Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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910 FXUS65 KBOU 110608 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1208 AM MDT Tue Jun 11 2024 .KEY MESSAGES... - Snowmelt producing minor impacts from high streams, mainly in Grand County. - Hot and mainly dry weather is expected Wednesday and Thursday. There is potential for a Heat Advisory on Thursday depending on the timing of the cold front. - 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 807 PM MDT Mon Jun 10 2024 An outflow boundary from convection over the plains has pushed back into the I-25 Corridor. Still have decent instability around so may get some additional development along portions of the I-25 Corridor this evening. && .SHORT TERM /Through Tuesday/... Issued at 201 PM MDT Mon Jun 10 2024 Airmass is unstable again this afternoon with MLCAPE of 700-1500 J/kg. Sounding out of Fort Collins shows a capped airmass until temperatures reach the mid 80s. An upper level trough moving across the Northern and Central Rockies will provide lift for thunderstorm develop and help overcome the cap in places. Models generally agree a broken line of storms move across the Front Range and nearby plains. As this line progresses eastward into the more moist and unstable air, the line of storms fills in. Threat for severe storms is low today because of the lack of shear. However, a few brief severe storms will be possible with hail slightly larger than 1 inch in diameter. Heavy rain could cause localized flooding, where storms reform or remain stationary. The stronger storms are expected to be east of the area by mid evening with a few weaker storms lingering to around midnight. Weak cold front drops south across the area after midnight. The slightly cooling with the cold front will keep highs in the 80s over northeast Colorado. The airmass dries with precipitable water falling a little below an inch and dew points dropping into the upper 40s to lower 50s. Airmass remains unstable with MLCAPE climbing to 500-1500 J/kg. An upper level ridge begins to build over Colorado Tuesday, bringing warmer air aloft. Even though the airmass will be moist and unstable, the warming aloft will cap convective development for most places. Storms may be able to break through the cap over/near the Palmer Divide. If storms are able to form, they`ll drift east-southeast across Lincoln County. Can`t rule out a brief severe store with one inch hail, but the lack of shear will keep most storms sub severe. && .LONG TERM /Tuesday night through Monday/... Issued at 201 PM MDT Mon Jun 10 2024 Colorado will be under the right exit region of a mid to upper level jet on Wednesday with strong subsidence creating hot and dry conditions. Ensemble guidance has locked in on highs in the mid 90s across the I-25 corridor. The NBM 50th percentile and ECMWF ensemble MOS 50th percentile both have a high of 95 F in Denver so the forecast is exactly that. A high of 95 F would be only 2 degrees from the record daily high of 97 F in Denver set in 1952. With such strong subsidence, some of the CAMs are showing no rain at all. It can`t be ruled out that a couple light showers form, however. The axis of a strong ridge aloft will be over Colorado on Thursday with 500 mb heights of 2 standard deviations above normal. Meanwhile, there will be a shortwave trough that will move over Lake Superior during Thursday afternoon. There is a cold front associated with this trough that will move through northeast Colorado during the day on Thursday. Recent model runs have been slightly more progressive with this front and have it moving through Denver in the early afternoon. Some ensemble members are starting to show highs in the 80s on Thursday which would be the cool scenario. However, the majority of the ensemble members still have a high in the mid to upper 90s in Denver and the rest of the plains. Given the majority of ensemble runs have such warm conditions and there will be very warm air aloft, the forecast high in Denver was left at 97 F. There is still a chance that Denver reaches close to 100 F which would require a Heat Advisory given the early season heat. There is still not enough certainty to issue a Heat Advisory so no highlights are in effect. Otherwise, the steep lapse rates will allow for some showers and perhaps a storm to form. There will be more wind than rain with these showers and storms. A decently strong shortwave trough for mid June will move through Colorado Friday afternoon. At the surface, there will be lee cyclogenesis over eastern Colorado with southeast surface winds. These winds will draw in moisture and there will be moderate instability. With moderate southwest winds aloft and southeast winds at the surface, there will be moderate deep layer shear. All of the parameters seem to be coming together for an active severe weather day. Large hail and damaging wind gusts will be the primary threats. Thunderstorms will again be possible on Saturday but there will be lower coverage than Friday. Ridging will build in on Sunday with southwesterly flow throughout the atmosphere. Given the downslope flow and plenty of sunshine, ensembles have locked in a very hot day for Sunday. Highs could reach the upper 90s across the plains. && .AVIATION /06Z TAFS through 06Z Wednesday/... Issued at 1204 AM MDT Tue Jun 11 2024 VFR conditions will prevail through Tuesday. There is a chance (30%) of IFR or MVFR ceilings for a few hours 10z-15z at KDEN/KBJC, with a lower threat at KAPA. Isolated thunderstorms are expected in the Denver area 22z-02z, with a slight chance (20%) of wind shifts with gusts to 30 knots. && .HYDROLOGY... Issued at 201 PM MDT Mon Jun 10 2024 Winds aloft remain weak today, leading to slow storm motions, but a bit faster than Sunday. Heavy rain from slow moving storms could produce localized flooding. Elevated flows continue across the upper Colorado River basin. Remain cognizant of the dangers of these cold flows, and be aware of any Flood Advisories and Warnings. Flow may increase mid to late week as warmer temperatures return to the area. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...RPK SHORT TERM...Meier LONG TERM...Danielson AVIATION...Gimmestad HYDROLOGY...Meier