815 FXUS65 KTFX 192155 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 255 PM MST Tue Feb 19 2013 .DISCUSSION... TONIGHT THROUGH THURSDAY...An upper level low pressure trof will move through the Pacific Northwest tonight. The main dynamics of the system will drop well south of the CWA by Wednesday and leave the zones underneath split flow aloft. Light snow will move into the extreme southwest zones tonight and move north into central Montana Wednesday morning. Surface winds will shift to the north and provide weak upslope forcing across the plains but most snowfall accumulations will remain across the higher terrain of central Montana and Southwest Montana. Will issue a winter weather advisory for snow beginning around midnight for extreme southwest Montana, and Wednesday morning for areas north into the central zones. The trof will move east of the zones Wednesday night and the air mass will dry. West winds aloft will strengthen during the day Thursday and brisk surface winds will develop across the Northern Rockies and adjacent plains by afternoon. Temperatures will remain below normals Wednesday and begin a trend towards normals again on Thursday. Zelzer Thursday night through Tuesday...The latest forecast models have changed a bit for Friday...as some models now prog a strong wind event to occur over the western portions of North Central MT Friday through Friday night. The strongest winds will be over the Rocky Mountain Front...but the strong winds could extend as far east as the Interstate 15 corridor. Additionally...the stronger winds will also allow for some warmer temperatures to develop North Central MT on Friday. The mild temps will not last long...as the next storm system to affect the region moves in by early Saturday morning. The most impacted area from this weekends upcoming storm system will be locations south of a line from Helena to Lewistown. As of this morning...currently forecasted snow amounts for this weekend do not seem excessive...with 1 to 3 inches possible at lower elevations and 4 to 7 inches possible in the mountains. The precipitation could linger into Sunday morning...especially over Southwest Montana. The airmass still remains a bit unsettled for Monday and Tuesday...thus there will be the chance for isolated/scattered snow showers over much of the region early next week. Afternoon temperatures will generally remain a few degrees below normal for early next week as well. Brusda && .AVIATION... Updated 1800Z. Moisture will continue to increase through at least 18Z Wednesday in a southerly flow aloft ahead of a large-scale upper level trough of low pressure. Most of the area will remain under VFR conditions with mid level cloudiness and mainly mountain snow showers through around 03Z. However, breezy easterly upslope surface winds will keep high IFR/low MVFR ceilings in the KCTB area and along the Rocky Mountain Front through this time. After 03Z, these IFR/MVFR ceilings with the possibility of fog, with a source region in southern AB/southern SK, will advect south over the plains as winds shift more northerly. Also after this time, the mid level moisture will bring an increasing threat of snow with the IFR/MVFR conditions to the area, mainly across southwest (KBZN KHLN) and central (KGTF KLWT). Widespread mountain obscuration in clouds/snow is generally expected after 03Z as well. Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 12 27 15 37 / 20 50 20 10 CTB 12 27 13 38 / 40 60 20 10 HLN 21 32 18 37 / 30 60 30 10 BZN 20 31 19 36 / 30 60 50 20 WEY 15 30 9 27 / 30 70 40 20 DLN 21 29 16 32 / 40 80 50 20 HVR 0 17 5 29 / 20 30 10 10 LWT 12 22 10 30 / 20 40 30 10 && .TFX WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY from 5 AM Wednesday to 5 AM MST Thursday Broadwater...Cascade...Central and Southern Lewis and Clark... Fergus...Jefferson...Judith Basin...Meagher. WINTER WEATHER ADVISORY from 11 PM this evening to 5 AM MST Thursday Beaverhead...Gallatin...Madison. && $$ weather.gov/greatfalls