961 FXUS65 KSLC 172118 AFDSLCArea Forecast Discussion National Weather Service Salt Lake City UT 318 PM MDT Wed Sep 17 2025
.SYNOPSIS...The storm system slowly pushes east out of the area this evening with dry and warm conditions in its wake Thursday. Moisture returns to the area on Friday, lasting through the weekend with increasing chances for showers and thunderstorms.
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.SHORT TERM (Through 12Z/6AM Friday)...This afternoon, the persistent upper low will continue slowly progressing east with one final vorticity maxima sliding south across the northeastern portion of the forecast area. Confidence has decreased this forecast cycle regarding storms across the Uintas and the Uinta basin due to drier air pushing further east than anticipated, thus resulting in PoPs decreasing across the area. Showers and thunderstorms this afternoon across the aforementioned region should remain isolated at best.
This afternoon across the rest of the CWA, transient ridging is forecast to build into the area with large scale subsidence keeping the area dry. With dry northwest flow and increasing geopotential heights, this will result in a brief drying and warming trend through Thursday evening. While a substantial warmup isn`t expected, temperatures should be near-normal for this time of year tomorrow across the forecast area.
Near the end of the short term forecast early Friday morning, we will begin to see PoPs increase across far southwest UT as moisture begins to return to the area as another system moves in. More activity is expected in the afternoon, though some morning showers and thunderstorms cannot be ruled out across the aforementioned area, particularly across lower Washington County.
.LONG TERM (After 12Z/6AM Friday), Issued 318 AM MDT... Utah and southwest Wyoming`s weather will remain modestly active moving forward, with the hemispheric wave number favoring a more progressive pattern overall. After a brief break in the action earlier in the week, moisture will return on Friday as the upper-level ridge overhead shifts eastward, resulting in overall moist, southwesterly flow. Showers and thunderstorms are likely to develop across southwestern Utah on Friday, increasing in coverage/intensity during the afternoon. There is still some question as to how far north and east these storms reach on Friday, depending on 1) how quickly the mid-levels moisten and 2) if there is more synoptic support from a weakening closed low over the Great Basin. Compared to yesterday, models favor a more western track of this low over Nevada, meaning that northern Utah/southwest Wyoming are less likely to see these showers on Friday afternoon.
Isolated to scattered showers and thunderstorms will redevelop on Saturday afternoon across the forecast area. Dry microbursts will be the main threat on both days given dry low levels, with perhaps an isolated flash flood threat across southwestern Utah. Sunday will bring more isolated storms, likely tied to higher terrain given lack of synoptic support.
Heading into early next week, a brief period of zonal flow is expected across Utah, with a trough passing well to our north helping to bring drier air to our area. A ridge will redevelop following this trough, producing gradually warming temperatures and overall quiescent conditions. However, this quiet weather may not last long. While still a ways out in the forecast timeline, remember the overall progressive nature of the pattern; around 60-70% of ensemble members currently suggest the development of a longwave trough potentially reaching the western US late next week.
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.AVIATION...KSLC...VFR conditions are expected to persist at KSLC through the TAF period. Diurnal winds are expected this evening with light winds out of the south-southest developing around 04z.
.REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions are expected to prevail across all terminals through the TAF period. Generally diurnal light winds are expected through tonight with little cloud cover other than KSGU and KCDC.
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.FIRE WEATHER...A system moving east over WY continues to provide a chance for isolated showers and perhaps a rumble of thunder over the Uintas/Uinta Basin. Following this, a drier and warmer trend will continue settling in across UT Thursday before a more unsettled pattern develops Friday. On Friday morning, southwest winds will transport moisture up from the south increasing humidities and chances for showers and thunderstorms across the state through the weekend. For southern UT, Friday appears to be the best chance for a wetting rain across the area. For northern UT, dry microbursts appear possible Saturday afternoon. Following this, another dry and warm pattern develops to kick off the week.
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.SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. &&
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SHORT TERM...Worster LONG TERM...Cunningham AVIATION...Worster FIRE WEATHER...Worster
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NWS SLC Office Area Forecast Discussion