520 
fxus65 ktfx 211742 
afdtfx 


Area forecast discussion 
National Weather Service Great Falls Montana 
1145 am MDT Thursday Aug 21 2008 


Update... 


Minor adjustments have been to the forecast package this morning. 
Chances of precipitation have been increased for the Glacier park 
and along the Rocky Mountain front...citing recent observations 
and trends. West and southwesterly winds east of The Rockies have 
maintained low level drying across the north Central Plains... 
causing much of the precipitation aloft to evaporate before 
reaching the ground. However...low level moistening appears to be 
intensifying this morning across the central mountains and 
valleys. Cold air aloft combined with daytime heating will likely 
support a weakly stable atmosphere...with scattered rain showers 
and embedded isolated thunderstorms anticipated to be present 
throughout most of north Central Plains through this evening. 
Zumpfe 


&& 


Aviation... 
bands of rain showers and a few thunderstorms will continue to 
develop and move east through the area this afternoon and early 
evening. Although predominately VFR conditions are expected there 
will be local IFR conditions...both ceilings and visibilities 
..in heavier rain. Also expect isolated thunderstorms this 
afternoon and early evening. Gusty southwest winds early this 
afternoon will shift to the west and northwest from middle to late 
afternoon. Local gusts to 45 knots are possible. Expect clouds to 
decrease this evening. Expect to see some cloudiness in Canada 
spread southeast near and after midnight over the plains. Models 
differ on whether there will be ceilings or not and have decided to 
go with ceilings 5000-7000 feet. There is a possibility of MVFR 
ceilings and rain with this cloudiness mainly over hill and Blaine 
counties. Blank 


&& 


Previous discussion... 
/issued 357 am MDT Thursday Aug 21 2008/ 


Today through Saturday...an upper level low pressure trough will 
move east along the Canadian border toward Montana today. The 
resulting increasingly moist and unstable southwesterly flow aloft 
will bring at least scattered showers and isolated thunderstorms 
to southwest...central...and north central Montana today into this 
evening. The best chances for precipitation will be in the 
mountains along the Rocky Mountain front and in central Montana. 
The heaviest precipitation will occur in the mountains of central 
Montana due to enhanced dynamics from a 100+ knots jet streak at 300 
mb moving across the area. The airmass will also become slightly 
unstable for a chance of thunderstorms. Again...due to the jet 
across southwest Montana...a few storms there could mix down 
especially strong winds and develop some small hail. 
However...precipitable water amounts are somewhat light (between 
0.50 and 1.00 inch)...which will keep hail sizes generally small. 
Breezy westerly downslope winds will increase across the entire 
area during the day...which will keep precipitation amounts low 
over the plains and in the valleys. Snow levels will gradually 
fall from the west due to the approaching trough...reaching around 
7500 feet along the Rocky Mountain front this afternoon. Snow will 
mostly mix with rain at higher elevations across the area...but 
some light accumulation is possible above 8500 feet. The trough 
will exit the area overnight for decreasing precipitation and 
winds. A few showers will linger into Friday in the mountains and 
east of Havre due to the resulting northwest flow. However...most 
precipitation is expected to dissipate Friday afternoon. 
Temperatures will generally remain below normal through Friday. An 
upper level ridge of high pressure will then move into the area 
from the west Friday night into Saturday for dry and warming 
conditions. Coulston 


Saturday night through Tuesday night...the biggest changes to the 
previous forecast were to slightly warm the lows on Sunday night 
and the maxes on Monday. Also dried out the probability of precipitation on Monday. The 
upper ridge remains in place through Monday with very warm 
temperatures. A weak weather system moving across the area will 
trigger some thunderstorms into the early evening hours on Monday. 
The upper ridge moves eastward on Tuesday and Wednesday as an 
upper trough develops over the West Coast and cooler air filters 
in across the area. This cooler air will bring a seasonal chance 
of precipitation with low probability of precipitation across the area Tuesday and 
Wednesday. Db 


Wednesday and Thursday...long range models indicate an upper 
level low pressure system moving into the Pacific northwest. 
During this period used climatology for precipitation due to 
timing of disturbances flowing through the northwest flow aloft 
and the position of the jet stream. Temperatures are expected to 
be near normal for much of west and central Montana. Saucier 


&& 


Preliminary point temps/pops... 
gtf 76 46 76 44 / 60 20 0 0 
ctb 68 43 68 42 / 30 20 0 0 
hln 77 50 78 49 / 70 40 0 0 
bzn 77 43 77 41 / 60 30 0 0 
wey 72 37 71 39 / 40 30 0 0 
dln 74 40 74 42 / 40 20 0 0 
hvr 78 45 72 39 / 40 30 20 0 
lwt 74 43 69 41 / 70 40 0 0 


&& 


Tfx watches/warnings/advisories... 
none. 
&& 


$$ 
Update...zumpfe 
short term...coulston 
long term...db/Saucier 
aviation...db 


Weather.Gov/greatfalls