066 FXUS65 KTFX 240356 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 955 PM MDT Sun Jul 23 2017 UPDATED AVIATION .SYNOPSIS... A Canadian cold front will move across the plains tonight and result in cooler and breezy conditions for Monday. Thunderstorm chances return to start the week especially over central and southwest Montana. Temperatures will remain slightly above-normal before more hot weather returns by late week. && .UPDATE...Latest models, satellite imagery and surface observations continue to support a weak and dry surface cold front pushing south from Canada by morning. So far, quiet conditions have prevailed this evening and early evening models have dropped any suggestion of thunderstorms overnight. Have therefore updated forecast to remove PoPs and mention of dry thunderstorms, although Monday afternoon and evening could still see an isolated storm or two, mainly south and east of the Little Belt Mountains. I also made some minor adjustments to overnight lows and forecast high temperatures for Monday as well as sky condition tonight through late Monday afternoon based on short term model consensus tools. Finally, allowed the Red Flag Warning (RFW) to expire at 9 PM MDT as planned. RFW and a Fire Weather Watch remain in place for Monday afternoon and evening for the Great Falls fire weather forecast area. I am not convinced that widespread critical fire weather conditions will be met, but will leave them in place to allow the midnight shift to make the final decision. mpj && .AVIATION... Updated 0355Z VFR expected next 24-hours. Southwesterly to westerly flow aloft will persist as a disturbance advances E'ward over western Canada and another approaches from the Pac NW toward the end of the TAF period. A surface cold front accompanying the former of the two disturbances should move SE'ward across the Hi-Line between 06Z and 10Z/Mon before reaching the Central MT mountains by 15Z/Mon, where the front should dissipate soon thereafter. Surface winds will veer from southwesterly to northwesterly with the front's passage. While a stray shower or thunderstorm accompanying the cold front cannot be ruled-out, the probability is very low. A better chance for isolated showers and thunderstorms exists over/near the higher terrain of Southwest and Central MT after 18Z/Mon. Jaszka && .FIRE WEATHER... A cold front will move southward through the region during the overnight hours tonight. Expect a wind shift to the north over the plains east of Interstate 15. The winds will be strong/gusty at times overnight...especially over North Central MT. On Monday expect breezy west winds to develop by the afternoon hours along with low humidity, with critical fire weather conditions expected along the Rocky Mountain Front and along and west of the Big Belt Mountains, including Helena National Forest and western Lewis and Clark National Forest. Additionally there is a small chance for a passing dry thunderstorm, mainly south and east of the Little Belts. Some storms could produce strong gusty erratic wind gusts. Brusda/Cassell && .PREV DISCUSSION... /ISSUED 446 PM MDT Sun Jul 23 2017/ Rest of today through Monday night...Isolated thunderstorms are developing at this time over the mountains surrounding Ennis and Bozeman in association with a compact upper low moving through the area. This evening, a few thunderstorms may develop further north across parts of central Montana. The threat is conditional on there being just enough sufficient moisture, as well as the timing of any lifting mechanism in the form of a shortwave disturbance or possibly a weak lee-side SFC trough. Over southern Alberta, a SFC low continues to develop and will push east tonight, sending a cold front quickly SE across the area. Breezy winds will likely accompany the front late tonight/early Monday morning across central Montana and will usher in lower temperatures (ie. about 10 degrees or so lower than today). While SW MT may see a slight lowering of temps on Monday, it doesn't look nearly as breezy as farther north. On Monday, a s/w moving quickly through the area may kick off a few thunderstorms, mainly along/south of a Helena to Lewistown line. The primary threat with any thunderstorm through Monday should be gusty winds. At this time, severe weather is not anticipated. CC/MARTIN Tuesday through Sunday...Latest model guidance continues to illustrate a notable drying trend through the long range. Beginning with Tuesday and early Wednesday, a closed upper low rotating off the northern Coast of California will begin to get pulled slowly northwards in response to weak ridging breaking down in SW Canada. This shortwave will help feed increasing tropospheric moisture into the area overnight Tuesday with small, perhaps terrain enhanced nocturnal clusters of showers and storms making its way as far north as SW parts of the CWA through daybreak Wednesday. It is looking like by the daytime hours on Wednesday that most areas will remain dry as the aforementioned weak ridge holds tight over the majority of the area. However, by later in the afternoon and evening, increasing spotty convection area wide will become a good bet, with a few storms being strong given modest instability across central and southern areas. Another important note will be lightning activity as recent drought conditions may enhance the possibility of new fire starts. Also, breezy conditions are looking possible Thursday afternoon and evening with the passage of the shortwave trough that may exacerbate fire weather conditions. We begin to see a pattern shift beginning on Friday and lasting into next weekend with the return of the dominant four-corners ridge in the desert southwest. With good agreement on most long range model guidance, I've started to bump temperatures up enough to reflect this with highs easily reaching the lower to mid 90s area wide, with perhaps upper 90's for some through next weekend. Of course this will continue to be fine-tuned as we get closer in the week. KLG && .PRELIMINARY POINT TEMPS/POPS... GTF 58 85 51 84 / 10 10 10 0 CTB 52 80 46 81 / 10 10 0 0 HLN 62 91 57 88 / 10 10 10 10 BZN 56 90 52 86 / 0 10 20 10 WEY 46 81 45 77 / 10 20 20 30 DLN 55 87 53 84 / 0 10 20 20 HVR 59 83 51 85 / 10 10 10 0 LWT 60 84 53 82 / 10 10 20 0 && .TFX WATCHES/WARNINGS/ADVISORIES... Red Flag Warning from 1 PM to 9 PM MDT Monday Eastern Glacier/Toole/Central/Eastern Pondera/Liberty...Helena and Townsend Ranger Districts of the Helena National Forest...Lewis and Clark National Forest Rocky Mountain District-Rocky Mountain Front...Lincoln Ranger District of the Helena National Forest. Fire Weather Watch from Monday afternoon through Monday evening Central and Eastern Lewis and Clark National Forest Areas... Chouteau and Fergus Counties...Hill and Blaine Counties. && $$ weather.gov/greatfalls