Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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305 FXUS65 KBOU 071746 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1146 AM MDT Fri Jun 7 2024 .KEY MESSAGES... - Temperatures will be warmer today with scattered late day showers and thunderstorms. - Minor snowmelt impacts from rising streams, mainly in Grand County - Increasing chances for showers and thunderstorms this weekend into early next week, along with cooler temperatures. A couple storms could be strong to severe. - Hot and mainly dry weather towards the middle of next week. && .UPDATE... Issued at 1132 AM MDT Fri Jun 7 2024 A hot start to the day today, with many stations across the I-25 corridor reporting temperatures above 90 already. Officially we`ve already hit 90 at DEN and at Fort Collins (CSU). Cloud cover is increasing a bit as some mountain wave clouds develop - signaling the onset of better mid-level moisture - and so it`s difficult to say how much more warming we have left. Most guidance gets the Denver metro/urban corridor solidly into the mid 90s and thus the main chance this morning was to bump up our forecast highs a couple of degrees. Isolated to scattered high-based showers and storms remain in the forecast by this afternoon hours as we approach convective temperature. ACARS soundings already show a pretty well established inverted-V profile with HRRR DCAPE values exceeding 1500 J/kg later this afternoon. With any showers/storms this afternoon gusty winds will certainly be likely with minimal rainfall expected. Have made some minor changes to the PoP grids through tonight to try to better capture the timing shown by most of the HREF members. && .SHORT TERM /Through tonight/... Issued at 444 AM MDT Fri Jun 7 2024 Enhanced southerly downslope flow off the Palmer Divide and into Denver has weakened a bit early this morning which has allowed temperatures to drop into the 60s. Fairly mild morning regardless, setting up for a warmer day ahead. A flattened upper ridge prevails over the region today under weak synoptic ascent and mid-level moisture gradually advecting into the region. Instability and high temperatures will be dependent on how quickly the mid-level clouds move in with the increasing moisture. With the axis of the thermal ridge positioned over the region today highs be a couple degrees warmer than yesterday. Highs in the lower 90s are likely across most of the urban corridor and plains. If clouds don`t develop as quickly in the afternoon, can`t rule out higher values into the mid 90s. Marginal instability builds in the afternoon with MLCAPE values 200-1000 J/kg from west to east respectively. This is sufficient to support afternoon scattered showers and thunderstorms. Model soundings across the urban corridor exhibit the classic inverted-V profile. DCAPE values range around 800-1200 J/kg. A good indicator of gusty outflow winds with any convective showers/storms (35-45 mph). Scattered showers and storms continue across the region through the early evening hours. && .LONG TERM /Saturday through Thursday/... Issued at 444 AM MDT Fri Jun 7 2024 Lots of tricky questions for this weekend`s forecast as we`ll have potential for quite a bit of convection, but we`re also looking at fairly marginal environments with the trade off of higher moisture but cooler air over eastern Colorado. It doesn`t help that the models are struggling with details of the shortwave moving across the northern plains, which impacts how strong the push of cooler moist air into our area is. Saturday looks like the most active day and probably the easiest forecast. A cold front drops across the plains early in the day bringing modest cooling and moistening. The a shortwave will move across the area from west to east. This looks well timed for the afternoon hours. Model soundings show a weakly capped environment over the plains, with potentially warmer but still moist enough air over the mountains for convection to start there. Between the mountain initiation and a little QG lift/low level convergence from the short wave and post frontal upslope, we should get a pretty good batch of storms, maybe a solid line, moving from the mountains onto the plains in the afternoon. The degree of capping will likely determine how widespread the storms will be and whether they evolve into a strong line of storms on the plains or more disorganized and mostly elevated convection in the evening. With 40-50 knots of shear and 1000-1500 J/kg of CAPE, along with decent storm motions and a good chance of linear structure, there`s a decent severe hail and wind threat. Limiting factors might be a higher areal coverage of storms if they don`t form a nice line and potential early cloud cover or too early timing of the storms. There could be a tornado threat, but it seems like the storms might be too early to the western part of our plains to get a good southeasterly low level wind and then the linear structure could create outflow driven storms further east. Slower timing of the storms or a faster turn to southeast surface winds would increase the risk. Sunday is a lot harder. Some models are bringing in pretty chilly air, with cloud cover and highs around 70 that would confine surface based convection to the mountains. These runs have decent upslope winds into the foothills, but this might just bring persistent showers. Even the warmer solutions look pretty capped on the plains, but could be warm enough for more vigorous storms along the west edge of the moisture, in and near the Front Range. In these scenarios there could be a threat of some heavy rain as the winds aloft are lighter and we could have slow storm motions. The low level upslope would favor eastward propagation though and reduce the threat of stationary storms. Hard to argue with the intermediate solution we get from the NBM with high PoPs over the foothills diminishing eastward and a quarter to half inch of rain in the favored areas. Monday is a transition day with temperatures recovering but low level moisture remaining on the plains. This could be a good balance for less storm coverage, but still a decent severe threat with just enough of all of the ingredients. Cooler solutions still struggle to get warm enough. After that, we`re warmer and drier with lower storm coverage Tuesday and maybe nothing on Wednesday. Details on the next trough are uncertain, Thursday could still be hot and dry, or there could be a front and some mid level moisture/lift ahead of the next system. That seems more likely for Friday, but the little cooling and low PoPs in the NBM seem appropriate. && .AVIATION /18Z TAFS through 18Z Saturday/... Issued at 1132 AM MDT Fri Jun 7 2024 VFR through the TAF period, with afternoon convection the main focus both today and Saturday. Wind shift arrived a little ahead of schedule this morning, and generally northwest to northerly winds are likely through the afternoon hours. As high showers/storms develop, variable and gusty winds will be possible... especially after 21z. Some of this activity may linger into the evening hours. Drainage flow is expected tonight, with a turn to northeast or easterly winds by Saturday morning. Better moisture and an approaching shortwave trough should provide better focus for more organized convection as we approach 18z Saturday. && .HYDROLOGY... Issued at 444 AM MDT Fri Jun 7 2024 Elevated flows continue across most of the higher elevation rivers and streams, particularly across the upper Colorado River basin. Continued snowmelt and additional rainfall this weekend could lead to additional increases in river flows. Remain cognizant of the dangers of these cold flows, and be aware of any Flood Advisories. In the forecast period, the main concern is a limited threat of burn area flash flooding by Saturday. Moisture increases substantially as PWATs remain close to 150-200% of normal across the high country from Saturday into Monday. Better instability should be in place on Saturday, but storm motions will be fast enough to limit the flood threat to quick storms in the burn areas. Storm motions will be slower Sunday and Monday. More widespread rain is likely Sunday, but the intensity may be limited. There is a flash flood threat is strong storms develop, with the greatest potential over the east slopes of the Front Range. By Monday, there will be some drying although a few storms with heavy rain are still possible. The threat is lower after that in a drier environment. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hiris SHORT TERM...Mensch LONG TERM...Gimmestad AVIATION...Hiris HYDROLOGY...Gimmestad/Mensch