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Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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173 FXUS65 KBOU 131648 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1048 AM MDT Tue Aug 13 2024 .KEY MESSAGES... - Another round of thunderstorms today, with a continued flooding threat, and a greater risk of severe weather. - Gradual drying trend expected from Wednesday through the end of the work week with near to slightly above normal temperatures. && .UPDATE... Issued at 1038 AM MDT Tue Aug 13 2024 A Flood Watch will continue until 11 PM MDT tonight. Minor updates to wind direction by shifting winds northeast across the plains and increasing cloud cover this morning. The forecast package remains on track with afternoon scattered thunderstorms and showers developing in the higher elevations spreading to the eastern plains late afternoon through late evening. It is possible storms could produce heavy rainfall across the region thus increasing the threat of flash flooding for recent burn areas and plains. && .SHORT TERM /Through Tonight/... Issued at 436 AM MDT Tue Aug 13 2024 Thunderstorms have finally ended, though there are a few weak showers exiting the northeast and entering the southwest part of our area. With increasing cloud cover, we`ll probably keep a lid on things until noon with only a few mountain showers. Not much change to today`s forecast; we`ve made adjustments to better show the convective timing (afternoon/evening mountains and mostly late afternoon/evening urban corridor with mostly evening over the eastern part of the plains). Some trends from yesterday: -- Just as much moisture with precipitable water close to an inch over the foothills and up to 1.6 inches on the plains by evening. -- Storm motions should be faster (10-20 mph) with less risk of backbuilding/training. -- More CAPE (1000-1500 J/kg in the urban corridor and 1500-2500 J/kg over the eastern plains by 00z.) -- Some areas will be more flood prone due to the rain of the last couple of days, though the overall impact on soil moisture has been limited. So we`ll still have a flood threat though the risk of significant flash flooding should be lower than yesterday. And the risk of severe storms is greater. Probably more of a mixed hail/wind threat, increasing eastward with greater CAPE. There`s probably a sweet spot in the central part of our plains (ern Weld/Logan counties south to Limon) again where we`ll have enough heating, higher CAPE, and a better wind profile in the late afternoon to early evening and supercell development is possible. And the potential damage is likely greater than yesterday with the higher CAPE and shear. It`s not a super tornado environment, but there`s probably some threat through that zone as I don`t really see any negative factors. While there should be some decrease in intensity, we`ll still have a moist unstable environment into the evening for weaker showers/storms to continue over the western part of our area. With a faster storm motion, the strongest storms should be through before midnight but lesser storms may linger much of the night over the plains. && .LONG TERM /Wednesday through Monday/... Issued at 436 AM MDT Tue Aug 13 2024 Drier conditions are expected for Wednesday as a shortwave trough skirts across the northern Rockies turning flow aloft to a more zonal regime. This will limit monsoonal moisture transport into the forecast area compared to the previous few days. There will still be enough moisture present (PWATs 95-105% of normal), and with the assistance of the passing shortwave to the north, scattered afternoon showers and storms will likely develop, with some capable of producing brief heavy rainfall. Forecast soundings show drier low levels across the plains with DCAPE values surpassing 1000 J/kg. As storms move east off the higher terrain, gusty outflows capable of reaching 40-50 mph may be possible, with a few stronger gusts possible in the stronger storms. High temperatures are forecast to be in the 80s across the plains, 70s for the foothills, and 60s for the mountains. A cool front looks to pass through the area in the late Wednesday to early Thursday time frame. This is expected to help keep high temperatures on Thursday a few degrees cooler than Wednesday`s. Increased drying is expected for Thursday and Friday as flow aloft transitions to northwesterly as ridging begins to redevelop over the Rockies. PWATs drop below normal and instability is expected to be minimal. Mid-level lapse rates may steepen enough with daytime heating over the high country to allow for isolated afternoon showers and storms to develop. With limited moisture in place, any storms that develop will likely produce light rainfall and gusty winds. Temperatures will begin a gradual return to the 90s on Friday as 700 mb temperatures increase by 5-8 degrees and the ridge continues to amplify. By Saturday, it looks like we have a shot at tapping back into some monsoonal moisture as mid-level southwesterly flow may draw it up around the high centered over Texas and New Mexico. This will increase chances for isolated afternoon showers and storms, mainly over the high country. Increased moisture for Sunday and Monday will increase chances and coverage of thunderstorms across the CWA. Temperatures are expected to be above normal through the weekend and into the beginning of next week. && .AVIATION /12Z TAFS through 12Z Wednesday/... Issued at 436 AM MDT Tue Aug 13 2024 Low clouds with IFR/MVFR ceilings in the Denver area should dissipate 14z-15z. After that, VFR conditions are expected. Thunderstorms are expected to be in the area again 20z-02z with scattered showers and storms possible after that. Main impact will be a couple of wind shifts with gusts to 35 knots, but a severe thunderstorm with heavy rain, 50 knot gusts, and large hail is possible. The main threat of that is 21z-00z. && .HYDROLOGY... Issued at 1038 AM MDT Tue Aug 13 2024 Faster storm motions are expected today, but plentiful moisture will persist. Stronger storms today will produce heavy rainfall of up to 2 inches in an hour. The likelihood of storms stalling or training over the same area for longer periods is lower today. The flood threat will be greatest over the Front Range burn areas during the afternoon, urban areas in the I-25 corridor in the late afternoon, and the eastern plains in the evening. A Flood Watch continues through 11 PM MDT tonight. Drier air starts to move into the area Wednesday, lowering the flash flood threat, but keeping a limited threat across our sensitive burn scars. By Thursday, if any storms are able to form, they are only expected to produce light rainfall. The drier conditions are expected to continue into Friday. Moisture begins to increase Saturday and by Sunday the heavy rainfall/flash flooding threat is expected to increase once again. && .BOU WATCHES/WARNINGS/ADVISORIES... Flood Watch through this evening for COZ033-035-036-038-039- 041>044-046-047. && $$ UPDATE...AD SHORT TERM...Gimmestad LONG TERM...Bonner AVIATION...RPK HYDROLOGY...AD/Gimmestad/Bonner