385 FXUS65 KTFX 221027 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 427 AM MDT Tue Aug 22 2017 .SYNOPSIS... A high pressure ridge will keep the region dry and warmer than normal with light winds into Wednesday. However, an increasingly moist and unstable southwest flow aloft will bring a chance of thunderstorms to southwest Montana on Wednesday, then to most of the region for Thursday. Westerly winds will also become breezy along the Rocky Mountain Front on Wednesday, then they will spread over most of the area on Thursday behind a Pacific cold front. Highs in the 80s to lower 90s are likely today and Wednesday, but they will cool into the mid 70s and 80s on Thursday. Lows will be in the mid 40s and 50s. && .DISCUSSION... Today through Thursday...High pressure aloft will keep the area dry with light winds and temperatures around 10 degrees above normal into the day on Wednesday, but more unsettled conditions are expected Wednesday afternoon into Thursday. A disturbance will eject from a weak low pressure area along the California coast Wednesday morning and move through the ridge Wednesday afternoon and evening, bringing a chance of thunderstorms to southwest Montana. A low pressure trough will also move east from the British Columbia coast on Wednesday onshore into BC and Alberta on Thursday. As a result, the flow aloft will increase and become more southwesterly over the forecast area, initially bringing breezy westerly winds to the Rocky Mountain Front on Wednesday. The flow aloft will then become increasingly moist and unstable Wednesday night into Thursday. A Pacific cold front moving through the area on Thursday will also cool temperatures closer to normal and bring a chance of showers and thunderstorms. The best chance will be along and south of a Great Falls to Lewistown line. Moderate instability and wind shear may cause some storms to produce strong gusty winds and some hail. Precipitable water values are predicted to be higher than normal for this time of year, so heavy rainfall could accompany the storms as well. Another concern on Thursday will be post-frontal winds. Forecast models indicate that mid level winds of around 40 kt are possible, which could translate down to the surface along the Rocky Mountain Front as wind gusts Thursday afternoon. Although high winds are not expected, the dry and breezy conditions Wednesday into Thursday could warrant fire weather highlights (please see the Fire Weather section for more details). Coulston Thursday Night through Tuesday...The aforementioned upper trough still looks to continue digging over our region Thursday night through Friday morning, allowing isolated to scattered showers and thunderstorms to persist. Thereafter, the trough should begin lifting northeastward Friday afternoon as high pressure aloft builds- in from the south and west. Accordingly, the potential and coverage of showers and thunderstorms should dwindle as Friday elapses. Drier weather is then expected during the upcoming weekend through next week Tuesday as the aforementioned high pressure ridge aloft continues building over the area. Temperature-wise, near-normal lows are expected throughout the period. Behind the aforementioned cold front, Friday will feature highs mainly in the 70's to near 80 degrees, which will be several degrees below-normal for many places. The building high pressure ridge should then yield near-normal to slightly above- normal highs this weekend through Tuesday of next week, with many locations experiencing readings in the 85 to 90 degree range. Jaszka && .AVIATION... Updated 0427Z. VFR conditions are expected at most, if not all, terminals through Tuesday night as an upper level ridge builds in. The only exception may be KHLN/KEKS/KBZN where wildfire smoke may cause reductions in VIS at times, possibly as low as MVFR. For now, I have continued to keep VIS at 6SM in FU/smoke at those sites, but we'll continue to monitor this through Tuesday. MARTIN && .FIRE WEATHER... Fire weather concerns heighten this week due to hot and dry conditions through Wednesday and the passage of a Pacific cold front on Thursday. Above normal temperatures will cause afternoon relative humidity values to fall well into the teens today and Wednesday, and maybe approaching single digits for some areas on Wednesday. Overnight humidity recovery at mid-slopes to ridgetops will also become increasingly poor through Wednesday night. A low pressure trough moving into British Columbia Wednesday into Thursday will bring an increasing southwest flow aloft. These winds may start to translate to the surface along the Rocky Mountain Front on Wednesday, then spread out over the rest of the plains on Thursday and possibly into Friday behind a Pacific cold front. Fire weather concerns on Wednesday lean more heavily on the very dry conditions than on the breezy winds, while winds on Thursday will be stronger than those on Wednesday, but with less critical dryness. The southwest flow will also become moist and unstable, bringing a good chance of thunderstorms to the area Thursday into Thursday night. Some of these storms may cause new lightning ignitions, but the precipitable water is forecast to be above normal during this time, which may cause heavy rainfall. This situation will be monitored closely over the next few days and we will coordinate with fire officials to determine if fire weather highlights are warranted. Hoenisch/Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 90 54 93 57 / 0 0 0 0 CTB 88 50 91 56 / 0 0 0 10 HLN 90 55 92 59 / 0 0 0 10 BZN 89 50 89 53 / 0 0 0 10 WEY 80 35 76 37 / 0 0 20 20 DLN 87 49 85 51 / 0 0 10 20 HVR 90 52 94 57 / 0 0 0 0 LWT 87 53 90 56 / 0 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ weather.gov/greatfalls