Area Forecast Discussion
Issued by NWS Salt Lake City, UT
Issued by NWS Salt Lake City, UT
587 FXUS65 KSLC 191023 AFDSLC Area Forecast Discussion National Weather Service Salt Lake City UT 423 AM MDT Wed Jun 19 2024 .SYNOPSIS...Temperatures will trend warmer across the area through Thursday before anomalous moisture spreads into eastern Utah late Thursday through Friday, bringing showers and thunderstorms with locally heavy rainfall and an associated flash flood risk. Drier conditions are expected over the weekend and into early next week with hot temperatures. && Key Messages: * Anomalous moisture will work into eastern Utah, mainly along and east of I-15 by Thursday night and Friday. This moisture will support locally heavy rainfall and an associated flash flood risk Thursday night and Friday. Areas most as risk include recent burn scars, slot canyons, normally dry washes and slickrock. * Heat re-surges across the forecast area, allowing high and low temperatures to rise to 10-15 degrees above average by Sunday. Hot temperatures combined with warm overnight lows will bring an increasing risk of heat related illness through at least Monday, especially for the urban areas. .SHORT TERM (Through 12Z/6AM Saturday)...Early Wednesday morning, increasing deep-layer southwest flow was commencing across the region in advance of a trough in place across the western CONUS coastline. As a result of the developing southwest flow, a warming trend will develop today, with temperatures returning to seasonal normals for mid-June. On Thursday, the above-mentioned trough will strengthen as it progresses eastward into the Great Basin. Meanwhile, the remnant moisture associated with Potential Tropical Cyclone 1 over the Western Gulf of Mexico will advect northwestward across the Four Corners. The leading edge of this anomalous moisture will reach southeast Utah late on Thursday. Along the leading edge of the moisture field, scattered showers and thunderstorms will develop over southeastern and eastern Utah late Thursday afternoon. Initially, the low-levels will remain quite dry, so isolated dry lighting and gusty outflow winds/microbursts will be the main threat. HREF wind probabilities show widespread convectively-induced gusts in the 50-60kt range from south-central Utah through eastern Utah, with a 30% probability contour for gusts reaching/exceeding 50kts having appeared in the 19.00Z run. Total column moisture advection will persist Thursday night and Friday, especially along and east of the I-15 corridor. At the same time, the above-mentioned trough and associated jet will promote an area of upper divergence across the area. Forecast soundings and plan views show the presence of a modest low-level jet nosing into SE Utah as well, providing mid-level convergence. Finally, PWAT values are forecast to increase to around 1.2" or 250% of normal (nearly 4SD), which is near-record for this typically dry time of year. GEFS QPF probabilities are in the 99th percentile for the time of year, and EFI reaches 0.8 with SoT values above 2. Model QPF shows a couple of corridors of 1-2" on Friday. As a result of these ingredients, and after collaboration with WPC and Grand Junction, a slight risk (level 2 of 4) was added to the Excessive Rainfall Outlook (ERO) for Day 4 (Friday). In addition, MUCAPE values surge into the 1000-2000J/kg range Friday, and 0-6km bulk shear increases into the 35-45kt range. These ingredients also point to the potential for a few organized, strong thunderstorms. As is typically the case in these very moist environments, there is lingering uncertainty regarding the total cloud cover. Thick cloud cover will limit SBCAPE generation, leading to weaker convection with a limited heavy rainfall threat. Indeed, models do indicate significant cloud cover during the morning, but tend to thin it out by afternoon. Thus, the strongest cells may actually form on the edge of the cloud shield (along the differential heating boundary) from Zion through central Utah. This will need to be watched. A Flood Watch may also be considered for Thursday night and Friday. What does this all mean for you? Know that given the ingredients will be in place to support strong thunderstorms capable of damaging winds, hail and locally heavy rainfall that could lead to a couple of instances of flash flooding. Areas where the vulnerability is highest include slot canyons, recent burn scars, normally dry washes and slickrock. Those with plans to recreate across Utah on Friday, especially along/east of I-15 may consider alternate plans. West of I-15, increasingly hot temperatures will return, with highs returning to 5F to 15F above normal for Friday, with the greatest departures across northern Utah. .LONG TERM (After 12z/6AM Saturday)...Heading through the weekend models maintain solid agreement on an area of high pressure building back into the forecast area. This area of high pressure will allow temperatures to rise back up to around 10-15 degrees above normal across the area, especially across the northern half of the area. This will be record challenging heat. For example, the high temperature forecast for SLC on Sunday, June 23 is 100 degrees while the record for the day stands at 101 degrees (set back in 2012). In addition to the daytime heat, overnight lows will remain fairly elevated in the low- to mid-70s, particularly across urbanized areas of northern Utah. For southern Utah, particularly lower Washington County, lows may not even drop below 80 degrees. The combination of the high daytime temperatures and minimal relief during the overnight hours raises concerns for those who are sensitive to heat and those with insufficient cooling methods. Will need to continue to assess the need for heat related headlines through at least Monday as this is the period where temperatures will be highest. Precipitation-wise, much of the northern half of the area will remain dry under the influence of the high, however, moisture will linger over the southern half of Utah and bring a chance for showers and thunderstorms through at least Monday. Ensemble guidance from the EPS and GEFS still shows precipitable water values of upwards of 175-225% of normal along roughly the southern half of Utah. There is still some uncertainty revolving around how far north this moisture will creep, which is dependent on how much an active northern jet stream will suppress the high early in the week. Nonetheless, should still see at least isolated to scattered showers and thunderstorms over southern Utah late in the weekend/ early in the work week. Higher than normal PWAT values will bring increased concern for flash flooding in the typical problem areas. Will need to see how models trend through the week... but the potential is there. && .AVIATION...KSLC...Minimal operational concerns are forecast for the KSLC terminal today. Light and variable flow will prevail through the mid-morning, transitioning to a light northerly flow around 15- 16Z. North winds prevail through the day, returning to southerly drainage flow in the evening. .REST OF UTAH AND SOUTHWEST WYOMING...VFR conditions under high level cloud cover across the northern area will prevail through the day. Winds will be generally light and terrain driven across most terminals through the day. && .FIRE WEATHER...A warming trend will get underway today with temperatures returning to seasonal normals for the middle of June. The warmup will be courtesy of strengthening southwest flow in advance of a developing trough near the California coast. Very dry air remains in place, especially across central and southern Utah. Pockets of near critical fire weather conditions will develop this afternoon, particularly over those areas of southern Utah where critically dry fuels, southwest wind gusts near 25 mph and humidities below 15 percent overlap. Moisture will gradually stream into the area from the southeast on Thursday. Enough moisture will work into the area to foster the development of isolated to eventually scattered showers and thunderstorms. Initially on Thursday afternoon, dry air will remain in place in the low levels, supporting isolated dry lightning and gusty thunderstorm outflow winds. Showers and thunderstorms will become increasingly wet Thursday night as moisture continues to flow into the area from the southeast. On Friday, the upper trough will be located just west the area. This will combine with the continued increasing moisture to support widespread showers and scattered wet thunderstorms for mainly areas along and east of I-15. Some of this activity will be capable of producing heavy rainfall and isolated flash flooding. Drier air will quickly move back into the area this weekend, but lingering low level moisture over eastern areas will promote isolated showers and thunderstorms. Hot and dry conditions will overspread the state on Sunday, with highs around 100F for northern valleys. Early next week, enough moisture lingers over southern Utah to promote isolated showers and thunderstorms. Otherwise, hot and dry conditions will persist, especially over central and northern areas. && .SLC WATCHES/WARNINGS/ADVISORIES... UT...None. WY...None. && $$ ADeSmet/Webber For more information from NOAA`s National Weather Service visit... http://weather.gov/saltlakecity