textproduct: Salt Lake City

KEY MESSAGES

- A slight risk (Level 2 out of 5) for severe thunderstorms is in place across portions of northern Utah and Uinta County, WY this afternoon and early this evening. There is a ~20% chance of wind gusts in excess of 58 mph in this area within 25 miles of a point and a ~10% chance of wind gust in excess of 65 mph within 25 miles of a point between noon and 7 PM today.

- Red Flag Warnings remain in effect for portions of southwestern Utah this afternoon and evening due to gusty winds and very low relative humidity.

- Strong wind gusts up to 60 mph will occur in the wake of a cold front across northwestern Utah near the Raft River Mountains and along I-80 from Wendover to Knolls from 6 PM until about 3 AM. A High Wind Warning is now in effect.

- Critical fire weather conditions may return to southwest Utah Saturday as gusty southerly winds will combine with low humidities in this area once again.

DISCUSSION

Early this afternoon, weak radar returns can be seen across portions of the state ahead of a subtle shortwave trough. This trough is drawing in mid-level moisture from the southwest which will interact with a separate grazing shortwave trough crossing the Interior Northwest, resulting in the heightened threat of severe thunderstorms this afternoon here in Utah. This severe threat is coupled with critical fire weather conditions developing this afternoon across southwestern Utah given increased southwesterly flow ahead of this northern shortwave trough and very low relative humidity (see Fire Weather section for more details).

While the ongoing showers are fairly weak, the real threat of dry microbursts and gusty outflow winds will start to ramp up after noon, with the main threat likely ending by 6-7PM or so. Model soundings suggest an inverted-V, characterized by dry air and steep lapse rates in the low levels and mid-level moisture. Instability is fairly limited, though still may approach up to 500 J/kg of MUCAPE in some areas, suggesting fairly shallow convection. While the best chances for severe gusts are across northern Utah and southwest Wyoming, there is still a sizable chance down to I-70 in eastern Utah, with even a couple severe gusts possible down to Lake Powell. Thunderstorms may be capable of producing very strong winds of 50-65 mph and even up to 65-75 mph on the higher end.

A cold front associated with the northern shortwave trough will push through the state this evening and overnight, weakening as it does so. Strong northwesterly winds will develop over portions of northwest Utah in particular given an initially strong pressure gradient, with prone areas expected to reach 60 mph...namely areas downwind of the Raft River Mountains like Park Valley and Rosette, and areas near Wendover. Temperatures will also cool behind this front, with high temperatures dropping by 15 degrees across northern Utah and 5-10 degrees across southern Utah between today and Thursday.

Behind this system, zonal flow will develop across the area, with largely dry, quiescent conditions expected Thursday and Friday. Another storm system is likely to move through this weekend, likely late Saturday into Sunday, which will bring cooler and wetter conditions once again. While there is still plenty of uncertainty regarding this system, models are generally in favor of a pretty stout cold front, with chances for showers and thunderstorms potentially both Saturday and Sunday, as well as freezing temperatures for some valleys by Monday morning.

REST OF UTAH AND SOUTHWEST WYOMING

Southerly winds will persist across most terminals this afternoon, with gusts up to 40 mph from gradient winds. High-based showers and thunderstorms will develop across the northern half of Utah after 19Z. There is a 20% chance of wind gusts in excess of 58 mph will occur within 25 miles terminals from roughly Utah County north and a 10% chance wind gusts will exceed 65 mph with 25 miles of terminals from Utah County north between 21-00Z today. A strong but dry cold front will bring a marked wind shift to the northwest for KENV between 01-03Z, with winds shifting across the remainder of northern Utah terminals after 03Z.

FIRE WEATHER

Breezy southwesterly winds will be in place across the state this afternoon as a storm system approaches from the northwest. Gusts outside of any thunderstorms may reach up to 40 mph this evening, particularly across southwestern Utah where Red Flag Warnings are in place for fire weather zones 495, 496, and 497. Minimum humidities this afternoon will be in the single digits, producing critical fire weather conditions. Across primarily northern and eastern Utah, high-based showers and thunderstorms will be capable of producing very strong outflow winds, with a 15-20% chance of wind gusts exceeding 58 mph primarily Utah county northward.

A dry cold front will push into northwestern Utah this evening, gradually weakening and shifting across the state. Strong northwest winds up to 60 mph will occur behind this front across portions of northwest Utah, with gusts up to 40-50 mph possible across the rest of northern Utah.

Temperatures will be cooler and conditions will be much quieter tomorrow and Friday. Another storm system is expected to track across the area late Saturday into Sunday, with another chance for critical fire weather conditions. However, chances for actual precipitation and not just virga are higher with this system, particularly on Sunday as a cold front moves through the region.

SLC WATCHES/WARNINGS/ADVISORIES

UT...High Wind Warning from 6 PM this evening to 3 AM MDT Thursday for UTZ101.

Red Flag Warning until 9 PM MDT this evening for UTZ495>497.

WY...None.