Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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674 FXUS65 KBOU 031803 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1203 PM MDT Wed Jul 3 2024 .KEY MESSAGES... - Strong to severe thunderstorms will be possible across the plains this afternoon/evening. - Elevated fire weather conditions across the high country and urban corridor this afternoon - Gorgeous weather conditions are expected on the Fourth of July with only a slight chance of an evening shower or storm. - Somewhat cool and mainly dry conditions will persist Friday through early next week. && .UPDATE... Issued at 1043 AM MDT Wed Jul 3 2024 Temperatures are warming into the mid to upper 70s this morning. No cloud cover being observed across the high country and urban corridor. Across the plains, areas of clouds around this morning are gradually diminishing or scattering out. No major changes made for this update. Made some minor updates to the PoP grids to better represent this morning`s model runs for this afternoon/eve severe potential. High-resolution models are still in good agreement for storms to initiate off the dry line that will position across the plains. However, there is still differing in solutions when it comes to where storms initiate along the boundary. There seems to be more agreement for storms to initiate along the northern segment, but there are some models that show a more southern segment as well going through Lincoln/Wash. Counties. && .SHORT TERM /Through tonight/... Issued at 303 AM MDT Wed Jul 3 2024 Another day, another complicated convective forecast across northeast Colorado. Weak elevated convection has persisted through most of the overnight hours tonight across Lincoln county into the southeastern portion of the state. SPC Mesoanalysis still shows roughly 500-1000 J/kg of MUCAPE across the plains, in part due to continued low-level moisture advection back into the state. Surface obs this morning show upper 50s dew points east of the urban corridor, which is a bit more moisture than most near-term guidance had predicted. Weak showers and a couple of storms will remain possible through the early morning hours as this convection gradually lifts to the north and east. The synoptic scale players are largely set for today, as a broad upper trough axis and accompanying jet streak move across the region this afternoon through tonight. This should provide some weak broad scale ascent, but neither of these features are particularly strong. What`s left are the mesoscale details. A surface dryline is expected to setup across the plains, with dry northwesterly flow on the dry side (more on this later), with moist southerly flow east of the boundary. Models generally have this boundary stalling near a Kimball NE - Fort Morgan - Deer Trail line. Areas east of the dryline should be in a broadly favorable environment for severe weather. With surface dew points in the upper 50s to low 60s, MLCAPE should increase to 1000-1500 J/kg. As mid-level flow increases ahead of the approaching shortwave, deep layer shear should also generally reach 35-45kt. With generally straight-line hodographs, this setup would favor splitting supercells with primarily a large hail/damaging wind threat. While a tornado or two can`t be ruled out, any tornado threat would be driven by subtle/mesoscale boundary interactions. Models also hint at some weak capping across the warm/moist sector this afternoon, which would likely limit overall convective coverage. This is (somewhat) well-modeled by the 00z HREF members, with paintball plots showing at least a couple of supercells, but little agreement in the exact location. Further west... warm, dry and breezy will be the story of the day. Guidance shows a deep, well-mixed boundary layer across the high country and the I-25 corridor, with relative humidity values falling to around 15%. BUFKIT momentum transfer plots suggest mixing down from ~500mb (if not higher), which should lead to a few gusts around 30-35kt, especially across the higher elevations. Did think for a bit about a Red Flag Warning, but don`t have the confidence that we`ll reach the areal/time thresholds for an RFW. With Independence Day just around the corner, please be mindful that there is still some fire danger on any dry/breezy days. Be aware of any local fire restrictions this week! A fairly strong cold front (for July standards) is expected to push into the region overnight tonight... but more on that below. && .LONG TERM /Thursday through Tuesday/... Issued at 133 AM MDT Wed Jul 3 2024 The Fourth of July will have very pleasant weather conditions. This is due to a cold front that will move through our forecast area Wednesday night and, as a result, Thursday will start off on the cooler side with lows in the low to mid 50s across the plains. As a shortwave trough moves east of the area, there will be mostly sunny skies for much of the day with subsident flow. The latest high resolution model runs are showing that there will be just enough instability due to steep lapse rates that a couple showers and perhaps a thunderstorm or two could develop in the evening hours. The models focus on northern Weld and Larimer Counties as the primary location for these showers and storms but there is a slight chance that they form anywhere on the plains. South Park will be the focus for the worst fire weather conditions on Thursday. Relative humidity will decrease to as low as 10 percent with gusts around 30 mph possible. Fire weather highlights may be needed for fire zone 214. Across the plains, the cool temperatures will limit fire weather conditions as minimum relative humidity will be above 22 percent. The upper level pattern will become stagnant for the rest of the long term period. There will be a strong ridge aloft over California which will create a heat wave out west. There will be troughing over the Midwest during this period which will put Colorado under northwesterly flow aloft between these features. Our forecast area will see a period of generally cool and dry weather from Friday through Tuesday. There are two primary exceptions, however. The first is on Saturday as temperatures will reach the 90s across the plains and fire weather conditions may near critical limits as relative humidity drops to the teens with gusts near 25 mph. The other exception is Sunday when a more substantial shortwave trough will move across Colorado. There will be a cold front at the surface that brings in cool and moist air which may lead to good coverage of afternoon showers and thunderstorms. At some point next week, the aforementioned ridge aloft over California will move eastward over Colorado. When this happens, Colorado will experience a heat wave. Over the past couple of days, models seem to hold off this ridge moving over Colorado until later in the week. && .AVIATION /18Z TAFS through 18Z Thursday/... Issued at 1203 PM MDT Wed Jul 3 2024 A very light wind circulation is being observed early this afternoon at the terminals with light W/WNW at DEN, ESE at APA, and VRB at BJC. Within the next 1-2 hours, breezy WNW winds mix down at at the terminals with gusts 18-25 kts through the afternoon. Storms are more likely to develop east of the terminals this afternoon; however, can`t rule out the low chance for a storm outflow reaching the airport from the storms to the east. Winds decrease this evening for a few hours before a cold front drops south across the terminals. The front will likely move through in the 05-07Z timeframe accompanied by a period of gusty north winds up to 30 kts. Confidence remains low in potential for stratus development overnight post-front. Not high enough to include in TAF, but a low chance for stratus after 08Z. Added in FEW020 to message this in the TAF for now until there`s more consistency in the models. Light NE/E winds at the terminals Thursday. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Mensch SHORT TERM...Hiris LONG TERM...Danielson AVIATION...Mensch