Special Weather Statement, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
341 AM MDT Fri Apr 7 2017

...SNOW POSSIBLE IN PORTIONS OF NORTH-CENTRAL IDAHO AND WEST-
CENTRAL/SOUTHWEST MONTANA SATURDAY INTO SUNDAY MORNING...

.DISCUSSION...Our next weather system will begin to move into the
Northern Rockies this morning. First, light rain showers will
spread northeast from north-central Idaho early this morning, into
western Montana later this morning after sunrise. This afternoon
the atmosphere will become more unstable with the afternoon
heating and lift from an approaching front. Along this front, we
are expecting isolated thunderstorms to develop, some could be
strong. The majority of these storms will remain below severe
limits (60 mph wind gusts & quarter size hail), however, some
convective parameters we look at (wind shear & lapse rates for
example) will be conducive for isolated wind gusts of 40 to 50
mph. Areas most likely to see the stronger storms will be points
between the Camas Prairie in Idaho, east to Missoula, and
northwest to Lincoln and Flathead Counties. Timing will be anytime
between 1PM-6PM MDT.

Conditions will quite down overnight tonight, before our next
disturbance begins to impact the region Saturday morning. The
difference with this disturbance from today's, will be a closed
mid-level low circulation which will bring cooler air down to the
surface. Snow levels could be as low as 4000-4500 feet by Saturday
evening under a localized enhanced band of precipitation,
described below.

As we move into Saturday evening model guidance are focusing on
an area of enhanced precipitation with a passing center of low
pressure. Rain will likely change to snow at all elevations in
the path of the low. So the main question is, what will the path
of this low be? The NAM and GFS have a similar path for the center
of low, which they have forecast to pass through eastern Idaho
County, near Missoula, and over Seeley Lake during the evening.
These two models have the timing of the low passage three hours
different with the GFS being faster. Overall, we need to watch the
progression of this low for moderate impacts and maybe a period
of high impact snow later in the day on Saturday and continuing
into Sunday morning in portions of north-central Idaho and west-
central/southwest Montana. Showers on Sunday will have a
decreasing trend through the day as the weather system exits.

Monday is forecast to start off under high pressure with another
trough to arrive by the afternoon and with it more precipitation.
On and off showers are possible for the remainder of the week
under southwesterly flow aloft, and extended model guidance show
the potential for a stronger weather system for the end of the
week.

&&

.AVIATION...Mid to high level clouds will be on the increase from
the southeast in central Idaho, to the northeast into western
Montana this morning. Light rain showers will develop just after
sunrise, that could briefly lower ceilings for all aviation sites
in the region. Later this afternoon, after 07/1800Z, a strong
cold front will move through north-central Idaho, into western
Montana that could also bring scattered thunderstorms along with
it. Aviation sites KMSO, KBTM, and perhaps KSMN have the best
chance for seeing any thunderstorms. These thunderstorms will be
capable of producing brief wind gusts up to 40kts. Timing will
likely be between 07/1900Z-07/2300Z.

&&

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

Special Weather Statement
National Weather Service Missoula MT
1003 AM MDT FRI APR 7 2017

MTZ001-004-071645-
Lower Clark Fork Region MT-Kootenai/Cabinet Region MT-
1003 AM MDT FRI APR 7 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN MINERAL...SOUTH
CENTRAL LINCOLN...NORTHWESTERN SANDERS AND SOUTHWESTERN FLATHEAD
COUNTIES UNTIL 1045 AM MDT...

At 1002 AM MDT, Doppler radar was tracking a strong thunderstorm over
Mullan, or near Wallace, moving northeast at 45 mph.

Pea size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Thompson Falls, Saltese, Snider, Belknap, White Pine, East Portal,
Trout Creek, Bend, Tuscor and Taft.

LAT...LON 4815 11558 4785 11486 4735 11556 4742 11569
      4742 11576 4745 11571 4746 11565 4748 11563
      4748 11568 4752 11571 4753 11570 4754 11575
      4759 11569 4762 11569 4764 11573 4770 11573
      4772 11578 4776 11581
TIME...MOT...LOC 1602Z 215DEG 48KT 4749 11579