Area Forecast Discussion
Issued by NWS Pueblo, CO
Issued by NWS Pueblo, CO
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603 FXUS65 KPUB 201709 AFDPUB Area Forecast Discussion National Weather Service Pueblo CO 1109 AM MDT Fri Sep 20 2024 .KEY MESSAGES... - One last day of above seasonal temperatures with spotty critical fire weather conditions across the plains. - Potent Fall storm will spread widespread showers and thunderstorms with high elevation snow across southern CO Saturday afternoon through Sunday morning. - Snow levels may drop down to 9000 feet with heavy wet snow accumulations of 2 to 9 inches for the higher peaks above 10-11kft north of Hwy 50. - Strong to severe thunderstorms possible Saturday afternoon and evening for the San Luis Valley, southern mountains and portions of the Raton Mesa Region. && .SHORT TERM /THROUGH TONIGHT/... Issued at 343 AM MDT Fri Sep 20 2024 Current water vapor imagery and upper air analysis has modest southwest flow aloft across the region, with upper level ridging in place across the southern Rockies into the southern High Plains along with an upper level circulation evident off the southern California coast. No big changes in the forecast for today and tonight, as models agree on slowly increasing southwest flow aloft across the Rockies through the day, as the southern California low digs into southwestern Arizona this evening and then continues to lift out across northeastern Arizona by 12z Saturday. Southwest flow aloft induces lee troughing across the plains, with breezy south to southwest winds again leading to some spotty critical fire weather conditions, mainly along and west of the I-25 Corridor this afternoon. The southerly low level flow will increase low level moisture further east across the plains, leading to the potential for a few afternoon and evening showers and thunderstorms. Models to indicate some modest SBCAPE of 200-600 j/kg, though with DCAPE up to 1000 j/kg, could expect to see gusty outflow winds up to 50 mph as the main threat from any storms that do pop up. Today also remains the last day for above normal temperatures for a while, with highs in the mid 80s to mid 90s expected across the plains, and mainly in the 60s and 70s across the higher terrain. Convection wanes through the early evening, with a slow increase in mid and upper level moisture across the Rockies through the overnight hours. Increasing flow aloft will also help to keep lows above seasonal levels in the 50s and 60s across the plains and mainly 30s and 40s across the higher terrain. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Issued at 343 AM MDT Fri Sep 20 2024 Models in good agreement tracking the upper low into the Four Corners region Saturday afternoon and into NE CO/SW NE by Sunday afternoon. There is some spread in the speed of its ejection towards the end of the period. A slower ejection, as portrayed by the NAM and Canadian members could support a slower drying trend for Sunday, but overall differences are slight at this time. As for sensible weather, a wave of showers and thunderstorms will lift northward late Saturday morning through the afternoon as the first round of WAA/upglide overspreads the front boundary which sets up across the TX Panhandle into eastern NM on Saturday. To the north of the boundary, instability increases as CAA advection from the approaching upper low spreads in, but CAPE seems limited across the plains and rain showers may help to stabilize the low levels initially. Deep layer shears are impressive across all of southern CO with 50-70 kts and long straight hodographs supportive of supercells capable of producing large hail and damaging winds. The challenging part of the forecast (and limiting factor for severe potential) will be the amount of instability. Suspect there could be sufficient elevated CAPE across southern portions of the southeast plains (northern slopes of the Raton Mesa region) for elevated low topped supercells. Where parameters come together better will be across the San Luis Valley as the dry slot advances eastward and elevated instability and increasing sfc dew points in southerly flow could yield CAPE values of up to 1000 J/kg. There are some helicity tracks across the San Luis Valley in HREF members so will need to watch this trend closely. SPC has shifted the Marginal risk westward as a result, which lines up well. Otherwise, snow levels will drop Saturday night as the deformation band takes shape across central CO, and easterly upslope flow intensifies into the southeast mountains. Most areas should see a good wave of showers and thunderstorms with some elevated CAPE spreading eastward across southern portions of the southeast plains through the evening as the column cools aloft with the approaching system. Could be looking at some small hail and gusty winds along with heavy rainfall with the stronger storms into the late evening hours across southern sections of the southeast plains. Elsewhere, widespread rain is expected with snow levels across the mountains dropping to around 9000 feet in the latest runs early Sunday morning. Most accumulating snow will be confined to above 10kft with up to around 8 inches or a little more across the higher peaks above 12kft of the Pikes Peak and the Sawatch and Mosquito ranges. There could be a brief rain snow mix down to 9000 feet early Sunday morning, though accumulations should be limited due to ground warmth. The precipitation band will shift northeastward as the upper low lifts into NE CO Sunday morning. Precipitation will continue across the central mountains and Pikes Peak region through the morning in area of wrap around, but overall should see a downward trend as subsidence behind the system spreads in. Temperatures will be quite a bit cooler with some scattered showers lingering in northerly flow across the southeast plains into the early afternoon depending on the timing of the departing system. Cool northwest flow remains over the region with quite a bit of spread in the models regarding the next system dropping southward Monday night and Tuesday. Operational EC still looks like the outlier with the retrograding closed low solution across the western U.S. portraying a wetter solution, even in its ensembles which favors weaker more general troughing hanging back across the Great Basin during this period. National Model blends keep some isolated pops through this period and even GFS Ensembles support some light precipitation across southern CO through the period. Drying and warming returns for late week as another upper ridge translates in. -KT && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 1057 AM MDT Fri Sep 20 2024 VFR at all taf sites the next 24 hrs. S-SW winds will strengthen across the area this afternoon, with gusts 20-25 kts at all terminals 19z-02z, then winds diminish overnight. Cold front dropping south through the plains will bring strong north winds to KCOS and KPUB Sat morning, with gusts over 30 kts likely beginning around 13z at KCOS and by 15z at KPUB. Outlook for after 18z Sat, widespread showers and thunderstorms will develop across the area, with periods of MVFR and brief IFR conditions likely at all sites, especially Sat night into Sun morning. Mountains and passes will be obscured from midday Sat into least midday Sun. Slowly improving conditions Sun afternoon/evening. && .PUB WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from noon Saturday to noon MDT Sunday for COZ058-060-082. && $$ SHORT TERM...MW LONG TERM...KT AVIATION...PETERSEN