A Wild Weather Week Ahead

Wasatch weather nerds and snow junkies rejoice! The latest forecasts appear to all but promise a prolonged period of unsettled weather across Northern Utah.

What’s Coming At You Tonight:

As Trey mentioned, the cold stretch we are experiencing is due to the deep, long-wave trough that is currently draped across the Western half of the country.  Upstream of the parent long-wave, resides a “kicker” trough over the PNW.  This short-wave will dive into the intermountain west this evening.  The result will be brutal cold (-18 C at 700 mb!) and limited moisture (~0.1-0.15″ SWE) for northern Utah.  The wildcard for this system will be, you guessed it, the lake-effect component.  Lake-700 mb temperature differences will be in excess of 20-22 degrees Celsius into the early morning hours.  The favorable temperature difference, low-level convergence over the lake and moderate winds aloft could result in lake effect for some places.  This is highly dependent on the 700 mb steering flow direction. If the flow is predominately northwesterly, the Cottonwoods will benefit.  If the flow veers to a more northerly direction, then the Oquirrhs will be in the line of fire.

700 mb Relative Humidity and streamlines.  Image: Pivotal Weather
GFS 700 mb Relative Humidity and streamlines.  Image: Pivotal Weather

All things considered, I will forecast 2-5″ for the higher elevations, with the Cottonwoods falling on the upper end of the scale if lake effect prevails.

 

Down the Pipeline:

After dropping to seasonal lows, temperatures will rebound nicely.  By Thursday evening, the Intermountain West will start to feel the effects of a plume of tropical moisture known as an atmospheric river.  Due to its tropical origins, the snow levels in this relatively warm event will struggle to reach the valley floor.

PWAT Anomaly. Valid 12 Z Friday.  Image: Pivotal Weather
PWAT Anomaly. Valid 12 Z Friday. Image: Pivotal Weather

Above 7000′, the precipitation will be falling as snow, and there should be a lot of it.  Heavy, wet, base-building snow.  Its a little early to throw out exact totals, but the NAEFS Ensemble mean is throwing out QPF totals upwards of 3″ through the weekend.

Midway through next week (8-10 days out), there appears to be another “atmospheric river” type event that could have implications for our area.  Just for fun, here’s the 10 day accumulated snow totals produced by the GFS (Note the ECMWF produces about half this accumulated snow):

GFS 240 hr total accumulated snowfall.  Image: WeatherBell
GFS 240 hr total accumulated snowfall. Image: WeatherBell

Nearly 100″ produced out in GFS model fantasy land!!! Realistic? Probably not.. Fun to think about? ABSOLUTELY.

ALL ABOARD THE HYPE TRAIN

Hype train featuring Reed Timmer and infamous OK Met Mike Morgan.   No idea who to credit with this masterpiece.
Hype train featuring Reed Timmer and infamous OK Met Mike Morgan.
No idea who to credit with this masterpiece.

Active Pattern Continues

The colder temperatures we’re seeing today are thanks in large part to a longwave trough situated across the Western U.S. Meanwhile, another reinforcing shortwave trough diving down from the Pacific NW will help bring the coldest air of the season for tomorrow into Wednesday. Temperatures at 700 mb (near ridge top height) are forecast to bottom out around -19C (or below 0 on the Fahrenheit scale)! If you’re headed up to the resorts mid-week it’ll be brutally cold. In terms of snowfall potential this storm has favorable dynamics but is limited in terms of moisture with the midlevels quickly drying after frontal passage (red circle shown below). Overall, I’m expecting 2-6 inches with the Northern Wasatch and Park City falling on the lower end of the range, higher amounts in the Cottonwoods.

screen-shot-2016-12-05-at-9-47-03-pm

There does appear to be a window for potential lake effect snow early on Wednesday morning. With very cold mid-upper level temperatures creating an unstable environment favorable for lake effect, the potential will likely hinge upon residual low-level moisture/relative humidity behind the front. If you believe the NAM and GFS the low-levels moisten sufficiently for a 6-12 hour window Wednesday AM (After 6z). Flow does look more NNW’ly than NW’ly meaning if any lake effect does develop it would go towards the Oquirrhs. Overall I’m not very impressed by the potential, but we’ll need to wait until tomorrow to have a better idea of the mesoscale details.

After this brief cold blast, we’ll quickly “warm up” on Thursday & Friday. This is when things may get exciting. A strong upper level jet will slam into the West Coast of the U.S. with a fetch of deep moisture from the sub-tropical Pacific – also commonly referred to as an atmospheric river. Shown below are Precipitable Water anomalies with the cooler colors (blues) depicting a column averaged airmass that’s far moister than normal. You can see this fetch is aimed right at Utah (if you believe the GFS model depiction). While temperatures will be on the warmer side, this would be optimal base building snow.

screen-shot-2016-12-05-at-10-01-05-pm

One potential inhibitor that has me slightly skeptical of the GFS’s high totals for the Wasatch is the presence of the Sierras. The black box I drew is a rough sketch showing where some of the highest portions of the Sierras (10,000 feet+) are located. Often as this moist air slams into the Sierras, they get dumped on, but it also depletes the moisture leaving the Wasatch with only the leftovers. A more favorable orientation tends to be farther from the SW or WNW.

naefspl_cln2016120512f168

Nonetheless, the GFS, GEFS, and European Ensembles are all pretty gung ho with the European operational model the least bullish. This storm certainly has the long duration aspect going for it and also appears to have the moisture. Because a small deviation in the jet pattern could really change things in a setup like this I’ll wait until tomorrow before getting completely stoked, but I’m definitely starting to get excited. If current model guidance holds, expect forecasts for FEET of snow through next weekend.

 

Where’d I Leave My Down Jacket…? Brrr!

The shape of things to come: The coldest air of the season so far will advance into the region this week. The first drop in temperatures and a round of precipitation will be associated with the passage of a cold front from the northwest in the early morning hours on Monday. Temperatures will rise slightly before the second drop in temperatures associated with the passage of another cold front on Tuesday night. This front ushers in a much colder, drier air mass, nearing -20C at 700 hPa, and so precipitation associated with this front will be very limited. Towards the weekend temperatures will warm to more seasonable temperatures with the chance of some significant precipitation in the Friday-Sunday window. There’s a lot of uncertainty with this one, so we’ll keep our eyes on the short range for now and wait for the models to hash this one out as it develops.

The GFS meteogram for Salt Lake City provides an overview of what to expect: Falling temperatures Sunday night, falling further on Tuesday night, and the general magnitude of precipitation. Note the pattern remains fairly active throughout the model forecast period.
The GFS meteogram for Salt Lake City provides an overview of what to expect: Falling temperatures Sunday night, falling further on Tuesday night, and the general magnitude of precipitation. Note the pattern remains fairly active throughout the model forecast period.

Nitty-gritty details: Plumes are great, but sometimes misleading or confusing, and Monday’s precipitation forecast is a perfect example of such a case. Currently, depending on which product you cherry pick from, we’re seeing liquid totals anywhere from 0.1 to 1.0.” Taking a closer look, the column begins to saturate as early as late afternoon in some ensemble members. As winds pick up from the southwest ahead of the cold front tonight, orographics could kick in and spin up the snow machine pretty early on, with dynamical support kicking in early Monday, with the greatest precipitation rates likely in the early evening. Mid-levels dry out late in the evening, bringing an end to significant snowfall, but light and intermittent snow showers are likely to continue high in the Wasatch. I think it’s fair to expect 2-5” by Monday night for the Northern Wasatch and Park City area, and 4-7″ for the Upper Cottonwoods. Snow showers could bump these totals a little higher for the Cottonwoods.

Tuesday night’s frontal passage has some moisture to work with, and there’s indicators for post-frontal instability. There will be a limited window before winds come fully around to the northwest and the column dries out for snowfall to fire. Currently 2-5” is a pretty reasonable estimate across the Wasatch.

GFS Time-Height for Alta, indicating the next three frontal passages and column RH, instability associated with them.

The system moving in for Friday-Sunday comes in on westerly flow, with the potential to put down some significant snowfall. The trouble with this event is a slight shift in the jet stream to the north or south will either boost or completely erase much of the forcing. I won’t put any graphics or numbers attached to this one out there yet as not to mislead anyone. We’ll keep you up to date as things become clearer!

GFS Jet-Level Winds for next weekend's potential storm system. The position of the jet will be critical to the forecast.
GFS Jet-Level Winds for next weekend’s potential storm system. The position of the jet will be critical to the forecast.

In all, cold, dry, soft turns should be the theme of the coming week as the little shots of snow keep the skiing in top shape.

A little snow Mon, a little snow Tues…a lot of snow late week?

I went skiing up at Snowbird today, and the snow quality was fantastic. Our huge dump of low-density snow last week and subsequent chilly temperatures have kept things nice and chalky. I guess Alta was skiing pretty well too:

This will change a little bit tomorrow, as many resort base areas will creep  slightly above freezing, but I would imagine the snow in most areas will remain in pretty good shape. Tomorrow will be the warmest day we’ve seen in a while, but it won’t last. Clouds will be present through the day, and they will begin to thicken in the afternoon as our next storm approaches.

I am expecting a weak storm to affect us early Monday morning and be out of the area by Monday afternoon. Then late Mon night/early Tues morning, another weak storm will scoot through, exiting Tues night. These two storms will be VERY cold. As Tom said, Wednesday morning will potentially see temperatures in the double digits below zero! Keep an eye on the MesoWest weather station in the Peter Sinks in northern Utah…if the model solutions verify, this site could dip below -30 Fahrenheit. Snowfall from this period will be modest…typically storms this cold have a hard time producing large totals, as cold air cannot “hold” as much water vapor. The snow will be quite low-density though, so even a small amount of liquid will yield a lot of snow. So these storms have that working in their favor at least. I would expect 3-6″ in most locations from the Monday morning storm, with 4-8″ possible in the Cottonwoods. For the Tuesday morning storm I will call for the same amounts at this point…we’ll see how that storm is looking tomorrow and potentially adjust.

 

screen-shot-2016-12-03-at-6-13-33-pm

Then Thurs night/Fri morning, a completely different pattern looks to be shaping up. Potentially very wet, windy, and warm. That’s all I can say for now…as the details will begin to become more certain in the coming days we’ll fill you in.

Storm Early Next Week

This weekend will feature comfortable early season conditions across the entire state.  It’ll generally be partly cloudy throughout the weekend with temperatures moderating to near freezing at the bases by Sunday.  With last weeks huge dump of snow, all resorts are now open with ample terrain.

As we head into early next week, we’re expecting a period of very cold, unsettled weather.  A trough is expected to cross through the region Sunday night and into Monday, followed by a weak shortwave trough.  This storm has been trending drier with time, but a lot of uncertainty exists.  The NAEFS is still forecasting a spread of 5-30 inches for the Upper Cottonwoods.    

The cold may end up being the story of this storm.  Below are the forecasted low temperatures for Wednesday.  We expect it to be well below zero up in the mountains.

Beyond this system early next week, the models continue to show a stormy, unsettled pattern.  Let’s hope another one of these systems goes big !

Coldest Storm of the Season Could Arrive Monday

Mountain areas have seen light snow showers this morning just in time for opening day at Powder Mountain and Snowbasin.  Alta and Solitude will open tomorrow, with Deer Valley opening on Saturday. Snow showers will continue through the early evening before the storm exits our area.  Snowfall accumulations will be on the low side with 1-3″ for most locations, with a few spots picking up 2-5″.

mtspcam
Dec. 1st 10:08 am Mount Superior Mountain Cam. Courtesy of alta.com

State of the Snowpack

The active storm track has allowed for many sites to catch up to near-normal snowpack conditions for this time of the year.  The northern mountains of Utah are still below average, but an active storm track should continue to bring relief to areas below average.

screen-shot-2016-12-01-at-10-33-59-am
Dec. 1st Utah Basin Averaged Snow Water Equivalent (SWE). Courtesy of www.wcc.nrcs.usda.gov.

 

Next Storm is on the Horizon

High pressure will build across Utah Saturday and Sunday ahead of the next storm system expected to arrive Monday.  A long wave trough will drop southward out of the Gulf of Alaska Sunday morning before moving into northern Utah Monday afternoon.  This system will likely bring the coldest temperatures of the season this far, but precipitation amounts in the Wasatch remain uncertain at this point in time.  Below is an image of the GFS Ensemble for Monday evening.  The GFS and CMC ensembles have trended further north and east with the storm track while the European model keeps the storm further south and west.  A storm track further south and west would favor higher snowfall amounts in the Wasatch, while a solution further north and east would result in less snowfall across the mountains.

gefs_z500_noram_19
Monday, Dec. 5th GFS Ensemble 500 mb chart. Courtesy of models.weatherbell.com

 

Due to the uncertainty in the storm track, there is considerable uncertainty in modeled snowfall amounts.  The mountains could see anywhere from 5-25″ with Monday’s system.  For now keep expectations low, but hope for the best!

 

 

Progressive and Cold

Despite what you may have thought from the title, this is not a post about the current political state of our country 😉  Rather, this is the atmospheric pattern we are experiencing.  A much different sentiment, but using the same adjectives.

As Alex mentioned in his post, the Wasatch front has seen some impressive snowfall totals the past few days. Bountiful bench finished with 15″, while Snowbird reported 44″ and PCMR saw 35″. Not a bad way to start the ’16/’17 season.

Wasatch Front Snowfall Totals, valid Tuesday 6 am. wrh.noaa.gov
Wasatch Front Snowfall Totals, valid Tuesday 6 am.    Image: wrh.noaa.gov

Short Term:

Over the next 24 hours, the Wasatch Front will see yet another, albeit quick, shot of snow.  Today, highs are forecasted to reach 35 degrees in the valley before bottoming out to a low of 28 on the first morning of December.

18 Z HRRR: KSLC Meteogram. Image: models.weatherbell.com
18 Z HRRR: KSLC Meteogram.     Image: models.weatherbell.com

Temperatures at crest level (700 mb) will hover between -10 and -12 C through Friday morning, putting us just inside that sweet spot known as the dendritic growth zone.  When these temperatures, optimal for crystal formation, are collocated with a vertical velocities maxima, we see enhanced growth of dendrites.  This is seen in the GFS forecast sounding and 700 mb vertical velocity for 18 Z on Thursday (noon).

Left: GFS point sounding for area max vertical velocity denoted by blue arrow. Right: Simulated vertical velocities at 700 mb. Both images valid Thursday 18 Z. Images: weather.cod.edu
Left: GFS point sounding for area max vertical velocity denoted by blue arrow. Right: Simulated vertical velocities at 700 mb. Both images valid Thursday 18 Z.
Images: weather.cod.edu

Timing:
A weak surface front will move across the area tomorrow mid-day.  Behind the front there will be moist west-northwesterly flow.  Throughout the duration of the event I would suspect the Cottonwood canyons will pick up 3-6″ of fresh snow with 2-4″ in other locations such as PCMR, Pow Mow, etc.

 

Long Range:

The Rossby wave pattern in the Pacific looks promising for continuing this progressive, trough-y, period we are currently loving.  We have seen enhanced cyclogenesis off the Kamchatka Peninsula, helping the shortwave troughs to march across the Pacific ocean.

GFS 500 mb heights valid Tuesday Dec 6, 06 Z. Image: models.weatherbell.com
GFS 500 mb heights valid Tuesday Dec 6, 06 Z.       Image: models.weatherbell.com

The above GFS image is valid for next Tuesday, which is coincidentally the next forecasted big snowfall.  As my synoptic professor back in Oklahoma always said, never underestimate the power of the downstream (or upstream for that matter) ridge.  In this case, it could not be more true.  The trough that will be bringing the impending dump is flanked by two ridges, which are enhancing the trough’s wavelength and intensity.

GFS 500 mb valid 12/6/16 6 Z. Downstream view.
GFS 500 mb valid 12/6/16 6 Z.   CONUS downstream view.

This intense trough will bring frigid temperatures from crest level, all the way down to the valley floor.  Notice the 540 dm line is plunging all the way down to Southern California and NW Arizona.  Early indications show -20 C temperatures at 700 mb.

Should be an interesting week.. Check back everyday for an updated forecast!

Weekend Roundup

What a way to start off the season. After two days of on-and-off (mostly on) snow, ski resorts in the Cottonwoods saw upwards of three and a half feet! The big winner was Eagle Point down in Beaver with a reported 54″ of snow. They had the benefit of being far enough south to do well with the Sunday storm and far enough north to pick up on the action Monday.

After this dumping, I wondered if we’ve started to make up on our deficit for the season. Looking at Snotel data, snow water equivalents in Utah are looking much healthier with sites in the high Wasatch being 80-100% of normal. Much of this storm was localized to Utah, so places to our north are still in the red.

screenshot_20161129_222334

Even though we can no longer complain about having no snow, we are still watching for every flake Mother Nature sends our way. Our next shot comes Thursday (only two days!) as undulations in the offshore ridge Mike mentioned yesterday sends a storm inland. The new, experimental, NAM 3KM model forecasts a band of snowfall moving through the Wasatch midday with possible lake nonsense that evening.

NAM 3KM courtesy WeatherBell
NAM 3KM courtesy WeatherBell

Right now we’re looking at 2-5″ in the mountains–no blockbuster but still fun. Beyond that, there is no bad news in sight. The pattern remains progressive, and there’s a possibility for another storm at the end of the next weekend.

Continuing to Produce…

Hopefully everyone’s been out enjoying what they can of this most recent storm system. Not only has it been snowing hard up in the mountains, the Salt Lake valley has gotten quite the treat as well, especially with some heavy lake effect cells this afternoon!

Snowing hard on the East Bench! 2-4PM MST 11/28
Snowing hard on the East Bench! 2-4PM MST 11/28

The short and sweet of what’s to come: Early evening is likely to see continued heavy precipitation in the mountains associated with one last shortwave moving through, until the flow shifts more northerly and our deep moist layer thins out at mid levels. A narrow but highly amplified ridge builds in at upper levels to our west, forcing the trough out of the region and bringing a break in the precipitation for late Tuesday afternoon through Wednesday. This should make for a beautiful non-storm day of skiing! The ridge will then begin to flatten, with models suggesting a weak disturbance moving through overnight into Thursday.

NAM12 Time-height for SLC, note drying at mid-levels through Wednesday with lingering low-level moisture.
NAM12 Time-height for SLC, note drying at mid-levels through Wednesday with lingering low-level moisture.

The Nitty Gritty: One last shortwave will provide the synoptic scale forcing for precipitation to continue, while localized instability and orographics will allow the mountains to squeeze the last bit of moisture out of the low-levels as mid-levels begin to dry. Lake effect will likely continue to fire overnight, but much to our dismay, as winds come around to the north, much of this snow will fall in the western Salt Lake and Tooele valleys. Much lighter snow showers will continue for the upper Cottonwoods, Northern Wasatch, and Park City areas through Tuesday morning, tapering off throughout the day. It would be reasonable to expect another 8-14” with the higher end of the scale in the Cottonwoods, lower end of the scale in the Northern Wasatch and Park City. This will bring snow totals across the Wasatch up to and well over 3 FEET since Sunday.

Ridging pays a visit...
Ridging pays a visit Wednesday making for a pleasant ski day…
...but soon enough we're back in business.
…but by Thursday we’re back in business.

At first look, the ridge building in over the west coast of North America seems concerning, but each of the forecast models continue to punctuate it with weak disturbances. While there’s no major storm in the near-term forecast, Wednesday night into Thursday should bring a few additional inches of snow along a weak front to freshen things up before the weekend. Models disagree slightly on the timing of the storm, though the trend has been towards snowfall starting later Wednesday night and carrying into Thursday. While it’s too early to narrow down the range, most ensemble members suggest on the order of 2-6” of snow across the Wasatch. The deterministic GFS, always overzealous, suggests the possibility of totals in the 6-10” range, but we’ll just have to wait and see how the models develop this system over the next 48 hours.

Welcome to Nuketown

We are in the midst of a beautiful, classic Wasatch storm cycle. From last night through 6pm this evening (Sunday), our resorts picked up anywhere from 7 to 16 inches of new snow, and much more is on the way.  BIG SNOW will fall Monday morning through Tuesday morning.

 

The deep through of low pressure that brought us our snow last night and today continues to sit over the Mountain West. The trough is situated such that we are getting a nice tap of Pacific moisture and a nice tap of Arctic air…perfect ingredients for lots of cold, dry snow:

 

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The 500mb pattern at 5am Monday, Nov 28th. Note the flow out of the Northwest stretching all the way from Alaska.

The lift, moisture, and cold air associated with this trough will keep the snowfall going over us for the next 2 days, and with each disturbance that moves through that trough, the snowfall rates crank up. Tonight we are between disturbances, so our snowfall rates will slow down a bit, but it will still keep piling up. The next disturbance comes in tomorrow (Monday) morning, and that’s when the real action starts. Snowfall rates will crank up bigtime, with periods of 2″ per hour (or more) snowfall possible. These will be beautiful, fluffy, low-density flakes and will pile up fast. The heaviest snowfall will be from morning through evening on Monday, and then the snowfall will gradually slowdown through the day on Tuesday. The storm should be over by Tuesday night.

This storm won’t be dropping a ton of liquid (1-2″), but with the potential for 20:1 snow-to-liquid ratios, this will be an absolute dump. I’m gonna go for 18-36″ of new snow for the Cottonwoods and the Northern Wasatch. Expect more like 12-24″ for the Park City side.