textproduct: Salt Lake City

KEY MESSAGES

- Areas of critical fire weather conditions will return to portions of southern Utah Saturday and Sunday afternoons.

- 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, potentially significant for some northern Utah 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 is noted on satellite imagery making its way into the PacNW, while a weaker, more diffuse shortwave disturbance is moving into CA. Ahead of these features, Utah remains under a near-westerly flow aloft but will soon be transitioning to more of a southwesterly flow by Saturday morning as the upstream features approach. Meanwhile, some weak high-based showers/virga continue this evening across southern Utah owing to a weak surface boundary. These showers are expected to largely taper off by midnight.

A cold front will push through northern Utah late Saturday morning into Saturday afternoon, then continue to make its way to southern Utah Saturday evening. Ahead of this front, gusty southwest winds can be expected, which when combined with low humidities, will create critical fire weather conditions. By peak mixing Saturday afternoon, this will largely include valleys across southern through east-central Utah. With modest midlevel moisture and instability in place, expect a few showers near the boundary, but mainly over/near the higher terrain. Precipitation amounts are not expected to be very significant, although the HREF does show 75th percentile values up to 0.3-0.4 across some central through northern mountains, which may represent higher-end amounts in heavier shower cores.

A trailing wave carving down the backside of the aforementioned PacNW trough is then progged to reach the Great Basin on Sunday. This will bring a stronger, reinforcing cold front and greater chance of precipitation to the area. West-southwesterly winds across southern Utah will potentially be stronger Sunday afternoon compared to Saturday afternoon ahead of this cold front, which would help maintain critical fire weather conditions mainly along the AZ border for Sunday. Behind the cold front, afternoon max temperatures will likely fail to reach 60F across most northern Utah valleys on Sunday. As this front continues south, temperatures on Monday will fall below normal areawide for Monday by around 15-20 degrees.

This stronger cold front will aid more widespread precipitation Sunday into at least Monday morning. The greatest amounts are expected across northeast Utah and southwest Wyoming. The NBM 25th-75th percentile of QPF ranges from around 1.25-1.75 inches across the Uintas, and 0.64-1.3 inches across southwest Wyoming. Most valleys in Utah have less than 0.7 inches at the 75th percentile. However, with the colder air comes lower snow levels, which are expected to fall as low as 5-6kft by early Monday morning. This will bring accumulating snow to the mountains and higher valleys. Upcoming shifts will need to evaluate the need for any winter weather highlights, especially for the Uintas and Uinta County Wyoming where a period of northerly to northeasterly flow presents favorable orographics.

Cooler air settling into the area will bring the potential for freezing conditions to many Utah valleys Sunday night/Monday morning and again Monday night/Tuesday morning. The first night will be more tricky given clouds/precipitation, but as skies clear out more for the second night, chances may be a bit better owing to enhanced radiative cooling.

The airmass will trend drier and should be accompanied by a gradual warming trend from Tuesday through late week. However, the large-scale pattern during this time looks to be largely represented by a northwesterly to near-zonal flow, so still expect some uncertainty with the extended portion of the forecast.

REST OF UTAH AND SOUTHWEST WYOMING

Scattered weak, high-based showers across southern Utah will diminish by ~08z or so, but may cause gusty and erratic winds until then. Otherwise, winds will be mostly light and terrain-driven overnight. Southwesterly winds will prevail ahead of a boundary Saturday afternoon with scattered showers and isolated thunderstorms capable of gusty and erratic outflow winds, mainly across eastern Utah. Northwesterly to westerly winds will prevail behind this boundary, initially located along roughly KMLF-KPUC around 18z.

FIRE WEATHER

Dry and mild conditions will continue into Saturday, with high temperatures near to 5F above seasonal normals across northern Utah and up to 10F above normal over southern Utah. With the approach of a cold Pacific Northwest storm system, winds will become breezy by Saturday afternoon. This will combine with the dry conditions over southern Utah to produce areas of critical fire weather conditions. Thus, a Red Flag Warning has been issued for most of the valleys of southern Utah for Saturday. The storm system will cross Utah Sunday into Monday, bringing temperatures up to 20F below seasonal normals both Sunday into Monday. Relative humidities will come up significantly over the area, but are still expected to be critically dry over far southern Utah. With winds a bit gustier than Sunday, have continued the Red Flag Warning into Sunday across far southern Utah. Snow levels are expected to drop as low as 5000 feet Sunday into Monday, with most mountains and mountain valleys seeing between two and six inches of snow. The exception will be portions of the western Uinta mountains, where up to 12 inches of new snow is possible. Behind the trough, the area will see a steady warming trend beginning Tuesday along with a drying trend.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Red Flag Warning from 11 AM to 9 PM MDT Saturday for UTZ489-494- 495.

Red Flag Warning from 11 AM Saturday to 9 PM MDT Sunday for UTZ497-498.

WY...None.