Thursday, May 30, 2013

Help Transform Mountain Weather and Climate Prediction

Photos courtesy Trevor Alcott and Jim Steenburgh
If you are a regular reader of this blog or just an occasional visitor, I hope you have enjoyed our discussions of mountain weather and climate.  Perhaps you also peruse and take advantage of some of our weather forecasting products at or  

If you like the Wasatch Weather Weenies blog and are interesting in helping us transform weather and climate prediction in mountainous regions, especially in the Wasatch Mountains and northern Utah, click here and consider making a donation to our Mountain Meteorology Fund. Created by an anonymous donor in 2005, the Mountain Meteorology Fund supports education and research in mountain weather and climate at the University of Utah.  

Now is a great time to give as I will personally match the first $500 in contributions.  So, consider a donation (typically tax deductable) and help us address challenges ranging from powder prediction in the Wasatch Mountains to helping Utah prepare for a warming world.  

Wednesday, May 29, 2013

Physics on a Manure Heap

Chapter 18 of Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics by Craig Bohren
One of the more important individuals in my academic development was Craig Bohren, a meteorology professor at Penn State University who was my undergraduate advisor and physical meteorology instructor.  Craig was a lunatic.  When they banned smoking on campus, Craig came into class smoking a cigarette and blowing smoke rings to teach us about vorticity.  When students asked him if they could bring a one page cheat sheet to the exam he responded, "you can bring whatever the hell you want, it won't help you one bit because I don't give those kind of tests."  His tests were indeed nasty.  If you got something like a 45 out of 100 on an exam, you were probably on track for an A.

Craig was a lunatic, but he was brilliant and inspirational (it took a few years past graduation to realize this).  He always carried a camera.  Whatever he saw on his long walks became the topic for his next class (this was in the pre-digital days, so he probably spent a fortune at one-hour photos).  Steam on a pile of manure?  That was a class in atmospheric physics covering mixing clouds, forward scattering, and backward scattering that eventually became a chapter in his book Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics.

I thought of Craig's Physics on a Manure Heap lecture yesterday afternoon as I walked home from the U and observed a mixing cloud over the asphalt.  It wasn't a manure heap, but it will suffice.

The processes responsible for forming this cloud are similar to that responsible for forming clouds around geysers or near the spout of a tea pot.  Many people call those clouds steam, but that is technically incorrect.  Steam is water vapor that is at a temperature that is equal to or greater than the boiling point.  Water vapor is invisible.  What you see instead is the mist of water droplets that form as the steam mixes with cooler environmental air.

In the photo above, the asphalt is likely warmer (probably much warmer) than the overlying airmass, which has been cooled rapidly by precipitation.  Relatively warm, water vapor enriched air near the asphalt is mixing with cooler environmental air, leading to the formation of a mixing cloud.  The concept is the same as that observed over a hot spring.

Perhaps on a future trip to Yellowstone I can find a steamy buffalo "deposit" next to a hot spring.  Add in someone's breath condensing and a contrail in the sky and you have the ultimate mixing cloud physics lecture.

Tuesday, May 28, 2013

Ireland or Utah?

You decide.  

Let It Rain

As can be seen in the loop below, your classic spring day is on tap today with showers and thunderstorms.  Put on some Clapton and enjoy, because July will be here soon.  

Sunday, May 26, 2013

Saturday, May 25, 2013

Contrasting Starts to Memorial Day Weekend

Looking for pow this Memorial Day?  The base is pathetic, but you can find freshies today in the Adirondacks of New York and the mountains of northern New England.

Whiteface Memorial Highway 25 May 2013
Source: Whiteface Facebook Page Morgan Langey
Meanwhile in Utah, the Wasatch snowpack is taking a beating with temperatures near 60 at 8000 feet.  I walked up to our observing site near Alta at about noon and was dismayed to find that a river runs through it!

If only I knew this site turned into a stream bed during the runoff!  Special thanks to whoever hung our interval board and snow depth sensor on the ladder.  Of course, it could have provided reliable stream depth measurements instead (they can do that).  This is a prime example of how it can be difficult to get representative information about the snowpack based on an observation collected at a single point!    

Friday, May 24, 2013

Nature Unleashed!

If you haven't been to the Natural History Museum of Utah, you should go soon as it is one of the most spectacular Natural History museums in the U.S. if not the world.  In addition, if you are a Wasatch Weather Weenie, there is a really good reason to visit between now and December 8 as they are hosting the traveling display Nature Unleashed: Inside Natural Disasters, which opens for members today and the public on Saturday.

I had the good fortune of attending the unveiling party last night.  There are displays on earthquakes, volcanoes, hurricanes, and tornadoes.

The hurricane exhibit asks the question, why does a hurricane form? This
is a great question because it actually remains inadequately answered by
scientists today.
Wasatch Weather Weenie, U atmospheric sciences
graduate student, and certified "storm chaser" Peter
Veals served as a subject matter expert last night.
 In July, they are adding an exhibit on wildland fires, which should be quite timely as we enter the peak of wildfire season.

Thursday, May 23, 2013

Benefits of a Relatively Dust Free Spring

Over the past few years, we have seen a number of wind-blown dust events, especially in the spring, which have turned our precious Greatest Snow on Earth into the Greatest Snirt on Earth (Snirt=part snow part dirt).  These dust events are typically "recorded" in the snowpack as dirty layers, which collect on the snow surface during the spring melt.  The intensity and frequency of dust events vary from year to year depending on meteorology and land surface conditions.  Below are examples of relatively clean and dirty spring snowpacks in the Wasatch Mountains.

This year has been relatively dust free.  I haven't been up in the Cottonwoods for a while, but reports suggest that the snowpack is relatively clean and that was the case in April when I last made turns.  Yesterday, however, we saw some wind-blown dust over the Salt Lake Valley, with some obscuration of the visibility both in the pre- and post-frontal environment.  

The lack of dust events is good for skiers.  It makes for better spring skiing, but also a longer ski season since it results in a longer duration of snow cover in the mountains.  Dirty snow is darker and absorbs more sun than clean snow, resulting in a faster snowmelt.

Courtesy: Tom Painter, NASA/JPL
It's also good for skiing, and modeling studies suggest that it might be good for runoff too, which should make water managers and users happy given that this otherwise was a below average year.

Wednesday, May 22, 2013

Mountains and Tornadoes

Climatologically, the highest frequency of significant (F2 or greater) tornadoes in the world occurs the southern Great Plains during the spring.  That's why the region is appropriately referred to as Tornado Alley and why Norman, Oklahoma has become the nexus for severe weather research, forecasting, and education in the United States (with a tip of the hat to many talented people who helped to make it so).  

Source: Storm Prediction Center
We don't usually think of Tornadoes as a mountain meteorology problem, but it turns out that the severe storm environment of the Great Plains is partly a consequence of topography and land-sea contrasts.  During the spring, the confluence of dry, downsloped air from the deserts and high terrain of the southwest US and northern Mexico (airstream SP below) with cooler, moister air originating over the Gulf of Mexico (airstream M) frequently leads to the development of the dryline.  The dry, downsloped air often continues to move eastward over the moist Gulf air, leading to the development of what meteorologists call an elevated mixed layer.  The confluence of these airstreams and the formation of the dryline is related to the development of lee troughing downstream of the Rockies.  In addition, the location and movement of the dryline can be influenced by the gradual slope of the Great Plains.  

Source: Carlson et al. (1983)
This elevated mixed layer is sometimes quite warm and dry and forms a cap or lid that can prevent the formation of thunderstorms.  However, in areas where the cap is weaker, or where a surface boundary or other feature can lead to strong, organized vertical motion, violent thunderstorms can form. 

Many of these characteristics can be seen in the regional analysis of 1000-mb dewpoint (contours below), wind, and radar/satellite imagery for ~2100 UTC 20 May, minutes after the tornado moved through Moore Oklahoma.  Note the confluence of dry air from the southwest with moist air from the Gulf of Mexico, which generated a pronounced dryline running from central Oklahoma to northern Mexico.  

In addition, the sounding from Norman, Oklahoma at 1700 UTC shows how dry, warm air from the southwest has moved over the cooler moister Gulf air, resulting in a temperature inversion just above 850 mb and an elevated mixed layer further aloft.  Imagine if you will in the analysis above that the dry air over and near the Texas Panhandle is moving over the Gulf air to the east to form the elevated mixed layer.  

The strength of the low-level jet and its impact on vertical wind shear and northward moisture transport is also influenced by the Rocky Mountains and the slope of the High Plains.  

So, the fingers of mountain meteorology are quite long, with influences that extend even into "flatland" regions.  

Tuesday, May 21, 2013

The Moore Tornado

Radar reflectivity loop of the Moore Tornado of 20 May, 2013.  Moore
area indicated by red box.  
When I heard yesterday afternoon that a tornado struck Moore, OK, I got a pit in my stomach.  Moore was devastated by powerful tornado that rated as high as F5, the highest rating for tornado intensity on the Fujita Scale, in May of 1999.  Sadly, tragedy had struck again.

Jeff Masters provides a far better summary of this event than I could on his WunderBlog site.  Click here to see his discussion of the historical context of the tornado and the storm structure.  I thought I would take a few moments to put this storm into context for those of us who live along the Wasatch Front.

Many of you will recall the tornado that hit Salt Lake City on August 11, 1999.  It was a day I will never forget as I watched the tornado move directly through the Avenues, very near my home.  It was the first tornado that I had ever seen, and, being a meteorologist, I was so excited to see a tornado that I failed to recognize the seriousness of the event as it was unfolding.

I had never seen tornado damage before and it was sobering.  It was as if someone cut through the Avenues with a surgical knife.  At the center of the path a home would be largely destroyed, while it's neighbors suffered modest damage.  The adjoining homes were nearly entirely undamaged, although they may have been covered with some debris (I discovered debris on the flat porch roof adjoining my home several months later).

The image below shows the results of the damage survey produced by the National Weather Service.  Areas in red suffered considerable damage consistent with an F2 tornado with winds of 113-157 miles per hour.

Until recently, tornadoes were rated on a scale of 0-5 based on a system developed by Ted Fujita.  Today we use the Enhanced Fujita Scale, which represents an update based on knowledge gained from storm surveys and damage over the past couple of decades.  The primary difference between the two scales is the magnitude of the wind speed assigned for each level based on damage.  As such, I'll stick with the old Fujuta scale for this discussion.

Tornado statistics such as those presented by McCarthey and Schafer (2004) show that the vast majority of tornadoes rate as F0 or F1.  F2's like the one that hit Salt Lake represent about 19% of all tornadoes (there are some variations in this estimate depending on the period examined).  F3-F5 tornadoes are considered strong to violent and represent a small subset of all tornadoes.  F4 and F5 tornadoes are especially rare.  In fact, you can find a listing of all 58 documented F5 events since 1950 on this web site.  On the other hand, F4 and F5 tornadoes produce the vast majority of tornado fatalities.

Source: McCarthey and Schafer (2004)
All tornadoes are terrible for those who sit in the path, but the damage contrast between an F2 tornado like the one that hit Salt Lake and an F4 or F5 tornado is staggering.  The F2 produces significant damage such as roofs torn off homes, uprooted trees, etc.  F4 or F5 tornadoes produce devastating or incredible damage.  Well constructed homes are completely leveled, and the damage path can be very wide – sometimes more than a mile.

On the other hand, the storms that produce F4 and F5 tornadoes tend to be long lived and are more easily identified with current radar systems.  Tornado warnings for F4 and F5 tornadoes can often be issued with lead times of many minutes (sometimes tens of minutes).  The tornado warning for Moore appears to have been issued at 3:01 PM CDT (2001 UTC) yesterday afternoon. (Correction: As noted in the comment by Andrew below and documented on the web page he cites, the original Tornado Warning was issued at 2:40 – the warning below is for a Tornado Emergency, indicating that widespread damage is continuing.  When I saw the warning and emergency below, the lead time was so impressive I wrongly assumed it was the original.  Kudos to the NWS).

Source: NWS/College of DuPage
Radar shows the hook echo of the tornadic system approaching the Moore area at roughly 3:16 PM (2016 UTC).

Radar image for 2016 UTC 20 May 2013
It is likely that hundreds of lives (maybe thousands) were saved by this warning, yet we still mourn the tragic loss of at least 24 people (maybe more) today.  Our thoughts and prayers are with the residents of Moore today, as well as others being impacted by this tornado outbreak.  

Monday, May 20, 2013

The Universe of Cumulus

For lovers of clouds, you don't get many days better than today.  Some probably like big cumulonimbus clouds, but I prefer a mixture and today we have just about everything from the cumulus humilis (a.k.a. cumulus patheticus) over extreme northwest Utah and northeast Nevada to cumulus congesus over northeast Utah.  There's also evidence of cloud bands downstream of the Great Salt Lake.

Watching this look you can learn a lot about the wind structure today.  Track the clouds to ascertain the wind direction.  You can find easterlies near the Uinta Mountains and North–Northeasterlies over and south of the Great Salt Lake.  You can also infer a lot about the temperature of the lakes of northern Utah.  The Great Salt Lake appears to be contributing to the initiation of cloud bands, whereas there is a clear cloud hole over and downstream of Bear Lake for much of this loop.  Presumably the Great Salt Lake is warm enough to destabilize the atmosphere, whereas Bear Lake is colder and thus the atmosphere is more stable over and downwind of it.

Meteorologists have developed computer programs that track cloud elements to infer the wind.  Using the cloud toop temperature derived from infrared satellite imagery, one can also estimate the height of the wind.  Here's an example of cloud track winds over the eastern Pacific today, with the color coding providing an estimate of the layer of the inferred wind.

Source: Naval Research Lab
These winds can be assimilated into computer models to improve their initial conditions.  Some day we may have space borne laser-based systems to further aid wind measurement, but until then, we'll squeeze all we can out of the available observations.  

Calling Noah

Der Bau der Arche Noah by Franzosischer Meister
Source: Wikipedia
The rains continue this morning and I'm wondering if it is time to start building an ark.  Here are a few of the bigger 48-hour precipitation totals over the northern Wasatch Front for the period ending at 7 PM last night as reported to the National Weather Service.  This is before the overnight deluge.

Logan Airport: 1.18 inches
Brigham City (4400 ft): 1.88 inches
Ogden Airport: 1.26 inches
Bountiful (4760 ft): 1.51 inches

For the 72-hour period ending this morning at 7 am, the Salt Lake Airport has received 0.52 inches.  That's not all that impressive, but it appears to be one of the drier areas in the Salt Lake Valley (as it often is).  A few sites along the upper east bench were near a full inch before the rains last night.  

For you gardeners out there, the next few days will offer up the best weeding and tilling conditions of the year.  

Saturday, May 18, 2013

Spring Deluge

Nearly everyone along the Wasatch Front from Draper north is getting a good soaking this morning and for that we can all be thankful.  A dump like this will really increase the soil moisture and help with the gardens and the lawns.

Plus, it is snowing again in the mountains.

Source: Snowbird
Many of the observing sites at the resorts have been shut down for the summer, but our site near the base of Alta shows a temperature of 32.5ºF with about 0.32 inches of snow-water equivalent since midnight and 0.56 inches in the past 24-hours.  It's probably cream on crust at upper elevations, but one shouldn't complain in May.

Friday, May 17, 2013

The Record Snows of Mount Shasta, Redux

Regular readers will recall the overhyped and inaccurate predictions of record snowfall (218 inches in four days) on Mount Shasta last winter which we discussed in two posts (Is a US Snowfall Record in Jeopardy and Mt. Shasta Update).  The storm that still holds the record for single-storm accumulation occurred on Mt. Shasta from 13–19 February 1959 (more below).  An article examining this storm (Hansen et al. 2013) is included in the inaugural edition of the Journal of Operational Meteorology, a publication of the National Weather Association.

Unfortunately, the article is payrolled except for National Weather Association members, but if you aren't a member, you can have a looksee at the abstract above and get the gist.

There does, however, seem to be some confusion concerning the record status of the February 1959 Mount Shasta storm.  Hansen et al. (2013) suggest that the 4.8 m (189 inches) of snow that fell on Mt. Shasta was unmatched and unbroken until the early 1990s, citing an web posting by Freeman (2011) for this statement.  Freeman (2011) states that "This storm was credited with producing the most snow in a single storm in North America until the late 1990s when an eastern state beat the record (de Blij and Muller)." I suspect the de Blij and Muller reference is for their book Physical Geography: The Global Environment, which I'll need to get at the library, but suspect there might simply be confusion between point and areal accumulations. I am unaware of any single-storm accumulation at any single location in the east approaching 189 inches, but the total area accumulations in their storms can be very large.  

Weather historian Christopher Burt includes Mt. Shasta as the single-storm record, but notes that a reliable measurement of 194 inches in four days was made at the Norden railway depot in the Sierra Nevada from April 20–23, 1880.

Thursday, May 16, 2013

News Bits

I thought I'd take a moment to report three items of interest making news this past week.  

1. Quantum Leap.  First, as discussed at the Capital Weather Gang, a major infusion of computer power is in the works for the National Centers for Environmental Prediction (NCEP), which is receiving support from the Disaster Relief Appropriations Act of 2013 (a.k.a., the Sandy Supplemental) to increase their computer capacity from 213 teraflops to 2,600 teraflops by the 2015 fiscal year.  The Capital Weather Gang called it a game changer, so I'll call it a quantum leap.  No matter what it is called, it is a badly needed infusion of computer power that will hopefully be leveraged to produce a significant advance in weather prediction capabilities for the nature. 


2. Strategic Planning.  Curiously, as NCEP gets this infusion of computer power, this week also saw the release of Forecast for the Future: Assuring the Capacity of the National Weather Service, a report from the National Academy of Public Administration.  I gave it a quick skim, however, and didn't see anything too earth shattering.  Given that the NWS is still living off the vapors of the Modernization effort of the 1990s, lets go after a quantum leap not just in terms of NCEP computing but across the agency.  Such an investment would not only benefit the public, but also a growing private-sector weather enterprise.  

3. 97% again.  As reported in the Guardian, another study has come out showing that ~97% of climate scientists/climate papers/climate abstracts conclude that climate change is caused by human activity.  More specifically, the latest study by Cook et al. (2013) finds that "among abstracts expressing a position on [anthropogenic global warming], 97.1% endorsed the consensus position that humans are causing global warming."  I find it remarkable that 97% keeps coming up in these surveys.  There must be a conspiracy...

Wednesday, May 15, 2013

Avenues Rainbows

There was a great rainbow display this evening in the Avenues with very distinct primary and secondary bows.  The primary is the brighter, inside bow, but unfortunately, the pot of gold was located just a bit east of campus.  That's a pity as we're always looking for more funding.

To compensate for my poor photographic skills and the fact that it was nearly impossible to take a picture given that wind was coming from the rainbow's direction and driving rain into the lens, I've doctored the photo below just a bit to help with contrast.

There was some evidence of supernumerary bows on the inside of the primary bow.  I tried to get a good photo, but alas, it was beyond my skills.

For you weather and optics geeks, Les Cowley's Atmospheric Optics site is the cat's meow.  He has a great page on rainbows.  I just learned that the dark area between the primary and secondary rainbow is known as Alexander's dark band and is named for Alexander of Aphrodisias who first described the effect in 200 AD.  Cool.  


If you think it has been hot in Salt Lake with maximum temperatures of 93ºF and 89ºF the past two days, it could be worse.  Temperatures in parts of Kansas, Nebraska, Iowa, and Minnesota reached or eclipsed 100ºF yesterday.

The ramp up to the 106ºF in Sioux City, Iowa is most impressive.  The call letters for this station are KSUX, and I think it is safe to say that the weather there SUX at present.

It was less than two weeks ago that it was snowing in Iowa (see From snow to 100 degrees, this is Iowa | Weather - KCCI Home).

Ah, the joys of spring!

Tuesday, May 14, 2013

Records and Rain

Yesterday's high of 93ºF broke the previous record for the date of 92ºF set in 1996.  The relative humidity dipped to as low as 11%.  We need rain.

There's a slight chance of thunderstorms the next couple of days, but then a bonafide trough coming in for Friday and Saturday (timing TBD).

Keep your fingers crossed.  We could use the rain.

Saturday, May 11, 2013

The Big 400

There is considerable media coverage this week discussing how CO2 concentrations at Mauna Loa observatory have eclipsed 400 parts per million for the first time since measurements began in 1958.  This somewhat ill defined but all important milestone is discussed in a press release issued by NOAA yesterday.

Charles David Keeling of the Scripps Institute of Oceanography began collecting CO2 measurements on Mauna Loa in 1958 and the graph illustrating the subsequent increase in CO2 to the present is often referred to as the Keeling Curve.  The graph usually is based on monthly average CO2 concentrations and thus shows both the long term increase in CO2, but also the decline of CO2 in the Northern Hemisphere spring and summer due to plant growth and a rise in the fall due to plant decay.
It is a bit hard to see, but the annual rate of rise has increased from about 0.7 parts per million per year in the late 1950s to about 2.1 parts per million per year in the last decade.  About 70% of the increase over pre-industrial CO2 concentrations has occurred since Keeling began collecting data in the late 1950s and half has occurred since the late 1970s.

I call the 400 parts per million milestone somewhat ill-defined because CO2 does fluctuate.  We hit 400 this week, but the drawdown from plant growth means we will drop below it in the coming months.  It will probably take about 3 years until CO2 is above 400 parts per million for the entire year.

The observatory at Mauna Loa is at high elevation in the central Pacific and one of the better places to measure the "background" CO2 concentrations.  You can find higher CO2 concentrations in areas where emissions are high, especially when the atmosphere is poorly ventilated.  Jim Ehleringer's group at the University of Utah maintains a number of CO2 sensors in the Salt Lake Valley.  This morning, the CO2 concentration in Sugarhouse was as high as 460 parts per million.

Going back to 2007, you can see a number of periods, usually characterized by persistent wintertime inversions, where the daily average CO2 has approached or exceeded 500 parts per million.  Perhaps not surprisingly, the most events of this magnitude occurred this past winter when we were plagued by persistent inversions.  

Those are daily averages.  My recollection suggests that higher frequency observations show spikes near 700 parts per million during the most intense events.

These high values merely reflect the trapping of CO2 produced primarily by fossil fuel combustion near the ground.  This CO2 eventually mixes into the free atmosphere and contributes to the ongoing increase reflected in the Keeling Curve.  

Friday, May 10, 2013

Summer Arrives

If you like it hot, get ready because your day is coming.  A high amplitude ridge will be building in over the Intermountain West this weekend and we will see temperatures climbing a bit more each day until we reach a blistering climax on Monday when 700-mb (mountain top) temperatures are forecast to be near 13ºC.

That translates to a maximum temperature at the Salt Lake airport approaching 90ºF.  Sounds like a good reason to get the swamp cooler or A/C tuned up, although the models suggest this will only be a brief flirtation with the big 90.

With such high temperatures, we probably will see the most intense runoff so far this spring on Monday afternoon and evening along the snow-fed streams of northern Utah.  Snowpack snow-water equivalent (SWE) peaked at Snowbird in late April and has been dropping steadily the past week, indicating that the snowpack is fully ripened and that any excess energy from the sun or atmosphere will be going directly into melting snow.

Source: CBRFC
It won't last long now.  Be careful near those rivers and streams.

Thursday, May 9, 2013

Mammatus – Oh My!

Doug Wewer sent me some remarkable photos of mammatus clouds that he took at about 1 PM yesterday (May 8) on highway 191 just north of Rock Springs, WY.

Photos courtesy Doug Wewer
The name for mammatus or mammary clouds derives from the breast like lobes at the cloud base.    Schultz et al. (2006) called mammatus clouds an "enigma of atmospheric fluid dynamics and cloud physics" as they have rarely been the subject of detailed scientific investigation and remain poorly explained.  Since their article, there have been several papers on the subject, but a so called "unified theory" has yet to emerge.  Most mammatus events in the Intermountain West feature a dry, well mixed layer beneath cloud base and cooling produced by the mixing of moist and dry at cloud base and the sublimation (i.e., evaporation) of ice crystals falling out of the cloud may be important contributors in generating the convection that produces the lobes (Kanak et al. 2008; Kudo 2013).

There is a nice summary of the other proposed mechanisms on Wikipedia.  That article, however, argues that mammatus does not pose a threat to society, but I disagree.  Turbulence generated within and beneath mammatus is a concern for aviation safety, as discussed by Kudo (2013).

Wednesday, May 8, 2013

Spring Rumblings

For the second day in a row we are being treated to flashes of lightning and rumblings of thunder on the University of Utah campus.  In both instances, the thunder and lightning are being produced by storms that moved in from the east or southeast.  Here's the latest showing the thunderstorms that are moving across the Wasatch and towards campus at about 2:15 PM today.

The culprit in driving these storms westward is of course the huge split flow that is present over North America along with an embedded upper-level trough that is stretched out like a rubber band from southern California to Colorado and driving easterly flow across northern Utah at 700 mb.

Given all these thunderstorms, now is a good time to remind everyone that when thunder roars, head indoors.   As discussed in today's Salt Lake Tribune, lightning yesterday damaged an Air National Guard plane and struck a house in West Jordan.  Take a few minutes to read our post Lightning Safety and take steps to minimize your exposure to lightning.

Tuesday, May 7, 2013

Oddities from the Big Split

Yesterday we discussed the anomalous split flow pattern that is dominating the weather of North America.  The pattern is producing some weird weather, as illustrated by the maximum temperature analysis for yesterday.

In particular, note how upside down the temperatures are in the west.  Maximum temperatures in the Pacific Northwest reached 87ºF in Seattle and 91ºF at The Dalles along the Columbia River.  Compare these to the 87ºF and 85ºF in Phoenix and Tucson, respectively.  Climatologically, the average Maximum temperature is 66ºF in Seattle and 73.5ºF at The Dalles, compared with 93.7ºF in Phoenix and 90.5ºF in Tucson.

If you look up into western Canada, you can find a few sites in the high 80s and even a 92ºF at what appears to be Lytton, BC, which is located at 751 ft MSL in the Fraser River Valley.

Similarly, the things are topsy turvy in the east.  Maximum temperatures in northern New England and southern Quebec at or above 80ºF, including an 86ºF at one location that exceeds the highest maximum temperature reported (on the map above) in Florida.

Yup, this is wacky.  Climate is what you expect.  Weather is what you get.

Monday, May 6, 2013

The Big Split

"When you come to a fork in the road, take it"
- Yogi Berra

Strong split flow presently persists over North America, with a strong polar jet over Canada and a strong subtropical jet over Mexico and the Gulf of Mexico.  I've crudely identified these jets on the dynamic tropopause (jet level) wind speed analysis below.  This strikes me as an unusually strong example of split flow in May, but some digging is needed to ascertain how unusual.

This split flow extends further downstream across the North Atlantic and into Europe and Africa, making this a hemispheric-scale event.  This is a good time to be flying westward across the North Atlantic or continental US as you aren't fighting the westerly flow that is commonly found at mid latitudes.

One nice aspect of this pattern is that it doesn't favor strong Intermountain cyclogenesis and associated southwesterly flow.  This has contributed to the dearth of dust storms this spring.

Sunday, May 5, 2013

A Major Forecast Bust

There are times when I get a pit in my stomach as I come to the realization that something is happening that wasn't well forecast.  I had such a feeling when I got home last night around 10:30 and felt an east wind blowing at my house in the Avenues.  We have had a good run of forecasts pertaining to downslope winds over the past year or two, but the event last night was poorly forecast and illustrates that we have some work to do.

Here are a few time series from overnight.  They illustrate easterly downslope winds reaching 60 mph at Farmington, 55 mph at Logan, and 51 mph at the University of Utah.  

We really whiffed on these forecasts.  Here are the NWS forecasts issued 3:39 PM yesterday afternoon.  The zone forecast for the Salt Lake Valley has no mention of downslope winds:


And, for the Northern Wasatch Front, they have a mention of east winds, but the forecast ultimately underestimates the strength of the event by a large degree:


Having forecast for a field program Saturday morning, I know I probably would not have called for such a strong downslope wind event either.  

Thus, this is an event worthy of further study to ascertain the ingredients of the strong downslope winds  in this event.  At issue is whether or not such strong winds could have been better anticipated and what improvements might be needed in numerical modeling to help better anticipate such events in the future.