Flooding in Eastern Washington, Driest May on Record for Western Washington

If you like dramatic contrasts, Washington State offers a world-class example--and I am not talking about politics.

Over eastern Washington a number of rivers are at flood stage, some reaching record levels.

Thunderstorms and heavy rain have been pummeling the Columbia Basin and northeast WA. The National Weather Service has issued a flood warning for several counties including Okanogan, Bonner, Chelan, Ferry and Pend Oreille, and the Kettle River, which flows through Ferry and Stevens counties, had a record high on May 10 of 22.54 feet on May 10, busting the previous record of 21.1 feet in 1948.

In contrast, over the west, many locations have had little precipitation in May, and there is chance Seattle will have its driest May on record.

Not black and white.  But dry and very wet.   But why?  And is spring flooding in eastern WA unusual?

Let's start by checking out the flooding situation, with information from the NOAA/NWS River Forecast Center in Portland (below).  Red dots are floods, blue dots indicated moderate floods, and purple are major floods.  And several other locations are at bank-full.

What is going on?   The combination of a healthy mountain snowpack and warming temperatures, resulting in rapid melting of snow, and the filling of regional rivers.

Here is the snowpack numbers for April 15th, from the very nice SNOTEL web site. Washington, northern Idaho, and Montana had snow-water amounts well about normal...in some locations above 150% of what is typical.

And snowpack in British Columbia, from which the Columbia River drains was also very high (see table)

So going into spring with a bountiful spring snowpack was step 1. 

Then a combination of warming temperatures and increasing spring solar radiation caused rapid snowmelt.  The departure of average temperatures from normal (below) shows our temperature anomaly (difference from normal) for the past two weeks, with much of eastern WA and northern Idaho being 6-8F above normal for that period.

So the normal rapid snowmelt of spring was supercharged by warmer than normal temperatures. 

But like a late-night commercial, I should note that there's more.    The weather pattern has produced wetter than normal conditions east of the Cascade crest (and drier than normal to the west)--see map below of the precipitation departure from normal for  5/3-5/16.

During the past few days, showers and thundershowers have moistened eastern Washington (see radar image for 3 PM yesterday), with the last 24-h totals being impressive.  A number of locations in northeast WA have gotten over 1 inch during the last day.

So why wet east of the Cascades and dry west?  Because there has been a persistent ridge of high pressure along the coast, with troughs (low pressure) moving into California and northward into eastern WA and Idaho (see upper level--500 hPa--map for 5 PM Thursday to illustrate.)  The ridge has kept western WA dry, while the transient troughs have initiated thunderstorms east of the Cascade crest.

It is important to note that spring-time flooding in eastern Washington and along the Columbia is the normal state of affairs in our region.  Before the Columbia and Snake River dams were in place, major and often catastrophic flooding was commonplace. 

One of the most famous events was the great snowmelt flood of May 1948.  Just as in this year, regional mountain snowpack was above normal, unusually warm temperatures hit during mid-month, and thunderstorms dampened eastern Washington. Richland flooded and the surge of water moved down the Columbia, inundating and destroying the city of Vanport (near Portland), which was never rebuilt.

As global warming reduces the regional snowpack later during this century, the threats of such springtime flooding should gradually decline over time.

from Cliff Mass Weather and Climate Blog https://ift.tt/2Gu2Ypy

Flooding in Eastern Washington, Driest May on Record for Western Washington

If you like dramatic contrasts, Washington State offers a world-class example--and I am not talking about politics.

Over eastern Washington a number of rivers are at flood stage, some reaching record levels.

Thunderstorms and heavy rain have been pummeling the Columbia Basin and northeast WA. The National Weather Service has issued a flood warning for several counties including Okanogan, Bonner, Chelan, Ferry and Pend Oreille, and the Kettle River, which flows through Ferry and Stevens counties, had a record high on May 10 of 22.54 feet on May 10, busting the previous record of 21.1 feet in 1948.

In contrast, over the west, many locations have had little precipitation in May, and there is chance Seattle will have its driest May on record.

Not black and white.  But dry and very wet.   But why?  And is spring flooding in eastern WA unusual?

Let's start by checking out the flooding situation, with information from the NOAA/NWS River Forecast Center in Portland (below).  Red dots are floods, blue dots indicated moderate floods, and purple are major floods.  And several other locations are at bank-full.

What is going on?   The combination of a healthy mountain snowpack and warming temperatures, resulting in rapid melting of snow, and the filling of regional rivers.

Here is the snowpack numbers for April 15th, from the very nice SNOTEL web site. Washington, northern Idaho, and Montana had snow-water amounts well about normal...in some locations above 150% of what is typical.

And snowpack in British Columbia, from which the Columbia River drains was also very high (see table)

So going into spring with a bountiful spring snowpack was step 1. 

Then a combination of warming temperatures and increasing spring solar radiation caused rapid snowmelt.  The departure of average temperatures from normal (below) shows our temperature anomaly (difference from normal) for the past two weeks, with much of eastern WA and northern Idaho being 6-8F above normal for that period.

So the normal rapid snowmelt of spring was supercharged by warmer than normal temperatures. 

But like a late-night commercial, I should note that there's more.    The weather pattern has produced wetter than normal conditions east of the Cascade crest (and drier than normal to the west)--see map below of the precipitation departure from normal for  5/3-5/16.

During the past few days, showers and thundershowers have moistened eastern Washington (see radar image for 3 PM yesterday), with the last 24-h totals being impressive.  A number of locations in northeast WA have gotten over 1 inch during the last day.

So why wet east of the Cascades and dry west?  Because there has been a persistent ridge of high pressure along the coast, with troughs (low pressure) moving into California and northward into eastern WA and Idaho (see upper level--500 hPa--map for 5 PM Thursday to illustrate.)  The ridge has kept western WA dry, while the transient troughs have initiated thunderstorms east of the Cascade crest.

It is important to note that spring-time flooding in eastern Washington and along the Columbia is the normal state of affairs in our region.  Before the Columbia and Snake River dams were in place, major and often catastrophic flooding was commonplace. 

One of the most famous events was the great snowmelt flood of May 1948.  Just as in this year, regional mountain snowpack was above normal, unusually warm temperatures hit during mid-month, and thunderstorms dampened eastern Washington. Richland flooded and the surge of water moved down the Columbia, inundating and destroying the city of Vanport (near Portland), which was never rebuilt.

As global warming reduces the regional snowpack later during this century, the threats of such springtime flooding should gradually decline over time.

from Cliff Mass Weather and Climate Blog https://ift.tt/2Gu2Ypy

Moisture Hole Reaches California

Today's water vapor imagery shows a dramatic "moisture hole" crossing central California. 

Here are two amazing shots for 1 AM and  6 AM PDT this morning.
It almost looks scary. 

These images show the temperatures of water vapor in the atmosphere.  White areas indicate lots of water vapor in the upper troposphere (roughly 15,000 to 30,000 ft), while dark areas indicate little.  Thus, dark colors show dry conditions in the middle to upper troposphere--the moisture hole.

This "moisture hole" is associate with a pronounced upper level low, as shown by the WRF model run last night (the 500 hPa, about 18,000 ft, heights are shown, with winds and temperature).  This year we have gotten an unusual number of spring upper level lows heading into California...and there is another---even stronger--predicted for next week.

This pattern has brought clouds, precipitation and thunderstorms to northern CA, southern Oregon, and northern Nevada.  The NWS radars show lots of showers, some heavy moving westward over Oregon

And the lightning strikes for the 24-h period ending 1 AM this morning were impressive. Quite a number.

Precipitation totals over the West Coast for the 24-h period ending 8 AM had some significant totals over northern CA, which is obviously good for their water situation.  CA reservoirs are in very good shape and the late spring moisture helps keep the ground moist.

With all the action going south, Puget Sound was dry again, with only .08 inches in the Sea-Tac rain gauge so far this month.  Will we beat the all-time record (.12 inches)?   The next model run will probably provide the answer.

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

Moisture Hole Reaches California

Today's water vapor imagery shows a dramatic "moisture hole" crossing central California. 

Here are two amazing shots for 1 AM and  6 AM PDT this morning.
It almost looks scary. 

These images show the temperatures of water vapor in the atmosphere.  White areas indicate lots of water vapor in the upper troposphere (roughly 15,000 to 30,000 ft), while dark areas indicate little.  Thus, dark colors show dry conditions in the middle to upper troposphere--the moisture hole.

This "moisture hole" is associate with a pronounced upper level low, as shown by the WRF model run last night (the 500 hPa, about 18,000 ft, heights are shown, with winds and temperature).  This year we have gotten an unusual number of spring upper level lows heading into California...and there is another---even stronger--predicted for next week.

This pattern has brought clouds, precipitation and thunderstorms to northern CA, southern Oregon, and northern Nevada.  The NWS radars show lots of showers, some heavy moving westward over Oregon

And the lightning strikes for the 24-h period ending 1 AM this morning were impressive. Quite a number.

Precipitation totals over the West Coast for the 24-h period ending 8 AM had some significant totals over northern CA, which is obviously good for their water situation.  CA reservoirs are in very good shape and the late spring moisture helps keep the ground moist.

With all the action going south, Puget Sound was dry again, with only .08 inches in the Sea-Tac rain gauge so far this month.  Will we beat the all-time record (.12 inches)?   The next model run will probably provide the answer.

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

Roller Coaster Weather Season in the Northwest

The temperature variations this time of the year are often like a roller coaster, with a steady temperature increase over a few days, followed by an abrupt cooling over a few hours.

Only half-jokingly I call the period from middle spring into early summer, the roller coaster temperature season here in the Pacific Northwest.

During the last month or so we have experienced a number of roller-coaster temperature changes (see the temperatures at Seattle-Tacoma Airport below).  An earlier major event around March 13 had a rise to about 73F, followed by a drop to 45F.  Or the recent one around April 25th, with a rise to about 80F, followed by a drop to around 50F.   Plus, several more minor declines.

The biggest one-day temperature changes in our area are NOT in the middle of winter when fronts and storms are strong, but during spring.

Don't believe me?  Here is the proof from a paper I did a number of years ago.  The figure shows the average number of days per month with one-day temperature drops of certain magnitudes.

For the biggest one-day declines (10°C or more), May is the biggest month by far.  For somewhat lesser drops (7.2-9.4°C), June takes the lead.   For moderate temperatures drops, the summer is tops, with August taking first place.

 Temperature drops in winter are small in comparison.

How does one explain this bizarre state of affairs?  Why do temperatures drop more when it gets warm around here?

As we will see, the big issue is the vast Pacific Ocean and the seasonally changing temperatures differences between land and water.

During winter, we are dominated by onshore flow off of a cool (roughly 50F) and vast Pacific Ocean.  Air temperatures over land (west of the Cascades) are just a minor tweak of the ocean temperatures.

Weather fronts coming across the vast Pacific Ocean are heavily modified by their long traverse across water, with temperatures changes at low levels greatly weakened.    A strong front coming off of Asia, with large temperatures differences at low levels, barely produces a few degree change when it hits are shores.

Yes, the Pacific Northwest suffers from wimpy fronts at low levels.  Something I try not to admit to outsiders.

But in spring as the sun warms up and clouds abate, something changes.  The land starts warming up, particularly east of the Cascade crest--and  yes, even on our side to a lesser degree.  But the eastern Pacific Ocean sea surface temperatures hardly change.     Thus, a large contrast between ocean and land temperatures can develop over the Pacific Northwest.  And there lies the answer.

When we have days with onshore (westerly) flow off the ocean, our temperatures are controlled by the ocean temperatures, and thus remain cool.  By when we get periods of offshore (easterly) flow, our temperatures zoom up.

Cool, onshore flow is the default.   But in spring, there are still upper level weather systems moving through, which can result in high pressure building west of us, resulting in offshore flow...and thus we can get periods of warming.

Here is the plot of wind direction at Hoquiam on the Washington coast for the past four weeks.  Some major swings of direction as weather systems move by.  But look closely around April 24th when we got warm...the winds were easterly (or offshore), pushing the cool, ocean influence out to sea.

The warming tends to take time as offshore flow brings warm air down into western Washington, but the influx of cool air (often associated with an approaching trough) comes in fast...and we have a name for it:  the onshore or marine push.

Why are the largest temperature changes in May, rather than in early August when the temperature contrasts between ocean and land are greatest?  Because weather systems that cause the offshore flow and incite rapid onshore flow tend to weaken during the summer over the midlatitudes. 

Why?  Because north-south temperature differences--the drivers of midlatitude disturbances--are less during midsummer.

Anyway, being on a roller coaster can be fun, particularly if you understand how it works.

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

Roller Coaster Weather Season in the Northwest

The temperature variations this time of the year are often like a roller coaster, with a steady temperature increase over a few days, followed by an abrupt cooling over a few hours.

Only half-jokingly I call the period from middle spring into early summer, the roller coaster temperature season here in the Pacific Northwest.

During the last month or so we have experienced a number of roller-coaster temperature changes (see the temperatures at Seattle-Tacoma Airport below).  An earlier major event around March 13 had a rise to about 73F, followed by a drop to 45F.  Or the recent one around April 25th, with a rise to about 80F, followed by a drop to around 50F.   Plus, several more minor declines.

The biggest one-day temperature changes in our area are NOT in the middle of winter when fronts and storms are strong, but during spring.

Don't believe me?  Here is the proof from a paper I did a number of years ago.  The figure shows the average number of days per month with one-day temperature drops of certain magnitudes.

For the biggest one-day declines (10°C or more), May is the biggest month by far.  For somewhat lesser drops (7.2-9.4°C), June takes the lead.   For moderate temperatures drops, the summer is tops, with August taking first place.

 Temperature drops in winter are small in comparison.

How does one explain this bizarre state of affairs?  Why do temperatures drop more when it gets warm around here?

As we will see, the big issue is the vast Pacific Ocean and the seasonally changing temperatures differences between land and water.

During winter, we are dominated by onshore flow off of a cool (roughly 50F) and vast Pacific Ocean.  Air temperatures over land (west of the Cascades) are just a minor tweak of the ocean temperatures.

Weather fronts coming across the vast Pacific Ocean are heavily modified by their long traverse across water, with temperatures changes at low levels greatly weakened.    A strong front coming off of Asia, with large temperatures differences at low levels, barely produces a few degree change when it hits are shores.

Yes, the Pacific Northwest suffers from wimpy fronts at low levels.  Something I try not to admit to outsiders.

But in spring as the sun warms up and clouds abate, something changes.  The land starts warming up, particularly east of the Cascade crest--and  yes, even on our side to a lesser degree.  But the eastern Pacific Ocean sea surface temperatures hardly change.     Thus, a large contrast between ocean and land temperatures can develop over the Pacific Northwest.  And there lies the answer.

When we have days with onshore (westerly) flow off the ocean, our temperatures are controlled by the ocean temperatures, and thus remain cool.  By when we get periods of offshore (easterly) flow, our temperatures zoom up.

Cool, onshore flow is the default.   But in spring, there are still upper level weather systems moving through, which can result in high pressure building west of us, resulting in offshore flow...and thus we can get periods of warming.

Here is the plot of wind direction at Hoquiam on the Washington coast for the past four weeks.  Some major swings of direction as weather systems move by.  But look closely around April 24th when we got warm...the winds were easterly (or offshore), pushing the cool, ocean influence out to sea.

The warming tends to take time as offshore flow brings warm air down into western Washington, but the influx of cool air (often associated with an approaching trough) comes in fast...and we have a name for it:  the onshore or marine push.

Why are the largest temperature changes in May, rather than in early August when the temperature contrasts between ocean and land are greatest?  Because weather systems that cause the offshore flow and incite rapid onshore flow tend to weaken during the summer over the midlatitudes. 

Why?  Because north-south temperature differences--the drivers of midlatitude disturbances--are less during midsummer.

Anyway, being on a roller coaster can be fun, particularly if you understand how it works.

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

Time to Fix the Yakima Airport Temperature Sensor

With all the concerns about global warming and the need for agricultural interests to have reliable temperatures to guide operations, accurate temperature readings at key airport sites are crucial.

That is why continuing problems with the Yakima Airport temperature sensor is so concerning.  So the message to my colleagues in the National Weather Service  is clear:  it is time to swap out the problematic sensor.

The Yakima Airport sensor provides temperatures that are several degrees too warm.  Let me prove this to you.

Here is departure from average of the maximum temperature across Washington State, averaged over the past year.    There is a major hot spot, with temperatures 4-5F above normal.  Nothing like it in the neighborhood.

The hot location?  Yakima.

There is someone who has been documenting the serious issues with the Yakima Airport temperature sensor:  Mark Albright, who was previous State Climatologist and Deputy State Climatologist.  This guy knows the local meteorology as well as anyone.  His hobby is to drive around the State with a temperature sensor checking out the accuracy of the temperature readings at various locations.  A very noble pursuit and appreciated by all of us worried about the integrity of our key observing systems.

Mark Albright

So let me show you some recent documentation he has come up with regarding the Yakima situation.

Consider last August.    Here are the temperature anomalies for normal for stations around the State (look at the TDPTR column).  The greatest departure from normal (6.5F) was at Yakima...with no other station even close.

Want a winter month?  No problem.  Here is the same information for January.  Biggest warm anomaly in the State?  Yakima.

Now, I could show you a dozen more of these monthly summaries--all prepared by Mark, but the story would be the same.  Something is very wrong at Yakima.

I have heard complaints from some agricultural interests that have used Yakima temperatures to make decisions for planting, spraying, and other issues.  Too warm and not representative of the area.

One thing is clear--this warming is not due to local development, since the temperature sensor is found near a secondary runway, with no development going on nearby (see map).

Anyway, the Pendleton office of the NWS is responsible for calibrating and replacing this sensor, which I hope they will do very soon.  This problem has been going on for years and needs to be dealt with.

And if you think this is the only place in the country with a bad temperature sensor....it is not.  Here is the mean departure from average for minimum temperatures over Utah for the last year.  Oh....oh.-- a big warm anomaly southeast of the Great Salt Lake.  And then there is the infamous warm bias at Seattle-Tacoma Airport.

The problem with these failures is that they tend be one sided--generally producing temperatures that are too warm.  Often this warmth  is associated with a failing fan, which brings in cooler environmental air into the sensor enclosure.   And most siting problems (too near roads, buildings, or non-vegetated surface) tend to cause a warm bias as well.   

How much such problems influence trends in the surface temperature record is one of some debate and controversy..and I won't get into it right now.  My vegetable garden needs attention.

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