FXUS65 KTFX 081459 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 859 AM MDT Sun Sep 8 2024 .SYNOPSIS... Warm temperatures will remain through tomorrow with a chance for afternoon showers and thunderstorms along southwestern Montana today. A change to cooler temperatures along with a better chance for precipitation develops around the middle of next week. && .UPDATE... No major update was needed to the forecast this morning. Smoke aloft will continue to bring hazy conditions as it lifts north this morning across Southwest MT and portions of North Central MT. An upper level wave will bring isolated showers and thunderstorms this afternoon mainly across Southwest MT and Southern Rocky Mountain Front with gusty winds as the main threat. Little rain amounts are expected with precipitation. -Wilson && .AVIATION... 08/12Z TAF Period VFR conditions are expected to prevail across the CWA through the period. The exception will be areas of smoke reducing distant visibility, but overall prevailing visibility will generally be greater than 6SM for the terminal sites. Adjustments will be made to TAF sites should the prevailing visibility of the smoke get denser. Otherwise, a few late afternoon thunderstorms are possible this afternoon along the Rocky Mountain Front and across Southwest MT. The probability of a storm at a terminal site is less than 20 percent, thus no mention of storms at the TAF sites at this time. Mountains/passes will be obscured by smoke across the CWA through the period. Brusda Equipment Note: Due to no transmission of observations from both KEKS and KWYS, no amendments are scheduled until further notice. Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .FIRE WEATHER... Isolated thunderstorms develop late Sunday afternoon over fire zone 118 and then into fire zone 117 by Sunday evening. Very little precipitation is expected and some storms could produce strong gusty/erratic winds. Breezy to locally windy conditions develop on Monday and a fire weather watch has been issued for fire weather zone 112 (Glacier and Toole counties) for gusty winds and low humidity Monday afternoon. Wind gusts to 30 mph are likely in this area in combination with afternoon humidity 15-20%. Hoenisch Outside of fire weather zone 112, elevated to near-critical fire weather conditions are expected on Monday north of a line between Great Falls and Lewistown. The primary limiting factor remains the timing and duration of the highest wind gusts with the lowest relative humidity. The latest model guidance keeps the window of potentially critical conditions down to a couple hours at best. Even then confidence is shaky and, as such, the fire weather watch was left with its current boundaries. -thor && .PREV DISCUSSION... /ISSUED 440 AM MDT Sun Sep 8 2024/ Key Points: - Continued above average temperatures through Monday - Chance for isolated to scattered showers and thunderstorms across southwestern Montana this afternoon and evening - Breezy winds and continued dryness will bring elevated fire weather concerns on Monday - Increasing confidence in cooler temperatures and widespread moisture mid to late next week Today through Monday... The upper level ridge will continue to weaken over the next couple days as it departs to the east. In the meantime, moisture from a weak embedded shortwave will provide just enough instability to kick off some showers and thunderstorms this afternoon across southwestern Montana and along the southern Rocky Mountain Front. In general, very little precipitation is expected with these showers with gusty/erratic winds along with lightning being the main concerns. Smoke and haze will continue to linger across southwestern Montana today causing reductions to air quality across the region. The latest HRRR smoke model points towards a wave of smoke/haze making its way north towards the hi-line by late morning. Most of the smoke that makes it this far north is expected to stay aloft so significant impacts to visibility and air quality are not expected north of Helena. As is par for the course when there is thick smoke aloft and a chance for thunderstorms, there is a lingering chance (<20%) that the smoke will inhibit afternoon convection to some degree. Thus, there is a chance that this afternoon may not live up to its full potential, however, forcing mechanisms and the expected near- surface moisture content are still favorable enough that a few pop-up showers and thunderstorms are possible. On Monday, some lingering shortwave energy will kick off another round of isolated afternoon showers and thunderstorms. The difference will be that coverage will be a lot less compared to today. Overall, the main concern for Monday will be near-critical to critical fire weather conditions along north-central Montana. Critical conditions are possible for Glacier county and along the northern Rocky Mountain front where gusts up to 35 mph are expected at the same time as humidity dips down into the upper teens. Tuesday through Saturday... Relief will arrive in the form of cooler temperatures heading into the middle of next week as the upper level trough starts to move onshore along the PacNW Tuesday into Wednesday. Seasonable to below normal temperatures will persist through the rest of the work week as the trough settles over the western CONUS. Along with cooler temperatures, a more robust chance for precipitation is expected. Compared to previous precipitation events of the past month, this event is starting to look more promising with regards to widespread heavier amounts of rain that will, at the very least, help reduce current fire weather concerns. The latest probabilities for storm total amounts north of I-90 (valid Wednesday afternoon through late Friday night): - 40-60% chance of at least 0.50 inch - 30-50% chance of at least 0.75 inch - 20-40% chance of at least one inch Additionally, north of a line between Helena and Lewistown there is a 10-20% of exceeding 1.5 inches during this time frame. There is greater uncertainty further into southwestern Montana south of I-90 with the heaviest rain amounts expected to stay to the north. That being said, the latest NBM guidance still puts around a 30% probability of at least half an inch of rain south of I-90 during the time period between Wednesday afternoon and late Friday night. More specific details remain uncertain at this time but with each successive model run over the past 36 hours there is a continuing trend towards higher amounts and the likelihood that central Montana may see its first widespread significant rainfall in a long time. -thor && .PRELIMINARY POINT TEMPS/POPS... GTF 92 59 89 50 / 0 10 10 0 CTB 88 58 85 48 / 0 10 0 0 HLN 93 57 89 54 / 10 20 0 0 BZN 91 50 87 49 / 10 20 0 0 WYS 80 39 77 37 / 20 20 0 0 DLN 84 47 82 47 / 20 20 0 0 HVR 94 57 94 51 / 0 10 10 0 LWT 91 57 86 52 / 0 10 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Fire Weather Watch from Monday afternoon through Monday evening for Eastern Glacier/Toole/Central/Eastern Pondera/Liberty. && $$ http://www.weather.gov/greatfalls