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fxus65 ktfx 181748 aaa 
afdtfx 


Area forecast discussion...updated 
National Weather Service Great Falls Montana 
1148 am MDT Friday Jul 18 2008 


Updated aviation discussion 


Update...slight tweaks made to todays pop and weather grids to 
better represent current showers and embedded thunderstorms tracking 
east between Helena and Bozeman. Still looking for an active 
afternoon/evening with scattered thunderstorms across the region with some 
cells producing small hail and gusty winds. Waranauskas 


&& 


Aviation... 
a moderately strong disturbance in westerly flow aloft will bring 
scattered showers and thunderstorms the region through early this 
evening. Isolated thunderstorm activity is already progressing 
across central Montana this morning with additional development currently 
occurring over Idaho and SW Montana to expand northeast this afternoon. 
Gusts in excess of 40 kts and small hail will be possible across the 
entire area this afternoon...with the threat lingering into this 
evening east of a line from kgtf to khvr...including klwt. 
Thunderstorms along and east of a line from khvr to klwt may contain 
larger hail and gusts over 50 kts. By 06z tonight...most of the 
showers and thunderstorms are expected to have moved east of the 
region. Outside of thunderstorms...westerly surface winds are 
expected to increase through this afternoon west of a line from khvr 
to kgtf to kbzn with southeast winds to the east of this line. Winds 
will shift to the west over the remainder of the forecast area as 
thunderstorm activity diminishes this evening. Hoenisch 


&& 


Discussion... 
today through Sunday...for today there will be southwest flow 
aloft ahead of an upper trough extending from British Columbia 
into Washington and Oregon. One weather disturbance embedded in 
this flow was resulting in some thunderstorms over north central 
Montana early this morning. Other showers and thunderstorms could 
develop farther south during the morning. Another disturbance 
could affect central or southwest Montana during the afternoon. 
There are some indications that a drier airmass could move into 
the western zones during the afternoon but for now will continue 
with the broadbrush forecast of isolated to scattered 
thunderstorms. Although severe storms are expected to be mainly 
east of the forecast area...will be mentioning gusty winds and 
hail with the thunderstorms today. The upper trough will be moving 
through northern portions of the forecast area tonight and early 
Saturday. Could see some isolated showers/thunderstorms through 
the night in the north but expect showers/thunderstorms to end by 
dark in the south. Saturday the area will begin to feel the 
effects of an upstream upper ridge so expect a generally dry day. 
The upper ridge then develops over the area Saturday night and 
expect generally clear skies. Sunday the area returns to southwest 
flow aloft and daytime temperatures will be quite a bit warmer 
than on Saturday. There could be some moisture over southwest 
Montana along with an unstable airmass so will continue with the 
idea of a slight chance of thunderstorms in that region for Sunday 
afternoon. Blank 


Sunday night through Wednesday night...an upper level ridge of high 
pressure over the southwestern Continental U.S. Will result in temperatures 
above seasonal averages and mostly dry conditions across the 
forecast area early next week. High temperatures on Monday are expected to 
be 5 to 10 degrees above seasonal averages...with lower 90s across 
lower elevations. Temperatures will begin to gradually cool through 
midweek...as the upper level ridge breaks down in response to one or 
more Pacific troughs moving onshore. The European model (ecmwf) appears to flatten 
the ridge quite a bit faster than the GFS. As a result...the GFS is 
pointing toward warmer temperatures through midweek compared to the 
European model (ecmwf)...along with drier conditions and a storm track north of the 
forecast area. More weight has been given to the GFS in the extended 
forecast...as the large amplitude of the ridge and climatology would 
favor a slower deamplification and a more northern storm track. 
Also...good consistency among members of the GFS ensemble has been 
noted for the extended period. However...by midweek...flow aloft 
becomes more southwesterly as both the GFS and European model (ecmwf) indicate a 
deepening Pacific trough approaching the region with increasing deep 
layer mean flow over the area. As low level moisture increases over 
the region...isolated thunderstorms will become possible once again 
by Wednesday afternoon and evening...with a smaller chance and 
mainly over higher terrain Tuesday afternoon. Otherwise...skies will 
be partly to mostly clear through the period. Cohen 


Thursday and Friday...latest extended model solutions indicate a 
southwest flow aloft with periodic disturbances flowing through. 
Inserted climatology probability of precipitation through the period. Temperatures are expected 
to be near normal for the north Central Plains. Saucier 


&& 


Preliminary point temps/pops... 
gtf 84 51 82 48 / 20 10 10 0 
ctb 81 48 79 46 / 20 10 10 0 
hln 86 54 86 53 / 20 10 0 0 
bzn 86 48 88 46 / 20 10 0 0 
wey 73 42 77 44 / 30 10 0 0 
dln 80 45 84 46 / 20 10 0 0 
hvr 86 53 80 47 / 30 20 10 0 
lwt 80 49 78 46 / 30 20 10 0 


&& 


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


$$ 


Short term...blank 
long term...cohen/Saucier 
aviation...hoenisch 


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