Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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594 FXUS65 KBOU 291101 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 501 AM MDT Wed May 29 2024 .KEY MESSAGES... - Scattered thunderstorms this afternoon and evening. A few severe storms are likely with large hail and strong winds in areas east of I-25 the main threat. - Scattered afternoon showers and thunderstorms Thursday-Friday. A few could be severe Thursday from the Palmer Divide eastward. - Warmer and drier beginning Saturday. Hottest temperatures so far this year likely Sunday into Monday. && .SHORT TERM /Through Wednesday Night/... Issued at 500 AM MDT Wed May 29 2024 Well, that was interesting. Cloud remnants of the convection that blew up around Greeley in the late evening are moving across the northeast corner at this hour. There`s a little pressure couplet associated with that which has turned low level winds more SSW across our plains for now, which could be a wrinkle in today`s plans. The HRRR seems to have some idea of this. Its last several runs have been really aggressive about bringing drier air into the Denver area and setting up a sharp dryline with dew points in Denver around 20 by noon. That seems like too much, but maybe not since we already appear to be eroding the west edge of the richer moisture that was coming in last evening. The tricky part is the battle between the rate of drying and the warming. How far north and east, and how strong, will the drying be when we get convective initiation? I had been skeptical of the limited amount of storms forecast for the I-25 corridor given that today was supposed to have better moisture, but now that is looking like it might be correct and we may even still have too much if it`s going to dry thoroughly be early afternoon. One question is the shape of the evolving dryline. How much will it bend back towards Weld or even Larimer counties as SSE winds redevelop on the plains and wrap westward north of the Palmer Divide? Given what`s currently happening, I`m not too worried about a big moisture recharge for Greeley/Fort Collins but they may not dry out as much as Denver. That could keep a threat of marginally severe hail for those areas if they can hang on to CAPES of 800-1000 J/kg. The HRRR has capes under 800 J/kg along and west of the dryline with 1000-1500 J/kg east of it in the late afternoon, which looks reasonable and matches the HREF means. There are runs with up to 3000 J/kg but that looks quite unlikely. So this may wind up being a fairly typical late May/early June day with a few severe thunderstorms with the main threat being 1 to 2 inch hail. We could have heavy rain issues too as stronger low level winds than mid levels will favor a backbuilding tendency or at least slow storm motions. But the expected linear nature of the storms should promote better outflow propagation. If there are hydro issues, it would be more likely on the eastern plains in the early evening. For now, we didn`t make too many adjustments, some minor trimming of the PoPs in the less likely areas. && .LONG TERM /Thursday through Tuesday/... Issued at 500 AM MDT Wed May 29 2024 A cold front will push through most of our forecast area Thursday morning, bringing with it more stable conditions and slightly cooler temperatures. Low-level moisture will also be quite limited behind the front. This should taper the strong thunderstorm potential for the northern tier of the forecast area, although isolated convection will still be possible late afternoon and into the evening. Parameters will be more favorable for areas from the Palmer Divide eastward into Lincoln County, where both moisture and instability will be maximized. Storms here will likely be better organized and could carry a severe threat, mainly in the form of hail and gusty outflow winds. Friday will see a weak shortwave embedded in largely zonal flow aloft zip over Colorado, with low-level flow shifting back to a generally southeasterly direction bringing some increase in moisture. Unstable conditions in the afternoon look to be more expansive compared to Thursday and would support slightly greater coverage of afternoon convection from the mountains into the plains. We`ll start to transition to a drier and warmer pattern on Saturday, with a downward trend in moisture and instability but still some lingering potential for isolated afternoon convection. Subsident flow becomes much more prevalent for Sunday under weak ridging and rising 700mb temperatures, accelerating the warmup and significantly reducing precipitation potential regionwide. Could be Denver`s first shot at 90 degrees this year. EC and Canadian ensemble suites have the thermal ridge and downslope flow (and consequently temperatures) peaking Monday, while the GFS leans towards some tapering of the heat with a cold front passage. Regardless, we`ll be staying dry Monday and likely much warmer than average. Model spread increases quite a bit for Tuesday with varying solutions in the upper-level pattern, precipitation chances, and longevity of the above-normal temperatures. && .AVIATION /12Z TAFS through 12Z Thursday/... Issued at 500 AM MDT Wed May 29 2024 VFR through tonight. Scattered thunderstorms are expected in the Denver area between 20z and 24z. The most likely impact would be a couple of wind shifts with gusts to 35 knots. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Gimmestad LONG TERM...Rodriguez AVIATION...Gimmestad