Updated Details for Sunday’s Storm

Posted Saturday, December 29th, 2018 by marcelcaron

Just got back from holidays back east, and while it was wonderful to be with family for the week, I’ve been missing Utah’s powder. Skiing ice in the Maryland rain just doesn’t quite cut it.

Without much ado, I want to cover tomorrow’s storm for this post. You might have seen some forecasts already estimating the snowfall, therefore I’m just going to examine the most recent model runs for you here.

The Next Week

First looking at the next week as a whole, we’re blessed with a continual and anomalous cold streak after Sunday’s quick-hitter for at least a few days. Unfortunately, this looks to be accompanied by a period of relatively uneventful weather, and I’m worried valley-dwellers may be breathing a few days of relentless polluted air. This might also mean frigid conditions in the mountains, with little or no new accumulation. Nevertheless, the possibility that a weak system or two could clear the air within the next seven days is definitely on the table. See this weeks posts for the updates.

Sunday’s Storm

A shortwave trough is digging into the western US and will usher in a cold air mass behind a brief but heavy snow dump at all elevations. Yesterday’s model run (ex. FV3-GFS) simulated a Sunday noonish timing in northern Utah and some prefrontal snow showers at upper elevations during the storm’s preceding twelve hours.

Within the 24-hour mark, the fine-scale models (ex. HRRR) are capable of providing more confidence to the details in the forecast. The HRRR confirms a fast-moving front hitting northern Utah around 2 or 3 PM, but has been hinting at an initial wave of showers around 10 AM at upper elevations. The NAEFS members suggest an impact time a couple of hours earlier.

Potential for Lake Effect

I expect, also, some post-frontal lake effect precipitation lasting into the evening Sunday. The current lake temperature is at an average of about 2 degrees C, and the HRRR forecasts a relatively cold -12 degrees C 700-mb temperature proceeding frontal passage tomorrow. A (relatively) warm lake underneath a cold air mass provides the instability necessary for lake effect precipitation. The impacts of tomorrow’s lake effect will vary dramatically by location as these always do, but for what it’s worth winds are generally northwesterly and tilting nearly westerly by Sunday evening according to the latest HRRR forecast. This means that eastern Salt Lake and Davis County benches and central Wasatch mountains will perhaps benefit the most from lake effect snowfall tomorrow. Consider an extra inch or two in these areas.

Great Salt Lake Surface Temperature
AVHRR-derived 48-Hour Average Lake Surface Temperatures, Great Salt Lake, period ending 10 AM Saturday December 29 2018. Appropriate credits labeled in the image.

Accumulations

With that, here’s my rough estimate of snow accumulations across northern UT as a result of Sunday’s end-of-the-year storm:

Valleys: 1-3″

Wasatch Back: 3-5″

Northern Wasatch resorts: 4-8″

Central Wasatch resorts: 6-10″

Furthermore, highest amounts occur in the Cottonwood Canyons, and again increase amounts where lake effect precipitation ultimately occurs.

Enjoy the snow and hope you all have a great final 2018 weekend.

-Marcel

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