Flood and Heavy Rain in Idaho, March 16, 2017

Area Forecast Discussion
National Weather Service Missoula MT
322 AM MDT Thu Mar 16 2017

.DISCUSSION...Moisture has been plentiful overnight in most
locations, and as expected north central Idaho and northwest
Montana have been the hardest hit. Six hour rain totals ending at
midnight MDT show between 0.40”-0.60 in northern Idaho County
and Clearwater County Idaho with around 0.25”-0.35” along the
ID/MT border of northwest Montana, and just under 0.50” in the
Glacier Region. Additional rock/mudslides and drainage issues have
been reported overnight and these threats will remain through
this morning.

The cold front is beginning to move through the region so rain is
shifting southeast, snow levels are lowering, and winds are
increasing. Precipitation depicted by high resolution model
guidance this morning show the possibility for intense showers
with the passing front through mid morning, and one area that will
need to be watched for potential snow accumulations will be from
Lost Trail Pass through Georgetown Lake and east to Anaconda/Deer
Lodge/Butte/Homestake and MacDonald passes. Once the potentially
intense showers pass chances for precipitation will greatly
decrease for the rest of the day and widespread gusty winds will
prevail. Most can expect to see wind gusts between 20-30 mph by
this afternoon.

Friday is still on track to have morning fog and warm afternoon
temperatures.

The next weather system of interest will begin late Friday with
another round of relatively warm and wet weather. Periods of light
to moderate precipitation will begin in north-central Idaho and
northwest Montana later Friday afternoon and continue into
Saturday evening with high snow levels, generally above 6000 ft.
The rest of western Montana will see more sporadic precipitation,
thus Saturday should turn out to be a mild and breezy day with
only occasional showers. A cold front working west to east across
the region will provide a focused period of heavier precipitation
on Saturday afternoon into Saturday evening. Overall this system
looks similar to the weather disturbance of yesterday/early today,
although slightly higher precipitation amounts are probable. Rock
and mudslides, as well as small creek and stream flooding will
continue to be a threat.

A cool down is expected on Sunday which will slow the snow melt
and associated concerns. Yet another warm and wet storm system is
anticipated the middle of the coming week, so hydrology related
issues will prevail.

&&

.AVIATION...Conditions will be very changeable this morning with
the passage of a cold front. Rain continues to fall in much of
north central Idaho and western Montana ahead of the front and
conditions are becoming increasingly convective with the front.
Snow levels will lower with the cold front which will bring
accumulations to the high terrain and mixed precipitation into
places like KBTM. By 16/1200z the front will be well into the area
and winds will start to shift to more westerly. Gusty winds are
likely to accompany the front and are forecast to remain through
today with gusts in the 25 knot range to be common region wide
into this afternoon. Precipitation is forecast to decrease quickly
behind the front and this will be particularly true in valleys
where downslope winds will cause drying affects. Forecast
soundings show winds to decrease during the evening. Other than
some passing cirrus skies should be rather clear tonight so valley
fog is possible Friday morning.

&

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

&&

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