Monday, September 29, 2014

Positively Pixelated

You don't see this every day, but for the 24-hour period ending at 1200 UTC (0600 MDT) Sunday, all of Utah received measurable precipitation, at least as estimated by the National Weather Service's Advanced Hydrologic Prediction Service.

The Salt Lake City forecast office put together the graphic below summarizing the remarkable increase in river flows during the event.

Source: NWS
How about that Beaver Dam Wash in Arizona, which went from no flow to 11,800 cubic feet per second!

Source: NWS
In case you are wondering where Beaver Dam Wash is, it runs along the Utah Nevada border and eventually empties into the Virgin River in NW Arizona (see the BEA in the map below).

Source: NWS

Sunday, September 28, 2014

Late September Teaser

A sprinkling of snow in upper Cardiff Fork this morning serves as a teaser for the approaching ski season.   Some aspens are pre-peak, others past peak, so enjoy the fall colors while they last.

Saturday, September 27, 2014

Washout Game on Tap

It's been impressively wet overnight and thus far today, especially in western Utah.  Twenty-four hour accumulations for the period ending within 1 hour of 1841 UTC (1241 MDT) show several locations in the Dugway area with more than an inch of rain (ignore sites with 0 or very light accumulations as these are almost surely bad).  The 1.22" maximum observed at a couple of sites represents about 15% of their 7.75" annual average.  Accumulations in the Salt Lake Valley and surrounding area are generally around 0.6", with more to come.

Source: MesoWest
A south–north oriented precipitation band is slowly moving across the Utah and is likely to be bringing periods of rain, possibly heavy at times, this afternoon and during the Ute football game this evening.  

The forecast from the High Resolution Rapid Refresh (HRRR, courtesy NOAA's Earth Systems Research Lab), which will become operational in the near future and provide short-range forecasts at 3-km grid spacing for the continental United States, shows bands of heavy showers moving through the Salt Lake Valley prior to and during the game, with just a few short-lived breaks.  Here are the hourly radar reflectivity forecasts for 2300 UTC (1700 MDT) through 0400 UTC (2200 MDT).

The HRRR lightning threat product shows the potential for some lightning during this period (one time selected for brevity).

The bottom line is that a Washout Game is on tap for tonight, with the potential (but not a guarantee) for a lightning delay. 

Friday, September 26, 2014

Potential Ute Football Deluge

There's not much change in the forecast from yesterday except that the storm is moving in just a bit slower.  The net result of this slight delay is that the 1200 UTC model runs generally put the heaviest precipitation directly over Rice–Eccles Stadium for tomorrow's football game.  The NAM, for example, is putting out more than 0.5" of rain from 6–9 PM tomorrow.  Kickoff: 6 PM.  Bring the galoshes.

If you are interested in tracking the moisture surge, see the NOAA Earth Systems Research Lab's GPS meteorology web site.  They use delays in GPS satellite radio signals to estimate the water vapor content of the atmosphere (sometimes called "precipitable water").  Observations from Needles, CA, for example, show a dramatic increase in precipitable water over the past 24-hours.  

Meanwhile in Salt Lake City, we're starting to see things moistening up from the dry air that was in place yesterday (hence the developing cumulus cloud cover this afternoon).  Values should exceed a full inch by tomorrow and, with cooler air moving in, that equates to a "washout" game instead of a "blackout" or "whiteout" game.

Thursday, September 25, 2014

Outlier Mode Begins

Although there remain some differences in timing and details between the models, we remain on track for what could be an extremely wet period in northern Utah and other portions of the state.  Given the heat today, I'm officially declaring the start of "Outlier Mode."

The record high for today is 92ºF, which is also the latest 92ºF day in the record books at the Salt Lake City International Airport.  As of 1:35 PM, it was 89ºF at the airport.  I'm guessing a 91ºF max is probably most likely, but maybe we can squeeze out a record.

Tomorrow there's a chance of showers and thunderstorms as the upper-level trough approaches, afterwhich your ark-construction needs must be complete as the system taps into juicy air over the eastern Pacific and Gulf of California.  The forecasts below show the forecast integrated water vapor transport produced by the GFS (bottom) and the average of all members of the Global Ensemble Forecast System (GEFS) on Saturday morning.  There is a narrow plume of strong water vapor transport extending from Baja into Utah.

Source: NWS
Moisture transport of the intensity forecast is fairly unusual in the Intermountain West this time of year, with return intervals of about once every 10 years in late September and early October.  

Source: NWS
Not surprisingly, given the moisture and strong forcing associated with the approaching upper-level trough and frontal system, the models are going berserk for precipitation.The graph below shows the accumulated precipitation produced by the 21 members of the Short Range Ensemble Forecast (SREF) system.  The mean (black line) calls for nearly an inch of precipitation at the Salt Lake city airport from about 0000 UTC (6 PM) Friday afternoon to 0000 UTC (6 PM) Saturday afternoon.

There is, however, quite a bit of spread and much is going to depend on timing and location.  By and large, Saturday looks like a fairly wet day.  Those of you heading to the Utah–Wazzu football game should keep an eye on the forecast and hope for a break.  Coach Wittingham might want to consider having his players practice with wet footballs today and tomorrow.  There's even a possibility of thunderstorms, so hopefully the University has an appropriate lightning safety plan in place as we have discussed previously.  Kudos to the University of Michigan for taking proper precautions last week.

In case you are wondering, it appears that there have only been five calendar days during which more than 2 inches of rain was recorded at the Salt Lake City Airport (or probably downtown for really old observations), but two of those days are in September.

May 3, 1901
June 5, 1885
July 13, 1962
September 5, 1970
September 26, 1982

September is a good month for a deluge because of the combination of monsoon moisture with cool-season storm systems.  I won't be surprised if we see some locations with 2+ inches on Saturday.  

Wednesday, September 24, 2014

Life after Death

Although there has been quite a bit of variation between the models concerning the details, especially timing, things appear to be coming together for what should be an exciting period this weekend.

As discussed in the previous post, the precipitation accompanying the Pacific cold front that made landfall along the Pacific coast overnight is expected to die off as the system moves inland.  This is, however, a case of life after death as the cold front will be rejuvenated once the pre-frontal southerly flow begins to move past the Sierra Nevada, enabling juicy air over the eastern Pacific and Gulf of California to push into the Intermountain West.

The GFS loop below, which shows the 700-mb (10,000 ft) temperatures, surface winds, and precipitable water (a measure of the total water vapor content of the atmosphere, color fill).  Note as the front pushes across California and Nevada that it eventually draws moist air up the lower Colorado River Valley and into Utah.  

1200 UTC 24 Sep 2014 GFS Forecast of 700-mb (10,000 ft) temperature, surface winds, and precipitable water (color fill) from 1200 UTC (0600 MDT) 24 Sep – 0000 UTC 28 Sep (1800 MDT 27 Sep). 
Some of the moisture increase reflects what meteorologists call moisture convergence along the front, but tapping into the juicy stuff to the south plays an important role.

The GFS is currently really excited for late Friday night and Saturday, with heavy precipitation along the front over Utah (apologies for the crappy color scale; Friday night and Saturday are near the end of the loop.

1200 UTC 24 Sep 2014 GFS Forecast of 700-mb (10,000 ft) temperature, surface winds, and 6-h accumulated precipitation (color fill) from 1200 UTC (0600 MDT) 24 Sep – 0000 UTC 28 Sep (1800 MDT 27 Sep). 
Here's a better image showing the 6-hour accumulated precipitation for the period ending 6 PM Saturday.  The GFS is putting out up to just over an inch of rain in portions of northern Utah.

Who gets what will ultimately depend on factors that are not reliably predictable this far in advance, but it does look like late Friday Night and Saturday could be pretty wet with some thunderstorms thrown in just for fun.

After that, things look showery and cooler for northern Utah, but as things stand now, I don't think we'll see much more than some light accumulations in the highest elevations.

Tuesday, September 23, 2014

Frontal Death

The latest GFS forecast shows the remarkable decay of the precipitation band accompanying the Pacific cold front that makes landfall tonight as it pushes eastward across the Cascades.

1200 UTC 23 Sep 2014 GFS forecast valid 1800 UTC 23 Sep – 1200 UTC 26 Sep 2014
Easy come easy go.  It's such a shame to see good rain die like that.  Is there life after death?  We'll find out in the coming days.

Monday, September 22, 2014

A Look Inside Secrets

Click here for a look inside my forthcoming book Secrets of the Greatest Snow on Earth.  Utah State University Press did a great job putting it together.  It will be released in November, but you can advance purchase it at Utah State University Press or Amazon

I'm hoping to make use of figures and diagrams from the book as we explore mountain weather this winter.  Here's one to get you excited.  Do you remember October 2004, which produced 122 inches at Alta and enabled Brighton to open on October 29?  Many described October 31, 2004, when a major lake-effect snowstorm erupted, as the best day of October skiing ever.  Radar image below.

Source: Radar image from 9:24 am 31 October 2004.  Removal of ground
clutter causes the "holes" over the high ridges surrounding the Cottonwood
Canyons.  Source: Steenburgh (2014).

Sunday, September 21, 2014

The Joy of Hiking in the Rain

Few things in life are as satisfying and enjoyable as a fall hike in the rain.

Until I moved to Utah, most of my life was spent hiking in the Adirondacks and Cascade Mountains, both of which are well known for wet misery.  I actually rate the Adirondacks higher than the Cascades on the wet misery scale, as the Cascades enjoy a pronounced dry season during the summer.  In contrast, suffering in the Adirondacks is a year round affair.  Nothing hardens you for outdoor pursuits like cross country skiing in freezing rain or forced marches in muggy, driving rain to black fly infested leantos.

So, when I woke this morning to the pitter-pat of rain, a smile ran across my face.  There's nothing better than a fall hike in the rain, especially since wet in the Wasatch is typically fairly tolerable. Below is the only patch of mud I ran into the entire morning.

And, with the mountains obscured, one's focus tends to turn to the wonderful fall colors.  

Saturday, September 20, 2014

Long Wait for Utes?

The Utah–Michigan game is delayed due to lightning.  It could be a long wait as there is mass of lightning producing storms moving toward Ann Arbor from the west and the west-southwest.

I'm guessing is it will be at least an hour, maybe longer, until the teams can take the field.  At least the Utes are winning 26–10 and are poised for another score.

Let the Hype Begin

The latest (and some of the previous) GFS forecast is calling for a bonafide fall trough to move into Utah for next weekend.  The coveted 0ºC 700-mb temperature contour is draped across the Great Salt Lake at noon next Saturday.

Before waxing the skis, some recognition of the chaotic nature of these long-term forecasts is needed.  We start with the North American Ensemble Forecast System, which consists of 21 forecasts from the US Global Ensemble Forecast System and 21 forecasts from the Canadian Ensemble Forecast system.  The plot below is known as a spaghetti diagram and includes contours of 500-mb geopotential height from all the members, along with a thick red contour for the ensemble mean.  This chart shows that most ensemble members put a trough over the western U.S. but the coverage of spaghetti suggests quite a bit of variability in terms of placement and strength.  
Source: NWS
Moving to the gold standard ECMWF, I didn't have time to hunt down a spaghetti diagram this morning, but the mean of their ensemble also puts a trough in the west (note that there are slight variations in the time all these forecasts are valid).  

Source: ECMWF
My take on this is that it looks like we may have a deep trough entering the western U.S. late next week or next weekend, but we'll have to see how it shakes out in terms of strength and timing.  I suspect, however, that these forecasts are enough to jumpstart the weather hype machine.

Friday, September 19, 2014

That Was Largely a Bummer

Yesterday was a depressing day to be a meteorologist, with nothing but "cumulus patheticus" developing along the Wasatch Front and all the excitement to our northwest.

KMTX radar loop for 0000–0202 UTC 19 Sep (1800–2002 MDT 18 Sep) 
The storms shown above developed near a surface trough that was draped across the Intermountain West.  I thought something would bubble up ahead of that trough, but alas, it wasn't to be.  Even the strong outflow boundary that you can see pushing southeastward across the Great Salt Lake in the loop above couldn't get anything going.  What a pity.  The storms above did produce some severe weather, with 1-inch hail reported in Caribou, ID yesterday afternoon.  Mother Nature just seems to have Idaho's number this year.

On the other hand, we did have a nice rumbler move through the Salt Lake Valley early this morning and park over the Avenues.  It doesn't look like much on the radar, but the thunder was pretty regular and disturbed my sleep enough to make me grumpy this morning.

KMTX radar loop for 0939–1119 UTC (0339–0519 MDT) 19 Sep
The lightning map below provides a nice summary of yesterday and last night with a large number of strikes running from northeast Nevada to southeast Idaho and just some scattered stuff along the central and southern Wasatch Front.


Thursday, September 18, 2014

Record Heat Locally and Globally

Yesterday's maximum temperature of 94ºF at the Salt Lake City International Airport set a new record for the day.  In addition, the only higher maximum temperature record later in the year is 97ºF, set on Sep 19, 1956.  Thus, we were in rare but not unprecedented territory for so late in the year.

On a global scale, data released by the National Climatic Data Center shows that August 2014 was the hottest in the instrumented record.

Source: NCDC
You might recall that August was relatively cool here in Utah and this shows up well below.
Source: NCDC
Globally for the year to date, 2014 is now the 3rd warmest behind 1998 and 2010.

Source: NCDC
It will be interesting to see how things play out in the home stretch.

Wednesday, September 17, 2014

An Interesting Situation Tomorrow and Tomorrow Night

As a forecaster this time of year, one needs to be alert when midlatitude troughs interact with monsoon moisture.  For much of the summer, monsoon thunderstorms in Utah form in an environment of weak to moderate instability and weak flow.  The primary forecast concerns are flash flooding and, in some instances, strong winds from microbursts.  

Add a midlatitude trough to the mix, and you have stronger synoptic forcing, stronger instability, and stronger flow.  If the instability, moisture, and shear are right, strong or severe thunderstorms can develop.

I'm not sure if we have the necessary mix of instability, moisture and shear for strong or severe thunderstorms tomorrow in parts of Nevada and Utah tomorrow (and tomorrow night), but the pattern warrants attention.  The forecast for tomorrow afternoon (6 PM MDT) shows a midlatitude trough extending across northern California with large-scale southwesterly flow over Nevada and Utah.  

Although much of the moisture associated with the remnants of Hurricane Odile are in Arizona and New Mexico, some does sneak into Nevada and Utah through tomorrow afternoon (green color fill at upper left below).  In the NAM forecast for tomorrow afternoon, one can also see a tongue of Convective Available Potential Energy (CAPE, yellow to orange color fill at upper right) along the Nevada–Utah border.  

CAPE is a measure of instability.  The maximum CAPE in that tongue exceeds 1000 J/kg, which is high for the Intermountain West, but on the margins for generating severe convection.  Further, although we have some monsoon moisture to play with, it's not exactly a juicy airmass.  So, as things stand now, portions of Nevada and Utah may see some showers and thunderstorms tomorrow, but the risk of strong or severe storms seems low. That being said, this is a pattern that I typically watch carefully as surprises sometimes happen in the Intermountain West and things could get interesting if the conditions prove a bit juicier than currently forecast. 

Tuesday, September 16, 2014

Coverage for Secrets of the Greatest Snow on Earth

Ski Utah has put together a nice piece on my book Secrets of the Greatest Snow on Earth.  The videos of snow and powder skiing should help stoke you for the coming season.

Secrets will be released in November, just in time for the ski season.  You can preorder it from Utah State University Press or  I'm hoping we'll have a preview available soon, but until then, here's the intro photo for chapter one.  

Monday, September 15, 2014

Odile...or Not?

Over the past two days, Hurricane Odile has been rumbling northeastward and crossed the southern tip of the Baja Peninsula overnight.  High integrated precipitable water values (contours below) are rumbling up the Gulf of California with and in advance of Odile, posing the potential for another major monsoon surge and related convection over the next couple of days.   

IR and GFS precipitable water analyses from 1500 UTC 13 Sep – 1500 UTC 15 Sep 2014
As with Hurricane Norbert, the long-range forecasts of Odile by the GFS have been super wacky (a technical term).  The forecast from Saturday morning (13 Sep) called for Odile to move westward and be located well off the Baja coast (near the bottom of the plot below) at 1200 UTC Friday 19 Sep.

The forecast from Sunday morning called for Odile to weaken with just some remnants over the northern Baja Peninsula by 1200 UTC Friday 19 Sep.

And now the forecast from this morning calls for Odile to curve hard to the east and be in New Mexico by 1200 UTC Friday 19 Sep.

The latest ECMWF model forecast favors southeast Arizona at 1200 UTC Friday 19 Sep.

Ah, the forecast joy of eastern Pacific hurricanes interacting with midlatitude troughs!  As the computer said in War Games, the only winning move is not to play.

Friday, September 12, 2014

Canyon Winds

Our first canyon wind event of the season is underway this morning.  Unlike big downslope wind events that typically roar along much of the northern Wasatch Front, this morning stronger winds are confined to a few locals including near Weber Canyon (currently gusting to 36 mph in the canyon) and near Centerville (25 mph).

Wind and wind gust observations within one hour of 14:47 UTC (8:47 MDT).  Source: MesoWest.
There are also east winds on the University of Utah Campus and Parley's Canyon.

Wind and wind gust observations within one hour of 14:47 UTC (8:47 MDT).  Source: MesoWest.
The winds at Parley's Canyon increased at a very gradual rate overnight.  The peak gust of 49 mph occurred early this morning.

The cause of these canyons winds is an area of high pressure that slid down the east side of the Rockies and is currently centered in northwest Nebraska.  The resulting pressure gradient is driving easterly flow into northern Utah.

This easterly flow is, however, very shallow.  By the time one gets up to 700-mb (10,000 ft), the flow over the northwest portion of the state is northwesterly.

As a result, this event is confined to some of the deeper canyons (e.g., Weber, Parleys) and areas where the Wasatch Crest to the east is relatively low (e.g., the University of Utah).

The key ingredient missing from this event and preventing it from being a big, widespread downslope windstorm is a closed upper-level low centered near Las Vegas.  Such an upper-level low is needed to drive easterly flow at mountain-top level.

These east winds should slacken later this morning.