Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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820 FXUS65 KBOU 191029 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 429 AM MDT Sun May 19 2024 .KEY MESSAGES... - Isolated to scattered high based showers and storms continue tonight with gusty outflow winds. - Slight chance of a severe storm or two across the far northeast plains this afternoon. Another round of strong to severe storms possible Monday afternoon into Monday evening across most of the eastern plains. - Cooler, wetter pattern late Monday into Tuesday as a couple weak systems track across the region - Warming/drying trend for the second half of next week && .SHORT TERM /Through tonight/... Issued at 415 AM MDT Sun May 19 2024 Water vapor imagery shows a broad trough has moved over the western US with southwesterly flow over Colorado. There is decent mid level moisture and weak large scale ascent which has led to a few showers forming over the far northeast plains this morning. Drier air moving in along with downslope surface winds will help high temperatures reach well above normal with highs in the 80s across the urban corridor and pains this afternoon. During the afternoon, there will be slight instability that forms across much of the CWA which will allow for weak showers and perhaps a thunderstorm or two to form. The dry low level airmass with steep lapse rates means that any showers or storms that form could create strong wind gusts potentially up to 45 mph. Across the far northeast plains, it will be a different story. There will be much higher low level moisture to the east of a dryline. Instability will be much greater with most unstable CAPE values exceeding 1,500 j/kg. With sufficient shear and forcing, strong to severe storms may form with large hail and damaging wind gusts possible. The most likely area for the severe storms would be east of a line from Sterling to Akron. Showers and storms will dissipate tonight. There will be a couple weak cold fronts that will allow for temperatures to cool into the 40s across the plains. && .LONG TERM /Monday through Saturday/... Issued at 315 AM MDT Sun May 19 2024 More organized convection is expected across portions of the forecast area on Monday. Guidance is largely in good agreement with the synoptic scale pattern here, but important mesoscale details remain uncertain across our forecast. Broad southwesterly flow aloft is anticipated ahead of an approaching positively tilted trough axis. A weak southern stream shortwave is expected to race across the region from Monday afternoon into Monday night, with lee cyclogenesis expected somewhere in eastern Colorado. To the north of this low, moist, east/northeasterly flow is expected to develop, with surface dew points gradually increasing into the upper 40s to mid 50s in northeastern Colorado. Wherever this warm/moist sector develops, guidance depicts a favorable environment for strong to severe storms for a brief period late Monday afternoon into Monday evening, with MLCAPE values near 500-1000 J/kg in along with good 0-6km speed/directional wind shear. A few hi-res models try to develop storms as far west as the I-25 corridor, though HREF/NCAR FV3 ensembles generally keep the higher probability corridor near the eastern edge of our CWA. These marginal events are always difficult to forecast, and therefore it wouldn`t be surprising to see shifts in the current SPC outlook as we get closer to the event... but at the very least, a conditional severe storm threat is becoming more likely for Monday. By Tuesday, the first shortwave should be exiting the region, with some lingering showers/storms possible across the northeast plains. With the passage of a strong cold front, highs should be much cooler across the region... only peaking in the upper 50s to low 60s. Still, modest boundary-layer moisture combined with larger scale ascent from a trailing shortwave should be enough for additional showers and a few storms by the afternoon, especially across the Front Range/urban corridor where shallow upslope flow should develop. Model soundings show a humidity rich 700-400mb layer with only modest instability, which in all likelihood would limit the severe threat. Still couldn`t rule out briefly heavy rain along with some hail, but the potential certainly looks lower than Monday`s threat. Wednesday will be much quieter across the forecast area with temperatures warming back up into the 60s/70s. A drier airmass should advect into the region with typical inverted-V type soundings with minimal CAPE. Can`t rule out a few high-based, mostly virga, showers but these should stay isolated in coverage. A continued warming/drying trend is expected into Thursday as southwesterly flow aloft strengthens. A weak shortwave is forecast to track to our north with minimal impacts from this feature. Again a few showers and storms will be possible across the higher elevations and along the northern border of our CWA. As we enter the latter half of the week into next weekend, forecast uncertainty increases quickly. There is generally good agreement that a broad upper trough/closed upper low will meander across the Pacific Northwest, with one or more shortwaves pivoting around the main trough axis. However, there is little agreement in the timing and placement of any of these finer-scale details and thus little reason to deviate from the multi-model mean. The general pattern would favor near normal temperatures with daily chances (20-40%) of showers and thunderstorms across the region. && .AVIATION /06Z TAFS through 06Z Monday/... Issued at 1134 PM MDT Sat May 18 2024 There will be stronger than usual drainage tonight with gusts up to 25 knots possible at DEN and APA. The showers seen over the mountains currently are expected to dissipate as they move off the terrain so there should be no impacts tonight. The main concern for Sunday will again be gusty showers. These showers should not impact visibility or ceilings but could create gusts up to 35 knots. The most likely timing for these showers/outflow winds will be between 20-23Z at all terminals. Models seem to agree that there will be a weak outflow boundary/cold front that will move through the terminals in the early evening(01-03Z) with northerly winds behind it. Winds will quickly become light about an hour or two after this front. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Danielson LONG TERM...Hiris AVIATION...Danielson