textproduct: Salt Lake City

KEY MESSAGES

- There is a Moderate Risk for Excessive Rainfall (level 3 of 4) across portions of southern Utah, as a surge of moisture brings widespread rainfall across the region. A Flood Watch is in effect for much of southern and east central Utah through this evening.

- Accumulating mountain snow is expected across all Utah mountains through Monday morning. Upwards of 12" of snow is expected above 9000 feet, and 3-6" of snow down to around 7000 feet. Upper elevations of the Cottonwoods and western Uintas may see localized accumulations 18-24".

- Cool, dry, and stable conditions will temporarily build in by Tuesday before the passage of a weak storm system Wednesday into Thursday.

DISCUSSION

Seeing widespread valley rain and mountain snow across Utah and southwest Wyoming this morning with ample moisture and instability in place from the combination of a landfalling atmospheric river and a strong trough over the Great Basin. The cold front associated with the storm system is currently in the vicinity of the Utah/Nevada border with this boundary moving across the area during the day as the system continues eastward. Thus, widespread coverage of precipitation will continue through the day and into tonight, with snow levels steadily lowering into the 6,500 to 7,000 foot range. All Utah mountains will see accumulating snow, with significant accumulations for areas favored in northwest flow, particularly for the Wasatch Mountains south of I-80 as well as the western Uintas. Going Winter Weather Advisories cover the current threat well.

In southern Utah, flooding is ongoing in a variety of areas including Zion National Park, the Paria River, and the Escalante River. With rain continuing to fall steadily throughout the day, additional areas of flooding area likely through the afternoon and a Flood Watch for southern Utah remains in effect through the evening. Already high flows and saturated soils from recent previous flooding events will only exacerbate the problem.

Monday morning, the Pacific trough is expected to quickly exit the area as high pressure moves in behind it. The vast majority of precipitation is expected to end by midday, with perhaps a few showers hanging around over the higher terrain of northern Utah Monday afternoon. The ridge will remain in place through Tuesday, resulting in dry and unseasonably cool temperatures with maxes running up to 15F below seasonal normals.

Guidance indicates that the ridge will break down and shift east by Wednesday as another Pacific trough moves across the area. Confidence is increasing that associated moisture with this system will be significantly less than the last few systems, leading to a much more limited threat of precipitation. The primary impact is expected to be on temperatures, which should remain quite unseasonably cool into the latter part of the week. Behind that system, drier conditions are expected to prevail with the potential of a blocking ridge developing off the Pacific coast. In a northerly flow, temperatures are still expected to remain on the cool side into the upcoming weekend.

HYDROLOGY

Widespread rainfall, locally heavy, will bring elevated potential for localized flash flooding and rises to area waterways, particularly over southern Utah as well as portions of central Utah. The most significant period of precipitation will continue through this afternoon. Already seeing areas of flooding in southwest and south central Utah. A landfalling atmospheric river is providing substantial moisture as a potent Pacific trough moves into the area. Thus, the potential for heavy rain will continue through the afternoon and into the early evening before associated precipitation becomes more showery. Total rainfall amounts of 1-2.5" are likely through early Monday, and given antecedent conditions, will efficiently runoff the landscape promoting widespread rises for all waterways, including streams, creeks, normally dry washes, slot canyons, and rivers across the region.

AVIATION

KSLC...Persistent rain will continue into this afternoon, maintaining CIGS below 7kft along with mountain obscurations. There will be periods of MVFR conditions during this time with a 20% chance of some brief IFR conditions in heavier rain. Light southerly or light and variable winds are expected to become prevailing northwesterly early this afternoon with the passage of a cold front. There is a 30 percent chance of some erratic wind directions from showers ahead of the boundary. By early evening, precipitation should become more showery but a low (20-30) percent chance of MVFR conditions will remain.

REST OF UTAH AND SOUTHWEST WYOMING...Widespread rain will continue across the airspace through at least mid-afternoon before precipitation starts trending more showery. There will be widespread mountain obscurations in this precipitation with many areas of MVFR conditions. Heavier precipitation will also bring brief pockets of IFR conditions into the afternoon. Precipitation will become increasingly confined to the mountains through the night.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory until 11 AM MST Monday for UTZ111-112.

Flood Watch through this evening for UTZ120-121-123>125-127>131.

WY...None.