range across some of the high coastal terrain. Ensemble forecast tools corroborate this with the ECMWF extreme forecast index showing a good agreement of model members well above climatology and cluster analysis advertising solid agreement in the overall pattern. As such, winds have been nudged toward the 75th percentile in the forecast for late Friday night through Sunday. Judging based on the forecast trend, winds could be adjust higher in future forecast packages if the trend continues. Keep up with the latest forecasts for the most up to date information as the timeline moves closer.

AVIATION
(00Z TAFS)
Issued at 845 PM PDT Tue Apr 29 2025

The marine layer depth varies from 800 to 1000 feet. Coastal stratus and fog /MVFR-IFR-LIFR/ will continue tonight and Wednesday morning with local inland intrusions of stratus and fog due to onshore winds. Sea surface temps 49F to 54F are running in good contrast to lower level temperatures in the 60s, both Fort Ord and Point Sur show a well developed lower level temperature inversion. Adding complexity to the forecast, a 500 mb trough (with near late April normal height and temp) arrives tonight and Wednesday with a reflection of weak cyclonic circulation developing at 850 mb and 925 mb early Wednesday within the lower level temperature inversion/lower level thermal ridging. Light offshore winds aloft North Bay will sustain the lower level warmth and stability, while onshore winds to the south will slowly erode the lower level warmth and stability, deepening the marine layer but perhaps not fully eroding the lower level warmth Wednesday.

Best chance for afternoon convection will be inland, however there may be enough residual lower level warmth i.e. stability and/or surface cooling depending on extent of inland marine air intrusion limiting surface convective temperature. Based on NAM, HRRR convective parameters and global model QPF and precipitable water there will be potential for a few inland showers/downpours; at this time not expecting any impacts to our forecast area airport terminals.

Vicinity of SFO...VFR, onshore wind through the period. Low confidence MVFR ceiling Wednesday morning, if the marine layer deepens there's a better chance of a stratus ceiling.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...IFR-LIFR due to stratus and fog, however with the development of a weak cyclonic circulation in the lower levels beginning early Wednesday morning, onshore winds through a greater depth as well as weak cooling will deepen the marine layer in this area. May need to adjust TAFs to reflect IFR gradually lifting to MVFR early Wednesday, with subsequent mixing out to VFR likely by late morning or early afternoon.

MARINE
(Tonight through next Monday)
Issued at 712 PM PDT Tue Apr 29 2025

Northerly flow will persist thanks to high pressure anchored to the west. Winds will be locally stronger, especially over the outer waters leading to hazardous conditions for smaller craft through Wednesday. Moderate seas and moderate northwesterly breezes will prevail Thursday and Friday. Strong northwesterly breezes and rough seas return Saturday to the outer waters.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Wednesday for Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory until 3 AM PDT Thursday for Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory until 3 PM PDT Wednesday for Pigeon Pt to Pt Pinos 10-60 NM.