textproduct: Salt Lake City

KEY MESSAGES

- Near record to record heat expected through Wednesday.

- Critical fire weather conditions are expected across southwestern Utah Wednesday afternoon and evening. Red Flag Warnings have been issued accordingly.

- A marginal risk for severe thunderstorms is outlooked across portions of northern Utah and southwestern Wyoming Wednesday afternoon and evening. There is a 5-14% chance of wind gusts in excess of 58 mph near any thunderstorms.

- Gusty post-frontal winds are possible Wednesday evening near prone areas in northwest Utah such as Wendover, Park Valley, and Curlew Junction. A High Wind Watch has been issued.

- Another round of critical fire weather conditions may occur ahead of another cold front Saturday afternoon and evening across southwestern Utah.

DISCUSSION

As high pressure resides over our area today, expect yet another day of sunny skies and near-record temperatures reaching 15-20 degrees above normal. HeatRisk will reach Moderate/Orange (Level 2 out of 4) across many valleys in Utah, including along the Wasatch Front, given this anomalous warmth. Those who are sensitive to heat should take precautions to limit time outdoors.

While high temperatures tomorrow are expected to decrease by a few degrees, sensible weather will change as a couple of shortwave troughs bring more active weather. The weaker shortwave, coming from SoCal, will act to draw mid-level moisture northward, which will interact with a stronger shortwave that grazes across northern Utah. This will bring a few different hazards to the area on Wednesday afternoon and evening: breezy southwesterly synoptic winds, a hefty convective/outflow wind threat across primarily northern Utah/southwest Wyoming, blowing dust, and critical fire weather conditions across southwestern Utah (see Fire Weather section for more details).

As southwesterly flow increases ahead of this shortwave trough, areas across southwest Utah have a 30-40% chance of exceeding 45 mph Wednesday afternoon, alongside a chance for blowing dust and reduced visibility.

Mid-level moisture will begin to push into southern Utah this evening, though isolated showers will not begin to form until late Wednesday morning as that southern shortwave approaches. Showers will increase in coverage and intensity along a stark moisture gradient with daytime heating and better synoptic lift. Typically when we see a stark moisture gradient, it's associated with a quick increase in moisture, such as with a monsoon surge. However in this case, much drier air pushes into southwestern Utah behind this gradient, almost resembling a dry line, resulting in higher coverage of showers and thunderstorms northeast of this northwest- southeast oriented gradient. Instability will be fairly limited, generally less than 400 J/kg of MUCAPE, however model soundings show a clear inverted-V, favoring dry microbursts particularly as we consider increased 0-6km shear ~30-40kts from that northern shortwave trough. High-res guidance favors this threat of strong outflow winds, with a 5-10 percent chance of exceeding 58 mph, primarily across the northern two-thirds of Utah and southwest Wyoming. Some storms may be capable of producing even stronger winds closer to 75 mph, though this chance is low (<1% chance within 25 miles of a point). Longer-lasting storms could even produce some small hail.

Storms will decrease in coverage from southwest to northeast as that drier air pushes across the state, with most convection ceasing by mid-evening. A cold front associated with the northern shortwave will push into northwestern Utah around 6-8PM or so, weakening as it crosses the state during the overnight hours. Strong downsloping winds may develop in prone areas across northwest Utah, such as near Park Valley, Curlew Junction, and Wendover, where there is a 50-70% chance of exceeding 58 mph for a 1-3 hours period behind the frontal passage.

Temperatures will be much cooler on Thursday behind this cold front, with high temperatures dropping 20 degrees across northern areas, and around 10 degrees across southern Utah. As zonal flow sets up to end the work week, temperatures will slowly rebound. There is a chance that another cold front swings through the area on Saturday, though model guidance is still very uncertain in the trough's amplitude as it moves through the Intermountain West.

REST OF UTAH AND SOUTHWEST WYOMING

VFR conditions will persist for the entire airspace through the period. Dry and stable conditions with clear skies will continue with light and diurnally driven winds. On Wednesday afternoon gusty southwest winds will result in gusts up to 40 knots across southwest Utah and may kick up blowing dust across western Utah. In addition north and east of a line from Wendover to Richfield, isolated to widely scattered high- based thunderstorms will be capable of producing dry microburst winds in excess of 60 mph.

FIRE WEATHER...UPDATE

Red Flag Warnings have been issued for Fire Weather Zones 495-497...Previous discussion as follows...Very dry conditions will continue across the region today with another round of near record to record high temperatures expected. As a disturbance approaches the region Wednesday, a combination of increasing southwesterly winds up to 45 mph and continued very low humidities will bring critical fire weather conditions to southwestern Utah.

As a cold front approaches northwestern Utah Wednesday afternoon and evening, isolated to widely scattered dry thunderstorms will develop across much of the region. Expect strong, gusty microburst winds up to 60 mph near any of these thunderstorms along with lightning.

The cold front will cross the state Wednesday evening into Thursday morning, bringing the most pronounced cooling on order of 15 degrees or so across northern Utah, around 5 degrees closer to the Arizona border. Dry conditions will build into the state behind this system Thursday, with temperatures around 10 to 15 degrees above normal by Friday. Another cold front will cross the state Saturday, bringing the potential for another round of critical fire weather conditions to southwestern Utah Saturday afternoon and evening.

SLC WATCHES/WARNINGS/ADVISORIES

UT...High Wind Watch from Wednesday evening through late Wednesday night for UTZ101.

Red Flag Warning from noon to 9 PM MDT Wednesday for UTZ495>497.

WY...None.