Wasatch Weather Weenies

It looks like an active Labor Day weekend (not to mention tomorrow) in the weather department.  The models are advertising a potent monsoon surge similar to the two previous big ones we've had so far this summer.   The GFS forecast below for 0000 UTC 2 September (6 PM MDT Friday) shows an upper-level trough over northern California and an upper-level ridge over Kansas. Between these two systems is southerly flow and northward vapor transport at all levels with moisture streaming into Utah from the subtropics and Gulf of California.   Bottom line is expect showers and thunderstorms beginning tomorrow and through the Labor Day weekend.  I'll add that the models are also forecasting that the west-coast trough will become mobile over the weekend and move through Utah late Sunday and Sunday night, which could yield a frontal passage and an especially active period of thunderstorms and rain.   It's been a wet water year (October – September), so it seem...

You may have seen some guesses about what will happen this coming ski season.  Such predictions are often issued with great fanfare and overconfidence.  I'll pick on AccuWeather here because they are an easy target.  The outlook they issued in late September 2022 included the following. "Unfortunately, we have bad news as far as the drought goes in parts of California, Nevada and the Southwest," Pastelok said. "The main storm track will be even farther north than it was the first half of the winter season last year including the late fall." Then there was the accompanying snow outlook.  What a spectacular crash and burn! The reality is that these seasonal forecasts, based largely on the loading of the dice due to the anticipated presence of El Nino or La Nina, have somewhat limited practical utility for most applications.  If you didn't have any knowledge of meteorology, you might expect there to be a 33% chance of below average, 33% chance of near average,...

Yesterday Deer Valley dropped one of the biggest stories in Utah ski history, announcing plans to add 16 new chairlifts, 3700 acres of terrain, and 135 ski runs in an area including, around, and above the nascent Mayflower resort.  This includes terrain south of the current Jordanelle Gondola and below the Sultan and Mayflower lifts, above the developing Mayflower resort (labeled "new base area" below), and the ridge that extends southward from Bald Mountain toward Heber Valley, including Park Benchmark Peak (9384 ft).   That is an enormous expansion, but this is a blog about mountain meteorology and snow snobbery, so lets take a look at the meteorology.   For my book Secrets of the Greatest Snow on Earth , I produced an analysis of mean annual snowfall in the Wasatch Range.  It illustrates what, in the 1930s, meteorologist S. D. Green called the natural advantages of the Cottonwood Canyons.  Snowfall in the high terrain around the Cottonwoods, especia...

As anticipated, Hilary brought quite the deluge to SoCal and Southern Nevada.  Below are non-quality-controlled gauge reports to MesoWest for the 3-day period ending this morning (there are a few erroneous observations plotted if you look).  Widespread reports of more than 2 inches in the LA Basin, 5 inches in portions of the San Gabriel Mountains, more than 5 inches in the southeastern end of the Sierra Nevada, 3 inches in the Amargosa Valley, and 5 inches in the Spring Mountains.   A few reports that caught my eye include: Mt. San Jacinto with 11.75" .  What an unbelievable forecast by the HRRR model discussed in an earlier post. Palm Springs Regional Airport with 3.23" . The mean annual is about 5.5 and comparison with Mt. San Jacinto to the immediate west illustrates remarkable orographic enhnancement.  Hunter Mountain with 5.89" .  This site is in the mountain forming the northern end of the Panamint Valley just west of Death Valley.  Despite...

It's just after noon on Saturday with a very eventful 60 hours or so on tap for SoCal, Nevada, and possibly portions of adjoining states due to one of the more significant tropical cyclone events in recent memory for the southwest US.   According to the latest (12 PM MDT Saturday August 19), Hurricane Hilary is currently a category 3 hurricane with 115 mph winds.  Satellite imagery showed the circulation center of Hilary just west of the southern tip of Baja California with high clouds extending northward across Baja, SoCal, Nevada, and even northern Utah.   Source: College of DuPage Beneath those high clouds is a predecessor monsoon surge that is working its way up the lower Colorado River Valley and environs.  Radar imagery at 1200 MDT (1800 UTC) Saturday showed showers and thunderstorms in southwest Arizona and southeast California. The heaviest were near and within an area with precipitable water values at or above 50 mm (2 inches).   Precipit...

Three days ago we discussed the possibility of a major monsoon surge into the Great Basin (see Intricacies of Medium Range Monsoon Forecasts ).  The large-scale pattern producing that surge now looks as if it will deliver in spades to the Southwest US and Northwest Mexico over the next several days in the form of not only the surge, but also the tracking of Hurricane Hilary along Baja California and then through SoCal after it has decayed into a tropical storm or depression.   The GFS forecast shows the situation for 1800 UTC (1200 MDT) Sunday.  Hilary is off the Baja California Coast.  Tropical moisture in the form of a Monsoon Surge streams up the Gulf of California and into the Great Basin between an upper level trough along the Pacific Coast and a beastly ridge over the central US.  The latter has maximum 500-mb heights over 6000-m, which is quite high.   This pattern persists through 1500 UTC (0900 MDT) Monday, with Hilary weakening but movin...

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...

At least 36 people have been killed by tragic wildfires on Maui.  The NASA/USFS Fire Information Resource Management System shows fires/hotspots around Lahaina and over interior Maui.   Prior to this event, the National Weather Service was well aware of the potential for strong and damaging trade winds, as evident in the forecast discussion below from 3:53 PM HST Monday August 7.    They had also issued a red-flag warning for leeward (west) areas on the islands due to low humidity and strong winds with gusts over 60mph.  It was noted that any fires would "spread rapidly."   I could not find any observations from the Lahaina area through my usual channels.  Instead, I will use data from the Kealia Pond National Wildlife Refuge with is about 20 km to the southeast (and south of the high terrain immediately east of Lahaina.  This difference could be very important as the topography of the Hawaiian Islands has highly localized impacts on air...

It's always exciting in the dog days of summer to see a trough embedded in the midlatitude westerlies pay a visit to Utah. The GFS forecast below shows the trough moving through Utah at 1800 UTC (1200 MDT) August 8 (today).  At 700 mb there is even...wait for it...a temperature gradient with cold air advection (i.e., the transport of cold air into the area).   It's difficult to find evidence of a well-developed front at the surface, but there is evidence of some enhanced northerly or northwesterly flow over the west desert and along portions of the northern Wasatch Front at around 8 AM this morning.  Winds in the Salt Lake Valley, which are often southerly or southeasterly in the morning if there's no large scale forcing, show a bit more disorganized character.    That could reflect some of the showers that moved through, but also the fact that the surface trough is nearby or just downstream.   The NWS forecast for today calls for scattered shower...

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 ...

Some impressive heat records have fallen from the month of July.  Phoenix had it's hottest month ever. It's official, this July was the hottest month in Phoenix on record, with an average temperature of 102.7°F. This beats the previous record of 99.1°F set back in August 2020 by 3.6°F. It was certainly a month for the record books.🌡 #azwx pic.twitter.com/AvtODKN00s — NWS Phoenix (@NWSPhoenix) August 1, 2023 The Washington Post is reporting that is the hottest monthly average temperature ever recorded in a U.S. city, breaking the previous record of 102.2°F set in Lake Havasu City in 1996.   My daughter lives in Phoenix and was on a flight to Seattle yesterday.  When they landed they asked everyone to lower their shades because it was "hot out." She said the entire flight erupted in laughter.   A bit further to the north or west, Las Vegas, Kingman, and Needles all set July temperature records.   2023: Hottest July on Record for 3 Climate Sites....