Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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406 FXUS65 KBOU 020149 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 749 PM MDT Sat Jun 1 2024 .KEY MESSAGES... - A chance (20-30%) of one or two severe storms Sunday over the northeast corner of the state - Summer heat through most of next week, with a few 90 degree readings over the plains. && .UPDATE... Issued at 749 PM MDT Sat Jun 1 2024 Latest radar and GOES-16 satellite imagery shows the strongest convection has nearly exited the northeast corner o f Colorado. Storm intensity has weakened significantly over the past couple hours such that the severe weather threat is less than 5% now. Thus, we have cancelled the severe thunderstorm watch for the counties in our CWA. The PoP forecast was updated to reflect the latest trends, which hold onto 10-15% through midnight for the northern mountains. PoPs across the far NE corner and Lincoln County drop below 10% after 9 PM this evening. Should be a quiet night across the area, with skies becoming mostly clear. Temperatures were left alone as they appear to be on track, with lows from the upper 40s in the cool valley spots to mid 50s in the urban corridor, and 30s in the mountain valleys. && .SHORT TERM /Through Sunday/... Issued at 222 PM MDT Sat Jun 1 2024 Dry line is currently a little west of a line from Sterling to Limon. The dry line will progress eastward through the rest of the afternoon and be east of the area by early evening. ML CAPE is expected to reach 2000 J/kg. This combined with 0-6km Bulk Shear of 35-40 knots should produce a few supercell thunderstorms. Large hail up to tennis ball size and damaging winds will be possible with these thunderstorms. To the west of the dry line, ML CAPE only reaches 500 J/kg. Dew points are falling into the 20s and 30s which will result in high-based showers and thunderstorms. Gusty outflow winds to 50 mph will be the main threat with these thunderstorms. The showers and storms come to an end this evening as the airmass stabilizes. For Sunday, a wave embedded in the westerly flow aloft will track across the region. At the surface, lee side trough will extend from far eastern Colorado north-northeast into South Dakota. Best lift from the passing wave will be over northern Colorado into Wyoming. Isolated high-based showers are expected to form over far northern Colorado. Eventually an organized outflow from the storms in Wyoming dives south and increases low level moisture which will bring a better chance for rainfall. Over the far northeast corner of Colorado where it will be more unstable, a severe storm or two will be possible. Airmass continues to warm Sunday, with highs across northeast Colorado expected to reach the mid to upper 80s. && .LONG TERM /Sunday night through Saturday/... Issued at 255 PM MDT Sat Jun 1 2024 Zonal flow is expected across the CWA Sunday night well into Monday, then a weak upper trough moves across Monday night into Tuesday. There is neutral synoptic scale energy over the CWA Sunday night with weak upward motion Monday through most of Monday night. Downward vertical velocity is progged on Tuesday. Looking at moisture, precipitable water values are progged in the 0.30 to 0.80 inch range Sunday night, then they increase into the 0.50 to 1.10 inch range Monday afternoon and night, then they decrease again Tuesday. For CAPE, models show values under 1,000 J/kg over the far northeast corner Sunday night. On Monday afternoon and evening there is limited CAPE, under 600 J/kg, over much of the CWA with slightly higher values over the far northeast corner. There is no CAPE progged on Tuesday. So for pops, will go with 10-30%s over the far northeast corner Sunday evening, then 10-20%s for the northern half of the CWA Monday afternoon and evening. That`s it. Temperatures stay above seasonal normals through the periods, with both Monday`s and Tuesday`s highs very closed to Sunday`s readings. The plains will see mid 80s to lower 90s both days for highs. For that later days, Wednesday through Saturday, models have upper ridging to dominate the weather for the forecast area into Friday. The center of an upper ridge is over southern Utah Wednesday, then central New Mexico on Thursday. By Friday, the upper ridge axis is pushed west and northwest of Colorado due to a strong upper low over the Great Lakes. By Saturday, the upper ridge axis moves back east towards and into Colorado. Moisture is sparse Wednesday, Thursday and Saturday, with a bit more progged on Friday. Overall, it will be dry and pretty warm with the only decent chance of showers and thunderstorms to be on Friday. && .AVIATION /00Z TAFS through 00Z Sunday/... Issued at 548 PM MDT Sat Jun 1 2024 VFR through Sunday and into Monday. There is still a fair amount of virga around but the boundary layer has stabilized such that convection is weak, and downdrafts/gust fronts are also weaker than mid-afternoon. Given the latest radar/satellite trends, we don`t feel the need to include particularly gusty winds in the TAFs the rest of the evening. Can`t rule them out, but too low a chance to include. Northerly flow at APA and DEN should give way to drainage (SSW) after 06Z near 10 kts. At BJC, it should stay pretty much WNW all evening into Sunday morning. On Sunday, we are not expecting as much convective showers as there were today, and thus less chance of convective outflows and rapidly shifting winds. We will still probably need a TEMPO group for convective outflows/gusty wind from virga, but not confident enough to include it just yet for late Sunday afternoon. Generally winds should be out of the WNW and gusting 20-25 kts from midday into the evening hours. There is model agreement in a wind shift via cool front or convective outflow from the north, either way the result is the same: gusty winds (20 kts) out of the NNE after 00-01Z across the TAF sites, so have introduced it into DEN`s TAF. && .HYDROLOGY... Issued at 255 PM MDT Sat Jun 1 2024 Alpine snowmelt will increase runoff the next few days. Hydrologic forecasts from the River Forecast Centers show a few streams getting to action stage by Monday or Tuesday, which means flows will be high and fast but flooding threat appears limited. Please use caution and respect these fast moving and cold flows in the high country. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Schlatter SHORT TERM...Meier LONG TERM....RJK AVIATION...Schlatter HYDROLOGY....RJK/Barjenbruch