Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 270933
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
333 AM MDT Sun May 27 2018

.SYNOPSIS...

An upper level disturbance will bring another round of showers
and thunderstorms today...mainly across southern Montana. Central
and northern portions will see continued warm temperatures with
only an isolated thunderstorm threat. Gusty winds...small
hail...and localized heavy rain will be possible with any
thunderstorm today. A similar weather pattern is then expected for
Memorial Day. Temperatures will remain above normal throughout
the holiday weekend.

&&

.DISCUSSION...

Today through Tuesday Night...Upper level low will be the main
weather maker for today and again on Monday. The low is expected
to be stationed somewhere across northern UT/CO or southern WY.
The result will be more chances for showers and thunderstorms
today, mainly across southern Montana. A moist and weakly unstable
airmass also sets up across some central and northern portions
this afternoon and evening, bringing some isolated thunderstorms
to these areas as well. Shear will be low today, making today`s
main threat from thunderstorms being localized heavy rain from
slow moving thunderstorms along with some small hail and gusty
winds. The heavy rain potential may need to be monitored across
southwester portions as already saturated conditions could add
even more water into the local creeks and streams. A similar
situation sets up for Monday, although instability will not be as
abundant. Still expected to see isolated to scattered slow moving
showers and thunderstorms, mainly across the south. Ridge of high
pressure briefly moves in for Tuesday. Mainly dry conditions will
be a result, although cannot rule out a few mountain
thunderstorms. Overall temperatures will remain above normal
during the short term period with highs in the 70s to low 80s and
lows in the 40s and 50s. Anglin

Wednesday through Saturday...An active weather pattern is still
looking to set up during the long term period, with cooling
temperatures also possible. Wednesday sees a sharp cold front
passage. This combined with modest instability and ample shear
could bring a decent chance of widespread showers and
thunderstorms. Some storms could be on the stronger side, which
will need to be monitored. Ridging across the northern plains will
cause this front to stall across the region for Thursday into
Friday. This combined with a broadscale trough looks to bring
widespread chances for showers to the area, and with 700 mb temps
below freezing some high elevation snow is still possible. The
mentioned trough ends up wrapping into a large upper low and
brings more widespread shower activity for Friday night into
Saturday. This low then either moves into Canada leaving us with
cool and breezy conditions or lingers across the region leaving us
with cool and showery conditions. Either solution is a stark
change from the current pattern. Temperatures ahead of the front
on Wednesday will be above normal, then we return to near or even
below normal temperatures Thursday into the weekend. Some models
are even showing high temps struggling to get into the 60s late
in the week, although didn`t go that cold yet. Active weather may
also bring increase water to already high running rivers and
streams. Anglin

&&

.AVIATION...
Updated 0600Z.

Shower and thunderstorm activity will become more isolated through
tonight...bringing mostly VFR conditions to are sites. Generally
VFR conditions are then expected for Sunday. An upper level
disturbance may bring a few showers and thunderstorms to
southwestern sites Sunday afternoon...with MVFR conditions and
erratic winds possible. This would mainly impact sites from KDLN
to KEKS to KBZN and south. North of this line is expected to see
partly cloudy skies...VFR conditions...and minimal chances for
showers through the forecast period. Anglin

&&

.HYDROLOGY...

Areal Flood Advisory for the Lincoln area will continue through
Monday morning. Heavy rain from yesterday`s evening thunderstorms
produced localized areas of flooding and increased run off,
especially near the Park Creek Burn Scar. Impacts from this event
should diminish later this morning, although additional
thunderstorms could return the threat throughout today.

The Sun River at Simms has risen above flood stage. The latest
forecast will keep the river at/or above flood stage for the next
several days, with a good rise expected later in the weekend into
early next week. Thus a flood warning is now in effect until
Thursday evening of next week for this section of the river.

Canyon Ferry is going to increase releases into the Missouri River.
The current forecast/plan is to keep the river below flood stage at
Ulm, Great Falls, and Fort Benton. However the river could rise to
near bankful in low areas. No flood watch will be issued at this
time, but any adjustments in the next few days could change that.

For the Missouri River near Landusky, including the James Kipp
Campground, the river is likely to go above flood stage sometime
next week with the increased releases. Flood highlights are likely
for this section of the Missouri River in the coming days.

The small stream flood advisory for Meagher County has been extended
until Sunday evening. Local DES reports minor problems continue.
With scattered thunderstorms through Saturday, minor problems are
expected to continue through much of the weekend.

Showers and thunderstorms will again be found today. A lack of
shear could bring slow moving storms...possibly causing some
localized heavy rain. The best chances for this heavier rain will
come across the southwest. Those in these already water logged
areas should be alert for possible increased flooding or flash
flooding today...and again on Monday.

Current Highlights:

Small stream flood advisory for Meagher County until 615 PM Sunday.

Flood Warning until 715 PM Thursday for the Sun River in Cascade
County west of the city of Vaughn.

Flood Warning in effect until 300 PM MDT Sunday for the Big Hole
River near Melrose in Beaverhead and Madison Counties.

Flood Warning in effect until 145 AM MDT Monday for the Jefferson
River near Three Forks.

Flood Warning in effect until 1000 PM MDT Saturday for the Missouri
River near Toston in Broadwater County.

Flood Warning in effect until 1015 PM MDT Saturday for the Gallatin
River near Logan.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  76  52  78  53 /  20  20  10  20
CTB  76  49  80  51 /  10  10  10  20
HLN  74  50  76  50 /  20  40  20  20
BZN  70  46  69  47 /  40  70  50  30
WEY  62  38  60  38 /  60  60  60  40
DLN  68  45  68  44 /  40  70  40  30
HVR  80  52  81  53 /  20  20   0  20
LWT  71  49  70  49 /  20  20  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Numerous flood highlights are in effect until further notice.
Please see Hydrology section above for additional details.

&&

$$

http://www.weather.gov/greatfalls



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