Category Archives: Large-Scale Flow

Inversion Tidbits and Long-Range Prospects

Yesterday's satellite imagery summarized the ridge-dominated weather of western North America quite well with extensive fog found in the major basins, many of the valleys of British Columbia and the Northwest United States, and the Great Salt Lake Basin.  At the same time, smoke from the California Fires covered much of the offshore eastern Pacific Ocean.  If you look carefully, it appears that some of this smoke has been carried northward to the Queen Charlotte Islands.

Composite MODIS image from NASA.
Within the Salt Lake Valley, the pollution went into overdrive yesterday, with PM2.5 levels skyrocketing in the morning to unhealthy levels.  Unlike previous nights, when PM2.5 dropped considerably, levels declined only modestly overnight and remain unhealthy for sensitive groups. 

PM2.5 concentrations at Hawthorne Elementary.  Source: DAQ
Looking for a brightside?  The frosty trees make for a beautiful Christmassy scene.  


We are so desperate for weather that I feel the need to mention that there is actually a weak short-wave trough dropping down the back (eastern) side of the ridge and passing through our area Wednesday night.  


Yup, that's your weather for the week.  It will bring somewhat cooler temperatures to the mountains, perhaps helping with the snowmaking efforts and might stir the upper part of the inversion a bit.  Emphasis on might.  Low elevations will likely remained mired in pollution. 

I am a bit more optimistic that the trough on Saturday is strong enough to give us at least a partial mix out.  It's still soon to say if it will scour it all out.  Sometimes, the coldest, most polluted air at the lowest elevations can be quite stingy. 


Snowfall totals for the mountains presently look paltry.  About half the members in our downscaled NAEFS ensemble generate 2 inches or less.  A few members go for more.  A game changer is unlikely. 

The word "pattern change" is being thrown around a lot, but I bet you'll have a hard time finding anyone who can tell you what that means.  I have yet to see any indication from any ensembles that we are going to shift from the high-amplitude pattern that has dominated for weeks and in which there are very deep ridges and troughs at upper levels, to a more progressive pattern with stronger westerly flow.  Instead, there may be some shifts in the position of the ridges and troughs.  For example, some of the GEFS 10-day forecast members below have a ridge upstream of the west coast of North America, rather than near its present location along the west coast or just inland. 

Source: Penn State E-wall
Those shifts could be important if they lead to a slowly evolving but wet pattern for Utah.  However, looking at the GEFS solutions above, some might bring us some snow, others keep us dry.  Why waste time talking about this range of possibilities?  Like thermonuclear war, the best option is not to play.  


Thus, hope we get something from the trough on Saturday and at minimum hope it cracks the inversion.  It's the only slim hope we have for mountain snow over the next week.  After that, your guess is as good as mine. 

Heartbreak Ridge Tightening the Inversion Noose

Noontime smog yesterday, looking southwest from the Natural History Museum of Utah, University of Utah
Given that our last storm was winding down on Monday, I'll call today Day 4 of Heartbreak Ridge.

So far, the pollution buildup has been modest.  Because the center of the ridge has been along the Pacific Coast, we've been on the downstream side, temperatures aloft have been cool, and the inversion relatively weak and elevated.  This has enabled some vertical mixing of pollutants through a decent portion of the valley atmosphere.  As a result, the increase in pollution has been gradual and we've been fluctuating between good and moderate air quality.  

Source: Utah Division of Air Quality
However, Heartbreak Ridge is sliding eastward and the inversion is strengthening, as can be seen in the soundings from yesterday afternoon (top panel below) and this morning (bottom panel below).  


Source: University of Wyoming
Note in particular the warming in the layer between about 800 and 700 mb (6500–10000 feet), which equates to a strengthening of the "lid" over the valley atmosphere.  This morning, temperatures near the base of that layer increase about 5ºC through a depth of around 50 mb (1500 feet). 

The NAM sounding loop below (note: this is a skew-t diagram, not directly comparable to the diagrams above) shows further warming aloft over next two days, with temperatures aloft warming an additional 5ºC.  
Thus, the inversion will be strengthening and lowering through the weekend.  It appears we will be in the grips of the inversion at least through the next work week, unless a system stronger than presently advertised slides down the back side of the ridge and gives it a stir. 

Model Products Information

We have been having some problems with the server that hosts weather.utah.edu and it has been down intermittently the past two days.  Behind the scenes (and unrelated to the outages), I've been updating some of our products.  Options for the GFS now include global and regional plots from the 0.25 degree latitude-longitude grid (we've been using the old 0.5 degree grids), higher frequency (every 3-h to 240 hours), more regional sectors (e.g.,  Intermountain, Northwest, Southwest), and time-height section options that match the time period of the NAM for comparison.  Some little used plots are gone, such as the Indian Ocean sector.  




Heartbreak Ridge Provides One Blutarski of Precipitation Through Mid December

The Sunday Storm delivered at the upper end of expectations, which was great for skiers and storm chasers.  That's the good news.  The bad news is that Heartbreak Ridge is here, and maybe to stay, at least for a while.

The latest GFS dynamic tropopause (jet-stream level) forecast below ain't mobile friendly, but it tells it like it is.  A ginormous ridge is building over western North America this week, diverting the storm track into northwest Canada and Alaska.  Although that ridge eventually weakens and moves downstream, another builds behind it.


Total precipitation produced by the GFS in Utah over the next 10 days is precisely "one Blutarski."  In other words, zero-point-zero.


For those of you who don't know what a Blutarski is, watch this clip from Animal House and work harder to expand your educational horizons. 


Most medium-range ensemble members are similarly going for dry conditions over the area and nearly the entire mountain west.  Perhaps the ridge will be weaker than advertised, shift a bit westward allowing something to spill over the top, or go north enough for the southern branch of the jet to come into our area.  That's about all we can hope for.

I'm not one to extrapolate already medium-range forecasts even farther into the future.  Much can happen at long lead times.  Blocking patterns like this can be very persistent, but I'm inclined not to make forecasts for the 2nd half of December at this time. 

For Wasatch Front dwellers, now is the time to reduce driving, carpool, and take transit.  The inversion begins to develop today and the cold pool it isolates in the Salt Lake Valley and adjoining lowlands probably won't be going anywhere for a long time unless we can get some sort of dry cold front to slide down the back side of the ridge.  That's not impossible, but I wouldn't count on it.  Expect today's emissions to be tomorrow's smog.

Typhoon Lan Has It In for Utah Skiers

Typhoon Lan has been rampaging in the western Pacific, reaching a maximum intensity of category 4 on the Saffir-Simpson scale.  It made landfall early Monday morning (local time) in Japan, southwest of Tokyo.  Some spectacular photos of LAN were taken from the International Space Station.

Although half a world away, Lan will have some dramatic influences on the upper-level flow and unfortunately has it in for Utah skiers.

The image below shows the situation at 1200 UTC 21 October (0600 MDT Saturday) when LAN was still south of Japan.  Sea level pressure contours are colored (cooler colors indicate lower pressure) and 500 mb (upper-level) height contours black.  At this time, the upper-level flow over the mid-latitude north Pacific was primarily zonal, meaning from west to east, with a broad trough over the high-latitude North Pacific and Bering Sea. 


Lan struck its first blow for Utah skiers as it moved northward and across Japan.  During this period, the northward transport of tropical warmth and moisture, combined with condensational warming near and ahead of the system, built a ridge over the western pacific and perturbed the midlatitude flow, which quickly broke down across the entire Pacific basin.  At 0000 UTC 23 October (1800 MDT Sunday), a broad ridge was amplifying upstream of Utah, deflecting Pacific moisture to our north with just a few high clouds spilling across our area. 


Blow two comes as Lan undergoes extratropical transition and explosively develops as a midlaitude cyclone off the Kamchatka Peninsula.  This encourages further amplification of the large scale flow, which by 0600 UTC 24 October (0000 MDT Tuesday) features a high-amplitude trough along the entire US west coast. 


Thus, the beautiful fall weather we will experience in Utah this week comes from Russia with love.  Beware in California, however, as Diablo and Santa Ana winds are possible.

But, Lan isn't finished yet.  Although she weakens weakens, she continues to drift eastward across the Aleutians where the southward flow ahead of her can link up with that associated with a closed low further south and north of Hawaii. 


This ultimately leads to a new tap of tropical warmth and moisture that connects well into the tropics and reinforces the west coast ridge. 


Here's the whole thing in motion.


So, what does this all mean?  Well, it means we won't be seeing any significant snow around here through the end of October.  It means the start of ski season is officially on hold until November.  And it means you should get that bike tune up you've been putting off because you will be spinning instead of skinning. 

Is this unusual?  Nope.  Disruptions of the midlatitude flow by tropical cyclones are common in the fall. 

Last Half of October Looking "Ridgy"

The period from mid September to mid October was relatively cool in northern Utah, ranking as the 12th coldest on record at the Salt Lake City International Airport and the coldest since 1986. 

Source: NOAA Regional Climate Centers
The period also brought a bit of snow to the mountains, which continues to linger on shady upper-elevation slopes.

However, the pattern is shifting for the latter half of October.  Although we have a cold front moving through the area on Friday, bringing a temporary cool down for the first half of the weekend, the extended range forecasts are strongly hinting that the next 10 days or more will be dominated by ridging over our area.  Below are GEFS forecasts valid 6 AM Monday and Wednesday mornings, showing the jet either to our north on Monday, raking the area along the US-Canadian Border, and high amplitude ridging over our area on Wednesday.  

Source: Penn State e-wall 
Source: Penn State e-wall 


A strong tendency for ridging is also suggested by most members of the GEFS for late next week. 

Source: Penn State e-wall 

By and large, this is not a recipe for October skiing.  We might get a little snow with the front on Friday, and it's possible that something could "slip through the net" over the next 10 days, but by and large, these are pretty pessimistic forecasts for those looking for October turns.

On the other hand, that's not necessarily a bad thing.  Early snow often turns into weak snow (as is happening on the shady aspects where snow lingers) and if we have our druthers, a season that comes on strong in early November is preferred to one that comes in with a bit here and there in October.  The key is for this pattern to change in November, preferably early.  Let's hope that happens.  

Where Will Harvey Go?

Now Tropical Storm Harvey now holds the record for the longest time remaining a named storm (i.e., with at least tropical-storm-force winds) after landfall in Texas.   At present, it is having a significant impact not only on Texas, but also southwest Louisiana, where the brunt of Harvey's randbands are currently moving onshore.  


Harvey is currently moving slowly southeastward and back over water.  It is expected to remain offshore through Tuesday, before making another landfall, somewhere along the northeast Texas Gulf Coast.  Although some strengthening is possible, Harvey is not expected to regain hurricane status prior to landfall.  


Nevertheless, it really isn't the wind, but the precipitation and flooding, that is the main issue with Harvey, and unfortunately he's going to continue to be a problem for Texas and Louisiana for the next few days (and longer in terms of recovery). 

Beyond that, Harvey is expected to move slowly up the lower Mississippi River basin, although the cone of uncertainty for the probable storm track is quite broad.  

Now, let me annoy mobile users with a very large loop, and perhaps violate all of my principles about extended range forecasts, by showing a GFS 10-day forecast loop (click to enlarge).  In this particular forecast, the upper-level trough spawned by Harvey is caught up in the circulation of the western ridge and, remarkably, slides eastward across the US-Mexico border, eventually reaching Baja and Southern California. 


Of course, if that were to happen, the main impact of Harvey would likely be to contribute to an increase in monsoon convection and precipitation.    

It's an interesting forecast, but it needs to be noted that Harvey is moving into an area of strong deformation where potential tracks are likely to "bifurcate" into two routes, one similar to the one above, another moving eastward.  Plus, there's always great uncertainty at such time ranges.  So, at present, I share this simply as a curiosity.  

Plus, I can note that the next 10 days, other than a brief system brush by later this week, Utah will be dominated by ridging.  Maybe some monsoon moisture can sneak in here or we get a thunderstorm for cooling, but for the most part, it looks like our hot summer weather will continue into early September.  

Summer Doldrums

For a synoptic meteorologist, the weather pattern right now over Utah is about as boring as it gets.  Weak flow, slow moving large scale weather systems, and just some scattered thunderstorms about.


Throw in some smoke and it's downright depressing.

Requests for controversial topics for discussion are now being accepted!

Deep Trough to Hit Northwest Mexico and I Give Love to Park City

Yes, I know you are probably interested in the President's Day Weekend forecast, but you can get that elsewhere.  We try to look at things differently here at the Wasatch Weather Weenies.  Thus, we're going to Mexico, with a return trip to California and Utah.

Why?  An exceptionally deep upper-level trough will be impacting northwest Mexico Friday and Saturday as part of the storm system that is also sweeping across the western United States.  The GFS forecast loop below shows the band of heavy precipitation sweeping through the Mexican states of Baja California, Baja California Sur, Sonora, and Sinaloa with the 500-mb trough.


That 500-mb trough is exceptionally deep for such a low latitude.  As it sweeps over Cabo San Lucas, the 500-mb heights are lower than anything observed during this 3-week period in the Climate Forecast System Reanalysis record for 1979-2009.  Basically, the jet stream has decided its had enough of the cold mid latitudes and is dipping down and flirting with the tropics.

Prior to that, as the upper-level trough moves down the California coast, it is accompanied by a surface cyclone with unusually low sea level pressures.  The NAM forecast images below, valid at 5 PM MST this afternoon, 5 AM tomorrow morning, and 5 PM tomorrow afternoon, show the cyclone directly down the California coast.  The Santa Ynez Mountains look to get a pounding today as they are oriented perpendicular to the landfalling atmospheric river ahead of the low center.  




Utah will see warm-frontal precipitation develop late today.  If you look at the top panel above,  you will see low-level southeasterly flow.  This is a situation where Deer Valley and PCMR will likely see the most precipitation.  Brighton often does well and sometimes the Supreme area of Alta.  Lesser amounts typically as one moves westward.  Indeed, even the 12-km NAM produced a 3-h precipitation forecast for the period ending at 0600 UTC (11 PM MST) tonight that has more precipitation east of Alta (red dot) than west.


The NCAR ensemble picks up on this a bit.  Note the shift to slightly higher values from Alta-Collins (top) to Brighton (bottom, note scale change).



The change is not large, but these two locations are separated by only a couple of grid points, so that's pretty good for a model with 3-km grid spacing.  

The latest 12Z NAM is putting out about 0.35 inches of water through tomorrow morning at Alta.  I've been burned more times than I'd like to admit in these warm frontal events as they sometimes underproduce, especially during their early stages.  Thus, I'm thinking of something like 2-5 inches of snow for Alta and Snowbird and 4-8 inches for upper elevation areas along and east of the Wasatch Crest, including Deer Valley, through 8 AM tomorrow morning.  Snow levels could flirt with the base of PCMR this afternoon, but otherwise should remain at or below 7000 feet.  

So for you Park City skiers, Professor Powder gives you a little love today.  The real question is will Mother Nature?

Make America Cold Again

The weather is relatively benign across the contiguous today and ideal for voter turnout.  A high-amplitude ridge prevails over the western half of the country, with a weak upper-level trough bringing a few showers and thunderstorms to eastern Texas and the Ohio and Mississippi River Valley region this morning.


I rummaged quickly for an analysis showing the departure from average temperature forecast for today and found the one below from Intellicast.  Cartoony yes, but it gets the point across that most of the contiguous US is experiencing mild or warm weather today.  Snow will not prevent anyone from getting to the polls.  Even in Alaska, the weather doesn't look terrible by their standards (and we needn't mention Hawaii).

Source: Intellicast
I suspect that this is good news for the Democrats, who I think get a bit of a boost with high voter turnout.  Regardless of the results, skiers look forward to making America cold again.  

How to Excite Skiers with Medium Range Forecasts

Good news!  The GFS is predicting the passage of a bonafide upper-level trough and surface cold front next Thursday.  Snow is coming at last, right?


Not so fast.  It's so easy cherry pick from the medium-range forecast models and ensembles a solution that will raise the stoke.  Alternatively, I could just say that there's some hope in the forecasts for later in the month.

The more complete picture is that there is remarkable spread in the forecasts for next Thursday.  Just look at the GEFS forecast below.  You can find whatever you want in those forecasts.  The spread is HUGE.


In other words, we have no idea what the weather will be like next Thursday.  Sure, there are a few solutions that suggest the possibility of a storm, but others that show continuation of the same boring, monotonous pattern.  Endorsing either of these solutions makes little sense scientifically.

Don't be a cherry picker.  And, more importantly, don't forget to vote.