Point Pinos to Point Piedras Blancas out 10-60 NM Marine Forecast
|Today...Nw Winds 5 To 15 Kt. Wind Waves 1 To 2 Ft. Nw Swell 2 To 4 Ft At 10 Seconds, Increasing To 4 To 6 Ft At 10 Seconds This Afternoon. Swell S Around 2 Ft.|
|Tonight...N Winds 15 To 25 Kt With Gusts Up To 30 Kt. Wind Waves 3 To 4 Ft. Nw Swell 5 To 6 Ft At 10 Seconds And S Around 2 Ft At 13 Seconds.|
|Mon...Ne Winds 15 To 25 Kt With Gusts Up To 30 Kt. Wind Waves 3 To 4 Ft. Nw Swell 4 To 6 Ft At 10 Seconds And S Around 2 Ft At 12 Seconds.|
|Mon Night...Nw Winds 5 To 10 Kt. Wind Waves 1 Ft. Nw Swell 4 To 6 Ft At 14 Seconds.|
|Tue...Nw Winds Up To 10 Kt. Wind Waves 1 Ft. Nw Swell 3 To 4 Ft At 15 Seconds.|
|Tue Night...Se Winds Around 5 Kt. Wind Waves 1 Ft. Nw Swell 3 To 4 Ft At 13 Seconds.|
|Wed...Nw Winds 5 To 10 Kt. Wind Waves 1 Ft. Nw Swell 2 To 4 Ft.|
|Thu...Nw Winds 5 To 10 Kt. Wind Waves 1 Ft. Nw Swell Around 2 Ft.|
| 828 AM PDT Sun Oct 25 2020 |
Synopsis for the Central California Coast and Bays Including the Monterey Bay, Greater Farallones and Cordell Bank National Marine Sanctuaries - PZZ500
Generally light north to northwest winds across much of the waters this morning and into the afternoon with locally stronger winds still over the northern outer waters. Winds will increase this evening and shift out of the northeast. Gale force gusts are forecast from then until tomorrow morning, particularly over the San Francisco Bays and through the Delta as well as along the Sonoma Coastline, Bodega Bay, and down the San Mateo coast to Pigeon Point. Winds will gradually diminish tomorrow morning. These winds will generate steep fresh swell resulting in hazardous seas, especially for smaller crafts. Mixed seas will persist with a moderate northwest swell and a longer period southerly swell.
| Area Forecast Discussion|
National Weather Service San Francisco Bay Area
1044am PDT Sunday Oct 25 2020
Cloudy skies this morning will turn sunny this afternoon as drier air filters into the region. Becoming windy in the North Bay hills before dark then spreading over the rest of the Bay Area tonight with strong and damaging northeast winds. Red Flag Warnings and Wind Advisories in effect for the entire Bay Area while the bulk of the winds will not impact the Central Coast. Winds slowly ease Monday at lower elevations but it will remain breezy in the hills with a very dry airmass in place keeping fire danger high. Building high pressure Monday through Friday will bring sunny and warm days but with cool nigheights as lows drop into the mid and upper 30s for the interior valleys with 40s elsewhere. No rain forecast through the end of the month into early November.
as of 09:30am PDT Sunday...Starting the morning off with marine stratus across much of the Bay Area. Bodega Bay Profiler currently suggesting a depth just under 2500 ft, translating into high RH values along the coast and into the coastal valleys of the North and East Bay. Much like what we observed yesterday, expect for marine stratus to clear out by midday over much of the area. The axis of the positively tilted trough goes through our CWA today as offshore (NE) winds begin to enter our high-terrain locations and quickly mix down to the surface. The SFO-WMC gradient has rapidly increased to 5.3 mb this morning and is forecast to get up to 17 mb by around this time tomorrow morning.
Essentially, everything is on track for this offshore wind event. Only minor changes have been observed in some of the short-range model guidance, including a slight decrease in the progged offshore surface gradients through the overnight hours. It goes without saying, however, that this dry air mass is still set to bring some of the strongest winds to that the CWA has measured during this historic fire season. NAM-3km and HRRR (High-Resolution Rapid Refresh) continue to pick up on strong wind gusts in the 40-50mph range at some of our higher elevations >2000 ft, with the possibility of wind gusts as high as 70mph in our highest points (e.g. Mt. Diablo). In terms of RH values, short- term guidance picks up on low-level jet that will advect the dry air mass all the way into the coast overnight. RH values are forecast to fall into the single-digits in spots that this morning are currently shrouded under the marine layer (this includes the NAM run for the overnight hours, which has historically had a slight precipitation bias). Strong wind gusts are also forecast for much of the Bay Area, including much of the valleys and coastal spots. From Monterey Bay area southward, winds will be lighter (with the exception of some isolated pockets along the northern Big Sur Coast. Winds around the Dolan and Coleman Fire also expected to be light during the next couple of days. The NE flow that will mix down to the surface will predominantly be steered towards the SF Peninsula coast while the Santa Cruz Mountains will help to naturally steer them away from the Central Coast as a result. Nonetheless are still expecting low RH values and next to no overnight humidity recoveries across the entire CWA.
These critical fire weather conditions will be observed over much of the State in the next couple of days. As a result, questions have come up regarding the differences between the Diablo Winds, Sundowners, and Santa Ana winds. Want to clarify that all of these naming conventions refer to the offshore winds that develop across a given region. Here in the Bay Area, strong offshore winds are referred locally as the Diablo Winds. Regardless of their naming convention, they refer to the same setup when katabatic (downsloping) winds descend from higher-terrain locations down to the coast.
While main focus has been on the North Bay, it should be noted that the burn scars in the area may actually help mitigate some of the fire risk there given the amount of burning that has already happened there this fire season. That being said, any new wildfire starts, especially under these circumstances, is the last thing that firefighting operations need at this time. Other critical concern is for the East Bay hills, as they have historically dealt with wildfires that have made it into urban areas under critical conditions. For some historical background on the wildfires that have occurred under extremely critical fire weather risk events, have including previous discussion. It also goes without saying that air quality will be entirely at the mercy of whether or not wildfire starts occur during this critical fire weather setup. Should any wildfires develop, will be monitoring smoke plumes closely as well. As always, be sure to reach out to the Bay Area Air Quality Management District for any new alerts and AirNow forpm and ozone concentrations.
track with no real changes of note in terms of upcoming wind.
Synoptic pattern features a longwave trough over the Rockies with a strong jet stream aloft coming down the backside of the trough into Nevada. This will allow very cold air to spill into the Great Basin setting up a strong surface pressure gradient across the Sierra. The SFO-WMC is neutral and will rapidly increase to about 18-19 mb over the next 24 hours. Initial shot of north winds will work down the Sac Valley today and should reach the Napa hills by early afternoon. Strong wind gusts in excess of 50 mph will hold off until 4-7 pm. Wind Advisory officially starts at 4 pm and that timing looks good. Most of the Bay Area will maintain light winds through that time. Things will change quickly as the dry cold front and associated dry air quickly spill into the Delta region and fans out across the rest of the North/East Bay and quickly passes over the rest of the Bay Area. We dont often get to see true synoptic frontal boundaries that are so clearly defined but this well be obvious for anyone paying attention. The airmass change will be abrupt as very dry air filters over the region and it wont discriminate between the hills and valleys.
In terms of winds, everything is still on track. The 925 mb winds first show gust potential across the Napa hills between 00-03z this evening. As is often the case as the sun goes down the winds will increase. Between sunset and the overnight hours the northeast winds will howill across much of the Bay Area. Models show strongest wind potential will be with the initial burst of winds. If things go down hill in terms of new ignitions we should know before midnight. Model cross sections show very strong winds aloft with downward sinking air. There wont be any inversion of note to keep the strong winds from mixing down, though some of the the valleys of the North Bay and Santa Clara Valley will be more protected there is too much small scale topographic interaction to pinpoint that level of detail. In terms of magnitude if memory recalls the models were showing perhaps stronger wind strength during the 2017 wine country and 2019 Kincade fires but this event looks to be more widespread. Another noted difference is the strong east winds over the Sierra region west of Tahoe. During these setups those winds take a straight beeline towards Mt Diablo and then under the right conditions will drop down into the East Bay hills region above the 880 corridor. Wind damage still appears likely overnight as the high momentum wind gusts will take out drought and fire weakened trees/limbs/powerpoles across the region. In addition temporary tents and other structures will likely be compromised. Trash and other debris will whip around and cause hazardous driving conditions.
Of course ironically the fresh burn scars will preclude those areas from burning but any fire prone locations will be of concern tonight. At this point looking back at history may be germane. Recall the 2017 Tubbs Fire took on a similar scar to the 1964 Hanly Fire. More recently of course is the 1991 Oakland Hills Fire. 1923 Berkeley fire was in September but shows the urban potential. The Vision fire of 1995 near Pt Reyes will be worth remembering as the models show strong winds downwind of Mt Tamalpais. So we can say that winds look especially strong tonight, fuels are historically dry and humidity is even drier than normal in association with this airmass. Unlike normal offshore wind events we dont expect the strongest winds to be confined to the hills as the atmospheric profile will be conducive to mixing those winds down. The wildcard of course will be any new ignitions. Will also mention though we haven't focused as much on it do expect strong winds along Skyline Blvd in the Santa Cruz mtns and down along Hwy 1 so those locations outside the CZU burn scar will be of concern. Inside the CZU burn scar the prospect of fire weakened redwood trees falling is of grave concern as well.
As the sun comes up Monday morning skies will be crystal clear (hopefully) and temps noticeably cooler as the dry airmass filters in. East to Northeast winds will still be blowing but should ease by mid morning. Models do show an early secondary burst of winds for the North and East Bay hills so the Red Flag Warning will continue. We of course will have to re-evaluate the Wind Advisory and Red Flags by Monday morning and extensions may be necessary. For clarity of message no changes have been made to start and stop times for now.
The dry airmass and offshore winds continue Monday night into Tuesday so should any fires start containment will be challenging.
Next item of note will be if frost advisories will become necessary. Winds may be strong enough in the hills to preclude that and all focus for now is on winds. However, those with ag interests should be ready for some upcoming cold nights. Will note the ECMWF (European Centre for Medium-Range Weather Forecasts) mos for Santa Rosa is 32 Tuesday morning. If power outages occur or linger the cold overnigheights could become problematic.
Ironically enough afternoon highs will be showing a warming trend Monday afternoon though much of next week as high pressure builds. Offshore winds and the dry airmass will set up ideal adiabatic compression. Should we get through the wind event unscathed the weather pattern next week looks quiet with high pressure and seasonably warm days followed by clear and cool/cold nights.
High confidence for no rain through the end of the month and early signals looking dry through the first week of November.
as of 4:21am PDT Sunday...No changes to Red Flag headlines. The Warnings officially start at 11 am for the North and East Bay hills. The timing looks good for the North Bay as winds will start to hit northern Napa around this time. Admittedly the strong winds will hold off for the East Bay hills until late afternoon but for clarity of messaging and to avoid confusion will keep start times as is for now. The rest of the Red Flags for the Bay Area start at 8 pm which looks good though some areas may notice the increased winds slightly earlier.
In terms of overall setup, as noted above not much change in thinking. Cloud coverage and high humidity to start the day should fool nobody. Boundary will arrive late this afternoon. Main event will be from roughly 6 pm (north bay) through the overnight hours but the strongest initial burst of winds may occur before midnight. Wind gusts 40-50 mph at lower elevations, downwind of the hills (East Bay hills, coastal Marin, Pacifica/Half Moon Bay) with expectation for gusts 60-70 mph for the higher elevations of of the North and East bay hills, roughly above 2500 feet.
Heavy fuels remain at or near record dry levels. Humidity values will plummet late this afternoon and overnight with essentially no recovery. Should any ignitions occur this evening its likely that all model simulations will fail to capture the true spread potential. Long range spotting, record dry fuels, wind gusts 50-70 mph and humidity in the teens would all be valid model inputs along with a highly turbulent/unstable boundary layer. Boots on the ground should give strong consideration to LCES. Expect egress to be blocked and normal comms to potentially be disrupted.
Winds will persist all night into Monday morning. Models show winds slowly easing at lower elevations but increasing again in the hills with gust potential still to around 50 mph though early Monday afternoon.
Persistent east flow will continue Monday night into Tuesday morning with no humidity recovery for all elevations. Its possible that Red Flags may need to be extended but that will all be re-evaluated Monday morning.
Long range shows dry with high pressure next week, no rain. Warm days and cool nights. No marine layer expected for most of next week.
as of 08:28am PDT Sunday...Generally light north to northwest winds across much of the waters this morning and into the afternoon with locally stronger winds still over the northern outer waters. Winds will increase this evening and shift out of the northeast. Gale force gusts are forecast from then until tomorrow morning, particularly over the San Francisco Bays and through the Delta as well as along the Sonoma Coastline, Bodega Bay, and down the San Mateo coast to Pigeon Point. Winds will gradually diminish tomorrow morning. These winds will generate steep fresh swell resulting in hazardous seas, especially for smaller crafts. Mixed seas will persist with a moderate northwest swell and a longer period southerly swell.
.MTR WATCHES/WARNINGS/ADVISORIES... .Tday...Wind Advisory...CAZ006-505>513-529 Red Flag Warning...CAZ507-511 GLW...SF Bay from 5 PM SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 PM