July Enters "Like a Lamb"

July is climatologically the hottest month of the year in Salt Lake City, but so far, the first three days of July have been relatively pleasant.  One might even say that July has entered like a lamb.

It's worth a look at July from a historical perspective.  July is not only the hottest month in Salt Lake, but it also features relatively little variability from year to year.  The range in average temperature from July to July is around 5˚F, with a few exceptions (e.g, 1993). 

Source: NOAA Regional Climate Centers

One can also clearly see that recent July's have been quite warm.  During the 20th century (1901-200), the average July temperature in Salt Lake City was 77˚F.  We have not had a July below that average since 1997 (75˚F) and since 2010 the average temperature in July has been a miserable 81.6˚F, more than 4˚F above the 20th century average.  Further, since 2010, even the coolest July, 2015 (77.4˚F) was warmer than the 20th century average.  

So, on this 4th of July, we should thank our lucky stars that the first three days of July were relatively pleasant.  On the 1st, the minimum and maximum temperatures were 53˚F and 88˚F, both below average (average here based on 1981-2010).  On the second, they were 59˚F and 90˚F, below and at average, respectively.  And then on the 3rd, we reached 68˚F and 95˚F, which are above average, but I've learned not to complain about 95 in July.

By and large, the forecast for 4th of July weekend looks great, with the only blemish being a possible isolated shower or thunderstorm, mainly in the mountains of central and eastern Utah, as noted by the National Weather Service graphic below.

Additionally, the extended forecast ain't awful, with highs in the low-to-mid 90s through next Friday.  

Based on those forecast temperatures, the average temperature for the week would be 78.5˚F.  Hot and higher than the 20th century average temperature, but a bit lower than the average for Julys since 2010. 

Thus, I'll take it and will hope that we will continue to keep it at or below 95.  

Bizarro World

It's sort of a bizarro-world situation right now with coronavirus running amok, wildfires threatening homes, and late June turning into late April.

Saturday night and Sunday, wildfires threatened homes near Lehi, Draper, and Saratoga Springs as two separate fires raged in the urban-wildland interface.  The Traverse Fire near Lehi and Draper was apparently caused by fireworks.  The cause of the Knolls Fire near Saratoga Springs remains undetermined.

The cooler weather today is a blessing, but conditions Saturday night and Sunday must have been difficult with strong winds from varying directions.

Observations from the flight park near Point of the Mountain show south-southeast winds Saturday morning through about 1300 MDT, then a shift to S-SSW, and finally a shift to north at about 1800 MDT.  Winds from about 1300-1800 MDT were sustained at 35 mph with gusts to nearly 50 and then after the frontal passage peaked with gusts over 60 mph. 

Source: MesoWest

The remarkable late-June airmass change is quite evident in the temperature trace which shows an afternoon maximum yesterday of 88˚F, a rapid drop in temperature of over 15˚F with the frontal passage, and then a continued decline to current temperatures just above 40˚F.  Thankfully, the lower temperatures, higher humidity, and lighter winds this morning should greatly assist firefighters.

We will thankfully be under the grips of this late-June trough through Tuesday.  It will be unseasonably cool today with valley highs in the 60s, which is more like late April.  The Alta Devils Castle webcam is even showing a trace of snow above about 10,000 feet. 

Tip of the hat this morning to all health-care workers, first responders, and anyone helping with relief efforts for all that you do. 

A State Divided

In our previous post, we discussed some uncertainties in the forecasts for early next week, with differences in the amplitude and timing of a late-June upper-level trough that was expected to affect Utah's weather. 

The model spread has decreased some in the past couple of days with both the GFS and the ECMWF now going for a solution that favors a frontal passage over northern Utah on Sunday (probably noon or later, but follow forecasts as this could change) with the front moving very slowly across the state through Tuesday.

On Monday, we will be a state divided meteorologically.  At 0000 UTC 30 June (1800 MDT Monday), the GFS forecast puts the surface cold front over central Utah, with unseasonably cold, northwesterly flow over the northern and western portions of the state and warmer southwesterly flow over southwest Utah. 

The ECMWF has a very similar solution, as illustrated by the surface temperature forecast below, with a 30˚F temperature contrast between southeast Utah and Cache Valley. 

Source: Pivotal Weather

Direct model temperature forecasts can exhibit large biases, so I don't use the absolute values of those numbers above for anticipating actual temperatures, but the National Weather Service is currently forecasting a high of 67˚F for the Salt Lake City airport on Monday, which would be 22˚F below average. 

Monitor forecasts for evolving details, but be prepared for big changes.

Late June Troughs

A weak trough will move over northern Utah tomorrow, lowering maximum temperatures in the Salt Lake Valley into the mid 80s and bringing a chance of scattered showers and thunderstorms. 

I mentioned how great it is that we keep seeing these troughs in my previous post, and there's a chance of another, stronger one, early next week, but the impacts on northern Utah vary substantially depending on the forecast model. 

The GFS forecast valid 1200 UTC (0600 MDT) Monday shows a deep trough over the northwest U.S. with a cold front moving through northern Utah. 

The GFS then brings the trough directly through the northern half of the state and by 1200 UTC (0600 MDT) Tuesday, forecast 700-mb temperatures are just below 0˚C, cold enough for snow in the upper elevations above probably 9000 feet, although possibly lower. 

However, the ECMWF has a much different evolution for northern Utah.  It stalls the trough over the Pacific states. 

We would probably see a cold frontal passage at low levels in that solution, but it's a tough call.  Additionally, it would be drier and snow levels would not be as low. 

Thumbnail 500-mb plots from the GEFS all show a trough over the western US, but with varying amplitudes and speeds. 

Source: Penn State E-wall

This means there's a great deal of uncertainty about how things will play out early next week.  In fact the ECMWF drags the trough very slowly across the western U.S. which would be a fly in the ointment for weather for much of the week as the 4th approaches.

The bottom line is that you should monitor forecasts in the coming days to see how this plays out.  Ahead of the trough we could see elevated fire-weather risk with wind and low humidities.  Near the trough, a chance of showers and thunderstorms.  Much will depend on track, intensity, and movement and the range of possible outcomes for any given location in northern Utah is quite large. 

A Pleasant June So Far (By Recent Standards)

The average temperature at the Salt Lake City International Airport for the first three weeks of June was 68.9˚F.  This is quite comparable to the first three weeks of last June (68.6˚F) and considerably cooler than the first three weeks of June 2015, 2016, 2017, and 2018, when mean temperatures were at or above 74˚F. 

Source: NOAA Regional Climate Centers

So, compared to recent standards, this has been a pretty nice June.  However, it's still about 2.4˚F warmer than the 20th century average for Salt Lake City.

It's also been a June of extremes.  Just check out the roller coaster we've been on below.  We hit 100 on June 5, the earliest 100 ever recorded at the airport, then plunged downward with highs of 60 and 55 just 2 and 3 days later, respectively.  We subsequently seen big swings continue through today.   

Source: National Weather Service

Today looks splendid with a high of 84 forecast for the Salt Lake City Airport by the National Weather Service.  Temperatures will climb into the low 90s by Wednesday, but then another trough moves in on Thursday.  The GFS forecast for late Thursday afternoon (MDT) shows the trough over northern Utah bringing a chance of showers and thunderstorms.  Hooray!

Climatologically, we are entering the least synoptically active part of the year, so each trough we see now is a blessing.

The Days Are Getting Shorter!

Yesterday's summer solstice is behind us and the days are now getting (slowly) shorter.  There is still much summer and fall to enjoy, but the orbital parameters strongly suggest that ski season will come.

What the ski season will look like is a big question.  Perhaps we'll be close to a vaccine or there will be a treatment breakthrough that allows us to move forward as we have in the past.  We all hope that's the case, but there's also the possibility that our best strategies remain non-pharmaceutical interventions such as distancing, masking, etc., as they are today.

Some hints at what things might look like are being provided by resort plans in Australia, where resorts are beginning to open.  Traveller reports that resorts are beginning to open this coming week with what Falls Creek resorts calls "business as unusual."  It sounds like lift tickets are being sold in advance, chairlifts will be loaded with half capacity (unless riders are from the same household), lift line queues are being spaced apart, and skiers are being encouraged to bring their own lunches. 

It should be noted that Australia (and New Zealand), unlike the United States, have crushed the curve (cases per million people below, with New Zealand the unlabeled purple line).  Yet these practices are still being implemented. 

In Utah there will be other challenges.  How will people get to the Cottonwood resorts?  UTA busses on ski days are crowded.  Will anyone want to ride them if coronavirus is prevalent?  Should carpooling be encouraged if it means people from different households are social bubbles riding together?  What will traffic in the canyons be like on a powder day?  

Perhaps we might also see a major uptick in backcountry skiers, as occurred after the resorts closed last season and accelerating a trend that has been apparent now for many years.  This could put further pressure on parking at trailhead lots.

Perhaps I worry too much.  Let's at least hope we have a good snow season.