Wasatch Weather Weenies

As mentioned in prior posts, a major surge of cold air will affect a significant portion of the continental United States over the next several days.   To be sure, an impressive pool of cold air lies over Alberta this morning with many stations at or below -30˚F and a few in the -40s.  Cold air is pushing into the northern Plains already with temperatures in North Dakota already as low as -29˚F.  At least it's windy too! The large-scale setup for this cold surge involves interactions between high-latitude and midlatitude circulation features.  Last night, at 0600 UTC 29 Dec (11 PM MST Monday), an upper-level ridge was parked just north of eastern Siberia in the high latitudes with a weaker ridge in the midlatitudes over the northeast Pacific.  Over the next two days, the upper-level ridge north of eastern Siberia strengthens further into an upper-level anticyclone while the midlatitude ridge migrates eastward.  Concurrently, an upper-level trough drift...

 Beijing China is 15 hours ahead of Salt Lake City and 8 hours ahead of the Coordinated Universal Time (UTC) used widely by forecasters.  The former means that you can watch morning and early afternoon events from the next day before going to bed and the evening events from that day on delay when you get up in the morning.   The past two nights I've watched some of the training for the Men's Downhill.  There are multiple story lines here.  Let's begin with the venue, the Yanqing National Alpine Skiing Centre.  I visited it in 2018 as part of an educational meeting on Olympic weather monitoring and forecasting.  It was in the early stages of construction.  It certainly looked to have the vertical and steepness needed for a decent Olympic downhill, but prior to the building of the resort, the area was largely undeveloped.   We were told that it the resort averaged 25 inches of snow a year, but it is possible that was 25 cm (about 10 i...

With the end times near, today would be a good day to get out and enjoy the mild fall weather.  It should be sunny and warm by seasonal standards.  Tomorrow will be colder, a harbinger of things to come.   The first blow to mild fall weather comes this evening in the form of a cold front that the HRRR forecasts to be moving through Salt Lake City at around 0400 UTC (10 PM MDT).   The front will spread across Utah tonight and tomorrow, with strong northerly to northwesterly flow and colder air in its wake.   The National Weather Service forecast highs for the Salt Lake City International Airport today and tomorrow are 72˚F and 52˚F, respectively.  A bit of a breeze will make the change feel even more dramatic.  Then the weekend is "interesting."  First, we have a brushby system on Saturday.  The GFS forecast keeps most of the precipitation to our north and northeast, with just a few light valley showers and high-elevation snow s...

I don't know about you, but the anticipation for colder air and some exciting weather is high today.   And, the push of the cold front through Montana, Idaho, and Wyoming is simply fascinating.   Let's first get a quick look at where things stand at 16:30 UTC (10:30 MDT).  As indicated by the MesoWest observations below, northerly winds and the leading edge of the cold air has surged through Montana and is now pushing through north-central Wyoming, having just reached Riverton.  Further West, northerlies have surged down the Madison Valley and other valleys in southwest Montana and are just cresting the Continental Divide.  Apologies for the ugly analysis, but it gets the job done.   Basically, the shallow, leading edge of the cold air is surrounding the high terrain in and around Yellowstone, although that region will be "submerged" eventually.   MesoWest observations at 1030 MDT 7 Sep 2020 The 4-hour HRRR forecast valid at 1900 UT...

 It's hard not to get excited about the first major cold surge of the season after the blistering heat we've suffered through the last several weeks.  Mother Nature is going to make us suffer this weekend, but MAJOR change is coming by Tuesday.   The loop below shows the GFS forecast 500-mb heights (black lines) and 925-mb temperatures (colored lines) from 1200 UTC (0600 MDT) this morning through 1200 UTC (0600 MDT) Tuesday.  There are two major large-scale circulation changes that occur at upper levels.  First, the ridge from hell that has dominated our weather for so long weakens and shifts upstream.  Second, the upper-level pattern becomes much more strongly amplified, meaning that the ridges and troughs get stronger, resulting in a more wave like pattern, which by Tuesday morning features a high-amplitude ridge over the northeast Pacific and a deep trough digging into the Rocky Mountain region.  With that trough comes one hell of an airmass c...

Afternoon highs on Sunday and Monday were 49˚F and 47˚F respectively, with a stiff breeze blowing.  Under the circumstances, when it would be nice to lie outside in the warm sun to soothe the soul, this is weather fit for neither man nor beast!  If you are wondering, the average high this time of year is about 60˚F, so we are unseasonably cool. Today we'll make it to perhaps the low 50's before another we begin the transition with the next cold surge tomorrow.  The setup for this cold blast is the high amplitude upper-level pattern over the North Pacific and North America with an upper-level ridge over the Gulf of Alaska and a deep trough over central North America.  A short-wave trough (dashed brown line) that was over the Aleutians at 1200 UTC (0600 MDT) 12 April moved over the ridge and across Alaska on the 14th and will dive southward in the large-scale northerly flow today.  Preceding this trough will be mountain snow showers and a few valley r...

Here are two things that have never been observed before in Salt Lake City in October. First is yesterday afternoon's sounding, with a 700-mb (10,000 ft) temperature of -18.5˚C, more than 3˚C colder than the previous record of -15.3˚C. Source: SPC If you are wondering, temperatures aloft have already started to increase, so this morning's 700-mb temperature is -15.7˚C.  That's not as cold, but it is the 2nd lowest on record. Second is the overnight minimum temperature of 14˚F, which is the lowest temperature recorded in the month of October in Salt Lake City with records going back to 1874. As of 3:37 AM the temperature at Salt Lake City fell to 14°F. This not only sets a record low temperature for today (10/30), but is also the coldest temperature ever observed in the month of October (records back to 1874). The previous record for both was 16°F (10/30/1971). #utwx — NWS Salt Lake City (@NWSSaltLakeCity) October 30, 2019 Beyond Salt Lake, it was col...

October is the new January, at least in Salt Lake City where if you think it is cold this morning, just wait. Really, the past month has been quite cool relative to climatological norms.  The mean temperature at the Salt Lake City International Airport for September 27 through October 27 was 49.8˚F, the lowest mean for that period since 1982 and the 4th lowest on record at the Salt Lake City International Airport (records back to 1928). Source:  http://scacis.rcc-acis.org/ The reason for this cool weather has been a persistent, long-wave, upper-level pattern featuring ridging over the Gulf of Alaska and troughing over the northwest United States.  This has led to northwesterly flow over the western United States, with a series of systems dropping into our area from the northwest or north. Source: NOAA/ESRL Yesterday, steady light snow fell along the east bench in the wake of the first of two major upper-level troughs that will plunge us into a deep freeze th...