Another Rare June Tropical Cyclone Remnant Visit

The passage of tropical cyclone (TC) remnants across the southwest U.S. is rare, but not unprecedented in June.  As illustrated by Ritchie et al. (2011),  rainfall events associated with TC remnants are most common over the southwest U.S. in September.  Action in June is more limited.  During the 1992–2005 period examined by Ritchie et al. (2011), there were only 2 rainfall events associated with TC remnants in June.

Number of eastern Pacific tropical cyclones, number of tropical cyclone remnants that brought rain to the southwest U.S., and number of tropical cyclone remnants that did not bring rain to the southwest but had other impacts.  Study period 1992–2005.  Source: Ritchie et al. (2011)

We've already had one this year associated with TC Andres, and now we'll have another associated with TC Blanca.  Blanca was a category 4 hurricane, but as of this morning had weakened to a tropical storm centered near the Isla Santa Margarita off the west coast of the Baja Peninsula.  High clouds in advance of Blanca were already streaming into southern Arizona.

As can be seen in the contours above, Blanca is accompanied by a slug of high integrated water vapor (a.k.a. precipitable water) and preceded by a surge of high integrated water vapor up the Gulf of California.  This moisture is expected to push into southern California and Arizona today and stream into southern Utah late tomorrow.  At the same time, moisture from the midlatitude Pacific also pushes into the Intermountain region from the west.

Thus, although we're in a bit of a break today and tomorrow, with just some isolated mountain showers and thunderstorms, the action should be on the increase after Tuesday with a good chance of showers and thunderstorms statewide on Wednesday and Thursday.

After nearly turning on my sprinklers in April, I still haven't run them and if we can get more rain midweek, I'll likely make it to at least the middle of the month.

The East Pac Is Jacked!

Sea surface temperatures in the tropical and subtropical eastern Pacific are running generally at least 1ºC above average and 2–3ºC above average west of Mexico (lower panel below).  A warm tongue of warm water off the coast of South America and along the equator is indicative of El Nino conditions.

Source: NOAA/CPC

El Nino years are typically associated with above average hurricane seasons in the east Pac and we've already had two names storms, Andres and Blanca, both of which have reached Category 4.  Andres has dissipated, with the last remnants of its cloud mass near 23 N and 123 W.  High clouds extend northeastward from the Andres remnants and into the southwest US.  Blanca is still churning away.  Although it has weakened to Category 2 strength, having attained Cat 4 earlier, it represents the earliest second major hurricane on record in the east Pac.

Source: NOAA/NHC

The showers that came through the Salt Lake Valley this morning can be traced to a surge of moisture originating in the subtropical eastern Pacific just to the east of Andres.  The loop below, which covers the past 2 days and includes contours of integrated water vapor (a.k.a., precipitable water) and 850-mb winds shows this surge nicely.  Note how the moisture tongue pushes across Arizona and wraps across eastern Utah into the northern part of the state.  

If you are wondering if this is a trend for this summer, it's tough to say.  An above average hurricane season in the east Pac seems to have a good chance.  Monsoon precip from July–September?  Less clear for our part of the world.  El Nino stacks the deck in Arizona for below average monsoon precipitation, but not so much northern Utah (our monsoon precipitation is fickle here to begin and can be hit or miss, making all these statistical inferences "dicier").  Based on a variety of factors, the Climate Prediction Center is giving us slightly better than chance odds of above average precipitation.  I wouldn't bet the farm on this (or even a small side wager), but I'll hope it verifies and I'll enjoy anything that falls from the sky the next few days.  

Secrets for a Great Price!

If you haven't already purchased a copy of Secrets of the Greatest Snow on Earth, you can get it now from University Press of Colorado for 50% off.  Direct link is http://www.upcolorado.com/utah-state-university-press/item/2390-secrets-of-the-greatest-snow-on-earth.  Enter promo code 50FOR50 at checkout as noted below.  They have other great books too for the same killer deal.  

We're celebrating our 50th anniversary with a 50% off sale! Just head to http://t.co/sSON2IbcDB and use promo code 50FOR50 at checkout!

— Univ. Press of CO (@UPColorado) June 4, 2015

I wonder if they will have 100% off for their 100th anniversary?

The Bear Lake Boating Tragedy

On Monday night, strong winds and waves on Bear Lake capsized a small boat killing one adult and three children.  It sounds like a terrible tragedy and my thoughts and prayers go out to the friends, family, and all involved.

Bear Lake straddles the Idaho/Utah border and is roughly 30 km long and 10 km wide.  The accident apparently happened in the Idaho portion of the lake.  

Although details are still fuzzy, the Salt Lake Tribune reports that winds gusted to 76 mph, with waves reaching 10 feet in height.  Seven people were on board when the boat capsized, all with life jackets on.  The water temperature, however, was only 53º.  It is likely that the victims died from exposure or downing before they could reach the lake shore.  

I've taken a quick look at the weather contributing to this tragedy and it provides a cautionary tale about just how quickly disaster can strike on Utah waters (and elsewhere) seemingly from nowhere. 

The strongest wind gust I could find near Bear Lake from observations collected by MesoWest was  48 mph at the Bear Lake County Airport, just north of the lake.  The meteograms below show that at 1655 MDT (~5 PM), the temperature was 79ºF with sustained winds of 14 mph.  Then things changed dramatically for the worse.  At 1755 MDT (~6 PM), the temperature was 60.3ºF with sustained winds of 35 mph and gusts to 48 mph.  The tempest continued for another hour and and by 1855 MDT (~7 PM) winds were still gusting to 46 mph and the temperature had dropped to 54ºF.  

In addition, satellite and radar imagery shows that Bear Lake was on the edge of most of the thunderstorm activity (the lake is just west of the UT-ID-WY triple point), which was associated with a weak cold front that was moving through the area.

Source: NCAR/RAL

Source: NCAR/RAL

Although there were some weak radar returns in the vicinity of Bear Lake, the strength and duration of the strong winds strongly suggests that a mesoscale outflow boundary (a.k.a. gust front) produced by precipitation and thunderstorms to the north and west likely propagated through the area.  

Indeed, numerous sites in the area reported strong winds during this period, including the Grace RAWS station just northeast of Bear Lake, which hit 65 mph.  There probably were some clouds and showers in the vicinity of Bear Lake ahead of the gust front, but the change in wind, temperature, and waves experienced by the boaters would have been abrupt and severe.  Further, the persistence of strong winds and waves combined with a further drop in temperature following the gust front passage greatly increased the likelihood of drowning or hypothermia before the boaters could reach shore.   I suspect the boaters were hit by something that they never saw coming, or had little time to respond to, and were cast into a nightmare situation.  

This sort of weather situations is, however, not all that uncommon in Utah, highlighting the need for boaters to remain vigilant for rapidly changing conditions when storms are around.  It's especially important to recognize that the strong winds and rapid temperature changes associated with outflow boundaries can sometimes propagate well away from the generating storms, in some cases into areas experiencing clear skies.  

The Snow Is Going Fast

Although we had a stay of execution for most of May, the snow is going fast now that the heat is on.  Snow melt at the Snowbird SNOTEL went into overdrive in late May with the snowpack water equivalent dropping from 9.5 inches on May 27th to 0.3" yesterday, a mean melt rate of about 1.5" a day.  0.3" rounds to 0, so I'm officially calling an end the snow-cover season at this site.

Source: CBRFC.  

The snow depth at Alta Collins has similarly been plummeting and is now down to 52 inches.

Source:  MesoWest

The Alta Lodge web cam shows patch cover at the base of Alta.  If you want a top-to-bottom run, you'd better get on it ASAP.

Source: Alta Lodge

The end is near.  Much work will be needed to earn turns after this week.

Happy 20th Anniversary KMTX!

Weather prediction over northern Utah reached a major milestone this week with the 20th anniversary of the KMTX WSR-88D radar on Promontory Point (right image in the @NEXRADROC tweet below).

Celebrating 20 years for KMSX @NWSMissoula and KMTX @NWSSaltLakeCity #wsr88d pic.twitter.com/WhDlSBS8YX

— NEXRAD ROC (@NEXRADROC) June 1, 2015

WSR-88D stands for Weather Surveillance Radar, 1988, Doppler, a name only the National Organization for the Advancement of Acronyms [(a.k.a., National Oceanic and Atmospheric Administration (NOAA)] could love.  The non-technical name is NEXRAD, for NEXt-generation RADar.

The development, installation, and subsequent operation of the 160-radar NEXRAD network is a great success story, paying dividends to the American taxpayer many times over.  Mike Smith, author of the book Warnings: The True Story of How Science Tamed the Weather, calls the NEXRAD network "one of the best investments the federal government has ever made when viewed on a cost/benefit basis."

The NEXRAD network replaced the pre-existing network of WSR-57 and WSR-74 radars, adding increased resolution and the ability to measure Doppler velocity, the magnitude of the flow towards or away from the radar, which is critical for warnings related to severe convective storms and tornadoes.  The NWS recently added polarimetric capabilities to the NEXRAD network, which allows each radar to send and receive horizontal and vertical radar waves and better discriminate between rain, hail, snow, and other precipitation types.

Although beneficial across the country, the NEXRAD network was a revolutionary advance across most of the western United States and northern Utah, which were completely uncovered by the WSR-57 and WSR-74 radars.

Source: National Academies Press (1995). http://www.nap.edu/catalog/9056/assessment-of-nexrad-coverage-and-associated-weather-services.

In fact, prior to the installation of the KMTX radar, forecasters at the Salt Lake City National Weather Service Office relied on hand-drawn analyses from a FAA radar — hardly a recipe for success during rapidly evolving severe and hazardous weather events.

Today, thanks to KMTX, you can view radar loops in real-time on your smart phone while skiing in the Wasatch.  That's what I call progress!  Chances are you are using radar apps developed by private sector companies, which have leveraged the NEXRAD network to tap into all sorts of emerging markets in weather sensitive areas.  None of this was possible when I started graduate school.  Kudos to all in the weather enterprise who have contributed to these advances.