Wasatch Weather Weenies

It sure can get exciting around here when monsoon (and tropical storm remnants) can interact with a mid-latitude trough.  This morning in the Salt Lake Valley has been incredible with round after round of heavy rain and thunder.  These are not those high-based "virga storms" that we sometimes get around here, but the real deal with pretty good downpours and loud, crashing thunder.  Love it. We discussed the ingredients for today's rain in the post from a couple of days ago entitled An Unusual Moisture Pathway .  Those ingredients included the remnants of tropical storm Iselle and a front that was expected to develop over central Nevada.  Indeed these ingredients came together ahead of a deepening trough along the Pacific Northwest coast.  The front is especially apparent at 700 mb (lower left panel below) where there is temperature contrast and wind shift between southern Utah and northern Nevada and Utah.  The large-scale wind pattern is one that mete...

The last few days have brought regular afternoon and evening thunderstorms to the Salt Lake Valley.  It's worth taking a closer look at the drivers for the storms and who has gotten the rain.   On average, the 500-mb heights in August are characterized by  a ridge that is centered roughly over west Texas and a trough over or just to the west of the Pacific coast.  This pattern yields mean easterly flow at 500-mb over central Mexico which turns clockwise (cyclonically in meteorology speak) near Baja California before moving into Utah.   Source: climatereanalyzer.org The pattern above is characteristic of the so-called North American Monsoon.  This monsoonal pattern has been amplified the past several days.  As an example, below are the 500-mb height anomalies (departures from average) for today.  Positive height anomalies over the western US and Mexico are strongest over west Texas and the Mexican border area to the west, right where the ...

Monsoon thunderstorms developed over the Salt Lake Valley this afternoon and brought heavy rainfall to the northeast corner of the Salt Lake Valley, especially the University of Utah.  The event started with the development of a cell over or just downstream of the Salt Lake International Airport.  This one moved off over North Salt Lake.  Shortly therafter, two cells formed just to the south of the track of the first cell and pounded the Avenues and Avenues Foothills.   Then things got interesting as a cell exploded west of Murray and moved northeastward to the University of Utah.  This was the beginning of a series of training storms that pounded the area around the U before things settled down.  The full sequence is below.  I'm hoping the video will upload properly as I'm working with some limitations currently.   Storm total Radar precipitation estimates through 2200 UTC (1600 MDT), which does not quite capture the entire storm period...

August is off to a blistering start.  Seven out of ten days to start the month with high temperatures above 100. Six days with low temperatures 70 or above including an 81 on August 9.  The average temperature for the first 10 days of August at the Salt Lake City International Airport was 85.2°F, the second highest on record behind only 2024 (86.3°F). Relief is coming, however, due to a subtle change in the large-scale pattern.  The upper-level ridge that has been over us the past few days is weakening and sliding eastward slowly while troughing is developing along the Pacific Coast.  The GFS forecast for 0000 UTC 14 August (1800 MDT Thursday) shows the trough along the Pacific Coast (red dashed line) with a plume of elevated integrated vapor transport streaming up the lower Colorado River Valley and into Utah (red arrow).  A weak trough is also evident at 700 mb over central Nevada and far northwest Utah.   The net impact of these changes will be a de...

I wish I could say I'm glad to be back in Utah, but the aridity and dust leave much to be desired. Yesterday at around 2000 MDT strong outflow wind from convection north of Salt Lake City picked up dust and briefly caused a spike in PM25 in some areas of the Salt Lake Valley.  Below is a photo of the dust looking south from the upper Avenues at 2007 MDT. Observations from the University of Utah show a spike in PM2.5 to almost 40 ug/m3 at 2020 MDT.   Source: MesoWest There's a good chance that the exposed bed of the desiccating Great Salt Lake was a contributor to some if not most of the dust in this event.  

Spring and summer mountain thunderstorms can produce precipitation that sometimes includes graupel or small hail that can penetrate well below the freezing level.   A good example happened yesterday over the Nordkette ridge just north of Innsbruck.  I had a great view of it from my office. The storm popped up around 2 PM local time.  The streaky virga in the right of the photo below srongly suggested the presence of graupel or small hail.  A bit farther to the west (left in the photo) though was less precipitation and even a bit of sun peaking through a hole in the clouds.   After a couple of rumbles of thunder, the storm was over quickly.  Light graupel accumulations were evident where the cell was, with accumulations reaching down to about 1900 meters, whereas the high ridge farther west, which reaches over 2300 meters, was still snow free.   A web-cam on the portion of the ridge that received precipitation showed some graupel accumula...

September has been dry so far (0.15" at KSLC) but looks to go out with some rain as a weak front moves through tomorrow.  The latest GFS has precipitation over the area at 1800 UTC (1200 MDT) Tuesday.   I suspect the precipitation will be in the form of scattered showers and thunderstorms.  The operational models run by the National Weather Service struggle to properly generate such small-scale precipitation systems. The HRRR does the best and it shows the scattered nature of the precipitation at 1900 UTC (1300 MDT) tomorrow.   The experimental RRFS is a six-member ensemble run at 3-km grid spacing.  For the 24-hour period ending at 0600 UTC 1 October (0000 MDT Wednesday) it's mean precipitation over the northern Salt Lake Valley (upper right panel) is between 0.1 and .25", but there are some members that skunk us (see the minimum at lower left).  Maximum is around 0.5".   Let's hope we get some.  We can sure use it.

I thought that might get your attention.  Nothing to get excited about, but in these desperate times, we all need some optimism. It isn't much, but our HRRR snow product is putting out a skiff of snow for the High Uintas, with one spot getting 4". The time series for Kings Peak shows a hit of snow this evening and then again tomorrow afternoon and evening for a total of about 1.3".   The snow is being produce by convective storms each afternoon/evening, so who gets it and when is actualy a little uncertain.  However, if you happen to be at upper elevations, you might see a burst of snow (or graupel) if you are in one of the cells.  Our snow forecast system doesn't account for melt on the ground, so the time series of accumulated snow above never goes down.  Most likely though that the snow produced in these storms will experience some melt after they are over, especially during the day.   It is, however, a sign of things to come.

The models are advertising the slow movement of a mid-latitude trough across the western US this week.  It's not an unusually deep one, and we've had some weak troughs move through the area recently, but this is one of the better "put together" troughs we have seen in a long time.   The overnight GFS forecast has the trough approaching the California coast later this afternoon (0000 UTC 9 September with rain in the California and Orgegon Coastal Mountains.  Oh to be there for this frontal rain.  It just warms the cockles of my heart to see it! As exciting as that is to see, the trough moves very slowly across the western US and is not a strong one.  The result for us will be a few days of light-moderate southerly to southwesterly flow at mountaintop level and a bit of enhanced southerly flow for the valleys.  A few pockets of monsoon moisture might be embedded in this flow, but at least right now, hit-and-miss thunderstorms look to predominate through...

Our excruciating wait for "real rain" is almost over.  The isolated showers and thunderstorms that have largely missed many portions of the Salt Lake Valley or provided only some paltry precipitation amounts are now in the past.  Today we will see more widespread showers and thunderstorms.   This morning's 1334 UTC (0734 MDT) radar imagery shows fairly widespread precipitatio over the south arm of the Great Salt Lake and Bear River Bay, as well as showers farther south in Utah County and southeast Tooele County. This morning's sounding is "juicy" with a surface dewpoint of 56 and 1.2 inches of precipitable water, which is the depth of water you would have if you condensed out all of the water vapor in the column.  Although not exceptional, it's fairly high.  The daily record for August 26 in the sounding climatology is 1.17", although we have seen values as high as  1.66" on August 14 and 1.43" on September 3.   Source: SPC Models like the...

You know you are desperate when you get excited about the shallow cumulus that are developing over the Salt Lake Valley today,  Below is a loop showing the development of these clouds looking south from the University of Utah through about 1450 MDT.  There's even some virga!  Those clouds are developing ahead of a weak upper-level trough that is near the Pacific Coast and a weak surface boundary that is in advance of the upper-level trough near the boarder of Idaho and Nevada/Utah.  The 2119 UTC radar image shows that area is producing stronger cells than the "cumulus patheticus" that we've had over the Salt Lake Valley so far today.   Source: NCAR/RAL Moisture will, however, be on the increase through Friday.  This is not a major monsoon surge, but we will see the coverage of clouds and possibility of thunderstorms and precipitation increasing.  Let's have a look at what the Rapid Refresh Forecast System (RRFS) ensemble does over the next few day...

We had a brief interruption of weather monotony yesterday evening in northern Utah with thunderstorms in portions of northern Utah including Utah County, southern and eastern Salt Lake County, Wasatch County, Summit County as illustrated by the radar-estimated precipitation for the 6-hour period ending 0600 UTC 19 July (0000 MDT Saturday).   Source: https://mrms.nssl.noaa.gov/qvs/product_viewer/ Northern Salt Lake County, including my place, was largely skunked other than some sprinkles or light showers and gusty winds.  We did get a bit of a light show from the lightning, as well as some weakly developed mammatus and a primary and secondary rainbow.  In other news, I am enjoying a temporary office-free period as my boxes were moved from the INSCC building to the new Applied Science building late last week, but I still don't have access to the latter.  If memory serves correct, I spent 27 of my 30 years at the U in 488 INSCC.  I leave behind lots of gr...

I don't know about you, but I look forward to another rainy day or night and have started to surf through the forecasts looking for hope.   There is some potential for later this week and weekend, but subtle differences in the large-scale pattern could make a big difference. To illustrate this, I'll compare the GFS and the ECMWF (a.k.a. Euro) forecasts valid 0000 UTC 19 August (6 PM MDT Friday) and 1200 UTC 21 August (6 AM MDT Monday).  The GFS forecast for 0000 UTC 19 August (6 PM MDT Friday) shows two key large-scale circulation features: (1) ridge centered over Oklahoma and (2) a trough off the SoCal coast at 500 mb (top left panel below).  Southerly flow between these two features transports moisture from the Gulf of California region up the lower Colorado River basin and into Utah.   The tricky thing for the Salt Lake City area is that there is a sharp contrast cross northern Utah between air that originates from northern Mexico and the Gulf of Califo...

Yesterday brought another day of heavy monsoon convection to northern Utah.  The National Weather Service 24-hour precipitation analysis for the period ending at 1200 UTC 4 August (6 AM MDT Friday) shows totals in northern Utah reaching over 5 inches in the area north of Brigham City.   An observing site near Honeyville near that maximum reported a 48-hour total of 5.83".  There is some concern about the veracity of that sensor, so this will need to be verified, but other stations in that area reported over three inches.   Meanwhile a bit further south, convection moved across the southern Salt Lake Valley and northern Utah County yesterday evening.  The storms produced a remarkable amount of lightning.   Well played Mother Nature. Well played. pic.twitter.com/vyogDD4U2j — Jim Steenburgh (@ProfessorPowder) August 4, 2023 The analysis above indicates maximum accumulations of between 1.5 and 2 inches, although there is one pixel that may be abo...

What a day yesterday and what a morning this morning.   As anticipated, a very juicy airmass moved into Utah this week.  The 5-day time-series from the airport shows the gradual increase of dewpoint and decrease of temperatures from July 29th to August 1st.  Then, dewponts really jumped on the night of the 1st, reaching 65˚F and ultimately hitting 70˚F during the day yesterday.  They have remained at or above 60˚F since about midnight on the 2nd.   Yesterday, a powerful squall line moved northward through western Utah and ultimately through the Salt Lake Valley in the afternoon.  The loop below shows the system moving northward and illustrates how the National Weather Service tracks these storms and updates warnings accordingly.  Utahn's don't see this much, but a good example of how @NWSSaltLakeCity continuously tracks and updates severe thunderstorm warnings pic.twitter.com/Egjv1cjh4Y — Jim Steenburgh (@ProfessorPowder) August 2, 2023 The ...

A few people have commented to me that it feels a little "sticky" today.  Of course, that's a Utah sticky, which means quite comfortable for anyone from the southeast US.   Observations from the University of Utah show that the dewpoint climbed steadly from July 29th to today and now sits near 50˚F.  This isn't "unprecedented" this month as we've eclipsed 50 during a couple of prior periods (and even hit 50), but still it is noticeable.   Looking at just the past 24-hours shows that the dewpoint peaked this morning and has actually dropped back a bit into the upper 40s.   Nevertheless, this is the beginning of a juicy period through at least Wednesday night and possibly into Thursday.  The GFS forecast below shows a strong monsoon surge pushing into northern Utah tomorrow with enhanced vapor transport (lower right hand panel) coming up the lower Colorado River Valley and into northern Utah from the Gulf of California at 0000 UTC 2 August (6 P...

Since about May 12th, we've been locked into what I'll call the large-scale doldrums with relatively weak flow at upper levels and a lack of strong synoptic systems and fronts.  The average 500-mb height analysis for May 12 to May 27 shows the pattern that has predominated quite well with a long-wave trough over the central Pacific, ridge over western North America, and trough over the Canadian maritimes.   Image source: NOAA/PSL At the same time, the pattern over Utah and indeed a good chunk of Nevada and the Sierra Nevada has been quite active from a thunderstorm perspective.  The reason for this is the weak short-wave trough that is embedded in the long-wave ridge (indicated by the dashed line above).  Systems have moved through this trough, modulating thunderstorm coverage and intensity, but it has refused to go away.   As a result, we've seen lightning and thunder on a regular basis in the Salt Lake Valley.  Other than that, there hasn't been...

Excuse the gloating, but yesterday's thunderstorms favored for once my are with the Avenues, downtown Salt Lake, and the University of Utah coming in with the highest precipitation totals in the Salt Lake Valley.  Observations for the 24-hour period ending this morning show several sites reporting accumulations of around 0.3 inches.   Source: MesoWest Multisensor precipitation estimates of 24-hour accumulated precipitation show a band of precipitation extending from West Valley City across the Salt Lake Valley and into the Avenues Foothills.  This pattern primarily reflects three thunderstorms systems that developed and intensified in the southwesterly flow as they moved across the northern Salt Lake Valley.  The heaviest precipitation was actually in the mountains northeast of Salt Lake City.   Source: https://mrms.nssl.noaa.gov/qvs/product_viewer/ The first system moved across the northern Salt Lake Valley from about 4:30 to 5:30 PM MDT, interru...