textproduct: Glasgow

KEY MESSAGES

- Periods of showers today with thunderstorms becoming more numerous in the evening hours. Some storms may be slow moving, producing heavy rainfall.

- Lake Wind Advisory for Fort Peck Lake from noon today through 6 PM tomorrow.

- The upper trough will maintain cooler temperatures across the region into Monday and Tuesday, with periods of rain showers and thunder continuing through the week.

DISCUSSION

WEATHER PATTERN OVERVIEW:

Periods of showers will continue today with thunderstorms yet again becoming more numerous this afternoon and evening. Some of the storms will be prolific rain makers with the latest HREF 3 hour max QPF guidance ranging from 1 to 3 inches across portions of NE Montana during this time. Forecast soundings show precipitable water values near climatological maximums. Surface dew points have been in the 50s and 60s and these soundings show moist conditions through the vertical. The storms have been tending to track along an axis of elongated low pressure situated over the area, tending to move from southeast to northwest and this will tend to continue for today. This evening, as the surface low shifts east, winds will switch to the west and increase, with a Lake Wind Advisory set for Fort Peck Lake from noon today through 6 PM Monday.

For Monday and Tuesday the upper trough and closed low will remain anchored across the region with seasonably cool temperatures and continued chances for showers at times along with isolated thunder. By the middle of the week, ensembles want to push the low eastward with a shallow ridge moving in from the west. The next shortwave will quickly approach from the west by about Thursday evening with additional chances for showers and thunderstorms, continuing what looks to be a fairly active weather pattern.

FORECAST CONFIDENCE & DEVIATIONS:

Adjusted PoPs for collaboration and consistency across the next few days.

Portions of our eastern most zones under a slight risk for Tuesday. That being said, there exists a marginal risk east of Glasgow. GEFS is suggesting as high as 1000 J/kg MUCAPE while the NAM shows lower at 500-700 J/kg. Forecasted dew points range from 50 to 55, which is on the low end, but with steeper lapse rates and stronger shear than we've seen the past few days, there's a greater likelihood for thunderstorms producing a severe gust or some 1" hail. NAM soundings are more optimistic for hail - a more curved hodograph and both large and significant hail parameters of around 7. But again, with such low CAPE, it would be difficult for storms to sustain strong enough updrafts for long enough to produce significant hail.

AVIATION

Updated: 1930Z.

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: West winds 15 to 20 kts gusting to 35 kts.

GGW WATCHES/WARNINGS/ADVISORIES

Lake Wind Advisory until 6 PM MDT Monday for Central and Southeast Phillips-Central and Southern Valley-Garfield-McCone- Petroleum.