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Area forecast discussion
National Weather Service Great Falls Montana
559 PM MDT Thu Jun 21 2018

..update to aviation...

Synopsis...
showers, thunderstorms, and localized flash flooding are possible
this evening through Saturday as multiple weather disturbances
move through the area. A few thunderstorms may be severe this
evening with quarter-size hail and damaging wind gusts. An
overall drying trend is expected Saturday night into Sunday as
high pressure builds over the area. Low temperatures will mainly
be in the 50s, while highs will mainly reach the 70s or 80s
through this weekend.

&&

Discussion...

Tonight through Saturday...upper level disturbance continues
moving eastward across the region this evening with scattered to
numerous showers and thunderstorms expected. A few storms could
become strong to severe late this afternoon through early this
evening. The airmass remains unsettled for Fri/Sat, with scattered
showers and thunderstorms continuing. Some storms could produce
heavy rain with a marginal risk for flash flooding this afternoon
through Saturday, mainly south of a line from Helena to Lewistown.
Afternoon temperatures will be seasonable through the period,
generally within a few degrees of normal. Brusda

Saturday night through Thursday...shortwave trough exits our County Warning Area to
the east Saturday night, giving way to shortwave high pressure
ridging for Sunday. Thus, an overall drying trend is expected as
shower and thunderstorm probabilities decrease. On Monday, a
longwave trough aloft and embedded disturbances are progged to
slowly overspread our County Warning Area from the west and break-down the shortwave
ridge. In addition, a Pacific cold front looks to cross our County Warning Area from
west to east Monday night, perhaps resulting in some showers and
thunderstorms. Appreciable instability and vertical wind shear may
support a few severe thunderstorms and this potential scenario will
continue to be monitored. The longwave trough aloft and embedded
disturbances continue moving generally eastward over our region
Tuesday through Wednesday. At this time, models suggest showers and
thunderstorms will be isolated, but would not be surprised if the
forecast trends wetter with future model runs. By next week
Thursday, subtle high pressure ridging aloft is progged to build
over our area behind the departing longwave trough, resulting in
fair weather. Low temperatures trend near or slightly-above normal.
Highs will be within several degrees of normal (i.E. Mid 70's to
lower 80's) for most days. The exception will be Monday, when strong
warm advection ahead of the aforementioned longwave trough should
contribute to highs reaching well into the 80's to lower 90's for
most. - Jaszka



&&

Aviation...
updated 2359z.
Upper level low pressure trough currently over western Montana will
move very slowly eastward, reaching southeast Montana late Friday
afternoon. Scattered showers and thunderstorms can be expected
through much of the forecast period, with a few stronger storms
possible through 03z Friday. VFR conditions expected to prevail but
brief IFR/MVFR conditions possible in precipitation. Mountains
partially obscured at times. Mpj

&&

Hydrology...
Lewis And Clark County...Flood Warning will continue for the
entire County. Flooding is slowly decreasing across the County but
it will take time for all the flooding to end.

Teton County...Flood Warning will continue for the whole County
for potential further runoff. Flooding is decreasing in the
western portion of the County with peak flows expected this
morning in the eastern portions of the County on the Teton river.

Cascade County...Flood Warning will continue. The Sun River has
generally crested, and will slowly fall over the next few days.
The Missouri River has crested at the city of Cascade, and should
crest later today near moderate flood stage around Ulm.

Jefferson river...between Whitehall and Trident...Flood Warning
continues. Minor flooding is expected into Friday.

Meagher County...Flood Warning continues for flooding around
Martinsdale. This warning will be evaluated later this morning.

Marias river south of Shelby...Flood Warning continues. Minor
flooding is expected to continue through today.

Pondera...flood advisory continues into this evening.

Broadwater County...flood advisory continues into this morning for
minor flooding around Toston.

Big Hole river around Melrose...flood advisory continues for minor
flooding through today. The river is showing a falling trend, so
the minor flooding should not last too long in this region.

Fergus County...a Flood Watch is currently out for the potential
of heavy rain and new flooding or flash flooding on Thursday.
Flooding may then continue into the weekend along the Missouri
River...especially at the James Kipp campground.

Region wide...scattered showers and thunderstorms will affect the
region for the next several days. There is the potential that some
thunderstorms could produce brief periods of heavy rain and
additional flooding or even flash flooding. A Flood Watch remains
in effect for portions of north central and southwest Montana. Any
heavy rainfall over any areas currently under a Flood Warning or
advisory could make the situation worse or extend the flooding
problems. Anglin/brusda

&&

Preliminary point temps/pops...
gtf 57 77 53 73 / 30 50 30 30
ctb 54 75 51 70 / 20 60 30 40
hln 56 76 52 72 / 40 40 20 30
bzn 51 73 48 69 / 60 60 30 30
wey 42 63 40 60 / 40 50 20 50
dln 49 73 46 65 / 60 60 20 40
hvr 55 81 55 77 / 20 50 40 40
lwt 53 71 51 69 / 70 60 40 30

&&

Tfx watches/warnings/advisories...
Flood Watch through Friday morning Beaverhead...Broadwater...
Gallatin...Jefferson...Judith Basin...Madison...Meagher.

Flood Watch through Friday morning Fergus.

Numerous flood highlights remain in effect until further notice.

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