textproduct: Great Falls

KEY MESSAGES

- Hazy, very warm, and dry conditions continue for another day with red flag conditions over southwest Montana.

- A Pacific weather system and increased moisture will bring scattered to numerous shower and thunderstorm activity and cool temperatures down late Wednesday through Friday.

- While some areas may see beneficial rains, this activity may also initiate a few stronger storms with localized strong wind gusts, hail, and localized flooding of normally prone areas.

- Scattered shower and thunderstorm activity capable of strong wind gusts and cloud to ground lightning will continue into the weekend while temperatures trend above average again.

DISCUSSION

- Meteorological Overview:

Ridging aloft will maintain the hazy, very warm, and dry conditions for the next 24 hours or so. Shortwave energy and instability capable of initiating shower and thunderstorm activity looks to remain north of the Canadian border, though some isolated storms may begin to creep towards the Hi-Line this evening and tonight. Seasonably breezy conditions will continue with wind gusts exceeding 20 mph at times.

A Pacific trough begins to move southeastward through BC/AB and into the Northern Rockies late Wednesday through Friday. Ensembles remain in agreement with temperatures falling below average Thursday and Friday, but still differ on how widespread the rainfall will be. The Wednesday night through Thursday time period is generally favored to see the most widespread rainfall. While some areas may see beneficial rains and cooling temperatures, the convective nature of this activity may also bring a few robust storms with localized strong gusty winds, hail, and heavy downpours capable of flooding of normally flood prone areas. ML CAPE values will initially run in 200 to 500 J/kg range on Wednesday before rising to around 300 to 900 J/kg on Thursday when convective activity looks to peak. It begins to decrease again on Friday with showers and thunderstorms retreating to southwest MT.

Ridging aloft begins to build back in heading into the weekend, but another trough approaching from the Pacific NW will bring southwesterly flow aloft back to the Northern Rockies. This will result in temperatures warming back up, along with daily scattered shower and thunderstorm activity. - RCG

- Forecast Confidence & Scenarios:

Breezy conditions, shifting winds, and localized elevated to critical fire concerns...

The combination of very warm, dry, and breezy conditions will result in localized elevated to critical fire weather conditions for another day. Surface boundaries and or diurnal mixing will bring wind shifts and gusts in excess of 20 mph at times. Afternoon humidity will fall to or near critically low levels with only moderate to poor overnight recoveries. The hottest, driest, and breeziest conditions will be focused over southwest MT where a red flag warning is in effect today. Those working to contain ongoing fires should continue be mindful of the hot, dry and breezy conditions.

Cooler temperatures, some stronger storms, and beneficial rains for some Wednesday through Friday...

Ensemble guidance remains in agreement with cooler and wetter conditions moving in late Wednesday through Friday. Climate anomaly indices, including the ECMWF Extreme Forecast Index are showing signals for precipitation amounts above climatology for this time of year. While this rainfall is definitely welcome, there are some caveats to consider. The convective nature of this precipitation will result in uneven distribution and increased instances of stronger storms capable of localized strong wind gusts, hail, and even flooding of normally prone areas. At this time, the most widespread precipitation looks to occur on Thursday.

Scattered gusty thunderstorms this weekend...

Southwesterly flow aloft returning to the Northern Rockies will maintain mid-level moisture and shortwave energy this weekend while the surface boundary layer warms up and dries out. This will result in scattered showers and thunderstorms for both days, mostly in the afternoon and evening. The primary hazards will be localized strong, gusty winds, and cloud to ground lightning. - RCG

AVIATION

11/06Z TAF Period

The main concern will be smoke reducing visibility through the period. IFR visibility is possible at times, especially over Southwest MT. Expect mountains/passes to be obscured across the CWA through the period.

For KGTF: Overall winds will remain light through the period. The probability of cross winds over 15 knots is generally less than 10 percent. The main concern will be visibility which could be as low as about 4SM at times. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 54 86 54 79 / 0 0 0 60 CTB 50 81 48 67 / 0 0 10 70 HLN 54 89 54 81 / 0 0 0 30 BZN 52 90 53 86 / 0 0 0 20 WYS 42 85 46 81 / 0 0 0 20 DLN 50 88 52 84 / 0 0 0 20 HVR 53 86 52 79 / 10 0 20 40 LWT 52 83 51 78 / 0 0 0 70

TFX WATCHES/WARNINGS/ADVISORIES

Red Flag warning for portions of Southwest MT for Tuesday.