textproduct: Glasgow

KEY MESSAGES

- Periods of showers today with thunderstorms becoming more widespread by the late afternoon and evening hours. Some storms may be slow moving, producing heavy rainfall.

- Upper trough will maintain seasonably average temperatures and much wetter conditions across NE Montana into early next week.

- The trough will push east with drier conditions and moderating temperatures by the middle of next week.

DISCUSSION

WEATHER PATTERN OVERVIEW:

WPC maintains a slight risk of excessive rainfall for western portions of the CWA for this period. Periods of showers will continue at times today with thunderstorms becoming more numerous during the afternoon and evening hours.

High end HREF guidance is showing 3 hour max QPF on the order of 2-3" with the heaviest, slowest moving convection this evening. This suggests at times, very locally intense rainfall rates with isolated cells, since the boundary to maintain a spatially constant source of lift for training thunderstorms does not exist near the surface. Coupled with very low CIN, any source of lift will be sufficient to raise parcels and allow for convection to form. However, very little shear can mean cells that do develop this afternoon will not necessarily be strong, long lived severe storms. The setup is ideal for widespread weak thunderstorms that are prolific rain producers within an environment of record maximum PWATs of 1.2-1.4" and MLCAPE approaching 1,000 J/kg. Mid to low level high RH (>80%) and large warm cloud layers will keep rain from evaporating, allowing for very efficient rainfall productions with these storms.

The upper trough/closed low pattern will likely maintain wet and cool conditions over the region into early next week, with high temperatures for Sunday and Monday into the 60s for much of the weather. This will come as a relief from the recent hot and dry weather conditions across the area. Ensembles show a general eastward progression of the trough such that a shallow ridge builds in for the middle of the week. This would allow drying conditions and moderating temperatures.

FORECAST CONFIDENCE & DEVIATIONS:

Blended PoPs with HiRes ARW and SREF to better match HREF guidance and collaboration.

Confidence is high for wet weather conditions and widespread wetting rains through early next week.

While peak total rainfall amounts will likely come in between 1.5" and 3" through Monday, these will be isolated and confined to where slow moving storms persist. The exact timing and placement of these storms is difficult to pin down, but overall expect highest probabilities west of Glasgow to Jordan with lower probabilities toward the MT/ND border.

Given dry conditions leading up to this event flooding concerns are minimal, but will have to monitor low lying areas, open fields, small streams, poor drainage areas where slow moving thunderstorms with intense downpours occur.

AVIATION

Updated: 2000Z

FLIGHT CATEGORY: MVFR. Brief IFR possible in intense thunderstorm downpours.

DISCUSSION: Periods of showers will continue today, with thunderstorms becoming more numerous in the evening hours. Some of the storms may produce intense and persistent downpours.

WIND: East at 10 to 15 kts gusting to 25 kts, increasing and becoming west after 18Z tomorrow. Gusty and shifting winds are possible with any storms.

GGW WATCHES/WARNINGS/ADVISORIES

None.