We really haven't had much of a winter this year in the Salt Lake Valley. Snow has been scant (only 12.7" through yesterday, the 3rd lowest on record through that date) and temperatures mild (7th warmest mean temperature on record through yesterday).
It's been sunny and mild the past few days, so it definitely feels like spring. Things will change late tomorrow with the passage of a cold front. A couple of days ago I was going to call it the Start of Winter for the valley, but the storm is splitting and right now not looking as large as I thought a couple of days ago, although it could still have impacts.
The GFS forecast valid 0000 UTC 14 March (6 PM Thursday) has the front and frontal band moving through northern Utah.
Frontal passage at the airport in the GFS occurs at about 2200 UTC (4 PM Thursday) and the HRRR about 000 UTC (6 PM Thursday) so expect it to get here in the late afternoon to around dinner time. Pre-frontal conditions will be windy and mild, with perhaps a few valley showers or maybe a thunderstorm. Temperatures and snow levels will drop rapidly behind the front, with what looks to be a brief period of heavy snow to the valley floor.
Below is a time series for the Salt Lake City International Airport from the HRRR that includes our machine learned snow-to-liquid ratio and snowfall amount forecast. Yes, it is possible to produce these for anywhere in the continental US on weather.utah.edu if you know where to look. One can see the frontal passage at around 6 PM with the drop in the height of the 0.5C wet-bulb level. Precipitation also picks up at that time. Precipitaiton with the front persists through about 9 or 10 PM (although it's light( and then there is another brief period in the early morning hours associated with some HRRR lake effect.
Snowfall with the front adds up to a bit more than an inch and then the lake band adds another inch or so, although that's a relatively low probability possibility.
I think it's worth keeping an eye on official forecasts tomorrow for the evening commute. A brief period of heavy snow with post-frontal wind can make things nasty quickly, although perhaps the warmth of the roads will help stave that off some. A lot will depend on intensity and duration and perhaps elevation. I took a look and the official NWS forecast is for 1-2" at the airport and a bit more on the bench, which makes sense to me. Their forecast discussion expresses similar concerns to mine above: "A rapid changeover to snow could bring some impacts to the Thursday afternoon commute."
Thanks for another great post. On the HRRR KSLC snowfall guidance, do you punch in the coordinates by hand, or is there a point and click option. I replicated your results punching in -111.965, 40.77. If you know what you are doing you know those coords, for the rest of us ...
ReplyDeleteJust noticed wetbulb0.5 is below 4000 ft on the point time series, but wetbulb0 is 7000 ft in the HRRR LCC guidance. Seems inconsistent, inclined to believe 7000. Ofc 0 is above 0.5 in terms of elevation, but 3000 ft seems like too much
DeleteGuessing you were looking at runs initialized at direct times so the forecast hours don't line up with the same verification time. Those two products are different progressing streams and don't appear at the same time. If you grab them just right one will be from an older run.
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