Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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056 FXUS65 KBOU 080225 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 825 PM MDT Fri Jun 7 2024 .KEY MESSAGES... - Hot and dry this afternoon, with gusty outflow winds. - Shower and storms likely this weekend into early next week, with strong to severe storms possible, especially on Saturday. - 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. && .UPDATE... Issued at 822 PM MDT Fri Jun 7 2024 Gusty winds from decaying thunderstorms will continue across the urban corridor and plains through 10 PM MDT. Expect storms to produce more wind than rain. PoPs were increased through midnight to keep slight chances of storms for the eastern plains. && .SHORT TERM /Through Saturday/... Issued at 209 PM MDT Fri Jun 7 2024 Satellite and radar have shown an increase in high-based convection over the past couple of hours. Unsurprisingly, this convection has had little precipitation and a lot of wind with it. A decaying shower over Boulder county has produced a substantial swath of 50-60+ mph wind gusts across the northwest metro. This will likely be the theme of the afternoon across the lower foothills and plains given how hot/dry the airmass currently is. An 18z sounding launched by CSU from Fort Collins showed DCAPE near 1250 J/kg, and DCAPE is likely a bit higher further south/east. Convection should wane towards sunset as the modest surface-based instability decreases. A quiet night is expected with mild overnight lows. Near-surface moisture will increase substantially by Saturday as easterly low-level flow develops. Surface dew points are forecast to rise back into the low 50s across most of the plains, with precipitable water values around 150-200% of normal. Aloft, a subtle shortwave/speed max should track across the region during the late morning to mid-afternoon hours, which should be the focus for convective initiation across the area. Forecast soundings would generally support both a severe hail and wind potential given ample shear and >1000 J/kg of CAPE in the early afternoon. While most models show straight line hodographs that would favor splitting cells and more of a hail threat, there are a few that show more curved hodographs east of the metro that could support a brief tornado threat. Storm mode remains a question, though CAMs quickly congeal any early convection into a larger MCS that tracks across eastern Colorado and into Kansas. There are also still some questions regarding the degree of capping/surface heating before storms initiate, but those likely won`t be answered until tomorrow morning. && .LONG TERM /Saturday night through Friday/... Issued at 209 PM MDT Fri Jun 7 2024 Storms will be ongoing Saturday evening but they are expected to mostly move out of our forecast area by the late evening. A risk for strong to severe thunderstorms will again be present on Sunday. During the afternoon, there will be moderate instability that forms with mixed-layer CAPE up to 2,000 j/kg. The instability profile is consistent with some of the larger severe hail cases we have seen. In addition, there will be light upslope flow in the low levels and adequate moisture levels for thunderstorm formation. The question will be the forcing. There is weaker flow aloft than previous days with winds at 500 mb at only 30-40 knots. There does not appear there will be a shortwave trough at this time but models may be able to resolve one at short time ranges. There will also be an inversion around 700 mb that may put a cap on storms. The most likely scenario seems to be that there will be enough forcing for strong to severe storms mainly across the I-25 corridor and adjacent eastern plains. However, there is a chance the forcing will not be enough and very few strong storms form. The primary threat would be large hail but severe wind gusts and a tornado or two could occur as well. Upper level ridging will move over Colorado on Monday with warmer temperatures aloft. This will reduce instability and there will be lower coverage of storms compared to the weekend. A couple of the storms could be strong with hail possible. There will not be a widespread severe threat given the reduced instability. A strong upper level ridge will dominate Colorado`s weather Tuesday through the end of the work week. 80 F high temperatures are expected on the plains on Tuesday with the 90s coming back on Wednesday. These days may have stray showers or storms mainly across the higher terrain. The ensemble guidance is in rather good agreement that Thursday will be very hot. The warm 700 mb temperatures along with downslope winds and plenty of sunshine will allow temperatures to get to the mid to upper 90s across the plains. When focusing on DIA, the ECMWF has the majority of its ensemble members at 95 F or above and there is one showing a high of 100 F. Given the early season heat, it is possible that a Heat Advisory will be needed for the I-25 corridor. Friday could also be just as hot or hotter but the confidence in the heat is much lower. High temperatures will depend on the timing of a shortwave trough that moves from off the Baja California coast to Colorado by Friday evening. If this trough is slower than expected to move across (which can be typical for these cut-off troughs), highs will once again be in the upper 90s to around 100 F across the plains. However, if the trough moves through quickly, showers and storms will keep temperatures down to around normal. && .AVIATION /00Z TAFS through 00Z Saturday/... Issued at 609 PM MDT Fri Jun 7 2024 VFR conditions are expected through the TAF period. There is a low chance of another round of thunderstorms mainly between 02Z-05Z this evening for KDEN and KAPA. Generally, winds should shift northwest then shifting clockwise south by midnight for KAPA and KDEN. Expect light wind speeds Saturday morning before mid-day. There is high confidence for thunderstorms arriving to all terminals Saturday afternoon. Variable and gusty winds will be possible through 00Z Saturday. && .HYDROLOGY... Issued at 209 PM MDT Fri Jun 7 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. Thunderstorms will be likely across the recent burn areas Saturday through Monday. The strongest storms may occur on Saturday but with strong winds aloft, they will be moving quickly. Therefore, there is a minor threat of flash flooding Saturday. The flow aloft will weaken on Sunday and Monday which will lead to slower moving storms. Considering strong storms are still possible on Sunday, there will be a moderate threat for flash flooding. By Monday, storms will likely be weaker and the threat will be minor again. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...AD SHORT TERM...Hiris LONG TERM...Danielson AVIATION...AD HYDROLOGY...Danielson