Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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309 FXUS65 KBOU 040159 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 759 PM MDT Wed Jul 3 2024 .KEY MESSAGES... - Gusty winds behind a cold front for a few hours late this evening - Quiet Fourth of July forecast with mostly sunny skies and cooler temperatures - Potential for critical weather conditions for southern Park County Thursday afternoon - Somewhat cool and mainly dry conditions will persist Friday through early next week. - Best chance for showers and storms in the extended will be Sunday. && .UPDATE... Issued at 753 PM MDT Wed Jul 3 2024 Severe storms have ended early this evening. A cold front is moving quickly southward and is near the CO-WY border at 02Z. This front will continue southward with a brief period of gusts from 40-50 mph as it moves across the plains. Doesn`t appear convection will develop with or behind its passage except possibly over the far northeast corner. && .SHORT TERM /Through Thursday/... Issued at 339 PM MDT Wed Jul 3 2024 Active afternoon with thunderstorms continuing to initiate along the dryline positioned across the eastern plains. So far, this was predicted decently by the high resolution CAMs runs today. A lot of the action has been on the northerly segment of storms across the northeast corner with a couple severe storms. Radar shows storms firing on the southerly portion of the boundary now. SPC mesoanalysis shows a favorable severe environment in Elbert, northern Lincoln, and Washington counties as well. Large hail, damaging winds will be the main threat with these storms as they move eastward across the plains this afternoon/early evening. Storms exit the far east plains by mid evening. The next feature to impact the region will a fairly strong cold front the drops southward in the 10 pm to 12 am timeframe overnight. Model guidance expresses the potential for gusty northerly winds, especially at the initial onset of the front. Generally could see onset gusts as high as 35-45 mph, but some spots closer to the northern border could see higher for a short period of time. Thursday, Colorado sits in a post-frontal airmass with northwesterly flow aloft. This will make for cooler temperatures for the Fourth of July holiday. Highs in the upper 70s to low 80s across the lower elevations, 60s for the foothills, and 50s/60s for the mountains. With subsident flow, it will be dry and stable for most areas tomorrow. The mountains and northern Larimer county develop marginal instability in the afternoon supporting the low chance for an isolated shower in the afternoon. The east plains and the high country will be breezy in the afternoon with gusts mainly 20-25 mph. The high mountain valleys will be dry and breezy in the afternoon, leading to at least areas of elevated conditions in the afternoon. More in the Fire Discussion. && .LONG TERM /Thursday night through Wednesday/... Issued at 128 PM MDT Wed Jul 3 2024 A slight chance for showers and perhaps a thunderstorm will continue into the evening of the 4th of July. SBCAPE not impressive, up to 200J/kg and the same goes for moisture, with precipitable water values only 75 percent of normal. Any shower or storm that forms during the evening is expected to be weak and short lived. Models continue to favor northern Larimer/Weld Counties and the Palmer Divide for these showers/storms, though the latest model trends have been for fewer showers/storms. Upper level high will remain west of the Central Rockies and over California/Nevada through at least early next week. Flow aloft across Colorado will be northwesterly. Temperatures under this pattern are expected to be near to below normal. Shower and thunderstorm chances will depend on the location and timing of the weak waves embedded in the northwest flow, but overall rainfall chances will be on the low side through at least Saturday. Friday`s forecast continues to look cool with highs in the lower to mid 80s. The airmass will be stable across northern Colorado. May be unstable enough for a few weak showers and storms along and south of the Palmer Divide. There are some differences on the strength and location of a short wave Friday night and early Saturday. The ECMWF is stronger and farther west with this wave and brings a round showers and thunderstorms with it to far northeast Colorado late Friday night and early Saturday morning. In addition to the convection, a cold front brings another shot of cooler air for Saturday. Meanwhile the GFS and NAM are weaker with this trough, keeping it too far northeast of Colorado for showers and storms. Temperatures are also 5-10 degrees warmer under GFS/NAM scenario. Will start to trend the forecast towards the cooler scenario, with recent extended guidance generally being too warm. Another wave is expected for Sunday, which will reinforce the cooler air, and bring a better chance for showers and storms. For early to mid next week, cooler temperatures continue through at least Tuesday under northwest flow aloft. When/if the upper level high begins to move over the Central Rockies expect temperatures to climb into the 90s. Not sure when this will occur. Over the past week, models have been way too progressive shifting this ridge eastward and the latest trends have been to continue to slow the eastward progression of the ridge. && .AVIATION /00Z TAFS through 00Z Thursday/... Issued at 541 PM MDT Wed Jul 3 2024 Gusty NW winds should diminish before 01z. A cold front will move across around 05z with gusty north winds up to 35 mph. These winds will subside by 08z. There is low confidence in whether stratus will develop in the 08z-11z time period so have left a sct group in for now. On Thu, light and variable winds in the morning will become east by 18z. && .FIRE WEATHER... Issued at 339 PM MDT Wed Jul 3 2024 It will be breezy across the high country Thursday afternoon with gusts up to 30 mph. Relative humidity values drop into the 12-20 percent range. This may lead to elevated to spotty critical fire weather conditions at times. Southern Park County in particular displays higher probabilities of more consistently meeting Red Flag criteria in the afternoon. Went with a Fire Weather Watch for southern Park County from noon to 6 PM for now. Didn`t go straight to a Warning due to lower confidence in how widespread the 25 mph+ gusts will be. It is possible it ends up being spottier in coverage. && .BOU WATCHES/WARNINGS/ADVISORIES... Fire Weather Watch Thursday afternoon for COZ214. && $$ UPDATE...RPK SHORT TERM...Mensch LONG TERM...Meier AVIATION...RPK FIRE WEATHER...Mensch