textproduct: Salt Lake City

DISCUSSION

Increasing moisture from south to north across the state today will be driven by a shortwave trough moving through central Utah during peak heating this afternoon. With a moisture gradient developing across the state, storm across southern Utah will tend to run on the wetter side today and tonight, while farther north across central and northern Utah storms will trend progressively drier in nature. Expect storm initiation across west-central Utah early this afternoon with storms evolving eastward as the shortwave drive them along. The 18Z SLC sounding is very indicative of the environment that storms would be moving into, with and elevated 520J/kg of CAPE with cloud bases around 550 mb setting up deep inverted-V profiles with 1600-1900 J/kg of DCAPE. These parameters all fall with our local climatology for days with severe thunderstorm wind gusts, with the only knock against particularly widespread severe wind gusts being that mean storm motion is only around 20 knots, where our more widespread wind gust days have mean motions closer to 40 knots. Overall the environment will favor isolated to widely scattered severe thunderstorm wind gusts to around 60 mph, with likely much more widespread outflow wind gusts in the 30-40 mph range. As the shortwave rolls over northern Utah later this evening, expect a transition of convection to focus along the convergent boundary through central Utah this evening where it may linger the longest and have the best chance to actually pick up some measurable precipitation. Farther south across southern Utah, the flash flood potential rating remains in the lowest category of "Possible" where convection will be somewhat suppressed given morning cloud cover and some showers limiting instability there.

On Thursday, moisture will linger across northern and eastern Utah. For southeast Utah there is a higher threat of flash flooding with a rating of "Probable" from Capitol Reef and the Swell south-eastward toward Blanding. With moisture pooled in those eastern basins, and better daytime heating building CAPE values of 700+J/kg along with more westerly flow and a drying moisture gradient moving in from the west there will be increased forcing for storms to develop off the terrain and move out of the low deserts of southeast Utah in the westerly flow, thus there is more confidence in a localized flash flood threat in that area tomorrow. Meanwhile across northern Utah, a very similar thermodynamic profile will be in place with a background westerly flow and west to east moving storm motions around 20 knots again. This will again favor isolated to widely scattered strong to severe thunderstorm wind gusts mainly across northern Utah which would be generally diurnally timed to potentially move into the Wasatch Front by late afternoon/early evening if that line of storms can develop tomorrow.

For Friday and Saturday we will see rapidly drying conditions along with increasing southwesterly winds across the state as a large and fairly unseasonable storm system move into the area from the Pacific Northwest. On Friday wind gusts of 40-50 mph are expected mainly across western Utah, with that axis of strongest winds shifting eastward into eastern Utah on Saturday as the trough continues to deepen to our west. This setup looks favorable for wind advisory level winds across portions of the area, but more importantly this will setup a significant critical fire weather event given the prolonged period of very warm, dry and windy conditions stretching from Friday into Saturday. But more on the fire weather specifics below. Otherwise, a cold front will push into northern Utah on Saturday, with reinforcing cool air arriving on Sunday. This will drive our temperatures down by about 25 degrees across northern Utah by Sunday. Snow levels even drop around 8500-9000 feet across northern Utah by Sunday morning, so while there isn't significant precipitation expected, higher elevations of the northern Utah mountains could see a little snow in the air. Otherwise, hot and dry conditions will continue across southern Utah, where critical fire weather conditions may linger well into next week as we see warming and drying again state wide behind the weekend cold front.

AVIATION

KSLC...Continued haze from smoke aloft potentially affecting slantwise visibility at times moving forward, but remaining VFR. Currently in the transition to NW winds through early afternoon, but expecting -TSRA development tracking in from the south to occasionally produce gusty outflow winds focused within the 22-03z window today, with a 30% of these storms tracking overhead of the terminal. Expecting another round of -TSRA development after 20z Thursday providing similar impacts to those mentioned for today.

REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions are expected to prevail, though wildfires will result in areas of smoke downwind, with local IFR conditions and mountain obscuration expected. In large, expecting modestly gusty southwesterly winds to prevail today, but increased coverage of -TSRA and high based showers will create locally strong outflow conditions across namely central/northern Utah mid afternoon through this evening.

FIRE WEATHER

A moisture gradient will develop over Utah today brining scattered showers and thunderstorms. Across southern into south- central Utah storms will be tend to lean a on the wetter side, while farther north into central and northern Utah drier air will remain in place supporting high based thunderstorms that will lean on the dry side with the potential for strong gusty outflow winds. Outflow wind gusts of 30-40 mph will be common across west- central Utah into the Wasatch Front today, with localized wind gusts up to around 60 mph from the stronger storms. For this threat, a Red Flag Warning has been issued today for scattered dry thunderstorms and strong outflow winds.

This moisture will linger across Utah on Thursday but will start to dry out from west to east, which will shift the best coverage of thunderstorms across northern into eastern Utah with drier air intruding across west-central and southwest Utah. This will bring a localized flash flood threat across southeast Utah on Thursday, but also will still bring the potential for isolated dry thunderstorms and gusty winds across northern into north-eastern Utah.

There is then high confidence in a signficiant critical fire weather pattern for Friday into Saturday across the state with very strong southwest wind gusts of 40 to 50 mph combined with low RH values in the 5-10 percent range, and extremely poor recoveries Friday night. This pattern will develop from a strong system moving in from the Pacific northwest, thus there is high confidence in a strong wind field developing across Utah ahead of this approaching cold front, while very dry air gets drawn up across Utah ahead of the front as well, quickly sweeping out the mid-week moisture. Some locations across southeast Utah may see critical fire weather conditions from wind and RH last for more than 24 hours from Friday with no break Friday night and right into Saturday.

We are growing increasingly concerned with this setup could be the most signficiant fire weather setup we've seen this year, coming on the heels of an active week with large fires burning already, the potential for dry thunderstorms today and Thursday which could result in new fire starts and then concluding the week with a higher end wind and poor overnight recover event. The only silver lining is that the cold front will bring temperatures 25 degrees cooler across northern Utah by Sunday with an increasing humidity. However southern Utah will only cool by about 10-15 degrees with min RH values only coming up to around 15%.

SLC WATCHES/WARNINGS/ADVISORIES

UT...Red Flag Warning until 11 PM MDT this evening for UTZ478-482-484- 488-489-492-493.

Red Flag Warning from noon Friday to midnight MDT Saturday night for UTZ478-482-484-488-489-492-495-497.

Red Flag Warning from noon Friday to 3 AM MDT Sunday for UTZ493- 494-496-498.

WY...None.