Wednesday, July 30, 2014

The Juicy Aftermath

A blanket of stratus obscures the Wasatch in the aftermath of two days of monsoonal rains
What a great couple of days.  Cooler temperatures and high humidities have done wonders for my skin and my disposition.  Let's have a look at some of the more remarkable aspects of the event.

Integrated precipitable water reached nearly 1.4 inches.  Although not a record, this is beyond the 99th percentile for the month and more than 3 standard deviations above the mean.  

Source: NWS
Given that we live in a region that is typically fairly dry, but punctuated by occasional monsoon surges with high moisture contents, one needs to be cautious in interpreting these moisture statistics.  That being said, I think it is safe to conclude this was a fairly juicy event, but there's been juicier.  

Dewpoints at the Salt Lake City airport have been at or above 58ºF now for 36 hours, with peaks at 65ºF yesterday morning and this morning.  A couple more mornings like this and I'll save a fortune on skin cream. 

Source: MesoWest
Preliminary maximum storm accumulation reports by region include 0.71" in Logan (Cache Valley), 1.73" in Corinne (northern Wasatch Front), 1.37"in Sandy (Salt Lake Valley), 1.32" in Levan (southern Wasatch Front), .83" in Cedar Mountain (Western Deserts), 1.64" near Morgan (Wasatch Mountain Valleys), 1.81" at Red Spur (Wasatch Mountains north of I-80), .65" at Alta–Collins (Wasatch Mountains south of I-80), 1.23" at Norway (Uinta Mountains), .35" in Duschesne (Uinta Basin), .18" at the Carbon County Airport (Castle Country), 1.12" at San Pete Reservoir (San Pete/Sevier Valleys), 1.31" in Fillmore (west-central Utah), and Ok, that's enough!

Basically, this wasn't a hit or miss event.  There were wide-spread variations in accumulations, but nearly everyone got something and there weren't any outrageous accumulations, although it is possible that the gauges missed something.  For example, there was a strong, stationary cell near Eureka yesterday afternoon, as well as another northwest of Eagle Mountain in Utah County, that may have put down more than indicated in the observations above. There was some localized flooding in places, including Eagle Mountain, but for the most part, we were spared the really nasty stuff.  

Still a chance of some showers and thunderstorms today, although they should be more scattered.  

Tuesday, July 29, 2014

Let's Build an Ark!

The University of Utah @ 12:40 PM
The University of Utah is currently experiencing a nice soaking rain, but stronger downpours are occurring elsewhere and could affect us later in the day.

Rdar imagery shows a nice cyclonic (counterclockwise rotating) circulation center over the West Desert.  Although there is widespread shower activity across much of northern Utah, some very strong cells can be found in the Salt Lake Valley and the area around Eureka, not to mention coming off the high terrain in far northwest Utah.

The Oak Springs weather station northwest of Eagle Mountain in Utah County recorded 1.94 inches in the past three hours.  Quite a deluge.  Guess we can turn off the sprinklers for a few days.

Very Refreshing!

Some of yesterday's storm activity in the Wasatch Mountains
The juicy tap delivered a refreshing evening last night with widespread rain and thunderstorms along the Wasatch Front and across much of Utah.  Integrated precipitable water, the depth of water in an atmospheric column if it were all precipitated as rain, reached nearly 4 cm yesterday afternoon, which is fairly high for northern Utah.  Values remain high this morning.  
Observations from the Salt Lake City Airport show how temperatures dropped from a high of 92ºF early yesterday afternoon to about 68ºF with the onset of rain in the afternoon.

Source: MesoWest
Since then, temperatures remained nearly flatlined at 68ºF.  Further, dewpoints are currently sitting around 64ºF.  That's very high for northern Utah.  I don't know what the record dewpoint is for the Salt Lake City Airport, but I think the highest dewpoint I can remember seeing there since moving here in late 1995 is 68ºF.  Maybe an adventurous student out there can rifle through the records.

It looks like a cool, humid day (by Utah standards) is on tap today with some showers and thunderstorms.  How refreshing!

Monday, July 28, 2014

A Juicy Tap

Utah will be under the influence of a juicy tap of monsoon moisture today and tomorrow thanks to the amplification and eastward shift of an upper-level ridge over the interior western United States.

This has pretty much opened us up to southwesterly flow and a juicy tap from the southwest U.S. and northern Mexico.  Tropical Storm Hernan also lurks off the tip of Baja (see red box), but right now appears to be heading westward.

If you've had an eye to the sky the past couple of days, you already know that moisture levels have been on the rise.  Integrated precipitable water, the depth of water in an atmospheric column if it were all precipitated as rain, has climbed from about 0.6 inches Saturday afternoon to over an inch this morning.
Showers and thunderstorms are expected statewide today, with the potential for some heavier downpours and flashflooding, especially in southern and central Utah where the National Weather Service has issued a flash flood watch.

Source: NWS
All in all an exciting day.  Keep in mind that yesterday lightning from monsoonal thunderstorms killed 1 and injured 13 at Venice Beach, California.  Let's be careful out there.

Saturday, July 26, 2014

Long Lift Lines, But Worth It

Perhaps against better judgement, we travelled up to Alta this morning to sample the wildflowers, which are probably near peak in Albion Basin.  Being that it was the Wasatch Wildflower Festival this weekend, the Yogi Berra quote, "nobody goes there anymore it's too crowded" came to mind as we pulled into the parking lot.

Perhaps there was a capacity closure of the canyon as the lift lines were long and the slopes packed.

I don't think I've ever seen it busier during the summer at Alta.  That being said, it was good to see so many people, young and old, enjoying the the Wasatch Mountains.

East Greely looked like East Greenley today.  Spectacular.

The wildflowers higher up below the Castle weren't as spectacular as lower in the basin, but still nice.  There's still some snow patches for those of you desperate for turns (actually, there is remarkably little snow left for July).

It's always good to reacquaint with old friends.

If you head up tomorrow (Sunday), plan on walking from the Albion base as the lines for the shuttle are long.  The best flowers we saw all day were in the lower basin anyway.

Friday, July 25, 2014

The Southwest Drought

The New York Times occasionally runs a series of maps and charts examining a variety of issues, including their latest, Mapping the Spread of Drought Across the U.S.

Drought severity across the U.S. on July 22, 2014.  Source: New York Times.  
 Drought is an under appreciated natural disaster.  The onset and end are not typically sudden, but the costs can be quite high.  If you scan the list of billion dollar weather disasters since 1980, drought appears 18 times, with combined loses of almost $250 billion in current dollars.

Droughts are often through to be periods of abnormally low rain, but they are actually quite multifaceted with considerable geographic variability.  There's more to the story than precipitation as the conditions that lead to low soil moisture are also affected by temperature and other weather, climate, and soil factors.  Although there are many different ways to both define and determine the severity of drought, the most widely used index is the Palmer Drought Severity Index (PDSI), which attempts to account for a variety of factors that affect soil moisture.

Plots like the one above derive from the U.S. Drought Monitor, which blends a number of drought measures and expert judgement.

The Southwest is currently in the grips of widespread drought, with drought conditions rated as exceptional over portions of California and Nevada (the "more" region above).  To the first order, this drought reflects the influence of climate variability.  As concluded by Hoerling et al. (2013) in the Assessment of Climate Change in the Southwest United States:
"It is likely that most of the recent dryness over the Southwest is associated with natural, decadal coolness in tropical Pacific sea-surface temperatures, and is mostly unrelated to influences of increased greenhouse gases and aerosols." 
In other words, more persistent La Nina conditions have played an important role in the long-term drought conditions.  This is not to say that global warming has had no influence on the drought.  It is an exacerbating factor with higher temperatures, by contributing to soil drying, increasing in drought coverage and intensity.

Thus, we should be cautious in attributing the current drought to global warming.  On the other hand, we also shouldn't assume that all is well and good in the coming century.  The evidence suggests a decline in water resources over the Southwest over the long term.  As discussed by Gershunov et al. (2013) in that same Assessment of Climate Change in the Southwest United States:
"Drought, as expressed in Colorado River flow, is projected to become more frequent, more intense, and longer lasting, resulting in water deficits not seen during the instrumented record (high confidence)" 
"In terms of soil moisture, drought is expected to generally intensify in the dry season due to warming (high confidence)"