Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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922 FXUS65 KBOU 091547 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 947 AM MDT Thu May 9 2024 .KEY MESSAGES... - Snow will increase over the higher terrain through this afternoon and continue tonight into Friday. The heaviest snow is expected along and south of I-70 including South Park and above 7500 ft in the southern Foothills. - Cool and unsettled weather will be in place across the rest of the area into Friday with the best chance of showers along the I-25 Corridor and Palmer Divide. - Gradual warming this weekend into early next week along with scattered late day showers and thunderstorms. && .UPDATE... Issued at 947 AM MDT Thu May 9 2024 The forecast is in pretty good shape with scattered showers developing this morning. So far, they have been strangely focused in the northern foothills extending through Fort Collins toward Greeley, while mostly dry conditions had persisted south of that including Boulder & Denver, where showers had not yet developed behind this morning`s frontal surge. We do expect that to change with shallow instability, as noted by the developing stratocumulus field that was actually a bit bumpy on top. There have been some peeks of sunshine to aid destabilization in the weak upslope flow, so scattered showers should develop farther south in/near the foothills and then push back into the Front Range this afternoon in the deepening but relatively weak upslope environment. There is another lobe of instability and moisture rotating southwest from the Black Hills area, and some of these showers/isolated storms could work onto the northeast plains this afternoon. Overall, the forecast is on track with only minor changes to PoPs to reflect the latest trends. Mountain and foothill locations above ~7,000 feet should be mostly snow. The Winter Weather Advisory starting in those areas along/south of I-70 late this afternoon, and especially tonight and Friday morning when more impacts are expected, is looking good. && .SHORT TERM /Through tonight/... Issued at 316 AM MDT Thu May 9 2024 The upper level low that was over the central US will split into two parts as one piece of energy reforms into a weaker closed low over ern UT and wrn CO. This feature will then slowly retrograde into ern NV and wrn UT by late tonight. At the sfc, a cool front will move across the plains this morning with upslope flow developing thru the day and continuing tonight. Overall, there is only weak QG ascent across the area thru tonight but moisture depth and lapse rates will be favorable in and near the higher terrain. In addition, persistent upslope flow should allow for precip enhancement east of the Divide and across portions of South Park. At this time, heaviest qpf should be mainly along and south of I-70. Mosquito Range in Park county probably will end up with the heaviest snow which may reach warning criteria. However the majority of zn 34 will stay in the advisory range along with South Park. Across the srn Foothills amounts may reach advisory criteria as well above 7500 feet. Across the plains, precip chances will be considerably less as best chc of showers will be along and west of I-25 and across the Palmer Divide. Highs across the nern CO will mainly be in the 50s. && .LONG TERM /Friday through Wednesday/... Issued at 350 AM MDT Thu May 9 2024 Models are still showing an upper closed low over the southern Great Basin at 12Z Friday morning along with weak upper troughing stretched west to east across the forecast area. These features move little on Friday and Friday evening. By Saturday afternoon, the upper low is over the Four Corners and right over the CWA by 12Z Sunday. This is a bit slower than yesterday`s 00Z model runs indicated. There is neutral to weak QG upward vertical velocity over the CWA Friday through Saturday night. The low level pressure and wind fields have weak upslope over the plains on Friday into the evening, Normal diurnal wind patterns kick in after that and continue through Saturday night. For moisture, cross sections show it to be fairly deep early on Friday, with some decrease over the plains in the afternoon. It dries out quite a bit Friday night, even in the mountains late. On Saturday into Saturday night, moisture is pretty good again for much of the CWA. CAPE values are a bit better on Saturday, with even some out on the plains with better heating expected. So for pops, "likely"s for the mountains and 10-40%s over the plains, with the highest pops next to the foothills. Will keep some "isolated" thunderstorms going as well. Pops look a bit higher on Saturday with the better heating. Will go with 30-70%s for the entire CWA during the afternoon and evening, then 10-30%s overnight. Again, with keep some mention of thunder going, with better chances in the alpine areas. Snow will be relegated to the mountains and higher foothills on Friday, and mainly just for the mountains on warmer Saturday. Looking at temperatures, Friday`s highs will be below seasonal normals but 2-3 C warmer than today`s highs. By Saturday, highs will climb 2-5 C and be right at seasonal normals with mid 60s F to lower 70s F on the plains and 30s to 40s F in the mountains. For the later days, Sunday through Wednesday, models have the upper closed low moving east and out of the CWA Sunday and Sunday evening. There is some short wave upper ridging for Monday. By Tuesday and Wednesday, some of the models indicate weak upper troughing and northwesterly flow aloft while others show more zonal flow. There does seem to be enough moisture and heating available for late day convection all four days, although significant precipitation is not expected. Temperatures will be at or a bit above seasonal normals all four days. && .AVIATION /12Z TAFS through 12Z Friday/... Issued at 513 AM MDT Thu May 9 2024 Cold front should reach DIA around 13z with light SE winds becoming NNE. Should see IFR ceilings develop behind front with a few light rain showers possible. IFR ceilings should become MVFR by 19z with NE winds thru the aftn. For tonight, MVFR ceilings will continue with NE winds. By 07z ceilings may drop back to IFR with a slight chance of showers overnight. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 PM this afternoon to noon MDT Friday for COZ034-036-037. && $$ UPDATE...Barjenbruch SHORT TERM...RPK LONG TERM....RJK AVIATION...RPK