Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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255 FXUS65 KBOU 091558 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 958 AM MDT Sun Jun 9 2024 .KEY MESSAGES... - More thunderstorms today and Monday with a lower severe threat but a risk of heavy rain and localized flooding. - Minor snowmelt impacts from rising streams, mainly in Grand County. Thunderstorms this weekend could further increase stream flow. - Hot and mainly dry weather towards the middle to end of next week. There is potential for a day or two to need a Heat Advisory, most likely Thursday. && .UPDATE... Issued at 958 AM MDT Sun Jun 9 2024 Going forecast on track. Did make a few changes to match up with the current trends. Stratus looks to hold on into the early afternoon over eastern Larimer and Weld Counties and east/southeastward over the eastern plains. Lowered highs a few degrees in these area. Also lowered PoPs, especially over the eastern plains where it should stay too stable for storms today. Kept lower PoPs in the for Fort Collins and Greeley areas, but delayed the chances by a few hours. If this far northern Front Range see storms it would be this evening. Increased temperatures 1-3 degrees over the Denver area where mostly sunny skies are expected to prevail until convection fires mid afternoon. Speaking of convection, along the Front Range where it will stay mostly sunny, MLCAPE will reach 1000-2000 J/kg. Shear will be on the weak side, but a few brief severe storms with one inch diameter hail or slightly larger will be possible. Precipitable water values climb to an inch or slightly higher. Heavy, locally very heavy, rain will be possible with the thunderstorms today due to the moist unstable airmass with slow storm motions. && .SHORT TERM /Through tonight/... Issued at 400 AM MDT Sun Jun 9 2024 While showers have diminished across northeast Colorado, lingering low level moisture and easterly flow have supported fog and low stratus development across the plains. Nighttime Microphysics RGB satellite imagery shows the fog/low stratus in the far northeast corner/far east gradually filling in and extending westward early this morning. Can`t rule out some light drizzle in some of the widespread thicker layers. If widespread dense fog becomes more evident, a short-fused Dense Fog Advisory may be in order for the plains this morning. The question will be how far this will extend toward the urban corridor. It may be more favorable to extend north into Weld County, potentially even nudging south to parts of Boulder, Broomfield. Confidence is low in it getting that far south and west. Denver is tricky as they are observing sufficient SW flow which could hold the advancing fog/stratus further east. Any stratus/fog should start to scatter/erode mid-morning. Today an upper level ridge builds in from the west with the axis over the Four Corners region. This will bring weak NW flow aloft over CO. There will still be plentiful moisture under the ridge aloft and easterly surface flow will keep it in place across the plains and Front Range today. Although more stable than yesterday, there will still be instability building in the afternoon as long as there is an ample period of heating. This will depend on how extensive the stratus is this AM and how quickly it erodes. Ensemble guidance shows mean CAPE values in the 500-1200 J/kg range with the higher end of the range centered around the urban corridor where there will be more ample heating. Moisture and instability will be sufficient to support some strong to severe storms this afternoon; however, weaker 0-6km bulk shear will keep storms less organized. Wind and hail 1"/just above are possible. With weaker winds aloft, storm motions are expected to be slower which will add a heavy rain threat as well. More in the Hydro Discussion. Scattered thunderstorms develop closer to mid- afternoon, continuing through the early evening with the higher chances west of I-25. && .LONG TERM /Monday through Saturday/... Issued at 400 AM MDT Sun Jun 9 2024 Not a lot of change to the extended forecast this morning. Main trends are less warming on Tuesday and better confidence in increased thunderstorm activity on Friday. On Monday, the plains look mostly capped, but there should be enough instability over the mountains to generate scattered afternoon thunderstorms that should drift east onto the adjacent plains in the late afternoon and early evening. There`s still enough moisture for some strong storms with locally heavy rain, though storm motions should be a bit faster. There`s a little more emphasis to a weak shortwave that passes early Tuesday. This ushers in drier air aloft, but also a bit of cooling in the lower atmosphere. The result is that this day may not have much warming and could even be less capped. There should be less moisture and instability though, and faster storm motions, so perhaps it`s just a low grade convective day with fairly benign storms. An upper level ridge does build west and south of us for Wednesday and Thursday, with pretty good agreement on temperatures reaching into the 90s. Thursday has been looking like the hottest day, and it still could be, but there are quite a few model runs that are showing a little cold front associated with a weak wave passing over the northern plains that could drop our temperatures a few degrees and even bring some clouds and isolated showers/storms to the northern border areas. There are still some runs that have the temperature close to 100 degrees in Denver, but sticking with the NBM keeping us in the mid 90s looks reasonable given the increasing chance of some clouds or a puff of less hot air from the north. Another change associated with that shortwave in combination with a trough approaching from the southwest is that there`s an influx of low level moisture onto the plains for Friday. There may be some high level moisture too, with dry air in between. Convective activity will be determined by how much cooling there is with the incoming air. Latest guidance mostly shows just a little cooling which would make this a fairly ripe convective day. && .AVIATION /12Z TAFS through 12Z Monday/... Issued at 538 AM MDT Sun Jun 9 2024 Still continuing to monitor the fog/low stratus potential early this morning. Fog/low stratus has developed to the north and east. It would take 1 or two hours for it to reach the edge of DEN (around 14Z) and with solar heating, shouldn`t last too long if it did get there or it could sit at the edges of the field. Similar story for BJC. Confidence low on if it gets to DEN/BJC before it erodes/scatters, but worth mentioning with recent trends on satellite. Any fog/stratus should start eroding mid morning. There is potential for showers and a few thunderstorms this afternoon, mainly after 21Z. Chances are a little higher at BJC/APA compared to DEN. Nearby or passing storms may bring brief gusty winds up to 35 kts and outflow boundaries bringing vrb wind direction changes. Early evening, any remaining showers/storms weaken and move eastward. Enhanced southerly flow persists for most of the overnight period at APA/DEN and lighter at BJC. && .HYDROLOGY... Issued at 400 AM MDT Sun Jun 9 2024 Elevated flows continue across the upper Colorado River basin and additional rainfall this weekend could lead to further increase in the flows. Remain cognizant of the dangers of these cold flows, and be aware of any Flood Advisories. Storms will be moving much slower today and Monday. However, they will likely be weaker than Saturday. The primary threat during the forecast period will be in Cameron Peak today as a moderate threat for flash flooding will exist. The threat will be minor again on Monday. Periods of heavy rain are possible in storms today, mainly west of I-25 with a marginal risk for localized flood impacts. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Meier SHORT TERM...Mensch LONG TERM...Gimmestad AVIATION...Mensch HYDROLOGY...Gimmestad/Mensch