A Vigorous Cold Front & Snow Expected Monday Night into Tuesday.

The current El Nino winter has brought plenty of precipitation to Utah. Most areas are above average on liquid water since October 1st, including the Wasatch Front Valleys. Mountain snowpack is well above 100% of average across the state. 

Mild temperatures have kept much of the valley precipitation in the liquid form, unlike last year. Snow has been hard to come by in the valleys with an active mild southern stream jet. Only 2.2" of snow has fallen at the SLC airport this month (10.7" avg month of February). As you can see, snowfall since start of the October 1st water year is running less than half of normal: 

I fully expect to end the valley snow season well below average even with above average rainfall. But, we can certainly add to our meager seasonal snow amounts at SLC! Here's a look at the jet stream forecast Monday 5pm:

You can see a cold polar jet driving a low-pressure system from the Pacific Northwest into Utah. A sub-tropical jet will be pumping moisture into Utah ahead of the cold front. This will add juice to our storm! You can see Precipitable Water will reach near 200% of average as the front approaches Monday evening:

Models remain very consistent in showing a vigorous surface front with sharp temperature gradient. Any brief rain will quickly change over to snow sometime after midnight Monday night. There is a bit of uncertainty with timing. But good agreement on a strong front as seen using the 850-700 mb thickness values-

With the milder moist air in place as the front pushes through, strong lift should produce 2-3 hours of moderate to heavy snow. We could also get some thunder as the front moves through, maybe thundersnow!! As for amounts, 2-4" of snow seems like a good early estimate for most valley locations. Slightly higher along the benches. This is a fast mover which will limit larger accumulations. 

There is some question regarding possible lake effect and if that will add to amounts through Tuesday evening. It's just too soon to know yet but watch the forecast! Be prepared for slippery road conditions for the Tuesday morning commute.

 

Another S.W. Atmospheric River this Week. A Colder Storm Possible Next Week.

Here we go again! Another El Nino driven storm is delivering copious amounts of rain and mountain snow to California.  Other parts of the interior Southwest and Rockies will benefit as well. 

Looking at the water vapor satellite image allows us to easily visualize the upper flow pattern. Strong low pressure is centered off the Northern California coast. You can see the sub-tropical moisture tap into the Southern part of the state. Many flood warnings are in effect. 

Precipitation is also spreading inland. Rain will reach the Wasatch Front this evening and snow will become heavy in the mountains.

Periods of valley rain and mountain snow will impact Utah and Colorado the next few days. Wet news is good news out West!

A check on mountain SWE (snow water equivalent) that feeds the Colorado River Basin reveals we are generally near to slightly above average across the Basin. Only SW Wyoming is lacking a bit. Green colors are near average, the blues are above and reds below. Classic El Nino pattern with below average snowpack in the Pacific Northwest. 

 

How much rain should we expect through Thursday? Here's the model blend total liquid precipitation forecast through the end of the work week:

Red colors are 2+ inches. California coastal and mountain areas could receive localized amounts over 4 inches, impressive! That's on top of rain that has fallen already. Let's zoom in on Northern Utah:

Wasatch Front Valleys favored by SW flow will get the higher rain amounts. Provo and Orem will probably receive over 1+ inches the next few days. Locations that shadow in SW flow, will see less. This means much of the Salt Lake Valley (central/south) will be more in the 1/2 to 1 inch range. 

Translating to snow for the higher mountains gives about 1-2 feet, with 3+ feet in parts of the upper CottonWoods. Check the road report before traveling in the canyons.

El Nino is typically mild given the active southern jet stream. That pattern will keep precipitation mostly in the form of rain for the valleys this week. Take a look at the temperature forecast for Salt Lake City:

Notice the dip in temperatures early next week? Well, it's still a way's out but a colder storm could bring some valley snow before heading into March. Here is the forecast upper air pattern on Tuesday the 27th:

The GFS shows a cold upper trough arriving from the Northwest. A good trajectory for most Wasatch Front Valleys. Models are not all in agreement, with the Euro showing a weaker and faster moving storm, so stay tuned! 

It's often helpful to check the ensembles, which are many "tweaked" runs of one model. In the case of GEFS, it is 30 runs plus one primary control run. Extended forecasts are simply better if you look at the average of possible outcomes. This is the latest output for Salt Lake City:

Again, this is very far out. Don't focus on exact amounts. Follow the green line which is a running 24-hour snow accumulation at the SLC airport. It shows perhaps two waves of snow, one with the front late Monday and a follow-up wave late Tuesday. This could deliver decent valley snowfall but let's not get into specific numbers yet. 

Finally, I should note that El Nino is waning and a transition to neutral conditions are expected by summer. Of interest, the CPC (Climate Prediction Center) is forecasting a good chance of La Nina conditions next fall/winter. While ENSO is a poor predictor for precipitation, I would generally expect lower snow levels next winter season across Northern Utah.

Moderating Heat & a Chance of T-Storms Across Utah

The last couple of days were the hottest so far this summer in Salt Lake City and much of Utah. The SLC airport hit 106F Sunday and 105F Monday, just below the all-time high of 107F. If you want some relief from the heat, you're in luck!

A weak front moved into Utah last night bringing slightly milder air, and a bit of moisture as well. Satellite imagery this morning shows this clearly, with the main band of limited clouds across the North Central part of the state. My friend in Broomfield, Colorado is likely waking up to sunny skies, lucky him! Here in Utah, there's a mix of mid-high clouds but some sunshine as well. 

 

So, let's talk temperatures first. The Salt Lake area can expect high temperatures about 10 degrees cooler than Monday. That's nice! Temperatures will remain moderated the next couple days until this lingering front moves on. Then, yes, a warmup! Here's the National Weather Service forecast highs for Salt Lake City into the weekend.

 

Now for the potential for showers and thunderstorms. The central and south part of the state have the highest likelihood of brief heavier thundershowers. This is due to the best dynamics along the residual front just south of the Wasatch front.

However, moisture will increase aloft across Northern Utah as well, giving a chance of dry thunderstorms initially, then perhaps some precipitation. This is a recipe for strong thunderstorm downburst winds. First off, here's the Storm Prediction Centers convective outlook for today. There's a slight to moderate risk over parts of Utah. 

The almost classic inverted-V sounding is evident on the SLC morning sounding which measures temperatures, winds, and humidity (and more) through the atmosphere in the vertical. The dew point and temperatures lines are far apart below 500 mb, which is dry. Thy are closer above 500 mb indicating more moisture. If convection (thunderstorms) deveop, precipitation falling into the dry layer will accelerate downward, resulting in a gusty wind potential. It's not a given, but a potential later today.

While dry outflow winds are likely at the start, eventually the lower levels will moisten up. Dry thunderstorms will transition to wet thunderstorms, especially over central and southern areas where moisture is deeper. The SLC National Service issued this graphic to show where some heavier rainfall could cause flash flooding. This is not a major even but still dangerous for those unaware and engaging in outdoor activities in flood prone areas. 

The shower and thunderstorm threat decreases Thursday into Friday. Hotter and dry weather likely this weekend. Current forecast information is available at Salt Lake City, UT (weather.gov)

Mini Heat Wave Across Utah, with a Transition to Cool & Wet Weather

It was a rather warm day across the state of Utah today. Sunday looks to be a repeat, then changes are on the way. Here's a round up of the high temperatures Saturday:

Records fell, including at the SLC airport. It reached near 90 in parts of the St. George area.

Before we get to the outlook, let's take a glance at where the SLC airport stands with regard to precipitation and snowfall for the water year (Oct 1st - current):

As you can see, precipitation is very close to average to date for the water year. It's hard to believe, but the very wet October and December last year really saved the season. Snowfall is roughly 5" short of the 30-year average. Now that's the valley, what's really important is snowpack or snow water equivalent (SWE) across the mountains in Utah. It determines how much our reservoirs fill for the summer.

Not good, much of the state is only 3/4 of average. That's coming off a very dry previous year and low reservoir levels. Expect worse reservoir levels this summer than last year, especially up north. It could be worse, but really we need above average snowpack to get some relief. And just for reference, Alta Ski Resort is at 352" for the year. They average 80" for the month of April, but even if they get that, they will very likely end below average for snowfall this season. 

We do have one more dry, warm day across the state, then things will begin to change. As for temperatures, here's the forecast at SLC for the week:

You can see we have cooler air on the way Tuesday, behind a front. And some rain is expected, although generally light. Here's the rainfall total projection through the next week:

Most of the rain will fall Tuesday into Wednesday, and perhaps a little next weekend. These weak systems won't be a big snow producer for the higher mountains, but several inches of fresh snow is likely at the ski areas. That's something, but not what we need. 

Beyond the week, is there hope for bigger rain/snow amounts for Utah? The Climate Prediction Center does not think there's a great chance. They are going for above average temperatures and near average precipitation in the 8-14 day outlook. Bummer, hope that changes.