A Decent Spring Cold Front

We are entering the time of year when we see the strongest cold-frontal passage.  This is due in part to the fact that (1) we actually get cold frontal passages this time of year and (2) the high sun angle drives processes that increase and sharpen the temperature contrast across the front.  

The cold front that will move across northern Utah tonight and tomorrow looks to be a good one, but the timing as currently forecast is off for Salt Lake City to maximize the sharpness and intensity of the frontal temperature drop.  

Below is the NAM forecast for 1800 UTC (1200 MDT) tomorrow showing a shift from prefrontal southwesterly flow and post-frontal westerly flow across the front, which is draped over the Salt Lake Valley.  

Because of the frontal passage, the change in temperature from this afternoon to tomorrow afternoon will be dramatic.  The forecast high for the Salt Lake City International airport for today is near 70˚F, whereas tomorrow afternoon we'll see rain changing to snow on the benches and temperatures more than 20˚F colder than today.  It will be a big change, but the front won't be quite as sharp or intense as it would be if it came in a few hours later when the sun would have had its greatest impact.  Still, something to look forward to and we need the precipitation.  Badly.

If you are looking for late-season powder, model forecasts for the storm vary from dust on crust to low-end Goldilocks.  For Alta, the SREF mean is around 6" of snow, but there are five members that crack the coveted 10" mark through Sunday morning.

The NAM is around 3", whereas the GFS, which is typically wetter, comes in with around 10".  We can't apply our snow-to-liquid ratio algorithm to the Euro, but in terms of water equivalent, it's even wetter than the GFS (0.7" vs. 0.53").

Probably the key to getting this thing to > 10" is the post-frontal crapshoot.  The GFS time-height section below shows post-frontal moisture and instability and northwesterly flow at some times and levels.  This could produce, but it's not a lead-pipe cinch since the relative humidity is moderately high and the flow is not locked in.  

The NWS is going for an 8-14" storm total, and I'm inclined to lean toward those numbers.  Tomorrow is probably a day to ski late as conditions will improve during the day and Sunday is probably a day to ski early.