Wasatch Weather Weenies

Models have been trending toward an easterly downslope wind event tonight.  NWS has now issued a warning for the northern Wasatch Front.  Monitor forecasts, especially if you are in downslope wind prone areas. High Wind Warning & Advisory for Northern Wasatch Front tonight-Sat morning. Gusts up to 50mph, local 70mph. #utwx https://t.co/Aj99BLjZvC — NWS Salt Lake City (@NWSSaltLakeCity) March 31, 2017

With April Fools Day tomorrow and a crazy month of weather behind us, today brings a fitting "Bizzaro World" end to the month of March. First, let's recap.  It has been simultaneously hotter than hell and anomalously wet this month.  We set five daily records for maximum temperature over a 7-day span from the 15th to the 21st, including a 79 on the 18th, dashing hopes of powder skiing over the U's Spring Break.  For all but today, the average temperature for the month is 50.2ºF, a full half degree warmer than the previous warmest March on record from 2015.  Although today will likely lower that 50.2ºF just a titch, a half degree gap is sufficient that this March will go down as the warmest on record. But it's also been quite wet, at least at the Salt Lake City Airport.  Right now, 2017 rates as the 9th wettest march on record with 3.51 inches.  We may add a bit more to that today.  A record is out of reach, however, as 1891 saw a whopping 4.66 ...

As we discussed yesterday, the pattern for today and tonight is one that poses a number of challenges for detailed forecasting in the Wasatch Range.  The basic problem is this.  We have a closed low developing over the Intermountain West and the position and intensity of the closed low development strongly influences the position and movement of the cold front that will push into northern Utah today, as well as the subsequent direction and intensity of the flow impinging on the Wasatch Mountains.  Mountain snowfall is strongly dependent on both of these factors, and thus there is a wide range of possible outcomes for storm totals through tomorrow. Let's focus initially on the 0600 UTC initialized NAM forecast for 0000 UTC (1800 MDT) this afternoon.  At that time, the NAM calls for the closed low to be centered over southern Nevada.  There are two bands of precipitation over Utah, one over the central part of the state, the other over western Utah.  The la...

The forecast for tomorrow and Friday is one that falls into my "interesting" category. It's interesting primarily because it is one in which the large-scales are evolving rapidly.  Linear extrapolation from the west coast won't cut it in a storm like this.  It is only through the magic of numerical weather prediction that we can anticipate the rapid development of a closed low over the Intermountain west. To highlight the remarkable change, let's first take a look at the situation at 1800 UTC (Noon MDT) today.  Utah is under the influence of a short-wave ridge (hence the beautiful blue skies), but further upstream, an upper-level trough lies over the eastern Pacific, with precipitation downstream over the Pacific Northwest.   Presently, as evinced in the plot above, the trough is what we call  open wave, because the height lines (and flow streamlines) do not close in a circle.   The models, however, forecast for the trough to undergo rap...

Yesterday afternoon from noon to 1 PM MDT,  Alta was pounded with intense snowfall.  The automated Alta-Collins stations recorded 0.25 inches of water equivalent in that hour, and the interval snow-depth sensor reported an increase in snow depth of 7 inches. Due to round off errors and other issues, perhaps the 1-hour snowfall wasn't 7 inches, but something closer to six, which is what I've heard reports of from friends in the vicinity. In any event, it sounds like a very intense snowfall period.  The question is why. And the answer is that I don't know! Nothing jumps out from the radar loop for the period (Alta identified roughly with a red box near the center of the frame).  There is a brief period with relatively high radar reflectivities (yellow color fill indicates >35 dBZ) that would be consistent with strong, localized snowfall, afterwhich the echoes are actually non-existent. Often, there is a very poor correlation between snowfall rates and...

After a long delay, the National Centers for Environmental Prediction (NCEP) finally implemented their long awaited and likely final upgrade to the North American Mesoscale Forecast System (NAM) on March 15th. The changes are extensive.  The grid spacing of the NAM nest over the continental US decreases from 4 to 3 km.  Calls to major model physics packages are more frequent, updates to cloud microphysics parameterizations (critical for the simulation of precipitation), a new data assimilation system (to create model initial conditions), assimilation of new observational datasets, and more.  A complete rundown is available here . NCEP is also providing NAM output now at higher frequency.  I've updated weather.utah.edu so that it is now possible to access the NAM 3-km nest at hourly temporal resolution.  The loops are great and should aid in anticipating the onset and ending of precipitation.  Below is last night's NAM forecast of 1-h accumulated precipi...

Yesterday we were in clear outlier mode in Salt Lake City as we broke the all-time record for precipitation on a calendar day in March and experienced one of the wettest days ever.  I mangled some of the numbers in the previous post, so we'll take a little bit of time today to look back on the event and set the record straight. The primary large-scale feature driving the event was a mid-level trough that moved very slowly across Salt Lake City and stalled very near the Wasatch Crest for most of the day.  This trough was a large-scale feature extending northeastward to the Canadian border, and served as the locus for precipitation development along much of its lengths.  The image below shows the scene at 2000 UTC (2 PM MDT).  Wind barbs are at 700 mb (10,000 ft).  Gaps in the radar echo coverage in portions of Wyoming reflect both poor radar coverage and some orographic effects. Cloud and precipitation bands of this type are sometimes called "wrap-around" ...

Editors note : Post has been updated to note that the records are for Salt Lake City, specifically the airport and prior to that downtown. Editors note 2 : ARGH!  I can't do math either, and daily records are probably based on MST rather than MDT.  NWS is reporting 1.59" so far, so scratch the 1.70" noted in the post below (we may get there eventually) and use 1.59", putting us at #13.  Yes, still very wet!  Please forgive me... ---- If my math is correct, we have now had 1.70" of precipitation (water equivalent) at the Salt Lake City airport from Midnight to Noon. That would rank as the wettest calendar day ever in March and the 11th wettest calendar day ever in the Salt Lake City area based on online records at the NOAA Regional Climate Centers.  Prior to today, here's the rankings. Source: NOAA Regional Climate Centers I think it is pretty likely that we will move into the top 10, but suspect that top 5 is out of reach.  Still, this has bee...

After a stretch of remarkably dry and unseasonably warm weather, precipitation and cooler weather has finally returned to northern Utah.  Radar imagery this morning shows widespread precipitation over much of the Wasatch Front. Source: NCAR/RAL Take a close look, however, and you might notice that the echoes over the central Wasatch are weaker than those upstream and indeed that has been the case for most of the night.  In addition, total precipitation from midnight to 8 AM MDT at the Salt Lake City International Airport is a whopping 1.35 inches, but only 0.29" at Alta Collins. Mother Nature slaps powder skiers across the face yet again! And if you want to see why, check out the radar loop below.  Note how the slow moving trough has been camped right over the central Wasatch for the past couple of hours.  No flow. At least it is snowing and not raining now in the mountains, and snow will continue today.  Although it's a slow start, with only 3 in...

Well, it's a juicy one out there this morning.  The meteogram from the Salt Lake City airport shows and abrupt 5ºF drop in temperature and 9ºF rise in dewpoint just before midnight MDT as the flow shifted to NW-N with the passage of a modest cold front. Source: MesoWest Source: MesoWest Dewpoints increased further to the high 40s by about 6 AM and as I write this are lingering around 45ºF.  For the most part, a dewpoint in the high 40s doesn't get much attention, but for us, they are the highest observed in the past 30 days (see blue line below) and possibly much longer than that (MesoWest only provides point-and-click access to the past 30 days). Source: MesoWest Thus, my skin and lungs greatly appreciated the pulse of moisture I felt when I went out for the paper at 6 AM. Although we've cooled off some, temperatures remain above average for a morning in March in both the valleys and the mountains.  In the case of the latter, at 7 AM it was 36ºF at the...

The weather over the past week in northern Utah has been pretty outrageous.  Over the past 7 days, maximum temperatures at the Salt Lake City airport have been in the 70s and we will add an 8th today.  The overnight minimum last night was 61ºF, 6ºF warmer than the average high on this day.  We set daily records on four days and have a shot at another today (the current record is 74ºF). The maximum temperatures during the past week are consistent with the average maximums from mid May to early June.  The lowest maximum temperature observed over the past 7 days is 70ºF, consistent with the average high on May 10.  The highest, 79ºF, is consistent with the average high on June 5th. Spring is a period of great weather variability so swings from one extreme to another are not unusual.  However, the past week blows everything previously observed completely out of the water.  For the March 14-20 period, we have averaged 60.9ºF, a full 4ºF warmer than the...

Last July, we closed on a new home and moved to another location in the Avenues.  Our first order of business was to replace the roof, which was nearing end-of-life, and install solar. We worked through the University of Utah's Community Solar program , which provides a discount on solar installations.  The install was done by Creative Energies, who did a great job.  Due to the popularity of the program, we had to wait a couple of months for install, which finally happened in early December. Solar install in early December. We are fortunate to have great exposure for solar, with a roof that faces south-southwest and has no major shadowing from local buildings or trees.  We lose just a little solar late in the day due to coniferous trees on the west side of the home, but the impact is small and the cooling we receive from those trees in the summer probably reduces our electrical usage more than what we would gain if we removed them. There was some anxiety in...

It's no surprise that this week's record setting warmth has destroyed the the low-elevation snowpack.  We have precious few low-elevation SNOTEL locations, but the one at Ben Lomond Trail has lost about 4 inches of water equivalent through yesterday and I suspect it will see another couple of inches go away today.  On the plus side, it still sits well above average for this time of year, although it is located in an area that is somewhat shaded from the afternoon sun. Curiously, some of the upper-elevation SNOTEL sites have shown declines the past couple of days including Brighton and Mill-D. I haven't been out in the central Wasatch during this warm spell and don't have a good feel for what is happening at those sites.  Although it has been warm, I suspect the snowpack is not ripe yet and that those declines are not necessarily due to melt.  It's possible they are due to sublimation given how hot and dry it has been.  The graphs above don't include...

OK, this is getting ridiculous. Saturday's forecast high of 79 at SLC is the normal high temperature for June 5th. #utwx — NWS Salt Lake City (@NWSSaltLakeCity) March 17, 2017 If that forecast verifies, it will be the earliest 79ºF recorded at KSLC.  The record high for March is 80ºF, recorded on March 31, 2012.

Shockingly, given the blistering heat of late, the first half of March (through the 15th), only rates as the 11th warmest all time in the Salt Lake area. Source: NOAA Regional Climate Centers Granted, we are still running well above average, and we're not too far behind the warmer "half Marches", but still not in record territory. A big reason we're behind is the two cold surges that occurred around the first of the month and then on the 6th.   The one on the 6th really knocked the temperatures down.  Ah, the good old days!