735 
fxus65 kbyz 082231 
afdbyz 


Area forecast discussion 
National Weather Service Billings Montana 
331 PM MST Thursday Jan 8 2009 


Short term...valid for Friday and Sat... 


Will be cancelling Ice Storm Warning and Freezing Rain Advisory for 
eastern counties with this package. Calls to law enforcement 
revealed very light scattered precipitation and melting ice on 
roadways. Will leave Wind Advisory for gap areas going for now due 
to pressures falling over the area and to cover an additional 
possible advisory gust. 


Few showers were occurring west of kbil this afternoon under right rear 
quadrant of upper jet. At 21z...cold front was perched along 
Montana/Canadian border. Models brought the front through the region 
after 06z tonight with a period of 850-700 mb frontogenesis. 
Time-height cross sections did not show very strong lift with the 
front and only shallow instability. Quantitative precipitation forecast amounts and snow ratios 
suggested a few inches of snow possible in northerly upslope areas 
of Big Horn and Sheridan counties. Otherwise...snow amounts will be 
low with this event. Winds will increase over the area behind the 
front...and will be the strongest over the southeast zones where 850 mb 
winds increase to 40 knots for short period of time behind the front. 
Thus kept mention of blowing snow in the forecast. Red Lodge and 
beartooth foothills did not appeared favored in this event due to 
winds being north to northwest. Probability of precipitation tonight were in good shape...except added 
20 probability of precipitation this evening over areas that were in the path of the showers 
on radar. 


Models had the precipitation shifting quickly south Friday morning. 
Kept highest probability of precipitation over northerly upslope areas. Combination of 
snowfall accumulations tonight and Friday morning supported issuing 
Winter Weather Advisory for snow and blowing snow for Big Horn and 
Sheridan counties from 06z tonight through 18z Friday. Expect most of 
the northern zones to be dry Friday afternoon and kept chance probability of precipitation 
across the southern zones. Lowered temperatures a bit with early 
frontal passage. 


A northwest flow aloft with limited moisture will be over the area Friday 
night through Sat. Winds will likely increase to advisory/warning 
levels again in favored gap areas late Friday night due to a developing 
Lee trough. Will mention this in severe weather potential statement. A shortwave will push Pacific 
moisture into the area again on Sat night...supporting the low probability of precipitation 
already in forecast. Raised mins Friday night due to expected windy 
conditions. Temperatures were in good shape Sat and Sat night. Arthur 


Long term...valid for sun...Mon...Tue...Wed...Thu... 


Models remain in good agreement through Monday...models diverge a 
bit as to depth of cold air moving into the area at that 
point...but main pattern still remains active. Overall 
relatively few changes through the extended. 


Models remain in good agreement for shortwave moving into the area 
Sunday...with a pretty good chance for precipitation through the area. 
Baroclinic zone sets up for late Sunday through the beginning of 
the week bringing a chance of precipitation in the forecast through the 
end of the extended. Did bump probability of precipitation a bit higher...a bit further 
into the period. 


Temperatures were the biggest difficulty of the extended. Warm temperatures are 
expected to continue through the bulk of the extended for western 
and central zones. Arctic cold will again impact eastern zones as 
ridge over Pacific coast shunts the bulk of the cold air through 
the upper Midwest. Ec seems to be bringing in Arctic air deeper 
into the region on Monday and pushes out Tuesday...while GFS 
brings big push of Arctic air deep into the area on Wednesday. 
Have continued to mainly split the difference...with some minor 
adjustments for collaboration. Will require attention in later 
shifts. 


As for Wind...Gap flow areas will continue to see a good chance 
for strong gusty winds through the bulk of the extended. Gilstad 


&& 


Aviation... 


A strong cold front will cross the region tonight...bringing more 
snow...and a windshift to the north across the plains. 


Scattered rain showers remain in east and northeast but continue 
to diminish...with reduced areas of freezing rain as temperatures begin 
to rise. The precipitation is expected to continue to taper off from west 
to east through the remainder of the afternoon. 


Scattered snow is also expected to continue in the mountains 
through the day...intensifying and spreading into the foothill and 
Western Plains through the afternoon...and across the plains 
overnight as a cold front pushes through the area. MVFR to IFR 
conditions will prevail in and around areas of 
precipitation...with localized LIFR conditions in heavier precipitation. 


The foothills of the beartooth...absaroka and Crazy Mountains... 
including klvm today...will continue to see strong gusty 
winds...with gusts around 50 knots possible through the day. 
Southwesterly winds will become westerly as the cold front 
move through. Gilstad 




&& 


Preliminary point temp/pops... 


Friday Sat sun Monday Tuesday Wednesday Thursday 
----------------------------------------------------------- 
bil 027/034 023/040 027/044 024/038 018/041 020/030 012/025 
64/S 00/north 23/o 33/o 33/o 32/S 22/S 
lvm 026/037 024/038 025/040 026/039 021/045 024/036 017/031 
55/o 00/north 23/o 33/o 33/o 32/o 22/S 
hdn 022/029 014/039 022/045 021/037 014/036 015/028 006/024 
65/S 00/b 23/o 33/o 33/o 32/S 22/S 
mls 018/019 012/037 019/036 016/024 005/030 005/019 001/016 
54/S 00/b 23/S 33/S 33/S 32/S 22/S 
4bq 021/023 013/039 020/040 015/030 012/032 011/025 003/020 
55/S 00/b 23/o 33/S 32/S 22/S 22/S 
bhk 009/016 006/034 016/035 007/019 000/017 903/016 904/010 
55/S 00/b 23/S 33/S 33/S 22/S 22/S 
shr 022/030 012/040 020/042 020/035 013/038 016/032 009/024 
67/S 00/b 23/o 33/o 33/o 32/S 33/S 


&& 


Byz watches/warnings/advisories... 
Montana...Winter Weather Advisory in effect from 11 PM this evening to 
11 am MST Friday for zones 38-57. 
Wind Advisory in effect until 6 PM MST this afternoon for 
zones 65-66. 
Wyoming...Winter Weather Advisory in effect from 11 PM this evening to 
11 am MST Friday for zone 99. 


&& 


$$ 
Weather.Gov/Billings