Expires:No;;318036 FXUS65 KBOU 242330 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 530 PM MDT Wed Apr 24 2024 .KEY MESSAGES... - Slight Risk of severe thunderstorms Thursday, east of a line from Sterling to Akron, including large hail, damaging winds and isolated tornadoes. A marginal risk south and west of this area. - Cool and unsettled Friday into the weekend, with accumulating moderate snowfall in the mountains, widespread rain showers over the plains && .SHORT TERM /Through Thursday/... Issued at 324 PM MDT Wed Apr 24 2024 Northern border shower activity is running a couple hours ahead of schedule. The edge of the drier air is lifting northward and there does appear to be more stable air upstream west of the Front Range, so the end of this over the mountains may also be faster, in the early evening or sooner. On the plains the showers will be encountering the south winds that could keep them going longer, although there's not really more moisture out there yet. Further south, there's just a slight chance of very light showers, we'll probably just have virga. A surface low will develop early Thursday on the broad shear zone on the edge of the southerlies on the plains, probably starting near Denver but then drifting eastward. Moisture will be increasing in the southerlies tonight. There is a stratus deck from western Kansas into Texas that will advect into the northeast Corner of Colorado tonight, and it will likely develop westward late tonight. The increase in moisture is gradual at first, but richer air will arrive by Thursday morning. Between the wind speeds and the existing stratus deck, it looks like this will probably be off the ground instead of producing fog. Thursday's severe potential is complicated by this cloud deck and the fact that the moist air is considerably cooler and should be capped, at least for most of the day and possible into Thursday evening. So the question becomes where there will be both enough moisture and heat, or enough convergence to break the cap. If we can get convection rooted in that moisture, it's a pretty favorable supercell environment with mainly a large hail threat. I see two severe scenarios, both of which are questionable, and both of which could happen together. One is on the west edge of the better moisture, extending on the north side of the surface low, probably across northeast Weld, or possibly Logan or Morgan counties. This area could be the sweet spot which has increased moisture but still gets warm enough. While CAPEs in this area won't be as high as further east, it's still a supercell environment and this area might have the best potential for tornadoes early in the life of the storm with a more backed low level wind field. This would most likely be for a couple hours during the late afternoon. The second scenario would be that the dryline convergence is enough to overcome a weak cap. Most of the convective allowing models we've seen like this idea, and insist on it happening in the late afternoon. This seems like it might be too fast given the model soundings we've seen which are mostly still pretty cool in the moist air in the late afternoon. It may take increasing convergence along with peak heating/moistening into the evening if that's going to happen. This would be more likely on the east side of the low, east or northeast of Akron, and a few hours later. In this case also, the severe threat is probably just a couple of hours and then we're dealing with elevated convection over the cooler moist air. Behind the low during the afternoon, we'll have a relatively dry environment, though still probably enough moisture/instability for some higher based weaker storms. The bulk of that may wait for evening as well with some cooling aloft and moisture advection from the north/northeast behind the low. For now, minimal changes have been made as this was the general forecast scenario we've had going. The main question remains the heating of the moist air late Thursday. && .LONG TERM /Thursday night through Wednesday/... Issued at 324 PM MDT Wed Apr 24 2024 As the backside of the cyclone brings northwest flow to the northeastern plains, the threat of severe storms could continue through midnight. Counties such as Logan, Sedgwick, and Phillips have the greatest chance of additional severe storms while elsewhere instability decreases overnight. Although a nocturnal threat of severe weather isn't new, those areas listed above should remain weather aware Thursday evening until midnight. Light snow prevails throughout elevations above 9k ft overnight into Friday morning. With increasing snow and mid-level cloud cover across the region Friday, this forecast package includes an adjustment to afternoon highs as well Friday night lows. The next trough axis approaches Utah quickly but Friday afternoon may become a break in additional precipitation before the next shortwave trough enters western Colorado. Therefore, kept a chance of scattered PoPs (40-50%) along the urban corridor Friday afternoon. WPC Super Ensemble QPF fields display at least 0.50-0.75 inches over majority of the CWA Friday night into Saturday morning. It is likely areas across the mountains could receive periods of light to moderate snowfall. If traveling to mountain passes, prepare for winter travel conditions. Snowfall rates could approach 1-2 inch/hr above 10k ft especially by Saturday afternoon. Heavy rainfall will likely occur across the lower elevations Saturday as precipitable water values 0.7-1 inches. Numerous showers continue through Sunday morning. It is possible these showers will remain less convective as daytime heating will be limited. Our region will transition into zonal flow by Monday and weak lingering mid-level moisture could lead to isolated showers throughout Jackson and Grand counties. By Tuesday, dry conditions continue across the region. && .AVIATION /00Z TAFS through 00Z Thursday/... Issued at 524 PM MDT Wed Apr 24 2024 VFR conditions should prevail through the TAF period. A broad Denver cyclone has been observed again this afternoon with the main boundary/wind shift located between BJC and DEN. Current expectation is for this to remain fairly steady-state through the next couple of hours, and then gradually weaken later this evening as drainage flow establishes. Next forecast challenge comes early Thursday as models hint at some potential for a brief period of fog or very low stratus tomorrow at DEN. BUFKIT profiles would favor fog, but the majority of guidance keeps this just north/northeast of the field in southern Weld county. Finally, there's still some uncertainty in the winds and overall convective/shower potential Thursday afternoon, with DEN reasonably close to the dryline. Will need to re-evaluate with tonight/tomorrow AM hi-res guidance to get a better feel, but a broad period of VCTS/VCSH is likely. Eventually may see some lower cigs develop after 00z as well. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Gimmestad LONG TERM...AD AVIATION...Hiris