Saturday, August 1, 2015

Coolest July in SLC Since 1997

Well, that was pleasant.  July was the coolest in Salt Lake City since 1997.

Source: NOAA Regional Climate Centers
Of course, if we go back a few decades, it would have rated as a bit warmer than average.  It's only in terms of the recent warmth that it was cool.  Nevertheless, we'll take it.  

Let's hope next July is like July 1993, which was the coolest on record.

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?