280 
fxus65 kggw 292105 
afdggw 


Area forecast discussion 
National Weather Service Glasgow Montana 
305 PM MDT Friday Aug 29 2008 


Short term...for northeast Montana...tonight through Sunday... 
surface high pressure continues drifting southeast into the 
Dakotas this afternoon ahead of a broad upper level ridge axis 
poised over western Montana. Well defined trough presently along 
the British Columbia coast will then become the focus for an 
unsettled latter half to this Holiday weekend. This trough will 
drive a noticeable cold front into the County Warning Area starting Saturday 
afternoon with chances for precipitation materializing late Saturday 
evening in the Post-frontal environment. Ahead of this front...the 
models agree in focusing the 850-700mb thermal ridge axes 
generally over the eastern half of the County Warning Area with gusty southerly 
winds unfolding in the southeast zones. Given low humidities and 
gusty winds...have maintained Fire Weather Watch for zone 
122...see fire discussion for more details. 


The front is advertised to briefly stall out just to the 
southeast of the forecast area Sunday as much of the upper trough/S 
energy dives into the central rockies. Models have pulled back on 
quantitative precipitation forecast fields since yesterday...but generally agree in focusing some 
bands of rainfall along the 700mb front. Widespread chances for 
precipitation look much better just beyond this forecast window as 
leading edge of upper height falls overspread the region. Mcz 


Long term...Sunday night through Friday... 
decent model consistency this set of runs...thus higher 
confidence. A large upper low will impact much of the northern 
High Plains Sunday night through Tuesday night. This will make for 
below normal temperatures along with good chances for 
precipitation each period. Wednesday will see a short lived warming 
trend along with dry conditions as weak ridging builds in ahead of 
the next system. Wednesday night through the end of the week will 
see a reinforcing shot of cooler air/unsettled conditions as 
another trough digs in. Biggest changes were to cool temperatures late in 
the period under the second trough. Gilchrist 


Previous discussion...the extended period begins with a large 
energetic closed upper low centered over the Great Basin region 
ejecting moist flow north into Montana. Models agree with this 
general pattern Sunday night and Monday. Main area of instability 
will be east in the Dakotas...so will not mention thunder for now. 
Already have high chance probability of precipitation in grids which seem adequate for 
now. There are some differences in quantitative precipitation forecast between European model (ecmwf)/Gem and the 
GFS but the model consensus is that it will be wet. The low center 
lifts into Montana Monday night with the upper jet rounding the 
base of the low right over the forecast area. Models agree with 
the low lifting into Canada around Tuesday night ending 
precipitation. Then a fairly strong open wave moves into the 
region Wednesday generating more chance for precipitation through 
the remainder of the extended period. Temperatures through the 
period will remain below normal. Scattered 


&& 


Aviation... 
VFR...the few cumulus that developed this afternoon will quickly 
diminish around sunset. The overnight hours will see just a few 
high clouds passing from time to time. Winds will generally be 
less then 06kts...with the exception of kggw where southeast winds 
around 12kts will develop around sunset. Southwest winds at 10 to 
20 miles per hour will develop Saturday afternoon across northeast Montana ahead 
of an approaching front. Winds will then go northeast winds at 20 
to 30 miles per hour Saturday evening behind the front. Gilchrist 


&& 


Fire weather... 
a Fire Weather Watch remains in effect for fire weather zone 122 
Saturday afternoon and evening. Although southerly winds will only 
gust up to around 20 miles per hour...very low humidity values around 10 
percent remain supportive of potentially critical fire weather 
conditions. Conditions elsewhere will be more marginal given 
lighter winds just ahead of a cold front...so have chosen not to 
expand current headlines. Gusty north-northeast winds will take 
shape behind this front Saturday evening and night...but humidity 
values will recover substantially among much cooler temperatures. 


&& 


Glasgow watches/warnings/advisories... 
Fire Weather Watch from Saturday afternoon through Saturday 
evening for mtz122. 


&& 


$$ 


Weather.Gov/Glasgow