Tropical Air over Seattle

Breath deeply this morning. 

A few days earlier the air was over the tropics.  Moist, warm and soothing to our wind and cold whipped skin.  And we just broke a major low temperature record.  This morning, our low temperature (56F) was the HIGHEST low temperature ever recorded in November at Seattle Tacoma Airport.  That is a big record to break.

Yesterday, Bellingham broke their daily high temperature record (60F) and today all sorts of daily high temperature records will be broken around the region.  



To certify the tropical origins of our air, I used the NOAA Hysplit trajectory model to trace the origin of the air above us at 500 meters (blue), 1500 meters (red), and 3000 meters (green) for the past 150 hours.  Our low level air, came from just east of Hawaii.  The 1500 meter air from the deep tropics.  No wonder many of us are fighting the urge to grab a Mai Tai today.


A plot of the winds and temperatures above Seattle for the past day (below), shows a freezing level of 10,000 feet, with strong southwesterly winds aloft--a sign of a potent atmospheric river event.

Over the past 24 hr (ending 5 AM), portions of the SW slopes of the Olympics received over 6 inches of rain, with the north Cascades getting as much as 3-5 inches.



But perhaps more impressive than the rain on the windward sides of the mountains, is the profound rain shadowing in the lee of the Olympics, where some locations only received 1-2 hundredths of an inch (see below).  Just amazing.


However, the wacky weather award yesterday had to go to Bellingham, Washington, where in less than an hour (around 4 PM Tuesday),  the winds turned southerly and surged to over 40 knots, and the temperature rose from 46 to 60F (see report below).


The temperature trace there shows the story and the fact the temperatures are EVEN WARMER right now--62F (and there are strong winds at Bellingham currently as well).
Perhaps just as unusual was the existence of sea fog (a.k.a., warm advection fog) over Lake Washington  this morning (see below).  The air was so humid and warm (dew point at Seattle-Tacoma Airport was 57F at 7 AM), that the cooler waters of Lake Washington (51F according to the Lake WA buoy) was able to bring the air to saturation.



The temperatures today will delight you.  A plot of temperatures during the past two weeks at Seattle shows that our current morning temperatures are WAY higher than the normal highs (purple line below).
 And the UW high resolution model forecast for surface air temperature at 2 PM  today shows 60s all over western Washington.  Some locations in the upper 60s.


 So pull out a short-sleeve shirt and breath in the tropical air.  Today, will not feel like normal Seattle weather fare of November.



Giving Thanks for the NCAR Ensemble

For nearly three years, the National Center for Atmospheric Research (NCAR) has produced a daily, 10-member, cloud permitting ensemble at 3-km grid spacing known as the "NCAR Ensemble". 

For those of us in the western U.S., the NCAR Ensemble forecasts, available from web sites hosted by NCAR and the University of Utah, attempted to do something that no current operational forecast system could three years ago — capture the extreme spatial contrasts and quantify the inherent uncertainty of precipitation over the western United States. 

Last night's forecast, for example, shows the major deluge expected to affect the Pacific Northwest through Thanksgiving.  At 3-km grid spacing, the NCAR ensemble accounts for many regional and local topographic influences and, with 10-members, one can derive statistics related to the range of possible forecast outcomes and the likelihood of precipitation above certain thresholds (our standard 1" and 2" thresholds work well for the Wasatch, but not the Cascades!). 
Plume diagrams allow one to examine precipitation at various locations, including Mt. Baker Ski Area below.  Such a pity that nearly all of that water will fall in the form of rain.

These products are popular with readers of this blog, friends in the snow-safety community, and operational forecasters.

Recently, NCAR announced that the NCAR Ensemble will sunset at the end of the calendar year.  More information is below. 


Although I'm sad to see it go, I believe this move makes sense.  NCAR is a research lab, not an operational center.  They need to be unshackled from routine forecasting and free to explore creative ideas and pursue modeling breakthroughs.  The NCAR Ensemble did this for three years.  It has allowed us to learn a great deal about cloud-permitting ensembles.  For example, we have a paper examining the performance of the NCAR Ensemble that may be the subject of a future post.   

Given that tomorrow is Thanksgiving, it seems fitting to toast the NCAR Ensemble team that includes Kate Fossell, Glen Romine, Craig Schwartz, and Ryan Sobash.  Thanks so much! We look forward to a few more weeks of NCAR Ensemble forecasts, and hope that Mother Nature shifts this damn pattern so that we can actually use them for powder hunting in Utah!

Interesting contrail in North Dakota

As mentioned in a Tweet from NWS Grand Forks (above), an interesting contrail was seen over eastern North Dakota on 21 November 2017. They noted that the contrail was most easily seen using imagery from the water vapor bands.

A comparison of GOES-16 ABI Lower-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (below) showed the formation and motion of the contrail feature (which was likely caused by military aircraft, based in Grand Forks and/or Minot, performing training exercises).

GOES-16 Lower-level (10.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images, with surface station identifiers plotted in cyan [click to play animation]

GOES-16 Lower-level (10.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images, with surface station identifiers plotted in cyan [click to play animation]

A comparison of three of the GOES-16 Near-Infrared bands (below) showed that the high-altitude ice crystal contrail feature was also very apparent in “Cirrus” (1.37 µm) images; the contrails themselves were very subtle in the “Vegetation” (0.86 µm) and “Snow/Ice” (1.61 µm) images, but their darker shadows which were cast upon the surface (to the east-northeast) were more obvious — for example, on the 2132 UTC images.

GOES-16 Vegetation (0.86 µm, left), Cirrus (1.37 µm, center) and Snow/Ice (1.61 µm, right) images [click to play animation]

GOES-16 Vegetation (0.86 µm, left), Cirrus (1.37 µm, center) and Snow/Ice (1.61 µm, right) images [click to play animation]

Mini Snow Eater Conditions

It's not quite like an east-coast snow-eater event when temperature are near 50, fog, and rain, but for Utah, this is as close as it gets.

Current (7-8 AM) temperatures in the central Wasatch are 37 at Spruces, 39 at the base of Park City, 38 at the base of Alta, and 33 at Alta-Collins, and 31 at Germania Pass.  That puts the freezing level at about 10,000 feet. 

In addition, dense, mid-level overcast is draped over the mountains, with some west snow at upper elevations, rain at mid elevations, and the transition zone in between.  The Alta webcam below summarizes the dreary conditions quite well. 


For the most part, snow on north facing aspects will survive just fine this time of year under clear, dry conditions, even when temperatures are above 32ºF.  Without direct sunlight, you simply don't have enough energy to melt snow.

However, if you can add humidity and cloud cover to the mix, things change.  You lose the cooling effect of snow sublimation and gain the energy input of infrared radiation from the clouds. 

The eastern U.S. gets these conditions in spades at times, with fog and rain doing it's number on snow frequently during the cool season. 

We don't really get such a snow-eating extreme in Utah.  Today is about as close as it gets.  Above 9000 feet, everything will be fine.  Below 8000 feet, we're going to see snow losses.  In between there may be a net loss, but it probably not a huge one. 

Fall continues it's grip on the Wasatch, with no desire to let go and let winter take control....

Warm Temperature Records Will Fall As A Strong Atmospheric River Hits the Pacific Northwest

The next 48-hr will be stunning in a number of ways:  very heavy precipitation in the mountains, river flooding, and temperatures that will reach record levels.

The forecast for today at 1 PM, shows the story, a strong plume of moisture from the south that is heading directly into the Northwest (blue and white colors indicate the largest values).


The moisture channel satellite image from last night at 9:30 PM shows an amazing plume of water vapor heading directly from the tropics.  It has our name on it.

Accompanying this plume of tropical moisture will be near-tropical warmth, something illustrated by a forecast chart for 1 PM Tuesday at the 850 hPa (about 5000 ft) level.  Red/orange are warm temperatures, driven northward by powerful southwesterly flow aloft


Or we could look at the forecast temperatures (red lines, °C), winds, and humidity (shading) over Seattle (see below). Time increases to the left and the heights are in pressure (700 hPa is 10,000 ft). The blue line is the freezing (0°C) level. 

Unbelievable...the freezing level rises about 10,000 ft.  This means rain everywhere...even over the high terrain of the Cascades.  The atmosphere is very moist (green colors), with strong southwesterly winds aloft.


Now let me show you the  forecast precipitation with 24 hour totals.

Ending 4 PM Tuesday...heavy rain in the mountains, with 2-5 inches in the Olympics.

 Even more the next 24h (ending Wed. at 4 PM)

 Just as much the next 24 h.  Yikes.


Add them all together for the 72h total ending 4 PM Turkey Day.  Much of the mountains get 5-10 inches, with a few places in the Olympics getting more.  Expect flooding on a number of rivers. And  yes, our snow will do some serious melting.


 But what really will be amazing will be the temperatures.  Here are the forecasts from the National Weather Service SREF ensemble for Seattle...many of the members will reach into the LOWER 60s on Wednesday....probably breaking the daily record.


Well...this is climatologically the wettest weak of the year!

Precipitation Overprediction Problems with the NAM Conus Nest

High resolution forecast models are not necessarily better forecast models and precipitation forecasts produced by the NAM Conus Nest (hereafter the NAM-3km) are a prime example of this. 

The NAM-3km covers the continental US at a grid spacing of 3 km, four times the resolution of the 12-km NAM in which it is nested.  With such high resolution, you would think the NAM-3km would be especially useful for precipitation forecasting over the complex terrain of the western US, but it isn't, because it has a major overprediction problem.

Tom Gowan, a graduate student in my research group, recently led a study examining the performance of several forecast models at mountain locations across the western U.S. during last winter.  I have been holding off on publicly sharing these results broadly since the paper describing this work is still in review, but the results are too pertinent to forecast needs right now not to share at this juncture.  In the case of the NAM-3km, we used pre-operational test runs from last winter that were kindly provided by NCEP.

The plot below shows the ratio of mean-daily precipitation produced by the NAM-3km to that observed at SNOTEL stations.  Overprediction is evident at the majority of sites, with on average the NAM-3km producing 1.3 times as much precipitation as observed.
Source: Gowan et al., in review.
A major reason for this is that the NAM-3km produces far more major precipitation events than observed, especially over the interior western US.  In the plot below, the frequency bias is the ratio of the number of forecast events to the number of observed events in each event size bin.  The NAM-3km has by far the largest overprediction problem.  Note that the NCAR ensemble also produces too many large events, although the magnitude of the problem is not as acute.  

Source: Gowan et al. in review.
I bring up these issues today because the NAM-3km is going batsh-t crazy for the storm later today and tonight.  For Alta-Collins, the 12-km NAM is producing .08" of precipitation through 10 AM tomorrow.  In contrast, the 3-km NAM is producing 2.04"! 

The loop below shows steady, drippy precipitation over the Wasatch and nearby ranges during the overnight period. 


Now, it is always dangerous to say a model is wrong before the forecast verifies, but I'm going to say it anyway.  This forecast is wrong.  There's little evidence to support such huge precipitation totals.  Even in the NCAR ensemble, 7 of the 10 members produce less than 0.2" of precipitation, and the wettest goes for about .57".  

This issue plagued the NAM Conus Nest when it was run at 4-km grid spacing and it appears to carry over to the higher resolution upgrade. 

The bottom line is this.  If you want great deep powder skiing, consider using the NAM-3km for your holodeck experience.  However, if you live in the real world, avoid using the NAM-3km precipitation forecasts unless you want to be severely disappointed on a regular basis.  

Three Thoughts on This Sunday

1. Yes Virginia, there is skiing

I debated for a while whether or not to ski this weekend.  I'm not a fan of low snowpack, bony conditions and often stick to skiing the main run along Alta's Collins lift under such conditions.  With Alta closed to uphill, we opted to take a couple of laps at Brighton in the Great Western area since rumors were that they were asking tourers to avoid other parts of the mountain.  I pulled out my oldest sticks for the day, a pair of Karhu Jak BCs that are probably 10-12 years old.


However, I was pleasantly surprised to survive both runs without harming a single rock.  I was also glad to rediscover that the Jak BC really was a great ski, even if you didn't see them much in Utah. 

We stuck to grassy runs that were heavily traveled.  The touring and skimo crowd cut up the area pretty good. 


Some sections of untracked could be found in some areas and we went home satisfied, without injury, which is the main goal of any first day.  

2. The snowpack isn't really all that meager

It's worth remembering that it is only November 19.  Thanksgiving is pretty early this year.  Our snowpack seems pretty meager, but really it isn't.  The Snowbird SNOTEL is measuring 3.1 inches of snow water equivalent (SWE).  Median is 4.1 inches.  An inch of water equivalent is basically one modest storm.  So, we're one storm below median.  Yes, it hurts to look at the snowpack in the Tetons and Sawtooths (or should I say Sawteeth?), but we're not really doing all that bad.........yet.

3. The next week may suck

The model forecasts for Thanksgiving week don't look so great for Wasatch skiers.  The NAM forecast for 5 PM MST tomorrow (monday) shows a classic "dirty ridge" scenario with moisture spilling over a low-amplitude ridge and into Utah.  700-mb temperatures are a balmy 0ºC.  This is a recipe for riming and perhaps some wet, rimed snow at times in the mountains.  It probably won't add up to much for the snowpack and we'll probably see a net loss at elevations below 7000 feet (not that there's much there currently).


Eventually, a high amplitude ridge builds over for Thanksgiving Day.  Beautiful weather across Utah for driving over the river and through the woods to grandmother's house.  Good valley mountain biking.  Good canyoneering. 


However, 700-mb temperatures are a whopping +6ºC, which would be a record for the last week of November (although we have observed 700-mb temperatures of +8ºC in mid December).   Brighton was making snow today where they could, with the low-angle sun and dry conditions allowing for it in shady spots.  The resorts will probably need to continue to selectively pick spots and times over the next few days for making snow.  

Cyclone Numa in the Mediterranean Sea

Terra MODIS and Suomi NPP VIIRS true-color RGB images [click to enlarge]

Terra MODIS and Suomi NPP VIIRS true-color RGB images [click to enlarge]

A toggle between Terra MODIS and Suomi NPP VIIRS Red-Green-Blue (RGB) images, viewed using RealEarth (above), revealed the well-defined eye structure of Cyclone Numa over the Ionian Sea (between Italy and Greece) on 18 November 2017. Tracing its origin back to the remnants of Tropical Storm Rina (track), Cyclone Numa had acquired subtropical characteristics on this day, making it a relatively rare Medicane.

EUMETSAT Meteosat-10 High Resolution Visible (0.8 µm) images (below) showed the evolution of the storm on 18 November. Plots of hourly surface reports (in metric units) are plotted on the images.

Meteosat-10 Visible (0.8 µm) images, with plots of hourly surface reports [click to play MP4 animation]

Meteosat-10 Visible (0.8 µm) images, with plots of hourly surface reports [click to play MP4 animation]

Meteosat-10 Infrared Window (10.8 µm) images (below) showed cloud-top infrared brightness temperatures around -60ºC (darker red enhancement) associated with some of the convective bursts during the 18-19 November period, as the system eventually moved inland across Greece.

Meteosat-10 Infrared Window (10.8 µm) images, with plots of hourly surface reports [click to play MP4 animation]

Meteosat-10 Infrared Window (10.8 µm) images, with plots of hourly surface reports [click to play MP4 animation]

The Real Signs of Human-Caused Global Warming

Human being are causing a rapid increase of greenhouse gases in the atmosphere, with carbon dioxide and methane gases being the most well known.

But how have increasing greenhouse gas influenced the weather and climate we experience todayWhat current effects are unequivocal, right now?
The media is full of claims regarding the current impacts of increasing greenhouse gases, but many of these claims are without a good basis in science.    Some recent examples include:

  • That Hurricane Harvey's heavy rains were a sign of global warming.
  • That the recent California wildfires were the result of human-caused warming.
  • That winter storms in the Northwest are becoming more intense due to global warming
  • That global warming is causing more droughts in the West.
  • That increasing greenhouse gases are causing more cold waves over the eastern U.S.

And there are many, more.  A weakness of many of media and activist claims is that one extreme event can not provide "proof" of human-caused global warming.   Only statistically significant trends have meaning when one is talking about climate change.  And many of the claims are inconsistent with climate models and basic statistics.

But let me be clear: increasing greenhouse gases associated with human activities are changing our climate  in profound ways, and there are "fingerprints" of human effects today that provide compelling evidence of human influence.

When one wants to identify a thief, finding their fingerprints often provide incontrovertible proof of their guilt.   What are some "fingerprints" of increasing greenhouse gases on the weather/climate system?

1.  Fingerprint 1:  Greater warmer in the Arctic than the midlatitudes.

When climate models are run with increased greenhouse gases, virtually all of them not only show warming, but they show a similar distribution of warming.  Below is an an example, showing an average for several global climate models of the change in surface temperature during this century assuming that greenhouse gases keep up increasing at the current pace.

 Blue is cooling, red is warming.  All warming.  Note that the Arctic warms more than anywhere else, and the continents warm up more than the oceans.

Change in average surface temperature (a) and change in average precipitation (b) based on multi-model mean projections for 2081–2100 relative to 1986-2005 under the RCP2.6 (left) and RCP8.5 (right) scenarios. The number of models used to calculate the multi-model mean is indicated in the upper right corner of each panel. Stippling (i.e., dots) shows regions where the projected change is large compared to natural internal variability, and where at least 90% of models agree on the sign of change. Hatching (i.e., diagonal lines) shows regions where the projected change is less than one standard deviation of the natural internal variability

The greater Arctic warming is a major fingerprint of increasing greenhouse gases, one that is reflected in the observed changes in temperature during the last 70 years (see map below).  There are a number of reasons that the Arctic warms faster, including the loss of reflective sea ice and some subtle radiative effects, I won't get into.

A plot of the temperature change over the same period, but averaged by latitude clearly shows the Arctic warming.

2.  Stratospheric Cooling While the Lower Atmosphere Warms

Perhaps the most compelling support for the influence for increasing greenhouse gases might come as a surprise to many:  the cooling of the stratosphere.   Increasing CO2 warms the lower atmosphere through a process that is analogous to how a blanket warms you when sleeping...by slowing the loss of heat away from your body.  But having an efficient emitter of infrared radiation aloft actually results in cooling of the upper atmosphere.   So warming below and cooling aloft is a potent fingerprint of the influence of CO2.

Observations in the stratosphere and in the layers above (e.g., mesosphere, thermosphere), shown below and in the literature, demonstrate the cooling trend.  In the first figure, the blue and purple colors show cooling between 1979 and 2012 in the lower stratosphere, while the second figure shows cooling in the layers above the stratosphere (which ends about 50 km above the surface).



The cooling above the middle stratosphere is very important, because another issue (the weakening of the ozone layer from human emitted freon and other chlorfluoromethanes) could have produced some cooling.  But not in the layers above.

3.  Warming of the Earth's Atmosphere and Oceans and Model Experiments

As described in many places, the general temperature change of the past century determined by all the major centers are very similar, with cool temperatures during the late 19th century, warming during the first half of the 29th century, a leveling off from roughly 1950 to 1975, warming during the late 20th century, and a leveling off during the past 15 years.  The warming has been about 1C during the the entire period.  Analyses of the impacts of human emitted greenhouse gases suggest that our influence on warming would be mainly significant after 1970.


At first glance, this warming is not a compelling argument for human influence, since there was warming during the early part of the 20th century, which was probably natural.  There is some research that suggests that the pause during the middle of the 20th century might be associated with human-produced particles that scattered solar radiation back to space.

As I noted before, atmospheric scientists run climate models to simulate the evolution of the earth's atmosphere. If we run the model with only natural forcing (e.g., volcanoes, keeping greenhouse gases constant at pre-industrial values), the simulations do ok until about 1970,  but are way too cool during the past 40 years (see top figure below, the black line is the observed global temperature, the red and green lines are the average of collections of climate models).    But add changing greenhouse gases and the models are much closer to the truth (although they are a bit too warm during the last decade).


This is strong evidence of the important of human-produced greenhouse gases during the last half century.    Not as compelling perhaps as my first two fingerprints, but together with them, a pretty strong argument that humans are changing the climate.

The media and many politicians have not given enough emphasis to the above fingerprints, which are really the best evidence we have for human-caused global warming.  Instead they have pushed much weaker "proofs", such as a few big tropical storm events (e. g., Katrina, Sandy, Harvey) and the Washington/California wildfires.  As described in a excellent analysis by NOAA's GFDL, the connection of current contemporary hurricanes  with global warming is a weak one.  And the increase in western wildfires reflects in part the


mismanagement of our forests, suppression of natural fires for 70 years, the spread of invasive cheatgrass, and huge increase of people living and recreating in the forest environment.

In short, there is plenty of strong evidence of human impacts on climate change, it just takes a little study to appreciate why they are compelling and important.


Alaska’s first -40º temperature of the 2017-2018 winter season

NOAA-18 Infrared Window (10.8 mm) image, with surface identifiers and air temperatures plotted in red [click to enlarge]

NOAA-18 Infrared Window (10.8 mm) image, with surface identifiers and air temperatures plotted in red [click to enlarge]

Alaska’s first (official) surface air temperature of -40º or colder for the 2017-2018 winter season was reported by the Cooperative Observer at Chicken (-43ºF) on 19 November 2017. A NOAA-18 Infrared Window (10.8 µm) image at 0320 UTC (above) showed cold air drainage into river valleys, with the coldest infrared brightness temperatures around -40ºC/-40ºF (darker blue color enhancement). Chicken is located about midway between Eagle (PAEG) and Northway (PAOR), where 03 UTC surface air temperatures were -17ºF and -24ºF, respectively. However, PAEG reached their minimum temperature around 11 UTC after additional hours of cloud-free radiational cooling.

An automated RAWS site at Chicken reached a minimum temperature of -34ºF at 1120 UTC — the dew point at that time was -42ºF. However, a MesoWest map (below) shows that the RAWS tower is located on a small hill (at an elevation of 2060 feet) — and the Cooperative Observer instrument shelter was likely located in the lower elevations of the settlement.

MesoWest map showing the location of the Chicken RAWS site [click to enlarge]

MesoWest map showing the location of the Chicken RAWS site [click to enlarge]

For comparison, note the 2011-2012 and 2010-2011 winter seasons.