Vegetable Growing Season Begins TODAY!

If you are waiting to put place those bean or zucchini seeds into the ground.

If you are waiting to plant those tomato seedlings.

Your wait has ended.  

TODAY is the day.

We are now on the verge of a major regional warm-up, and even when it ends, temperatures will remain considerably warmer than normal.

From my discussions with master gardeners and a perusal of online materials, soil temperatures must be at least 50F for tomato plants to thrive.  Many vegetable seeds require soil temperatures above the mid-50s to have much chance.

Air temperatures below 40F are not good for plant business.

Current Soil Temperatures

Here in Seattle, the current soil temperature at a depth of 2 inches (orange line below) has risen to nearly 60F late in the afternoon on several days during the past week and is only dropping into the low 50s at night.  

I expect the soil temperatures to warm by several degrees during the next few days, making it viable for tomatoes, beans, and other warmer soil seeds/plants.

Forecast Temperatures

The latest forecasts are consistent with prior ones:  highs near 80F on Friday and Saturday, with lows in the lower to mid-50s.  Classic mid-summer weather.

Cooling by a few degrees on Sunday followed by a week of temperatures in the upper 60s.   

Keep in mind that such temperatures are above normal for Seattle,  whose highs are typically around 65F this time of the year.   The plants and seeds will be happy!

But perhaps you are a gardener who really plans ahead.   What does the long-term outlook look for temperature?

Below is the latest European Center extended-range temperature forecast for the next 46 days, actually the predicted difference from normal.  Most of the region will be near normal, with a bit warmer than normal conditions over NW Washington and east of the Cascades.

Your plants will remain happy.

Looking forward to getting my garden started today!  

Announcement

By popular demand, I am bringing back my podcast starting on Friday!

Heatwave Ahead!

Almost every May we enjoy a "heatwave" during the middle of the month, a few days in which temperatures surge into the upper 70s or low 80s west of the Cascade Crest.

This year will be no exception.

For those gardeners frustrated by the cool, showery weather, get your plants and implements ready!

To "warm up" the conversation, consider the daily forecasts of temperature at SeaTac Airport from the National Weather Service's National Blend of Models, a statistical combination of major weather forecast models (see below).  Usually highly skillful.

This forecasting system predicts a steady warm-up this week, with high temperatures on both Friday and Saturday near 80F, followed by a cooling to around 70F.

East of the Cascades in the Columbia Basin?   Same story, but add about 10°F and delay one day (see temperatures in the Tri-Cities below). Roughly 90°F on Saturday and Sunday.

The Northwest heatwave is associated with the development of an upper-level high-pressure center (also known as a ridge) over southwest British Columbia (see map below for 2PM Thursday at 500 hPa--about 18,000 ft).

The shading indicates the difference from the climatological normal, with red indicating above-normal heights/pressures. Although significant, this high is not in the same league as those producing record-breaking warmth, such as in June 2021.  

A ridge of high pressure is associated with sinking air, which warms by compression.  It is also associated with low-level offshore-directed (easterly) flow, that produces further compression as it sinks on the slopes of local terrain.  And easterly flow keeps the cooling influence of the Pacific at bay.

The mid-May heatwave is a local favorite

Remember last May?  A heatwave around May 13th (see a plot below for Seattle, blue are the May 2-23 temperatures, red indicates record highs).   

This year will not be as warm.

Or consider the highest temperatures each year between May 7 and May 21 in Seattle since the late 1940s (shown below).  Two-thirds of the years have at least one day above 75F.  There is only a slight upward trend in the highest temperatures during mid-May.

Why do we often get mid-May warm spells, followed by cooler weather?

First, the sun is very strong and the days are quite long at this time of the year.  Pretty much the same as late July.  So solar heating is potentially powerful.

Second, weather disturbances such as lows and highs are still fairly energetic (they are strongest during mid-winter) and these disturbances are crucial to get a big heat wave. To get a strong heat wave in the Northwest one needs a well-defined high-pressure area over coastal British Columbia.

Third, during mid-summer, low-level high pressure builds to the west of our coast, resulting in strong, cool onshore flow.  Often associated with low clouds as well, such onshore flow keeps temperatures down from late May into mid-summer.

Anyway, I am really looking forward to the warmth.   And I know others that feel the same way:

Sea Surface Temperatures: West Versus East Coast.

Perhaps, this blog spends too much time talking about the atmosphere, so to make amends today, let's see what is happening to the temperature of the ocean surface.  And see whether anything unusual is going on.

 Let's start with yesterday's sea surface temperatures around North America (below).  Sorry, it is all in °C.   Keep in mind that 10°C is roughly 50F,  20°C is around 68F, and 30°C is approximately 86F.

The eastern Pacific near the West Coast is cold (about 50F), with central California's waters a bit cooler than ours. You must head to the southern tip of the Baja Peninsula to find the water warm enough for comfortable swimming.

The East Coast is a study in contrasts.  The water off of New England is crazy cold (dropping below 7C), while the uber-warm Gulf Stream is found along the west coast of Florida, moves past the Carolinas, and then heads northeastward into the Atlantic.    

There is a HUGE temperate contrast between the Gulf Stream current and the cold water of the Northeast.    A blow-up of the sea surface temperatures off the Northwest really shows the amazing horizontal temperature changes north of the Gulf Stream

Look closely and you will waves in the interface between warm and cold water in the Atlantic and a fascinating loop in the warm water over the Gulf of Mexico (first image above).    Very warm water over the Caribbean and west of Central America

Your next question is probably:  is the current pattern of sea surface temperature unusual?  

To evaluate this, the next map shows the difference between yesterday's sea surface temperature and normal conditions (also called the SST anomaly).

Pretty close to normal off the Northwest coast.  A few degrees colder than normal for California's coastal waters. And near normal on Mexico's west coast.   Most of the Gulf and Atlantic coast is slightly above normal. Temperature is cooler than normal north of the Gulf Stream, which suggests that the Gulf Stream is south of its normal position by a hundred miles or so.

The biggest sea surface temperature story is what is happening in the tropical Pacific.  Last year, a strong El Nino brought MUCH warmer than normal sea surface temperatures from South America, westward into the central Pacific.  

But something major has happened.  The tropical Pacific surface waters are rapidly cooling, resulting in cooler than normal waters in many locations (see map, with arrows showing you some of the coolest spots).

El Nino is dead.  Long live La Nina, its frigid cousin!

A Very Unstable Spring Atmosphere

Spring is the time when our local atmosphere is most unstable, often percolating in upward and downward motions like hot cereal in your stove-top saucepan.

The visual expression of such unstable motions is cumulus convection, ranging from relatively benign fair-weather cumulus to towering cumulonimbus.  

On Tuesday, the atmosphere became unstable and a full range of cumulus clouds was evident.

During the afternoon, relatively shallow cumulus clouds had formed by 2 PM (see below from the Seattle PanoCam on the Space Needle).  No precipitation was evident underneath them.

By 5 PM, following afternoon surface heating, vertical turrets start to form, indicating greater instability and vertical development.

The 6 PM image showed even more vertical development and the formation of two cirrus anvils (the flat, elongated objects at the top of the image.)

30 minutes later the anvils had explored in size.  Very impressive!  It was raining underneath the big cumulus clouds and lightning was observed

Cumulus clouds like this are a sign of vertical instability driven by large temperature changes in the vertical.

Stability 101

Most of the time the atmosphere is stable.   You push some air upwards and it comes back down.

But if the temperature declines with height rapidly enough, the situation changes.    In this case,  a displaced air parcel can accelerate upwards.   

The explanation for this behavior is something we describe in detail in my department's classes, but the essential point is this:

When temperature cools rapidly with height it becomes easier for an air parcel to be warmer and less dense than the surrounding air.  And such warm/less dense air parcels tend to be buoyant and rise.

Think of a hot-air balloon! (see below)

Here in the Pacific Northwest, the change in temperature with height is greatest during the spring.  That is why this is the best time of the year to see impressive cumulus clouds.

But why spring, you ask?

During the spring, after a long winter, the temperatures aloft are quite cold...in fact, the coldest of the year.  To show this, below are the temperatures around 10,000 ft (700 hPa pressure) at Forks, WA, on the NW coast.

Lowest temperatures in March and April.  Quite cold in early May.

While temperatures are cold aloft, solar heating is getting very strong now, particularly on days without extensive clouds.  Below is the plot of solar radiation reaching the surface in Seattle for the last year.  Getting pretty strong lately.    Keep you sunscreen handy.

May 2 sun is roughly as intense as early August!

So with strong heating at the surface and cool temperatures aloft, there is often a very large change in temperature with height during early spring, which fosters lots of cumulus clouds....from shallow ones to deep thunderstorm clouds.  

Just to drive the point home, here is a plot of the change in observed temperature with height (termed the lapse rate) at Forks/Quillayute between the surface and 3 km (about 10,000 ft).    Very high this time of the year.

Finally, you can see the growth of cumulus during the day produced by increasing temperature change with height.   Let's start with the visible satellite image over eastern Washington on Wednesday morning around 8 AM.  No clouds over the Columbia Basin.

By 2 PM, with plenty of solar heating at the surface, the temperature change with height is greatly enhanced and instability has developed, leading to lots of cumulus clouds.

toweromg 

The Hamas Encampment at the UW: A Sad Collection of Ignorant, Virtue-Signaling, Law-Breaking Students Enabled by a Weak UW Administration

Update

The UW Hamas encampment has tripled in size.

Jewish students have been attacked and had items stolen from them.

Media representatives have been attacked and bloodied.

Major pathways have been blocked.

All of this is documented on video. Where is the UW administration?  Why do we have to follow the path of Columbia and UCLA?

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The hapless anti-Israel encampment finally occurred yesterday at the UW and it would be hard to find a more ineffective, ignorant, and morally lacking group of university students.  

Originally scheduled for last Thursday, the whole affair had to be delayed because Muslim students were angered that they were not asked to participate and plan the event by the Progressive Student Union.  And when the camp was finally established yesterday morning on wet/muddy ground it was raining hard and continued to rain during the day.

Only a handful of tents were set up, the pro-Hamas activists numbered perhaps a dozen or two at the peak, with most UW students taking little notice.   Many of the anti-Israel crowd wore masks to avoid identification, like many lawbreakers.  Some were screaming  (at a student who was quietly holding an Israeli flag) in ways that suggested some kind of mental affliction.

These students were breaking the law.  Encampments are illegal on the UW campus and warning signs were placed around the quad, with the specific regulation cited (see below) 

I have passed the encampment several times and have never seen even a single member of the UW Police force in the area.

This encampment interfered with instruction in the many classrooms facing the quad due to the blaring noise from their bullhorns and loud music.  Some of the student bouncers were physically blocking individuals taking pictures.

The Hamas activists called for the destruction of the State of Israel (from the river to sea, Palestine will be free chants) and global violence (Global Intifada).  But they had particular hate for President Biden and the Democratic Party, with frequent screams of "Biden, Biden You Can't Hide, You are Guilty of Genocide".

The Democratic party was considered far right for many folks in this group.  Some wore Communist Party shirts while others held signs for the Revolutionary Workers Party (see below).

Some of the signs called for violence against police, which I suspect is illegal (see below).

But it was the stunning ignorance and lack of historical knowledge that really was shocking. 

 I calmly asked one the the folks in the yellow jackets why he was against Israel.  He told me that the Jews were colonialists. I calmly told him that he was incorrect. That the Jews were in the land for at least 3000 years and that the Arabs were the recent conquerors.  He told me that I was wrong, that there were no Jews in the region until the 1900s.  I noted that Jews were noted in both versions of the bible.  He countered that the bible was mythology.  I noted that Roman literature talked about Israel and there was definitive archeological proof.  He then walked away.

Some people call these Hamas supporters Nazis.   I can't agree.  They are so poorly grounded in history that I suspect they don't even know about the Nazis.  Or know about the Holocaust. 

They are ignorant.  They are foolish.  These are kids without meaning in their lives and trying to secure some meaning by screaming slogans about a conflict they don't understand.  Many appear to be outcasts or odd.  Kind of a sad group.  

I am not as charitable regarding the UW administration.

The encampment was illegal and notice was given.  But when this criminal activity occurred, an activity that interfered with the education of hundreds of students, the UW administration did nothing.

This is after many of the same students disrupted university functions a half-dozen times with bullhorns and drums.

Criminal destruction in the UW HUB

After they took over the Administration Building and the President's office.

After they disrupted the Chanukah celebration on Red Square.

And after they trashed the student union building, causing tens of thousands of dollars of damage.

All good parents learn that children will test authority and that being permissive for anti-social behavior leads to even worse behavior.

The pro-Hamas UW students are no different.  These are kids who don't have internal moral or ethical values and need to be taught that inappropriate and hurtful behavior has consequences.

Their near-complete lack of knowledge of history and society further cripples them.

The UW administration seems determined to follow the disastrous policies of Columbia and Harvard, which is a tragedy for the University and the region it serves.  

Substantial Late-Season Mountain Snow Ahead

Most folks are not thinking about substantial snow in the mountains during late April and early May, but such snow will be a reality this year.  

During the next 48-h, 3-8 inches will fall on the Cascade passes and more is predicted during the next week or so.

Stevens Pass on Sunday Afternoon

The key source of the upcoming cold, snowy weather are two upper-level lows that will move in tonight and Monday night (see upper-level maps at 2 AM Monday morning below).   This kind of pattern has been rare this El Nino winter.

So how much snow could we expect on Monday and early Tuesday?   

Below is the 5 AM Sunday accumulated snowfall forecast through 5 AM Tuesday of the high-resolution NOAA/NWS HRRR model.  

Impressive.    Over a foot at higher elevations. 4-8 inches in the passes.  Large values in the mountains of southern British Columbia as well.

The UW high-resolution modeling system has a similar solution, but we have even more to offer:   we run an ensemble of many forecasts to understand the uncertainty of the forecasts.   Using this system, the snow accumulation at Stevens Pass (around 4000 ft in the central WA Cascades) is shown below.  

Some uncertainty, but the average is about 6 inches for this event.

How unusual is a half foot or more of Cascade Mountain snow this time of the year?

To gain some insights into this interesting question, below is the daily average and daily extreme snowfall at Stampede Pass from 1944 to 2016.   

On average, this site receives about an inch around May 1.  But extreme days this time of year have received 10-15 inches.  So getting some snow at this point in spring is no big deal.

In any case, expect a significant bump up in regional snowpack by midweek.

But the impressive thing is that the snow and cold are not over on Tuesday.  The latest model forecasts have several more cold lows moving through during the subsequent week.

As a result, a LOT more snow is expected to fall.  For example, below is the predicted accumulated snowfall for the next five days from the highly skillful European Center model.  ANOTHER FOOT (or more) at some mountain locations.

And the extended forests after that have even MORE snow.

Regional ski areas should think about reopening for glorious May skiing.

And no, global warming does not cause bountiful May snow. 😉

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Announcement:  There will be no Northwest Weather Workshop this year.  

Why?  Because we lost two important partners.  The Seattle National Weather Service Forecast Office has told me they are no longer interested in hosting and participating in this regional weather gathering.   And the other partner, the Puget Sound Chapter of the American Meteorological Society, has died.    I am looking for new partners for next year. Keep tuned.

El Nino is Rapidly Collapsing

 It's finally happening.   

The pesky El Nino, with warmer than normal surface waters across the central and eastern tropic Pacific, is finally dissipating.  

And the effects of El Nino, including a wet California and warm Northwest, should be fading.

Consider the temperatures in the Nino 3.4 area of the tropical Pacific shown below (the difference from normal is illustrated).  El Nino peaked in late November at around 2.1C above normal sea surface temperatures.   Right now it is about 0.6C above normal and declining rapidly.

The latest prediction of the NOAA/NWS climate forecast model (CFSV2) is for the El Nino to be gone (0°C anomaly from normal) by the end of May (see below).  And then we move into a strong La Nina (cold tropical Pacific) by autumn.

This model predicts the extension of colder-than-normal surface water over the tropical Pacific during the next few months (see below).  Wow.  Talk about oceanographic whiplash.

With El Nino weakening, the large-scale weather patterns are unlocking and the Northwest weather situation is forecast to be very different during the next weeks compared to earlier in the winter.

During El Nino winters (and this one), southern California is very wet, with the Northwest being on the drier side.  In contrast, the latest forecast of accumulated prediction from the US GFS model through 11 May is shown below.  Virtually nothing will fall over southern California and wet conditions will prevail over the Northwest.   

Something has changed.

And a strong La Nina foretells major changes next winter, greatly increasing the chances for lots of mountain snow and colder-than-normal temperatures.  

My suggestion:  if you can make some good deals on ski equipment, do so....

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Announcement:  I will do a special online zoom session at 10 AM on Saturday for Patreon supporters, with a deep dive into the upcoming wet period and the implications for this summer.  Plus, I will answer your questions.

Drought-Buster Wet, Cool Weather Ahead

 As many suspected, with the rapid collapse of El Nino and the progression into spring, the weather patterns have shifted, opening the door to far wetter weather over the Northwest.

During the next 10 days, expect lots of precipitation, cool to seasonal temperatures, and even a good dump of snow in the mountains.

The official NOAA 6-10 day forecasts say it all (see below), with wetter than normal conditions and colder than normal temperatures over our region.

A vigorous weather system is arriving tomorrow, bringing a wet day.   The total precipitation through Friday morning at 5 AM is shown below.  A nice wetting for the entire region with some western slopes getting 2-3 inches.  That is a lot for late April.

But this is just the beginning, with multiple wet systems arriving over the next week.   The total accumulation through next Saturday morning (4 May) is impressive, with large areas of more than 3 inches.     Keep in mind you need to multiply that by roughly ten to get snowfall in the mountains.

Over the higher elevations, the temperatures will be cold enough for snow, with substantial accumulations through May 4th.  Some mountain locations will get several feet of new snow.

I suspect the snowpack will increase to around 80% of normal over Washington State and more than 100% of normal over much of Oregon within roughly 10 days.  

The latest NOAA River Forecast Center forecasts for 10 days out are for near-normal river levels.   For example, consider the Snoqualmie River (below).  Below normal now, but near normal in a few days...and staying that way.

This and subsequent wet periods are well-timed to ensure sufficient water levels this summer.

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Announcement:  I will do a special online zoom session at 10 AM on Saturday for Patreon supporters, with a deep dive into the upcoming wet period and the implications for this summer.  Plus, I will answer your questons.

The Other Type of Mountain Wave Cloud

 Folks love to talk about lenticular clouds, which are generally produced by air moving up (and down) downstream of a mountain barrier (see picture below).  Such clouds are generally found in the lower atmosphere at or just above the crest level of the mountain barrier that produces them.

Picture by Joel David-Aldridge

As shown by the schematic below, lenticular clouds, also called trapped lee wave clouds, often come in multiples downstream of the mountain barrier and have a lens shape (see below).    Such mountain-wave clouds are called "trapped" because the clouds and the motions associated with them are trapped in the lower atmosphere. Some folks think they look like flying saucers and more than one UFO scare has been initiated by such clouds. 

Why does the air go up and down downstream of the mountains?   Think of a kid's swing set.  You give the swing a push and it goes back and forth for a while.  Air pushed upwards by the mountain crest does something similar.

Interestingly, there is another type of mountain-wave cloud that is found much higher in the atmosphere, but still downstream of a mountain barrier.   In this case, the mountain wave energy propagates vertically in one very high amplitude wave, with high-level clouds just downstream of the mountain (see schematic below).  Such clouds can be associated with substantial turbulence aloft.

Certain conditions favor high-amplitude mountain waves, such as strong winds approaching the mountain crest and supportive changes in wind and temperature with height.

Yesterday was a super day to view a vertically propagating mountain wave just downstream of the Cascades.

 The image at 8:41 AM shows the feature clearly (below, see red arrow)

As did the image at 11:01 AM (below).

To show you how good the weather models have become, here is the simulated cloud field at 8 AM yesterday--the correct type of mountain wave cloud was evident.

Living here in the mountainous Pacific Northwest, we get to see mountain-wave clouds nearly every day, so it is important to know the two types.   And now you do.