Castle Dale, UT Weather

Key Messages

- Scattered showers with embedded thunderstorms will continue through Sunday across eastern Utah which will keep a low threat for flash flooding given the saturated soils.

- Pattern remains unsettled with a quick moving cold front Monday night followed by a more substantial storm by the end of the week.

Discussion

The large-scale pattern this evening consists of a closed low centered over northwest Arizona while upstream, another closed low is located off the southern BritCol coast. The low over Arizona resulted in some isolated to scattered showers over portions of southern and eastern Utah earlier today, with much of this having already decreased this evening. However, a vort lobe embedded within the low will rotate into southeast Utah tonight. This is expected to bring an increasing threat of showers with a few embedded thunderstorms back to southern and eastern Utah, mainly after midnight. As the rest of the upper low lifts through the Four Corners area through the day Sunday, expect generally scattered showers and thunderstorms to continue over roughly the spine of Utah and points east. Can not rule out an isolated flash flood with stronger showers moving over a sensitive basin.

A relative lull in precipitation is expected for Monday as a transient shortwave ridge crosses the area. Temperatures on Monday will trend warmer under the ridge, with northern Utah returning closer to normal while southern Utah will remain below normal.

Meanwhile, the closed low over the BritCol coast will move inland across the PacNW Sunday night into Monday before grazing northern Utah Monday night as a fast-moving shortwave trough. This trough will push a relatively shallow cold front into northern Utah Monday night. This will drop temperatures across northern Utah to generally 4-8 degrees below normal for Tuesday. Generally light precipitation is expected near the cold front, though amounts will depend in part on the strength of the cold front, of which subtle changes could make a noticeable difference. The latest deterministic GFS and NAM are leaning towards a weaker front with lower QPF compared to the EC. The 19z NBM has 25th-75th percentile values of around 0.15-0.6 in the northern Wasatch Mountains and Bear River Range (highest along the Idaho border), and from less than 0.05-0.4 inches in the adjacent valleys. Snow levels look to fall to between 6-7kft, so light snow accumulations can be expected in the mountains.

A near zonal flow pattern is expected to develop on Tuesday before southwesterly flow develops on Wednesday as a weakening and relatively benign trough grazes northern Utah. Thereafter, another storm system will reach the PacNW coast by Thursday. This will tap into some moisture and bring potentially widespread precipitation back to the area as early as Friday and continuing through the weekend. However, the details on how this storm system will evolve (whether it splits, and how quickly it moves through the area, etc) are still pending better model agreement.

Aviation

KSLC...A scattered to occasionally broken cloud deck around 7000 feet will continue through the overnight hours and south to southeast winds will continue through 18-19Z Sunday.

REST OF UTAH AND SOUTHWEST WYOMING...Showers will continue to impact portions of southern and eastern Utah, generally south of a line from roughly Cedar City to Hanksville, eventually impacting much of eastern Utah after 06Z. Local ceilings near 3000 feet will continue to occur in these areas with the exception of the greater St. George area. Local fog may develop tonight in areas that see clearing, particularly near the Idaho border.

Slc Watches

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