Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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102 FXUS65 KBOU 170112 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 712 PM MDT Sun Jun 16 2024 .KEY MESSAGES... - Isolated showers and storms over the northeast plains this evening. - Hot and dry across most of the area Monday, with critical fire weather conditions likely again. - Cooler by Tuesday and Wednesday. - Impacts from snowmelt across the high country will continue to diminish through the week. && .UPDATE... Issued at 712 PM MDT Sun Jun 16 2024 Updated the forecast to add a slight chance for showers and thunderstorms over the plains, mainly north of I-70 and east of I- 25. A few showers and storms have been able to survive and actually intensify moving off the higher terrain. The airmass is fairly capped over the plains, so expect the showers and storms to remain isolated. However if a storm gets enough forcing to overcome the cap, it could become severe as MLCAPE is 1000-2000 J/kg over the plains. && .SHORT TERM /Through Monday/... Issued at 232 PM MDT Sun Jun 16 2024 If you liked today`s forecast uncertainty, you`ll likely appreciate tomorrow`s as well. Little change in the overall synoptic pattern is expected in the next 24 hours, as a broad ridge continues to build to our east with a strong upper trough over the Pacific Northwest. The mid/upper level flow should gradually strengthen by tomorrow as the trough gradually approaches the region, but otherwise the pattern is quite similar. Despite the similar look aloft, there`s still quite a few parts to the forecast that remain uncertain. The shallow cold front that moved through earlier today continues to wreak havoc on my forecast grids, and guidance hints at yet another subtle frontal surge by tomorrow morning. This will have impacts on the temperature forecast here but also where the higher fire danger is across the lower elevations. At DEN, NAM MOS gives a high of 86 while the GFS/ECM MOS are in the mid 90s. It doesn`t take much searching to find hotter solutions (HRRR/RAP) as well as ones that keep the cooler/moist easterly flow in place across much of the plains. The current forecast is a blend of a lot of different things in an attempt to find the middle ground. If the hotter/drier solutions verify one could justify the need for Heat Advisories again tomorrow, but we`ll hold off until something becomes more clear. There are also widespread fire weather concerns tomorrow... see the Fire Wx section below for more details. && .LONG TERM /Monday night through Sunday/... Issued at 232 PM MDT Sun Jun 16 2024 Southwesterly flow aloft is expected through the work week as a troughing pattern persists over the western CONUS. The forecast area will get a short reprieve from the current pattern of above normal temperatures for Tuesday and Wednesday as a cold front is expected to drape across the state beginning late Monday night. Temperatures are forecast to drop below the freezing mark overnight Monday for elevations above 10,000 feet. With dry lower levels in place, precipitation is unlikely Monday night, with the exception of portions of the northeastern CWA where guidance indicates dewpoints may reach the 60s on the east side of a dryline. Depending on how far east the dryline sets up could mean sufficient moisture may be in place to allow for some isolated thunderstorms to develop. Tuesday`s high temperatures are expected to be more on par with the norm as they will likely reach the 70s and low 80s across the plains and foothills, 60s for the mountains. Lower level moisture will begin to increase Tuesday afternoon as the surface flow transitions to a more easterly component. This could allow for some isolated showers and storms to develop over the higher elevations. Confidence is low in this scenario as only ~20% of ensemble members show CAPE values increasing to greater than 500 J/kg, mainly for the Palmer Divide and portions of the adjacent plains into the overnight hours. Guidance indicates the increased instability looks to remain just south and east of the CWA. For Wednesday, 700 mb temperatures are likely to be a few degrees cooler than Tuesday, which will assist in keeping another day of high temps in the 70s and lower 80s across the lower elevations, and 60s for the mountains. East/southeasterly low level flow is expected to bring increasing moisture support from the Gulf throughout the day Wednesday. Skies are expected to remain cloudy throughout the day that may prevent surface heating across the plains and inhibit any convection from developing. With less cloud coverage expected over the higher terrain, and mid level lapse rates becoming unstable, there is a better chance for afternoon storms to develop in these higher elevations. Overnight, a weak shortwave embedded in the southwesterly flow aloft looks to pass through the area that may initiate convection across portions of the plains. Thursday will bring a return to above normal temperatures and better chances for afternoon storms as forecast soundings indicate MLCAPE values exceeding 1300 J/kg across portions of the plains. A few weak upper level disturbances embedded in the flow look to pass through the area Thursday and Friday. After this, solutions diverge on when the trough pattern will shift eastward and ridging will begin to build over the western CONUS. There will likely be a chance for afternoon storms through the weekend. && .AVIATION /00Z TAFS through 00Z Monday/... Issued at 545 PM MDT Sun Jun 16 2024 Northeast winds will continue to turn counter-clockwise and end up a northerly direction around 02Z at DEN. Winds back to the northwest prior to becoming light and variable. After 06Z, typical south- southwest drainage winds will prevail. Skies to remain mostly clear with few to scattered high-based cumulus clouds around 10,000 feet. High based showers are expected to pass south of DEN, but within 10 miles for VCSH. Slight chance outflow winds bring a wind shift to the southwest. For Monday, the 18Z models show low clouds forming over parts of northeast Colorado 09-12Z and then spreading southwestward. Added SCT010 to the TAFs with a tempo for broken 1000 feet (BKN010) at DEN and BJC. These low clouds dissipate 15-17Z. There`s a good amount of uncertainty regarding the wind direction in the 16-22Z time frame. Like today, most models show gusty southwest winds at DEN. However, the strong southwest winds have stayed well south of DEN. Will have easterly winds for late Monday morning and early afternoon (17-21Z). Eventually expect stronger south-southwest winds to arrive at DEN mid afternoon, around 21Z. There is the possibility the easterly winds hold strong again and the gusty southwest winds stay south of DEN. && .FIRE WEATHER... Issued at 232 PM MDT Sun Jun 16 2024 Another challenging fire weather forecast through tomorrow afternoon. Near critical to critical fire weather conditions have been observed across most the current RFW zones this afternoon and will likely continue for a few more hours this evening. The cool front/moist boundary has setup from roughly Monument Hill to just north of Limon and may drift north later this afternoon, but no additional changes are planned for today`s RFW. Humidity will struggle to recover overnight across the higher elevations under a very dry airmass. Across the plains, another weaker/subtle frontal surge should arrive overnight or early Monday AM. How strong this boundary is and how far south it progresses will likely determine the overall fire danger for most of the plains tomorrow afternoon. There is considerable uncertainty in the T/Wind/RH forecast tomorrow afternoon, with high resolution models showing the moisture/wind gradient as far south as the southern Denver metro/I-70 corridor and as far north as the Wyoming border. Have gone with additional RFWs where confidence is higher (south/west CWA) and a Fire Weather Watch for Denver and the adjacent plains to the north/east. && .HYDROLOGY... Issued at 232 PM MDT Sun Jun 16 2024 Elevated flows continue in the mountain streams, but have diminished over the past couple of days. While additional snowmelt could briefly push a few sites back towards advisory level stream flow, it appears that the peak of snow melt season has already passed. Continue to remain alert of the dangers of water that is running high and cold. && .BOU WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from 11 AM to 9 PM MDT Monday for COZ213-214- 216-241-246-247. Fire Weather Watch from Monday morning through Monday evening for COZ239-240-243>245-249. && $$ UPDATE...Meier SHORT TERM...Hiris LONG TERM...Bonner AVIATION...Meier FIRE WEATHER...Hiris HYDROLOGY...Hiris