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fxus65 kggw 082210 
afdggw 


Area forecast discussion 
National Weather Service Glasgow Montana 
310 PM MST Thursday Jan 8 2009 


Short term...for northeast Montana...tonight through Saturday... 


An Ice Storm Warning exists across southeastern and eastern sections 
through 06z tonight. 


A Winter Storm Warning for a combination for freezing rain and 5 to 
7 inches of snow continues to exist for Sheridan... Daniels... and 
Roosevelt counties through 12z tomorrow morning. 


A Winter Weather Advisory exists for western portions of the County Warning Area 
excluding the Zortman region and Petroleum County for snow and blowing 
snow until 12z tomorrow morning. 


The overrunning event is expected to continue through the early 
evening with a significant Pacific warm moisture plume feeding in 
above the cold pool. Radar trends have been gradually pulling back 
across western portions of the County Warning Area and appearing less common than 
previously mentioned. Updated model runs appear to have 
initialized correctly and tend to place higher amounts of quantitative precipitation forecast near 
a quarter to a half of and inch over the northeastern sections of 
the County Warning Area. Spotter reports also appear to confirm these trends. Low 
pressure to our northwest has begun its March towards the 
northeast of our County Warning Area pulling the warm frontal boundary behind it 
also helping to end some of the freezing rain to the west. 


Tonight into Friday morning... a cold front following behind the low 
pressure system should signal an end to the whole of the freezing 
rain event. The cold air behind this system will quickly 
transition any freezing rain to snow with 1 to 2 inches over much 
of the County Warning Area and 3 to 6 inches expected across northeastern sections 
of the County Warning Area. Strong winds sustained between 20 to 30 miles per hour with gust 
up to 40 miles per hour will accompany the cold front. Winds will act in 
concert with snow to create blowing snow conditions during the 
Friday morning hours which could reduce visibilities to less than 
1/2 a mile at times. 


Friday afternoon through Saturday... winds are expected to taper 
off as dry Arctic high pressure filter into the region. This 
should act to gradually reduce further chances for snow to near 
zero. Friday night lightening winds... snow pack and ice on the 
ground... and partly cloudy skies could reduce surface low 
temperatures to negative and positive single digits or lower 
across the area. The same partly cloudy and calm conditions Friday 
night should also help to gradually warm up conditions during the 
day Saturday. Hicks 




Long term...Saturday night through Thursday... 
decent model consistency continues through the early part of the 
period with nemont between a polar vortex to the east and a 
longwave upper ridge to the west. As discussed below the Arctic 
boundary will continue to lie across the forecast area...or just 
to the southwest with periodic shortwaves sliding southeastward in the 
northwest flow aloft. Said shortwaves will create some potential 
for -sn into the beginning of next week. 


Tuesday and beyond the models somewhat diverge...although all are 
reasonably consistent in bringing what could be a deeper Arctic 
push in by midweek. Didnt want to bite too hard onto this 
solution as the strength of the push is largely up in the air...but 
did feel confident in trending down temperatures for midweek and beyond. 
Gilchrist 


Previous discussion...the extended period will feature an upper 
ridge along the Pacific coast and a polar vortex upper low over 
Hudson Bay. A long wave upper trough south of the polar vortex 
will cover the central and eastern U.S. Through the period. This 
will put Montana in northwest flow aloft with frontal boundary 
separating Arctic air to the east and milder Pacific air to the 
west in central or eastern Montana most of the period. 


Eastern Montana will be on the warm side of the front Saturday 
night. A strong shortwave will move through the area on Sunday and 
bring the front south. Look for a chance of snow Sunday and Sunday 
night. Southwest zones will be warm enough for part of Sunday for 
rain. Arctic high will move from Saskatchewan into western North 
Dakota on Monday which will leave the northeast zones cold and 
dry. The southwest zones will be close enough to the front which 
will become stationary in central Montana to have a chance of 
snow. 


Beyond Monday...models waffle the quasi-stationary front back and 
forth across central and possibly eastern Montana. European model (ecmwf) keeps the 
front in central Montana most of the period while the GFS bring 
the front east into eastern Montana on Tuesday and back west 
Tuesday night. Will keep most of the forecast area on the cold 
side of the front for now as Arctic airmasses can be hard to get 
rid of especially with deep snow cover. Meanwhile...the shortwave 
moving through the area will bring a chance of snow. Another 
Arctic high will bring mainly dry weather Wednesday and Thursday. Forrester 




&& 


Aviation... 


The upper low that drove widespread freezing rain this morning has wrapped 
up the precipitation...keeping it largely confined to the 
eastern zones this afternoon. Thus -fzra is currently only 
impacting the kgdv and ksdy terminals. The associated surface cold 
front is currently pushing into the western hi-line and should begin 
to effect the terminals from west to east starting around 0100z. 
There is some potential for freezing rain redevelopment right ahead of the 
front for kggw and kolf...but the precipitation type should quickly 
become all snow with the front. Northwest winds at 20 to 30 kts 
will pick up with and behind the front as well...and will reduce 
visibilities in blsn into Friday morning. Gilchrist 




&& 


Glasgow watches/warnings/advisories... 
Winter Weather Advisory until 5 am MST Friday for central and 
southeast Phillips-central and southern valley-Garfield-northern 
Phillips-northern valley. 


Ice Storm Warning until 11 PM MST this evening for western 
Roosevelt-McCone-Richland-Dawson-prairie-Wibaux. 


Winter Storm Warning until 5 am MST Friday for Daniels-Sheridan- 
eastern Roosevelt. 


&& 


$$ 


Weather.Gov/Glasgow 

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