Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 262311
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
512 PM MDT SUN JUN 26 2016

AVIATION SECTION UPDATED

.DISCUSSION...

Tonight through Tuesday...Weak wave and associated cold front has
entered into norther MT with areas of scattered thunderstorms
currently occurring. Cape was able to climb to near 1000 J/kg
this afternoon across far northeastern portions of the
CWA...however the best shear still remains away from this wave.
Without the shear to help fully develop these storms...generally
brief heavy rain and lightning will be the main threats through
the evening...although cannot rule out a very isolated wind gust
near 30 knots and small hail. Fair weather CU...light winds...and
near average temperatures will be found across the remainder of
the CWA this evening. Thunderstorms end quickly tonight once the
sunsets...with mainly clear skies and near normal temps expected.
Ridge of high pressure will build across the area for
Monday...warming temperatures back into the 80s across many areas.
Plenty of instability will be found across the
region...however...a lack of moisture and no strong lift
mechanism...will lead to only isolated mountain thunderstorms for
Monday afternoon.

Monday night into Tuesday...A potential breakdown of the ridge
could return somewhat active weather to the region. NAM kicks off
the show now late Monday night into Tuesday morning with an
increase in moisture and weak wave going over the top of the
ridge. GFS is also hinting at this early show...so added slight
pops to account for it. Models now have become a little unsure for
how activity plays out on Tuesday. NAM shows ample instability and
a weak front sliding in with the broken down ridge from the
morning`s disturbance. This would place the best chances for
thunderstorms along and north of a line from Great Falls to
Lewistown. GFS only hinting at scattered activity...and ECMWF
delays the ridge breakdown until Tuesday afternoon...providing
more widely scattered showers and thunderstorms. Given
uncertainty...mainly left the previous forecast in then added
chance pops to northern area the NAM was hinting at as previously
mentioned. If thunderstorms can get going Tuesday...a few stronger
storms are possible given the modest cape and shear...along with
dewpoints returning into the 50s. Anglin

Tuesday night through Sunday...The models are in general
agreement in the medium range period, keeping an upper level ridge
over the western US through at least the end of the upcoming work
week. Of note, though, there has been a noticeable trend over the
last few days keeping the ridge from getting as amplified as the
models suggested a few days ago. And, by next weekend, there is a
bit more consistency regarding a possible breakdown of the ridge
as the upper level trough sitting off the west coast of North
America may begin to edge further inland. Temp-wise, this suggests
that temperatures this week may not get quite as warm as
originally forecast. It should be noted, however, that the models
have struggled some with forecasting the evolution of the trough
off the Pac NW coast late in the week which makes the forecast for
the July 4th weekend a lower confidence one at this time.

Beneath the ridge, it appears that a weak surface convergence zone
may setup in the lee of the Rockies from Canada to the Southern
Plains. Within this area, increasing instability and moisture
combined with the weak convergence should be enough to generate at
least isolated showers and storms most days. At this point, it is
too early to pinpoint which days may have a better coverage of
storms, so kept pops at slight chance / chance each afternoon /
evening for now. Very much a summer-time pattern. By the end of the
week, a Pacific front may sweep through the area, but this will
depend on whether or not the trough off the Pac NW coast can move
inland or not. If the trough doesn`t move inland, then isolated
afternoon storms will likely be the norm going into the holiday
weekend. Despite the better agreement regarding the trough, the lack
of consistency still leads to a lower confidence forecast then and
opted to keep pops on the lower end over the weekend for now.
Regarding the strength of the storms from Wednesday on, there isn`t
any significant severe weather signal on any day. But, a few strong
storms will be possible just about any day, especially across the
eastern half of the forecast area where the best instability/shear
may reside. Martin

&&

.AVIATION...
UPDATED 2310Z.

A weak upper level disturbance has brought scattered afternoon
showers and thunderstorms across northern portions of Central and
Southwest Montana. These storms will dissipate this evening and
mostly clear and dry conditions are expected through the night.
Surface winds will remain light with VFR conditions prevailing
through Monday.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  48  83  53  85 /   0  10  10  20
CTB  45  79  50  81 /  20  10  10  30
HLN  52  86  57  87 /   0  10  10  20
BZN  48  87  51  87 /   0  10  10  20
WEY  39  77  43  79 /   0  10  10  20
DLN  47  86  51  87 /   0  10  10  20
HVR  49  81  53  84 /  20  10   0  30
LWT  47  81  53  83 /   0  10  10  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



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