Wasatch Weather Weenies

The Sundance-Mid Mountain (SNM) MesoWest site is reporting a remarkable 24-h snow depth increase of about 15 inches with 3.56 inches of snow-water equivalent, a positively Cascadian snow density. Being an automated station, I'm wondering if these numbers are accurate, but we have seen some impressive precipitation rates at this location in the past.

Thusfar this year, the Cottonwoods have really cleaned up during most storms.  This morning, however, Mount Timpangos is getting the action.  Check out the latest radar loop, which shows an area of high radar reflectivity sitting over the Timpanogos ridge and environs. A quick look at the morning sounding from KSLC shows a shallow cold pool below 775 mb.  Above this layer, however, the flow is southwesterly to about 600 mb, which results in maximum upslope flow on the west face of Mount Timpanogos. Of course, the question that remains is why is Timpanogos lighting up compared to areas favored in southwesterly flow, such as Ben Lomond?  Something to ponder.

After a couple of days of sublime snow conditions and ideal weather, major changes are now underway that will bring much warmer and wetter weather to the Wasatch. A narrow filament of moisture, known as an atmospheric river , is being pulled from the subtropics and into California over the next couple of days, with the leftovers after passage over the Sierra Nevada and other western ranges penetrating into Utah.   The evolution of this atmospheric river is well captured by the latest SSMI/AMSRE-derived total precipitable water imagery from the Space Science and Engineering Center at the University of Wisconsin-Madison. In this loop, subtropical moisture is pulled northward just west of Hawaii where there is strong southerly and southeasterly flow between the subtropical high centered east of Hawaii and a subtropical low near the dateline (Long = -180).  This moisture curves anticyclonically (clockwise) around the subtropical high and then spreads eastward toward Ca...

There are a few days a year when the air is so clear, dry, and still that localized pockets of cold air can remain entrenched in the Wasatch anywhere the sun doesn't shine.  Today was such a day. Just have a look at some of the MesoWest observations this afternoon.  At Alta, it's 20F at the top of the Collins chair, but a frigid 8F in Collins Gulch and 12F at the base. The conditions are ideal for these cold pockets to persist through the day.  We had a calm, clear, dry night last night, so strong cold pools developed.  We are near the winter solstice, so the sun angle is very low.  Today the winds were light and the dewpoint very low, which enables the snow surface to remain very cold anywhere it is shady. Without much of a breeze to stir things up, we're just not going to mix out these cold pockets. Just to highlight how dry it is, check out the dewpoints on Mount Baldy.  They dropped below 0F at around 10 PM last night, and were near or below -20F...

A remarkable week is on tap as a series of storms will pummel the western United States and bring the warmth and wet to Utah.  Winter should persist until Friday, when the first surge of warm air and moisture moves into Utah late in the day. We will have it easy compared to California, which will be seeing heavy rain associated with two atmospheric rivers that are expected to impinge upon the Sierra Nevada the next few days.  An atmospheric river is a narrow plume of moisture that is typically connected to the subtropics or tropics and extends into the mid latitudes.  The GFS precipitable water and sea level pressure forecast for 1800 UTC 18 Dec (Saturday) produces a marvelous atmospheric river (black arrow) that extends from a region of subtropical moisture just north of Hawaii into California. 72-h GFS forecast of precipitable water (color fill) and sea level pressure valid 1800 UTC 18 Dec. The atmospheric rivers are especially dramatic if you examine the GFS ...

Only 7-8 inches last night in the Cottonwoods.  Not quite enough for a true Goldilocks day.  It will, however, freshen things up even if the porridge is a little too cold.

In the tale of Goldilocks and the Three Bears, Goldilocks shuns the porridge that is too hot, and the porridge that is too cold, for the porridge that is just right. In a Goldilocks storm, the powder is just right.  It snows enough and with the right profile of snow density for bottomless skiing, but not so much that you are wallowing in snow and cowering in the low-angle trees to avoid avalanche-prone slopes. Tonight and tomorrows storm has some potential to be a Goldilocks storm.  A cold front will pass through the area and the forecast models are suggesting a snowfall of perhaps 10-18 inches.  Further, the density of the snow should decrease with time, producing a great right-side up snowfall that is great for ski floatation. NAM Forecast for Alta-Collins and Mt. Baldy Courtesy: Trevor Alcott That should also be enough snow to bury the multitude of crusts that exist out there.  Let's hope that Goldilocks delivers.