Flood and Strong Wind in Idaho, April 7, 2018

Area Forecast Discussion
National Weather Service Missoula MT
343 AM MDT Sat Apr 7 2018

...Potential remains for small stream flooding, rock and
landslides, and large areas of standing water in north-central
Idaho through Sunday night...

.DISCUSSION...The current drier weather period is going to be
very short-lived. Precipitation is already developing, to the
west, and remains on track to arrive in Idaho during this morning.
Today is a fairly complex weather day. Precipitation, mainly warm
frontal in nature, is likely to result in light to moderate rain
during this morning (focused in north-central Idaho). A cold front
passage during this afternoon is the main focus for very
convective showers, which may organize into a line of moderate to
heavy rain, with embedded thunderstorms and gusty winds. Finally,
behind the cold front, scattered showers and isolated
thunderstorms are forecast for this evening.

Another wave of moisture arrives tonight; north-central Idaho
will transition from showers to steady light to moderate rain,
lasting through much of Sunday. Western Montana will remain in a
showery regime tonight and Sunday, but the high terrain is likely
to see fairly consistent snow tonight and Sunday. Precipitation
will linger through Sunday night, but a decreasing trend is
expected.

Flood potential in north-central Idaho:
Lower elevation rain totals today through Sunday night are likely
to add up to 1 to 3 inches. A Flood Watch remains in effect due to
the potential for a sharp rise in Orofino creek and other small
streams across Idaho and Clearwater Counties. Main stem rivers,
such as the South Fork of the Clearwater River, could approach
flood stage by Saturday evening as well.

Brief high pressure will then build over the Intermountain West
late Monday through Tuesday. In fact, given a good southerly flow
and the likelihood of winds mixing down to the surface Tuesday
afternoon, temperatures for valleys of central Idaho and parts of
west central Montana may see high temps reach the 60 degree mark.
Clouds will be on the increase as the next weather system moves
in, which may depress the full warming potential, but
nonetheless...Tuesday should be a very mild spring day across the
board.

Mid-week through the end of the week will see the return of
moist, unsettled weather for the Northern Rockies. For now, it
appears valleys will receive periodic rainfall while elevations
above 6000 feet will experience snow.

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.AVIATION...

GOES 16 fog products show an area of stratus in northern Idaho and
into northwest Montana; while mid-level cloud cover is spreading
into the region. The associated warm front is expected to bring
rising snow levels and widespread precipitation to north- central
Idaho during this morning, primarily after 07/1400z. By 07/1800z,
the warm front will arrive to western Montana, ceilings will
lower, and rain will become common. The cold front will quickly
follow during the afternoon, providing the opportunity for a line
of vigorous showers, gusty winds, and isolated thunderstorms.
Brief moderate to heavy rain is expected between
07/1900z-07/2300z, beginning in western Idaho and progressing east
during the afternoon. Showers will linger behind the cold front,
and a the next wet weather system will quickly follow for tonight,
so low cloud cover and precipitation will continue through
Sunday.

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.MSO WATCHES/WARNINGS/ADVISORIES...
MT...ID...Flood Watch from 11 AM PDT this morning through late Sunday
     night Northern Clearwater Mountains...Orofino/Grangeville
     Region...Southern Clearwater Mountains.

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