textproduct: Glasgow

KEY MESSAGES

- Scattered showers and isolated thunderstorms will be track from Central Montana over the Little Rockies, portions of Petroleum and Garfield Counties this afternoon and evening. Little to no QPF expected.

- Warm and dry conditions are expected through Tuesday. Monday especially looks to feature gusty conditions along with low relative humidity, potentially raising fire weather concerns.

- Forecast becomes potentially wetter Wednesday night into the weekend with more scattered showers and isolated thunderstorms possible.

DISCUSSION

WEATHER PATTERN OVERVIEW: Today through tonight: A shortwave has brought a series of small weakly organized showers to the region tracking through central Montana and grazing the SW corners of the GGW CWA. First wave is quickly exiting southern Petroleum county late this morning. The second wave should arrive tonight and will briefly graze the southwestern half of the CWA mostly before midnight. Due to later afternoon early evening timing there is a small chance for a thunderstorm or two embedded in the light showers.

Sunday through Tuesday: Expect a warm up with dry conditions as an upper ridging takes hold. On Monday specifically, the next shortwave looks to approach from the north with a weak cold front. Current support suggests northwest winds mixing down with this feature, though conditions remain mainly dry. Strong boundary layer mixing will bring pre-frontal warming and afternoon humidity readings below 20 percent. When combined with a low greenness index and strong NW wind gusts fire weather concerns will be raised. Main reason for not issuing a Fire Weather Watch for Monday already was that a Red Flag was already up next door and to avoid confusion will hold off until that expires.

Wednesday onward: Large ridge on Wednesday quickly topples over allowing a more zonal flow patterns with much smaller synoptic ridge/trough couplets embedded in it beginning Wednesday night. This will raise afternoon and evening chances for showers and thunderstorms in the region through the weekend with possible wetting rains or maybe even a severe potential depending on whether it matches up with peak heating. Individual ensemble members all disagree on what day/time any given ridge/trough couplet moves through though. So, currently low confidence on specifics like when or how much.

FORECAST CONFIDENCE & DEVIATIONS: Deviation from NBM include: Hourly PoPs was again the thing that had to be changed today. NBM PPI01 had a really weird disconnect in the data from hours 23 to 00Z with some correct PoPs changing suddenly to absolutely nothing. This massive jarring disconnect was also seen yesterday leaving us puzzled. The first wave through 00Z was already winding down on radar and generally seemed okay in the NBM PPI01. The second wave that covers more of the CWA from TFX to the BYZ borders from 00Z to 09Z that was absolutely not in the data at all in the PPI01. So, had to override it by using a kitchen sink CAMs NPoP blend from roughly 00 to 12Z Saturday morning. Then, slowly shrink stretched the highs of the final product down from 06-12Z to slightly wash out the final exiting/diminishing PoPs. Also Shrink stretched down the MinRH lows Sunday and Monday afternoon a couple percent to pull down the NBM MinRH high bias a bit.

Confidence is MODERATE on a band of showers and isolated thunder across the southwest zones through tonight.

Confidence is LOW on specific precipitation amounts given the nature of embedded convection and super dry surface layer.

Confidence is HIGH in a ridge with warm and dry conditions through Tuesday/Wednesday. Confidence in critical fire Weather Monday is HIGH as well.

Confidence is MODERATE in scattered showers and thunderstorms Thursday into the weekend.

Confidence is LOW in timing or placement of these showers and storms. GAH

AVIATION

LAST UPDATED: 1730Z

FLIGHT CAT RANGE: VFR.

DISCUSSION: Mainly dry weather with mid to high clouds across area terminals for the TAF period.

WIND: N at 10 to 15 kts through the afternoon. Veering NE to E and decreasing to less than 10 kts this evening through tonight. Veering further SE Sunday at 10 kts or less.

GAH

GGW WATCHES/WARNINGS/ADVISORIES

None.