Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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326 FXUS65 KBOU 100605 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1205 AM MDT Mon Jun 10 2024 .KEY MESSAGES... - More thunderstorms on 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. - Cooler conditions will arrive Friday and Saturday with scattered showers and storms. Some of these storms could be strong to severe with heavy rain. && .UPDATE... Issued at 809 PM MDT Sun Jun 9 2024 Strong storms late this aftn along portions of the I-25 Corridor produced very heavy rainfall, flash flooding and large hail in some areas. Rainfall sensors from varied networks showed 2.5" to 3.5" where the heaviest rainfall occurred. Overall, activity has pretty much ended in most areas with only widely scattered showers and a few storms over the higher terrain. Overnight, should see lingering activity end around midnight. && .SHORT TERM /Through Monday/... Issued at 214 PM MDT Sun Jun 9 2024 Low clouds over eastern Colorado will continue to slowly burn off this afternoon. These low clouds wrapped westward into the foothills of Larimer County. Under the low clouds, temperatures are only in the 60s. Where it has been sunny most of the day, temperatures have climbed into the 70s with highs expected to reach the upper 70s to lower 80s. With temperatures this warm, MLCAPE reaches 1000-2000 J/kg. There`s a good amount of moisture in place today with dew points in the mid 50s to lower 60s and precipitable water values at or slightly above an inch. Weaker storms are expected today because of the reduced shear, but a few marginally severe storms will be possible with hail to an inch in diameter or slightly larger. Storms have started to form over the higher terrain, of Park County and the southern foothills. Additional development to the north is expected, and could become focused over a north/south boundary just east of I- 25. Best chance for thunderstorms/rain will be across the southern Front Range where it has been sunny and most unstable. Chances slowly decrease to the north and east due to less instability and eventually running into a capped airmass. Storms dissipate mid evening as the airmass stabilizes. Low clouds are expected to reform late tonight and Monday morning. However, the extent of the low clouds should be less than this morning. On Monday, a short wave trough rounds the ridge that is centered over the Four Corners. Timing of the best lift looks to be during the afternoon and coincide with the best heating/instability. MLCAPE climbs to 600-1200 J/kg and precipitable water values will be around an inch. Shear will be lacking again, so we will be looking at another round of thunderstorms with heavy rain and small hail. Like today can`t rule out a few brief storms just reaching severe criteria. Hi-Res models show a broken line of storms forming ahead of the trough along the Front Range. The line then fills in over the plans as it encounters better moisture and instability. With fewer low clouds during the morning, expect a warmer day across the area with highs in the 80s over northeast Colorado. && .LONG TERM /Monday night through Sunday/... Issued at 214 PM MDT Sun Jun 9 2024 500 mb heights will increase on Tuesday as the northeast extent of an upper level ridge will move over Colorado. At the surface, a weak cold front will move through the area Monday night and southeast winds will develop during the day on Tuesday behind the front. This will keep decent moisture in place at the surface with dew points staying around 50 F in the afternoon. Given there will be warming aloft, there will be less instability and a stronger cap. Therefore, the majority of the forecast area will be dry. However, over places that have more natural orographic forcing like the Palmer Divide and Cheyenne Ridge, there could be a couple storms that form. These storms could produce some hail and gusty winds. Otherwise, highs will be a few degrees (3-5 F) above normal. On Wednesday, Colorado will be under the right exit region of an upper level jet which will provide strong subsidence and will likely keep conditions dry. Temperatures will be warming at 700 mb to around 17 C. Given the strong subsidence and plenty of sunshine, it will turn into a hot day. Temperatures will climb to the low to mid 90s across the plains. Denver could reach 95 F which is only 2 degrees from the record daily high of 97 F set in 1952. Frequent readers of the AFD are probably sick of me talking about how hot Thursday is going to be but attention needs to be drawn to it. A 500 mb ridge will strengthen and move slightly northeastward on Thursday putting Colorado closer to the axis of the ridge. There will be a shortwave trough that moves across the upper Midwest during the day and this will have a surface cold front associated with it that will eventually move through eastern Colorado. The timing of when this front moves through the eastern plains of Colorado will be important. If it moves through Thursday morning, high temperatures may only reach the low 90s across the plains (it`s not much of a cold front). However, what appears more likely is that the front will move through late enough in the afternoon such that very hot conditions will exist. The NBM 50th percentile and the ECM ensemble MOS 50th percentile both have a high of 97 in Denver. Based on the pattern recognition, this seems well within reason so the forecast high temperatures in the gridded forecast were kept at those levels. The "high end" scenario in this case is that the cold front holds off until later in the evening and the subsidence limits afternoon cloud cover. In that case, a high of 100 or 101 would be possible in Denver and the ensembles show that is certainly possible. The record daily high for the 13th is 99 in Denver and it could be the earliest 101 in Denver`s climate history. We may not know the timing of the cold front for a couple days so nailing in the forecast details may take some time. With that being said, a Heat Advisory looks like it may be needed as temperatures will spend a long time above 90 F and it is an early season heat. This is a day where Denver could hit 90 F by about 9AM. Otherwise, a couple of very gusty showers could develop given how hot it will be. There is growing confidence that a shortwave trough will move over Colorado on Friday with an increase in precipitable water. There should be scattered coverage of thunderstorms and the coverage could even reach widespread. Some of these storms could be strong to severe given moderate instability and decent wind shear. The cooler weather with scattered storms will continue during the weekend. && .AVIATION /06Z TAFS through 06Z Tuesday/... Issued at 1149 PM MDT Sun Jun 9 2024 Enhanced southerly component flow overnight at 10-15 kts. Winds weaken after 12z, becoming light and variable by 15z Monday. Light and variable winds transition easterly by the afternoon. Scattered showers and thunderstorms are possible after 21z, with the threat continuing through around 01z. Gusty outflow winds up to 35 kts are possible with any passing/nearby storms as well as wind dir/speed changes from outflow boundaries from other storms. && .HYDROLOGY... Issued at 400 AM MDT Sun Jun 9 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. Storms will be moving much slower today and Monday. However, they will likely be weaker than Saturday. The primary threat during the forecast period will be in Cameron Peak today as a moderate threat for flash flooding will exist. The threat will be minor again on Monday. Periods of heavy rain are possible in storms today, mainly west of I-25 with a marginal risk for localized flood impacts. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...RPK SHORT TERM...Meier LONG TERM...Danielson AVIATION...Mensch HYDROLOGY...Gimmestad/Mensch