Wasatch Weather Weenies

We are now moving into mid April where any possible powder day is a blessing from the heavens.  We have potential starting tomorrow. The latest NAM shows a classic Utah spring storm scenario with an upper-level wave digging into the western U.S. and closing off over Colorado.  The latest NAM forecast for 0900 UTC (0200 MDT) tonight whows the upper-level trough extending from the BC coast to California (dashed lines, 500-mb height contours black) with a classic Intermountain cyclone centered over northern Utah and the trough extending southwestward to the high Sierra.  At this time, not much is happening precipitation wise except in far northwest Utah.  Some strong southerly winds are possible, however, during this period, and the NWS has issued a high-wind warning for portions of western Utah.  Info below.  As the upper-level trough pushes inland and the surface cyclone moves northeastward, we get into northwesterly flow and precipitation is expe...

If you visited a National Weather Bureau (now the National Weather Service) forecast office in the 1920s, you would have found a team of meteorologists, in all likelihood exclusively male, spending a great deal of time analyzing weather maps. The Weather Bureau Forecast Office, Washington D.C., 1926 (Source: http://www.photolib.noaa.gov/htmls/wea01302.htm) That didn't change through the middle of the 20th century, but since then, meteorology, like all of science, has experienced dramatic transformation.  Surface observations are now largely automated.  Remote sensing from space or using ground-based instruments like radars and wind profilers allow us to infer meteorological conditions without taking direct measurements.  Observational data is distributed and processed nearly instantaneously.  Forecasts are produced by suites of numerical models, some running as frequently as every hour.  As a result, the role of forecasters and meteorologists has ...

Humans have a difficult time grasping events that our outside their range of experience.  I learned a lesson in that yesterday.  Interested in exercise and seeing the aftermath of the remarkably warm storm on Saturday, my partner and I opted for a short, low-angle ski tour above Alta.  What we found was a remarkably stout and slick rain crust between above about 9200 feet to where we opted to quit climbing at 9500 feet. This is the type of rain crust that I recall from my youth in upstate New York.  Essentially impenetrable by skis.  In this case, it was about 1 cm thick, with the snow below that still setting up. Meanwhile, it was graupeling and at the time it was 0 to 8 cm deep, with the variability due to wind transport on the very slick surface. We opted to head back down, skiing a low angle line.  Certainly what I thought was a very low angle line.  However, as my partner descended, the graupel began to sluff.  I shouted to him ...

In many ways, yesterday was a remarkable day meteorologically, but precip totals were a bit lower than forecast by the models.  Perhaps that's a good thing. On the remarkable side, yesterday morning's sounding tied for the highest April precipitable water in the Salt Lake City upper-air period of record with 0.77 inches.  Surely we were higher than that in the late morning and early afternoon, but soundings occur at 1200 and 0000 UTC (6 AM and 6 PM MDT, although the actual launch time is a bit before then) and thus missed out peak moisture.  Sadly, there used to be a network of GPS sensors used to estimate precipitable water at high frequency (yes, you can do that with GPS), including one in Salt Lake City, but it seems to have had the plugged pulled as I can't find the data anywhere.  If anyone knows if that data is available and what the link is, please pass it along. Rain was delivered, but the precipitation band shifted southward into Utah County pretty quick...

Humid and overcast this morning, with a puddle of haze along the valley floor Saturday has dawned humid and overcast with a more Cascadian-like feel than we are used to around here.  The morning sounding from the airport showed a "juicy" environment, with near-saturated conditions through the troposphere and a precipitable water of 0.77 inches, which ties the highest observed in the record at KSLC for the month of April. Source: SPC Note in the photo above the puddle of haze along the valley floor.  As can be seen in the sounding, there is a shallow inversion present with high humidity, which leads to haze as some of that water vapor condenses on aerosols (i.e. pollution) from the valley floor. The dewpoint (blue line below) has climbed steadily over the past three days and from yesterday through this morning has hovered around 45˚F. Source: MesoWest With so much moisture around, you might be wondering why it is not raining right now (about 9 am). The answ...

My meteorological excitement factor is relatively elevated today compared to where it has been much of the winter, mainly because of expectations of a strong frontal system pushing across the western US through tomorrow. Right now we are getting just a bit of an appetizer.  The analysis below is for 1200 UTC (0600 AM) MDT and shows a weak 700-mb trough approaching Utah (brown dashed line).  With this system is a slug of moisture, valley rain showers, and upper-elevation snow showers. After the remarkably low dewpoints earlier this week, the humidity just hit me in the face and felt so good when I walked out the door this morning.  The meteogram below shows how dewpoints (blue line) have climbed from the low single digits on Tuesday to 46 this morning.  Good for the skin! It's warm, with temperatures of 34˚F at the base of Alta (8560 ft) and 36˚F at Snowbasin Middle Bowl (7402 ft).  The 8000 ft snow cam at Snowbasin shows about 1.5" of wet sn...

As we have discussed the last couple of posts, a major atmospheric river event will bring significant precipitation, primarily in the form of rain except in the highest elevations, to California tonight through Saturday, but what will happen to this system as it moves inland to Utah? All weather systems are substantially modified as they approach and move across the complex terrain of the western United States.  In the case of atmospheric rivers, their landfall frequency during the cool season (November to April) is greatest along the Pacific Northwest coast and declines as one moves southward along the California coast.  This reflects the more active storm track over the Pacific Northwest.   Source: Rutz et al. (2014) The frequency of atmospheric rivers declines precipitously, however, as one moves inland.  Protrusions of higher frequency exist over the Columbia Basin and Idaho Panhandle and the Snake River Plain.  In contrast, a minimum in atmo...