Another Highly Predictable Windstorm/Wildfire Event: Ventura and Los Angeles Counties

It has happened again:  a major wildfire event initiated by strong offshore winds.  Again, the winds were caused by cool, high pressure moving into the intermountain west.  And again, the forecasts were stunningly good.  And I
suspect, again, problematic power lines will be involved in starting the fires.

Wildfires are burning right now in Ventura and Los Angeles counties, with the largest fire (the Thomas fire impacting Ventura, CA) starting in the hills and then descending down to town (just like the Tubbs fire that hit Santa Rosa on October 8-9).

As I write this, the Thomas Fire is out of control, having consumed more than 50,000 acres, with other fires on the southern slopes of the terrain surrounding the LA Basin (see map of its current extent).  

Over 200 buildings have lost, and more will soon join them.  The fires started abruptly as winds picked up late in the afternoon on Monday.  We went from nothing to tens of thousands of burnt acres in a few hours.   The NASA MODIS satellite tells a stunning story, with no smoke or fires yesterday and multiple large fires around noon today (see below).

The fires began around dinner-time Monday as strong, dry Santa Anna winds revved up.  Here are the maximum wind gusts for the 24h ending 7 PM Tuesday. A number of locations got about 60 mph (purple color), with several getting up into the upper 70s.  Huge variability in the winds, depending location and exposure.  These strong winds were from the northeast.

Over 200,000 customers were out of power by late Monday.  

Let me show you a sample of the wind evolution at a mountain site, Chilao, CA, located at 5490 ft in the hills north of Los Angeles.  Winds increased rapidly yesterday and around 72 mph starting around 4 PM Monday.  Now dropping but still strong.

Interestingly, temperature COOLED as the winds increased from around 50F to the lower 30sF as the winds increased.  This event is not about heat, it is about dry air and wind.

 The whole event was caused by cool, high pressure moving into the Northwest (yes, us!) and then southward into Idaho and Nevada (see map for 1 AM today, showing the pressure analysis).

 This pattern produced an offshore pressure gradient (higher inland, lower along the shore), which in turn produced offshore (easterly and northeasterly) winds over southern CA.  These winds were strengthened by their interactions with the substantial terrain of the region, producing what is known as Santa Anna winds.

 Numerical weather prediction models run by the National Weather Service and others skillfully forecast this event days before, with the predictions the day before being dead on.   For example, the Desert Research Institute (DRI) WRF model prediction initialized at 4 AM Monday showed huge sustained winds over the region later that day (forecast for 10 PM Monday is shown).

The forecast made two days before for the same time was essentially the same...and very threatening (see below).   So this event was highly predictable.

The National Weather Service High Resolution Rapid Refresh (HRRR) model initialized at 4 AM Monday predicted strong winds in the area later that day.  I could show you more forecasts, but the message is clear:  my profession has now gained the ability to skillfully forecast such downslope wind events days before.

 And the National Weather Service forecasters were providing excellent guidance, pushing the severe threat in their communications on Monday, before the fires started (see below).  Excellent messaging.

Could this have all been avoided?

Let me ask the same question I offered in my blogs on the Wine Country fires.

We had nearly perfect weather forecasts that called for very strong winds over and downwind of the regional terrain.  The fuels (grasses, bushes) were very dry. Their was a strong probability that power would be lost in large areas and that power lines could start fires, which would explosively develop.

So why not preemptively shut off the power, to all the power lines that ran in the vegetated hills?   Could we have stopped this growing disaster from ever happening?

Power companies and those in responsible positions need to rethink about how they respond to these predictable wind events.  We can radically reduce the damage toll and loss of life by taking more active measures, informed by excellent weather forecasts.

from Cliff Mass Weather and Climate Blog http://ift.tt/2B2kzqq

The Godzilla Ridge Returns

It is big, hard to get rid of, and persistent.  Scary for those who love fresh snow. 

Yes, it is the Godzilla Ridge.  One so powerful that is may be hanging around for 1-2 weeks.  Strong enough to give us sun in normally cloudy December.

A ridge is the term given to a high pressure area, and is usually applied when talking about upper level charts.  Here are a series of 500 hPa (about 18,000 ft) upper level forecast charts from NOAA/NWS. 

Monday at 4 PM...big ridge off our coast.  Godzilla is here.  And ridges bring descending air and warmer temperatures aloft.

 Wednesday at 4 PM.....EVEN STRONGER and closer to the coast.  A major trough on the East Coast, bringing colder weather there.

 Friday at 4 PM...a small shift eastward and slightly weaker.  Big cooling in the eastern U.S.

Sunday, December 13th...the ridge strengthens.  Unbelievable

The latest weather.com forecast for Seattle, shows lots of sun this week and the probability of precipitation stays at 10% or less through Tuesday Dec 12th.

An interesting aspect of all this is that temperatures will warm substantially aloft, while cold air  (and high pressure) moves into eastern Washington.  As a result, a very strong pressure difference will develop near the Cascades crest (see map at 1 PM Wednesday, with lines of constant pressure--solid lines--and temperatures---colors), with localized strong easterly winds.

The wind gust prediction at this time (below), shows some gusty winds along the Cascade crest, with stronger winds north of Mt. Rainier downstream of the Stampede Gap.   Strong easterly winds over the eastern Strait of Juan de Fuca.

With high pressure aloft and associated sinking air, the air above us will warm and dry.  Take a look at the sounding of temperature (red) and dew point (blue) for 4 AM on Thursday.   Temps and dew point are really separated, which means very dry air.  And the freezing level is above 10,000 ft (700 hPa is roughly that height).  Note the inversion (temp warming with height) near the surface.  Air quality will decline.

from Cliff Mass Weather and Climate Blog http://ift.tt/2zKDqlG

The Godzilla Ridge Returns

It is big, hard to get rid of, and persistent.  Scary for those who love fresh snow. 

Yes, it is the Godzilla Ridge.  One so powerful that is may be hanging around for 1-2 weeks.  Strong enough to give us sun in normally cloudy December.

A ridge is the term given to a high pressure area, and is usually applied when talking about upper level charts.  Here are a series of 500 hPa (about 18,000 ft) upper level forecast charts from NOAA/NWS. 

Monday at 4 PM...big ridge off our coast.  Godzilla is here.  And ridges bring descending air and warmer temperatures aloft.

 Wednesday at 4 PM.....EVEN STRONGER and closer to the coast.  A major trough on the East Coast, bringing colder weather there.

 Friday at 4 PM...a small shift eastward and slightly weaker.  Big cooling in the eastern U.S.

Sunday, December 13th...the ridge strengthens.  Unbelievable

The latest weather.com forecast for Seattle, shows lots of sun this week and the probability of precipitation stays at 10% or less through Tuesday Dec 12th.

An interesting aspect of all this is that temperatures will warm substantially aloft, while cold air  (and high pressure) moves into eastern Washington.  As a result, a very strong pressure difference will develop near the Cascades crest (see map at 1 PM Wednesday, with lines of constant pressure--solid lines--and temperatures---colors), with localized strong easterly winds.

The wind gust prediction at this time (below), shows some gusty winds along the Cascade crest, with stronger winds north of Mt. Rainier downstream of the Stampede Gap.   Strong easterly winds over the eastern Strait of Juan de Fuca.

With high pressure aloft and associated sinking air, the air above us will warm and dry.  Take a look at the sounding of temperature (red) and dew point (blue) for 4 AM on Thursday.   Temps and dew point are really separated, which means very dry air.  And the freezing level is above 10,000 ft (700 hPa is roughly that height).  Note the inversion (temp warming with height) near the surface.  Air quality will decline.

from Cliff Mass Weather and Climate Blog http://ift.tt/2zKDqlG

The Upcoming December Drought in the Northwest

A stunning transition is going to happen on Sunday.  

Precipitation over the Northwest will end. 

And we might not see another drop for over a week.  Maybe more.  An unusual occurrence in December.  You will see sun....but as we will note there is a threat:  low clouds and fog.

Let's take a look at the forecast upper level (500 hPa)  maps this week from the NOAA GFS model...and be prepared to have your jaw drop!

At 10 AM Sunday, a trough has moved passed us and a ridge of high pressure has started to build in the eastern Pacific.  The rain will be ending at this time.

One day later, the eastern Pacific ridge has amplified.   We are totally dry.

The ridging increases by Wednesday.... the ridge is HUGE and extends up to Alaska.

 Saturday at 10 AM.  The ridge is still there, but a bit weaker.    Plenty strong enough to keep us dry.

 It revs up even more on Sunday!

 And it is STILL THERE on Tuesday 12/12.

 And it continues after that for several more days.

Folks...we are talking about a total shut down of precipitation over us for 1-1.5 weeks.  In December.

OK, I know what you are saying.  What do the ensemble systems using many runs show?  Here is the anomaly (difference from normal) of 500 hPa heights for the mean of the NOAA GFS ensemble system for 4 PM Thursday.  Much higher heights than normal (high pressure) over the NE Pacific and our area.  BIG positive (high pressure) anomaly.

The forecast a week later IS THE SAME THING, just a little weaker.  Wow.

Next lets look at the precipitation forecasts from the vaunted European Center ensemble.  There are 51 different forecasts in this ensemble system.

No precipitation for virtually all of them for Dec 5-9th, and then nearly nothing through December 12th.  After that, a few members have some light rain--very light rain. And yes, some rain this weekend.

So we should be confidence in the forecast: after the rain stops Sunday morning it will be absent for a week, and maybe more.

There  will be sun ... plenty of it.  But after a few days of high pressure there is a good chance that low clouds and fog may form, at least in the mornings.  

Why?   Because clear skies from the high pressure will allow the earth to radiate into space, resulting in low-level cooling.  That cooling can bring the air near the surface down to saturation, producing fog/low-clouds.  The weak winds associated with the high pressure won't mix it out.  And the sun is so weak now, it will have a hard time burning off the low clouds.   We will see.

And a major tip:  if the low clouds form you can easily escape them and enjoy sun by going up...to an elevated park (e.g., Cougar Mt) or into the Cascades/Olympics.  Leaves will be nice and dry...making raking easy and fun.

from Cliff Mass Weather and Climate Blog http://ift.tt/2BCMQ3W

The Upcoming December Drought in the Northwest

A stunning transition is going to happen on Sunday.  

Precipitation over the Northwest will end. 

And we might not see another drop for over a week.  Maybe more.  An unusual occurrence in December.  You will see sun....but as we will note there is a threat:  low clouds and fog.

Let's take a look at the forecast upper level (500 hPa)  maps this week from the NOAA GFS model...and be prepared to have your jaw drop!

At 10 AM Sunday, a trough has moved passed us and a ridge of high pressure has started to build in the eastern Pacific.  The rain will be ending at this time.

One day later, the eastern Pacific ridge has amplified.   We are totally dry.

The ridging increases by Wednesday.... the ridge is HUGE and extends up to Alaska.

 Saturday at 10 AM.  The ridge is still there, but a bit weaker.    Plenty strong enough to keep us dry.

 It revs up even more on Sunday!

 And it is STILL THERE on Tuesday 12/12.

 And it continues after that for several more days.

Folks...we are talking about a total shut down of precipitation over us for 1-1.5 weeks.  In December.

OK, I know what you are saying.  What do the ensemble systems using many runs show?  Here is the anomaly (difference from normal) of 500 hPa heights for the mean of the NOAA GFS ensemble system for 4 PM Thursday.  Much higher heights than normal (high pressure) over the NE Pacific and our area.  BIG positive (high pressure) anomaly.

The forecast a week later IS THE SAME THING, just a little weaker.  Wow.

Next lets look at the precipitation forecasts from the vaunted European Center ensemble.  There are 51 different forecasts in this ensemble system.

No precipitation for virtually all of them for Dec 5-9th, and then nearly nothing through December 12th.  After that, a few members have some light rain--very light rain. And yes, some rain this weekend.

So we should be confidence in the forecast: after the rain stops Sunday morning it will be absent for a week, and maybe more.

There  will be sun ... plenty of it.  But after a few days of high pressure there is a good chance that low clouds and fog may form, at least in the mornings.  

Why?   Because clear skies from the high pressure will allow the earth to radiate into space, resulting in low-level cooling.  That cooling can bring the air near the surface down to saturation, producing fog/low-clouds.  The weak winds associated with the high pressure won't mix it out.  And the sun is so weak now, it will have a hard time burning off the low clouds.   We will see.

And a major tip:  if the low clouds form you can easily escape them and enjoy sun by going up...to an elevated park (e.g., Cougar Mt) or into the Cascades/Olympics.  Leaves will be nice and dry...making raking easy and fun.

from Cliff Mass Weather and Climate Blog http://ift.tt/2BCMQ3W