Take the Good with the Bad…

This weekend brought a much needed refresher to the mountains of Utah.. Over the past 48 hours, Snowbird reported a total of 18″, Brighton received 13″ and PCMR racked up 8″
According to the NRCS, we’re still sitting pretty at nearly 150% of normal for snow water equivalent for this time of year..

Feb 19, 2017 SWE via NRCS
Feb 19, 2017 SWE via wcc.nrcs.usda.gov

Unfortunately these warm temperatures are not going to help maintain the snowpack, especially at low elevations.  Today’s highs were unseasonably warm for February and the worst has yet to come.  Monday’s high temperatures should climb to above freezing all the way to crest level, which will unfortunately cause melting and refreezing on the top layer of snow, further worsening the conditions.

Overnight, some convective storms could initiate thanks to some weak low to mid-level instability from the warm surface temperatures we experienced today (see 00Z KSLC Sounding below).  This combined with the moist southwest flow, could result in isolated thunderstorms in the valley and snow or graupel-type precip at higher elevations, depending on the strength of the updrafts.  I would expect maybe 1-4″ of additional frozen precip in the high elevations of the Wasatch through Monday morning.

KSLC Sounding 00Z 2/20 via spc.noaa.gov
KSLC Sounding 00Z 2/20 via spc.noaa.gov

Looking ahead, there will be a few small disturbances Monday night through Tuesday, but Wednesday is when the real cool down occurs along with our next solid chance of snow in the Wasatch.

GFS Meteogram for Alta, UT
GFS Meteogram for Alta, UT

Freezings levels will plummet back down the valley floor for the anticipated “return of winter temps”.   Along with cold temperatures, it looks like this trough will supply a moderate amount of moisture.  QPF estimates range from 1-2.5″ for the Wednesday storm, with the GFS looking the most bullish.  I wont throw out any totals just yet, but it looks like it could be a good one!

Someone Is Holding Down the Refresh Button

If we condensed all of this weekend’s snow into one day, it would be a major storm. However, we get to enjoy the snowfall of a big storm without the inconveniences of closed roads and resorts. Friday started the weekend off with 2-5″ in the mountains with more snow falling in the south. Saturday has been much the same with another 1-4″, and Sunday will bring a little more. A plot of forecast precipitation amounts is a diagonal line.

Screenshot_20170218_145027
Downscaled SREF forecast for Alta from the University of Utah Atmospheric Science Department

What do we have to thank for these conditions? Currently a branch of the jet stream is oriented almost due north-south and bringing in a lot of moisture. There’s enough water in the air that the mountains are inducing orographic snow in the southerly flow. And, even as the flow direction changes tomorrow, showers should continue in the mountains as the winds maintain their strength.

Another shot of moisture is possible Monday as another atmospheric river blasts California. However, this may or may not happen depending on where exactly the river sets up as the high Sierras could completely steal the snow. Right now I’d put it as a 65% chance of 3-6″ with the remaining 35% going toward S-1″.

gfs_6hr_precip_cw_10
The GFS is in favor of more snow Monday

Beyond Monday we are looking to another shot on Wednesday. Snowfall amounts are still uncertain, but there is more certainty that a cold air mass will invade Utah from the north. Two major global models–the GFS and the ECMWF–are showing mountaintop temperatures reaching down to -16°C. It should be cold enough for snow all the way to the valley floor, and, if things set up perfectly, the lake might even get involved. We’ll be sure to keep you posted.

Refresh

A weak shortwave trough will continue moving across Northern Utah this evening providing a few inches of fresh snow for the slopes tomorrow (Saturday) morning. Overall, this is a relatively weak disturbance in the atmosphere but with modest moisture I’m expecting 2-4 inches in most locations. We should see a break in the action tomorrow during the afternoon as a more significant shortwave digs south.

Screen Shot 2017-02-17 at 10.59.20 PM
500 mb Vorticity from GFS showing anomalous deep trough digging into Mexico

This anomalous trough is digging very far south climatologically speaking and is prompting numerous Flash Flood Watches and Warning in Southern California. While the brunt of the storm will miss us to the south/west, we’ll still reap some of the benefits with sufficient moisture and forcing in place for some mountain snow. Right now the heaviest precipitation will likely fall early Sunday morning and throughout much of the day as the trough axis passes overhead – hopefully a free refills kinda day! It also should be a right-side up snowfall beginning with denser snow and ending with lower density pow on top. In terms of totals, I think another 3-7 inches for the Northern Wasatch.

A brief break should ensue early next week before things look to get active once again. I’ll refrain from getting into details due to model uncertainty, but it looks like more snow (and we might finally get into a colder pattern with opportunities for lower density fluff).

Active pattern once again

Quick review of the last 5 days using Reynolds Peak (9000 ft) in BCC as our reference: Lots of sunshine each day since Monday with little in the way of cloud cover to keep the snowpack from baking. Temperatures fluctuated around the freezing mark for much of the week at 9000 ft, peaking above freezing each day, and appear to have not been below freezing here since Wednesday morning. While any skiing is always better than no skiing, and we all love bluebird days, it’s time for some new snow.

Temperature and Moisture (Top) and Solar Irradiance (Bottom) 5-day Traces for Reynold's Peak, BCC
Temperature and Moisture (Top) and Solar Irradiance (Bottom) 5-day Traces for Reynold’s Peak, BCC

Taking a look at the webcams, cloud cover is increasing steadily across the Wasatch in advance of the next system, and a shift to more westerly winds this evening should begin to drive ridgeline temperatures down. The dry air firmly in place should help in keeping the Wet Bulb Zero below 8000 ft for the start of the next system, allowing us to make it out of the ran well enough at most resort bases.

NAM Meteogram - Short range forecast
NAM12 Meteogram – Short range forecast for Alta, UT

The GFS and the NAM both seem to be playing to the same tune at the moment, illustrating that the first trough (tonight/tomorrow’s snow) will lift out as it progresses onshore, with accumulations limited to 4-7″ in most high elevation locations by Saturday morning. Lower elevations could be closer to 2-4″. The Cottonwoods don’t do spectacularly well on southerly flow, so I wouldn’t be surprised to see totals in the Park City area to be similar. Winds will be pretty strong Friday night along with the new snow – expect pretty notable drifting and loading at high elevations and exposed areas.

The next trough goes way south. Even so, it’s likely to keep cloud cover around Sunday, with some weak dynamical support producing periods of snow for the mountains. Another 4-8″ is possible with this system with snow levels falling as low as the benches, and with a more westerly component, favored areas (Ben Lomond, Upper Cottonwoods) could see as much as 10″. We’ll update for more accurate snow forecasts as this system comes further into the NAM’s window.

GFS Meteogram - Mid range forecast
GFS Meteogram – Mid range forecast for Alta, UT

 

Wednesday-Thursday’s system continues to look good, but now we’re talking a week out at a time of year when models typically struggle with more uncertainty than usual. Stay tuned.

-Mike

The Storm Parade Gets Closer – Bad News for CA

In keeping with Tom’s description of the parade of (modest) storms that is lining up for us…the storm parade is getting closer. Just one more day (tomorrow) of mild and dry weather before we get back in that storm action. This is awesome news for us, but very bad news for our friends in northern California…some high elevation sites there are approaching 100 inches of precipitation this winter, with 60+ inches of that locked up in the snowpack. Some sites have never (in the instrumented record) seen this much precipitation year-to-date, so we are in exceptional territory. With reservoirs ALREADY overflowing from the low-elevation rain, the spring snowmelt season may be a nightmare for them. And this coming storm sequence could bring 10+ more inches to the high elevations of NorCal. Wow. Anyway, back to Utah.

 

Screen Shot 2017-02-15 at 4.27.44 PM
Precip amounts from the GFS…expect way less than this, but the timing of the precip periods is nice to look at on these meteograms.

The details have come into focus for the 1st and 2nd storms of the parade. The first one will be a little guy…Thursday night through Friday morning…not much more than a few showers. The second one will be a little stronger and will last from Friday night through Saturday morning. This won’t exactly be a powder day, but hopefully good for freshening things up with a few inches. Unfortunately neither of these storms will be very cold, but hopefully we can squeak by without much rain at the lower resort bases.

Screen Shot 2017-02-15 at 4.30.44 PM
11,000ft temperature forecast from the GFS…fairly warm for all of our upcoming storms

Then it looks like a 3rd storm Sun/Mon, with uncertainty increasing beyond that.

Parade of Storms Incoming

Tomorrow will be the last full day of clear skies and mild temperatures before this high pressure system departs from the region.  The models are keying in on an unsettled period lasting from Thursday through at least the middle of next week.  Large uncertainty still remains with regards to the timing and strength of each system as shown in the NAEFS below.

NAEFS for upper Cottonwoods
NAEFS for upper Cottonwoods

Most models do, however, agree that each storm will be a bit stronger than the one preceding it.  The animation below from the GFS shows this nicely.

6-hr precip from GFS
6-hr precip from GFS

The GFS also shows each succeeding storm colder than the one before it.  These systems won’t be pure atmospheric rivers like we’ve been dealing with this entire winter.  The GFS produces defined cold fronts with a period of moist NW flow in the systems towards the start of next week.

Dry Weather Continues Until Thursday PM

Today was another beautiful bluebird day across Utah, with base locations warming into the upper-30s to lower-40s, while upper elevation north facing aspects remained below freezing.  A positively tilted upper level ridge will continue to build across the western  U.S. leading to clear and mostly clear skies through Thursday afternoon.  High temperatures will remain in the upper-30s to lower-40s across resort locations through Thursday afternoon.  As Alex mentioned yesterday, air quality in valley locales is forecast by the Utah DEQ (http://air.utah.gov/) to be in the moderate category Tuesday and Wednesday.

Capture
GFS 500 mb height chart for Wednesday morning

A weak storm will impact northern Utah Thursday afternoon through Friday morning.  The dynamics and moisture associated with this storm are not overly impressive; however, at least a few inches of new snowfall will be on tap.

GFSMG_ALTA2017021312F180
GFS Meteogram for the Upper Cottonwoods. Courtesy of weather.utah.edu

Long-term

Looking ahead to Saturday, Sunday, and early next week, models are pointing towards the possibility of an active pattern, with a series of storms possibly impacting Utah.  NOAA’s Climate Prediction Center is giving central and northern Utah a 60% chance of above average precipitation 6-10 days from now (Monday, Feb. 13th), implying increased odds for snowfall in the mountains during this time-frame.

610prcp.new
6-10 Day Precipitation Outlook Courtesy of NOAA’s Climate Prediction Center. http://www.cpc.noaa.gov/

Dry Weather Resumes

Today was a gorgeous bluebird day: it wasn’t too hot or too cold, and the only clouds in the sky were contrails. Bases were above melting, but the higher elevations managed to stave off 0°C. If you enjoyed today’s weather, you can look forward to a string of carbon copies this week. A high pressure system has developed over the West and will be sticking around for a few more days. There may be some occasional clouds, but otherwise conditions will be stagnant.

The great irony of Utah weather is that the “nicest” weather is often the hardest to live in. Sunny skies very often mean valley pollution, and this week is no exception. The Utah Division of Air Quality is forecasting moderate health risks Monday and Tuesday, and Wednesday should be about the same. Conditions won’t be too bad this week as the inversion season is waning. There’s no valley snow and sun angles are increasing, so the pollution will be more diluted. I went up Big Beacon for sunset today, and I could clearly see how high haze reached today. Especially up against the Oquirrhs, there is a line demarcating moist valley air from the dry air above.20170212_174006

This winter has been relentless, and nothing is changing yet. This is merely a pause before the atmospheric river onslaught resumes. The high pressure will break down Thursday with unsettled weather arriving for Friday. How strong the next batch of storms will be is unknown at this point.

Another Weekend, Another Storm

After a very warm week with above average temperatures, the snowfall and cooler temperatures have definitely been a welcome relief. Overall, most areas above 8000 feet faired quite well with Friday night’s storm. Here are some of the totals:

Brighton – 20″

Alta – 17″

PCMR – 13″

Powder Mntn – 11″

What to expect over the next week? Unfortunately, for cold weather lovers and those wanting to preserve the fresh powder from this storm temperatures will rapidly warm up over the next few days. Tomorrow (Sunday) will probably be your best bet for backcountry skiing before things really get baked on Monday/Tuesday. I guess the good news from all this warmth, however, is the lack of snow on the ground in the valley. This will help prevent really bad inversion conditions during the period of ridging this week, so at least the mild weather can be enjoyed in the mountains as well as the valleys. I won’t get into any specifics but it looks like a return to an active pattern once again by next Friday and into the weekend.

KSLC_2017021112_eps_precip_240
ECMWF operational and ensembles for the next 10 days

 

Welcome back, winter.

Good riddance to the warmth… Most locations saw the maximum temperature for today at midnight with temperatures falling steadily as colder air begins to move in at all levels.

As of 3PM, S-Turns in Big Cottonwood and White Pine in Big Cottonwood have wet bulb temperatures around 40F and falling slowly, with Snowbasin checking in a hair cooler with a wet bulb around 34F. It’s likely these won’t change much for the first half of the night, the result being that snow levels won’t fall much below 8000 ft until morning.

NAM 12km Meteogram
NAM 12km Meteogram – Big shift in forecast wind direction this evening marking the passage of the frontal boundary – with the column drying out quickly Sat AM

With the NAM producing 1″ storm total water at Alta and temperatures falling slowly tonight at first, we should expect around 6-12″ of snow for the upper Cottonwoods, bonding well to the existing snowpack and upright. Park City area should fare similarly in liquid equivalent, but elevation is going to put a damper on the fun at first – expect about 5-8″ all said and done at most elevations, perhaps closer to 6-10″ at the ridgelines. Models pull in a little more water up north – Ogden and Logan resorts will fare quite well at upper elevations, in the 10-16″ range, with lower elevations closer to 4-8″ once we get a changeover to snow. Using the NCAR Ensemble for timing, it seems the heaviest precip rates will occur starting in the early evening today (Friday) through early morning hours Saturday, tapering off pretty quickly mid-morning.

The key piece here is the snow will fall on light sustained winds (gusts are still forecast to push the 30-40mph range at times) – this should keep scouring and drifting to a minimum, allowing most surfaces to see a nice repair from this cycle. It’s a step in the right direction, anyway.

Ridging returns for a few days, with the chance for another active (and warm-ish…) cycle on the doorstep around the 17th of the month.