Area Forecast Discussion
Issued by NWS Glasgow, MT
Issued by NWS Glasgow, MT
913 FXUS65 KGGW 152014 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 214 PM MDT Sun Sep 15 2024 .DISCUSSION... KEY MESSAGES: 1) Warm temperatures will continue through Tuesday. 2) Isolated showers Monday morning, then isolated thunderstorms Monday afternoon and Tuesday afternoon. 3) Cooler temperatures move in Tuesday night with widespread rain in the west through Wednesday evening. WEATHER PATTERN OVERVIEW: A shortwave ridge today, and then a slow moving warm frontal passage with an oncoming low pressure will help warm temperatures remain over the area through Tuesday evening. Then the cold front will pass through by Wednesday morning to keep temperatures near average for the remainder of the week. The slow moving low will drag Gulf and Pacific moisture into northeast Montana to bring PWATs above 1". There is disagreement among the NAM, ECMWF, and GFS on exactly how long this low will remain over the area. A slower moving low may result in rainfall totals in the west of up to 2", but a faster low may keep the amounts to below 0.5". Anyway, isolated thunderstorms associated with the warm front are expected Monday afternoon. As the trough gets closer on Tuesday, there is moderate (50 percent) confidence of strong to severe thunderstorms occurring in the afternoon/evening. The NBM 48 hour probability of 1 inch of rain remains at 60 to 70 percent for Phillips County from Tuesday night through Wednesday night and drop quickly south and east of there. Closer to the MT/ND Border, probability of an inch of rain is only around 10 percent while the probability of 0.25 inch of rain is 10 to 30 percent. Dry slotting is expected at times along the MT/ND border which will result in lower rainfall amounts. While the upper low moves north Wednesday night, varying degrees of upper trough remains over the area into next weekend with chances of showers at times. FORECAST CONFIDENCE & DEVIATIONS: High confidence exists on warm and dry weather today, Monday, and Tuesday. Compressional heating ahead of the cold front may allow temperatures to tick a few degrees warmer, but confidence is low on this solution. Low to medium confidence exists on thunderstorms Monday given the modest setup. Confidence for rain is high west and low to medium east for Tuesday and Wednesday with decent support for cooler and wetter weather unfolding. Consensus continues to indicate widespread rain in the west but there remains uncertainties in the coverage and amount of precipitation due to dry slotting at times, especially for eastern areas. Have opted to keep the forecast in line with NBM overall for now, which handles the big picture well. && .AVIATION... Last Updated: 2045Z Category: VFR, possible MVFR Monday afternoon. Discussion: With a ridge overhead, VFR conditions with clear skies will give way to high clouds overnight. A warm front may aid in isolated showers late Monday morning before isolated thunderstorms move in late Monday afternoon. Brief reductions to MVFR are expected in thunderstorms. Winds: Light and variable becoming east northeast at 8 to 17 knots after 00Z Monday, becoming southeast at 6 to 14 knots after 18Z. Erratic and shifting winds near thunderstorms. && .GGW WATCHES/WARNINGS/ADVISORIES... None. && $$ weather.gov/glasgow