Sunday, January 14, 2018

Record Heat in Western Washington and Oregon

Tuesday Update:  Monday's highs are shown below.  Lots of 60s, including mid to upper 60s on the western slopes of the Cascades and Olympics.  Even a few 70s in favored spots.  Daily records broken at Seattle, Quillayute, Hoquiam and a few other locations.   But places in which the fog held in (southern Sound), remained cooler.

Daily high temperature records were broken yesterday and more will fall today. Sea-Tac got to 58F (old record was 56F) and Hoquiam to 56F (old record of 55).

This morning's sounding at Quillayute, on the WA coast, shows a freezing level over 10,000 ft and an intense inversion (temperature increasing with height) in the lower few thousand feet (see below)

Yesterday's high temperatures got into the mid-50s all over the region yesterday, with some locations even rising into the mid-60s (only the highs above 54F are shown below).

The temperature this morning at 925 hPa (about 2700 ft)--16.4 C--was a record for the date and we have a strong offshore pressure difference this morning (much higher in eastern WA) that will produce offshore (easterly) flow and substantial downslope warming over the western slopes of the Cascades.  Mid-fifties will be commonplace and some locations downstream of terrain will get into the 60s.

Let me show you the latest UW WRF forecasts for surface (2-meter) air temperature--the details are fascinating.  Red indicates the warmest temperatures (check the legend below each figure).

At 8 AM, the State is divided in two:  cold east of the Cascade crest and warmer to the west.  But notice there are ribbons of greater warmth along the western slopes of the Cascades and to the west of the Olympics--this is due to the downslope warming (air warms by compression as it sinks down the slopes).   So at 8 AM, head to North Bend, WA or the Olympic Coast for warmth,

By 10 AM, the warmth along the Cascade slopes and along the coast will be profound, with lots of locations well into 50s and even near 60F.

But the situation at 2 PM will amaze, upper 50s to lower 60s everywhere, with some locations getting above 65F.  It will feel like spring.

The only thing holding things back is the strong inversion (which represent great stability and slow the mixing of warm air down) and the fog that covers some areas this morning (see 9 AM satellite picture).   Fog covers the southern Sound, parts of the Strait, and extreme NW Washington. And, of course the eastern slopes of the Cascades and the passes.

So enjoy the warm days...things will change greatly this week.

Saturday, January 13, 2018

Finally! A Transition to Cool/Moist La Nina Conditions in the Northwest

A warm front is moving through Washington State now, with a freezing level of around 8000 ft.   Rain is falling in the passes, and even the ever-positive Snoqualmie Summit snow report talks about " soft slop."

The last few days have been substantially warmer than normal , as shown by the observed temperatures at Stampede Pass (4000 ft) in the WA Cascades (normal highs and lows shown by purple and cyan).  Really warm today.
But I have some very good news for skiers and snow lovers: a major shift in the hemispheric flow patterns will result in much cooler/snowier conditions over the Northwest next week.  And much wetter over California.

Finally, we will see a more La Nina-like pattern, something that typically occurs in early January when a La Nina is in place, as it is this year.

Let me show you the upper level flow pattern for the next week, and for a change I will present the heights and winds at 300 hPa, roughly 30,000 ft:  the elevation where jets tend to fly and where the jet stream is often strongest.  Heights (like pressure) are shown in black and the wind speeds are color-shaded.  You can see the jet stream core by looking for the high speed areas (yellow and orange).

The jet stream is directly connected with temperature, with warmer temperatures to its south and cooler temperatures to the north.

Today at 4 PM shows a big ridge of high pressure (high heights) over the western U.S.   Warm and relatively dry for us.

Fast forward to Monday at 4 PM shows the shift:  the ridge has moved inland and the core of the jet is moving south towards California.

By Wednesday at 4 PM, a strong jet stream is approaching Oregon, with Washington on the cold side (good for snow here).

And the jet moves farther south on Thursday.

 And even farther south on Saturday...heading into the U.S. southwest.

The flow pattern this week will bring substantial precipitation to the West Coast, importantly including California.  We will cool down and substantial mountain snows are expected.

For example, here is the snowfall total from the UW WRF system for the 72 hr ending at 4 AM next Saturday.  Snow from the Sierra Nevada to southern BC.  Above 4000 ft there were be several feet of snow in the WA Cascades.  Southern BC mountains will be hammered.

The precipitation totals for the same period show 2-5 inches of liquid water equivalent over much of the western coastal terrain.

Good for water resources, good for skiing, and good for putting away the fire threats in the western U.S.  And with days getting longer, most folks won't mind the clouds.

Thursday, January 11, 2018

Scary But Deceiving Climate Statistics

How many times do you see a headline or read an article about climate change, where you are told that threat of some scary extreme event (flood, heat waves, cold wave, etc.) has increased five or ten or 100 times due to global warming?

But as we will see, such scare statistics may not mean as much as the headlines suggest.  In fact, they can be quite deceptive.  Let me explain.

Many of the scary stories talk about the frequency of exceeding some extreme threshold, such as the number of times temperatures exceed 90F in Seattle during the summer, or the frequency of daily precipitation exceeding 20 inches during the winter in the Cascades--that kind of thing.

The nature of extremes is that they are unusual.  So a very small increase of their numbers can result in the number of occurrences above some threshold increasing radically.

So if there are normally one day a year with temperatures over 90F during the summer and there is two one year, the frequency has DOUBLED.   A 100% increase!  Huge.

Let me do this a bit more quantitatively.  The climatological distribution of temperature is often Gaussian (also called the normal and bell-shaped distribution).

Below is an example of such a distribution, whose mean and most probable value is 75F.  The x-axis is temperature and the y-axis is frequency.   A measure of the spread or width of the distribution is the standard deviation (greek letter sigma is often used to denote it).  67% of the observations should be within one standard deviation of the mean (I have assumed a 3F  standard deviation in the figure below)

You notice the frequency (or probability) of observations drops rapidly for values much larger and smaller than the mean.

Now let's think about extremes.  What is the probability of experiencing a temperature more than 85F?   According to the calculation shown above:  .00043 (.043%)  Not much

OK, now lets warm things up by 1F, so the mean becomes 76F (I am keeping the shape the same).  You might not even notice that.  Here is the new distribution.

The probability has increased to .00135 (.135%).  OMG!   The probability of exceeding 85F has gone up by 3.14 times!

But think about it a bit more.   Instead of the scary increase of 3.14 times, think about the actual increase of probability of getting about 85F.

The increase is ONLY .1%.  Yes, a tenth of a percent increased risk of such warm temperatures.  Doesn't seem so scary all of sudden.

I could give a dozen other examples of this...but hopefully you get the idea.

So be very cynical when you read about increases of extreme events due to global warming (or anything else) and particularly when the increases are for exceeding some threshold and given as a factor (5 or 10 or 100 times more). 

Such numbers can be extremely deceptive and imply a big increase in risk in situations with minor changes.  

And there is more.  Even if global warming results in a higher frequency of exceeding some threshold, its contribution might be quite small.  Consider Hurricane Harvey.   Global warming may have increased the precipitation by a few percent, but nearly all of the event was the result of natural processes.  When folks hear that global warming has increased the probability of an event by some factor they tend to assume that most of the event was due to global warming, when that is generally not the case.

Finally, thresholds are generally arbitrary and subjective.  For example, why is 90F more special than 91F?   The use of thresholds for such climate communication is essentially deceptive and should be used far less. 

What really counts is not the frequency of crossing some threshold but the increase of the amount of the threat (e.g., the increase in high temperature, precipitation).   For example, by the end of the century, the Northwest snowpack will probably be down by 30-50%.   That is scary.  Or the heaviest precipitation in atmospheric rivers could be 20-40% larger.  Again, a major issue.

Global warming is too serious of an issue for us to use questionable, if not deceptive, statistics for communications of its impacts.

Tuesday, January 9, 2018

Norwegian Cruise Ship Heads Right Into a Well-Forecast Storm

On January 4th, its cruise ship Breakaway (I did not make this name up!) sailed right into the most dangerous portion of an explosively deepening, intense winter cyclone off the east coast, causing damage to the ship and greatly discomforting the passengers. And it did so by ignoring emphatic warnings by the meteorological community.

Some of the videos taken by passengers were terrifying, with large waves, water cascading down staircases, and items falling off the walls.  Here are a few sample videos:

The ship has a store called the "Tides Boutique"---and during this storm it has real tides.

So what happened?  The cruise ship sailed directly into the most dangerous sector of the storm.  This plot show the NWS surface analysis (sea level pressures and fronts) at 4 AM January 4th and the position of the ship at that time.  The ship was just south of the low center in a region of very strong winds---a region that is often called the "sting jet" in the weather business.

Here is a sustained wind analysis from the NOAA/NWS HRRR model with speed shown with the color fill, wind vectors with the symbols, and the black dot my estimated position of ship at the same time (4 AM Thursday PST).  At this point, they were in sustained winds of around 45 knots (52 mph), with higher gusts.  The ship was heading northward towards NY at this time. 

You will notice even stronger winds in front (north) of them, with a long fetch---allowing the development of big waves.   That morning the WindSat scatterometer satellite, which can measure surface winds from space (using the relationship between wind and small ocean waves,) went over the storm (and ship).  Here are the winds it found (wind vectors, color coded shown).  Sustained winds from the NW of 40-50 knots at the ship position off of North Carolina.

The most dangerous location in the Pacific cyclone is to the south and southwest of the low center, in the region of strongest pressure gradient.  This figure from a NOAA document indicates the region of very strong winds (red shading).  Guess what ship was very close to the worst part of the storm?

The forecasts for this storm were excellent, days ahead of time.  The forecasts made 24 hr and 48hr before the time shown above, had good forecasts of the storm (see below). The cruise line and the Captain had no excuses for being there.
                                          24h                                                                          48h
The NOAA Ocean Prediction Center (OPC) had an excellent forecast the day before for 80 kt wind gusts and 33 ft seas in the storm area.   Waves around the Breakaway were estimated at 30 ft.

And the NOAA 4-day forecast was highly accurate.
The storm was moving rapidly to the Northeast, so a delay of 24hr would have made a world of difference.

Something is really wrong when a ship with 4000 passengers and over 1000 crew heads into an historic storm of great intensity.   Thousands of lives were endangered and everyone on board had a very unpleasant experience.   It appears that the Captain ignored highly reliable meteorological guidance and needlessly put the ship and its passengers at risk.

Monday, January 8, 2018

Snow in Mountains, Wind, and Ample Precipitation: A La Nina-Like Pattern This Week

For those worried about the Cascade snowpack, salvation is at hand:  the atmospheric circulation is taking a turn towards more of a La Nina pattern, with cooler/wetter/windier conditions prevailing this week.

The upper level flow pattern for Wed and Thursday at 1 PM is predicted to include an offshore ridge and northweserly flow over the NW, with some disturbances moving SE in the cool flow.  Much more La Nina-like than we have seen in a while.

As a result the models are forecasting a major snowfall over the Cascades, BC, and NE Washington as illustrated by the 72 hr snow total ending 4 PM Thursday. We are talking about 1-3 feet above 3500 ft.

And we could get blustery on Thursday as la ow center moves into southern BC during the afternoon, with large pressure gradient established over WA (see below).    Haven't seen  too many of such vigorous systems this winter.

Precipitation? Substantial...but not enough for real flooding.  The 72 hr total ending 4 PM Thursday, show 2-5 inches over the mountains and about 1.5 inches over Seattle.

Saturday, January 6, 2018

Snowpack Update: Slightly Low Today But More Snow is Expected

It is just past the new year and folks are wondering about our snowpack.  What is the current status?  Will La Nina give us abundant snow in the future?    This blog will take these questions on.

First, the current status.  Here is the percentage of normal of snowpack (from the wonderful SNOTEL web site).  Snow water equivalent (SWE) is shown, the amount of liquid water that would result from melting the snow/ice.   

Low values (less than 50% of normal) in Oregon, California, and Nevada.   But much better over WA state, at 75% to 100% of normal.  Low, but not significantly down.
A better view is found in an expanded image over WA State.  The Olympics and north Cascades are in good shape, but the central and southern Cascades are closer to 75% of normal.  Enough to open our ski areas and not to worry about water next summer.

The snow levels (elevation of hitting snow) on the western side of the Cascades are certainly higher than during  the past few years. 

I can demonstrate this with the NOAA snow analyses for the region for this and the past two years (below), showing you the snow depths on January 6 for 2016, 2017, and 2018. 

Much less this year. Less snow over the high plateau of eastern Oregon, and MUCH less over the middle to lower slopes of the Olympics and Cascades.

 Interestingly, the average conditions (temperature and precipitation) over the past 90 days have not been that unusual over WA state (see below), with temperature being near normal and precipitation above normal.  But averages can be deceiving, we just haven't gotten the right weather set-ups for snow:  much of the time we had high pressure (cold and dry), with occasional warm/wet periods.  Neither are great for snow accumulation in the mountains.

But there is great reason for hope.

This is a La Nina winter, and the effects of La Nina (more snow in our mountains) usually don't snap in until after the New Year.  The latest sea surface temperature anomalies (difference from normal) over the central tropical Pacific show we are firmly in a La Nina, with colder than normal ocean temperatures (see below).  La Nina's tend to produce cool/wet conditions over the Northwest: which means SNOW.

To put it another way, the atmospheric dice are weighted for Northwest snow!  What about the new model forecasts from the UW WRF forecast system?  (see below).  Encouraging.

For the next 72 hr, substantial snow (.5 to 3 feet) in the north Cascades and southern BC.

And even more for the next 3-day period (ending 4 AM Friday).

So if you enjoy skiing and winter sports, I would be optimistic.  Things are ok now, but may get very good during the next month.  But no guarantees.😊