Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 122043

243 PM MDT Sat Jul 12 2014


Today through Monday...Scattered thunderstorms are developing in
higher terrain across southwest Montana this afternoon.
Thunderstorms with heavy rain, frequent lightning and small hail
will continue through this evening, mainly along and south of a line
from Helena to Bozeman as monsoonal moisture coupled with a weak
upper-level shortwave move over the area. Elsewhere, dry conditions
and light winds will persist. These storms will diminish by midnight
as a ridge of high pressure builds over the Northern Rockies. Mainly
quiet weather is expected on Sunday with very warm temperatures near
90 for many locations as the ridge axis moves over the Treasure
State. The ridge axis shifts east Monday as a Pacific shortwave
trough and weak surface cold front move into the Pacific Northwest.
This trough will bring an increased chance for widespread showers
and thunderstorms, some possibly strong by Monday afternoon and
evening. Temperatures will return to near seasonal averages. MLV

Monday Night through Saturday...Forecast models in reasonably good
agreement on expected conditions through midweek, but vary widely,
even from their own previous solutions, for the latter half of the
week. Extended period begins with a shortwave trof reaching the
Continental Divide Mon evening.  This system will bring along some
Pacific moisture, and possibly a small area of monsoonal moisture,
which the models turn into a broad swath of showers and
thunderstorms covering most of the area along/west of the Interstate
15 corridor on Mon night.  Have increased chances of precip for the
mentioned area but have some lingering concerns about how much
moisture will remain after storms develop west of the Divide on Mon
aftn. The trof weakens on Tues, but retains enough energy to
generate another round of scattered thunderstorms over southwest and
portions of central MT before slipping into south central MT and
Wyoming on Tues evening.  Dry conditions and warming temperatures
return for Wed through early Thurs aftn as high pressure ridging
moves across the state.  Forecast confidence from Thurs evening
onward is marginal at best, as model solutions struggle to find even
a hint of consensus at this point.  Since the ECMWF model shows at
least some slight continuity with its previous runs, current
forecast leans toward its solution of northwest flow aloft with
embedded shortwaves bringing scattered precipitation to central and
north-central MT on Fri and Sat, while southwest MT remains mostly
dry both days.  High temps will cool back to the upper 70s to low
80s in response to the northwest flow.


VFR conditions and light winds will prevail over the next 24 hours
as an upper-level ridge of high pressure remains over the Northern
Rockies. Weak shortwave energy coupled with monsoonal moisture may
trigger afternoon/evening thunderstorms across far southwest
Montana, mainly in higher terrain south of a line from KHLN to KBZN.
Have included VCTS for KBZN this afternoon and evening. Confidence
is low that a thunderstorm will affect KHLN so did not include VCTS
in the TAF. Any thunderstorms in these areas will diminish by
midnight. MLV


GTF  56  89  56  84 /   0   0   0  20
CTB  53  86  52  81 /   0   0   0  20
HLN  60  92  59  88 /  20   0   0  30
BZN  53  87  53  83 /  20  10  10  30
WEY  42  81  43  79 /  40  10   0  40
DLN  55  87  56  85 /  30  10  10  40
HVR  55  87  53  82 /   0   0   0   0
LWT  53  86  52  80 /   0   0   0  20



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