Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/19/21

Area Forecast Discussion
National Weather Service Glasgow MT
253 PM MDT Sun Apr 18 2021 .DISCUSSION... ...Accumulating snow expected today for the Little Rockies and Petroleum County... AFTERNOON UPDATE: With the latest update, snow was trimmed back even further. Southwest Phillips county over the Little Rockies now appears to be the only place where significant snow is likely. Will however leave the petroleum county Advisory up on the off chance that rain could transition back to snow in a significant form later this evening as the possibility while reduced still does exist. In fact there was an hour this early afternoon at KGGW where the rain attempted to transition to snow briefly before moving back to rain. So a minor change in wet-bulb aloft could easily reverse this fortune. The rest of the forecast looks to remain mostly unchanged through Thursday just before another cold front arrives. Ensemble data sets appear to phase out of agreement with each other from Friday onward with these time periods trending colder slightly. Confidence from here onward is low. GAH 815AM UPDATE: Snow coverage is highly sensitive to minor temperatures and dewpoint fluctuations through the day today. Started from observations and used the ConsShort diurnal curve to get the rises and falls correct over the day. This raised hourly temperatures and dewpoints over lower elevations which eliminated a lot of snow today in the valleys and coulees. Meanwhile, mountains, ridge tops and plateaus maintained most of their snow coverage which kept the far west of petroleum county under significant enough snow to maintain the Advisory. GAH MORNING DISCUSSION: A cold frontal passage today will lead to steady or falling temperatures across the region. Meanwhile, a mix of rain and snow will transition to snow as things shift south this evening. The steadiest precipitation will occur over the Little Rockies and Petroleum County where 2 to 4 inches of snow may accumulate. This will lead to reduced visibility and slippery road conditions. In addition, the cold and wet weather will likely stress out newborn livestock. Consideration was given to adding blowing snow over the Little Rockies, though wind speeds are a bit marginal. Especially if it falls as a wetter snow or the ground starts off wet, it may be a bit harder to get true blowing snow conditions. Drifting snow across area roadways is certainly possible, and will need to continue monitoring for the potential for blowing snow. Regardless, a Winter Weather Advisory is now in effect for SW Phillips and Petroleum Counties from 9 AM this morning until Midnight tonight. A Lake Wind Advisory has also been hoisted due to gusty conditions expected for the Fort Peck Lake area. Snow will taper off tonight, though lingering instability driven rain and snow showers are certainly a possibility into Monday as the upper level low remains over the forecast area. Ensembles show the height pattern reflecting a ridge toward the middle of the week building across SW Canada and the Pacific Northwest extending into the Northern High Plain, oriented in a west to east fashion. This will lead to gradually moderating temperatures and dry weather conditions due to larger scale subsidence. && .AVIATION... LAST UPDATE: 2015Z FLIGHT CAT: VFR - IFR ICING: With low clouds generating precipitation and surface temperatures so close to freezing, there is a chance for icing on aircraft surfaces with these clouds/ceilings. This threat should begin to diminish around 06Z. DISCUSSION: MVFR ceilings are expected through mid-afternoon. rain could transition to snow over some higher elevations. This would bring brief IFR visibilities to the areas southwest of the terminals though it is not out of the realm of possibility that it could briefly impact a single terminal like KGGW or KGDV before the day is over. VFR ceilings are anticipated again after about 22Z this afternoon. WIND: North to northeast at 10 to 20 kts gusting to 25 kts through the early evening. Then becoming north and calming to 5 to 15 kts around midnight and lasting through Monday afternoon. GAH && .GLASGOW WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until midnight MDT tonight for Petroleum...Southwest Phillips. Lake Wind Advisory until 9 PM MDT this evening For Fort Peck Lake for Central and Southeast Phillips...Central and Southern Valley...Garfield...McCone...Petroleum. && $$