548 
FXUS65 KTFX 250028
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
625 PM MDT Wed Jul 24 2013

UPDATED AVIATION SECTION

.DISCUSSION...
Tonight through Friday...The dominant weather feature affecting
the forecast area during the period will be an upper ridge over
the Pacific Northwest which will move to our forecast area Friday.
For tonight a weather disturbance aloft will sweep southeast
through the plains and adjoining mountains. This disturbance is
expected to trigger isolated to scattered thunderstorms by this
evening. Observations early in the afternoon were showing a
moderately unstable airmass near the Canadian border and moderate
wind shear. Will continue to mention a threat of small hail and
gusty winds with the thunderstorms over the northern east slopes
for this evening. On Thursday expect an unstable airmass over most
of the forecast area by the afternoon but do not see any weather
disturbances aloft to speak of. Will continue with the mention of
a slight chance of thunderstorms mainly over the mountains. With
the upper ridge moving over the forecast area on Friday and a
drier airmass expected have dropped the mention of thunderstorms.
Expect a surge of cooler air associated with the weather
disturbance aloft tonight. This will result in lower maximum
temperatures Thursday especially in then north. High temperatures
will rebound Friday with the upper ridge moving over the area.
Blank

Friday night through Wednesday...High pressure aloft will be over 
central Montana and the airmass will be warm and, in general, dry. 
However, some moisture will have moved into the southwest zones and 
the best chance for thunderstorm activity will be in this region 
Friday night. To the west, a low pressure trof will be moving over 
the West Coast. This will begin a period of slowly falling heights 
aloft along with a continued increase of moisture into the region. 
The result will be increased afternoon and evening instability and 
an increase in thunderstorm activity Saturday. The upper level trof 
will be approaching the Rockies by Sunday and the convective 
activity will further increase. The approach of the trof will also 
cool the airmass and begin a period of slightly cooler temperatures. 
Low pressure will remain over British Columbia and the zones will 
remain underneath unsettled, southwest flow aloft...and afternoon 
and evening convective activity will continue into the new week. By 
Tuesday, another low pressure trof will move over the West Coast and 
keep the unsettled, southwest flow in place through the end of the 
period. Temperatures will remain well above normals through 
Saturday. Although the approach of the upper level low pressure trof 
will bring some cooler temperatures into the region but temps will 
generally remain near or above normals through Wednesday. Zelzer

&&

.AVIATION...
UPDATED 0025Z.
An unstable airmass and a weak surface front moving into the area 
has allowed scattered thunderstorms to develop...mainly north of a 
KHLN to KBZN line. Some of these storms may become severe. 
Convective activity should end by 07z.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  85  55  90 /  20  10   0  10 
CTB  53  81  53  87 /  30  10  10  10 
HLN  57  89  58  92 /  10  10  10  10 
BZN  51  88  52  89 /  10  10  10  10 
WEY  41  80  42  82 /  10  20  20  10 
DLN  52  86  52  88 /  10  10  10  10 
HVR  54  81  54  85 /  30  10  10  10 
LWT  52  79  53  83 /  20  10  10  10 

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

weather.gov/greatfalls