textproduct: Salt Lake City

KEY MESSAGES

- Areas of critical fire weather conditions will continue across far southern Utah through Sunday afternoon.

- A quite unseasonably cold storm system will result in temperatures 10-20F below normal for Sunday and Monday along with accumulating mountain and mountain valley snow, significant for the Western Uinta mountains and in southwest Wyoming. - Freeze conditions will impact many Utah valleys outside of the Wasatch Front Monday and Tuesday mornings. Some areas that might see a hard freeze include the Cache Valley, Wasatch Back, west central Utah, southwest Utah, and the Sanpete Valley.

DISCUSSION

An upper trough with several embedded shortwave features is in place over the western CONUS this evening. Across Utah, a cold front has moved through most of the area and is now located across far southern Utah. Convection was in place near this boundary through much of the afternoon, but has trended weaker and will continue to decrease in coverage late this evening and overnight.

Another embedded trough dropping into the Great Basin for Sunday will push a stronger reinforcing cold front into the area. This will be accompanied by much cooler air and more widespread precipitation. Frontogenesis is expected to occur across central and southern Utah which should focus heavier precipitation Sunday afternoon/evening. This is also expected to bring even stronger prefrontal winds to far southern Utah compared to today, and combined with low humidities will result in another round of critical fire weather conditions along the AZ border.

The shortwave trough is then expected to pinch off into a closed low as it tracks across Utah Sunday evening through Monday morning. Moisture wrapping around this low with associated TROWAL feature will maintain precipitation through Monday, but becoming more confined to northeast Utah and southwest Wyoming from Monday afternoon onward. Precipitation amounts with this storm will likely be most significant across the Uintas and southwest Wyoming (with somewhat lesser amount across the central/southern mountains) given the frontogenesis and favorable upslope flow with the wraparound moisture. Models are quite aggressive with precipitation amounts across the Uintas and southwest Wyoming, with in excess of 1 inch in portions of southwest Wyoming and in excess of 2 inches in the high Uintas. However, would not discount this given the TROWAL. Additionally, the ECMWF Extreme Forecast Index does show a good signal for anomalous precipitation in this area.

With the cooler air spreading into the area behind the cold front, temperatures will fall well below climatological normals, with max temperatures failing to reach 60F across most northern Utah valleys on Sunday and across many northern, central and southwest valleys on Monday. This colder air will also bring snow levels down to near 5500-6000 ft, especially Sunday night into Monday morning. As such, accumulating snow can be expected in the mountains and mountain valleys and in southwest Wyoming. Greatest amounts and potential impacts will be over the Uintas and southwest Wyoming, coincident with the greatest QPF. Winter Weather Advisories are in effect for these areas. While the forecast is showing storm totals reaching warning criteria, given surface temperatures and sun angles this time of year, actual impacts will be moderated, so will not plan on upgrading at this time.

Freezing temperatures are still in the forecast for many valley areas especially Sunday night/Monday morning and Monday night/Tuesday morning. However, have some concerns about precipitation and sky cover limiting radiative cooling for the first night, especially in valleys below the snow level.

The airmass is expected to trend warmer and drier Tuesday into late week. However, a cyclonic flow is progged to remain in place on Tuesday, which could maintain a few showers across northeast Utah and southwest Wyoming. Model spread also increases for late week, as some models are trying to bring a storm of some sort back into the area by Thursday. Since high pressure will remain over the Pacific, the door does stay open for more storms to work their way into the area, but will have to wait for models to come to a better consensus before focusing on any details.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will persist for the entire airspace through the night and tomorrow morning. A cold front will keep winds out of the north for the northern terminals with gusty southerly winds across the southern terminals. Scattered showers develop tomorrow afternoon across the northern half of the airspace with increasing southerly winds across the southern half. Brief mountain obscuration will occur tomorrow afternoon for the northern half.

FIRE WEATHER

A stronger storm system will cross the area Sunday afternoon through Monday, bringing much colder temperatures and accumulating snow to the higher terrain of Utah. Winds will remain elevated over southern Utah, and while relative humidities will be increasing, they will remain critically low over far southern Utah, where a Red Flag Warning will remain in effect tomorrow. Behind the exiting system, conditions will trend drier and warmer for the remainder of the upcoming week.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Winter Weather Advisory from noon Sunday to midnight MDT Monday night for UTZ112.

Red Flag Warning until 9 PM MDT Sunday for UTZ497-498.

WY...Winter Weather Advisory from noon Sunday to midnight MDT Monday night for WYZ021.