Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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737 FXUS65 KBOU 082028 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 228 PM MDT Sat Jun 8 2024 .KEY MESSAGES... - Severe storms possible along the Urban Corridor and likely on the northeast plains this afternoon with large hail and damaging winds the main threats. - More thunderstorms Sunday and Monday with a lower severe threat but a risk of heavy rain and localized flooding. - Minor snowmelt impacts from rising streams, mainly in Grand County. Thunderstorms this weekend could further increase stream flow. - Hot and mainly dry weather towards the middle to end of next week. There is potential for a day or two to need a Heat Advisory, most likely Thursday. && .SHORT TERM /Through Sunday/... Issued at 200 PM MDT Sat Jun 8 2024 Early Forecast Discussion issuance for the short term to capture the upcoming severe weather this afternoon. Upper level trough will continue to progress east across Utah and western Colorado this afternoon providing lift for thunderstorm development. MLCAPE reaches 1000-1500 J/kg ahead of the convection along the Front Range and up to 2000 J/kg over the plains. This combined with 0-6 Bulk Shear to around 40 knots will lead to strong/severe thunderstorms. A few supercell thunderstorms will be possible at first with large hail (greater than 2 inches) and damaging winds. Storms then grow into a line with strong winds becoming the main threat. Hi-Res models in good agreement showing bowing segments in the line of thunderstorms, which may lead to very strong wind gusts (greater than 75 mph). The timing for the strongest storms across the Urban Corridor looks to be noon to 3pm and for the eastern plain, it will be a little later 2-6 pm. Isolated/scattered showers and weak thunderstorms will remain possible through mid evening once the strong/severe storms move off to the east. Brief heavy rain and lightning are the main threats with this. Low clouds and areas of fog move into eastern Colorado overnight, which will result in mild overnight lows. For Sunday, upper level ridging begins to build over the Four Corners with weak northwest flow aloft over eastern Colorado. At the surface, high pressure will be centered over the Northern and Central Plains. Clockwise flow around the high will bring southeast to east winds across eastern Colorado. This will continue to transport low level moisture into the area. Low clouds will form overnight and continue into Sunday morning. The moist layer may be thick enough to produce light rain/drizzle over far eastern Colorado. Some of these clouds will linger into the afternoon. The reduced sun leading to cooler temperatures will stabilize the airmass over the eastern plains. However, west of a line roughly from Greeley to DIA to Colorado Springs, better clearing will allow for more heating with highs in the lower 80s. IF temperatures reach the lower 80s, MLCAPE climbs to 1000-1500 J/kg. Enough instability for strong to severe storms. Shear, will be on the weaker side so no organized severe threat is expected, but brief one inch or slightly larger hail will be possible. Heavy rain may be a greater concern due to slower storm movement and high running streams/rivers from snow melt. Still some uncertainty how much and how far east the clearing will take place, but most of the 12Z models runs show scattered thunderstorms late Sunday afternoon across the Front Range (west of I-25). && .LONG TERM /Sunday night through Saturday/... Issued at 200 PM MDT Sat Jun 8 2024 A shortwave trough will pass to the north of Colorado on Monday with light winds aloft over our forecast area. At the surface, there will be cyclogenesis over eastern Montana with southeast winds across our forecast area. These winds will hold in the low level moisture and there will likely be low clouds in the morning on the plains. By the afternoon, there will be modest instability that develops with a strong cap forming around 700 mb. If convection overcomes this cap, there could be a few strong to severe storms that form mainly along and south of the Cheyenne Ridge and along the Palmer Divide. However, a good portion of the area will be too stable for storms to develop. Hail will be the primary threat. Northwest flow aloft will move over Colorado on Tuesday on the northeast edge of a broad ridge over the western US. There will be warmer air aloft that arrives and with mostly sunny skies, highs will warm to the mid 80s across the plains. There may be some light showers and storms over the higher terrain but this convection will be much weaker than previous days. The broad ridge aloft will strengthen and the 500 mb heights will become over 2 standard deviations above normal Wednesday and Thursday. The subsidence along with plenty of sunshine will lead to temperatures climbing well into the 90s. Thursday continues to be the day to focus on as there may be heat impacts. There are multiple ensemble members that show Denver hitting 100 F and given the pattern and time of year, that would seem to be reasonable. If that were the case, heat highlights would be needed as cooling shelters would almost certainly be spun up. There are a couple ensemble members that keep eastern Colorado much cooler on Thursday as they have a cold front making it through the area. While that is not likely, it is possible. A shortwave aloft will move over Colorado on Friday with a cold front at the surface. Friday should be much cooler with numerous storms as a result. There does remain some uncertainty though as the timing of the shortwave is not agreed upon in the models. && .AVIATION /18Z TAFS through 18Z Sunday/... Issued at 1138 AM MDT Sat Jun 8 2024 Thunderstorms are expected to affect the Denver airports this afternoon, in the 19-23Z time frame. A few of the storms will be strong/severe with hail and strong outflow winds. After the first round of storms, additional weaker storms will be possible through 02Z. Southeast winds are expected to prevail after the convection ends and then winds end up a southerly drainage direction after 06Z. Low clouds (1000-2000 feet) move into eastern Colorado overnight with about a 30 percent chance for them to reach DEN. If low clouds reach DEN, the main time window would be 12-16Z. There`s a chance for thunderstorms late Sunday afternoon, after 23Z. The best chance for storms are expected to stay south and west of DEN with the best chances for APA and BJC. && .HYDROLOGY... Issued at 200 PM MDT Sat Jun 8 2024 Elevated flows continue across the upper Colorado River basin and additional rainfall this weekend could lead to further increase in the flows. Remain cognizant of the dangers of these cold flows, and be aware of any Flood Advisories. Multiple rounds of thunderstorms are expected over the higher terrain today. These storms will be moving quickly so the flash flood threat will remain minor. It may increase the flow in the Colorado River, though. Storms will be moving much slower on Sunday and Monday. However, they will likely be weaker than today. The primary threat during the forecast period will be in Cameron Peak on Sunday as a moderate threat for flash flooding will exist. The threat will be minor again on Monday. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Meier LONG TERM...Danielson AVIATION...Meier HYDROLOGY...Danielson