Special Weather Statement, NWS Missoula, MT

Area Forecast Discussion
National Weather Service Missoula MT
300 PM MDT Fri Sep 30 2016

.DISCUSSION...A nice layer of dry air has given much of western
Montana and northern Idaho a lovely, Indian Summer day with above
normal temperature yet again. This abundant sunshine has lead to
enhanced instability and helped kick off convection over south
central Idaho and most recently, SW Montana. This trend will
continue into the evening, with showers and isolated
thunderstorms spreading north across many of the same places which
saw storms last night. It is possible they may drift a bit farther
to the north and impact the northern Bitterroot or even Missoula.

There will be a brief lull in the activity before another round
of showers moves into central Idaho and Montana during the pre-
dawn hours Saturday morning. This activity is forming out ahead of
a surface cold front that will slowly work its way through the
Northern Rockies on Saturday. Models are generating most of the
precipitation during the morning hours along the instability
generated by this slow moving cold front. However additional
showers, albeit a bit more localized in nature, are still
possible Saturday afternoon. But by evening much of this activity
should be either along or even east of the Continental Divide with
clearing quickly moving in overnight. Some patchy fog may locally
inhibit visibility across NW Montana with fog development farther
south possible if heavier precipitation persists Saturday,
sufficiently moistening the lower atmosphere. The clearing
overnight will result in a rather crisp Sunday morning. But
another round of showers are likely as a wave of moisture and
instability, associated with a larger storm system digging along
the Pacific coast, pushes north into the Northern Rockies.

The consensus of the models is for the low pressure to swing
through the Great Basin of Nevada/Utah then lift northeastward
into central Montana/western North Dakota on Monday through
Wednesday. The path of the system should cause wrap around
precipitation to impact southwest Montana down into Lemhi County.
The Butte/Pintlar area will receive the heaviest precipitation
from this system with the Pintlar mountains seeing a few inches
of new snow above 6000 feet. Temperatures will be running around 5
to 10 degrees below average for this time of year.

The weather pattern will remain fairly active through the
remainder of the week as another system approaches the region by
Friday. The path and strength of this next system is still
uncertain at this time.

&&

.AVIATION...Scattered showers with isolated thunderstorms may
possibly affect airfield operations at KBTM and KSMN through
10/0400. Brief downpours, brief gusty winds to 30 knots along with
occasional lightning are possible. Elsewhere expect increasing
clouds with isolated showers at KMSO and KGPI, but with little
impact to aviation operations. Additional precipitation will move
across the region very early Saturday morning with variably lower
cloud decks. FROPA is anticipated to slowly occur at all TAF sites
Saturday morning, but with minimally gusty winds or notable wind
shift.

&&

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

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE MISSOULA MT
444 PM MDT FRI SEP 30 2016

MTZ001-302315-
KOOTENAI/CABINET REGION MT-
444 PM MDT FRI SEP 30 2016

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN LINCOLN COUNTY UNTIL
515 PM MDT...

AT 443 PM MDT...TRAINED WEATHER SPOTTERS REPORTED A STRONG
THUNDERSTORM 16 MILES NORTHEAST OF MOYIE SPRINGS...OR 21 MILES
NORTHEAST OF BONNERS FERRY...MOVING NORTHEAST AT 40 MPH.

NICKEL SIZE HAIL AND WINDS IN EXCESS OF 40 MPH WILL BE POSSIBLE WITH
THIS STORM.

THIS STORM WILL REMAIN OVER MAINLY RURAL AREAS OF NORTHWESTERN
LINCOLN COUNTY.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TORRENTIAL RAINFALL IS ALSO OCCURRING WITH THIS STORM...AND MAY LEAD
TO LOCALIZED FLOODING. DO NOT DRIVE YOUR VEHICLE THROUGH FLOODED
ROADWAYS.

THIS STORM MAY INTENSIFY...SO BE CERTAIN TO MONITOR LOCAL RADIO
STATIONS AND AVAILABLE TELEVISION STATIONS FOR ADDITIONAL INFORMATION
AND POSSIBLE WARNINGS FROM THE NATIONAL WEATHER SERVICE.

&&

LAT...LON 4900 11549 4878 11605 4899 11605 4900 11603
TIME...MOT...LOC 2243Z 231DEG 36KT 4891 11597