Areal Flood Warning 3, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
352 AM MDT Sun May 6 2018

.DISCUSSION...An area of showers will continue to move through
central Idaho and portions of west-central and southwest Montana
early this morning. This shower activity is expected to end by mid
morning, bringing a period of sun through early afternoon.

Things are expected to get more interesting late this afternoon
and evening as a vigorous wave of energy moves into the region
ahead of an upper level low pressure system. The atmosphere is
expected to become quite unstable ahead of this wave, and with
abundant moisture accompanying, numerous showers and thunderstorms
are expected to develop. It looks as though this activity will
begin in central Idaho by mid afternoon, moving into southwest and
west-central Montana late this afternoon into the early evening,
eventually shifting into northwest Montana tonight. A few storms
could become strong, with heavy rain, gusty winds and even small
hail being the main threats. The stronger storms look most likely
from roughly Lookout Pass to Missoula to MacDonald Pass and south.
Those with outdoor plans this afternoon and evening should keep
an eye to the sky. Locally heavy rain could exacerbate already
high rivers and small streams across the region.

Showers will linger into Monday, with the main focus shifting
into the Idaho panhandle and northwest Montana (generally from
Missoula northward). A short break in precipitation is expected by
Tuesday as high pressure builds over western Montana and central
Idaho.

It still looks as though a cold front will pass through the region
on Wednesday, bringing another round of precipitation and cooling
temperatures a few degrees.

Confidence in the forecast beyond Wednesday is still quite low as
forecast models continue to differ significantly, particularly for
the Friday into Saturday time frame.

For more information on flooding, please see the HYDROLOGY
portion of this discussion below.

&&

.AVIATION...Mid level cloud cover with a few showers will continue
to move through north central Idaho and portions of west-central
and southwest Montana this morning. The higher terrain will be
obscured locally. Showers are expected to come to an end by mid to
late morning, bringing a period of sunshine for much of western
Montana and central Idaho. Showers and thunderstorms are expected
to develop by mid afternoon across north central Idaho, shifting
into southwest and west-central Montana late this afternoon and
early evening. There is potential that a few of these storms could
become strong with the main threats being gusty winds, small hail
and locally heavy rain. KSMN is most likely to see this activity
between 06/2100z and 07/0100z, KMSO between 06/2300z and 07/0200z
and KBTM between 07/0000z and 07/0300z. Showers will shift into
northwest Montana by mid evening, though the potential for
thunderstorms will begin to decrease.

&&

.HYDROLOGY...Snowmelt runoff has caused rivers to rise quickly as
warm conditions continue across the region. Major mainstem rivers,
such as the Clark Fork River above and below Missoula, the
Bitterroot River and the Yaak River are all forecast to see
significant rises in the next several days. Most notably, the
Clark Fork River above Missoula is forecast to reach Major Flood
Stage (13 FT) by Friday, May 11th.

Needless to say, rivers are on the rise and will continue to run
high, fast, and dangerous in the coming days across the entire
Northern Rockies region. This includes small streams and creeks as
they reach bankfull and spill over their banks. Please be alert to
your local bodies of water and ensure you have a plan in the event
of flooding.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&