textproduct: Great Falls

KEY MESSAGES

- Hazy, very warm, and dry conditions generally continue for the next few days.

- A passing weather system and increased moisture will introduce shower and thunderstorm activity and cool temperatures down Wednesday through Friday, particularly for northern areas.

- There will be daily scattered shower and thunderstorm activity and warming temperatures next weekend.

DISCUSSION

- Meteorological Overview:

Ridging aloft will maintain the hazy, very warm, and dry conditions for at least the next few days. The main area of instability and associated shower and thunderstorm activity will generally stay north of the Canadian border during this period. Seasonably breezy conditions will continue with surface boundaries bringing transient gusty northerly wind shifts, mostly over central/north-central MT.

A trough begins to move southeastward through BC/AB and into the Northern Rockies sometime Wednesday into Thursday. There are some disagreements with the evolution of this system, but PWATs look to rise towards the three quarter to one inch range by late Wednesday into Thursday according to the North American Ensemble Forecast System (NAEFS). Shower and thunderstorm activity looks to increase from north to south with areas along the Hi-Line seeing scattered showers and storms as early as Tuesday evening. The Wednesday night through Thursday time period is generally favored to see the most widespread rainfall, especially for north-central areas. While some areas may see beneficial rains and cooling temperatures, the convective nature of this activity may also bring some strong to severe storms with localized strong gusty winds, hail, and heavy downpours. With that being said, ML CAPE doesn't looks overly impressive at this point with values generally maxing out between 300 and 800 J/kg.

The ridging aloft begins to build back in heading into next weekend, but another trough approaching the Pacific NW coast will bring southwesterly flow aloft within striking distance of the Northern Rockies. This will result in temperatures warming back up, along with daily shower and thunderstorm activity. - RCG

- Forecast Confidence & Scenarios:

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

The combination of very warm, dry, and breezy conditions will cause localized fire weather conditions for the next couple of days. While wind gusts will generally be below the 20 to 25 mph threshold, surface boundaries will bring daily northerly wind shifts, most notably over central and north-central MT. Afternoon humidity will fall to or near critically low levels with only moderate to poor overnight recoveries, driest over Southwest Montana. There are no plans for fire weather highlights at this time; however, those working to contain ongoing fires should beware of dry conditions and breezy, shifting winds.

Increased shower and thunderstorm activity and cooler temperatures Wednesday through Friday...

There has been ensemble disagreements and poor run to run consistency for this time period. The primary question is how far south this trough will go, which will determine how widespread the showers will be and whether temperatures cool below average. In addition to this uncertainty, there are also timing discrepancies with a growing number of members shifting the most widespread precipitation to Thursday into Friday rather than Wednesday into Thursday. The cooler solution would support more beneficial wetting rains over central and north-central MT while the warmer solution would support more scattered precipitation, but with increased instances of stronger storms capable of localized strong wind gusts, hail, and heavy downpours. - RCG

AVIATION

09/12Z TAF Period

Main impact will be visibility reduced by smoke over Central/Southwest MT through the period. IFR visibility is expected at times, especially over Southwest MT. Mountains/passes will be obscured across the CWA through the period. Do expect some surface wind shifts over North Central MT over the next 24 hours, but with light winds, impacts will be minor.

KGTF: Winds will be light and variable over the next 24 hours. Main impacts will be the shifting winds from time to time. Brusda

PRELIMINARY POINT TEMPS/POPS

GTF 86 55 89 55 / 0 0 0 0 CTB 79 51 82 50 / 0 0 0 0 HLN 88 55 88 55 / 0 0 0 0 BZN 87 52 91 53 / 0 0 0 0 WYS 85 44 86 42 / 0 0 0 0 DLN 85 52 89 51 / 0 0 0 0 HVR 86 52 88 53 / 10 0 0 0 LWT 83 51 86 52 / 0 0 10 0

TFX WATCHES/WARNINGS/ADVISORIES

None.