Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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228 FXUS65 KBOU 081143 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 543 AM MDT Sat Jun 8 2024 .KEY MESSAGES... - Severe storms likely on the northeast plains this afternoon and early evening 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 tonight/... Issued at 415 AM MDT Sat Jun 8 2024 More active weather day expected today, including the threat for strong to severe thunderstorms across the plains. Moisture and synoptic forcing are currently upstream of northeast CO early this morning. Mid-level water vapor imagery shows a defined shortwave trough in UT, moving east. Weak ascent ahead of this incoming wave has already spit out some showers in northern Larimer and Weld Counties early this morning. The incoming moisture is also quite notable, rounding the flat ridge ahead of the incoming system. A shortwave trough coupled with a mid-level speed max will provide sufficient synoptic ascent and favorable shear. An axis of MLCAPE values > 1000 J/kg orients across the central eastern plains. Some guidance shows values around 2000 J/kg across east Elbert Co. and Lincoln Co. Moisture will also be a big player. Anomalous moisture is expected to shift into the region, about 150-200% of normal. Upslope flow establishes by the afternoon, which will help bring in higher dewpoint air westward. A few initial boundaries will set up across northeast CO and help initiate the first storms of the day, likely in the 12-2PM timeframe. One boundary along the north border with the shortwave and another weak boundary extending off of the Palmer Divide. Daytime heating will be something to keep watch of, especially more north where there were showers around this morning. This may inhibit initiation early this afternoon (poss. failure mode). Soundings/hodographs support singular/supercell mode initially. The CAMs model suite reflectivity favors this evolution and continues to hint at the transition to more linear mode with upscale growth later on. Large hail upwards of 2" and damaging winds will be the primary threats with any severe storms on the plains. Hodographs are a mix of straight to a slight curve in shape at the lower levels, to support splitting cells and a low tornado threat on the plains. Around the urban corridor, can`t rule out a few strong to severe storms with gusty winds being the more likely threat. Late afternoon/early eve, storms move across the far east plains. There is a marginal threat for excessive rainfall, more in the hydro discussion. Temperatures will be considerably cooler today compared to previous days with highs in the 80s across the urban corridor and plains. && .LONG TERM /Sunday through Friday/... Issued at 415 AM MDT Sat Jun 8 2024 There`s been some convergence in model solutions for Sunday and Monday, though significant questions remain on whether it will be too cool for much convection and the related severe storm and flooding threats. The NBM does seem to be a fair consensus solution with highs from the mid 70s in the northeast corner to around 80 near the mountains on both days. Depending on the dew points, this may be a little shy of the convective temperature, which would lead to convection being forced by upslope into the foothills and the plains ridges, but then probably able to drift east or southeast for a while after initiation. Warmer solutions would have more storms on the plains, while the cooler solutions would be pretty well capped over the plains but likely still have some showers and a few storms over the foothills. The lack of shear will limit any severe threat, though there could still be a weakly capped 1000-1500 J/kg if the warmer end of the forecast range is realized, enough for some severe hail with stronger pulses. The main threat though should be heavy rain with precipitable water around an inch and storm motions under 10 knots. In this pattern sometimes the initial storms are stationary for an hour or two, and the greatest threat is for that to happen in a susceptible area. After that, there should be some storm motion into the low level winds but a localized storm producing 1 to 3 inches of rain in a couple of hours would still be possible in areas just east of the mountains in the late afternoon and evening. Monday had been looking a little drier and warmer, and possibly more of a severe threat if it got warm enough. But now it looks like the winds aloft will still be fairly light and the low level air may not be much different, with a little drying possibly offsetting any warming. Threats may be similar to Sunday or less due to the drying. Not much change to the warming and drying forecast for the rest of the week. We`ve got low to mid 90s for Wednesday through Friday with Thursday the warmest day. It could be a few degrees warmer than that. Still questions about timing of some moistening Friday, but the current slight cooling and chance of storms is reasonable. It could be slower to get here. && .AVIATION /12Z TAFS through 12Z Sunday/... Issued at 543 AM MDT Sat Jun 8 2024 VFR conditions are likely today. Light, variable winds this morning, gaining more of a light N/NE component through the AM. Easterly flow likely increases in the 16-18Z timeframe. Main concern for impacts will be the showers and thunderstorm potential in the afternoon. Development looks likely after 18z with scattered thunderstorms around the terminals for the afternoon, potentially lingering into the early evening. Variable gusts will likely accompany any nearby or passing storms with gusts up to 30-40 kts. Keeping an eye on potential for low stratus tonight (after 02Z) once the storms exit, mainly at BJC and DEN. Not seeing enough evidence/confidence to message strongly in the TAF yet, but included a SCT020 for now. && .HYDROLOGY... Issued at 415 AM 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. Thunderstorms will be likely across the recent burn areas today through Monday. The strongest storms may occur today, but with strong winds aloft, they will be moving quickly. Therefore, there is a minor threat of flash flooding today. The plains are under marginal risk per the Excessive Rainfall Outlook (WPC) for today. This threat mainly applies further east. Stronger winds aloft should favor quicker moving storms to keep this threat limited. 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 lower. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Mensch LONG TERM...Gimmestad AVIATION...Mensch HYDROLOGY...Gimmestad/Mensch