textproduct: Glasgow

KEY MESSAGES

- There is decent shot of showers and storms occurring from now through Friday evening. Some storms may be severe.

- There is decent chance that July Fourth will be dry with near normal temperatures. - A weak ridge under partially southwest flow aloft will allow isolated showers and storms to occur at various times after Sunday.

DISCUSSION

WEATHER PATTERN OVERVIEW: A small upper level trough is expected to remain over the area through tomorrow. A shortwave trough is expected to move through today and tomorrow through the overall flow. This in combination with recent rains and daytime heating will bring chances for showers and storms. The main hazards in the largest storms are damaging winds, heavy downpours, and large hail. An isolated tornado cannot be ruled out in the early overnight tonight for Sheridan County. The worst case seems to be up to EF-2 strength. The timing for strongest storms is between 2 PM and 8 PM, 10 PM tonight and 2 AM tomorrow, and then again after 12 PM tomorrow through about 10 PM.

Based on 0-6km bulk shear and a small amount of surface CAPE over central Montana on July Fourth, there is enough evidence to suggest an isolated strong storm moving across the western counties in the afternoon. This is according to the latest NAM NEST model run, but there is uncertainty in how much warm air aloft move in. That would inhibit storm activity.

The NBM ensembles are suggesting near normal temperatures make their way in after Saturday, and partial southwest flow aloft will help any shortwave troughs move into the area. There is potential for high based showers and storms based on the assessment of the latest ECMWF and GFS ensembles.

FORECAST CONFIDENCE & DEVIATIONS: No deviations were made.

There is high confidence in showers and storms occurring for most locations today and tomorrow. Some storms could be severe.

There is moderate confidence in July Fourth being dry, and low confidence in an isolated strong storm occurring in the west in the afternoon and evening.

There is high confidence in west southwest flow occurring aloft from Sunday onward, and moderate confidence in off and on high based showers and storms occurring each day through mid week.

AVIATION

LAST UPDATED: 1830Z

FLIGHT CATEGORY: VFR. MVFR-IFR in thunderstorms.

DISCUSSION: A shortwave trough and surface stationary front are expected to work through the area today and tomorrow. The main timeframe for the strongest storms is between 20Z and 02Z, and again from 18Z Friday to 06Z Saturday. There is moderate to high confidence of MVFR occurring in thunderstorms that affect TAF sites, and low confidence in IFR conditions. Some of these afternoon and evening cells today and tomorrow could become severe with large hail and damaging wind.

WIND: Variable at 5 to 13 knots becoming light and variable after 06Z. Gusty erratic winds near any thunderstorm.

GGW WATCHES/WARNINGS/ADVISORIES

None.