Area Forecast Discussion
Issued by NWS Glasgow, MT
Issued by NWS Glasgow, MT
397 FXUS65 KGGW 210239 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 839 PM MDT Mon May 20 2024 .DISCUSSION... Scattered showers over north-central Montana are expected to push NE into southern Sask tonight as an upper low digs a bit to our north. Showers over NE Montana for the most part are dissipating with the loss of daytime heating, northern Phillips county being the exception. Going forecast for the most part has this scenario well in hand and changes to going forecast this evening should be very slight. TFJ Previous Discussion... KEY MESSAGES: 1) Isolated showers and thunderstorms will continue during the afternoon and evening hours today and to a lesser degree on Tuesday. 2) A more widespread chance for showers and thunderstorms will begin late Wednesday through Friday. Unsettled weather will remain likely at times into the upcoming weekend. WEATHER PATTERN OVERVIEW: An upper trough will prevail across the western CONUS this week with occasional shortwaves helping produce enough lift and instability for daily shower and thunderstorm chances. A more organized low pressure system will track through the northern Rockies for the second half of this week with a more widespread opportunity for wetting rains from showers and thunderstorms. This unsettled weather pattern looks to linger into the upcoming weekend. There currently exists about a Upper trof will be over the western states through the end of the week. As shortwave push through the base of the trof, occasional showers and thunderstorms are expected. The greatest probability for rain will be Wednesday through Friday as a lower pressure pushes through the northern Rockies and into the northern plains. The NBM 72 hour probability of 0.50 inches or more of QPF ending Saturday morning ranges from 40 to 50 percent along and south of HIghway 2 and between 30 and 40 percent to the north. CONFIDENCE LEVEL and POTENTIAL DEVIATIONS FROM BASE FORECAST: Confidence is high that a wetter weather pattern is set to unfold for the second half of this week with ensembles showing strong consensus for a broad trough pattern and low pressure system pushing through the region. Confidence is lower on exact precipitation amounts and precise location given the convective nature of expected precipitation, but in general, expecting greater QPF to the southwest and lesser to the northeast. For now, have decided to remain close to the base forecast given that the NBM lines up with consensus view of a cool but wet pattern unfolding and the above average confidence. As the event works its way into the short term and human detail gains greater input value, some deviations become increasingly likely to better capture mesoscale details and placement of precipitation. && .AVIATION... Updated at 0235z... VFR conditions will continue into Tuesday. DISCUSSION: Mainly clear skies are expectd tonight while isolated showers over north-central Montana mainly move into southern Sask tonight. Isolated to scattered showers will be developing SW of the terminals Tuesday with the slight possbility of a stray shower in the Yellowstone valley (affecting KSDY-KGDV). WINDS: Northwest tonight at 5 to 9 kts, at times light and variable. TFJ && .GGW WATCHES/WARNINGS/ADVISORIES... None. && $$ weather.gov/glasgow