Flood in Montana, June 1 to 12, 2018

Area Forecast Discussion...UPDATED
National Weather Service Missoula MT
609 PM MDT Thu May 31 2018

.UPDATE...Cancelled the Severe Thunderstorm Watch for Silver Bow,
Deer Lodge, Granite, and Powell counties.

&&

.DISCUSSION...The threat for severe thunderstorms has now moved
well east of the Divide. The aforementioned counties are expected
to experience just some general, non-severe thunderstorms for the
next several hours. As such, the Severe Thunderstorm Watch has
been cancelled. Rainfall is still anticipated to continue, being
heavy at times through the night, so the Flood Watch for small
streams and creeks remains in effect for southwest Montana through
Friday morning.

&&

.AVIATION...Strong thunderstorms today will continue this evening,
mainly affecting terminals KSMN, KBTM, and KMSO. The strongest
storms for KMSO have already occurred, with strong storms picking
up for KBTM around 21Z and lasting until after 00Z. Showers and
some thunderstorms will continue through the night for KSMN and
KBTM.

&&

.PREV DISCUSSION... /ISSUED 212 PM MDT Thu May 31 2018/

DISCUSSION...Thunderstorms and convection have started pretty
early today. The threat of storms strong enough to be classified
as severe is marginal, but if there are any, they will most
likely be from Anaconda and Deer Lodge to the south and east.

Thunderstorms will mainly be very wet with heavy rain and small
hail. Normally this would be a big concern for flash flooding, but
the storms today are moving fast at over 30 mph. So even though
they are raining heavy, they don't last too long at any one
location, which greatly reduces the risk of flash flooding. On
the other hand, area streams and creeks are running high due to
recent snow melt and rains. So if a stream basin gets hit by two
or three storms in a row right after one another, flooding is
possible. Again, the Deer Lodge, Anaconda, and Butte areas are
most at risk from this, which is why a flood watch remains out
for that area. Other threats from the storms include winds around
40 mph and small hail that may accumulate on the ground. Showers
and thunderstorms will continue through the evening and taper off
Friday.

A ridge building over the region will cause the weather to slowly
improve Friday, but Saturday will be a very nice day to get
outside, with afternoon temperatures in the low to mid 70s. Most
of Sunday will be nice, with temperatures rising into the low 80s
in most area valleys.

Sunday night into Monday, models agree well on a cold front
moving across central Idaho and stalling out in western Montana
between Missoula and Butte. Monday will be another showery day
with afternoon thunderstorms along the stalled cold front. Tuesday
looks breezy with some northwest winds 15 to 20 mph in the
afternoon.

Beyond Tuesday, the region remains under a ridge with shortwaves
moving through it. Overall, this will cause some showers and
thunderstorms, but these will be relatively weak. Temperatures
will remain above average for this time of year.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Flood Watch through Friday morning Butte/Blackfoot Region.

ID...None.
&&