Friday, July 31, 2015

Hotter Than Salt Lake in the PacNW

The Pacific Northwest west of the Cascade Crest is often a wonderful place to be in the summer with dry cool weather for much of July and August.

They are, however, sweltering at the moment and you are probably better of in Salt Lake than say Portland. Here's a quick comparo.  High temperatures in Portland the last two days of 97ºF and 103ºF, respectively, compared to 86ºF and 93ºF in Salt Lake.  Overnight minimum temperatures in Portland the last two nights of 63ºF and 65ºF (the latter the lowest hourly) compared to  58ºF and 62ºF in Salt Lake.  Plus dewpoints in Portland are running in the low-to-mid 50s, compared to the 20s and 30s in Salt Lake.

Source: MesoWest
With highs expected to be 100–105ºF this afternoon, the NWS has issued an excessive heat warning for the Willamette Valley.  More on this heat wave at the Cliff Mass Blog.

Source: NWS
A friend who escaped Utah for the PacNW and some cool weather should have stayed home!

Wednesday, July 29, 2015

It's Extremely Dry for Late July

If you've been suffering with a dry throat and drinking a lot of water since yesterday, there's a good reason.  It's extremely dry for late July.

We typically think of July as a dry month because we receive little precipitation (on average), but in terms of the total water vapor content of the atmosphere, late July is about as wet as it gets climatologically.

The precipitable water is the total depth of water that you would have if you were to condense all of the water vapor out of the atmosphere.  Below is the climatology for Salt Lake City, with red indicating the record high value for each day of the year, blue the record low, and black the average.  Note the peaks in late July or early August.

Source: SPC
Average values for this time of year are around 0.8 inches.  Record low values are around 0.25 inches.  In yesterday afternoon's sounding, we were sitting at only 0.24 inches, which is a record for the date and the 2nd lowest value on record during the last week of July.  The profile below shows why values are so low.  The dewpoint trace (green line) shows a surface dewpoint of only 28ºF (average for late afternoon this time of year is 47ºF), with even lower values aloft.  There's simply not much moisture out there.  

Source: SPC
As a result, if you are looking for a cloud, good luck with that.  We're talking "severe clear" conditions.

I don't look at time-height sections much in the summer, but check the one below from the NAM forecast through Saturday afternoon (time increases to the left).  That darkish yellow color indicates areas with a relative humidity below 10%.  Near the surface we're a little higher than this, and some higher humidity air creeps over us at upper levels beginning on Friday, but for the most part we're bone dry.

The bottom line is to keep sunblocking and drinking water despite the climatologically cool temperatures. 

Tuesday, July 28, 2015

Yesterday's Air Quality Was Briefly Bad, But Pioneer Day Was Worse

If you were out and about yesterday morning just after the frontal passage, you may have gotten a mouth or eye full of dust.  Visibility was low, the sky grey, and the mountains partially or even fully obscured at times.

Looking east at the dust obscured Wasatch Range from the University of Utah at 10:25 AM 27 July 2015
Observations from our mountain meteorology observatory on the east side of campus near the mouth of Red Butte Canyon show the pronounced spike in PM2.5 that occurred during the dusty period, with a maximum of around 45 ug/m3.

Now here's what's interesting.  If you thought yesterday was bad, Pioneer Day was worse if you were in an area that was affected by the fireworks.  The PM2.5 trace below is from the DAQ sensor at Hawthorne Elementary, just south of Liberty Park.  You can see the bump in PM2.5 concentration yesterday morning to a maximum of around 18 ug/m3 (the DAQ observations are hourly averages, which results in a lower peak than seen in the higher frequency data from out mountain meteorology lab), but if you go back to the evening of the 24th (Pioneer Day), the peak is much higher, reaching 47 ug/m3.  That peak was likely produced by the Liberty Park fireworks.  
Source: DAQ

Monday, July 27, 2015

Cool Goodness On the Way!

For much of July, temperatures have been tolerable, but the high yesterday was 98ºF and the overnight minimum through 6 am only 77ºF.  However, when the wind at the airport shifts to northwesterly from 7 to 8 am, as was the case this morning, you know some cool goodness must be on the way.

Bonafide midlatitude troughs can be rare sightings in Utah in July, but one is moving in as we speak.  The NW wind shift at the airport this morning marks the leading edge of cooler air at the surface accompanying and upper-level trough that was centered over Nevada at 6 AM MDT (1200 UTC) this morning.

With yesterday's blistering heat, our 700-mb temperature was around 16ºC, but the air accompanying the upper-level trough this morning is several degrees cooler.

By this afternoon, our 700-mb temperature will be about 6ºC, about 10ºC (18ºF) lower than yesterday afternoon.

Right now, believe it or not, it's 66ºF with a 45 knot wind along I-80 on the Salt Flats.  That cold air is on the way.  Temperatures this afternoon will be in the 70s.  Strangely enough, the max for the calendar day (midnight to midnight) will end up being 85ºF because that's what it was shortly after midnight.

Sunday, July 26, 2015

Evidence of Bad Snow Years

Snow is a pretty good integrator of past weather and climate, especially in those areas where it tends to linger late into the season.

We've had some bad snow years of late and it really shows when one looks at the views of the Wasatch from Snowbird. The photo below was taken this morning.  Nothing in the bowl below Pipeline and a few lingering patches elsewhere, including in upper Hogum (click to enlarge).

For a comparison, the photo below was taken on August 4th, 2013.  Still a patch in the bowl below the Pipeline, with patches in similar spots to the one above.  Nearly a dead heat, although the photo below was taken a week later.

In case you are wondering, 2012-13 was a 382.5" season (Nov-Apr) at Alta-Guard compared with 267.5" this year.  However, May-July of 2012-13 was about 2.5ºF warmer than this year, which had a cold, snowy May and a cool mid July, so the two years end up being almost even steven with perhaps 2014-15 running just a tad behind 2012-13 for lingering snow.

I suspect that linking turns is currently impossible in the central Wasatch.  Those of you who feel the need to ski, there's always the Timp "Glacier" (photo from Wednesday).

Will any of this snow survive until we begin to accumulate snow in the fall?

Thursday, July 23, 2015

Perspectives on Our Fantastic July

Wonderful July weather continues in Salt Lake City.  Most of the month has simply been fantastic with tolerable temperatures and the occasional showers and thunderstorms to help moisten things up.  The National Weather Service graphic below shows the observed highs and lows (bars) for the month at the Salt Lake City International Airport compared to the 1981–2010 average for each day.  We suffered through some well above average temperatures through the 4th, but since then, we've only had one day with a maximum temperature above average and we've even had a few minima that have been below average.  Simply splendid.

Source: NWS
Let's have a closer look at how this July (so far - keep this in mind for the discussion below) compares to past Julys at the Salt Lake City International Airport since 1928.  In terms of average temperature, this July would actually rank above the long-term average for the entire period, but it is the coolest July since 1999.

Source: NOAA Regional Climate Centers
However, if you look at the graph above, the average temperature this July isn't a heck of a lot lower than it was in 2009, 2010, or 2011.  Why does this year seem so cool.  The answer is provided the graph of the average maximum temperature which shows this July is really quite an anomaly compared to the recent past with an average maximum temperature of 89.2ºF, the lowest since 1993.  In addition, since 1993, there has only been one other July with an average maximum temperature below 90ºF, 1997.  And, considering that the four hottest days of the month were the 1st to the 4th, the past two weeks have been unusually cool in terms of the maximum temperatures compared to what we've seen for about 20 years.

Source: NOAA Regional Climate Centers
Curiously if you look at the minimum temperature, one finds that this year has been fairly warm compared to past Julys at the Salt Lake City International Airport.
Source: NOAA Regional Climate Centers
This is somewhat consistent with the high humidities and frequent cloud cover we've seen this month, which typically reduces the daily temperature range.  However, there is a clear upward trend in minimum temperature that is much stronger than evident in maximum temperatures for the month.  Whether or not this reflects changes in instrumentation, movement of the observing site, changes in the characteristics of the land surface around the observing site, a stronger urban climate influence, or climate change is something that warrants further investigation.

We have 9 more days to go, so the numbers for this July could change.  We'll have to see where we end up when we get to August, but I'm quite thankful for the weather we've experienced the past couple of weeks.

Tuesday, July 21, 2015

Tour de France GFS Forecast

The Tour de France hits the Alps beginning tomorrow for what should be four exciting days of racing.

For your TDF weather entertainment purposes, below is a GFS forecasts for the days ahead.  The loop begins 1200 UTC today and goes through 1200 UTC Saturday (add two hours for central european summer time).  The GFS produces persistent shower activity over the Alps for much of the duration.  I suspect this is overdone, and that this translates to a chance of showers and thunderstorms during the afternoons.  Two passing weather systems bring an elevated risk of showers and thunderstorms late tomorrow (probably after the conclusion of the stage) and then on Saturday, with a bit of a break in between.  Precipitation units in the color scale at right are mm.

With luck the weather will hold, but there is the potential for a bit of rain to affect the race.  Valley highs will be near 30ºC during the period.  That's warm climatologically, but a bit cooler than what they've been dealing with the past few days.

Monday, July 20, 2015

More Record Global Temperatures with El Niño on Tap for Winter

The National Centers for Environmental Information released their global analysis for June today.  The global surface temperature for the month was easily the warmest on record, beating last year's record by a 0.12ºC (0.22ºF).

Source: NCEI
For the calendar year to date, we're also well into record territory with the January–June 2015 temperature .09ºC (.16ºF) higher than the previous record holder, 2010.  

Source: NCEI
In addition to the long-term global warming trend, this year is jacked up by El Niño, and many seasonal climate models are calling for a strong event this winter.  The Climate Prediction Center is now calling for a 90% chance that El Niño will continue through the winter and an 80% chance it will persist through early spring.

As we have discussed many times previously (e.g., Outlook for the 2013–2014 Ski Season), there is not a strong correlation between El Niño and snowfall in the central Wasatch, as can be shown below for snowfall records at Alta.  A pessimist might say the odds are weighted slightly toward lower snowfall, but I wouldn't bet the ranch on that given the scatter.

This is generally consistent with the maps below showing the average precipitation rank by climate zone during El Niño events for November to December (top) and January to March (bottom).  Evident is a pronounced precipitation dipole favoring wetter than average conditions in the southwest and drier than average conditions in the interior northwest.

Source: CPC
Source: CPC
You'll see maps like these in the coming months.  There may be some variations depending on the definition of El Niño used and the length of the period of record, but the basic idea of a precipitation dipole with northern Utah sitting in the transition zone is a robust feature.  

Nobody has to be more excited about this than California, which sorely needs the rain.  Although they can be skunked during El Niño years, the odds of a wet winter are clearly stacked.   

Source: CPC
Ditto for Arizona and especially New Mexico. 

This relationship between El Niño and precipitation forms a strong basis for the the Climate Prediction Center precipitation outlooks below.  Dry northwest interior with a wet southwest.  

Source: CPC
Let's hope the southwest finally gets some this winter, but that it also comes in manageable amounts.  Let's also hope that the storm track sets up in a way that the Wasatch benefit too.  

Sunday, July 19, 2015

SoCal Gets Some in July

Rain in portions of SoCal is few and far between typically in July, especially along the coast.  The average July rainfall is .02" at San Diego-Lindbergh Field (KSAN), .02" at the Santa Monica Pier, .02" at Los Angeles International (KLAX), and, you guessed it, .02" at Santa Barbara.

Yesterday, however, much of coastal SoCal got some as showers and thunderstorms developed in association with a surge of monsoon moisture ahead of former Hurricane Dolores.

KSAN got pounded with 1.03" of rain, which sets new records for the most rain on a calendar day in July and the most rain observed for the month since 1850 at that site.  I haven't seen an official report yet, but the .36" observed in downtown LA and .32" observed at LAX are apparently new monthly records.

Dolores is currently classified as a post-tropical cyclone, with maximum sustained winds in the last advisory from the National Hurricane Center (0300 UTC 19 July) of 25 knots.  Nevertheless, even early this afternoon, she still has a nice, well-organized circulation as she moves northward, with a healthy rainband moving northward along the central California Coast.  In addition, more thunderstorms are likely to trigger over SoCal today.

All of this is further evidence that it never rains in Southern California, it pours.

Note: Apologies for color aliasing problems in the loops above.

Friday, July 17, 2015

What Will Dolores Do?

Dolores is currently a weakening hurricane off the southern tip of Baja, but she is giving meteorologists in the southwest U.S. headaches.

The basic problem is this.  Although Dolores is weakening, she is moving northwestward into an area of weak flow that could take her out to sea or have her circulation remnants move close to the SoCal coast with her moisture remnants moving into SoCal.  The latest (0600 UTC) GFS brings her moisture remnants across SoCal late Sunday and Monday and eventually into northern Utah on Tuesday.  Preceding Dolores is a surge of moisture into the southwest that would bring an increasing potential for showers and thunderstorms to SoCal as early as tomorrow (gasp!).

Here are a two closeups of the GFS precipitable water and 6-h accumulated precipitation forecast for for 1800 UTC (1200 MDT) tomorrow (Saturday) and 1200 UTC (0600 MDT) Monday.  The former shows the early stages of the moisture surge preceding Dolores into SoCal and Arizona, the latter the moisture remnants of Dolores moving into SoCal.

All that is fine and dandy, but a look at the 0000 UTC initialized Global Ensemble Forecast System forecasts valid for 0000 UTC Tuesday (1800 MDT Monday) show that most keep the remnants of Dolores to the west, with only one bringing a strong moisture remnant to SoCal.

Source: Penn State E-Wall
Will this be just a monsoon surge of moisture into SoCal with some showers, thunderstorms, and localized gully washers or a more significant precipitation event for some locales?  I'll be keeping an eye on this the next couple of days.

Thursday, July 16, 2015

June Was Record Setting Hot

Although we've known for some time that we saw the warmest June on record at the Salt Lake City International Airport, recently released numbers from the National Centers for Environmental Information show it was also warmest for the statewide average temperature, just topping 1918.  

Source: NCEI
For January to June, the statewide average temperature was the 2nd highest on record, just behind 1934, which serves as the ultimate "black swan" year in our instrumented record.  

Source: NCEI
Fortunately, Mother Nature has dialed it back a bit so far this July and we're running only 3.8ºF above the 1981-2010 monthly average for the minimum temperature and 2.4ºF below average on the maximum temperature so far.  The latter has made late afternoon and evening workouts far more bearable than they typically are in July.

Tuesday, July 14, 2015

Shockingly Average Weather Threatens Utah!

After a winter of warmth, a May of rain, and a scorching June, shockingly average weather now threatens all of Utah.  "We're totally used to extremes," said one local, who was considering a move to Antarctica because, "it's just too boring here."  One meteorologist exclaimed, "we thought that climate was what to expect, but weather was what you get.  This pattern just sucks!"

The July upper-level flow climatology features an upper level ridge centered over Texas (105 W, 32.5 N), a trough just off the west coast, and Utah in southwesterly large scale flow.

Long term mean 500-mb height.  Source: ESRL.
And here's how things looked yesterday afternoon.  Ridge over Texas, trough along the west coast, and Utah in southwesterly large-scale flow.  Not quite a perfect match, but close enough for Rock 'n' Roll.

And the net result?  High and low temperatures yesterday at the Salt Lake City airport of 91 and 70 (close to the averages of 93 and 65), some afternoon clouds, and a thunderstorm here or there.  Ho hum.  And the NWS forecast through the end of the work week?  Fairly seasonal.

Source: NWS
Really, this weather is just splendid.  These are tolerable temperatures for July.

Sunday, July 12, 2015

It's All Good

What a remarkable weekend in the Wasatch.  The weather was simply splendid and the grasses and flowers are simply spectacular.  It's all good this year.  I mountain biked in the Glenwild area on Saturday and can't remember ever seeing it so lush.  I was pretty beat up today, so I did a short ridge hike following old 4x4 tracks and game trails in the mountains east of Bountiful.

Many people don't realize that you can actually drive a passenger car all the way to the ridgeline above Bountiful.  There is a dirt road, known as the Skyline Drive, that will take you right to the top of the ridge and along (but not to the top) of Bountiful Peak.  The road is pretty rough this year, perhaps due to the heavy spring storms and the recent downpours, but is passable.

It's been many years since I was up there, so I enjoyed seeing some new terrain.  Salt Lakers have a habit of spending too much time in the central Wasatch.  It's almost always worth a trip elsewhere.  Here are a few photos.

Looking south towards the Session Mountains and, in the distance, the central Wasatch. 
Looking north toward Bountiful Peak.  Note the Skyline Drive. 
Views of the Great Salt Lake, or at least what is left of it, are spectacular from this area.
Off the ridge, a carpet of wildflowers even at this modest (8500 ft) elevation.  Sessions Mountain road below.

Friday, July 10, 2015

What Is the Monsoon?

We've reached the time of year where the word monsoon is used to describe just about everything related to the weather.  Monsoon moisture.  Monsoon rains.  Monsoon storms.  Just what is the monsoon?

Monsoon derives from the Arabic word mausim, which means season or wind shift.  Monsoon has traditionally been used to describe the alternating wet and dry seasons that occur during the summer and winter, respectively, in India and southeast Asia.  For example, the monthly rainfall in Bombay shows the dramatic contrast between the wet (roughly June to September) monsoon and dry monsoon on the west coast of India.
Source: Douglas et al. (1993)
The signal of the North American monsoon is less pronounced, but strongest in Mexico, as illustrated by the monthly rainfall data from Badiraguato in the mountains of western Mexico (note the rainfall scale change).

Source: Douglas et al. (1993)
The word monsoon is often used to describe not only precipitation but also the large-scale circulation, land-surface, and ocean/sea changes associated with the wet and dry seasons.  In North America, the focus is usually on the wet season of Mexico and the southwest U.S. from about June to September or October.  North American Monsoon or North American Monsoon System refer collectively to the precipitation, atmospheric circulations, land-surface conditions, and ocean/sea conditions occurring during this period.

The North American Monsoon includes a wholesale shift in the large-scale circulation over North America.  For most of the winter and spring (e.g., May, pictured below), the mean large-scale flow over most of North America is westerly.  As we move into the summer, however, intense solar heating builds an upper-level anticyclone (high-pressure) that on average is centered over Texas, resulting in mid-level easterly flow over Mexico (e.g., July, pictured below).  This seasonal easterly flow is a canonical feature of the North American monsoon.
Douglas et al. (1993)
Source: Douglas et al. (1993)
Precipitation during the North American Monsoon is produced by convection (e.g., showers and thunderstorms), more organized mesoscale convective systems (sometimes called MCSs), and tropical cyclones and their remnants.  Moisture sources include the Gulf of Mexico, the Gulf of California, and the tropical and subtropical eastern Pacific.  The contribution of these regions has not been fully quantified and varies geographically, from year to year, and from storm to storm.

The amount of precipitation produced during the monsoon and its contribution to the total annual precipitation is greatest in Mexico and decreases as one moves northward into the southwest U.S.  Stations in western Mexico and portions of New Mexico and Arizona show a very pronounced precipitation maximum in July or August and receive much of their annual precipitation in these and the adjoining months.  As one moves northward, however, the amount of precipitation produced during the monsoon lessens and in many areas the greatest precipitation falls in winter (high elevations) or spring (lower elevations of much of the Great Basin).
Monthly rainfall at selected sites. Source: Adams and Comrie (1997)
Thus, it can often be difficult to ascertain whether or not the precipitation produced in Salt Lake originated from the monsoon region (i.e., the Gulf of Mexico, Gulf of California, and tropical and subtropical Pacific).  In addition, many of our storms this time of year and in the early fall (especially September) occur as traditional midlatitude systems (e.g., fronts, upper-level troughs) interact with moisture originating from the monsoon region.  Most of the time, any elevated moisture and precipitation occurring in July and August in our area is called "monsoonal" although there are times when this moisture and precipitation may have stronger ties to the midlatitudes.

Every year, the North American Monsoon takes on a different flavor.  It's onset, end, geographic extent, and intensity vary from year to year due to a variety of factors, including the fickle nature of atmospheric convection.  Even in an active monsoon year, one can sometimes find a few locations with below average precipitation simply because they missed out on the thunderstorm activity (and vice versa, there can be locations that get a lot of precipitation during a relatively poor monsoon year).

Thursday, July 9, 2015

The Amazing Strobe-Light Storm

Although I was in desperate need of a long night's sleep, last nights spectacular lightning display kept me mesmerized and jacked up through about midnight.

The system swept through the Salt Lake Valley from about 9 PM to 1 AM MDT.  It featured a number of strong convective cells, followed by a more continguous region of precipitation in their wake.

The system was highly electrified.  Although frequent lightning of this type is common east of the Rockies and sometimes in the southwest U.S., I don't know if I've ever seen such a long period of frequent lightning before in northern Utah.  Hence, I'll call this the Strobe-Light Storm since the combination of thunder, heavy rain, and lightning gave it a discotheque feel.

Some of the most intense precipitation fell at about 11 PM MDT near downtown Salt Lake City and especially near the junctures of I-215, I-80, and I-15.  At this time, a broad swath of heavy precipitation with radar reflectivities exceeding 50 dBZ, with maxima above 60 dBZ, pummeled the area.

Storm-total radar-estimated precipitation in this area peaked at a whopping 2.5 inches (brownish pixels below) with a large area exceeding 1.5 inches.  The average July rainfall at the Salt Lake City Airport is only .61 inches.

The maximum radar-estimated 1-h accumulation in that area was near 2 inches.  Such an hourly rainfall rate has a return interval of about 200 years at that area of the Salt Lake Valley according to data on the the NOAA Precipitation Frequency Data Server.  Although there are a variety of problems with the use and interpretation of those intervals, especially in a changing climate, such numbers illustrate that it was "raining like hell" in that area last night by Salt Lake City standards.

Showers and thunderstorms are possible again today.  What a great start to July.