Per Dr. Daniel Swain of Weather West…
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Update: will wait until tomorrow for the new post. Sunday offshore wind event could be a very big deal, and I want to see more model runs before having that conversation…
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It means it is in the upper echelon of what you’d expect wind speeds to be for the single area, for the single date… based on 20 year return interval. So 0% would be about ‘normal wind speed’, while 100% would be the strongest maximum wind event for that day, recorded in the last 20 years.
Here is the GEFS HOT-DRY-WINDY index which is similar:
Here is another example showing that deep cold air east of the Sierra… on the scale it’s -92% of what would be the maximum expected coldest temperature within 20 years, for that point on that given day. So this run shows it at about 8% warmer than has ever been recorded for that point, for this day in the last 20 years.
From NWS Reno:
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Sacramento Valley/Northern Sierra/Cascades
Gusty winds and low humidity will result in critical fire danger conditions today and a Red Flag Warning is set to stay in place through 5pm Friday for the valley, foothills, and a portion of the Sierra. Trinity, Mendocino, and Siskiyou County areas will be under a Red Flag Warning for high fire danger through 11am Friday. We are also under a Wind Advisory in the valley through 8pm tonight. Sustained winds to 30mph out of the north will be possible today in the valley, and there is potential for gusts up to around 45mph. Winds will also be very strong tonight through early Friday in the foothills, and favorable canyons. Gusts up to 60mph out of the northeast will be possible in areas around the Feather River Canyon late tonight through mid day Friday. High pressure off the coast in the Pacific continues to interact with low pressure in the great Basin to our east today and that is resulting in the strong wind even we’re starting to see early Thursday. Winds will be the biggest issue and will drive high to critical fire danger conditions through Thursday and into at least early Friday. Sustained winds over 20mph are already being observed in the valley this morning, and gusts up to 45mph will be possible today. Humidity will dip into the 5 to 25 percent range this afternoon. High temperatures will mostly top out in the upper 70’s to lower 80’s in the valley, and in the 60’s to 70’s in the foothills and mountains this afternoon.
Winds will become stronger in the gaps and canyons of the Sierra Foothills tonight, and this will result in critical fire danger concerns through early Friday. Gusts up to 60mph are possible in areas surrounding the Feather River Canyon. Winds will start to diminish after mid morning on Friday, and we’re expecting much lighter winds for the afternoon. Lighter winds, and much cooler temperatures will then be ahead for Saturday. Valley areas will mostly top out in the low to mid 70’s, while foothill and mountain areas mostly end up in the 60’s to around 70 degrees on Saturday afternoon. We’ll end up a few degrees cooler on Sunday, but we will also start to see the next wind event ramping up as we head into Sunday night. This is currently expected to be the most substantial wind even we’ve seen this season, and will result in critical fire danger from Sunday afternoon through Monday. Gusts upwards of 60mph will be possible out of the northeast in the favorable gaps and canyons during this event. The biggest impacts are expected in the Sierra Foothills. Valley areas will also have stronger winds, but they are not expected to be as bad as today during this time.
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Extreme Fire Weather conditions for Sunday and Monday in Nor Cal. Gusts to 70 mph in the favored passes.
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Wind is “fairly” calm so far, Just occasionally windy . Heavier on the west side of the Sacramento Valley . But the Paradise/Jarbo Gap area is a normal day so far… It is always breezy here.
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It’s going to be fire watch or upgraded red flags every week until rain gets here.
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Perhaps Todays Wind event is not going to be as strong as first thought in the foothills. Most of the wind seems to be down in the Sacramento Valley. I just got notified that weather conditions have improved and PGe is doing line inspections with the hopes of restoring power earlier that anticipated. However they have updated their information for this weekend
Winds will decrease somewhat this afternoon before a second but weaker peak in winds develops tonight into tomorrow morning. Offshore flow will gradually diminish throughout the day Friday and become onshore overnight into Saturday. This will result in cooler temperatures and increased humidity. However, a much stronger weather system is expected to move through the region Sunday into Monday which could result in another round of breezy to gusty offshore winds increasing through the day Sunday, peaking Sunday night into Monday, and possibly lingering in some regions through early Tuesday.
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Meteorological setup is different for this wind event than our previous Red Flag Warnings so far this fall. As usual expect first burst of winds to spread over the North Bay Sunday afternoon as winds come down the Sac Valley and spread over the Bay Area. Since this wind event will be synoptic driven it wont have the usual strong diurnal tendencies. Expect increasing winds during the late afternoon/evening hours before dark. Then as the sun goes down Sunday night a strong burst of winds will rapidly pass over the Bay Area. Of course the strongest wind potential will be in the hills but there is fairly high confidence that winds will mix down into the lower elevations and then crash along the coastline from Bodega Bay to Half Moon Bay before spreading offshore. Thus High Wind Watch covers the entire Bay Area, not just the hills. Wind damage will be likely for any fire weakened trees. Downed trees, branches and powerlines will be a high possibility. In simple terms this event looks to be on par with the 2017 wine country fires and last years Kincade fire (that occurred Oct 26-27th 2019). Will say the meteorological setup is slightly different. Cold advection looks stronger which should favor better mixing of winds to the surface. In addition though the North Bay may take the brunt of the wind much of the East Bay, SF Peninsula and Santa Cruz mountains will see high wind potential as well as the Highway 1 corridor Sunday night. The 2017 wine country and 2019 Kincade peaked between 9 pm and roughly 1-3 am at night. This event may arrive slightly earlier but should any fires start it will be a long night of gusty winds. In addition the airmass appears to be much drier with humidity values forecast to plummet into the single digits and teens. There will be no marine layer so even the valleys will be bone dry. And as has been noted throughout the week this will all occur on top of record dry fuels. So yes it has similarities to the 2018 Camp Fire as well. Trying to think back and this pattern shows strong signals to some memorable Sierra East Wind events where the winds howl down the corridors of Interstate 80 and Hwy 50 pouring out across the Bay Area. Believe the 2004 Fred, Power and Rumsey fires showed big growth days under a similar setup.
Current model solutions show winds peaking between 7 pm and midnight Sunday (gusts to 70 mph looks likely)
Just looked at fuels and ERC readings setting new records. The stratus coverage the next 1-2 days will temper some of the fine fuels but it wont matter. Other high confidence element here is the incredibly dry airmass that will quickly overspread the region Sunday night into Monday. High pressure next week with no rain through the end of the month.
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Upgraded to Red Flag: “Winds are expected to be the strongest of the 2020 fire season with critically dry conditions.”
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From NWS Bay Area AFD tonight:
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That is not just geeky. It is sort of scary stuff. My studies in meteorology and aviation were decades ago but I remember the danger associated with mountain waves. Mountain waves are the result of flowing air being forced to rise up the windward side of a mountain barrier, then as a result of certain atmospheric conditions, sinking down the leeward side. This perturbation develops into a series of standing waves downstream from the barrier, and may extend for long distances over clear areas of land and open water. If the wave amplitude is large enough, then the waves become unstable and break, similar to the breaking waves seen in the surf. Within these ‘breaking waves’, the atmospheric flow becomes turbulent. lenticular clouds, rotors or eddies and all sorts of wild turbulence. Would not want to be flying into Sac or the Bay Area Sunday night. So in layman’s terms all hell is going to break loose. or could. In The mountain passes and places like Jarbo Gap at the mouth of the feather river canyon it could be devastating. Sitting 4 miles from Jarbo gap on the west branch drainage one gets a sense of Deja Vu . None of this sounds appetizing in the least. Better rest up Sunday night could be a long one . Da@#
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NWS SF - Friday: Red Flag Warning officially starts for the North and East Bay hills at 11 am Sunday. Timing may be a bit early, especially for the East Bay but initial winds will start to increase over Napa hills by midday.
The latest SFO-WMC gradient looks to peak around 18 mb late Sunday night. All fire weather parameters will be off the charts (fuels, wind, humidity). Long range spotting of up to 1 mile would certainly be possible. ERC charts still setting records for the Diablo and Santa Cruz mtns with much of the North Bay and lower regions of the Bay Area critically dry.
We often have to wait for humidity to lower several hours after the winds. In this situation there will be a clear dry air boundary that will allow RH to plummet well into the teens and possibly single digits. This dry boundary will help to propagate strong winds from the hills down into the valleys. Between nightfall and before midnight the entire region will feel the strong and gusty offshore winds as the airmass dries out and humidity values plummet well under 30 percent. Northeast winds will be strongest in the hills but high confidence that locations in the lee of the hills such as the North Bay valleys, coastal Sonoma/Marin, the 880 corridor including the populated areas of the East Bay hills will all see gusty winds. Model timing continues to suggest the strongest winds to be from roughly 6-7 pm through midnight Sunday night. In some ways this is good news as most people wont be sleeping as was a problem during the 2017 wine country fires. The fuels remain at record dry levels so the combination of incredibly strong winds and low humidity would allow for dangerous rates of spread. Power outages will be likely throughout the region as well, both planned and unplanned. In summation its going to be windy Sunday night and the initial burst between 6 pm and midnight is likely to be the most dangerous time frame. Those locations on the lee of the hills (north bay valleys, Berkeley hills) will be susceptible to strong downslope winds Sunday evening. Expecting numerous reports of wind gusts in excess of 50 mph with local gusts in excess of 70 mph very likely. Even places like the City of San Francisco and coastal locations from Bodega Bay, Stinson Beach, Pacifica and Half Moon Bay will see gusty northeast wind gusts from 40-50 mph.
No rain forecast through Halloween and looking dry through the first week of November.
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The very strong La Nina that’s developed could push the rain back well into winter and be the start of another drought like 2014-2016.
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He made a special statement this morning…
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Weather West19 minutes ago editedFeatured by Weather West
These kinds of projected winds over the entire Bay Area and Sierra Nevada western slopes are frankly…scary, given the record dry vegetation levels right now. This is perhaps the highest risk Red Flag event in parts of NorCal this decade–which is saying a whole hell of a lot. I’m hoping these model forecasts are simply wrong, as if this happens I don’t really see how we escape at least a couple of very dangerous fires in the urban interface even with widespread PSPS.
All I can say is: have a plan for Sunday. The worst of this will probably occur between 5pm and midnight Sunday, when new ignitions will be most likely, although conditions will be adverse all the way through Tuesday. If you’re in a particularly high risk zone with limited egress routes, you might even want to consider pre-emptively evacuating before a fire ignites on Sunday (apparently Berkeley is officially recommending this action for folks in the hills).
I’ll probably be online all night Sunday unless (by some miracle) there are no ignitions by midnight. Twitter is still, unfortunately, one of the best ways to follow what’s going on in real-time–local traditional news is likely to be behind the curve and even cell phone alerts/reverse 911 calls are still relatively lagged. Feel free to use this public list: you can bet that if a fire starts that the folks here will know about it within minutes."
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I see folks have already summarized my recent thoughts here (accurately and succinctly, I’m pleased to say!), but just wanted to briefly chime in.
The Sun/Mon extreme wind/Red Flag event is about as concerning as I’ve seen in northern California, and after the last few years that is saying quite a lot. These winds will not only be quite strong but the will be unusually widespread for an offshore wind event–cold air advection and the possible development of mountain waves suggests that very strong gusts could reach sea level/valley floors. Additionally, atmospheric humidity during this event will be exceptionally low–about as close to zero as at ever gets in this part of the world. Fuels are already at record dry levels in many places.
For these reasons, I am concerned that areas outside of the current PG&E PSPS zones could easily see winds strong enough to knock down trees/wires and ignite poweline fires in areas that have not been de-energized–even down into the urban core of the Bay Area. Gusts of 50+ mph are possible in some areas down to sea level, with gusts of 65-75 mph in the hills and perhaps very locally even as high as 95-100mph in the windiest spots just west of the Sierra Nevada crest on the western slope.
This is the kind of event that puts much of the highly populated WUI in the SF Bay Area at great risk–including places like Marin and Alameda counties that have very high background risk but have been spared very serious fires in recent years. These will be scary times for the Oakland Hills and the Mill Valley areas. I am also concerned about the towns along the Sierra Nevada western slope–this is a potential nightmare weather setup for places like Placerville.
(If you’re interested, I did a full write up on this 36 hours ago:
https://weatherwest.com/archives/7691)
Not to be outdone, critical to extremely critical conditions are also likely in SoCal. I’m just highlighting the NorCal risk due to the fact that the risk there for about an 18 hour period from early Sun evening until noon Monday will be truly exceptional. I am hopeful that PG&E and SCE’s PSPS plans will help mitigate the risk of powerline ignitions, but we’re going to be very lucky indeed if we make it through this without at least or or two serious fires in the WUI. Fingers crossed…
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California’s Office of Emergency Services (Cal OES) has strategically prepositioned firefighting resources and personnel in nine counties in Northern California to be prepared for the upcoming wind even and Red Flag warning. The event is forecast to have the lowest humidity and the strongest winds of the fire season.
Strike teams of fire engines, firefighters, hand crews, water tenders, helicopters, dispatchers, and overhead staff in nine counties across the state. A strike team includes five fire engines with 15 firefighters and a strike team leader.
The prepositioned fire resources include:
• Tehama County: 1 Cal OES Strike Team (5 Cal OES Type 3 Engines)
• Colusa County: 4 Local Government Type 3 Engines, 1 Local Government Type 1 Water Tender
• Lake County: 2 Local Government Task Forces (8 Local Government Type 3 Engines), 2 Local Government Type 1 Water Tenders, 1 Local Government Type 2 Dozer, 1 Dispatcher
• Napa County: 1 Local Government Task Force, (1 Local Government Type 2 Engine, 2 Local Government Type 3 Engines, 2 Local Government Type 6 Engines)
• Marin County: 1 Local Strike Team (5 Local Government Type 3 Engines), 1 Local Government Type 1 Water Tenders, 2 Dispatchers
• Santa Clara County: 1 Local Government Task Force, (3 Local Government Type 3 Engines, 1 Local Government Type 1 Engine, 1 Local Government Type 6 Engine)
• Solano County: 4 Local Government Type 3 Engines
• Alameda County: 1 Cal OES Strike Team (5 Cal OES Type 3 Engines), 1 Local Government Type 1 Water Tender, 1 Dispatcher
• Nevada County: 1 Dispatcher
Looks like we are not the only ones concerned about the upcoming wind event. A little extra help never hurts. How exactly do you adequately prepare for this ? I mean really …
Outlook for Upper Sacramento Valley, Cascade and Northern Sierra Mountains
Hurricanes have sustained wind speeds greater than 74 mph. We won’t see sustained winds that strong but in some mountain canyons and gaps, we could see winds gusting that strong. This is quite serious. Quick and significant fire spread will be possible if a wildfire is started in a strong wind-prone area, and even more dangerous in areas such as as Jarbo Gap or along some ridgelines. Winds will be strongest as a low pressure system to our east slides south in Utah and Nevada into Arizona .The strongest winds will be on Sunday gusting 30-40 mph in the valley from the north and 40-60 mph in the Sierra-Cascades and Coast Ranges. Some canyons and gaps in the Sierra foothills could gut more than 70 mph. Humidity could get as low as 5%! Monday will still be breezy with gusts 15-40 mph, but extremely dry conditions will continue, keeping fire danger critical. Overnight lows in the valley Sunday night could get in the 40s and overnight lows in the Sierra-Cascades will be in the teens to single-digits. A very hard freeze indeed. It is going to be a long and noisy night. With all the knowledge that is in the comments you have all written in this discussion we all know what is coming. It is just a question of how bad , bad will be. Fire Danger could not be much worse. Conditions are primed and ready . I was in Upper Paradise clearing lots today. Everything was so dry they were brittle. There is still so much to burn here.
Indeed… 
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Sonoma: 2 OES prepo Strike Teams, 1 LG Strike Team, 3 overhead, additional Dispatcher in REDCOM.
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Hold on to you’re hats folks!! Let’s hope we’re no talking about this one ten years from now!!! Everyone stay vigilant and safe!!
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