Category Archives: OREO

A Great Month of Outreach, Education, and Radar Meteorology with DOW7

Professor Powder attempts to keep DOW7 from leaving
After more than a month in Salt Lake City, DOW7 departed the University of Utah campus and began its trip home to Boulder this morning.

It had a great run in northern Utah, despite an uncooperative Mother Nature who was quite stingy providing storms.  We exhibited the DOW for 1500 visitors at the Natural History Museum of Utah and 300 at the University of Utah.

Meteorological outreach at the Natural History Museum of Utah.  DOW in the background. 
In the DOW during sidewalk exhibit at the University of Utah

Several graduate students are now fully trained DOW operators.  Students in our cloud microphysics, synoptic meteorology, mountain meteorology and a radar special topics class were able to participate in operations either on campus or in the field.  My mountain meteorology class is presenting results this afternoon from their initial analysis of a precipitation event in the Ogden Valley.

Seven people stuffed in the DOW.  A common scene during field operations. 
Officially, we did eight "intensive observing periods", or IOPs:

IOP0- Practice IOP scanning some weak snow showers over the northern Wasatch (Location: Antelope Island Marina)

IOP1- Leeside precipitation in the Ogden Valley (Location: Huntsville)

IOP2- Frontal precipitation over the Salt Lake Valley and mountain-induced precipitation over the northern Wasatch (Location: Fielding Garr Ranch, Antelope Island)

IOP3- Exploratory effort to examine precipitation over Ben Lomond (Location: Just south of Willard Bay)

IOP4- Exploratory effort for eared grebe migration (Location: Lakepoint)

DOW near Lakepoint in the Tooele Valley scanning for eared grebes on November 25th.  National Weather Service radar imagery showed the first signs of migration last night, so the truck returned to Boulder just a little too soon. 
IOP5- Cold front with topographic interactions over Tooele Valley (Location: Stansbury Island Causeway)

IOP6- Cold front, influence of Oquirrh and Wasatch range on precipitation, small-scale precipitation structure in and around Cottonwoods (Location: South Jordan Trax Station)

DOW at the South Jordan Trax Station with frontal/orographic cloud over Wasatch
IOP7- Mountain and lake-effect precipitation (Location: Baccus Highway near 7000 South)

Mother Nature's stinginess forced us to take what we could get and do a couple of all-night operations.  IOP1 and IOP2 covered the same storm.  We just moved the DOW from Huntsville to Antelope Island as the storm slid south, changing the IOP number.  IOP6 and IOP7 were also the same storm and we just moved the radar from the South Jordan Trax Station to the Baccus Highway as the winds veered and orographic and lake-effect precipitation evolved.  Knowledge of meteorology, terrain, and potential site characteristics are a real key to making such efforts successful.  Not to mention some motivated graduate students willing to work graveyard shifts.  During such operations, we rotate crews and bring in a fresh driver for moving the DOW in the morning.

Special thanks goes to our sponsor, the National Science Foundation, and the operators of the DOW, the Center for Severe Weather Research, for making the visit possible.  The Center for Severe Weather Research extended the DOW visit a few days to let us capture our most recent storm and for that we are grateful.  I'm fairly certain that storm will make it into at least one master's thesis and maybe more.

A Day and Night of Great Utah Storm Chasing

Finally, a decent storm!  Our storm chasing activities this month were somewhat curtailed by Mother Nature.  Storms were limited, but we made the most of the three major opportunities we had, including our efforts yesterday and today.

Yesterday, we set up camp in the South Jordan Train Station parking lot for the frontal passage and post-frontal precipitation.


We operated here in 2011 when it was in the boondocks.  Although development is spreading westward (note the building behind the DOW), we were able to use it effectively yesterday, although we may need to find an alternative for future deployments.

There was a great deal going on and I suspect we have a great dataset for both an MS thesis and at least one paper.  Here are a few snippets.

The photo below from U undergraduate Spencer Fielding is taken facing ESE shows the situation shortly after the surface cold front has passed and was located just south of Point of the Mountain.  A pronounced cloud rope was evident above the frontal interface with the cloud structure suggesting ascent in the strong southwesterly flow over and downstream of the front.  It was black as coal over the Cottonwoods, but we saw very little on radar during this period.  Instead, the precipitation was falling further downstream (relative to the flow aloft) in the area east of Mill Creek Canyon.  This appeared to be a classic situation of precipitation growth, transport, and fallout with the growth happening in the ascent region, but the particles needing sufficient time to grow big enough to fall out, which happened further downstream.  It was unclear if the mountains really mattered at all in this period.  Making all of this easy to see was the fact we seemed to be in a rain shadow east of the Oquirrh Mountains.


That Oquirrh rainshadow was a prominent feature for a couple of hours after frontal passage.  The image below is a vertical slice taken facing northwest toward the Oquirrh Mountains (Grey region marked with an "OM."  The color fill is Doppler velocity, which measures the speed of the flow toward (cool colors) or away (warm colors) from the radar.  The northwesterly flow is clearly evident.  Note how it descends into the Salt Lake Valley southeast of the Oquirrh Mountains.


That descending flow is quite consistent with surface observations at the time which showed WNW flow at most sites along and east of the Mountain View Corridor (highway 85) in the western Valley.  This was about the time of the frontal passage at our location.


An hour later, the front had pushed through Point of the Mountain.  There was a clear boundary over the southwest Salt Lake Valley between the downslope westerlies and the along-valley northerlies.  Curiously, the downslope flow was colder than the northerly flow to the east.  Downsloping air warms compressionally, so for that to occur, precipitation must have cooled the airmass.


The photo below was taken shortly after the MesoWest analysis above and was taken facing NNW.  Here you can see quite well the dark, low-level clouds that accompanied the front into the Salt Lake Valley.  To the left, however, one can see snow (fibrous clouds) that is spilling over into the lee of the Oquirrhs.  The sublimation of that snow presumably contributed to the cooling of the airmass.  Note also how the subsidence has eroded the low-level cloud away on the west side of the photo.


Looking west, you can see this spillover really well in the radar reflectivity.  Note in particluar the shallowing of the echoes toward the radar due to the downslope flow.  One might think of this as a "snow foot."



Eventually, the cold air deepened and the flow aloft veered (turned clockwise) to westerly and eventually westnorthwesterly and we got quite a treat as the area around Little Cottonwood Canyon finally lit up.  One example is below, which is a vertical slice taken facing east directly up Little Cottonwood Canyon.  The bright yellow/orange colors are ground clutter produced by the sloping canyon floor.  Above that clutter, there's not much happening in the lower canyon, but from mid canyon up, there are strong returns, indicating heavy snowfall.


The photo below was taken about 2 hours earlier when it was still light, but shows perhaps what was happening with little or no precipitation falling at the base of the mountains and in the lower canyon (v-shaped notch in background to left of radar dish), with heavy snow in the middle and upper canyon.  


At times, away from the mountains, we also saw some beautiful fall streaks.


Google it and look at the photos and you'll know what I mean.

We eventually deployed to a site we could scan further north for the orographic and lake-effect precipitation that fell overnight.  I went home and tried to sleep, but it was largely a night spent looking at the radar and hoping we were getting great data, which we were.  You'll probably hear a lot of talk about the snow being lake effect, but in the mountains, most of it wasn't.  It was just good old mountain lifting doing the job until early this morning when we got a bit of lake effect.

We surveyed the lake-effect showers for most of the morning.  At one point, we decided to forget about doing anything except two rapid fire vertical slices taken through the lake-effect convection as it moved inland.  A still is below, but these slices were taken every 16 seconds.  I can't wait to process the data and see a video.


All of this brings to an end the OREO field phase.  Although storms were limited, we actually have some great data from three major storm cycles, and the students enjoyed a smorgasbord of precipitation and wind phenomenon.  

Special thanks to the National Science Foundation for sponsoring this visit and the Center for Severe Weather Research (CSWR) for making it happen.  The CSWR deserves extra special thanks for letting us keep the DOW a few extra days to catch this latest storm.

Storm Chasing Update

Prefrontal southerlies are cranking over the Salt Lake Valley, which is filled with dust as I write this just afternoon. 


We have a complicated day/night of storm chasing ahead of us.  The Doppler on Wheels is currently deployed near Daybreak where we hope that the skies are dusty enough to give us a nice picture of the cold-front penetration through the Salt Lake Valley.  We are also hoping that behind the front we will eventually get some precipitation for observing some of the interactions between the Oquirrhs and the Wasatch Range, as well as fine-scale precipitation structures in the central Wasatch. 

After this evening, we still haven't figured out what the heck we're gonna do.  The model are advertising the passage of a secondary trough during the late night hours.  At 1000 UTC (3 AM MST), the trough is pushing through the Bountiful area in the 1700 UTC initialized HRRR forecast. 


We may have some orographic snow showers and possibly some lake effect as well, but the devil is in the details.  Thus, we have some consternation about where to put the DOW.  It is a mobile platform, but we can do better science if we can operate in one area for an extended period.  We'll see what happens.  I've mentioned that this is a crapshoot enough already.

Yesterday’s Storm Chasing Bounty

Yesterday's frontal passage was a bummer for skiers, providing little in the way of the white stuff in the Cottonwood Canyons, but provided us with plenty of excitement thanks to the Doppler on Wheels.

We deployed that morning to a rattlesnake speedway in the Utah desert where a dark cloud rose from the desert floor and we headed straight into the storm.  If you have no idea what that means, watch the video below. 


More accurately, we set up along the side of the causeway to Stansbury Island, just north of the Tooele Valley.  When I drove out to meet the team, the surface front had already pushed into the northern Tooele Valley, with low level "fractus clouds" seen in the photo below at levels just abouve the ground, near its leading nose.  At this time, the front was quite shallow.  


The rattlesnake speedway in the Utah desert was actually the Stansbury Island Causeway, ideal for surveying the frontal structure over the Tooele Valley and precipitation processes over the Oquirrh Mountains.  We could also can over the Stansbury Mountains (background below). 


The shallow nature of the front was very apparent in the radar data we collected.  A Doppler radar is capable of measuring how fast scatterers in the atmosphere, in this case snow and rain, are moving toward or away from the radar.  This allows us to use radar scans, known as PPIs, which are oriented at a slight angle to the horizon, to infer changes in the wind across the area and in the vertical.  In the plot below, cool colors represent flow toward the radar, warm away, with the radar in the middle of the image.  There is a clear indication of flow from the northwest near the radar and south-southwest at ranges more removed from the radar site.  Since the radar scan is tilted at a slight angle to the horizon, this is an indication of strong vertical wind shear in the frontal zone not far above the Earth's surface.  


We can also configure the DOW to scan in vertical slices, known as RHIs.  The RHI below is oriented to the east and scans over the southern Great Salt Lake, eventually hitting the lower slope of the Oquirrh Mountains near Point of the Mountain where they rise above the south lake shore.  Doppler velocities in this image are primarily away from the radar, consistent with northwesterly flow, except near the ground just to the west of Point of the Mountain.  This reflects the splitting of flow around the north end of the Oquirrh Mountains, with the flow there having perhaps a slight NNE component, which results in a weak flow component toward the radar (green).  


The DOW is also a polarimetric radar, which means it sends out and receives radar energy in two planes, one horizontal and one vertical.  The shape of the raindrops or snowflakes can be inferred using this information.  One product we use to do this is known as "differential reflectivity," with reflectivity the amount of radar energy is scattered by back to the radar.  If the horizontal and vertical radar energy is similar, the differential reflectivity is zero, and the precipitation is likely circular.  If on the other hand, the horizontal radar energy is larger, then the precipitation is wider than it is high, and the differential reflectivity is positive.  Dendritic snow, those wonderful flakes with six arms that produce blower powder, often produces high differential reflectivity, because the flakes tend to fall "flat." 

The RHI below shows two layers of high differential reflectivity (indicated by yellows).  One is near the ground and reflects the melting layer in which snowflakes are sticking together and falling relatively flat.  The other is farther aloft and likely reflects a layer in which dendrites are growing and falling.  The temperatures in this layer were likely between -12ºC and -18ºC, which favors the formation of dendrites.  


An interesting aspect of the storm was a near-complete lack of any enhancement of precipitation over the mountains.  It was a frontally forced event, rather than a mountain forced event.  In fact, it clearly precipitated more over the Tooele Valley than over the Oquirrh Mountains.  Only in the late stages of the event did the front finally decide to move over the Oquirrhs.  An example is the RHI of horizontal radar reflectivity below, taken looking east-south-east across the northern Oquirrhs.  The yellows are ground clutter from the radar energy bouncing off the Earth's surface, with the sloping area representing the western slope of the Oquirrh Mountains.  Above the ground clutter, the transition from light to dark blue reflects increasing precipitation toward the mountains, but this doesn't reflect an orographic effect, but is the frontal band as it moved into the Oquirrh Mountains.  


It's such a pity that the storm didn't produce much in the Wasatch.  However, thanks to the mobile capabilities of the DOW, we were able to go to the storm and get a wonderful dataset.  

So Much Weather, So Little Time

Looking west from the University of Utah Campus at about 7:15 AM this morning
It was a Mordor-like sunrise over the Salt Lake Valley this morning (e.g., above), simultaneously spectacular and apocalyptic.  With the overnight southerly flow, there is a decent plume of dust over the western valley (evident below the fire-lit clouds above), but clear skies to the east. 

The weather over the past 24 hours has been quite remarkable if you know where to look.  While it was quite mild across much of northern Utah during the holiday weekend, a thin lens of cold air remained over the relatively cold waters of the Great Salt Lake.  Our Hat Island observing site, for example, hasn't eclipsed 55ºF over the past five days. 

Source: MesoWest
Yesterday, that airmass made its presence known by penetrating into the northern Salt Lake Valley.  At 4 PM (2300 UTC), a sharp lake-breeze front extended across the central part of the valley with southerly flow to the south and northwesterly flow to the north.  Temperatures dropped from 70ºF in the Sandy "banana belt" to near 50 (or lower) near the Great Salt Lake.  Almost climatology! 

Source: MesoWest
The sounding from the Salt Lake City airport at about that time showed the shallow nature of the cold lens, with a surface temperature of just under 10ºC (49ºF), but temperatures of almost 17ºC at 827 mb (about 5600 feet). 

Source: SPC
Forecasters predicting a record high for the Salt Lake Airport were likely flummoxed! 

Fortunately, the south winds saved the "day", blowing the lake breeze north and causing temperatures to rise rapidly around 8 PM. 

Source: MesoWest
The transition from cold, damp lake-modified air to warmer, drier air was remarkably abrupt, and led to a high temperature for the calendar day of 69ºF.  That is the 2nd latest 69ºF temperature recorded at the airport on record (December 1st is the latest), and it happened in the dark.  In addition, a temperature of 68ºF was recorded after midnight, which sets a record high for today.   This is not your grandparents (or even parents) climate that we are living in.

Moving on to the weather this morning, we are still in the warm southerlies with some wind-borne dust over the western Salt Lake Valley.  However, cooler air remains over the Great Salt Lake with northwesterly flow developing over northwest Utah. 


The HRRR brings the surface front into the northern Salt Lake Valley at 1900 UTC (1 PM MST) this afternoon.  It will be a dry frontal passage, with the precipitation trailing the surface front. 


We will be "storm chasing" with the DOW, which we plan to deploy just south of Stansbury Island to examine the front penetrating into the Tooele Valley and across the Great Salt Lake.  Although a dry frontal passage, we're hoping there is enough dust in the air to be able to examine some fine-scale aspects of the frontal passage.  We'll then work on whatever precipitation comes through, focusing on the frontal-band interaction with the Stansbury and Oquirrh Mountains.

For skiers, this looks like a pretty pathetic event.  The models have the band fall apart as it moves in.  Snowshowers are possible, but it won't add up to much, as we discussed over the weekend.   Sad!

Update on Storm Chasing Efforts during IOP2

I like to joke that "storm chasing" Utah style involves sitting in one place and scanning storms repeatedly, which is exactly what we've been doing today for OREO IOP2.

After our overnight team returned to Salt Lake late last night, today's day team deployed to Antelope Island near the Fielding Garr Ranch.


Antelope Island is a great place to operate the DOW as there are unblocked vistas of much of the northern Wasatch and even the Salt Lake Valley.  It's a bit farther from the Cottonwoods than we like, but we can do a great deal looking at other parts of the Wasatch.

Much of the day we scanned a relatively broad frontal band.  Pretty boring by our standards, but it might still yield some interesting data.  However, during the afternoon, the flow shifted to WNW and the atmosphere destabilized, yielding some shallow convective showers. 


These showers produced a bit of graupel in downtown Salt Lake City and the Avenues (and perhapse elsewhere).


One thing we can do with the DOW is take vertical scans through storms.  The orange and yellow stuff at the bottom of the vertical scans below are ground clutter produced by mountains, but the purples are some of the convective showers, which you can see are shearing off downstream with height. 


Given a relatively pessimistic storm chasing forecast after Monday night, we'll probably work this shallow stuff to the last gasp.

Storm Chasing Update

Forget lectures and death by powerpoint.  This is what I call teaching.
Too busy to write much this morning.  We had a great night in Huntsville last night getting some very interesting data.  We are now redeploying the Doppler on Wheels to Antelope Island where we hope to get some data on today's precipitation. 

We got some great coverage last night from KUTV.  Check it out at http://kutv.com/news/local/doppler-on-wheels-helps-u-of-u-scientists-improve-weather-forecasting.

DOW7 Deployed in Huntsville for IOP1

DOW7 is now deployed in Huntsville for OREO IOP1.

The weather is perfect right now.  Radar has shown a quasi-stationary precipitation cell immediately downstream over the Wasatch crest and over our area.  For a while, it was noticeably clearer west of the Wasatch from our vantage point.

This is just the sort of thing that we're looking for and trying to better understand. Very few studies have examined lee-side precipitation processes.

OREO IOP1 Is ON!

It's great to finally have some weather again in northern Utah.  I was woken last night by strong southerly winds, and they appear to have transported in a pretty good plume of dust this morning. 

We have a team leaving the University of Utah today at noon to begin operations for the Outreach and Radar Education in Orography (OREO) Intensive Observing Period 1 (IOP1).  Every meteorological field program needs a good acronym (hence OREO) and we usually name each observing period as an "IOP."  IOP0 is typically used for a practice IOP, which we did about 10 days ago on Antelope Island.  Since then we've been waiting on weather.

We plan to operate this evening and tonight from a site just east of Huntsville to examine the spillover of precipitation across the northern Wasatch and into the Ogden Valley.   Already, there's some interesting things happening there.  Radar imagery very clearly shows echoes developing not on the windward side of the Wasatch, but downstream.  Much of this is just sprinkles or virga, but it is a hint that perhaps there is some sort of lee wave present at the moment. 


The HRRR forecast for 1Z (6 PM MST) is optimistic, with band of precipitaiton extending across central Nevada to the northern Wasatch.  The location and movement of that area of precipitation will partly dictate the success or failure of our mission tonight.  We're hoping it is in the right place at the right time. 


Tomorrow, we may be working on post-frontal snowshowers in northwesterly flow.  We have a couple of sites selected to operate out of, but will make final decisions in the morning with updated forecasts in hand.

Keep your fingers crossed!

Core Dump on Our Pending Storm

The Doppler on Wheels (DOW) has been in town now for two weeks, and we've yet to have a significant storm during that period.  At Alta, the best we've done is 4 inches on November 4th, which isn't much of a storm.  We've kept ourselves busy with various educational and outreach activities, but are in desperate need of a storm.

Fortunately, it looks like Mother Nature will give us something tomorrow afternoon through Friday.  It's been an interesting storm to follow in the forecast models for a number of reasons.

1. It's taking forever to get here.

The GFS forecast initialized at 0000 UTC 12 November (5 PM MST Saturday) showed the upper-level trough making landfall onto the Pacific Northwest coast at 1800 UTC 16 November (11 AM MST Thursday), with precipitation across the Wasatch Mountains, Uintas, and even western Colorado.  Under this scenario, we'd want to be out storm chasing early tomorrow (Thursday).


During the past three days, however, the GFS has really slowed the progression of the trough.  The forecast from 0000 UTC 15 November (5 PM MST Tuesday) has the trough much farther west and well off the coast at 1800 UTC 16 November (11 AM MST Thursday).  Precipitation is just sneaking into the northern Wasatch and Bear River Range area, and there's no precipitation over Colorado.  Instead, we'll be able to sleep in tomorrow!


2. The Sierra Nevada really take a bite out of storms

Through flow blocking and water vapor depletion in mountain-induced rain and snowfall, the Sierra Nevada have a dramatic impact for the worse on moisture transport into the Great Basin.  This can be seen in the GFS forecast pannels immediately above.  Note in particular the how the column-integrated relative humidity in the lower left panel decreases abruptly across the southern "High" Sierra, with moisture only able to sneak in across the lower northern Sierra north of Lake Tahoe.  This effect is also apparent in theNAM forecast for the same time and, in this case, it is a contributor to the delay of precipitation spreading into northern Utah.  Without the High Sierra, moisture would penetrate more easily into the Great Basin and the Wasatch would light up even earlier.  Pity.


The time-height section from the NAM shows a classic "cloud-storm" environment tomorrow over the Salt Lake Valley.  Cloud storm is a phrase we jokingly call events with high clouds and virga, but little precipitation reaching the valley floor.  There's copious moisture at mid levels, but dry environment down low.  Deep moisture doesn't penetrate into the Salt Lake Valley until Friday night.  More evidence of further delays in the storm really getting going over the Salt Lake Valley.


Add all this up — the delay in the arrival of the trough, the drying influence of the High Sierra, and the dry low levels over northern Utah — and you have a recipe for restless natives anxious for the arrival of a storm that has been promised for Thursday.

3. Many storm chasing options

We of course have a mobile radar, so we can put it wherever we want and don't have to necessarily wait in the Salt Lake Valley for weather.  That being said, it takes time to move the DOW around and configure a reasonable scanning strategy to do real science.   We have a number of possible targets through Friday afternoon, including the spillover of precipitation across the northern Wasatch Mountains and into the Ogden Valley, multi-ridge interactions between the Stansbury and Oquirrh Mountains or Oquirrh and Wasatch Mountains, a cold frontal passage presently forecast for Friday morning, and post-frontal convection in northwesterly flow in the wake of the cold front.  It's going to be a busy time!  We'll have an interesting planning session this afternoon and then will need to keep a close eye on things in the field to maximize our opportunities.

4. Mountain snow possibilities

The situation this week has been pretty grim for skiers.  Not only has it been dry, but it has also been warm.  I don't follow the snowmaking activities at the resorts, but I suspect they were limited at best.  That situation will continue today and even tomorrow looks to be pretty warm.  In addition, the early phases of the storm when it does arrive look quite warm.  For example, the NAM forecast for 1200 UTC (5 AM MST) Friday morning has 700-mb temperatures of around -2ºC.  That equates to a snow level around 7000 feet or so.


Thus, while the upper elevations of Snowbasin are likely to get a pasting, the base may see rain for at least a portion of the storm.  PCMR may also see rain at the base during the early stages.

However, the snow level will be lowering during the period, especially on Friday.  Friday has some potential to be productive in the Cottonwoods due to cold, unstable, northwesterly flow.  Overall, the NAM-12km is generating about an inch of water and 9 inches of snow at Alta Collins through late Friday.  The numbers, however, vary widely across models and ensemble members.  At this point, I'd lean toward 6-12 inches at upper elevations in Little Cottonwood, with the potential for more if the post-frontal environment is highly productive.  Water totals in the northern Wasatch should be higher.

Snowmakers had better be ready to release the torrents Friday, Friday night, and Saturday morning.  After that, ridging returns and more marginal snowmaking conditions return for a couple of days.

Addendum at 10:15 AM 15 November

The SREF plume diagram below was unavailable when I wrote this post, but I've added it here and it shows remarkable spread for the event at Alta Collins.  Talk about forecaster heartburn!  Hope for the high members to verify.