Little Cottonwood Creek Valley, UT Weather

Key Messages

- A couple of weak systems brushing northern Utah through mid-week will keep temperatures seasonably cool, with some showers across the north tonight and again Tuesday night.

- Two storm systems bring wetter weather back to the region Friday into the weekend, with widespread precipitation through this period resulting in an increased risk for flash flooding.

- Colder air moving in late Saturday into early Monday will result in lowering snow levels, allowing for accumulating snowfall generally above 8500 feet.

Discussion

A cold front is marching through northern Utah this evening, associated with a shortwave trough grazing the area. This front is not expected to push much farther south than the central Wasatch Front before weakening later tonight. Showers with isolated embedded thunderstorms are accompanying this front. Given the fast-moving nature of the parent trough, expect precipitation to be short-lived, tapering off for the most part shortly after midnight. Expect generally light amounts of precipitation with a few tenths of an inch at best of snow in the higher elevations of northern Utah.

After a brief period of zonal flow tonight, the flow will turn more southwesterly again for Tuesday as the next shortwave trough swings towards the Great Basin. This trough will eject across northern Utah Tuesday night, gradually weakening as it does so. This is expected to bring another quick round of light valley rain and mountain snow to northern Utah and southwest Wyoming Tuesday night.

Attention will then turn to the weekend storm system which could bring more widespread precipitation to the area. During the second half of the week, a closed low will slowly move into the PacNW. Ahead of it, Utah will see a return to a southwesterly flow aloft. On Friday, a weak shortwave disturbance rotating around the low is progged to lift across Utah, bringing an initial round of precipitation to the area. Unsettled weather will then continue into Saturday as the upstream low slowly nudges inland. By Sunday, a southern stream trough associated with more abundant moisture will phase with this low, bringing more significant precipitation to the desert southwest. However, latest model runs are trending a bit farther south with this southern stream system, suggesting the bulk of the heavier precipitation may remain over Arizona. While fairly widespread precipitation can still be expected over Utah on Sunday, there remains quite a bit of uncertainty regarding precipitation amounts. For example, the latest NBM 25th through 75th percentile amounts between 12z Sunday and 12z Monday range from around 0.55 to 2.2 inches in the southern mountains and from around 0.4 to 1.8 inches in the southwestern valleys. If the higher amounts verify, there will be an increased potential for flash flooding.

Cooler air arriving with the storm system on Sunday will bring lowering snow levels to the area. By the tail end of the precipitation, H7 temperatures are progged to fall to near -7C across northern Utah and around -2C across southern Utah. Accumulating mountain snow will be likely, with amounts mirroring the uncertainty in the QPF. However, a general 3-6 inches with locally higher amounts in the upper Cottonwoods, high Uintas, and near Brian Head seem reasonable at this time. Precipitation is expected to wind down by Monday afternoon. However, both the latest deterministic GFS and EC bring a trailing vort lobe into Utah which is expected to be accompanied by a cool but drier continental airmass through the early part of next week.

Aviation

KSLC...VFR conditions will persist for the KSLC terminal through the period. A shallow cold front will move through the terminal ~06Z with a wind shift out of the north. There is ~15% chance of brief showers between 04-06Z, but most of this will stay just north of the terminal. Another brief switch to southerlies will be possible in the early morning before the diurnal north lake breeze sets back up during the afternoon.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions will persist for the entire airspace through the period. A weak cold front will be grazing this northern airspace overnight with isolated showers north of the Salt Lake Valley to the Idaho border between 03-06Z. Only the northern terminals will see a light northerly wind establish behind the front. Elsewhere winds will remain primarily out of the south with light and diurnally driven winds during the day tomorrow.

Slc Watches

UT...None. WY...None.