382 FXUS65 KTFX 100321 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 921 PM MDT Sun Apr 9 2017 .UPDATE...Snow is tapering off across most of central Montana but some light accumulations are still expected across my eastern zones through midnight. Have gone ahead and cancelled the Winter Storm Warning for most of the area but have continued it in Fergus County since light snow still continues at Lewistown. Have also issued a Special Weather Statement to alert travelers to the likelihood of black ice developing as wet roads freeze this evening. Used short term model consensus tools to re-evaluate the likelihood for widespread dense fog overnight and believe that the earlier forecast may have overstated the risk so have cut back wording to emphasize areas of fog with only a few locations expected to become dense. Finally, after examining stability parameters and convective indices have decided to remove mention of thunderstorms for Monday afternoon. mpj && .AVIATION... Updated 2335Z Weather system over central and eastern Montana continues to move east with precipitation tapering off and skies clearing from west to east during the evening hours. Lingering MVFR conditions will give way to widespread VFR conditions as mid-level shortwave ridging builds over Montana for mostly clear to partly cloudy skies late tonight and much of Monday. Only exception to clear skies will be the possibility for areas dense fog causing LIFR/IFR conditions 08Z to 15Z. Next weather system will approach Montana after 18Z Monday with scattered showers/TSRA developing over Southwest Montana. mpj && .HYDROLOGY... 24hr precipitation totals have exceeded 1.25 inches at several observation points in Cascade, Judith Basin, and Fergus Counties. A combination of spotter and SNOTEL reports suggest that snow accumulation may have peaked at mid slope elevations. Although temperatures will turn colder tonight, the combination of sunny skies and warmer temperatures over the next few days will contribute to a rapid snowmelt runoff. Stream hydrographs are in good order this evening, but will continue to monitor closely for rises on small streams and creeks in central Montana. && .PREV DISCUSSION... /ISSUED 535 PM MDT Sun Apr 9 2017/ Rest of Today and Tonight...Light snow continues over portions of North-central MT. Snow ratios this afternoon have been lower than 10:1, with a 6:1 snow ratio determined at our forecast office in Great Falls. Primary roads have remained wet or slushy despite 3-6" of new snow since sunrise. The Fort Benton area never changed to snow, with rain all day. Above 4000 feet within the winter storm warning area, reports suggest 10 to 18 inches have accumulated, with some power outages and vehicles slipping off slushy roads across Judith Basin and southwest Fergus County. Snow has already lingered a bit longer than forecast as low level northeasterly upslope flow wraps around the closed 700mb low centered over southeast MT. Radar trends and short- term guidance do suggest the precipitation will gradually end for Cascade county by about 00z. Snow may linger into the evening further east, but overall the dry air noted on Water vapor imagery will work its way west to east. This will create problems with a potential flash freeze for wet roads as temperatures drop into the low 20s. That said, the low temperature forecast is rather low confidence since areas of dense freezing fog are expected to develop. PN Monday and Tuesday...A short-lived period of mainly dry conditions lasts from late tonight through early Monday afternoon before the next upper level trough moves onto the west coast and into the Northern Rockies Monday night. A cold front in association with this system moves east across the region late Monday afternoon and evening. Showers will develop ahead of this system and track NE across central and SW MT Monday afternoon and evening with a few isolated weak thunderstorms also possible. Windy but generally dry conditions follow the frontal passage Monday night through Tuesday as low pressure moves east across southern AB. Hoenisch Tuesday night through Sunday...The medium range period will feature an active jet stream across the northern half of the US. Within this active jet, several systems are likely to impact part, if not all, of the forecast area. The models are in good agreement through about Friday, but then begin to diverge. The majority of the differences appear to stem from the evolution of an upper level low over the northern Pacific. If it stays offshore longer, that would favor a milder/drier Easter weekend. Regarding more specific details, a warm front will likely surge north through the area Wednesday into Wednesday night, possibly bringing a few showers with it. A Pacific cold front will then quickly move through the area on Thursday. Ahead of the cold front, breezy and mild conditions are likely, especially east of I-15. Thursday afternoon, prior to the front's arrival, instability may be sufficient for a few showers and thunderstorms to develop via daytime heating over higher terrain and then move out over the valleys/plains. Regardless of what happens Thursday afternoon, the front itself will likely bring a round of showers with it. For Friday into early Saturday, more wet weather is possible as another disturbance may move eastward over the CWA. At this time, the rest of Easter weekend looks to be somewhat warmer and drier courtesy of upper-level ridging building over the region. Martin/Jaszka && .PRELIMINARY POINT TEMPS/POPS... GTF 24 47 29 52 / 20 20 20 0 CTB 25 49 29 49 / 20 20 0 0 HLN 26 51 30 54 / 10 40 20 0 BZN 24 52 27 54 / 10 20 20 0 WEY 16 37 20 41 / 20 30 30 10 DLN 25 49 26 51 / 0 20 0 0 HVR 30 56 30 55 / 40 20 10 0 LWT 21 45 25 48 / 70 20 30 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until midnight MDT tonight above 4000 feet for Fergus. && $$ weather.gov/greatfalls