Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 250525

Area Forecast Discussion
National Weather Service Great Falls MT
1120 PM MDT SUN JUL 24 2016

Aviation Section Updated.

Current forecast package remains on track and no changes are
necessary. High pressure aloft will continue to provide dry and
stable conditions with slightly warmer temperatures Monday.


Updated 05200Z.
Skies will remain clear and winds will be light through mid-day
Monday. Surface high pressure building over southern Alberta Monday
afternoon will switch winds to northerly. An upper level disturbance
will produce scattered afternoon showers and thunderstorms over
southwest Montana Monday afternoon. VFR conditions prevail, except
briefly MVFR conditions possible directly under any convective
activity. PN


.PREV DISCUSSION...Issued 233 AM MDT SUN JUL 24 2016

Tonight through Tuesday...Mainly clear and dry conditions with
relatively light winds will continue through Monday morning as an
upper level ridge of high pressure drifts east across the region. By
late Monday, the upper level ridge de-amplifies with very weak
shortwave energy moving in from the west while at the surface low
pressure deepens to the south across the Great Basin. This will
allow for some destabilization Monday afternoon and likely lead to
the development of more widespread cumulus as well as a few isolated
showers and thunderstorms, primarily initiating over the higher
terrain of central and SW MT. Similar conditions exist on Tuesday
with the addition of some upper level jet energy nosing into the
Northern Rockies by late Tuesday. In addition, the deepening low
pressure across the Great Basin will maintain low level winds from
north, bringing in some slightly higher dewpoints/moisture for
somewhat better coverage of afternoon showers and thunderstorms late
Tuesday. Temperatures will remain very warm Monday and Tuesday with
many lower elevation locations approaching or exceeding 90.

Tuesday Night through Sunday...Period begins with one day of active
weather (Wed) then gets progressively more quiet heading into the
weekend.  Models have maintained good continuity and reasonable
agreement on a weak shortwave trof tracking through the Northern
Rockies on Wed. Scattered thunderstorms associated with the trof
will develop mainly along and east of line from Glacier NP to Great
Falls to White Sulphur Springs, with more isolated storm coverage in
southwest MT. Biggest question at this point is how much rainfall
can be expected with some of these storms, as precipitable water
values have trended upward in latest model runs.  This is especially
true for the Hi-Line counties where model soundings now indicate PW
values of 1.00-1.20 inches around Cut Bank and Havre. While
thunderstorms in our region usually only convert a fraction of all
that moisture into rainfall at the surface, the current model
precipitation estimates seem a bit low, with values of only 0.05-
0.15 inch for Wed aftn/eve across the Hi-Line.  We`ll have to see
how PW and precip totals trend over the next several model runs to
get a better handle on expected rainfall.

After this shortwave heads into the Dakotas Wed night, a minor
secondary shortwave arrives Thurs eve, bringing another round of
isolated storms from the Little Belt Mtns east to Blaine/Fergus
counties.  That may be the last chance for precip for a few days as
the persistent high pressure ridge over the Southwest US amplifies
northward, giving us mostly dry conditions and temperatures
returning to the upper 80s and low 90s through the weekend.


GTF  53  90  56  91 /   0  10  10  20
CTB  51  84  53  84 /   0  10  10  30
HLN  58  92  60  92 /   0  10  10  20
BZN  51  91  53  91 /   0  10  10  20
WEY  41  80  43  81 /   0   0  10  20
DLN  51  88  52  88 /   0  10  10  20
HVR  55  90  58  89 /   0  10  20  30
LWT  56  87  58  87 /   0  10  20  30



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