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Area forecast discussion
National Weather Service Great Falls Montana
545 am MDT Sat Jun 23 2018

..updated aviation section...

Synopsis...

A low pressure system will bring another round of scattered
showers and thunderstorms to the region through Sunday. Some
storms could produce brief heavier rain. The passage of this
system will keep temperatures below normal through tonight. The
showers and thunderstorms will decrease from the west on Sunday
with a slight rebound in temperatures, as the system exits to the
east. High pressure will bring warming and drying conditions
Sunday night into Monday, as temperatures warm to at least 10
degrees above normal.

&&

Discussion...

Today through Sunday...a slow-moving low pressure system will move
into the forecast area today, bringing another round of scattered
showers and thunderstorms. Precipitable water values remain
unseasonably high, so brief heavy rain is possible with some
storms. As the system begins moving out of the area tonight into
Sunday, moisture will wrap around the system and combine with a
more northerly upslope flow to continue the scattered shower and
thunderstorm activity. Again, some storms could produce brief
heavy rain. The shower and thunderstorm activity will start to
decrease from the west somewhat Sunday afternoon as the system
moves more so out of the area. The passage of this system will
keep temperatures below normal, but temperatures will start to
rebound back to normal on Sunday.
Coulston

Sunday night through Saturday...the latest forecast model have
been fairly consistent with the solution during this period. High
pressure aloft in the wake of the weekend system will bring
warming and drying conditions Sunday night into Monday, as
temperatures warm to at least 10 degrees above normal. A low
pressure trough will also move into western North America on
Monday, and a Pacific cold front ahead of this system will move
into Montana Monday afternoon. The combination of increasing winds
aloft and shifting winds with the front could cause increasing
wind shear, and the warm temperatures ahead of the front will make
for an unstable airmass. As a result, scattered strong storms may
develop Monday evening with some showers lingering overnight. A
more westerly flow aloft will keep the area dry Tuesday through
Wednesday, as temperatures rebound from the cold frontal passage.
However, a deepening low pressure trough will bring cooling
temperatures and an increasing chance for showers and
thunderstorms to the forecast area beginning Thursday afternoon
and continuing into the weekend, with the best chance for more
widespread shower activity on Saturday. We will continue to
monitor this situation to determine just how widespread and heavy
the precipitation could be, as there is still some uncertainty in
the forecast model depictions.
Coulston

&&

Aviation...
updated 1145z.

VFR conditions are generally expected through most of the forecast
period. A low pressure system will cause showers and thunderstorms
to increase across the forecast area through 21z, but especially
after 17z. Some storms may produce brief MVFR conditions in brief
heavier rain. As the system starts exiting the area after 22z, a
more northerly flow aloft will bring more widespread showers to the
north central and central Montana terminals, along with a continued
chance of thunderstorms and brief MVFR conditions through around
06z. As the system slides farther southeast, showers will decrease
along the hi-line, but they will persist across the central Montana
terminals and spread into southwest Montana with a continue
chance of MVFR ceilings.
Coulston

&&

Hydrology...
as of Saturday morning, rivers generally continue to fall, but
water impacting nearby areas will take a bit more time to totally
recede or soak into the ground. Therefore, the warnings will
continue for now.

Also, scattered showers and thunderstorms this afternoon and
evening could bring brief heavy rain, which continues the threat
for brief minor additional flooding.

Specific County/river situations...

Teton County into western Chouteau County...Flood Warning will
continue. The Teton river near Dutton has fallen below flood
stage as of Saturday morning, but farther downstream near Loma it
has yet to fall.

Cascade County...Flood Warning will continue. The Sun River and
Missouri River gauges indicate that those rivers have fallen below
flood stage as well, and they should continue falling over the
next few days.

Jefferson river...between Whitehall and Trident...Flood Warning
continues. The river is still above flood stage, but it is
expected to fall below flood stage through the weekend.

Fergus County...a Flood Warning is in effect for the Missouri
River, especially at the James Kipp campground. The river level
appears to be cresting about halfway between minor and moderate
flood stage, and it is forecast to gradually fall into early next
week.

Coulston

&&

Preliminary point temps/pops...
gtf 70 54 76 56 / 50 70 50 10
ctb 69 53 77 53 / 60 50 20 10
hln 69 53 76 53 / 50 50 50 10
bzn 68 47 71 49 / 50 50 50 20
wey 60 37 64 38 / 50 40 30 10
dln 65 44 70 47 / 40 30 20 10
hvr 76 57 78 56 / 70 60 50 20
lwt 70 50 69 51 / 60 60 60 30

&&

Tfx watches/warnings/advisories...
flood warnings are in effect until further notice
for portions of the Teton, sun, and Missouri rivers in central
Montana, and for a portion of the Jefferson river in southwest
Montana.

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