textproduct: Salt Lake City

KEY MESSAGES, Issued 1110 AM MDT Fri Sep 18 2026

- Periods of showers and thunderstorms will continue tonight into Friday, with the best coverage over northern Utah and southwest Wyoming. Hail, heavy rain, and lightning will be the primarily threats. Flash flooding remains a threat as well. - A weak cold front will bring drier conditions with more seasonable temperatures Saturday through the remainder of the weekend.

- Moisture is expected to increase again Tuesday, with another period of shower/thunderstorm chances Tuesday onward, especially for areas east of I-15.

DISCUSSION, Issued 1110 AM MDT Fri Sep 18 2026

A busy morning for northern Utah and southwest Wyoming with multiple rounds of convection moving through. Water vapor satellite imagery shows a circulation center upstream along the NV/OR border, with broad southwesterly flow into the eastern Great Basin and implied synoptic lift over our area. SPC mesoanalysis shows a favorable shear environment as would expected upstream of a closed low, with 30-50kts of effective bulk shear. It also shows plenty of instability to realize with around 1000 J/Kg of MUCAPE, less than the KSLC morning sounding which has an impressive (for our area) 1700 J/Kg of surface-based CAPE. Also worth noting, the morning sounding shows a freezing level of 9,700' MSL, which places the majority of that instability in the hail growth zone.

Convection this morning has been linear and quick moving, as would be expected from the strong southwesterly steering flow aloft. Have already had reports of nickle-sized hail and minor urban flooding, particularly in Utah and Wasatch counties which received the brunt of the convective activity from about 7a to 10am. For the rest of today, convection-allowing models have been showing a general theme of a late-morning / early afternoon lull (if you could call the current activity north of I-80 a lull), followed by another round this afternoon. Current visible satellite imagery suggests the next round is soon to materialize, given the streets of agitated CU showing up in the area of general clearing from around I-80 south and US-89 west. Machine learning guidance has been suggested a hail threat in particular over northern Utah, matching up with the thermodynamic indicators mentioned above, especially in vicinity of the Great Salt Lake and into western Box Elder County. SPC has this area generally highlighted with a 5-14% chance of severe hail in vicinity. Based on 12Z CAMs, the main threat period extends through about 7pm, and potentially a little later.

In addition to the severe hail and general thunderstorm risk, given the PWATs of around an inch (about 150% of average) and the instability yet to be realized, there is a flash flood risk if training lines of storms park over the same sensitive area. We'll be watching the usual burn scars, slot canyons, and urban areas for that threat. Castle County and the San Rafael Swell are at particular risk because of recent heavy rains that have left soils near saturation.

The closed low to our west that is responsible for the increased moisture and convective activity is forecast to lift northeastward and brush by our area to the north Saturday, pushing a weak cold front through northern and central Utah this evening and overnight. The passage have a noticeable effect on temperatures for all but southern Utah, with highs into the weekend running 5-10F below seasonal normals for northern Utah and southwest Wyoming, and near seasonal normals for southern Utah. As the trough exits, the flow aloft will move to a more west to northwesterly direction, allowing some drier air to move in. With the trough not entirely out of the picture on Saturday, still anticipating some scattered convection focused over northeastern portions of the forecast area, with Sunday expected to be dry with weak ridging moving in.

Guidance indicates the break in the action will be short lived, however, with yet another low approaching the Pacific coast Sunday afternoon. Most guidance shows this system tracking eastward into the Desert Southwest to start the work week, but the ensembles diverge noticeably with the regard to the potential track of the system and how much it will weaken once onshore. Still, confidence is increasing with regard to a relatively quick return to unsettled weather, at least for southern Utah.

AVIATION, Issued 12:15 PM MDT Fri Sep 18 2026

KSLC...The SLC terminal will see VFR conditions through the TAF period, with a 10% chance of brief high MVFR conditions in any passing thunderstorms this afternoon into early evening. The primary impact from any potential storms will be gusty and erratic winds up to 30kts. Southerly winds may transition to northerlies around 21z, for now carrying VRB with prob30 storms for that window. Storms are expected to diminish by 04z with the diurnal wind switch to southeasterlies or potentially light and variable delayed until 05- 07z.

REST OF UTAH AND SOUTHWEST WYOMING...Showers and thunderstorms are expected to persist across the northern terminals through early evening, with periodic IFR windows possible in the heaviest storms. Winds will be primarily driven by these storms, with gusty and erratic periods when storms impact terminals, with diurnal patterns expected to resume after sunset.

FIRE WEATHER

SLC WATCHES/WARNINGS/ADVISORIES

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