Monday, September 9, 2019

Signs of Fall (and Winter)

The times they are a changin', with the transition from summer to winter now clearly underway.

We're finally starting to get a tease from the mid-latitude storm track here in Utah.  The loop below shows yesterday's trough passage, as well as a deeper trough expected to affect our weather this week.

Yesterday's trough, and associated showers and thunderstorms, yielded a high for the day of only 79˚F.  We haven't had a day with a high that low since June 22nd, so it was well deserved.

The trough anticipated this week will be eventful in a few ways.  First, in advance of the trough, we will see increasing temperatures and southerly flow on Tuesday, which will likely complicate efforts to contain wildfires in central Utah.

The trough itself and associated surface cold front and precipitation band is currently forecast to push into northern Utah Tuesday night. Although it is coming in at night, with some monsoon moisture and instability to play with, it could bring in some thunderstorms in addition to rain.

Behind the trough, 700-hPa (about 10,000 ft above sea level) temperatures are currently forecast to drop to as low as 0–1˚C on Wednesday, sufficiently cold for snow at upper elevations if precipitation occurs.

Critical for the snowfall forecast in this case is how much precipitation we get once temperatures have dropped to below about 1˚C.  Currently, our downscaled SREF guidance has 5 out of 26 members generating > 1 inch of snow, with a maximum of 5 inches, at Alta Collins near 9500 feet.

Other members produce nothing, due either to slightly higher temperatures or a lack of precipitation.  Overall, if one looks like 15 to 25% of SREF members produce snow in the upper elevations of the Wasatch and the Uintas.

Thus, do not be surprised to see some white on the higher peaks by late Wednesday, although accumulations are likely to be limited.  Nevertheless, keep an eye on forecasts if you are planning high elevation adventures such as a backpack trip this week.

Moving across the pond, winter made an appearance in the Alps over the weekend as a short-wave trough dug from the North Atlantic into central Europe, bringing with it cold air to lower snow levels to mid elevations.

Some of the more impressive scenes were in northeast Italy.

Stubai Gletscher opens for the season this coming Friday, 13 September.  My pass is still good!


  1. Interesting scenario for early tomorrow (Tuesday) morning. Some models show a strong low level moisture surge from the Gulf of California up into Utah now through tonight, with potentially high CAPE values and good shear profile at SLC by 12Z or so. Might start off the morning with a strong storm or two.

  2. Is it time for your winter predictions post yet?