Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 111147
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
530 AM MDT Fri Jul 11 2014

AVIATION SECTION UPDATED

.DISCUSSION...

Today through Sunday...A low pressure trof over Canada has moved
east and the associated cold front has pushed down into central
portions of the zones. The northern and central portions of the CWA
will see significantly cooler temps today but the southward push of
the front will weaken and the southwest zones will once again be
quite warm. Showers and thunderstorms will be ending across the
northern tier this morning while, to the south during the afternoon,
the air mass will be rather unstable in Southwest Montana. Another
shortwave will be over the Northern Rockies this afternoon but flow
aloft will be very weak and this feature should not have much affect
over the zones. Heights aloft will build Saturday and a ridge will
be over the Rockies by Sunday. Thus, conditions will not be as
unstable across Southwest Montana Saturday afternoon and most
locations will have trouble reaching convective temps...but late
afternoon and evening thunderstorm development is still expected.
The air mass will become quite dry Sunday and convection will be
hard to start. With the building ridge Saturday and Sunday, the
air mass will trend warmer and temperatures will be well above
normals. Zelzer

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 synch on this system as yet, with the ECMWF being notably quicker
and wetter than the GFS and GEM model solutions.
Waranauskas

&&

.AVIATION...
UPDATED 1130Z.
Weak cold front associated with an upper-level trof moving along the
US/Can border has made it to KHLN as of 1130Z and will continue to
slowly move southward.  Front is expected to stall out near KBZN by
late morning and then linger over central/southwest MT during the
day.  Current satellite imagery shows widespread low-level moisture
behind the front has generated broad area of BKN-OVC clouds, mostly
above 5000 ft (with some patchy MVFR ceilings), north of a KHLN-KLWT
line.  Expect these cloud decks to persist through most of the
morning, then gradually dissipate.  Meanwhile over southwest MT,
monsoonal moisture returns this aftn, generating scattered -SHRA and
-TSRA from KLWT to KDLN.
Waranauskas


&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  76  53  85  57 /  10  10  10  10
CTB  73  50  84  52 /  10  10  10  10
HLN  83  56  89  58 /  10  10  20  20
BZN  83  53  83  53 /  20  20  20  20
WEY  79  43  77  41 /  40  30  40  30
DLN  85  53  83  54 /  10  20  30  30
HVR  78  53  88  55 /  30  10  10  10
LWT  76  52  84  54 /  20  10  20  10

&&

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

$$

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