925 FXUS65 KTFX 171108 AFDTFX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GREAT FALLS MT 408 AM MST Sun Feb 17 2013 .DISCUSSION... Today through Tuesday Evening...After a brief preview of mild spring-like conditions yesterday, we return to more typical February weather with colder temperatures and periods of mostly light snow expected across the region much of today. The system responsible for this change is the upper-level shortwave trof currently making its way thru the northern Rockies. Satellite imagery at 4am shows the trof axis extending from southwest Saskatchewan to near Missoula and continuing to western Idaho. The surface cold front from this system crossed the Interstate 15 corridor around midnight is presently just west of Havre and Lewistown with areas of light rain along the front and light snow behind it. Precipitation coverage will remain spotty thru mid-late morning as we wait for a secondary front, located just south of Cut Bank, to bring colder Canadian air into our region. As the cold airmass arrives, look for areas of light snow to increase and spread south this aftn/eve. No change to the expected snow totals (2-4 inches in the plains/valleys and 6 to 9 inches in the mountains), so the winter weather advisory remains in effect through early tomorrow morning. Still some concern for amounts of 12 inches or more in the Bridger/Snowy/Little Belt mountain ranges where locally unstable conditions and increased snow-to- liquid water ratios will be favorable for heavier snowfalls, possibly requiring additional winter headlines. Temperatures will hold steady in the low-mid 30s thru early afternoon then steadily decrease as the Canadian airmass settles into our region. Snow will begin to taper off tonight as the shortwave trof moves into the Dakotas. Residual moisture will allow light snow showers to continue along the Rocky Mtn Front and over the central mountains through Monday morning. This activity will dissipate quickly and skies will clear around midday as a quick-moving high pressure ridge arrives from the west. The ridge is projected to be in eastern MT by Tuesday morning with the leading edge of moisture from the next Pacific weather system making it into central and southwest MT on Tues aftn. Snow will develop over the Rocky Mtn Front and southwest mountains by the end of this forecast period. High temperatures on Mon and Tues return to more typical seasonal values of upper 20s to mid 30s. Waranauskas Tuesday night through Sunday...Expect a much cooler and unstable weather pattern to continue to reside over the region for much of the second half of next week. No significant warming is expected...rather each day should see afternoon temperatures averaging between 4 and 10 degrees below normal for most locations. An overall upper level trof of low pressure will generally reside over the Northern Rockies region for the second half of next week. This trof will allow for colder Canadian air to generally reside over the region through the period. There will be a chance for light snow showers most days...especially over the rocky mountain front and in Southwest MT...while isolated or no precipitation is expected in the Havre and Harlem areas. Snow accumulations look to be quite low most days...generally less than 2 inches at lower elevations...with 2 to 4 inches possible in the mountains. The snow accumulations will be spotty though, as weak upper level disturbances move through the region each day...but the exact timing and locations of these disturbances is still a bit uncertain. Additionally...there will be some melting of the snow during the day...especially from late morning through the afternoon hours...when air temperatures are around freezing. However...with overnight lows in the teens and 20s...some untreated wet pavement roads will likely freeze over during the overnight hours. Brusda && .AVIATION... Updated 0542Z. An upper level trough will push east across the Northern Rockies tonight with an initial cold front moving east across the forecast area overnight. The front is currently crossing the Continental Divide and will mainly impact central/southwest MT terminals tonight with a brief period of snow showers possible at the KHLN and KLWT terminals and a period of more persistent snow expected late tonight at the KBZN terminal. Further north, the front will bring an increase in clouds and shift to more westerly winds but little or no precipitation. A secondary frontal boundary moving south from Canada will move through north central MT Sunday morning, bringing another surge of moisture and a shift to north or northwest winds. Expect a period of generally light snow at KCTB and KHVR tomorrow morning with this feature and a more widespread/persistent snow further south over central and SW MT terminals with a period of moderate snow possible at KLWT and KBZN. Mountain obscuration will become more widespread tonight with a period of MVFR/IFR conditions at KHLN/KBZN/KLWT overnight. MVFR/IFR conditions will impact north central and southwest MT terminals on Sunday. Hoenisch && .PRELIMINARY POINT TEMPS/POPS... GTF 37 18 34 18 / 90 50 10 0 CTB 34 14 33 14 / 90 50 10 0 HLN 37 20 35 20 / 90 50 10 0 BZN 36 14 31 13 / 80 60 10 0 WEY 28 4 27 3 / 80 40 10 10 DLN 34 12 33 15 / 70 40 10 0 HVR 35 12 23 7 / 90 40 10 0 LWT 33 16 28 11 / 90 60 20 0 && .TFX WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY until 5 AM MST Monday Beaverhead... Broadwater...Gallatin...Jefferson...Madison. WINTER WEATHER ADVISORY from 7 AM this morning to 5 AM MST Monday Cascade...Chouteau...Eastern Glacier...Eastern Pondera... Eastern Teton...Fergus...Judith Basin...Meagher...Toole. WINTER WEATHER ADVISORY until 5 AM MST Monday Central and Southern Lewis and Clark...Northern Rocky Mountain Front... Southern Rocky Mountain Front. && $$ SHORT TERM...WARANAUSKAS LONG TERM...BRUSDA AVIATION...BRUSDA weather.gov/greatfalls