Area Forecast Discussion
Issued by NWS Glasgow, MT
Issued by NWS Glasgow, MT
816 FXUS65 KGGW 172007 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 207 PM MDT Mon Jun 17 2024 .DISCUSSION... KEY MESSAGES: - Cool temperatures with widespread rain expected tonight and Tuesday. - Isolated to scattered thunderstorms tonight and again Tuesday afternoon and evening. Marginal risk for severe thunderstorms this afternoon and evening along the Yellowstone River. - Warm temperatures starting on Wednesday with frequent chances for showers and thunderstorm chances between Wednesday and Saturday, especially Friday evening. WEATHER PATTERN OVERVIEW: There will be an upper trough/low moving into western Montana today while a surface low develops over Wyoming. SW flow aloft ahead of the trough will bring deep moisture into the forecast area today which will allow widespread rain showers to develop by sometime this afternoon with embedded thunderstorms. To the northeast of the surface low today, an inverted surface trough along the Yellowstone River will bring somewhat warmer and more unstable airmass with a marginal risk of severe thunderstorms. At the same time precipitable water rises to 1.0 to 1.25 inches this afternoon and evening in the east. WPC has a marginal risk for excessive rain today and tonight and the best chance for excessive rain would come in any embedded thunderstorms that develop. The upper low moves through central Montana tonight and eastern Montana on Tuesday which will keep the rain going most of the time until the low moves to the northeast Tuesday night. At this point, there is a 60-80 percent chance of a half inch of rain and a 20-40 percent chance of an inch of rain today and Tuesday from this event. Montana spends the remainder of the week in an unstable WSW to SW flow aloft which will bring warmer temperatures and frequent chances for showers and thunderstorms. With the closer proximity to the upper trough Friday Night, chances for precipitation are expected to be higher. With warmer temperatures, some of these thunderstorms could be severe. FORECAST CONFIDENCE and DEVIATIONS: For the system today through to Tuesday night, QPF amounts varied slightly from the previous forecast, with a probability around 70-100% for at least 0.25", 60-80% for 0.50", and 20-40% for 1". From Wednesday onward confidence is moderate on a gradual warming trend, but low on precipitation chances. Models agree on a broad western US and Canada trough with a WSW to SW flow aloft over Montana but disagree on the timing of waves within the flow aloft. && .AVIATION... LAST UPDATE: 2000Z FLIGHT CAT RANGE: VFR becoming MVFR this afternoon and IFR tonight. DISCUSSION: Clouds will continue lowering as rain moves into northeast Montana. Cloud bases will lower to MVFR levels between 19z and 23z this afternoon and to IFR levels between 00z and 03z this evening. Widespread rain and embedded thunderstorms expected by this evening becoming showery late Tuesday from west to east. WIND: East becoming ENE 10 to 20 knots and NE to north 10 to 15 knots tonight. TFJ && .GGW WATCHES/WARNINGS/ADVISORIES... None. && $$ weather.gov/glasgow