Area Forecast Discussion
Issued by NWS Pueblo, CO

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000 FXUS65 KPUB 222217 AFDPUB Area Forecast Discussion National Weather Service Pueblo CO 317 PM MST Sat Feb 22 2020 .SHORT TERM...(This evening through Sunday) Issued at 250 PM MST Sat Feb 22 2020 The closed low is currently over eastern California and southern Nevada as it continues its journey easterly towards Colorado. The Pacific moisture plume being advected by the low pressure system will be oriented from the southwest and be forced up the eastern San Juan Mountains causing orographic snowfall. The snowfall will spread east with time, impacting the Sawatch and Mosquito Mountains by around 8PM tonight followed by the Sangre de Cristo Mountains shortly after. All of the storm total snowfall forecast for the mountains (besides the La Garitas) have around 6 to 10 inches, with locally higher amounts over the higher elevations, which sits well as a Winter Weather Advisory. The moisture content is quite high and the temperatures are warm, which lowers the snow ratios to 10:1 to 15:1, lower than normal for a February in Colorado. One of the main concerns will be avalanches as heavy wet snow falls over the existing snow pack. As for over the plains and eastern mountains, the upper low is expected to propagate over southern Colorado and the surface low is expected to propagate over northern New Mexico. The surface low will undergo lee cyclogenesis and baroclinic cyclogenesis, but the limiting factor will be the baroclinic (temperature gradient) zone intensity. The rapidly intensifying cyclone will eventually become vertically stacked and have the characteristics of a TROWAL. The wrap around section of the cyclone (warm conveyor belt; isentropic lift) will create banding over I-25 corridor as the day progresses. At this point in time, the 700hPa flow is due east to northeast during the morning, which will enhance snowfall and rainfall rates over the I-25 corridor. Initially the precipitation over Pueblo and the rest of the lower Arkansas River Valley will start as rain, but will transition to snow at around noon and shortly after for the rest of the eastern plains. The temperatures over Pueblo, for example, are expected to remain above freezing, but the air just above the surface will be below freezing, so snow will fall over Pueblo, but how much of it will accumulate rather than melt. The other "wild card" is the convective aspect of this storm. SPC has put southeastern Colorado under the "general thunderstorm" category, which could enhance snowfall rates and rainfall rates over the far eastern plains. Could there be a few rumbles of thunder, perhaps thundersnow? Yup. Our decision was to issue a Winter Weather Advisory over the I-25 corridor and eastern mountains. As the low evolves into its mature stage, winds will pick up over the eastern plains, with wind gusts around 30 to 35 mph in our forecast. Another big question is how much blowing snow will happen with how moist and heavy it is. We put blowing snow in the forecast grids across the region though. The east to west oriented roads are expected to have the especially difficult travel due to blowing and drifting snow. The overall trends of the models have shifted the main snow band further south, so southern Pueblo County, Huerfano County, and Las Animas County, as well as the eastern mountains, have the best chance at being upgraded to a Winter Storm Warning, but at this time, they will be left as advisories. Another point of uncertainty is over the western San Luis Valley in places like Del Norte. When deep taps of moisture are advected towards the valley, the west San Luis Valley can get a lot of snow, but with the true tap of moisture not forecast to reach the valley, we put lower snowfall totals in the forecast. Overall, there is still plenty of uncertainty due to the CAPE in the atmosphere, the rain-snow line (snow level), how much snow will fall and actually accumulate over areas with warmer surface temperatures, and will the rapidly intensifying low pressure center shift north, south, or will it be stronger or weaker. The forecast issued is the based on the current data and will updated as new data comes in, so check back! .LONG TERM...(Sunday night through Saturday) Issued at 250 PM MST Sat Feb 22 2020 Sunday night... Precipitation will be ongoing at the beginning of this long term forecast period mainly across the plains and east facing slopes of the southern mtns, with the heaviest precip over the far eastern plains. Main concern during this period is what precip type will be ongoing, especially across the eastern plains. Upper low is expected to be in the vicinity of the CO/NM/KS border at this time and quite favorable deep easterly flow. A variety of forecast model soundings are saturated throughout, with temps at or just above freezing at 00 UTC Monday (early Sunday evening), and this would allow for snow to be falling as far east as the CO/KS border. Given the track of the surface low, orographics (Raton Mesa) and thermal profiles, the best chance for accumulating snow over the far eastern plains will generally be across Las Animas and a good part of Baca county. However, there is a possibility that we may see accumulating snow across the remainder of the far eastern plains with this system. Some thunder may also occur over the far southeastern plains during this time period (SPC has a `marginal risk` immediately south of Colorado Sunday evening) Based on the uncertainty with this system, will allow later incoming shifts to analyze latest data, and issue hilites if needed. At this time, believe any accumulating snow over the far eastern plains will occur mainly on grassy surfaces, although any areas of heavy snow will cause roadways to become slushy across the far eastern plains. Over the plains closer to the mtns, precip should be showery in nature but it is expected to be all snow. As the evening progresses, precip is expected to end from west to east during the late evening and early morning hours. Overall, after system clears the region, widespread storm total amounts of 0.25 to 0.50 liquid equivalent should have fallen over the lower elevations. Min temps by Monday morning should fall into the lower 20s across most of the plains with single digits and teens in the mtns and valleys. Monday through Wednesday... Powerful jet will affect the region during this time and will drive a very cold airmass into the region starting late Monday morning and lasting into Wednesday. This system will bring much colder air into all of the area starting Monday afternoon and lasting into early Wednesday. This heaviest precip with this system will occur across the central mountain Monday into Tuesday, although all of the higher terrain may see on and off snow showers with this system during this 3 day period. Additionally, some snow showers may also be possible across the lower elevations, especially Monday evening and Tuesday afternoon as embedded short waves in the strong NW flow moves across the area. The coldest day should be Tuesday. Thursday and Friday... Flow aloft remains Northwesterly although gradient will slacken significantly and drier air will advect in. Temperatures will recover to seasonable values with 50s and 60s returning to the plains by late week. /Hodanish && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 250 PM MST Sat Feb 22 2020 Rain and snow showers will be in the vicinity of KALS throughout the evening and overnight, a brief lull in precipitation chances in the morning, followed by more vicinity rain and snow showers. MVFR and IFR conditions are possible if snow or rain develops over the forecast point. VFR conditions are expected over KPUB and KCOS through the evening, but during the early morning lower clouds will begin to develop overhead lowering ceilings to MVFR to IFR. Precipitation is expected to form over KCOS and KPUB during the morning, lowering visibilities to IFR and MVFR with the possibility of LIFR. KCOS is expected to be all snow, whereas KPUB will start as rain and transition to snow around 1200 MST. These conditions are expected to last through the rest of the forecast period. && .PUB WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 8 AM to 11 PM MST Sunday for COZ077>080-083-086>088. Winter Weather Advisory from 8 PM this evening to 3 PM MST Sunday for COZ058-060-061-063. Winter Weather Advisory from 9 PM this evening to 8 PM MST Sunday for COZ072-073. Winter Weather Advisory from 5 AM to 8 PM MST Sunday for COZ076- 081-082. Winter Weather Advisory from 9 PM this evening to 11 PM MST Sunday for COZ074-075. Winter Weather Advisory until 3 PM MST Sunday for COZ068. Winter Weather Advisory from 8 AM to 8 PM MST Sunday for COZ084- 085. && $$ SHORT TERM...SKELLY LONG TERM...HODANISH AVIATION...SKELLY

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