Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 110306

905 PM MDT Thu Jul 10 2014

Update forthcoming. Lingering monsoonal moisture, along with
atmospheric instability along the southwest Montana/Idaho border, is
allowing isolated thunderstorms to continue. However, the moisture
source is beginning to decrease and convective activity should
further decrease with the loss of daytime heating. Have scaled back
the POP field through midnight, keeping POPs over extreme south and
southeast Montana. Have scaled back POPs even further after
midnight. In the north, circulation around an upper low centered
over western Saskatchewan is pushing moisture into an unstable
airmass and across the Canadian prairie. This moisture has combined
with a cold front moving south and the result is the development of
isolated thunderstorms. Satellite imagery indicates a strong
thunderstorm moving east-southeast across southern Alberta at this
time. RUC model data and HRRR analysis want to bring the core of
this storm south of the international border after 05z, affecting
areas along the Hi-Line. Have gone with low POPs across the northern
portion of the county warning area for this reason, bringing the threat
as far south as Lewistown and as far west as Great Falls per the
RUC. Temperatures look reasonable.


VFR conditions will continue across north central, central, and
southwest Montana at least through the day on Friday. Skies will
remain partly cloudy across the area through at least 06Z, with only
isolated thunderstorms possible along the SW Montana/NE Idaho
border, well south of the KBZN terminal. Moisture wrapping around a
low pressure system in central Canada combined with a weak cold
front moving into the area from the north between 06Z and 18Z. This
will bring increasing mid level cloudiness with isolated
showers/thunderstorms to much of north central (KCTB KHVR) and
central (KGTF KLWT) Montana. Have only mentioned VCSH in the TAFs at
this time, as am thinking that the chance for thunderstorms is lower
than the chance for showers due to this occurring during a
climatologically less unstable timeframe. However, will monitor
shower/storm development through 06Z for further potential updates.
Clouds/showers/storms will decrease after 18Z as the system exits
the area. However, monsoonal moisture will move back into southwest
Montana (including KBZN) after 18Z, bringing a chance of
thunderstorms there.


.PREV DISCUSSION...Issued 242 PM MDT Thu Jul 10 2014

Thursday through Saturday...Hot and dry conditions will continue
as the slowly moving large scale ridge continues to be dominant
force in the weather pattern over much of the Western United States.
Will continue to remain in a transition period on the edge of the
ridge through at least the next 24 hours. This will allow for
showers to develop as moisture allows. The best chance will be
with afternoon heating over the Mountains of Southwest Montana and
across the highline Thursday Evening as a weak disturbance moves
across the northern counties. By Friday a slight increase in
available moisture will allow for more showers and thunderstorms
to develop with afternoon heating...however showers will likely be
limited to scattered at best coverage. Another round of showers
will again occur on Saturday during peak heating mainly over the
higher terrain. Suk

Saturday night through Thursday...An upper level ridge high
pressure will be over the region this weekend...then the upper level
ridge will shift westward on a fairly strong upper level
low pressure over the Great Lakes area rotates a bit cooler air into
the region. As the upper level low over the Great Lakes begins to
move eastward on Tuesday...the upper level ridge will also start to
shift back eastward for Tuesday afternoon through Thursday. Thus
fairly warm temperatures are expected for Sunday...then seasonable
temperatures for Monday and Tuesday...with a return to slightly
above normal temperatures for Wednesday and Thursday. In terms of
precipitation...confidence is quite low on any one given day...thus
most days the chances for thunderstorms are fairly isolated. The
best time frame for any storms to occur will be late afternoon
through around Midnight...but again the thunderstorm activity should
be fairly isolated and not have significant impacts on any one given
day. Brusda


GTF  54  78  54  86 /  20  10  10  10
CTB  51  75  50  84 /  20  10  10  10
HLN  58  84  58  88 /  10  10  20  20
BZN  53  83  54  83 /  10  30  20  40
WEY  44  79  44  76 /  30  50  40  50
DLN  54  84  55  83 /  10  20  20  40
HVR  56  80  53  88 /  20  20  10  10
LWT  54  78  53  84 /  20  20  20  20



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