Rain Returns to a Dry Pacific Northwest

We have just experienced an extraordinarily dry second half of March, one in which weather systems and their accompanying precipitation was directed southward into California.

Well, all good things have to come to an end, and for us the spigot will be turned back on this week.

But first, let me impress you.  Here is the percent of normal precipitation for the past two weeks over Washington State.  The dark red is less than 25% of normal!    No wonder some some media outlets are throwing around the D word (drought!) or predicting a dry spring.

But percent of normal precipitation can be very deceptive, particularly in places or times that are relatively dry (like our summers or east of the Cascade crest).  Far better is to view the departure of precipitation from normal (in inches) as shown below.  Dry eastern Washington was generally less than an inch below normal.   The Puget Sound lowlands, 1-2 inches down.  More over the usually wet western slopes of the Cascades and Olympics.

But everything changes this week as the large-scale atmospheric configuration changes profoundly.  

For nearly two weeks,  there has a deep low over the eastern Pacific, with the jet stream and accompanying storms heading into California.  This is illustrated below by a weather map for 11 AM Wednesday for an upper tropospheric  level (300 hPa pressure level, about 30,000 ft).   Yellow colors indicate the strongest (jet stream) winds. Washington State gets little precipitation from such a pattern.  

But the pattern greatly changes this week, as low pressure retreats into the Gulf of Alaska (the normal position) and the jet stream moves northward right into us (see the forecast map for 8 AM next Sunday)  We get nailed and California finally dries out.

Let me show you the precipitation forecasts from the UW WRF modeling system.  Here in Seattle we have two more days of dry conditions, but Oregon gets hit earlier.   The total accumulated precipitation through 5 PM Tuesday (shown below) predicts that western Oregon will be very wet during the next two days.

One day later (5 PM Wednesday), it is clear that the hose has reached western WA, with the Olympics and north Cascades receiving several inches.

But why stop there?  Here is the accumulated precipitation through 5 PM Sunday.  Wow.  The Olympics and mountains of southwest BC get 5-10 inches, with the rest of western WA and Oregon enjoying 1-5 inches.

We had a cold/snowy February, a dry March,  and now a wet April?  We will see.

But one thing is sure....  you can not believe the long-term forecasts.  Here are the extended predictions of the NOAA/NWS CFSv2 seasonal forecast model run in late February for the precipitation anomalies (difference from normal) for the end of March.   The CFS was going for WETTER than normal conditions over our region for the period....when it was very, very dry.
No skill.   

from Cliff Mass Weather and Climate Blog https://ift.tt/2CMJMVg

Rain Returns to a Dry Pacific Northwest

We have just experienced an extraordinarily dry second half of March, one in which weather systems and their accompanying precipitation was directed southward into California.

Well, all good things have to come to an end, and for us the spigot will be turned back on this week.

But first, let me impress you.  Here is the percent of normal precipitation for the past two weeks over Washington State.  The dark red is less than 25% of normal!    No wonder some some media outlets are throwing around the D word (drought!) or predicting a dry spring.

But percent of normal precipitation can be very deceptive, particularly in places or times that are relatively dry (like our summers or east of the Cascade crest).  Far better is to view the departure of precipitation from normal (in inches) as shown below.  Dry eastern Washington was generally less than an inch below normal.   The Puget Sound lowlands, 1-2 inches down.  More over the usually wet western slopes of the Cascades and Olympics.

But everything changes this week as the large-scale atmospheric configuration changes profoundly.  

For nearly two weeks,  there has a deep low over the eastern Pacific, with the jet stream and accompanying storms heading into California.  This is illustrated below by a weather map for 11 AM Wednesday for an upper tropospheric  level (300 hPa pressure level, about 30,000 ft).   Yellow colors indicate the strongest (jet stream) winds. Washington State gets little precipitation from such a pattern.  

But the pattern greatly changes this week, as low pressure retreats into the Gulf of Alaska (the normal position) and the jet stream moves northward right into us (see the forecast map for 8 AM next Sunday)  We get nailed and California finally dries out.

Let me show you the precipitation forecasts from the UW WRF modeling system.  Here in Seattle we have two more days of dry conditions, but Oregon gets hit earlier.   The total accumulated precipitation through 5 PM Tuesday (shown below) predicts that western Oregon will be very wet during the next two days.

One day later (5 PM Wednesday), it is clear that the hose has reached western WA, with the Olympics and north Cascades receiving several inches.

But why stop there?  Here is the accumulated precipitation through 5 PM Sunday.  Wow.  The Olympics and mountains of southwest BC get 5-10 inches, with the rest of western WA and Oregon enjoying 1-5 inches.

We had a cold/snowy February, a dry March,  and now a wet April?  We will see.

But one thing is sure....  you can not believe the long-term forecasts.  Here are the extended predictions of the NOAA/NWS CFSv2 seasonal forecast model run in late February for the precipitation anomalies (difference from normal) for the end of March.   The CFS was going for WETTER than normal conditions over our region for the period....when it was very, very dry.
No skill.   

from Cliff Mass Weather and Climate Blog https://ift.tt/2CMJMVg

Advice to Californians: Vacation in Washington State for Sun and Dry Conditions

California is advertised as the "Golden State" with dry conditions and sun.  Washington is given the bad rap as a place of clouds and rain.

But not this March.  California should properly be called the "Sodden State", while much of Washington has been extraordinarily dry.

For example, it appears that Seattle-Tacoma Airport will end up with 1.37 inches (assuming the forecasts are right), resulting in the second driest March since the airport observations started in 1948.    And Seattle has had seven days with measurable precipitation

Typical March 2019 Weather

In contrast, San Francisco had 15 DAYS of measurable precipitation for a total of 4.43 inches.

Los Angeles has had 2.10 inches of rain this month. 

And Puget Sound has had less clouds and more sun than San Francisco.

To appreciate the recent dry conditions, here is the percent of normal precipitation for the past 30 days.   Large sections of western Washington received 5-25% of normal, while San Francisco northward had 200-400% of the typical amounts. Nevada, Utah and Colorado  were all very wet.

Central/northern California was wetter in March than western Washington.   And our dry conditions were also associated with some very warm periods with strong easterly winds.  The result:  a few days with several wildfires and a pollen storm that brought misery.

The origin of the situation?   A very persistent area of low pressure west of California, as illustrated by the upper level anomaly map (difference from normal heights or pressure) for the past month (see below).   The purple/blue colors indicate lower heights or pressures offshore.  Such low pressure sweeps weather systems into California.  Western WA gets the dregs on the north side of the low.  And high pressure (red colors) to the north of us, coupled with the low pressure to the south, sets up unusual easterly (offshore) flow aloft.  Such flow is dry and dries further as it descends our mountains.

A very unusual, but perfect, configuration to give us a dry, often sunny, but fire-prone month.

And there may be a contributor to this configuration:  a resurgent El Nino, which is associated with warmer than normal sea surface temperatures over the central and eastern tropical Pacific.  Such warmer water forces tropical thunderstorms that push energy into the tropical atmosphere above, in turn forcing a series of waves that propagate into the midlatitudes, resulting in the lower pressure areas west of California.  Think of a rock thrown into a very big lake, with waves moving away from where the rock hits the water.

Finally, if you are worried about Californians rushing northward into western Washington, you should be.  I was going to joke about putting up a wall, but thought better of it.

from Cliff Mass Weather and Climate Blog https://ift.tt/2CL15pF

Advice to Californians: Vacation in Washington State for Sun and Dry Conditions

California is advertised as the "Golden State" with dry conditions and sun.  Washington is given the bad rap as a place of clouds and rain.

But not this March.  California should properly be called the "Sodden State", while much of Washington has been extraordinarily dry.

For example, it appears that Seattle-Tacoma Airport will end up with 1.37 inches (assuming the forecasts are right), resulting in the second driest March since the airport observations started in 1948.    And Seattle has had seven days with measurable precipitation

Typical March 2019 Weather

In contrast, San Francisco had 15 DAYS of measurable precipitation for a total of 4.43 inches.

Los Angeles has had 2.10 inches of rain this month. 

And Puget Sound has had less clouds and more sun than San Francisco.

To appreciate the recent dry conditions, here is the percent of normal precipitation for the past 30 days.   Large sections of western Washington received 5-25% of normal, while San Francisco northward had 200-400% of the typical amounts. Nevada, Utah and Colorado  were all very wet.

Central/northern California was wetter in March than western Washington.   And our dry conditions were also associated with some very warm periods with strong easterly winds.  The result:  a few days with several wildfires and a pollen storm that brought misery.

The origin of the situation?   A very persistent area of low pressure west of California, as illustrated by the upper level anomaly map (difference from normal heights or pressure) for the past month (see below).   The purple/blue colors indicate lower heights or pressures offshore.  Such low pressure sweeps weather systems into California.  Western WA gets the dregs on the north side of the low.  And high pressure (red colors) to the north of us, coupled with the low pressure to the south, sets up unusual easterly (offshore) flow aloft.  Such flow is dry and dries further as it descends our mountains.

A very unusual, but perfect, configuration to give us a dry, often sunny, but fire-prone month.

And there may be a contributor to this configuration:  a resurgent El Nino, which is associated with warmer than normal sea surface temperatures over the central and eastern tropical Pacific.  Such warmer water forces tropical thunderstorms that push energy into the tropical atmosphere above, in turn forcing a series of waves that propagate into the midlatitudes, resulting in the lower pressure areas west of California.  Think of a rock thrown into a very big lake, with waves moving away from where the rock hits the water.

Finally, if you are worried about Californians rushing northward into western Washington, you should be.  I was going to joke about putting up a wall, but thought better of it.

from Cliff Mass Weather and Climate Blog https://ift.tt/2CL15pF

UW's Cherry Blossom Timing and Our Winter Weather

One of the singular events each year in Seattle is the stunning display of white/pink blossoms on the Arts Quad at the University of Washington.  At maximum bloom, the flowering is simply stunning.

Interestingly enough, there is quite a bit of variation of the date of peak bloom, the day when the crescendo of color reaches its apex.   A day that I have told follows the beginning of blossoming by about one week.

As shown below, since 2012 the peak bloom dates have varied from mid March through early April.  Talking to some cherry blossom experts today, it appears that this year's peak bloom should be on March 31, give or take a day (and I have plotted it). 

I have done some recreational reading about this important topic, including a very nice paper by Chung et al. that finds that Cherry blossom timing for the famous Washington DC blooms is closely related to winter and early spring temperatures.  Colder winters delay flowering.  And they used some of the UW blossoming data as well.

So can we explain the above variation in blossom date with local temperature variations?  And do the above variations suggest the influence of global warming?

Let me begin by plotting December through February temperatures for the Puget Sound lowlands from the NOAA Climate Division Data. 

The two warmest years were 2015 and 2016 and YES, they had the earliest peak bloom.  Very good.  2017 was the coldest year and its bloom was quite late (well into April).  But 2018 was late, but the temperatures were not exceptionally cold.  In short, there is clearly some kind of correlation, but it isn't perfect.  In fact, the Chung et al paper suggests this, revealing that to get flowering requires sufficient cold early in the season and a certain amount of heating late in the spring.  So the relationship is a bit more complex

One thing is sure, the short period shown above (2012-2019) does not suggest a progressive earlier flowering as would be expected with warming.   And certainly the winter temperatures plot does not suggest a warming trend....if anything temperatures have cooled this decade, with a warm spike in 2015.  But this is simply too short a period to have much confidence in any trends.

I am trying to acquire a longer term blossom date data base to secure a better estimate of a longer-term trend.  Will do another blog on this topic if I get it.  If anyone can help me get it, let me know.

from Cliff Mass Weather and Climate Blog https://ift.tt/2JLCZ4d

UW's Cherry Blossom Timing and Our Winter Weather

One of the singular events each year in Seattle is the stunning display of white/pink blossoms on the Arts Quad at the University of Washington.  At maximum bloom, the flowering is simply stunning.

Interestingly enough, there is quite a bit of variation of the date of peak bloom, the day when the crescendo of color reaches its apex.   A day that I have told follows the beginning of blossoming by about one week.

As shown below, since 2012 the peak bloom dates have varied from mid March through early April.  Talking to some cherry blossom experts today, it appears that this year's peak bloom should be on March 31, give or take a day (and I have plotted it). 

I have done some recreational reading about this important topic, including a very nice paper by Chung et al. that finds that Cherry blossom timing for the famous Washington DC blooms is closely related to winter and early spring temperatures.  Colder winters delay flowering.  And they used some of the UW blossoming data as well.

So can we explain the above variation in blossom date with local temperature variations?  And do the above variations suggest the influence of global warming?

Let me begin by plotting December through February temperatures for the Puget Sound lowlands from the NOAA Climate Division Data. 

The two warmest years were 2015 and 2016 and YES, they had the earliest peak bloom.  Very good.  2017 was the coldest year and its bloom was quite late (well into April).  But 2018 was late, but the temperatures were not exceptionally cold.  In short, there is clearly some kind of correlation, but it isn't perfect.  In fact, the Chung et al paper suggests this, revealing that to get flowering requires sufficient cold early in the season and a certain amount of heating late in the spring.  So the relationship is a bit more complex

One thing is sure, the short period shown above (2012-2019) does not suggest a progressive earlier flowering as would be expected with warming.   And certainly the winter temperatures plot does not suggest a warming trend....if anything temperatures have cooled this decade, with a warm spike in 2015.  But this is simply too short a period to have much confidence in any trends.

I am trying to acquire a longer term blossom date data base to secure a better estimate of a longer-term trend.  Will do another blog on this topic if I get it.  If anyone can help me get it, let me know.

from Cliff Mass Weather and Climate Blog https://ift.tt/2JLCZ4d

Aurora Forecast Bust and Dry Western Washington

Well, I have to admit disappointment, both in the lack of auroral activity over Washington on Saturday and the poor forecast by the NOAA Space Weather Center of the Planetary K-index, Kp, which is used to characterize the magnitude of geomagnetic storms.

As noted in my last blog, there was a solar disturbance last Wednesday and the NOAA center predicted that that impacts would be felt on Saturday, with the potential for an evening aurora.

The forecast of Kp made the day before is shown below, with the verification right below.  Values over roughly four suggest a moderate geomagnetic storm that might provoke some decent auroral displays.  The initiation was predicted to occur Saturday morning (18 h is 11 AM).

But what occurred was much less and much later.  The "event" started on Sunday afternoon and was only reach a Kp of 2.

There was some minimal auroral activity Sunday night, but not in our area. 

Well, I suspect that predicting the propagation of particles from the sun to the earth is far more difficult than weather prediction, so I won't be critical of the NOAA folks.  Still disappointed though.

And we are getting some light rain tonight, which is welcome.  The last month has been dry for western Washington, in some places more than 4 inches below normal.  But most of the west has been wetter than normal, particularly around the Bay Area.

As shown in the cumulative one-month rainfall below, Sea Tac Airport received roughly 2.5 inches less than normal (cyan is normal, purple is observed)

But Pasco, in eastern WA, was about right:

The dry conditions in western Washington were very obvious over the weekend when I was busy turning over the soil in my vegetable garden....the soil was quite dry through depth. Sure enough the soil moisture anomaly (difference from normal) for yesterday showed drier than normal soil conditions.  And one good thing about the rain--it should lessen the pollen count a bit.

from Cliff Mass Weather and Climate Blog https://ift.tt/2TyomAw

Aurora Forecast Bust and Dry Western Washington

Well, I have to admit disappointment, both in the lack of auroral activity over Washington on Saturday and the poor forecast by the NOAA Space Weather Center of the Planetary K-index, Kp, which is used to characterize the magnitude of geomagnetic storms.

As noted in my last blog, there was a solar disturbance last Wednesday and the NOAA center predicted that that impacts would be felt on Saturday, with the potential for an evening aurora.

The forecast of Kp made the day before is shown below, with the verification right below.  Values over roughly four suggest a moderate geomagnetic storm that might provoke some decent auroral displays.  The initiation was predicted to occur Saturday morning (18 h is 11 AM).

But what occurred was much less and much later.  The "event" started on Sunday afternoon and was only reach a Kp of 2.

There was some minimal auroral activity Sunday night, but not in our area. 

Well, I suspect that predicting the propagation of particles from the sun to the earth is far more difficult than weather prediction, so I won't be critical of the NOAA folks.  Still disappointed though.

And we are getting some light rain tonight, which is welcome.  The last month has been dry for western Washington, in some places more than 4 inches below normal.  But most of the west has been wetter than normal, particularly around the Bay Area.

As shown in the cumulative one-month rainfall below, Sea Tac Airport received roughly 2.5 inches less than normal (cyan is normal, purple is observed)

But Pasco, in eastern WA, was about right:

The dry conditions in western Washington were very obvious over the weekend when I was busy turning over the soil in my vegetable garden....the soil was quite dry through depth. Sure enough the soil moisture anomaly (difference from normal) for yesterday showed drier than normal soil conditions.  And one good thing about the rain--it should lessen the pollen count a bit.

from Cliff Mass Weather and Climate Blog https://ift.tt/2TyomAw

Potential Aurora Tonight!

One of the most extraordinary natural sights to behold is the aurora borealis and tonight and early Sunday morning, you might have a chance to see one in our region.

On Wednesday, there was a massive solar flare, followed by a coronal mass ejection (CME), on the sun.    It takes a few days for electrons and protons associated with the CME to reach the earth's atmosphere, and in fact, it has JUST ARRIVED.  This is evident from the latest planetary K index (a measure of the disturbance of Earth's magnetic field) form the NOAA Space Weather Prediction Center (see below).

 The Space Weather Center is predicting a moderate geomagnetic storm today (see below),

with higher (red and yellow) Kp indices (which means the potential for auroral activity) between 1800 UTC (11 AM) today and 0900 UTC tomorrow (2 AM Sunday).

Furthermore, they are suggesting the potential to view auroras between the yellow and red lines on the chart below, which includes most of Washington State.

The big question, of course, is cloud cover.  The UW WRF model cloud forecast for 11 PM tonight suggests that western WA has a chance for some clearing, with a veil of thin high clouds over eastern WA.

 The latest NOAA/NWS HRRR (High Resolution Rapid Refresh) forecast for the same time shows a similar picture.  Cloud forecasts are difficult, but it appears that the western side of the state may offer some gaps that night allow a view if the aurora does occur over us

 I will certainly be looking.  One of the most amazing experiences in my life was seeing one as a teenager after a star gazing event with my family.  Will never forget the curtains of colored lights, constantly changing as if a wind were blowing on them.



from Cliff Mass Weather and Climate Blog https://ift.tt/2uqPffH