Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 120300
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
550 PM MDT Fri Jul 11 2014

.DISCUSSION...
Update forthcoming. Weak short wave energy, combined with monsoonal
moisture being advected north from the Southwest U.S., has resulted
in showers and isolated thunderstorms across southwest Montana. This
convective activity should diminish by 06z though isolated showers
may persist overnight. An upper ridge will build over the area
Saturday but monsoonal moisture will continue to be trapped beneath
the subsidence allowing for isolated thunderstorms again over
southwest Montana Saturday afternoon. Further north, isolated
showers and thunderstorms have developed over the Little Belts and
the Big Snowies where pockets of instability and bulk shear values
of 40 to 50 kts exist. This activity will also likely diminish
within the next few hours. Overnight forecast temperatures look good.

&&

.AVIATION...
UPDATED 2350Z.
VFR conditions will likely persist through at least Saturday across
the area. The monsoonal moisture feed has caused a few thunderstorms
to develop along the Montana/Idaho border this afternoon and
will likely persist through around 04Z. Am not expecting them to
spread too far north, but they may develop close enough to KBZN to
cause occasional wind gusts to 30 kt. Otherwise, the weak
northwesterly flow aloft will persist across north central and
central Montana through the period. A weak disturbance may cause an
isolated shower/thunderstorm or two across the area overnight, but
am thinking that the likelihood that any activity will directly
impact a terminal is low. The monsoonal flow may then bring isolated
showers/thunderstorms to the KBZN terminal and areas south once
again after 21Z on Saturday.
Coulston

&&

.PREV DISCUSSION...Issued 239 PM MDT Fri Jul 11 2014

Tonight through Sunday...An upper level ridge of high pressure
will gradually expand NW through the weekend, bringing warm and
mainly dry conditions. Moisture and a weak upper level disturbance
originating from the SW US will move from UT Northeast into WY
tonight. Best chance for thunderstorm activity this afternoon and
evening associated with this feature will be along the ID and WY
border. Some moisture remains trapped beneath the building ridge
over far SW MT Saturday for isolated late day thunderstorms, mainly
in the Yellowstone Park vicinity and west along the ID border. The
upper level ridge axis gradually shifts to the east over the Northern
Rockies Saturday and Sunday, allowing temperatures to warm back
above seasonal averages over North Central MT on Saturday with most
of the forecast area seeing afternoon temps in the upper 80s and low
90s. Hoenisch

Sunday Night through Friday...Next week shaping up to have mostly
dry conditions with temperatures close to typical seasonal values.
For the first half of the week, central and southwest MT will be in
the transition zone between high pressure ridging along the West
Coast and an anomalously strong and cool longwave trof extending
from central Canada through the Mississippi Valley states.  This
will keep a mostly northerly flow pattern over our region, which
will limit high temps to the upper 70s to mid 80s through Wed aftn.
A mix of Pacific and monsoonal moisture crossing through the top of
the ridge will bring isolated-to-scattered showers and thunderstorms
on Mon aftn through Tues eve, but expected rainfall amounts are
generally light (less than 0.1 inch). The deep longwave begins to
slowly slide eastward during the midweek period, allowing the
western ridge to expand into the Great Basin and Northern Rockies.
This will a return of west-southwest flow aloft and subsequent
warming back into the mid-upper 80s for Wed/Thurs.  By Friday, an
upper-level trof and associated cold front is projected to swing
across southwest Canada and Montana.  Forecast models are not really
in sync on this system as yet, with the ECMWF being notably quicker
and wetter than the GFS and GEM model solutions.
Waranauskas

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  88  56  89 /   0  10  10   0
CTB  50  86  53  87 /   0  10  10  10
HLN  58  91  58  93 /  20  20  10  10
BZN  54  87  54  88 /  30  20  10  10
WEY  45  81  42  82 /  20  50  20  10
DLN  55  85  54  88 /  20  20  20  10
HVR  54  90  55  89 /   0   0  10   0
LWT  53  86  54  86 /  20  10  10  10

&&

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

$$

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