Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 05/16/21

Area Forecast Discussion
National Weather Service Denver/Boulder CO
944 PM MDT Sat May 15 2021 .UPDATE... Issued at 930 PM MDT Sat May 15 2021 There is a bit of convection still going over the northern border areas of Larimer and Weld Counties at this time. We ended the watch at 9 PM MDT. Will leave in the mention of fog in the zones. Will make a few sky cover fixes. && .SHORT TERM...(This evening through Sunday) Issued at 230 PM MDT Sat May 15 2021 An upper ridge remains over the area with disturbances moving through it to bring the storm activity to the forecast area. Easterly flow into the plains keeps dewpoints in the upper 40s to mid 50s, and PWAT near the max for mid-May. Stratus over most of the plains is keeping a substantial cap over the plains, shown on area ACARS data. THe initial storms moving off the foothills have died quickly in the capped environment. This cap will likely delay storm activity over most of the rest of the area. However the Palmer Divide has stayed clear which is where convective initiation is occurring and the strongest storms are anticipated due to steep mid-level lapse rates. It will take outflow from the storms firing over the more unstable mountains to try to break that cap and allow storms to spread further east onto the plains. However, the anvils of these storms may delay the breaking of the cap even further. A Denver convergence vorticity zone, formed by the turning of the southeasterly winds moving up over the Palmer Divide, has set up across Douglas County will likely be the focus of some stronger storms, and possible spin ups with the spin along the boundary. CAPE values over 1000 J/kg could stretch this spin into a weak tornado, matching well with SPC`s 2% chance of a tornado over this area. Otherwise, still expecting the main hazards this afternoon and evening to be large hail. Areas north of Denver and across the northeastern plains may not get much convection at all if this cap and stratus holds on. Decreased PoPs slightly over this area for that reason. After this initial storm formation this afternoon, clearing behind it should allow for better low level warming. Then a disturbance is being realized by the models to bring a push of more convection from the southwest near South Park, and pushing across the urban corridor after 6pm. If enough of the cap has broken by this afternoons activity, this round could be much stronger with the large hail threat continuing. This should spread further east out onto the eastern plains this evening. This second disturbance should have some drying and subsidence on the backside, with storms dying from west to east. However there could still be activity over the far eastern plains after midnight. Outflow combined with the moist easterly flow over the plains will again bring some stratus overnight. The upper disturbance will send a northerly push down the urban corridor early Sunday morning. This may bring fog in the northerly push for around sunrise and lasting into the mid-morning. Flow aloft will become slightly more west-southwesterly as a slow moving upper low digs into Arizona, and the ridge over the state will stretch back northwest slightly, which will decrease wind speeds aloft. Upslope flow into the high terrain will be increasing as a surface low deepens near the Four Corners. CAPE and shear will be slightly less tomorrow compared to today, so even less storm organization. However storm motions will be slower, which will increase the flooding threat over the burn scars. .LONG TERM...(Sunday night through Saturday) Issued at 230 PM MDT Sat May 15 2021 Northern Colorado will remain under an unsettled weather pattern through the middle of next week with temperatures slightly below normal and a continuation of likely showers and thunderstorms. The showers will be most numerous during the afternoon and evening hours. The culprit will be an upper level low pressure system which will initially be over West central Arizona on Sunday evening and then ever so slowly drift/meander over and across Colorado and surrounding areas on Tuesday and Wednesday. Long range models are now rather consistent with this overall pattern and track of the low. There is really only weak QG ascent with this system but there is ample moisture and a shallow upslope component to the winds which will remain through mid week. Precipitable water values will range from .50" in the mountains to .80" over the urban corridor and around an inch over the northeast plains. These values will be very close to our climatological maxes for this time of year. This system will be warmer than last week`s so any snowfall in the mountains will be confined to above 10,0000ft. The Sunday evening timeframe highlights the best chance for heavy rain with storms in potential for flash flooding (especially in the burn scars-see more in hydrology section). Nearly saturated airmass expected with weakening mid level flow and shallow upslope low level flow. Instability will be more marginal with expected continued clouds/minimal surface heating so majority of stronger storms expected foothills and higher plains elevations like the Palmer Divide. The Monday and Tuesday time frame again will have ample moisture and near saturation of the airmass but again instability will be even more marginal for storms. The plains will have stratus and any surface based CAPE will be over higher terrain of the foothills and Palmer Divide with values under 800j/kg. For Wednesday, the weakening upper low is right over Colorado and then shifts east on Wednesday night with slightly lower chances of showers and some warming. On Thursday and Friday, the weakening upper low/trof will have shifted east across the central plains states with temperatures finally rising to at or slightly above normals for this time of year. However, a new upper trof will be moving onshore from Northern California and will increase the southwest flow aloft over Colorado. Despite a slightly drier airmass, expect more typical rounds of afternoon and evening showers and thunderstorms each day. Temperatures across the plains will be in the 70s for highs later in the week. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 854 PM MDT Sat May 15 2021 Light winds are expected for DIA all night. Similar to last night. Cross section hit at some Stratus. Will keep some fog in, something like 1-3SM BR around 12Z. Ceiling could down into the BKN010-020 range around 12Z as well. && .HYDROLOGY... Issued at 230 PM MDT Sat May 15 2021 The heaviest rainfall from this evening`s convection was over southern Jefferson and the southern half of Douglas Counties. Radar storm total amounts range from 0.25 to 1.25 inches in those areas. Significant rainfall amounts did not occur across the CWA with this evening`s convection. rjk Some of today`s thunderstorms could produce heavy rains, mainly south and southeast of Denver where stronger storms are expected. Rainfall of 1-2 inches in an hour is possible which could cause minor flooding. For the burn areas in Boulder and Larimer counties, heavy rain is possible but the threat is lower due to this morning`s stratus which will keep the airmass cooler and therefore less unstable. There is a chance of a storm producing a half inch or rain in less than an hour. West of the Front Range the threat is lower still, though thunderstorms with brief heavy rain are possible. Less instability and organization of storms are expected on Sunday, however moisture in the atmosphere remains very high, near the climatological max for mid-May, and winds aloft will be slowing down to allow for slower moving storms. Model soundings still show long, skinny CAPE indicating that storms may be more efficient rain producers than usual. However a lot of cloudiness is expected starting early Sunday morning which may limit storm strength. Therefore, will keep an elevated threat for flash flooding over the burn areas with a marginal threat for flooding elsewhere. The best chance for any flash flooding, especially over the burn scars,will be Sunday evening with rather deep moisture, weaker storm motions, and a marginally unstable airmass. The flash flood threat will lower on Monday and Tuesday with even less instability with more general rainfall and showers with less intense rainfall from thunderstorms. Slightly drier conditions are expected from late Wednesday through Friday with more diurnally driven storms expected. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE.......RJK SHORT TERM...Kriederman LONG TERM....Entrekin AVIATION.....RJK HYDROLOGY....Kriederman/Entrekin
Area Forecast Discussion
National Weather Service Pueblo CO
905 PM MDT Sat May 15 2021 .UPDATE... Issued at 857 PM MDT Sat May 15 2021 ...TORNADO WATCH HAS BEEN CANCELED FOR CROWLEY, OTERO, BENT, AND BACA COUNTIES, THE TORNADO WATCH STILL REMAINS IN EFFECT FOR KIOWA AND PROWERS COUNTIES. THE SEVERE THUNDERSTORM WATCH FOR EL PASO COUNTY HAS BEEN CANCELED... PoPs have also been adjusted to reflect where current areas of convection are, and their anticipated progression for the next few hours. -Steward UPDATE Issued at 537 PM MDT Sat May 15 2021 ...SEVERE THUNDERSTORM WATCH HAS BEEN UPGRADED TO A TORNADO WATCH FOR OTERO, CROWLEY, BENT, KIOWA, PROWERS AND BACA COUNTIES... PoPs have also been adjusted to reflect where current areas of convection are, and their anticipated progression for the next few hours. -Steward && .SHORT TERM...(This evening through Sunday) Issued at 324 PM MDT Sat May 15 2021 Main Forecast Concerns/Challenges: 1) Strong to severe storms remain possible along and east of I-25 through mid to late evening. Main threats are large hail and damaging winds, though have growing concerns for the possibility of a tornado especially across locations closer to the CO and KS border. 2) Strong to severe storms are once again possible along and east of I-25 on Sunday. Flash flooding concerns across area burn scars will also increase. Convective activity has continued to increase across the area this afternoon, with latest radar imagery showing development over the higher terrain, just north of the Palmer Divide, and around the Raton Mesa. However, this development has remained on the weaker side. RAP analysis is still showing a fair amount of CIN in place over southern CO, with a more recent AMDAR sounding out of COS still showing a strongly capped environment. Despite being late in the day, still expect some additional warming along with increasing ascent that should aid in eroding this CIN late this afternoon into early evening. I think this should occur over the next couple of hours, upon which MLCAPE values approaching 2000 j/kg and effective shear of 35-40 kt will support quickly intensifying scattered thunderstorms into the early evening. Locations along the I-25 corridor still look to have the highest chances though late afternoon, with damaging winds and large hail the main threats. This development will likely persist and expand as it moves east across the plains through early to mid evening. Some lower confidence with convective mode with some CAMs showing more linear segments with this eastward moving development. However, given the shear, would anticipate some continued potential for supercells. This will be something to keep an eye on as moisture, instability, and helicity will increase further to the east this evening. In this location/environment closer to the CO/KS border, the highest risk for significant hail (2") will reside. Also, in this location/environment, the highest risk for tornadic development will reside. These latest trends are pointing towards an increased threat of tornadic development over the far eastern plains, closer to the CO/KS border, in the 6 to 9 pm time frame. While concerns are growing, the uncertainty with convective mode does keep some level of lower confidence. Nonetheless, will continue to keep a close eye on observational and radar trends into the evening. Thunderstorms should depart east into KS in the 10 PM to 12 AM time frame. On Sunday, upper trough/low is expected to approach the region with large scale setup continuing to favor thunderstorm development over much of the area. While instability and shear may not be quite as strong on Sunday, this instability and moisture will have the potential to push farther west up to the eastern mountains. So, not only will there be a continued threat of strong to severe storms across southern CO on Sunday, do think there will be an increased flood/flash flood threat as moist upslope flow will now be present. This will include the burn scars as well as other locations along and adjacent to the eastern mountains. .LONG TERM...(Sunday night through Saturday) Issued at 324 PM MDT Sat May 15 2021 Main Forecast Concerns/Challenges 1) Flash flood threat Monday for area burn scars 2) Active weather continues for Tuesday, and possibly into Wednesday Sunday night through Monday...The upper low pushes into northern AZ Sun night, then moves across the Four Corners on Mon. Surface flow is expected to remain out of the northeast through Sun evening, allowing lingering shower activity to persist. However, as the upper low nears on Mon, the surface flow is forecast to turn due east, drawing plenty of llvl moisture back towards the I-25 Corridor and eastern mts. With about 1000 j/kg of CAPE to work with along the eastern mts by midday, storms are expected to fire once again along the higher terrain. The placement of the upper low will be a crucial piece to the puzzle, however, as the steering flow will tend to keep any storms that do initiate close to the mts. Therefore, flash flooding of area burn scars is a definite possibility and is of the utmost concern for Monday aftn and evening. Plan on lows Sun night in the 30s to around 40F for the high valleys, and in the 40s to around 50F for the plains. High temps on Mon are forecast to warm into the 60s for most locations, and nearing 70F along the eastern border. Tuesday and Wednesday...The upper low begins to weaken early Tue as it starts to lift to the east-northeast, then tracks directly over CO through Wed. This track presents a very broad area of lift combined with abundant available moisture, so feel that there is a very good chance of widespread convection both days, with greater chances over the higher terrain and tied more to the aftn and early evening hrs due to heating. Model CAPE is not all that robust either day, and given the overall flow, feel that severe potential is low. High temps both days will climb into the 60s to lower 70s. Thursday through Saturday...Another upper low pressure system drops down out of the Pacific NW for the end of the week, with strong southwest flow developing across the Four Corners region. Multiple disturbances within the flow will most likely help motivate isolated to low-end scattered convection each aftn across the higher terrain and high valleys. As for temps, the southwest flow aloft will warm things up nicely across the cwa, with highs around 70F each day for the high valleys, and in the 70s to around 80F for the eastern plains. Moore && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 324 PM MDT Sat May 15 2021 KCOS and KPUB: VFR conditions are expected over the next 24 hours. Thunderstorms will continue to increase in coverage and progress eastward before diminishing late this evening. Dry conditions are expected through the night into early tomorrow afternoon, before thunderstorms greatly increase in coverage by mid afternoon. These thunderstorms will have the possibility to produce strong gusty winds and hail. These thunderstorms would drop either site below MVFR conditions if KCOS or KPUB found themselves under one. Even if KCOS and KPUB are not directly impacted by these thunderstorms, outflow boundaries will likely be present, and these would shift winds directions and increase wind speeds quickly. There is also possibility that low clouds/fog will develop overnight, but confidence is low in that scenario still at this time; if this scenario came to fruition, MVFR or lower categories would be expected. KALS: VFR conditions are expected over the next 24 hours. An isolated thunderstorm is possible late this afternoon and into the the evening over KALS, but otherwise expect dry conditions through tonight into tomorrow afternoon, before thunderstorms increase in coverage by mid afternoon tomorrow. These thunderstorms could produce strong gusty winds and would also drop visibilities below MVFR conditions if KALS found itself under one. && .PUB WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...STEWARD SHORT TERM...RODRIGUEZ LONG TERM...MOORE AVIATION...SIMCOE