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
1052 AM MDT FRI APR 7 2017

MTZ001-003-004-071745-
Flathead/Mission Valleys MT-Lower Clark Fork Region MT-
Kootenai/Cabinet Region MT-
1052 AM MDT FRI APR 7 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN LAKE...SOUTH CENTRAL
LINCOLN...CENTRAL SANDERS AND SOUTHWESTERN FLATHEAD COUNTIES UNTIL
1145 AM MDT...

At 1051 AM MDT, Doppler radar was tracking a strong thunderstorm 11
miles northeast of Thompson Falls, moving northeast at 40 mph.

Wind gusts up to 50 mph and small hail will be possible with this
storm.

Locations impacted include...
Snider, Eddy, Proctor, Bend, Weeksville, Lake Mary Ronan, Elmo,
Marion, Niarada, Dayton and Lonepine.

LAT...LON 4745 11514 4783 11554 4830 11465 4786 11420
TIME...MOT...LOC 1651Z 234DEG 36KT 4773 11520

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
1256 PM MDT FRI APR 7 2017

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1245 PM     TSTM WND DMG     1 W SWAN LAKE           47.93N 113.86W
04/07/2017                   LAKE               MT   EMERGENCY MNGR

            EMERGENCY MANAGER REPORTS TREES DOWN
            EVERYWHERE.

&&

Special Weather Statement
National Weather Service Missoula MT
112 PM MDT FRI APR 7 2017

MTZ001-003-004-072015-
Flathead/Mission Valleys MT-Lower Clark Fork Region MT-
Kootenai/Cabinet Region MT-
112 PM MDT FRI APR 7 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN MINERAL...
NORTHWESTERN MISSOULA...WEST CENTRAL LAKE...SOUTHERN LINCOLN...
CENTRAL SANDERS AND SOUTHWESTERN FLATHEAD COUNTIES UNTIL 215 PM
MDT...

At 111 PM MDT, Doppler radar was tracking a strong thunderstorm near
Haugan, or 10 miles south of Thompson Falls, moving northeast at 50
mph.

Winds in excess of 40 mph and small hail will be possible with this
storm.

Locations impacted include...
Thompson Falls, Superior, Plains, De Borgia, St. Regis, Haugan,
Paradise, Riverbend, Hot Springs, Snider, Belknap, Bend, Weeksville,
Camas Prairie, Saltese, Keystone, White Pine, Eddy, East Portal and
Taft.

LAT...LON 4758 11570 4761 11570 4799 11512 4752 11444
      4699 11506 4710 11514 4719 11530 4722 11529
      4726 11533 4726 11541 4730 11552 4737 11558
      4738 11564 4744 11574 4746 11565 4748 11563
      4748 11568 4753 11570 4755 11575
TIME...MOT...LOC 1911Z 215DEG 45KT 4745 11541

Special Weather Statement
National Weather Service Missoula MT
139 PM MDT FRI APR 7 2017

IDZ005-MTZ001-003-004-072045-
Northern Clearwater Mountains ID-Flathead/Mission Valleys MT-
Lower Clark Fork Region MT-Kootenai/Cabinet Region MT-
139 PM MDT FRI APR 7 2017

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN CLEARWATER...EASTERN
MINERAL...WEST CENTRAL MISSOULA AND SOUTHEASTERN SANDERS COUNTIES
UNTIL 245 PM MDT/145 PM PDT/...

At 138 PM MDT/1238 PM PDT/, Doppler radar was tracking strong
thunderstorms along a line extending from 23 miles south of De Borgia
to 17 miles east of Headquarters. Movement was northeast at 45 mph.

Half inch hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Superior, Alberton, Tarkio, Riverbend, Paradise, Ninemile, Lozeau,
Perma, Quartz, Camas Prairie, Keystone, Cyr and Stark.

LAT...LON 4694 11548 4694 11496 4697 11501 4697 11505
      4710 11514 4719 11530 4753 11460 4700 11439
      4659 11548
TIME...MOT...LOC 1938Z 227DEG 40KT 4705 11545 4669 11545